ClickCease
+1-915-850-0900 spinedoctors@gmail.com
Select Page
Korir Named Bowerman Award Semifinalist

Korir Named Bowerman Award Semifinalist

by | UTEP (Local) RSS

Related Articles

Emmanuel Korir has been named a semifinalist for college track and field’s highest individual honor, The Bowerman Award, the U.S. Track and Field and Cross Country Coaches Association (USTFCCCA) announced Thursday.

Korir wrapped up his freshman season with a sweep of both 800m national titles. The Kenyan is the first Miner to win the 800m NCAA title since Peter Lemashon outdoors in 1978, and the first to achieve the feat at both NCAA Indoors and Outdoors in the same year.

The All-American holds school records in the indoor 800m (1:46.75), the outdoor 800m (1:43.73) and the outdoor 400m (44.53). Korir is one of three athletes in the world to run a sub-45 400m and a sub-1:44 in the 800m.

Three finalists will be announced on Thursday, June 22 from the following list of semifinalists:

KeAndre Bates, junior, jumps, Florida

Edward Cheserek, senior, distance, Oregon

Christian Coleman, junior, sprints/jumps, Tennessee

Grant Holloway, freshman, hurdles/jumps, Florida

Fred Kerley, senior, springs, Texas A&M

Josh Kerr, sophomore, mid-distance, New Mexico

Emmanuel Korir, freshman, mid-distance, UTEP

Ioannis Kyriazis, junior, throws, Texas A&M

Filip Mihaljevic, junior, throws, Virginia

Lindon Victor, senior, combined events, Texas A&M

For more information on UTEP track and field, follow the Miners on Twitter (@UTEPTrack) and Instagram (uteptrack).

UTEP Tennis Pens Two for 2017-18 Season

UTEP Tennis Pens Two for 2017-18 Season

by | UTEP (Local) RSS

Related Articles

New UTEP Tennis Head Coach Ivan Fernandez announced his first two signees on Friday. Erandi Martinez Hernandez and Alisa Morozova will join the Miners for the 2017-18 season.

Martinez Hernandez graduated from Monterrey Institute of Technology and Higher Education, a prestigious high school in Mexico City. She has been ranked among the top-five under-18 players in Mexico and has won three Grade 1 tournaments in both singles and doubles.

Hernandez reached the semifinals of the Masters Championship, a qualifier for a Women’s Tennis Association (WTA) Tournament in Mexico, and reached the quarterfinals at the Tampico International Tournament last August, where she faced several players that are now playing Division I tennis.

“I have been recruiting Erandi for a couple of months already,” Fernandez said. “I know that she’s got a lot of wins in Mexico against players that are now in Division I, so I have a really good idea of the level that she’s going to bring to the program. She’s very solid in singles and doubles and I think that she’s going to be a great addition to this team, especially having competed against a lot of collegiate players. She’s going to come in with a lot of international experience and she has been highly ranked in Mexico for her whole career. I definitely expect her to make an immediate impact in the lineup.”

Morozova recently graduated from the Gusev Secondary School in Russia, where she has been ranked among the top under-18 players the last three years. Morozova represented the Yaroslavi Regional Team as the No. 3 singles player and has won more than 10 Russian Federation Tournaments in singles and doubles.

“I spoke with Alisa’s sister a little bit and she told me that if she had been playing here in the U.S. she would have a UTR [Universal Tennis Rating] of 9 or 10, which is a very high level,” Fernandez said. “Her sister, who played for four years at St. John’s and just graduated, told me that she would probably play in the middle of the lineup at St. John’s, who just won their conference and went to the NCAA Tournament. Alisa is a very young player but she is very well-rounded. She’s also going to be capable of playing in the middle of the lineup here. We’re very fortunate that we were able to get her in so quickly and get her signed right away. She’s a very solid player, she’s going to mature and keep developing and both she and Erandi will definitely be in the lineup as true freshmen.”

UTEP�s Korir, Amusan Garner C-USA Athlete of the Year

UTEP�s Korir, Amusan Garner C-USA Athlete of the Year

by | UTEP (Local) RSS

UTEP claimed two superlative Conference USA track and field honors as Emmanuel Korir and Tobi Amusan were named C-USA Male and Female Track Athletes of the Year, announced by the league office on Friday afternoon.

“Both athletes are very special and talented. He [Korir] was the best candidate for our league and would most likely do very well other top conferences as well,” head coach Mika Laaksonen stated. “A lot of work goes into these things and Tobi worked incredibly hard over these past two years and she absolutely deserves this award, they both do.”

Korir ran a world best 1:14.97 in the 600m earlier this year at the New Mexico Cherry & Silver meet, which was his first race on an indoor 200m banked track. The freshman followed that up by capturing the NCAA title in the 800m (1:47.48) at the same track in Albuquerque, N.M., with a time of 1:47.48. The freshman is one of three athletes in the world to run an outdoor sub-45 400m and a sub-1:44 in the 800m.

The Kenyan native won the NCAA outdoor title in the 800m (1:45.03) and is the first Miner to win both titles in the same year.

Amusan was the leading scorer for the Miners with 25 points at the C-USA Indoor Championships and notched a meet record in the 60m hurdles with a time of 8.01. The sophomore helped her team win its third consecutive conference title. Amusan qualified to the NCAA Indoor Championships in the 60m hurdles where she notched a sixth-place showing.

The outdoor season started with a bang, as she set a school record (12.63) in the 100m hurdles at the UTEP Springtime meet. She followed that with a first-place finish at the 2017 Clyde Little Field Texas Relays in the 100m hurdles, setting a meet record time of 12.72. The Nigerian native scored 24.5 points at the C-USA Outdoor Championships leading the women’s team to its first ever outdoor conference title.

Both athletes were named semifinalists for college track and field’s high individual honor, The Bowerman Award. The women’s three finalists will be announced on Wednesday, June 21 and the men’s finalists will be announced Thursday, June 22.

For more information on UTEP track and field, follow the Miners on Twitter (@UTEPTrack) and on Instagram (uteptrack).

UTEP�s Hernandez Named to Athlon Sports Preseason All-American Team

UTEP�s Hernandez Named to Athlon Sports Preseason All-American Team

by | UTEP (Local) RSS

Related Articles

Offensive lineman Will Hernandez was named to the 2017 Athlon Sports Preseason All-American third team on Tuesday.

The senior comes back after a stellar season where he garnered AP All-American second team, FOX Sports’ All-American second team, All-Conference USA first team and Pro Football Focus Best Pass Protector honors. The lineman has started all 37 games in his career for the Miners at the left guard position.

He led the offensive line that paved the way for Aaron Jones to rush for a single-season program-record 1,773 yards, while Jones also became UTEP’s all-time leading rusher last season. The Miners averaged 185.5 rushing yards per game and scored 20 touchdowns on the ground.

Hernandez is one of two student-athletes from C-USA that makes an appearance on the Athlon Sports All-American team. The Las Vegas, Nev., native also was named to the Athlon Sports Preseason All-C-USA first team.

Teammate Alvin Jones also garnered Athlon Sports All-C-USA first team recognition, while Devin Cockrell and Terry Juniel received second team honors. Jones was appointed to the 2016 All-C-USA second team after leading team in tackles 93 (44 solo). He ranked fourth in the league in tackles per game (9.3) and added 6.0 tackles for loss (28 yards), 2.5 sacks (22 yards) and a pass breakup.

Cockrell started all 12 games last season and ranked fourth on defense, while leading all defensive backs with 58 tackles (31 solo). He added 3.0 tackles for loss, a pass breakup, a quarterback hurry and a fumble recovery. The senior led team with 10 special team’s tackles (seven punt return tackles)

Juniel returns to the Miners special teams unit as the starting punt returner. The specialist was the team’s leading punt returner, tallying 203 yards on 22 returns (9.2 avg.), with a pair of long returns of 43 yards. Juniel led C-USA in punt returns and return yards. The junior returned nine kickoffs for 164 yards (18.2 avg.) with a long of 26 yards.

UTEP’s center Derron Gatewood and punter Alan Luna also received recognition on the All-C-USA Preseason fourth team.

U.S. Case Study: Chiropractic & Vertebrobasilar Stroke

U.S. Case Study: Chiropractic & Vertebrobasilar Stroke

by | Chiropractic, Chiropractic Examination, Chiropractic News, Physical Rehabilitation, Spine Care

Thomas M Kosloff1*�, David Elton1�, Jiang Tao2� and Wade M Bannister2�

CHIROPRACTIC & MANUAL THERAPIES

Abstract

Background: There is controversy surrounding the risk of manipulation, which is often used by chiropractors, with respect to its association with vertebrobasilar artery system (VBA) stroke. The objective of this study was to compare the associations between chiropractic care and VBA stroke with recent primary care physician (PCP) care and VBA stroke.

Methods: The study design was a case�control study of commercially insured and Medicare Advantage (MA) health plan members in the U.S. population between January 1, 2011 and December 31, 2013. Administrative data were used to identify exposures to chiropractic and PCP care. Separate analyses using conditional logistic regression were conducted for the commercially insured and the MA populations. The analysis of the commercial population was further stratified by age (<45 years; ?45 years). Odds ratios were calculated to measure associations for different hazard periods. A secondary descriptive analysis was conducted to determine the relevance of using chiropractic visits as a proxy for exposure to manipulative treatment.

Results: There were a total of 1,829 VBA stroke cases (1,159 � commercial; 670 � MA). The findings showed no significant association between chiropractic visits and VBA stroke for either population or for samples stratified by age. In both commercial and MA populations, there was a significant association between PCP visits and VBA stroke incidence regardless of length of hazard period. The results were similar for age-stratified samples. The findings of the secondary analysis showed that chiropractic visits did not report the inclusion of manipulation in almost one third of stroke cases in the commercial population and in only 1 of 2 cases of the MA cohort.

Conclusions: We found no significant association between exposure to chiropractic care and the risk of VBA stroke. We conclude that manipulation is an unlikely cause of VBA stroke. The positive association between PCP visits and VBA stroke is most likely due to patient decisions to seek care for the symptoms (headache and neck pain) of arterial dissection. We further conclude that using chiropractic visits as a measure of exposure to manipulation may result in unreliable estimates of the strength of association with the occurrence of VBA stroke.

Keywords: Chiropractic, Primary care, Cervical manipulation, Vertebrobasilar stroke, Adverse events

Background

The burden of neck pain and headache or migraine among adults in the United States is significant. Survey data indicate 13% of adults reported neck pain in the past 3 months [1]. In any given year, neck pain affects 30% to 50% of adults in the general population [2]. Prevalence rates were reportedly greater in more eco- nomically advantaged countries, such as the USA, with a higher incidence of neck pain noted in office and com- puter workers [3]. Similar to neck pain, the prevalence of headache is substantial. During any 3-month time- frame, severe headaches or migraines reportedly affect one in eight adults [1].

Neck pain is a very common reason for seeking health care services. �In 2004, 16.4 million patient visits or 1.5% of all health care visits to hospitals and physician offices, were for neck pain� [4]. Eighty percent (80%) of visits occurred as outpatient care in a physician�s office [4]. The utilization of health care resources for the treatment of headache is also significant. �In 2006, adults made nearly 11 million physician visits with a headache diagno- sis, over 1 million outpatient hospital visits, 3.3 million emergency department visits, and 445 thousand inpatient hospitalizations� [1].

In the United States, chiropractic care is frequently utilized by individuals with neck and/or headache com- plaints. A national survey of chiropractors in 2003 re- ported that neck conditions and headache/facial pain accounted respectively for 18.7% and 12% of the patient chief complaints [5]. Chiropractors routinely employ spinal manipulative treatment (SMT) in the management of patients presenting with neck and/or headache [6], either alone or combined with other treatment approaches [7-10].

