Shoulder Injuries: The Acromioclavicular (AC) Joint

Two surgeons discuss the diagnosis and treatment of acromioclavicular injuries in athletes. El Paso, TX. Chiropractor, Dr. Alexander Jimenez follows the discussion.

Acromioclavicular (AC) joint injuries most often occur in athletic young adults involved in collision sports, throwing sports, along with overhead activities like upper-extremity strength training. They account for 3% of all shoulder injuries and 40% of shoulder sports injuries. Athletes in their second and third decade of life are more often affected(1), and men are injured more commonly than women (5:1 to 10:1)(1,2).

Acromioclavicular dislocation was known as early as 400 BC by Hippocrates(3). He cautioned against mistaking it for glenohumeral (shoulder joint) dislocation and advocated treating with a compressive bandage in an attempt to hold the distal (outer) end of the clavicle in a diminished position. Almost 600 decades later Galen (129 AD) recognized his own acromioclavicular dislocation, which he sustained while wrestling(3). He left the tight bandage holding the clavicle down as it was too uneasy. In today’s era this injury is better known, but its treatment remains a source of fantastic controversy.

Anatomy

The acromioclavicular joint combines the collarbone to the shoulder blade and therefore links the arm to the axial skeleton. The articular surfaces are originally hyaline cartilage, which affects to fibrocartilage toward the end of adolescence. The average joint size is 9mm by 19mm(4). The acromioclavicular joint contains an intra-articular, fibrocartilaginous disc which may be complete or partial (meniscoid). This helps absorb forces in compression. There is marked variability in the plane of the joint.

Stabilizers

There is little inherent bony stability in the AC joint. Stability is provided by the dynamic stabilizers — namely, the anterior deltoid muscle arising from the clavicle and the trapezius muscle arising from the acromion.

Additionally, there are ligamentous stabilizers. The AC ligaments are divided into four — superior, inferior, anterior and posterior. The superior is most powerful and blends with muscles. The acromioclavicular ligaments contribute around two- thirds of the constraining force to superior and posterior displacement; however, with greater displacement the coracoclavicular ligaments contribute the major share of the resistance. The coracoclavicular ligament consists of the conoid and trapezoid. The conoid ligament is fan-shaped and resists forwards motion of the scapula, while the more powerful trapezoid ligament is level and resists backward movement. The coracoclavicular ligament helps bunch scapular and glenohumeral (shoulder joint) motion and the interspace averages 1.3 cm.

Mechanism Of Injury

The athlete who sustains an acromioclavicular injury commonly reports either one of two mechanisms of harm: direct or indirect.

Direct force: This is when the athlete falls onto the point of the shoulder, with the arm usually at the side and adducted. The force drives the acromion downwards and medially. Nielsen(5) found that 70 percent of acromioclavicular joint injuries are caused by an direct injury.

Indirect force: This is when the athlete falls onto an outstretched arm. The pressure is transmitted via the humeral head into the acromion, therefore the acromioclavicular ligament is disrupted and the coracoclavicular ligament is stretched.

On Examination

The athlete presents soon after the severe injury with his arm splinted to his side. The patient may state that the arm feels better using superiorly directed support on the arm. Most motions are limited secondary to pain near the top of the shoulder; the degree varies with the grade of sprain. The hallmark finding is localized swelling and tenderness over the acromioclavicular joint.

In dislocations, the outer part of the collarbone will appear superiorly displaced using a noticeable step deformity (in fact, it is the shoulder which sags beneath the clavicle). Occasionally, the deformity may only be apparent later, if first muscle spasm reduces acromioclavicular separation. Forced cross-body adduction (yanking the affected arm across the opposite shoulder) provokes discomfort. The clavicle can frequently be moved relative to the acromion.

Acromioclavicular Visualisation

The typical joint width measures 1-3mm. It’s regarded as abnormal if it is more than 7mm in men, and 6mm in women. Routine anteroposterior views of the shoulder reveal the glenohumeral jointnonetheless, that the acromioclavicular joint is over penetrated and so dark to interpret. Reduced exposure enhances visualization. The individual stands with both arms hanging unsupported, both acromioclavicular joints on one film. Weighted viewpoints (stress X-rays) are obtained with 10-15 lb weights not held but suspended from the individual’s wrists. They help differentiate type II-III injuries, but are of little clinical significance and therefore are no longer recommended in our practice.

Classification Of AC Separation

The importance of identifying the injury kind can’t be over emphasized because the treatment and prognosis hinge on an accurate diagnosis. The injuries are graded on the basis of that ligaments are injured and how badly they’re torn.

