1. History
- Mechanism of injury: Direct blow to the lateral/superior shoulder (most common), fall onto an outstretched hand (FOOSH), or fall onto the acromion with the arm adducted [1-2]
- Common in contact sports: football, hockey, rugby, boxing, martial arts, cycling [1][3]
- Ask about the force and direction of impact, arm position at time of injury
- Symptom characterization: pain localized to the top of the shoulder, worse with arm movement (especially cross-body adduction and overhead reaching)
- Timing: acute onset at time of trauma; inquire about prior AC joint injuries or shoulder surgeries
- Severity: ability to move the arm, functional limitations (dressing, lifting, sport)
- Associated symptoms: swelling, visible deformity/"step-off," clicking or popping
- Important negatives: neck pain, radicular symptoms, numbness/tingling in the hand, chest pain, dyspnea (to rule out associated injuries)
2. Alarm Features
- Tenting of the skin by the distal clavicle (suggests high-grade injury, Type IV–VI)
- Posterior displacement of the clavicle through the trapezius (Type IV) — can compromise overlying skin [1][4]
- Inferior displacement of the clavicle beneath the acromion or coracoid (Type VI — rare, often associated with severe trauma) [1]
- Neurovascular compromise: diminished distal pulses, paresthesias, weakness in the upper extremity
- Associated injuries: clavicle fracture, coracoid fracture, brachial plexus injury, pneumothorax (high-energy mechanism)
- Scapular dyskinesis or inability to elevate the arm — may indicate high-grade instability [5]
- Concomitant SLAP tear (increased incidence with AC joint injuries) [6]
3. Medications
- First-line analgesia: Acetaminophen and short-course NSAIDs (ibuprofen 400–600 mg q6–8h or naproxen 250–500 mg q12h) [7]
- Opioids should be used sparingly, if at all [7]
- Topical NSAIDs may be considered for localized pain
- Corticosteroid injection into the AC joint can be diagnostic and therapeutic for chronic AC joint pain or osteoarthritis, but is not standard in the acute traumatic setting [8]
- Avoid prolonged NSAID use; short-term use does not appear to impair ligament healing [7]
4. Diet
- No specific dietary triggers or restrictions
- Adequate protein and caloric intake to support tissue healing
- Ensure adequate calcium and vitamin D for bone health
- Hydration is important during the recovery and rehabilitation phase
5. Review of Systems
- Musculoskeletal: neck pain, ipsilateral arm weakness, prior shoulder injuries, contralateral shoulder symptoms for comparison
- Neurologic: numbness, tingling, or weakness in the ipsilateral upper extremity (brachial plexus)
- Respiratory: dyspnea, pleuritic chest pain (pneumothorax with high-energy mechanism)
- Vascular: coolness, color change, or swelling in the distal extremity
- Constitutional: fever (if concern for septic joint in subacute/chronic presentations)
6. Collateral History and Family History
- Witnesses to the mechanism of injury (especially in sports settings — sideline personnel, athletic trainers)
- Prior shoulder injuries, dislocations, or surgeries
- Occupation and activity level — critical for treatment decisions, especially for Type III injuries [1-2]
- Family history is generally not contributory, though generalized ligamentous laxity (Ehlers-Danlos, Marfan) may predispose to joint instability
7. Risk Factors
- Male sex, age 20–49 years [1]
- Contact/collision sports: football, hockey, rugby, martial arts [1][3]
- Cycling (fall onto the point of the shoulder) [2]
- Overhead athletes and weightlifters (risk for overuse-related distal clavicle osteolysis) [9-10]
- Prior AC joint injury
- High-demand occupations: military, manual labor [1]
8. Differential Diagnosis
- Distal clavicle fracture — can mimic AC separation; radiographs differentiate. Neer Type II fractures disrupt the CC ligaments and behave similarly to AC separations [11]
- Rotator cuff tear — pain with overhead motion, weakness on specific testing; may coexist
- SLAP tear — increased incidence with AC injuries; pain with overhead activity, positive O'Brien test [6]
- Glenohumeral dislocation/subluxation — different deformity pattern, loss of shoulder contour