While evidence syntheses suggest the benefits of SMT for neck pain [7-9,11-13] and various types of headaches [10,12,14-16], the potential for rare but serious adverse events (AE) following cervical SMT is a concern for researchers [17,18], practitioners [19,20], professional organizations [21-23], policymakers [24,25] and the public [26,27]. In particular, the occurrence of stroke affecting the vertebrobasilar artery system (VBA stroke) has been associated with cervical manipulation. A recent publication [28] assessing the safety of chiropractic care reported, �…the frequency of serious adverse events varied between 5 strokes/ 100,000 manipulations to 1.46 serious adverse events/ 10,000,000 manipulations and 2.68 deaths/10,000,000 manipulations�. These estimates were, however, derived from retrospective anecdotal reports and liability claims data, and do not permit confident conclusions about the actual frequency of neurological complications following spinal manipulation.

Several systematic reviews investigating the association between stroke and chiropractic cervical manipulation�have reported the data are insufficient to produce definitive conclusions about its safety [28-31]. Two case�control studies [32,33] used visits to a chiropractor as a proxy for SMT in their analyses of standardized health system databases for the population of Ontario (Canada). The more recent of these studies [32] also included a case-crossover methodology, which reduced the risk of bias from confounding variables. Both case�control studies reported an increased risk of VBA stroke in association with chiropractic visits for the population under age 45 years old. Cassidy, et al. [32] found, how- ever, the association was similar to visits to a primary care physician (PCP). Consequently, the results of this study suggested the association between chiropractic care and stroke was non-causal. In contrast to these studies, which found a significant association between chiropractic visits and VBA stroke in younger patients (<45 yrs.), the analysis of a population-based case-series suggested that VBA stroke patients who consulted a chiropractor the year before their stroke were older (mean age 57.6 yrs.) than previously documented [34].

The work by Cassidy, et al. [32] has been qualitatively appraised as one of the most robustly designed investigations of the association between chiropractic manipulative treatment and VBA stroke [31]. To the best of our knowledge, this work has not been reproduced in the U.S. population. Thus, the main purpose of this study is to replicate the case�control epidemiological design published by Cassidy, et al. [32] to investigate the association between chiropractic care and VBA stroke; and compare it to the association between recent PCP care and VBA stroke in samples of the U.S. commercial and Medicare Advantage (MA) populations. A secondary aim of this study is to assess the utility of employing chiropractic visits as a proxy measure for exposure to spinal manipulation.

Methods

Study design and population

We developed a case�control study based on the experience of commercially insured and MA health plan members between January 1, 2011 and December 31, 2013. General criteria for membership in a commercial or MA health plan included either residing or working in a region where health care coverage was offered by the in- surer. Individuals must have Medicare Part A and Part B to join a MA plan. The data set included health plan members located in 49 of 50 states. North Dakota was the only State not represented.

Both case and control data were extracted from the same source population, which encompassed national health plan data for 35,726,224 unique commercial and 3,188,825 unique MA members. Since members might be enrolled for more than one year, the average�annual commercial membership was 14.7 million members and the average annual MA membership was 1.4 million members over the three year study period, which is comparable to ~5% of the total US population based on the data available from US Census Bureau [35]. Administrative claims data were used to identify cases, as well as patient characteristics and health service utilization.

The stroke cases included all patients admitted to an acute care hospital with vertebrobasilar (VBA) occlusion and stenosis strokes as defined by ICD-9 codes of 433.0, 433.01, 433.20, and 433.21 during the study period. Pa- tients with more than one admission for a VBA stroke were excluded from the study. For each stroke case, four age and gender matched controls were randomly se- lected from sampled qualified members. Both cases and controls were randomly sorted prior to the matching using a greedy matching algorithm [36].

Exposures

The index date was defined as the date of admission for the VBA stroke. Any encounters with a chiropractor or a primary care physician (PCP) prior to the index date were considered as exposures. To evaluate the impact of chiropractic and PCP treatment, the designated hazard period in this study was zero to 30 days prior to the index date. For the PCP analysis, the index date was excluded from the hazard period since patients might consult PCPs after having a stroke. The standard health plan coverage included a limit of 20 chiropractic visits. In rare circumstances a small employer may have selected a 12-visit limit. An internal analysis (data not shown) revealed that 5% of the combined (commercial and MA) populations reached their chiropractic visit limits. Instances of an employer not covering chiropractic care were estimated to be so rare that it would have had no measurable impact on the analysis. There were no limits on the number of reimbursed PCP visits per year.

Analyses

Two sets of similar analyses were performed, one for the commercially insured population and one for the MA population. In each set of analyses, conditional logistic regression models were used to examine the association between the exposures and VBA strokes. To measure the association, we estimated the odds ratio of having the VBA stroke and the effect of total number of chiropractic visits and PCP visits within the hazard period. The analyses were applied to different hazard periods, including one day, three days, seven days, 14 days and 30 days for both chiropractic and PCP visits. The results of the chiropractic and PCP visit analyses were then compared to find evidence of excess risk of having stroke for patients with chiropractic visits during the

hazard period. Previous research has indicated that most patients who experience a vertebral artery dissection are under the age of 45. Therefore, in order to investigate the impact of exposure on the population at different ages, separate analyses were performed on patients stratified by age (under 45 years and 45 years and up) for the study of the commercial population. The number of visits within the hazard period was entered as a con- tinuous variable in the logistic model. The chi square test was used to analyze the proportion of co-morbidities in cases as compared to controls.

A secondary analysis was performed to evaluate the relevance of using chiropractic visits as a proxy for spinal manipulation. The commercial and MA databases were queried to identify the proportions of cases of VBA stroke and matched controls for which at least one chiropractic spinal manipulative treatment procedural code (CPT 98940 � 98942) was or was not recorded. The analysis also calculated the use of another manual therapy code (CPT 97140), which may be employed by chiropractors as an alternative means of reporting spinal manipulation.

Ethics

The New England Institutional Review Board (NEIRB) determined that this study was exempt from ethics review.

Results

The commercial study sample included 1,159 VBA stroke cases over the three year period and 4,633 age and gender matched controls. The average age of the patients was 65.1 years and 64.8% of the patients were male (Table 1). The prevalence rate of VBA stroke in the commercial population was 0.0032%.

table-1-8.png

There were a total of 670 stroke cases and 2,680 matched controls included in the MA study. The aver- age patient age was 76.1 years and 58.6% of the patients were male (Table 2). For the MA population, the prevalence rate of VBA stroke was 0.021%.

Claims during a one year period prior to the index date were extracted to identify comorbid disorders. Both the commercial and MA cases had a high percentage of comorbidities, with 71.5% of cases in the commercial study and 88.5% of the cases in the MA study reporting at least one of the comorbid conditions (Table 3). Six comorbid conditions of particular interest were identified, including hypertensive disease (ICD-9 401�404), ischemic�heart disease (ICD-9 410�414), disease of pulmonary circulation (ICD-9 415�417), other forms of heart disease (ICD-9 420�429), pure hypercholesterolemia (ICD-9 272.0) and diseases of other endocrine glands (ICD-9 249�250). There were statistically significant differences (p = <0.05) between groups for most comorbidities. Greater proportions of comorbid disorders (p = <0.0001) were reported in the commercial and MA cases for hyper- tensive disease, heart disease and endocrine disorders (Table 3). The commercial cases also showed a larger proportion of diseases of pulmonary circulation, which was statistically significant (p = 0.0008). There were no significance differences in pure hypercholesterolemia for either the commercial or MA populations. Overall, cases in both the commercial and MA populations were more likely (p = <0.0001) to have at least one co- morbid condition.

Among the commercially insured, 1.6% of stroke cases had visited chiropractors within 30 days of being admit- ted to the hospital, as compared to 1.3% of controls visit- ing chiropractors within 30 days prior to their index date. Of the stroke cases, 18.9% had visited a PCP within 30 days prior to their index date, while only 6.8% of controls had visited a PCP (Table 4). The proportion of exposures for chiropractic visits was lower in the MA sample within the 30-day hazard period (cases = 0.3%; controls = 0.9%). However, the proportion of exposures for PCP visits was higher, with 21.3% of cases having PCP visits as compared to12.9% for controls (Table 5).

The results from the analyses of both the commercial population and the MA population were similar (Tables 6, 7 and 8). There was no association between chiropractic visits and VBA stroke found for the�overall sample, or for samples stratified by age. No estimated odds ratio was significant at the 95% confidence level. MA data were insufficient to calculate statistical measures of association for hazard periods less than 0�14 days for chiropractic visits. When stratified by age, the data were too sparse to calculate measures of association for hazard periods less than 0�30 days in the commercial population. The data were too few to analyze associative risk by headache and/or neck pain diagnoses (data not shown).

These results showed there is an association existing between PCP visits and VBA stroke incidence regardless of age or length of hazard period. A strong association was found for those visits close to the index date (OR 11.56; 95% CI 6.32-21.21) for all patients with a PCP visit within 0�1 day hazard period in the commercial sample. There was an increased risk of VBA stroke associated with each PCP visit within 30-days prior to the index date for MA patients (OR 1.51; 95% CI 1.32-1.73) and commercial patients (OR 2.01; 95% CI 1.77-2.29).

The findings of the secondary analysis showed � that of 1159 stroke cases from commercial population � there were a total of 19 stroke cases associated with chiropractic visits for which 13 (68%) had claims documentation indicating chiropractic SMT was performed. For the control group of the commercial cohort, 62 of 4633 controls had claims of any kind of chiropractic visits and 47 of 4633 controls had claims of SMT. In the commercial control group, 47 of 62 DC visits (76%) included SMT in the claims data. Only 1 of 2 stroke cases in the MA population included SMT in the claims data. For the MA cohort, 21 of 24 control chiropractic visits (88%) included SMT in the claims data (Table 9).

None of the stroke cases in either population included CPT 97140 as a substitute for the more conventionally re- ported chiropractic manipulative treatment procedural codes (98940 � 98942). For the control groups, there were three instances where CPT 97140 was reported without CPT 98940 � 98942 in the commercial population. The CPT code 97140 was not reported in MA control cohort.

Discussion

The primary aim of the present study was to investigate the association between chiropractic manipulative treatment and VBA stroke in a sample of the U.S. population. This study was modeled after a case�control design previously conducted for a Canadian population [32]. Administrative data for enrollees in a large national health care insurer were analyzed to explore the occurrence of VBA stroke across different time periods of exposure to chiropractic care in comparison with PCP care.

Unlike Cassidy et al. [32] and most other case�control studies [33,37,38], our results showed there was no significant association between VBA stroke and chiropractic visits. This was the case for both the commercial and MA populations. In contrast to two earlier case�control studies [32,33], this lack of association was found to be irrespective of age. Although, our results (Table 8) did lend credence to previous reports that VBA stroke occurs more frequently in patients under the age of 45 years. Additionally, the results from the present study did not identify a relevant temporal impact. There was no significant association, when the data were sufficient to calculate estimates, between chiropractic visits and stroke regardless of the hazard period (timing of most recent visit to a chiropractor and the occurrence of stroke).

There are several possible reasons for the variation in results with previous similar case�control studies. The younger (<45 yrs.) commercial cohort that received chiropractic care in our study had noticeably fewer cases. The 0�30 days hazard period included only 2 VBA stroke cases. There were no stroke cases for other hazard periods in this population. In contrast, earlier studies reported sufficient cases to calculate risk estimates for most hazard periods [32,33].

Another factor that potentially influenced the difference in results concerns the accuracy of hospital claims data in the U.S. vs. Ontario, Canada. The source population in the Province of Ontario was identified, in part, from the Discharge Abstract Database (DAD). The DAD includes hospital discharge and emergency visit diagnoses that have undergone a standardized assessment by a medical records coder [39]. To the best of our know- ledge, similar quality management practices were not routinely applied to hospital claims data used in sourcing the population for our study.

An additional reason for the disparity in results may be due to differences in the proportions of chiropractic visits where SMT was reportedly performed. Our study showed that SMT was not reported by chiropractors in more than 30% of commercial cases. It is plausible that a number of the cases in earlier studies also did not�include SMT as an intervention. Differences between studies in the proportion of cases reporting SMT may have affected the calculation of risk estimates.

