Knee Pain & Acute Trauma Diagnosis Imaging Part II | El Paso, TX

Meniscal Tears

• Acute or chronic. Imaged with MRI (95% sensitivity & 81% specificity)
• Menisci are formed by a composition of radial and circumferential collagen fibers (97% type 1) mixed with cartilage, proteoglycans, etc. 65-75% H2O
• Aging can lead to meniscal attrition
• Acute tears are d/t rotational and compressive forces, ACL deficient knees show greater chances of meniscal tears
• Posterior horn of medial meniscus is m/c torn except in acute ACL tears when the lateral meniscus is m/c torn
• The meniscus is well vascularized in children. In adults, 3-zones exist: inner, middle and outer (above bottom image)
• Injury of the inner zone has no chance of healing
• Injury of the outer zone (25% in total) has some healing/repair

Clinical Presentation

• Pain, locking, swelling
• Most sensitive physical sign: pain on palpation at the joint line
• Tests: McMurry, Thessaly, Apply compression in prone
• Management: conservative vs. operative depends on location, stability, patient’s age, and DJD and the type of tear
• Partial meniscectomy is performed. 80% proper functions on follow up. Less favorable if >40-y.o and DJD
• Total meniscectomy is not performed and only viewed historically. 70% OA 3-years after surgery 100% OA after 20 years post surgery.

Axial MR

• Appearance the medial (blue) and the lateral meniscus (red)

Menisci Play Significant Role

• One of the critical roles is “hoop-stress” mechanism.
• Particularly radial tears may significantly interfere with this mechanism.
• Further reading: www.ncbi.nlm.nih.gov/pmc/articles/PMC3435920/

Types Location & Stability

• Types, location, and stability of tears are v. important during MRI Dx
• Vertical/longitudinal tears especially occur in acute ACL tears. Some longitudinal tears found at the periphery or “red zone” may heal
• Bucket handle tear: longitudinal tear in the inner edge that is deep and vertical extending through the long axis and may displace into a notch
• Oblique/flap/parrot-beak are complex tears
• Radial tear at 90-degree to plateau

Axial T2

• Axial T2 WI fat-sat and coronal STIR slices of the posterior horn of the medial meniscus.
• Note a radial tear of the posterior horn of the medial meniscus near the meniscal root. This is potentially an unstable lesion requiring operative care
• The meniscus, in this case, is unable to provide a “hoop-stress mechanism.”

MRI Slices Coronal & Sagittal

• Fat-sat coronal and sagittal proton density MRI slices revealing horizontal (cleavage) tear that is more typical in the aged meniscus
• In some cases, when this tear does not contain a radial component, it may partially heal obviating the need for operative care

T2 w GRE Sagittal MRI Slice

• Complex tear with a horizontal oblique and radial component.
• This type of tear is very unstable and in most cases may need operative care

Bucket Handle Tear

• Bucket handle tear are m/c in the medial meniscus esp. with acute ACL and MCL tear
• MRI signs; double PCL sign on sagittal slices
• Absent “bow-tie” sign and others
• Most cases require operative care

DDx From Meniscal Degeneration

• Occasionally meniscal tears need to be DDx from meniscal degeneration which may also appear bright (high signal) on fluid-sensitive MRI
• The simplest rule is that if there is a true meniscal tear aka Grade 3 lesion, it always reaches/extends to the tibial plateau surface

The Role of MSK Ultrasound (US) in Knee Examination

• MSK US of the knee permits high resolution and dynamic imaging of primarily superficial anatomy (tendons, bursae, capsular ligaments)
• MSK US cannot adequately evaluate cruciate ligaments and the menisci in their entirety
• Thus MR imaging remains modality of choice

Potential Pathologies Successfully Evaluated by MSK US

• Patellar tendionosis/patellar tendon rupture
• Quadriceps tendon tear
• Prepatellar bursitis
• Infrapatellar bursitis
• Pes Anserine bursitis
• Popliteal cyst (Baker cyst)
• Inflammation/joint effusion with synovial thickening and hyperemia can be imaged with US (e.g., RA) especially with the addition of color power Doppler

Patient Presented With Atraumatic Knee Pain & Swelling

• Radiography revealed sizeable soft tissue density within the superficial pre-patella region along with mild-to-moderate OA
• MSK US demonstrated large septated heterogeneous fluid collection with mild positive Doppler activity on the periphery indicating inflammation d/t Dx of Superficial pre-patella bursitis

Long Axis US Images

• Note normal lateral meniscus and fibers of LCL (above bottom image) compared to
• Horizontal degenerative cleavage tear along with protrusion of lateral meniscus and LCL bulging (above top image)
• Major limitation: unable to visualize the entire meniscus and the ACL/PCL
• MRI referral is suggested

Rupture of Distal Tendon of Quadriceps

• Note rupture of distal tendon of the Quadriceps muscle presented as fiber separation and fluid (hypo to anechoic) fluid collection within the substance of the tendon
• Advantages of MSK US over MRI to evaluate superficial structures:
• Dynamic imaging
• Availability
• Cost-effective
• Patient’s preparation
• Disadvantages: limited depth of structures, inability to evaluated bone and cartilage, etc.

Osteochondral Knee Injuries (OI)

• osteochondral knee injuries can occur in children 10-15 y.o presented as Osteochondritis Dissecance (OCD) and in mature skeleton m/c following hyperextension and rotation trauma, particularly in ACL tear.
• OCD-typically develops from repeated forces in immature bone and affects m/c postero-lateral portion of the medial femoral condyle.
• OI in mature bone occurs m/c during ACL tears mainly affecting so-called terminal sulcus of the lateral femoral condyle at the junction of the weight-bearing portion opposed to tibial plateau and the part articulating with the patella
• Osteochondral injuries may potentially damage the articular cartilage causing secondary OA. Thus need to be evaluated surgically
• Imaging plays an important role and should begin with radiography often followed by MR imaging and orthopedic referral.

OCD Knee

• 95% associated with some trauma. Other etiology: ischemic bone necrosis especially in adults
• Other common location for osteochondral injuries: elbow (capitellum), talus
• 1st step: radiography may detect osteochondral fragment potentially attached or detached
• Location: a posterior-lateral aspect of the medial femoral condyle. Tunnel (intercondylar notch) view is crucial
• MRI: modality of choice >90% specificity and sensitivity. Crucial for further management. T1-low signal demarcating line with T2 high signal demarcating line that signifies detachment and unlikely healing. Refer to orthopedic surgeon
• Management: stable lesion esp. in younger children>off weight-bearing-heals in 50-75%
• Unstable lesion and older child or impending physeal closure>operative fixation.

Knee Trauma