- Lateral clavicle osteolysis — insidious onset in weightlifters, no acute trauma; radiographic resorption of distal clavicle [9][12]
- Cervical radiculopathy — referred shoulder pain with neck involvement, dermatomal sensory changes
- Sternoclavicular joint injury — medial clavicle tenderness and deformity
- Os acromiale — unfused acromial apophysis, can be confused on imaging
9. Past Medical History
- Previous AC joint separations or shoulder injuries (recurrence risk)
- Prior shoulder surgeries (especially distal clavicle excision, rotator cuff repair)
- Connective tissue disorders or generalized ligamentous laxity
- Osteoporosis or metabolic bone disease (affects fracture risk)
- Chronic conditions affecting rehabilitation: diabetes, inflammatory arthritis
10. Physical Exam
- Inspection: Swelling, ecchymosis, and visible "step-off" deformity at the AC joint. In high-grade injuries, the distal clavicle is prominently elevated ("piano key" sign). Compare with the contralateral shoulder [1]
- Palpation: Point tenderness directly over the AC joint. Assess for crepitus and mobility of the distal clavicle
- Piano key sign: Downward pressure on the distal clavicle reduces the deformity, which springs back when released (Type III+)
- Cross-body adduction test (Scarf test): Pain at the AC joint with passive horizontal adduction — sensitivity ~77% [13]
- O'Brien's (active compression) test: Highest specificity (~95%) for AC joint pathology; pain with resisted forward flexion at 90° with arm adducted 10–15° and internally rotated, relieved with supination [13]
- AC resisted extension test: Sensitivity ~72% [13]
- Combining tests improves diagnostic accuracy [13]
- Assess range of motion: typically limited by pain, especially with abduction >90° and cross-body adduction
- Neurovascular exam: axillary nerve function (deltoid strength, regimental badge sensation), distal pulses
- Evaluate for scapular dyskinesis — may indicate high-grade instability (Type IIIB) [5]
11. Lab Studies
- No routine labs are indicated for isolated traumatic AC separation
- If concern for infection (subacute presentation with erythema, warmth, fever): CBC, ESR, CRP, blood cultures
- If surgical intervention is planned: standard preoperative labs per institutional protocol
12. Imaging
- First-line: Shoulder radiographs — AP, axillary lateral, and Zanca view (10–15° cephalic tilt AP, which best profiles the AC joint) [1][14]
- Compare with the contralateral side to assess coracoclavicular (CC) distance — increased CC distance indicates higher-grade injury [1]
- Cross-body adduction (Alexander) view: Can help distinguish stable (Type IIIA) from unstable (Type IIIB) injuries by demonstrating clavicle overriding the acromion [15-16]
- Weighted stress views: Historically used but falling out of favor; a Delphi consensus found AP and axillary views without traction or weight are sufficient [15]
- MRI: Not routinely indicated for acute AC separation. Useful for evaluating CC ligament integrity in equivocal cases, assessing for concomitant soft tissue injuries (SLAP, rotator cuff), and in chronic pain [14-15][17]
- Ultrasound: Can assess CC ligament integrity with sensitivity ~89% and specificity ~90% compared to MRI; useful as a bedside adjunct [18]
- CT: Rarely needed; may help with complex fracture patterns or preoperative planning
13. Special Tests
Rockwood Classification (the standard grading system): [1]
- ISAKOS subclassification of Type III: IIIA (stable, no overriding on cross-arm adduction) vs IIIB (unstable, clavicle overrides acromion) — helps guide surgical decision-making [5][15]
- Diagnostic AC joint injection: Lidocaine injection into the AC joint can confirm the joint as the pain source, especially in chronic or equivocal cases [19]
- Point-of-care ultrasound: Can rapidly assess AC joint widening and step-off at the bedside in the ED
14. ECG
- Not routinely indicated for isolated AC separation
- Consider ECG if high-energy mechanism with chest wall trauma or if the patient reports chest pain or dyspnea (to rule out cardiac contusion or other thoracic injury)
15. Assessment