Also, there were an insufficient number of cases having cervical and/or headache diagnoses in our study. Therefore, our sample population may have included proportionally less cases where cervical manipulation was performed.

Our results were consistent with previous findings [32,33] in showing a significant association between PCP visits and VBA stroke. The odds ratios for any PCP visit increase dramatically from 1�30 days to 1�1 day (Tables 6 and 7). This finding is consistent with the hypothesis that patients are more likely to see a PCP for symptoms related to vertebral artery dissection closer to the index date of their actual stroke. Since it is unlikely that the services provided by PCPs cause VBA strokes, the association�between recent PCP visits and VBA stroke is more likely attributable to the background risk related to the natural history of the condition [32].

A secondary goal of our study was to assess the utility of employing chiropractic visits as a surrogate for SMT. Our findings indicate there is a high risk of bias associated with using this approach, which likely overestimated the strength of association. Less than 70% of stroke cases (commercial and MA) associated with chiropractic care included SMT. A somewhat higher proportion of chiropractic visits included SMT for the control groups (commercial = 76%; MA = 88%).

There are plausible reasons that support these findings. Internal analyses of claims data (not shown) consistently demonstrate that one visit is the most common number associated with a chiropractic episode of care. The single visit may consist of an evaluation without treatment such as SMT. Further; SMT may have been viewed as contraindicated due to signs and symptoms of vertebral artery dissection (VAD) and/or stroke. This might explain the greater proportion of SMT provided to control groups in both the commercial and MA populations.

Overall, our results increase confidence in the findings of a previous study [32], which concluded there was no excess risk of VBA stroke associated chiropractic care compared to primary care. Further, our results indicate there is no significant risk of VBA stroke associated with chiropractic care. Additionally, our findings highlight the potential flaws in using a surrogate variable (chiropractic visits) to estimate the risk of VBA stroke in association with a specific intervention (manipulation).

Our study had a number of strengths and limitations. Both case and control data were extracted from the same source population, which encompassed national health plan data for approximately 36 million�commercial and 3 million MA members. A total of 1,829 cases were identified, making this the largest case� control study to investigate the association between chiropractic manipulation and VBA stroke. Due to the nationwide setting and large sample size, our study likely reduced the risk of bias related to geographic factors. However, there was a risk of selection bias � owing to the data set being from a single health insurer � including income status, workforce participation, and links to health care providers and hospitals.

Our study closely followed a methodological approach that had previously been described [32], thus allowing for more confident comparisons.

The current investigation analyzed data for a number of comorbid conditions that have been identified as potentially modifiable risk factors for a first ischemic stroke [40]. The differences between groups were statistically significant for most comorbidities. Information was not obtainable about behavioral comorbid factors e.g., smoking and body mass. With the exception of hypertensive disease, there are reasons to question the clinical significance of these conditions in the occurrence of ischemic stroke due to vertebral artery dissection. A large multinational case-referent study investigated the association between vascular risk factors (history of vascular disease, hypertension, smoking, hypercholesterolemia, diabetes mellitus, and obesity/overweight) for ischemic stroke and the occurrence of cervical artery dissection [41]. Only hypertension had a positive association (odds ratio 1.67; 95% confidence interval, 1.32 to 2.1; P <0.0001) with cervical artery dissection.

While the effect of other unmeasured confounders cannot be discounted, there is reason to suspect the absence of these data was not deleterious to the results. Cassidy, et al. found no significant differences in the results their case-crossover design, which affords better control of unknown confounding variables, and the findings of their case�control study [32].

Our results highlight just how unusual VBA stroke is in the MA cohort (prevalence = 0.021%) and � even more so � for the commercial population (prevalence = 0.0032%). As a result, some limitations of this study re- lated to the rarity of reporting VBA stroke events. Despite the larger number of cases, data were insufficient to calculate estimates and confidence intervals for seven measures of exposure (4 commercial and 3 MA) for chiropractic visits. Additionally, we were not able to compute estimates specifically for headache and neck pain diagnoses due to small numbers. Confidence intervals associated with estimates tended to be wide making the results imprecise [42].

There were limitations related to the use of administrative claims data. �Disadvantages of using secondary data for research purposes include: variations in coding from hospital to hospital or from department to department, errors in coding and incomplete coding, for example in the presence of comorbidities. Random errors in coding and registration of discharge diagnoses may dilute and attenuate estimates of statistical association� [43]. The recordings of unvalidated hospital discharge diagnostic codes for stroke have been shown to be less precise when compared to chart review [44,45] and validated patient registries�[43,46]. Cassidy, et al. [32] conducted a sensitivity analysis to determine the effect of diagnostic misclassification bias. Their conclusions did not change when the effects of misclassification were assumed to be similarly distributed between chiropractic and PCP cases.

A particular limitation in using administrative claims data is the paucity of contextual information surround- ing the clinical encounters between chiropractors/PCPs and their patients. Historical elements describing the occurrence/absence of recent trauma or activities reported in case studies [47-51] as potential risk factors for VBA stroke were not available in claims data. Confidence was low concerning the ability of claims data to provide accurate and complete reporting of other health disorders, which have been described in case�control designs as being associated with the occurrence of VBA stroke e.g., migraine [52] or recent infection [53]. Symptoms and physical examination findings that would have permitted further stratification of cases were not reported in the claims data.

The reporting of clinical procedures using current pro- cedural terminology (CPT) codes presented additional shortcomings concerning the accuracy and interpretation of administrative data. One inherent constraint was the lack of anatomic specificity associated with the use of standardized procedural codes in claims data. Chiropractic manipulative treatment codes (CPT 98940 � 98942) have been formatted to describe the number of spinal regions receiving manipulation. They do not identify the particular spinal regions manipulated.

Also, treatment information describing the type(s) of manipulation was not available. When SMT was re- ported, claims data could not discriminate among the range of techniques including thrust or rotational manipulation, various non-thrust interventions e.g., mechanical instruments, soft tissue mobilizations, muscle energy techniques, manual cervical traction, etc. Many of these techniques do not incorporate the same bio- mechanical stressors associated with the type of manipulation (high velocity low amplitude) that has been investigated as a putative risk factor for VBA stroke [54-56]. It seems plausible that the utility of future VBA stroke research would benefit from explicit descriptions of the particular type of manipulation performed.

Moreover, patient responses to care � including any adverse events suggestive of vertebral artery dissection or stroke-like symptoms � were not obtainable in the data set used for the current study.

In the absence of performing comprehensive clinical chart audits, it is not possible to know from claims data what actually transpired in the clinical encounter. Further, chart notes may themselves be incomplete or otherwise fail to precisely describe the nature of interventions [57]. Therefore, manipulation codes represent surrogate

measures, albeit more direct surrogate measures, than simply using the exposure to chiropractic visits.

Our study was also limited to replication of the case� control design described by Cassidy, et al. [32]. For pragmatic reasons, we did not attempt to conduct a case-crossover design. While the addition of a case- crossover design would have provided better control of confounding variables, Cassidy, et al. [32] showed the results were similar for both the case control and case crossover studies.

The findings of this case�control study and previous retrospective research underscore the need to rethink how to better conduct future investigations. Researchers should seek to avoid the use of surrogate measures or use the least indirect measures available. Instead, the focus should be on capturing data about the types of services and not the type of health care provider.

In alignment with this approach, it is also important for investigators to access contextual data (e.g., from electronic health records), which can be enabled by qualitative data analysis computer programs [58]. The acquisition of the elements of clinical encounters � including history, diagnosis, intervention, and adverse events � can provide the infrastructure for more action- able research. Because of the rarity of VBA stroke, large data sets (e.g., registries) containing these elements will be necessary to achieve adequate statistical power for making confident conclusions.

Until research efforts produce more definitive results, health care policy and clinical practice judgments are best informed by the evidence about the effectiveness of manipulation, plausible treatment options (including non-thrust manual techniques) and individual patient values [20].

Conclusions

Our findings should be viewed in the context of the body of knowledge concerning the risk of VBA stroke. In contrast to several other case�control studies, we found no significant association between exposure to chiropractic care and the risk of VBA stroke. Our secondary analysis clearly showed that manipulation may or may not have been reported at every chiropractic visit. Therefore, the use of chiropractic visits as a proxy for manipulation may not be reliable. Our results add weight to the view that chiropractic care is an unlikely cause of VBA strokes. However, the current study does not exclude cervical manipulation as a possible cause or contributory factor in the occurrence of VBA stroke.

Authors’ Contributions

DE conceived of the study, and participated in its design and coordination. JT participated in the design of the study, performed the statistical analysis and helped to draft the manuscript. TMK participated in the design and coordination of the study, and wrote the initial draft and revisions of the manuscript. WMB participated in the coordination of the study and the statistical analysis, and helped to draft the manuscript. All authors contributed to the interpretation of the data. All authors read and approved the final manuscript.

Author Details

1Optum Health � Clinical Programs at United Health Group, 11000 Optum Circle, Eden Prairie MN 55344, USA. 2Optum Health � Clinical Analytics at United Health Group, 11000 Optum Circle, Eden Prairie MN 55344, USA.