Allman (6) classified acromioclavicular sprains as grades I, II and III, representing respectively, no involvement, partial tearing, and total disruption of the coracoclavicular ligaments. More recently, Rockwood (1) has further classified the more severe injuries as standard III-VI.

The injuries are classified into six categories:

Treatment

The treatment of acromioclavicular joint injuries varies based on the seriousness or grade of the injury.

Initial treatment: These can be quite painful injuries. Ice packs, anti-inflammatories plus a sling are utilized to immobilize the shoulder and then take the weight of the arm. As pain starts to subside, it is important to start moving the fingers, wrist and elbow to prevent shoulder stiffness. Next, it’s important to begin shoulder motion in order to stop shoulder stiffness.

Un-displaced injuries only require rest, ice, and then a slow return to activity over two to six weeks. Major dislocations require surgical stabilization in athletes if their dominant arm is involved, and if they participate in upper-limb sports

What’s more, the patients treated non-operatively returned to full activity (work or athletics) earlier than surgically treated groups(10, 11). The exceptions to this recommendation include people who perform repetitive, heavy lifting, people who operate with their arms above 90 degrees, and thin patients who have prominent lateral ends of the clavicles. These patients may benefit from surgical repair(12).

Any discussion about the management of acute injuries to the AC joint must deal with which of the many methods of surgical therapy described is the best for their situation, but whether surgery should be considered at all. Surgery is generally avoided in athletes participating in contact sports since they will often re-injure the shoulder later on.

Surgery

Surgical repair can be divided into anatomical or non- anatomical, or historically into four types:

For the individual with a chronic AC joint dislocation or subluxation that remains painful after three to six months of closed treatment and rehabilitation, surgery is indicated to improve functioning and comfort.

Postoperatively, the arm is supported in a sling for up to six weeks. Following the first two weeks, the patient is permitted to use the arm for daily activities at waist level. After six weeks, the sling or orthosis is discontinued, overhead actions are allowed, formal passive stretching is instituted, and light stretching using elastic straps is initiated. Stretching and strengthening are begun slowly and gradually. The athlete shouldn’t return to their sport without restriction until full strength and range of motion has been recovered. This usually occurs four to six months following operation.

Conclusion

AC joint injuries are an important source of pain at the shoulder area and have to be assessed carefully. The management of these injuries is nonoperative in the majority of cases. Type I and II injuries are treated symptomatically. The present trend in uncomplicated type III injuries are a non operative strategy. In the event the athlete develops following problems, a delayed reconstruction might be undertaken. In athletes involved in heavy lifting or prolonged overhead activities, surgery may be considered acutely. Type IV-VI injuries are generally treated operatively.

No matter what kind of treatment is chosen, the ultimate purpose is to restore painless function to the wounded AC joint so as to reunite the athlete safely and as quickly as possible back to their sport. It is possible in the vast majority of acromioclavicular joint injuries.

References

Reza Jenabzadeh and Fares Haddad

1. Rockwood CA Jr, Williams GR, Young CD. Injuries of the Acromioclavicular Joint. In CA Rockwood Jr, et al (eds), Fractures in Adults. Philadelphia: Lippincott-Raven, 1996; 1341-1431.

2. Dias JJ, Greg PJ. Acromioclavicular Joint Injuries in Sport: Recommendations for Treatment. Sports Medicine 1991; 11: 125-32.
3. Adams FL. The Genuine Works of Hippocrates (Vols 1,2). New York, William Wood 1886.
4. Bosworth BM. Complete Acromioclavicular Dislocation. N Eng J Med 2 41: 221-225,1949.
5. Nielsen WB. Injury to the Acromioclavicular Joint. J Bone Joint Surg 1963; 45B:434-9.
6. Allman FL Jr. Fractures and Ligamentous Injuries of the Clavicle and its Articulation. J Bone Joint Surg Am 1967;
49:774- 784.
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9. Clarke HD, Mc Cann PD: Acromioclavicular Joint Injuries. Orthop Clin North Am 2000; 31(2): 177-187
10. Press J, Zuckerman JD, Gallagher M, et al: Treatment of Grade III Acromioclavicular Separations: Operative versus
Nonoperative Management. Bull Hosp Jt Dis 1997;56(2):77-83
11. Galpin RD, Hawkins RJ, Grainger RW: A Comparative Analysis of Operative versus Nonoperative Treatment of Grade III Acromioclavicular Separations. Clin Orthop 1985; 193 (Mar): 150-155
12. Larsen E, Bjerg-Nielsen A, Christensen P: Conservative or Surgical Treatment of AC Dislocation: A Prospective, Controlled, Randomized Study. J Bone Joint Surg Am 1986;68(4):552-555
13. Bosworth BM. Complete Acromioclavicular Dislocation. N Engl. J. Med. 241: 221-225,1949.