AC joint separation accounts for approximately 9% of all shoulder injuries and up to 40% in elite contact sport athletes. [3] The injury spectrum ranges from a mild sprain (Type I) to complete dislocation with severe displacement (Types IV–VI). The vast majority of injuries are Types I–III, which are managed nonoperatively with excellent outcomes in most patients. Up to 80% of Type III injuries have good outcomes without surgery. [1] Type III management remains the most debated topic in AC joint surgery, with recent evidence suggesting no significant functional difference between surgical and conservative treatment at one year, though surgery may offer better cosmetic outcomes and higher UCLA scores. [3][20] Complications of untreated or undertreated high-grade injuries include chronic pain, scapular dyskinesis, weakness with overhead activities, and post-traumatic AC joint arthritis. Distal clavicle osteolysis can develop after AC separation (estimated ~6% incidence) or as an overuse condition in weightlifters. [9-10][21]
16. Treatment Plan
Types I and II (Nonoperative): [1-2][7]
- Sling for comfort, typically 2 weeks; Jones strapping offers no clear advantage over a sling [15]
- Ice and analgesia: acetaminophen + short-course NSAIDs
- Early gentle ROM exercises (pendulum exercises) as pain allows
- Progressive rehabilitation: ROM → scapular stabilization → rotator cuff strengthening → sport-specific conditioning
- Return to activity when pain-free with full ROM and symmetric strength
Type III (Individualized): [1-2][15][20]
- Initial trial of conservative management for most patients (sling 2 weeks, then rehab)
- Consider early surgical referral for high-demand athletes, overhead workers, military personnel, or those with Type IIIB (unstable) injuries
- If conservative treatment fails after 3–6 months, surgical reconstruction is indicated [5]
Types IV–VI (Surgical): [1][4]
- Orthopedic surgery consultation — operative reduction and ligament reconstruction
- Surgical techniques include CC ligament reconstruction (autograft/allograft), hook plate fixation, suture-button devices, or arthroscopic-assisted techniques [2][4]
- Post-surgical rehab: sling 2–4 weeks → pendulum exercises → active ROM at 4–6 weeks → resisted exercises at 6 weeks → return to sport at ~4.5–6 months [2][22-23]
Return to Sport: [22-23]
- Pooled RTS rate after surgery: 91.5%, with 85.6% returning to pre-injury level; mean time to RTS ~5.7 months [23]
- Nonoperative RTS is faster: mean ~52 days vs 127 days for operative management [22]
- Criteria: pain-free, full ROM, symmetric strength, sport-specific functional testing [6]
17. Disposition
- Discharge from ED: Types I–III (with appropriate sling, analgesia, and orthopedic follow-up within 1–2 weeks)
- Orthopedic consultation in ED: Types IV–VI, open injuries, neurovascular compromise, or associated fractures requiring urgent intervention
- Observation: Generally not required for isolated AC separation
- Admission: Rarely needed; consider if polytrauma, associated injuries requiring inpatient management, or failed reduction of high-grade dislocation
18. Follow Up / Return Precautions
- Follow-up: Orthopedic or sports medicine follow-up within 1–2 weeks for all AC separations
- Type I: may follow up with primary care; expect recovery in 2–4 weeks
- Type II–III: orthopedic follow-up to reassess stability and functional progress at 2, 6, and 12 weeks
- Return precautions — seek immediate reassessment for:
- Worsening deformity or new "step-off"
- Increasing pain despite treatment
- Numbness, tingling, or weakness in the arm or hand
- Inability to move the shoulder after initial improvement
- Signs of infection (if post-surgical): fever, wound erythema, drainage
- Expected recovery: Types I–II typically recover fully in 2–6 weeks. Type III may take 6–12 weeks conservatively. Post-surgical recovery averages 4.5–6 months to full sport participation [22-23]
- Long-term counseling: Cosmetic deformity (visible bump) is common with nonoperative management of Type III injuries and does not necessarily correlate with functional impairment. Post-traumatic osteolysis or AC joint arthritis may develop months to years later [9][20-21]
References
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2. Surgical Versus Conservative Interventions for Treating Acromioclavicular Dislocation of the Shoulder in Adults. — Tamaoki MJ, Lenza M, Matsunaga FT, et al. The Cochrane Database of Systematic Reviews. 2019.