Received: 14 October 2014 Accepted: 28 April 2015

Published Online: 16 June 2015

References
1. Paulose R, Hertz R. The burden of pain among adults in the United States. In Pfizer Facts. Edited by Pfizer Inc. 2008. [http://www.pfizer.com/files/products/PF_Pain.pdf] Accessed May 14, 2014.
2. Carroll L, Hogg-Johnson S, van der Velde G, Haldeman S, Holm L, Carragee E, et al. Bone and Joint Decade 2000�2010 Task Force on Neck Pain and Its Associated Disorders: Course and prognostic factors for neck pain in the
general population: results of the Bone and Joint Decade 2000�2010 Task Force on Neck Pain and Its Associated Disorders. Spine (Phila Pa 1976).2008;33(4 Suppl):S75�82.
3. Hoy D, Protani M, De R, Buchbinder R. The epidemiology of neck pain. Best Pract Res Clin Rheumatol. 2010;24(6):783�92.
4. Jacobs J, Andersson G, Bell J, Weinstein S, Dormans J, Gnatz S, et al. Spine: low back and neck pain. In The Burden of Musculoskeletal Diseases in the United States. Chapter 2. Edited by Bone and Joint Decade USA
2002�2011. Rosemont, IL: The American Academy of Orthopaedic Surgeons; 2008:21�56.
5. Christensen M, Kollasch M, Hyland J, Rosner A. Chapter 8 � Patient Conditions. In Practice Analysis of Chiropractic: A Project Report, Survey Analysis, and Summary of the Practice of Chiropractic Within the United States. Greeley, CO: The National Board of Chiropractic Examiners. 2010:95�120.
6. Christensen M, Kollasch M, Hyland J, Rosner A. Chapter 9 � Professional functions and treatment procedures. In Practice Analysis of Chiropractic: A Project Report, Survey Analysis, and Summary of the Practice of
Chiropractic Within the United States. Greeley, CO: The National Board of Chiropractic Examiners. 2010:121�136.
7. D�Sylva J, Miller J, Gross A, Burnie S, Goldsmith G, Graham N, et al. Manual therapy with or without physical medicine modalities for neck pain: a systematic review. Man Ther. 2010;15(4):415�33.
8. Gross A, Miller J, D�Sylva J, Burnie S, Goldsmith G, Graham N, et al. Manipulation or mobilisation for neck pain: A Cochrane review. Man Ther. 2010;15(4):315�33.
9. Bryans R, Decina P, Descarreaux M, Duranleau M, Marcoux H, Potter B, et al. Evidence-based guidelines for the chiropractic treatment of adults with neck pain. J Manipulative Physiol Ther. 2014;37(1):42�63.
10. Bryans R, Descarreaux M, Duranleau M, Marcoux H, Potter B, Ruegg R, et al. Evidence-based guidelines for the chiropractic treatment of adults withheadache. J Manipulative Physiol Ther. 2011;34(5):274�89.
11. Childs J, Cleland J, Elliott J, Teyhen D, Wainner R, Whitman J, et al. Neck pain: clinical practice guidelines linked to the International Classification of Functioning, Disability, and Health from the Orthopaedic
Section of the American Physical Therapy Association. J Orthop Sports Phys Ther. 2008;38(9):A1�A34.
12. Clar C, Tsertsvadze A, Court R, Hundt G, Clarke A, Sutcliffe P. Clinical effectiveness of manual therapy for the management of musculoskeletal and non-musculoskeletal conditions: systematic review and update of UK
evidence report. Chiropr Man Therap. 2014;22(1):12.
13. Vincent K, Maigne J, Fischhoff C, Lanlo O, Dagenais S. Systematic review of manual therapies for nonspecific neck pain. Joint Bone Spine. 2013;80(5):508�15.
14. Bronfort G, Assendelft W, Evans R, Haas M, Bouter L. Efficacy of spinal manipulation for chronic headache: a systematic review. J Manipulative Physiol Ther. 2001;24(7):457�66.
15. Chaibi A, Tuchin P, Russell M. Manual therapies for migraine: a systematic review. J Headache Pain. 2011;12(2):127�33.
16. Racicki S, Gerwin S, Diclaudio S, Reinmann S, Donaldson M. Conservative physical therapy management for the treatment of cervicogenic headache: a systematic review. J Man Manip Ther. 2013;21(2):113�24.
17. Cassidy J, Bronfort G, Hartvigsen J. Should we abandon cervical spine manipulation for mechanical neck pain? No BMJ. 2012;344, e3680.
18. Wand B, Heine P, O�Connell N. Should we abandon cervical spine manipulation for mechanical neck pain? Yes BMJ. 2012;344, e3679.
19. Moloo J. What’s the Best Approach for Managing Neck Pain? NEJM Journal Watch 2012. [http://www.jwatch.org/jw201202090000004/2012/02/09/whats-best-approach-managing-neck-pain] Accessed May 14, 2014.
20. Schneider M, Weinstein S, Chimes G. Cervical manipulation for neck pain. PM&R. 2012;4(8):606�12.
21. Biller J, Sacco R, Albuquerque F, Demaerschalk B, Fayad P, Long P, et al. Cervical arterial dissections and association with cervical manipulative therapy:a statement for healthcare professionals from the American Heart Association/American Stroke Association. Stroke 2014, Epub ahead of print.
22. American Chiropractic Association: ACA Response to AHA Statement on Neck Manipulation. 2014 (Aug 7). [http://www.acatoday.org/press_css.cfm? CID=5534] Accessed August 15, 2014.
23. American Physical Therapy Association: APTA responds to American Heart Association cervical manipulation paper. 2014 (Aug 7). [http://www.apta.org/Media/Releases/Consumer/2014/8/7/] Accessed August 15, 2014.
24. Kardys JA. Declaratory ruling regarding informed consent. Connecticut State Board of Chiropractic Examiners � State of Connecticut Department of Public Health. 2010. [http://www.ctchiro.com/upload/news/44_0.pdf]
Accessed May 14, 2014.
25. Wangler M, Fujikawa R, Hestb�k L, Michielsen T, Raven T, Thiel H, et al. Creating European guidelines for Chiropractic Incident Reportingand Learning Systems (CIRLS): relevance and structure. Chiropr Man
Therap. 2011;19:9.
26. Berger S: How safe are the vigorous neck manipulations done by chiropractors? Washington Post 2014 (Jan. 6). [http://www.washingtonpost.com/national/health-science/how-safe-are-the-vigorous-neck-manipulationsdone-by-chiropractors/2014/01/06/26870726-5cf7-11e3-bc56-c6ca94801fac_story.html] Accessed January 10, 2014.
27. Group wants provincial ban on some neck manipulation by chiropractors. Winnipeg Free Press 2012 (Oct 4). [http://www.winnipegfreepress.com/local/Group-wants-provincial-ban-on-some-neck-manipulation-bychiropractors-172692471.htm] Accessed May 14, 2014.
28. Gouveia L, Castanho P, Ferreira J. Safety of chiropractic interventions: a systematic review. Spine (Phila Pa 1976). 2009;34(11):E405�13.
29. Carlesso L, Gross A, Santaguida P, Burnie S, Voth S, Sadi J. Adverse events associated with the use of cervical manipulation and mobilization for the treatment of neckpain in adults: a systematic review. Man Ther. 2010;15(5):434 44.
30. Chung C, C�t� P, Stern P, L’Esp�rance G. The association between cervical spine manipulation and carotid artery dissection: a systematic review of the literature. J Manipulative Physiol Ther 2014, [Epub ahead of print].
31. Haynes M, Vincent K, Fischhoff C, Bremner A, Lanlo O, Hankey G. Assessing the risk of stroke from neck manipulation: a systematic review. Int J Clin Pract. 2012;66(10):940�7.
32. Cassidy J, Boyle E, Cote P, He Y, Hogg-Johnson S, Silver F, et al. Risk of vertebrobasilar stroke and chiropractic care: results of a population-based case�control and case-crossover study. Spine (Phila Pa 1976).
2008;33 Suppl 4:S176�83.
33. Rothwell D, Bondy S, Williams J. Chiropractic manipulation and stroke: a population-based case�control study. Stroke. 2001;32(5):1054�60.
34. Choi S, Boyle E, C�t� P, Cassidy JD. A population-based case-series of Ontario patients who develop a vertebrobasilar artery stroke after seeing a chiropractor. J Manipulative Physiol Ther. 2011;34(1):15�22.
35. U.S. Census Bureau: State and County QuickFacts. Data derived from Population Estimates, American Community Survey, Census of Population and Housing, State and County Housing Unit Estimates, County Business
Patterns, Nonemployer Statistics, Economic Census, Survey of Business Owners, Building Permits. 2014 (rev July 8). [http://quickfacts.census.gov/qfd/states/00000.html] Accessed August 19, 2014.
36. Kosanke J, Bergstralh E. GMatch Macro (SAS program): Mayo Clinic College of Medicine. 2004. [http://www.mayo.edu/research/departments-divisions/department-health-sciences-research/division-biomedical-statisticsinformatics/software/locally-written-sas-macros]Accessed June 6, 2014.

37. Smith W, Johnston S, Skalabrin E, Weaver M, Azari P, Albers G, et al. Spinal manipulative therapy is an independent risk factor for vertebral artery dissection. Neurology. 2003;60(9):1424�8.
38. Engelter S, Grond-Ginsbach C, Metso T, Metso A, Kloss M, Debette S, et al. Cervical Artery Dissection and Ischemic Stroke Patients Study Group: Cervical artery dissection: trauma and other potential mechanical trigger
events. Neurology. 2013;80(21):1950�7.
39. Ardal S, Baigent L, Bains N, Hay C, Lee P, Loomer S: The health analyst�s toolkit. Ministry of Health and Long-Term Care Health Results Team – Information Management. Ontario (CA) 2006 (January) [http://www.health.gov.on.ca/transformation/providers/information/resources/analyst_toolkit.pdf]
Accessed January 12, 2015.
40. Sacco RL, Benjamin EJ, Broderick JP, Dyken M, Easton JD, Feinberg WM, et al. American Heart Association Prevention Conference. IV. Prevention and rehabilitation of stroke. Risk factors. Stroke. 1997;28(7):1507�17.
41. Debette S, Metso T, Pezzini A, Abboud S, Metso A, Leys D, et al. Cervical Artery Dissection and Ischemic Stroke Patients (CADISP) Group: Association of vascular risk factors with cervical artery dissection and ischemic stroke in
young adults. Circulation. 2011;123(14):1537�44.
42. Guyatt G, Oxman A, Kunz R, Brozek J, Alonso-Coello P, Rind D, et al. GRADE guidelines 6. Rating the quality of evidence � imprecision. J Clin Epidemiol. 2011;64(12):1283�93.
43. Krarup L, Boysen G, Janjua H, Prescott E, Truelsen T. Validity of stroke diagnoses in a National Register of Patients. Neuroepidemiology. 2007;28(3):150�4.
44. Goldstein L. Accuracy of ICD-9-CM coding for the identification of patients with acute ischemic stroke: effect of modifier codes. Stroke. 1998;29(8):1602�4.
45. Liu L, Reeder B, Shuaib A, Mazagri R. Validity of stroke diagnosis on hospital discharge records in Saskatchewan, Canada: implications for stroke surveillance. Cerebrovasc Dis. 1999;9(4):224�30.
46. Ellekjaer H, Holmen J, Kr�ger O, Terent A. Identification of incident stroke in Norway: hospital discharge data compared with a population-based stroke register. Stroke. 1999;30(1):56�60.
47. Braksiak R, Roberts D. Amusement park injuries and deaths. An Emerg Med. 2002;39(1):65�72.
48. Dittrich R, Rohsbach D, Heidbreder A, Heuschmann P, Nassenstein I, Bachmann R, et al. Mild mechanical traumas are possible risk factors for cervical artery dissection. Cerebrovasc Dis. 2007;23(4):275�81.
49. Mas J, Bousser M, Hasboun D, Laplane D. Extracranial vertebral artery dissection: a review of 13 cases. Stroke. 1987;18(6):1037�47.
50. Slankamenac P, Jesic A, Avramov P, Zivanovic Z, Covic S, Till V. Multiple cervical artery dissection in a volleyball player. Arch Neuro. 2010;67(8):1024�5.
51. Weintraub M. Beauty parlor stroke syndrome: report of five cases. JAMA. 1993;269(16):2085�6.
52. Tzourio C, Benslamia L, Guilllon B, A�di S, Bertrand M, Berthet K, et al. Migraine and the risk of cervical artery dissection: a case control study. Neurology. 2002;59(3):435�7.
53. Guillon B, Berthet K, Benslamia L, Bertrand M, Bousser M, Tzourio C. Infection and the risk of cervical artery dissection: a case�control study. Stroke. 2003;34(7):e79�81.
54. Symons B, Leonard TR, Herzog W. Internal forces sustained by the vertebral artery during spinal manipulative therapy. J Manip Physiol Ther.2002;25(8):504�10.
55. Wuest S, Symons B, Leonard T, Herzog W. Preliminary report: biomechanics of vertebral artery segments C1-C6 during cervical spinal manipulation. J Manip Physiol Ther. 2010;33(4):273�8.
56. Herzog W, Leonard TR, Symons B, Tang C, Wuest S. Vertebral artery strains during high-speed, low amplitude cervical spinal manipulation. J Electromyogr Kinesiol. 2012;22(5):747�51.
57. Centers for Medicare & Medicaid: Comprehensive error rate testing (CERT). 2015 (Jan. 15). [http://www.cms.gov/Research-Statistics-Data-and-Systems/Monitoring-Programs/Medicare-FFS-Compliance-Programs/CERT/index.html?redirect=/cert] Accessed February 4, 2015.
58. Welsh E: Dealing with data: using NVivo in the qualitative data analysis process. Forum: Qualitative Social Research 2002, 3(2): Art. 26 [http://nbnresolving.de/urn:nbn:de:0114-fqs0202260] Accessed February 4, 2015.

Chiropractic Care & Cervical Artery Dissection

Chiropractic Care & Cervical Artery Dissection

by | Chiropractic, Chiropractic News, Health

�Systematic Review and Meta-analysis of

Chiropractic Care and Cervical Artery

Dissection: No Evidence for Causation

Disclosures can be found in Additional Information at the end of the article

Background

Case reports and case control studies have suggested an association between chiropractic neck manipulation and cervical artery dissection (CAD), but a causal relationship has not been established. We evaluated the evidence related to this topic by performing a systematic review and meta-analysis of published data on chiropractic manipulation and CAD.

Methods

Search terms were entered into standard search engines in a systematic fashion. The articles were reviewed by study authors, graded independently for class of evidence, and combined in a meta-analysis. The total body of evidence was evaluated according to GRADE criteria.

