Abstract
The acromioclavicular (AC) joint is a diarthrodial joint found between the lateral end of the clavicle and the medial side of the acromion. The AC ligaments cross the joint. The coracoclavicular ligament begins at the coracoid process on the scapula and attaches to the clavicle. This complex provides passive support and suspension of the scapula from the clavicle while allowing rotation of the clavicle to be transmitted to the scapula. Injuries to the AC complex have traditionally been graded I to VI and are associated with trauma, overhead activities, or throwing activities. Types I and II and stable type III can be managed nonsurgically. Patients present with pain and a deformity at the AC joint. Examination can differentiate between isolated AC injuries or concomitant fractures or rotator cuff injuries. Conservative treatment includes modalities, relative rest, and possible immobilization for several weeks. Restoring motion and returning to activity occur as symptoms resolve and athletes can return to prior functional levels. Surgical treatment for unstable injuries requires longer periods of immobilization and rehabilitation. Most patients can return to chosen occupations or sports after surgical treatment. Complications are typically cosmetic. Type III injuries that fail conservative treatment can respond to surgery with good results at a later date.
Keywords
Acromioclavicular joint, Acromion process, Clavicle, Coracoacromial arch, Coracoacromial ligament, Coracoclavicular ligaments, Joint dislocations, Scapula, Shoulder joint
| Synonyms | |
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| ICD-10 Codes | |
| S43.50 | Sprain of unspecified acromioclavicular joint, ligament |
| S43.51 | Sprain of right acromioclavicular joint, ligament |
| S43.52 | Sprain of left acromioclavicular joint, ligament |
| S43.101 | Unspecified dislocation of right acromioclavicular joint |
| S43.102 | Unspecified dislocation of left acromioclavicular joint |
| S43.109 | Unspecified dislocation of unspecified acromioclavicular joint |
| Add seventh character for episode of care (A—initial encounter, D—subsequent encounter, S—sequelae) | |
Definition
The acromioclavicular (AC) joint is a diarthrodial joint found between the lateral end of the clavicle and the medial side of the acromion. The joint is surrounded by a fibrous capsule and stabilized by ligaments. The AC ligaments cross the joint. Three ligaments begin at the coracoid process on the scapula and attach to the clavicle (trapezoid and conoid ligaments, together referred to as the coracoclavicular [CC] ligaments) or the acromion (coracoacromial ligament) ( Fig. 10.1 ). This ligament complex provides passive support and suspension of the scapula from the clavicle while allowing rotation of the clavicle to be transmitted to the scapula.
Injuries to the AC complex have traditionally been graded I to VI and reflect the severity of injuries to the AC ligaments and the CC ligaments. A recent consensus statement advocated dividing Grade III injuries into III A (stable) and III B (unstable) ( Table 10.1 ).
| Grade of Injury | AC Ligament | CC Ligament | Clavicle Displacement | Treatment |
|---|---|---|---|---|
| I | Sprain | Intact | Mild superior displacement | Conservative |
| II | Torn | Sprain | Definite superior displacement | Conservative |
| III | Torn | Torn | 25%–100% increase in CC space | Conservative or Surgical—see subsets |
| III A (stable) | No clavicle overlap on cross-body adduction x-rays | Likely conservative | ||
| III B (unstable) | Clavicle overlap on cross-body adduction x-rays + weakness, decreased range of motion, and scapular dyskinesis | Likely surgical | ||
| IV | Torn | Torn | Posterior displacement | Surgical |
| V | Torn | Torn | 100%–300% increase in CC space | Surgical |
| VI | Torn | Torn | Subacromial or subcoracoid location | Surgical |
The coracoacromial (lateral) ligament is not disrupted in injuries to the AC joint. Therefore the fibrous connection persists between structures of the scapula emanating anteriorly and posteriorly. In rare instances, there is an intra-articular fracture of the distal clavicle in addition to the ligamentous injuries.