3. Acromioclavicular Joint Dislocation: Surgical vs. Conservative Interventions. — Yancey JR, Szczepanik M. American Family Physician. 2021.
4. Surgical Advances in the Treatment of Acromioclavicular Joint Injury: A Comprehensive Review. — Ma Y, Ma Z, Guo J, et al. Medical Science Monitor : International Medical Journal of Experimental and Clinical Research. 2024.
5. Current Concepts in Acromioclavicular Joint (AC) Instability - A Proposed Treatment Algorithm for Acute and Chronic AC-joint Surgery. — Berthold DP, Muench LN, Dyrna F, et al. BMC Musculoskeletal Disorders. 2022.
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9. Acromioclavicular Joint Disorders. — Turnbull JR. Medicine and Science in Sports and Exercise. 1998.
10. Frequency, Imaging Findings, Risk Factors, and Long-Term Sequelae of Distal Clavicular Osteolysis in Young Patients. — Roedl JB, Nevalainen M, Gonzalez FM, et al. Skeletal Radiology. 2015.
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12. Diagnosis and Management of Distal Clavicle Osteolysis. — DeFroda SF, Nacca C, Waryasz GR, Owens BD. Orthopedics. 2017.
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16. Acromioclavicular Joint Instability on Cross-Body Adduction View: The Biomechanical Effect of Acromioclavicular and Coracoclavicular Ligaments Sectioning. — Kurata S, Inoue K, Shimizu T, et al. BMC Musculoskeletal Disorders. 2022.
17. The Ligamentous Injury Pattern in Acute Acromioclavicular Dislocations and Its Impact on Clinical and Radiographic Parameters. — Minkus M, Wieners G, Maziak N, et al. Journal of Shoulder and Elbow Surgery. 2021.
18. Ultrasound of the Coracoclavicular Ligaments in the Acute Phase of an Acromioclavicular Disjonction: Comparison of Radiographic, Ultrasound and MRI Findings. — Faruch Bilfeld M, Lapègue F, Chiavassa Gandois H, et al. European Radiology. 2017.
19. Painful Conditions of the Acromioclavicular Joint. — Shaffer BS. The Journal of the American Academy of Orthopaedic Surgeons. 1999.
20. Functional, Radiological, and Scapular Motion Evaluation of Surgical Versus Nonsurgical Treatment of Type 3 Acromioclavicular Dislocations: A Randomized Controlled Trial With 24 Months' Follow-Up. — Lara PHS, Lima EBS, Andreoli CV, et al. The American Journal of Sports Medicine. 2026.
21. MR Observations of Postraumatic Osteolysis of the Distal Clavicle After Traumatic Separation of the Acromioclavicular Joint. — Yu YS, Dardani M, Fischer RA. Journal of Computer Assisted Tomography. 2000.
22. Return to Sport After Acromioclavicular Injury: A Systematic Review of Modifiable Factors. — Elliott WC, Olivo B, Abraham A, Hernandez EJ, Hanna T. Journal of Clinical Medicine. 2025.
23. Return to Play After Surgical Treatment for Acromioclavicular Joint Dislocation: A Systematic Review. — Cleary BP, Hurley ET, Kilkenny CJ, et al. The American Journal of Sports Medicine. 2024.