Results

Our search yielded 253 articles. We identified two class II and four class III studies. There were no discrepancies among article ratings (i.e., kappa=1). The meta-analysis revealed a small association between chiropractic care and dissection (OR 1.74, 95% CI 1.26-2.41). The quality of the body of evidence according to GRADE criteria was “very low.”

Conclusions

The quality of the published literature on the relationship between chiropractic manipulation and CAD is very low. Our analysis shows a small association between chiropractic neck manipulation and cervical artery dissection. This relationship may be explained by the high risk of bias and confounding in the available studies, and in particular by the known association of neck pain with CAD and with chiropractic manipulation. There is no convincing evidence to support a causal link between chiropractic manipulation and CAD. Belief in a causal link may have significant negative consequences such as numerous episodes of litigation.

Categories: Neurology, Neurosurgery, Public Health
Keywords: vertebral atery dissection, cervical artery dissection, chiropractic manipulation, cervical manipulation, internal carotid artery dissection, cervical spine manipulative therapy

Introduction

� Copyright 2016
Church et al. This is an open access article distributed under the terms of the Creative Commons Attribution License CC-BY 3.0., which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

How to cite this article

Church E W, Sieg E P, Zalatimo O, et al. (February 16, 2016) Systematic Review and Meta-analysis of Chiropractic Care and Cervical Artery Dissection: No Evidence for Causation. Cureus 8(2): e498. DOI 10.7759/cureus.498

 

Neck pain is a common complaint in physicians� and chiropractors� offices. Data from the Centers for Disease Control and from national surveys document 10.2 million ambulatory care visits for a neck problem in 2001 and 2002. By comparison, there were 11 million office-based visits for ischemic heart disease [1]. Many patients with neck pain seek chiropractic care and undergo cervical manipulation. As many as 12% of North Americans receive chiropractic care every year, and a majority of these are treated with spinal manipulation [2].

In contrast to the frequency of neck pain and chiropractic treatments, spontaneous cervical artery dissection (CAD) is rare. The annual incidence of internal carotid artery dissection has been estimated at 2.5�3 per 100,000 patients and that of vertebral artery dissection at 1�1.5 per 100,000 [3]. Stroke occurs in a small proportion of those with CAD, and its true incidence is difficult to estimate. Overall, dissection accounts for two percent of all ischemic strokes [4].

Case reports and case series of cervical dissection following manipulation have been published. Despite their rarity, these cases are frequently publicized for several reasons. Patients are often young and otherwise in good health. Dissection accounts for 10�25% of ischemic strokes in young and middle aged patients [4]. If dissection is caused by cervical manipulation it is potentially a preventable condition. Recent reports, including case control studies, have suggested an association between chiropractic neck manipulation and cervical dissection [5- 10]. Notably, a recent study from the American Heart Association evaluated the available evidence and concluded such an association exists [11]. This report did not include a meta- analysis, nor did it seek to classify studies and grade the body of evidence. We sought to examine the strength of evidence related to this question by performing a systematic review, meta-analysis, and evaluation of the body of evidence as a whole.

Materials & Methods

Search terms �chiropract*,� �spinal manipulation,� �carotid artery dissection,� �vertebral artery dissection,� and �stroke� were included in the search. We used the Medline and Cochrane databases. We additionally reviewed references of key articles for completeness. A librarian with expertise in systematic review was consulted throughout the search process.

Two study authors independently reviewed all articles (EC, ES). They selected any applicable studies for evaluation based on pre-specified inclusion and exclusion criteria. We included only human trials examining patients with carotid or vertebrobasilar artery dissection and recent chiropractic neck manipulation. We excluded non-English language studies. The articles were independently graded using the classification of evidence scheme adopted by the American Academy of Neurology [12-14]. A third author (MG) arbitrated any discrepancies in the class- of-evidence ratings for the included studies.

Data from all class II and III studies were included in a meta-analysis. A second meta-analysis excluding class III studies was also performed. The inverse variance method and a fixed effects model were employed. Additionally, we report results using a variable effects model. The analyses were performed using RevMan 5.3 software from the Cochrane Informatics and Knowledge Management Department. We did not compose a protocol for our review, although PRISMA and MOOSE methodologies were used throughout [15-16].

We evaluated the total body of evidence for quality using the GRADE system [17-20]. A final GRADE designation was achieved by consensus after discussions involving all study authors as recommended by GRADE guidelines. This system is designed to assess the total body of evidence rather than individual studies. The criteria include study design, risk of bias, inconsistency, indirectness, imprecision, publication bias, effect size, dose response, and all plausible residual confounding. Four possible final designations are specified: high, moderate,�low, and very low quality.

Results

Results of the systematic review

Our search strategy yielded 253 articles. Seventy-seven were judged by all reviewers to be non- relevant. Four articles were judged to be class III studies, and two were rated class II. There were no discrepancies between the independent ratings (i.e., kappa=1). Studies rated class III or higher are listed in Table 1. Figure 1 outlines our process of selecting studies for inclusion in the meta-analysis.

table-1-7.png

Meta-Analysis

Combined data from class II and III studies suggests an association between dissection and chiropractic care, OR 1.74, 95% CI 1.26-2.41 (Figure 2). The result was similar using a random effects model, OR 4.05, 95% CI 1.27-12.91. We did not include the study by Rothwell et al. because it describes a subset of patients in the study by Cassidy et al. [5,8]. There was considerable heterogeneity among the studies (I2=84%).

We repeated the meta-analysis excluding class III studies. The combined effect size was again indicative of a small association between dissection and chiropractic care, OR 3.17, 95% CI 1.30-7.74). The result was identical when using a random effects model.

Class II Studies

Smith et al. used a retrospective case control design, combining databases from two academic stroke centers to identify cases of arterial dissection [9]. They found 51 cases and 100 controls. Exposure to spinal manipulative therapy (SMT) was assessed by mail survey. The authors reported an association between SMT and VBA (P = .032). In multivariate analysis, chiropractor care within 30 days was associated with VBA, even when adjusting for neck pain or headache (OR 6.6, 95% CI 1.4-30). While this study controlled for possible confounders such as neck pain, there were several limitations. Head and neck pain as well as chiropractor visit were assessed in a retrospective fashion by mail survey, very possibly introducing both recall and survivor bias. The reason for reporting to the chiropractor (e.g., trauma) was not assessed. Further, there was significant variability among diagnostic procedures, which may reflect increased motivation by physicians to rule out dissection in patients with a history of SMT. Such motivation could result in interviewer bias.

Dittrich et al. compared 47 patients with CAD to a control group with stroke due to etiologies other than dissection [6]. They assessed for risk factors using a face-to-face interview with blinding. These authors found no association between any individual risk factor and CAD, including cervical manipulative therapy. They blame the small sample size for the negative result, and they point out that cumulative analysis of all mechanical risk factors <24 hours prior to symptom onset showed an association (P = .01). This study is subject to recall bias.

Class III Studies

Rothwell et al. used a retrospective case control design to test for an association between chiropractic manipulation and vertebrobasilar accidents (VBA) [8]. They reviewed Ontario hospital records for admissions for VBA from 1993�1998. There were 582 cases and 2328 matching controls. The authors report an association between VBA and visit to a chiropractor within one week (OR 5.03, 95% CI 1.32-43.87), but this was only true for young patients (<45 years). This study represented the first attempt to delineate the association between chiropractic manipulation and extremely rare VBA with controls. Limitations included requisite use of ICD-9 codes to identify cases and associated classification bias, as well as potential unmeasured confounders (e.g., neck pain).

In 2008, Cassidy et al. set out to address the problem of neck pain possibly confounding the association between chiropractic care and VBA [5]. Again using a retrospective case control design, they included all residents of Ontario over a period of 9 years (1993�2002, 109,020,875 person years of observation). They identified 818 VBA strokes resulting in hospitalization and randomly selected age and sex matched controls. Next, they examined ambulatory encounters with chiropractors and primary care physicians (PCPs) in the one year preceding the stroke, limited to cervical manipulation, neck pain, and headache. Associations between chiropractor visit and VBA versus PCP visits and VBA were compared. Indeed, there were associations between both chiropractor visit and VBA (<45yrs OR 1.37, 95% CI 1.04-1.91), and PCP visit and VBA (<45 yrs OR 1.34, 95% CI .94-1.87; >45 yrs and OR 1.53, 95% CI 1.36-1.67). The association for chiropractor visit was not greater than for PCP visit. This data was interpreted as evidence that a confounder such as neck pain may account for the association between chiropractor visit and VBA. This study was subject to many of the same limitations as previous efforts. Canadian health records would not reveal whether a patient with cervical complaints underwent cervical manipulation, and the researchers could not review each chart for imaging confirming dissection. Additionally, the incidence of comorbidities (e.g., hypertension, heart disease,�diabetes) was significantly higher among cases as compared to controls, and we are concerned that these differences were non-random.

In another case control study, Thomas et al. compared the records of 47 patients with confirmed or suspected vertebral or internal carotid artery dissection with 43 controls [10]. They limited their analysis to young patients defined as <55 years. These authors report a significant association between dissection and recent head or neck trauma (OR 23.51, 95% CI 5.71-96.89) as well as neck manual therapy (OR 1.67, 95% CI 1.43-112.0). An inconsistent standard for case ascertainment (a significant number of patients lacked radiographic confirmation of dissection) and lack of blinding weaken this study.

Engelter et al. evaluated data from the Cervical Artery Dissection and Ischemic Stroke Patients (CADISP) consortium, identifying 966 patients with CAD, 651 with stroke attributable to another cause, and 280 healthy controls [7]. The CADISP study involved both prospectively and retrospectively collected data at multiple centers in several countries. They assessed for prior cervical trauma within one month using questionnaires administered during clinic visits. Cervical manipulation therapy was more common for CAD versus stroke from another cause (OR 12.1, CI 4.37-33.2). The report notes that an association between any trauma and CAD was present even when restricting the analysis to prospectively recruited patients. However, in patients to whom the questionnaire was administered after dissection, recall bias may have been at work whether or not the patient was enrolled prospectively. Indeed, the frequency of prior cervical trauma in this study was substantially higher than previous reports (40% versus 12-34%). Additional weaknesses include a highly heterogeneous standard for case definition and no clear masking procedures.

Body Of Evidence Quality (GRADE Rating)

Having performed a systematic review and rated articles according to their individual strengths and weaknesses, we graded the overall body of evidence using the system proposed by Guyatt et al. [17-20]. The GRADE approach to rating quality of evidence proposes four categories that are applied to a body of evidence: high, moderate, low, and very low. In the setting of systematic review, a particular rating reflects the extent of confidence that the estimates of effect are correct. The GRADE approach begins with study design and sequentially examines features with the potential to enhance or diminish confidence in the meta-analytic estimate of effect size.

Our final assessment of the quality of the body of evidence using these criteria was very low. The initial rating based on study design was low (observational studies). Given the controversial nature of this topic and the legal ramifications of results, there is certainly potential for bias (-1 serious). However, blinding in the Class II studies mitigated this risk to some extent. Inconsistency and imprecision did not lower our rating. Because the body of evidence is derived from measures of association, the rating was lowered for indirectness (-1 serious). Publication bias is less likely because of the impact of a negative result in this case. The funnel plot from our meta-analysis was inconclusive with regard to possible publication bias because of the small number of studies included but suggested a deficit in the publication of small negative trials. There was not a large effect size, and currently there is no evidence for a dose response gradient. Moreover, the most worrisome potential confounder (neck pain) would increase rather than reduce the hypothesized effect.

Discussion

The results of our systematic review and meta-analysis suggest a small association between chiropractic care and CAD. There are no class I studies addressing this issue, and this conclusion is based on five class II and III studies. Scrutiny of the quality of the body of data�using the GRADE criteria revealed that it fell within the �very low� category. We found no evidence for a causal link between chiropractic care and CAD. This is a significant finding because belief in a causal link is not uncommon, and such a belief may have significant adverse effects such as numerous episodes of litigation.