Injuries to the AC joint can be associated with trauma and with overhead and throwing activities. Higher-grade injuries are more likely to be due to trauma, such as auto accidents, falls, or sports injuries. A survey of injuries among NCAA athletes documented injuries related to player-to-player contact more so than player-to-surface events. Furthermore, in sports with gender-equal participation (e.g., soccer, basketball, ice hockey), men had nearly five times the AC injuries. Men were more likely to have recurrent injuries, but the severity of injuries was not significantly different between men and women.
Concomitant injuries can vary on the basis of age; 86% of individuals older than 50 years had rotator cuff tears.
Most patients with Grade I or II injuries respond to conservative measures and become asymptomatic within 3 weeks.
Symptoms
Patients often provide a history of trauma to the shoulder or in the vicinity of the AC joint. Patients seek care because of pain in the anterior and superior aspect of the shoulder. This pain may radiate into the base of the neck and the trapezius or deltoid muscles or down the arm in a radicular pattern.
Patients may describe pain brought on by activities of daily living that bring the arm across the chest (e.g., reaching into a jacket pocket) or behind the back (e.g., tucking in a shirt). Pain can also occur with shoulder flexion (reaching overhead) or with adduction of the arm across the chest. Patients may not have pain at rest and may be able to complete many activities without discomfort.
Physical Examination
Appropriate examination for suspected AC injuries includes an examination of the neck and shoulder joint and girdle to eliminate the possibility of a radiculopathy or referred pain. Patients should have normal neck and neurologic examination findings. The presence of neurologic or vascular injury suggests that a greater degree of trauma has been sustained.
On inspection, there may be a raised area at the AC joint. This is caused by depression of the scapula relative to the clavicle or swelling of the joint itself. This area is commonly tender to touch. On active range of motion, the patient may complain of pain or wince near the extreme of shoulder flexion.
Shoulder range of motion is typically within normal limits. Supporting the arm at the elbow and gently directing the arm superiorly may decrease the pain and allow more complete assessment of the patient’s shoulder range of motion. The pain may become worse as the shoulder is further flexed, whether it is done actively or passively. This is in distinction to impingement syndromes, which often hurt at a particular point in the arc of motion but are painless as the motion proceeds. Pain is typically absent with static manual muscle testing of the rotator cuff. Rotator cuff injuries will be painful with activation of the muscles of the rotator cuff and will be best identified with the shoulder in a neutral position (i.e., elbow next to the body) because the rotator cuff muscles are in a lengthened position and are easily made symptomatic.
Special tests to identify AC joint disease attempt to compress the joint. The most common test is the cross-body adduction test. The shoulder is abducted to 90 degrees and the elbow is flexed to the same degree. The clinician then brings the arm across the patient’s body until the elbow approaches the midline (or the patient reports pain).
Scapular dyskinesis can be assessed by observing the motion of the medial border of the scapulae during arm extension and comparing the affected side to the unaffected side ( Fig. 10.2 ).
Other tests help differentiate between impingement syndrome and AC joint pain. If the shoulder is passively flexed while it is internally rotated, the greater tuberosity can pinch (impinge) the supraspinatus tendon and subacromial bursa. The same test performed with the shoulder externally rotated will compress the AC joint without impinging the subacromial space. In the active compression test, the shoulder is flexed to 90 degrees and then adducted to 10 degrees ( Fig. 10.3 ). The patient first maximally internally rotates the arm and then tries to flex the shoulder against the clinician’s resistance. This puts pressure on the AC joint and may reproduce pain if disease is present. The test is repeated with the shoulder in full external rotation. This will put stress on the biceps tendon and its labral attachment while excluding the AC joint.
In the AC resisted extension test, the shoulder is abducted to 90 degrees and adducted across the body to 90 degrees. The examiner resists active shoulder extension. A positive test result reproduces pain in the AC joint. A combination of positive findings with cross-body adduction, resisted extension, and active compression tests will improve the diagnostic accuracy from 75% with any one positive test to 93% with all three positive.
The Paxinos sign has a high degree of diagnostic accuracy in AC joint disease. The examiner stands behind the patient and, using the hand contralateral to the affected shoulder, stabilizes the clavicle and pushes the acromion into the clavicle with the thumb ( Fig 10.4 ). The test response is considered positive if pain occurs or increases in the region of the AC joint; the test response is considered negative if there is no change in the pain level.
