AC Joint Injury (Acromioclavicular Separation)
A "pop" with immediate pain localized to the AC joint following trauma strongly suggests an acromioclavicular joint sprain or separation, which requires initial radiographic evaluation followed by conservative management for most injury grades. 1
Immediate Diagnostic Steps
Obtain standard shoulder radiographs immediately with a minimum 3-view series: anteroposterior views in both internal and external rotation, plus either an axillary or scapula-Y view. 2, 1 The axillary or scapula-Y view is critical because AC joint dislocations are frequently misclassified on AP views alone. 2, 1
- Radiographs should be obtained with the patient upright when possible, as supine positioning can underrepresent shoulder malalignment and AC joint displacement. 1
- These images will classify the AC separation type (I-VI) and rule out associated clavicle fractures or other bony injuries. 3, 4
Classification and Management Algorithm
Types I, II, and III (Conservative Management)
For AC separations Types I-III, initiate conservative treatment immediately: 3, 4
- Pain control: Start with acetaminophen (maximum 4 grams daily) as first-line. 5
- Sling immobilization: Use for comfort only during the first 1-2 weeks, not for rigid immobilization. 4
- Early mobilization: Begin gentle range-of-motion exercises within days to prevent frozen shoulder. 4
- Progressive rehabilitation: Advance to scapular stabilization exercises and rotator cuff strengthening once pain-free motion is achieved. 5, 6
The outcome is usually excellent with full return of function following these injuries when managed conservatively. 7
Types IV, V, and VI (Surgical Referral)
Refer immediately to orthopedic surgery if radiographs demonstrate Type IV, V, or VI injuries, which show severe displacement or posterior/inferior displacement of the clavicle. 3, 7 These require operative reduction and fixation. 7
Advanced Imaging Considerations
If radiographs are normal but symptoms persist beyond 2-4 weeks, obtain MRI without contrast to identify occult injuries including rotator cuff tears, labral pathology, or AC joint capsular injuries that explain ongoing mechanical symptoms. 1
- In the acute post-traumatic setting, non-contrast MRI is preferred over MR arthrography because post-traumatic joint effusion provides sufficient visualization of soft tissue structures. 2
- MRI can also identify associated rotator cuff or labral injuries that commonly occur with AC joint trauma. 1
Age-Specific Considerations
- Patients under 35-40 years: AC joint injuries typically occur from sports or high-impact trauma; evaluate carefully for associated instability or labral pathology. 2, 4
- Patients over 35-40 years: Consider pre-existing AC joint osteoarthritis that may be exacerbated by trauma; degenerative changes are common and may complicate recovery. 8, 9
Common Pitfalls to Avoid
- Do not skip the axillary or scapula-Y view – dislocations are often missed on AP-only series, leading to misclassification of injury severity. 2, 1
- Do not assume isolated AC injury – examine thoroughly for associated clavicle fractures, rotator cuff tears, or glenohumeral pathology, as injury to one shoulder component predisposes to other injuries. 3
- Do not delay imaging even if the mechanism seems minor, especially in older patients where osteoporotic fractures occur with trivial trauma. 1
When Conservative Management Fails
If pain persists after 6 months of appropriate conservative treatment, consider:
- Diagnostic and therapeutic corticosteroid injection into the AC joint, which may provide short-term pain relief. 8
- Referral for surgical distal clavicle resection (open or arthroscopic) if conservative measures including injections fail. 8, 9
Physical therapy has limited benefit for isolated AC joint pathology compared to rotator cuff injuries, as therapeutic exercise plays only a minor role. 8