The studies included in our meta-analysis share several common weaknesses. Two of the five studies used health administrative databases, and since conclusions depend on accurate ICD coding, this technique for case ascertainment may introduce misclassification bias. It is not possible to account for the type of spinal manipulation that may have been used. Retrospective collection of data is also a potential weakness and may introduce recall bias when a survey or interview was used. Moreover, patients arriving at a hospital complaining of neck pain and describing a recent visit to a chiropractor may be subject to a more rigorous evaluation for CAD (interviewer bias). Another potential source of interviewer bias was lack of blinding in the class III studies. Further, we noted substantial variability among diagnostic procedures performed. All of these weaknesses affect the reliability of the available evidence and are not �corrected� by performing a meta-analysis.

Perhaps the greatest threat to the reliability of any conclusions drawn from these data is that together they describe a correlation but not a causal relationship, and any unmeasured variable is a potential confounder. The most likely potential confounder in this case is neck pain. Patients with neck pain are more likely to have CAD (80% of patients with CAD report neck pain or headache) [21], and they are more likely to visit a chiropractor than patients without neck pain (Figure 3). Several of the studies identified in our systematic review provide suggestive evidence that neck pain is a confounder of the apparent association between chiropractic neck manipulation and CAD. For example, in Engelter et al. patients with CAD and prior cervical trauma (e.g., cervical manipulation therapy) were more likely to present with neck pain but less often with stroke than those with CAD and no prior cervical trauma (58% vs. 43% for trauma and 61% vs. 69% for stroke) [7]. If patients with CAD without neurological symptoms came to medical attention, it was probably because of pain. Patients with neck pain would also be more likely to visit a chiropractor than those without neck pain.

Cassidy et al. hypothesized that, although an association between chiropractor visits and vertebrobasilar artery stroke is present, it may be fully explained by neck pain and headache [5]. These authors reviewed 818 patients with vertebrobasilar artery strokes hospitalized in a population of 100 million person-years. They compared chiropractor and PCP visits in this population and reported no significant difference between these associations. For patients under 45 years of age, each chiropractor visit in the previous month increased the risk of stroke (OR 1.37, 95% CI 1.04-1.91), but each PCP visit in the previous month increased the risk in a nearly identical manner (<45 yrs OR 1.34, 95% CI .94-1.87; >45 yrs and OR 1.53, 95% CI 1.36- 1.67). The authors conclude that, since patients with vertebrobasilar stroke were as likely to visit a PCP as they were to visit a chiropractor, these visits were likely due to pain from an existing dissection.

Cervical artery dissection is a rare event, creating a significant challenge for those who wish to understand it. A prospective, randomized study design is best suited to control for confounders, but given the infrequency of dissection, performing such a study would be logistically and also ethically challenging. Sir Austin Bradford Hill famously addressed the problem of assigning causation to an association with the application of nine tests [22]. These criteria include strength, consistency, specificity, temporality, biological gradient, plausibility, coherence, experimental evidence, and analogy. The specific tests and our assessment for the association between cervical manipulation and CAD are summarized in Table 2. In our appraisal, this association clearly passes only one test, it fails four, and the remaining four are equivocal due to absence of relevant data [23]. Further, a 2013 assessment of the quality of reports of cervical arterial dissection following cervical spinal manipulation similarly found lacking data to support a causal relationship [24].

In spite of the very weak data supporting an association between chiropractic neck manipulation and CAD, and even more modest data supporting a causal association, such a relationship is assumed by many clinicians. In fact, this idea seems to enjoy the status of medical dogma. Excellent peer reviewed publications frequently contain statements asserting a causal relationship between cervical manipulation and CAD [4,25,26]. We suggest that physicians should exercise caution in ascribing causation to associations in the absence of adequate and reliable data. Medical history offers many examples of relationships that were initially falsely assumed to be causal [27], and the relationship between CAD and chiropractic neck manipulation may need to be added to this list.

Conclusions

Our systematic review revealed that the quality of the published literature on the relationship between chiropractic manipulation and CAD is very low. A meta-analysis of available data shows a small association between chiropractic neck manipulation and CAD. We uncovered evidence for considerable risk of bias and confounding in the available studies. In particular, the known association of neck pain both with cervical artery dissection and with chiropractic manipulation may explain the relationship between manipulation and CAD. There is no convincing evidence to support a causal link, and unfounded belief in causation may have dire consequences.

Additional Information

Disclosures

Conflicts of interest: The authors have declared that no conflicts of interest exist.

Acknowledgements

The authors wish to thank Elaine Dean, MLS, of the Penn State Hershey Medical Center George T. Harrell Health Sciences Library, for her assistance with the systematic review.

References

 

1. Riddle DL, Schappert SM: Volume and characteristics of inpatient and ambulatory medical care for neck pain in the United States: data from three national surveys. Spine. 2007, 32:132�140.
2. Hurwitz EL, Chiang LM: A comparative analysis of chiropractic and general practitioner patients in North America: findings from the joint Canada/United States survey of health, 2002-03. BMC Health Serv Res. 2006, 6:49. 10.1186/1472-6963-6-49
3. Micheli S, Paciaroni M, Corea F, et al.: Cervical artery dissection: emerging risk factors . Open Neurol J. 2010, 4:50�55. 10.2174/1874205X01004010050
4. Schievink WI: Spontaneous dissection of the carotid and vertebral arteries . N Engl J Med. 2001, 344:898�906. 10.1056/NEJM200103223441206
5. Cassidy JD, Boyle E, C�t� PDC, et al.: Risk of vertebrobasilar stroke and chiropractic care: results of a population-based case-control and case-crossover study. Spine. 2008, 33:176�183.10.1097/BRS.0b013e3181644600
6. Dittrich R, Rohsbach D, Heidbreder A, et al.: Mild mechanical traumas are possible risk factors for cervical artery dissection. Cerebrovasc Dis. 2007, 23:275�281. 10.1159/000098327
7. Engelter ST, Grond-Ginsbach C, Metso TM, et al.: Cervical artery dissection: trauma and other potential mechanical trigger events. Neurology. 2013, 80:1950�1957.10.1212/WNL.0b013e318293e2eb
8. Rothwell DM, Bondy SJ, Williams JI: Chiropractic manipulation and stroke: a population based case-control study. Stroke. 2001, 32:1054-1060.
9. Smith WS, Johnston SC, Skalabrin EJ, et al.: Spinal manipulative therapy is an independent risk factor for vertebral artery dissection. Neurology. 2003, 60:1424-1428.10. Thomas LC, Rivett DA, Attia JR, et al.: Risk factors and clinical features of craniocervical arterial dissection. Man Ther. 2011, 16:351�356. 10.1016/j.math.2010.12.008
11. Biller J, Sacco RL, Albuquerque FC, et al.: Cervical arterial dissections and association with cervical manipulative therapy: a statement for healthcare professionals from the American Heart Association/American Stroke Association. Stroke. 2014, 45:3155�3174.10.1161/STR.0000000000000016
12. AAN (American Academy of Neurology): Clinical Practice Guideline Process Manual. Gronseth GS, Woodroffe LM, Getchius TSD (ed): AAN (American Academy of Neurology), St Paul, MN; 2011.
13. French J, Gronseth G: Lost in a jungle of evidence: we need a compass . Neurology. 2008, 71:1634�1638. 10.1212/01.wnl.0000336533.19610.1b 2016 Church et al. Cureus 8(2): e498. DOI 10.7759/cureus.498 10 of 11
14. Gross RA, Johnston KC: Levels of evidence: taking Neurology� to the next level . Neurology. 2009, 72:8�10. 10.1212/01.wnl.0000342200.58823.6a
15. Moher D, Liberati A, Tetzlaff J, et al.: Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. PLoS Med. 2009, 6:e1000097. Accessed: January 23, 2016: journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1000097. 10.1371/journal.pmed.1000097
16. Stroup DF, Berlin JA, Morton SC, et al.: Meta-analysis of observational studies inepidemiology: a proposal for reporting. Meta-analysis of observational studies in epidemiology (MOOSE) group. JAMA. 2000, 283:2008-2012.
17. Guyatt G, Oxman AD, Akl EA, et al.: GRADE guidelines: 1. Introduction-GRADE evidence profiles and summary of findings tables. J Clin Epidemiol. 2011, 64:383�394. 10.1016/j.jclinepi.2010.04.026
18. Guyatt GH, Oxman AD, Kunz R, et al.: GRADE guidelines: 2. Framing the question and deciding on important outcomes. J Clin Epidemiol. 2011, 64:395�400. 10.1016/j.jclinepi.2010.09.012
19. Balshem H, Helfand M, Sch�nemann HJ, et al.: GRADE guidelines: 3. Rating the quality of evidence. J Clin Epidemiol. 2011, 64:401�406. 10.1016/j.jclinepi.2010.07.015
20. The Cochrane Collaboration: Cochrane Handbook for Systematic Reviews of Interventions (Version 5.1.0). Higgins JPT, Green S (ed): The Cochrane Collaboration, 2011.
21. Lee VH, Brown RD Jr, Mandrekar JN, et al.: Incidence and outcome of cervical artery dissection: a population-based study. Neurology. 2006, 67:1809-1812.
22. Hill AB: The environment and disease: association or causation?. Proc R Soc Med. 1965, 58:295�300.
23. Herzog W, Leonard TR, Symons B, et al.: Vertebral artery strains during high-speed, low amplitude cervical spinal manipulation. J Electromyogr Kinesiol. 2012, 22:740�746. 10.1016/j.jelekin.2012.03.005
24. Wynd S, Estaway M, Vohra S, Kawchuk G: The quality of reports on cervical arterial dissection following cervical spinal manipulation. PLOS ONE. 2013, 8:e59170. Accessed: February 8, 2016: journals.plos.org/plosone/article?id=10.1371/journal.pone.0059170. 10.1371/journal.pone.0059170
25. Albuquerque FC, Hu YC, Dashti SR, et al.: Craniocervical arterial dissections as sequelae of chiropractic manipulation: patterns of injury and management. J Neurosurg. 2011, 115:1197�1205. 10.3171/2011.8.JNS111212
26. Debette S, Leys D: Cervical-artery dissections: predisposing factors, diagnosis, and outcome . Lancet Neurol. 2009, 8:668�678. 10.1016/S1474-4422(09)70084-5
27. Artenstein AW: The discovery of viruses: advancing science and medicine by challenging dogma. Int J Infect Dis. 2012, 16:e470�e473. 10.1016/j.ijid.2012.03.005

Ephraim W. Church 1 , Emily P. Sieg 1 , Omar Zalatimo 1 , Namath S. Hussain 1 , Michael Glantz 1 , Robert E. Harbaugh 1

1. Department of Neurosurgery, Penn State Hershey Medical Center
Corresponding author: Ephraim W. Church, echurch@hmc.psu.edu

Vertebrobasilar Stroke, Chiropractic Care & Risks

Vertebrobasilar Stroke, Chiropractic Care & Risks

by | Chiropractic, Chiropractic News, Health, Physical Rehabilitation

Results Of A Population-Based Case-Control & Case-Crossover Study

J. David Cassidy, DC, PhD, DrMedSc,*�� Eleanor Boyle, PhD,* Pierre Co�te ?, DC, PhD,*��� Yaohua He, MD, PhD,* Sheilah Hogg-Johnson, PhD,�� Frank L. Silver, MD, FRCPC, and Susan J. Bondy, PhD�

SPINE Volume 33, Number 4S, pp S176 �S183 �2008, Lippincott Williams & Wilkins

 

Study.png

Neck pain is a common problem associated with consid- erable comorbidity, disability, and cost to society.1�5 In North America, the clinical management of back pain is provided mainly by medical physicians, physi- cal therapists and chiropractors.6 Approximately 12% of American and Canadian adults seek chiropractic care annually and 80% of these visits result in spinal manipulation.7,8 When compared to those seeking medical care for back pain, Canadian chiropractic pa- tients tend to be younger and have higher socioeco- nomic status and fewer health problems.6,8 In On- tario, the average number of chiropractic visits per episode of care was 10 (median 6) in 1985 through 1991.7 Several systematic reviews and our best- evidence synthesis suggest that manual therapy can benefit neck pain, but the trials are too small to eval- uate the risk of rare complications.9 �13

Two deaths in Canada from vertebral artery dissection and stroke following chiropractic care in the 1990s attracted much media attention and a call by some neurologists to avoid neck manipulation for acute neck pain.14 There have been many published case reports linking neck manipulation to vertebral artery dissection15�and stroke.�The prevailing theory is that extension�and/or rotation of the neck can damage the vertebral artery, particularly within the foramen transversarium at the C1�C2 level. Activities leading to sudden or sustained rotation and extension of the neck have been implicated, included motor vehicle collision, shoulder checking while driving, sports, lifting, working over- head, falls, sneezing, and coughing.16 However, most cases of extracranial vertebral arterial dissection are thought to occur spontaneously, and other factors such as connective tissue disorders, migraine, hyper- tension, infection, levels of plasma homocysteine, vessel abnormalities, atherosclerosis, central venous�catherization, cervical spine surgery, cervical percutaneous nerve blocks, radiation therapy and diagnostic cerebral angiography have been identified as possible risk factors.17�21

The true incidence of vertebrobasilar dissection is un- known, since many cases are probably asymptomatic, or the dissection produces mild symptoms.22 Confirming the diagnosis requires a high index of suspicion and good vascular imaging. The cases that are most likely to be diagnosed are those that result in stroke.19,22 Ischemic stroke occurs when a thrombus develops intraluminally and embolizes to more distal arteries, or less commonly, when the dissection extends distally into the intracranial vertebral artery, obliterating branching vessels.22 The best incidence estimate comes from Olmstead county, where vertebral artery dissection causing stroke affected 0.97 residents per 100,000 population between 1987 and 2003.23

To date there have been two case-control studies of stroke following neck manipulation. Rothwell et al used Ontario health data to compare 582 cases of VBA stroke to 2328 age and sex-matched controls.24 For those aged 45 years, cases were five times more likely than con- trols to have visited a chiropractor within 1 week of VBA stroke. Smith et al studied 51 patients with cervical ar- tery dissection and ischemic stroke or transient ischemic attack (TIA) and compared them to 100 control patients suffering from other strokes not caused by dissections.25 Cases and controls came from two academic stroke cen- ters in the United States and were matched on age and sex. They found no significant association between neck manipulation and ischemic stroke or TIA. However, a subgroup analysis showed that the 25 cases with verte- bral artery dissection were six times more likely to have consulted a chiropractor within 30 days before their stroke than the controls.

Finally, because patients with vertebrobasilar artery dissection commonly present with headache and neck pain,23 it is possible that patients seek chiropractic care for these symptoms and that the subsequent VBA stroke occurs spontaneously, implying that the associ- ation between chiropractic care and VBA stroke is not causal.23,26 Since patients also seek medical care for headache and neck pain, any association between pri- mary care physician (PCP) visits and VBA stroke could be attributed to seeking care for the symptoms of verte- bral artery dissection.

The purpose of this study is to investigate the association between chiropractic care and VBA stroke and compare it to the association between recent PCP care and VBA stroke using two epidemiological designs. Evidence that chiropractic care increases the risk of VBA stroke would be present if the measured association between chiropractic visits and VBA stroke exceeds the association between PCP visits and VBA strokes.

Study Design

We undertook population-based case-control and case- crossover studies. Both designs use the same cases. In the case- control design, we sampled independent control subjects from the same source population as the cases. In the case-crossover design, cases served as their own controls, by sampling control periods before the study exposures.27 This design is most appropriate when a brief exposure (e.g., chiropractic care) causes a transient change in risk (i.e., hazard period) of a rare-onset disease (e.g., VBA stroke). It is well suited to our research questions, since within person comparisons control for unmeasured risk factors by design, rather than by statistical modeling.28 �30 Thus the advantage over the case control design is better control of confounding.

Source Population

The source population included all residents of Ontario (109,020,875 person-years of observation over 9 years) covered by the publicly funded Ontario Health Insurance Plan (OHIP). Available utilization data included hospitalizations with diagnostic coding, and practitioner (physician and chiropractic) utilization as documented by fee-for-service billings accompanied by diagnostic coding. We used two data sources: (1) the Discharge Abstract Database (DAD) from the Canadian Institute for Health Information, which captures hospital separations and ICD codes, and (2) the OHIP Databases for services provided by physicians and chiropractors. These data- bases can be linked from April 1992 onward.

Cases

We included all incident vertebrobasilar occlusion and stenosis strokes (ICD-9433.0 and 433.2) resulting in an acute care hospital admission from April 1, 1993 to March 31, 2002. Codes were chosen in consultation with stroke experts and an epidemiologist who participated in a similar past study (SB).24 Cases that had an acute care hospital admission for any type of stroke (ICD-9433.0, 433.2, 434, 436, 433.1, 433.3, 433.8, 433.9, 430, 431, 432, and 437.1), transient cerebral ischemia (ICD- 9435) or late effects of cerebrovascular diseases (ICD-9438) before their VBA stroke admission or since April 1, 1991 were excluded. Cases residing in long-term care facilities were also excluded. The index date was defined as the hospital admission date for the VBA stroke.

Controls

For the case-control study, four age and sex-matched controls were randomly selected from the Registered Persons Database, which contains a listing of all health card numbers for Ontario. Controls were excluded if they previously had a stroke or were residing in a long-term care facility.

For the case crossover study, four control periods were randomly chosen from the year before the VBA stroke date, using a time-stratified approach.31 The year was divided into disjoint strata with 2 week periods between the strata. For the 1 month hazard period, the disjoint strata were separated by 1 month periods and the five remaining control periods were used in the analyses. We randomly sampled disjoint strata because chiropractic care is often delivered in episodes, and this strategy eliminates overlap bias and bias associated with time trends in the exposure.32

Exposures

All reimbursed ambulatory encounters with chiropractors and PCPs were extracted for the one-year period before the index date from the OHIP database. Neck-related chiropractic visits were identified using diagnostic codes: C01�C06, cervical and cervicothoracic subluxation; C13�C15, multiple site subluxation; C30, cervical sprain/strain; C40, cervical neuritis/ neuralgia; C44, arm neuritis/neuralgia; C50, brachial radiculitis; C51, cervical radiculitis; and C60, headache. For PCP visits, we included community medicine physicians if they submitted ambulatory fee codes to OHIP. Fee codes for group therapy and signing forms were excluded. Headache or neck pain- related PCP visits were identified using the diagnostic codes: ICD-9307, tension headaches; 346, migraine headaches; 722, intervertebral disc disorders; 780, headache, except tension headache and migraine; 729, fibrositis, myositis and muscular rheumatism; and 847, whiplash, sprain/strain and other traumas associated with neck (These codes include other diagnoses, and we list only those relevant to neck pain or headache). There is no limit on the number of reimbursed PCP visits per year. However, there are limits chiropractors, but less than 15% of patients surpass them.24

Statistical Analysis

Conditional logistic regression was used to estimate the asso- ciation between VBA stroke after chiropractor and PCP visits. Separate models were built using different a priori specified hazard periods, stratified by age ( 45 years and 45 years) and by visits with or without head and neck pain related diag- nostic codes. For the chiropractic analysis, the index date was included in the hazard period, since chiropractic treatment might cause immediate stroke and patients would not normally consult a chiropractor after having a stroke. However, the in- dex day was excluded from the PCP analysis, since patients might consult these physicians after experiencing a stroke. We tested different hazard periods, including 1 day, 3 days, 1 week, 2 weeks, and 1 month before the index date. Exposure occurred if any chiropractic or PCP visits were recorded during the des- ignated hazard periods.

We also measured the effect of cumulative numbers of chiropractic and PCP visits in the month before the index date by computing the odds ratio for each incremental visit. These estimates were similarly stratified by age and by diagnostic codes related to headache and/or neck pain. Finally, we conducted analyses to determine if our results were sensitive to chiropractic and PCP visits related to neck complaints and headaches. We report our results as odds ratios (OR) and 95% confidence intervals. Confidence intervals were estimated by accelerated bias corrected bootstraps with 2000 replications using the variance co-variance method.33 All statistical analyses were per- formed using STATA/SE version 9.2.34

Results

A total of 818 VBA strokes met our inclusion/exclusion criteria over the 9 year inception period. Of the 3272 matched control subjects, 31 were excluded because of prior stroke, one had died before the index date and 76 were receiving long-term care. Thus, 3164 control subjects were matched to the cases. The mean age of cases and controls was 63 years at the index date and 63% were male. Cases had a higher proportion of comorbid conditions (Table 1). Of the 818 stroke cases, 337�(41.2%) were coded as basilar occlusion and stenosis, 443 (54.2%) as vertebral occlusion and stenosis and 38 (4.7%) had both codes.

Overall, 4% of cases and controls had visited a chiropractor within 30 days of the index date, while 53% of cases and 30% of controls had visited a PCP within that time (Table 2). For those under 45 years of age, 8 cases (7.8%) had consulted a chiropractor within 7 days of the index date, compared to 14 (3.4%) of controls. For PCPs, 25 cases (24.5%) under 45 years of age had a consultation within 7 days of the index date, com- pared to 27 (6.6%) of controls. With respect to the number of visits within 1 month of the index date, 7.8% of cases under the age of 45 years had three or more chiropractic visits, whereas 5.9% had three or more PCP visits (Table 2).

The case control and case crossover analyses gave similar results. (Tables 3�7) Age modified the effect of chiropractic visits on the risk of VBA stroke. For those under 45 years of age, there was an increased association between chiropractic visits and VBA stroke regardless of the hazard period. For those 45 years of age and older, there was no association. Each chiropractic visit in the month before the index date was associated with an in- creased risk of VBA stroke in those under 45 years of age (OR 1.37; 95% CI 1.04�1.91 from the case crossover analysis) (Table 7). We were not able to estimate boot- strap confidence intervals in some cases because of sparse data.

Similarly, we found that visiting a PCP in the month before the index date was associated with an increased risk of VBA stroke regardless of the hazard period, or the age of the subject. Each PCP visit in the month before the stroke was associated with an increased risk of VBA stroke both in those under 45 years of age (OR 1.34; 95% CI 0.94 �1.87 from the case crossover analysis) and 45 years and older (OR 1.52; 95% CI 1.36�1.67 from the case crossover analysis) (Table 7).

Our results were sensitive to chiropractic and PCP visits related to neck complaints and headaches, and we observed sharp increases in the associations when restricting the analyses to these visits (Tables 3�7). Overall,�these associations were more pronounced in the PCP analyses. However, the data are sparse, and we were unable to compute bootstrap confidence intervals in many cases.

Discussion

Our study advances knowledge about the association between chiropractic care and VBA stroke in two respects. First, our case control results agree with past case control studies that found an association between chiropractic care and vertebral artery dissection and VBA stroke.24,25 Second, our case crossover results confirm these findings using a stronger research design with better control of confounding variables. The case-crossover design controls for time independent confounding factors, both known and unknown, which could affect the risk of VBA stroke. This is important since smoking, obesity, undiagnosed hypertension, some connective tis- sue disorders and other important risk factors for dissection and VBA stroke are unlikely to be recorded in ad- ministrative databases.

We also found strong associations between PCP visits and subsequent VBA stroke. A plausible explanation for this is that patients with head and neck pain due to vertebral artery dissection seek care for these symptoms, which precede more than 80% of VBA strokes.23 Since it�is unlikely that PCPs cause stroke while caring for these patients, we can assume that the observed association between recent PCP care and VBA stroke represents the background risk associated with patients seeking care for dissection-related symptoms leading to VBA stroke. Be- cause the association between chiropractic visits and VBA stroke is not greater than the association between PCP visits and VBA stroke, there is no excess risk of VBA stroke from chiropractic care.

Our study has several strengths and limitations. The study base includes an entire population over a 9-year period representing 109,020,875 person-years of observation. Despite this, we found only 818 VBA strokes, which limited our ability to compute some estimates and bootstrap confidence intervals. In particular, our age stratified analyses are based on small numbers of ex- posed cases and controls (Table 2). Further stratification by diagnostic codes for headache and neck pain related visits imposed even greater difficulty with these estimates. However, there are few databases that can link�incident VBA strokes with chiropractic and PCP visits in a large enough population to undertake a study of such a rare event.

A major limitation of using health administrative data are misclassification bias, and the possibility of bias in assignment of VBA-related diagnoses, which has previously been raised in this context.24 Liu et al have shown that ICD-9 hospital discharge codes for stroke have a poor positive predictive value when compared to chart review.35 Furthermore, not all VBA strokes are secondary to vertebral artery dissection and administrative databases do not provide the clinical detail to determine the specific cause. To investigate this bias, we did a sensitivity analysis using different positive predictive values for stroke diagnosis (ranging from 0.2 to 0.8). Assuming non differential misclassification of chiropractic and PCP cases, our analysis showed attenuation of the estimates towards the null with lower positive predictive values, but the conclusions did not change (i.e., associations remained positive and significant�data not shown). The�reliability and validity of the codes to classify headache and cervical visits to chiropractors and PCPs is not known.

It is also possible that patients presenting to hospital with neurologic symptoms who have recently seen a chiropractor might be subjected to a more vigorous diagnostic workup focused on VBA stroke (i.e., differential misclassification).36 In this case, the predictive values of the stroke codes would be greater for cases that had seen a chiropractor and our results would underestimate the association between PCP care and VBA stroke.

A major strength of our study is that exposures were measured independently of case definition and handled identically across cases and controls. However, there was some overlap between chiropractic care and PCP care. In the month before their stroke, only 16 (2.0%) of our cases had seen only a chiropractor, while 20 (2.4%) had seen both a chiropractor and PCP, and 417 (51.0%) had�just seen only a PCP. We were not able to run a subgroup analysis on the small number of cases that just saw a chiropractor. However, subgroup analysis on the PCP cases (n 782) that did not visit a chiropractors during the 1 month before their stroke did not change the conclusions (data not shown).

Our results should be interpreted cautiously and placed into clinical perspective. We have not ruled out neck manipulation as a potential cause of some VBA strokes. On the other hand, it is unlikely to be a major cause of these rare events. Our results suggest that the association between chiropractic care and VBA stroke found in previous studies is likely explained by present- ing symptoms attributable to vertebral artery dissection. It might also be possible that chiropractic manipulation, or even simple range of motion examination by any practitioner, could result in a thromboembolic event in a patient with a pre-existing vertebral dissection. Unfortunately, there is no acceptable screening procedure to identify patients with neck pain at risk of VBA stroke.37 These events are so rare and difficult to diagnose that future studies would need to be multi-centered and have unbiased ascertainment of all potential exposures. Given our current state of knowledge, the decision of how to treat patients with neck pain and/or headache should be driven by effectiveness and patient preference.38

Conclusion

Our population-based case-control and case-crossover study shows an association between chiropractic visits and VBA strokes. However, we found a similar association between primary care physician visits and VBA stroke. This suggests that patients with undiagnosed vertebral artery dissection are seeking clinical care for head- ache and neck pain before having a VBA stroke.

Acknowledgments

The authors acknowledge the members of the Decade of the Bone and Joint 2000 �2010 Task Force on Neck Pain and its Associate Disorders for advice about de- signing this study. In particular, they acknowledge the help of Drs. Hal Morgenstern, Eric Hurwitz, Scott Haldeman, Linda Carroll, Gabrielle van der Velde, Lena Holm, Paul Peloso, Margareta Nordin, Jaime Guzman, Eugene Carragee, Rachid Salmi, Alexander Grier, and Mr. Jon Schubert.

References
1. Borghouts JA, Koes BW, Vondeling H, et al. Cost-of-illness of neck pain in The Netherlands in 1996. Pain 1999;80:629�36.
2. Co�te� P, Cassidy JD, Carroll L. The Saskatchewan Health and Back PainSurvey. The prevalence of neck pain and related disability in Saskatchewan adults. Spine 1998;23:1689�98.
3. Co�te� P, Cassidy JD, Carroll L. The factors associated with neck pain and its related disability in the Saskatchewan population. Spine 2000;25:1109�17.
4. Co�te� P, Cassidy JD, Carroll L. Is a lifetime history of neck injury in a trafficcollision associated with prevalent neck pain, headache and depressive symptomatology? Accid Anal Prev 2000;32:151�9.
5. Co�te� P, Cassidy JD, Carroll LJ, et al. The annual incidence and course of neck pain in the general population: a population-based cohort study. Pain 2004; 112:267�73.
6. Co�te� P, Cassidy JD, Carroll L. The treatment of neck and low back pain: who seeks care? who goes where? Med Care 2001;39:956�67.
7. Hurwitz EL, Coulter ID, Adams AH, et al. Use of chiropractic services from 1985 through 1991 in the United States and Canada. Am J Public Health1998;88:771�6.
8. Hurwitz EL, Chiang LM. A comparative analysis of chiropractic and general practitioner patients in North America: findings from the jointCanada/United States Survey of Health, 2002�03. BMC Health Serv Res 2006;6:49.
9. Aker PD, Gross AR, Goldsmith CH, et al. Conservative management of mechanical neck pain: systematic overview and meta-analysis. BMJ 1996; 313:1291�6.
10. Gross AR, Kay T, Hondras M, et al. Manual therapy for mechanical neckdisorders: a systematic review. Man Ther 2002;7:131�49.
11. Hurwitz EL, Aker PD, Adams AH, et al. Manipulation and mobilization of the cervical spine. A systematic review of the literature. Spine 1996;21:1746�59.
12. McClune T, Burton AK, Waddell G. Whiplash associated disorders: a review of the literature to guide patient information and advice. Emerg Med J 2002;19:499�506.
13. Peeters GG, Verhagen AP, de Bie RA, et al. The efficacy of conservative treatment in patients with whiplash injury: a systematic review of clinical trials. Spine 2001;26:E64�E73.
14. Norris JW, Beletsky V, Nadareishvili ZG. Sudden neck movement and cervical artery dissection. The Canadian Stroke Consortium. CMAJ 2000;163:38�40.
15. Ernst E. Manipulation of the cervical spine: a systematic review of case reports of serious adverse events, 1995�2001. Med J Aust 2002;176:376�80.
16. Haldeman S, Kohlbeck FJ, McGregor M. Risk factors and precipitating neckmovements causing vertebrobasilar artery dissection after cervical trauma and spinal manipulation. Spine 1999;24:785�94.
17. Rubinstein SM, Peerdeman SM, van Tulder MW, et al. A systematic reviewof the risk factors for cervical artery dissection. Stroke 2005;36:1575�80.
18. Inamasu J, Guiot BH. Iatrogenic vertebral artery injury. Acta Neurol Scand 2005;112:349�57.
19. Schievink WI. Spontaneous dissection of the carotid and vertebral arteries. N Engl J Med 2001;344:898�906.
20. D�Anglejan-Chatillon J, Ribeiro V, Mas JL, et al. Migraine�a risk factor for dissection of cervical arteries. Headache 1989;29:560�1.
21. Pezzini A, Caso V, Zanferrari C, et al. Arterial hypertension as risk factor for spontaneous cervical artery dissection. A case-control study. J Neurol Neurosurg Psychiatry 2006;77:95�7.
22. Savitz SI, Caplan LR. Vertebrobasilar disease. N Engl J Med 2005;352: 2618�26.
23. Lee VH, Brown RD Jr, Mandrekar JN, et al. Incidence and outcome of cervical artery dissection: a population-based study. Neurology 2006;67: 1809�12.
24. Rothwell DM, Bondy SJ, Williams JI. Chiropractic manipulation and stroke: a population-based case-control study. Stroke 2001;32:1054�60.
25. Smith WS, Johnston SC, Skalabrin EJ, et al. Spinal manipulative therapy is an independent risk factor for vertebral artery dissection. Neurology 2003;60: 1424�8.
26. Arnold M, Bousser MG, Fahrni G, et al. Vertebral artery dissection: presenting findings and predictors of outcome. Stroke 2006;37:2499�503.
27. Maclure M. The case-crossover design: a method for studying transient effects on the risk of acute events. Am J Epidemiol 1991;133:144�53.
28. Kelman CW, Kortt MA, Becker NG, et al. Deep vein thrombosis and air travel: record linkage study. BMJ 2003;327:1072.
29. Mittleman MA, Maclure M, Tofler GH, et al. Triggering of acute myocardial infarction by heavy physical exertion. Protection against triggering by regular exertion. Determinants of Myocardial Infarction Onset Study Investigators.
N Engl J Med 1993;329:1677�83.
30. Redelmeier DA, Tibshirani RJ. Association between cellular-telephone calls and motor vehicle collisions. N Engl J Med 1997;336:453�8.
31. Janes H, Sheppard L, Lumley T. Overlap bias in the case-crossover design, with application to air pollution exposures. Stat Med 2005;24:285�300.
32. Janes H, Sheppard L, Lumley T. Case-crossover analyses of air pollution exposure data: referent selection strategies and their implications for bias. Epidemiology 2005;16:717�26.
33. Efron B, Tibshirani RJ. An Introduction to the Bootstrap. New York: Chapmanand Hall/CRC, 1993.
34. STATA/SE [computer program]. College Station, Tex: Stata Corp, 2006.
35. Liu L, Reeder B, Shuaib A, et al. Validity of stroke diagnosis on hospital discharge records in Saskatchewan, Canada: implications for stroke surveillance. Cerebrovasc Dis 1999;9:224�30.
36. Boyle E, Co�te� P, Grier AR, et al. Examining vertebrobasilar artery stroke in two Canadian provinces. Spine, in press.
37. Co�te� P, Kreitz BG, Cassidy JD, et al. The validity of the extension-rotation test as a clinical screening procedure before neck manipulation: a secondary analysis. J Manip Physiol Therap 1996;159�64.
38. van der Velde G, Hogg-Johnson S, Bayoumi A, et al. Identifying the best treatment among common non-surgical neck pain treatments: a decision analysis. Spine 2008;33(Suppl):S184�S191.

Key words: vertebrobasilar stroke, case control stud- ies, case crossover studies, chiropractic, primary care, complications, neck pain. Spine 2008;33:S176�S183

From the *Centre of Research Expertise for Improved Disability Outcomes (CREIDO), University Health Network Rehabilitation Solutions, Toronto Western Hospital, and the Division of Heath Care and Outcomes Research, Toronto Western Research Institute, Toronto, ON, Canada; �Department of Public Health Sciences, Management and Evaluation, University of Toronto, Toronto, ON, Canada; �Department of Health Policy, Management and Evalua- tion, University of Toronto, Toronto, ON, Canada; �Institute for Work & Health, Toronto, ON, Canada; �University Health Net- work Stroke Program, Toronto Western Hospital, Toronto, ON, Canada; and Division of Neurology, Department of Medicine, Fac- ulty of Medicine, University of Toronto, Toronto, ON, Canada. Supported by Ontario Ministry of Health and Long-term Care. P.C. is supported by the Canadian Institute of Health Research through a New Investigator Award. S.H.-J. is supported by the Institute for Work & Health and the Workplace Safety and Insurance Board of Ontario. The opinions, results, and conclusions are those of the authors and no endorsement by the Ministry is intended or should be inferred.

The manuscript submitted does not contain information about medical device(s)/drug(s).
University Health Network Research Ethics Board Approval number 05-0533-AE.

Address correspondence and reprint requests to J. David Cassidy, DC, PhD, DrMedSc, Toronto Western Hospital, Fell 4-114, 399 Bathurst Street, Toronto, ON, Canada M5T 2S8; E-mail: dcassidy@uhnresearch.ca

Mastodon