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Disease/ Disorder


Acromioclavicular (AC) joint injury is a common yet underdiagnosed cause of shoulder pain.1 Joint damage can occur due to a range of acute and chronic conditions with varying levels of severity. Disorders of the AC joint primarily include acute ligamentous injuries, from minor sprains to complete dislocation,1 and progressive degenerative disease.2


Most AC joint injuries are caused by a direct trauma or a sudden axial load to the superolateral aspect of an adducted shoulder. Injuries are common from falls, motor vehicle accidents and sports. Indirect trauma can result from falling on an outstretched elbow or hand, forcing the humeral head superiorly into the acromion.1

Epidemiology including risk factors and primary prevention

Shoulder girdle injuries involve the AC joint approximately 10% of the time.1 AC joint injury is five times more common in males1 and primarily occurs in the third decade of life.3 Incomplete injuries occur twice as frequently as complete dislocations. 1 The incidence of AC joint dislocation in the general population is 3-4 per 100,000 and 25-52% occur during sports.4 The highest rates of joint sprains have been reported in contact sports including rugby,3 ice hockey, wrestling, and football.5  


The AC joint is formed by the articulation between the distal clavicle proximally and the acromion distally. It is surrounded by a capsule and reinforced by muscles and ligaments. The deltoid, trapezius, and serratus anterior muscles serve as the main dynamic stabilizers of the joint. Static stability is reinforced by the coracoclavicular (CC) and quadrangular AC ligament– composed of the superior, inferior, anterior, and posterior ligaments.1 The AC ligament is typically injured first, followed by the CC ligament.4  

Disease progression including natural history, disease phases or stages, disease trajectory (clinical features and presentation over time)

The six-stage Rockwood Classification System is currently the most widely accepted system for grading AC joint injuries. The severity of AC joint injury is based on the sequential disruption of the AC and CC ligaments with higher stages correspond to varying radiographically determined clavicular displacement from the acromion (Table 1).6 The degree of disruption leads to instability of the AC joint complex which may require surgical intervention.4 In a clinical setting, this can present as significant shoulder pain directly over the AC joint and shoulder disability.7

GradeAC LigamentCC LigamentACJ CapsuleClavicular DisplacementManagement
IPartial tearIntactIntactNoneNon-operative
IIComplete tearIntact or sprainedDisrupted< 100% superior displacementNon-operative
IIIComplete tearPartial or complete tearDisruptedApproximately 100% superior displacementNon-operative versus operative
IVComplete tearComplete tearDisruptedPosterior displacement, with or without superior displacementNon-operative versus operative
VComplete tearComplete tearDisrupted> 100% superior displacementOperative
VIComplete tearComplete tearDisruptedInferior displacementOperative

Table 1: Rockwood Classification System

Specific secondary or associated conditions and complications

Although infrequent, fractures of the acromion or distal clavicle can occur in association with severe ligamentous damage or complete dislocation of the joint.1 Chronic injury may also develop as repetitive microtrauma leads to degenerative changes in the joint over time.2

Essentials of Assessment


Key historical information includes mechanism of injury, onset of pain whether it is acute (sprain/separation) versus chronic (arthrosis/distal clavicular osteolysis), location and quality of pain, exacerbating and alleviating factors, and functional limitations. Details of prior shoulder injuries and surgeries should be elicited, cervical or radicular pain or upper extremity weakness, as should previous treatments or interventions. 

Physical examination

Examination should begin with inspection of the shoulder complex for warmth, swelling or asymmetry including any abnormal bony protuberances at the level of the AC joint, palpation of bony prominences, and assessment of strength and range of motion, followed by comparison to the contralateral side.

Special tests evaluating reproduction of pain over the AC joint include8 

  • Cross arm adduction: Sensitivity 77%, specificity 79%9
  • Active Compression Test (O’Brien’s): sensitivity 41%, specificity 95%9
    • This test is commonly used when investigating labral pathology and carries a different sensitivity and specificity for that specific injury. 
  • Paxinos test: manual compression of AC joint
  • Resisted Arm Extension: sensitivity 72%, specificity 85%9

Clinical functional assessment: mobility, self-care, cognition/behavior/affective state

AC joint injury may cause significant pain and difficulty performing activities of daily living that require reaching across midline or overhead, poorly impacting an individual’s quality of life.2

Laboratory studies

Laboratory studies are not commonly used in the diagnosis of AC joint injuries.


Standard shoulder x-ray are useful however, a Zanca view is the most accurate way of evaluating the AC joint. It is performed by angling the beam 10 degrees cephalad and reducing the penetration to half that of a standard shoulder x-ray.7 When differentiating Type 3 vs Type 4 lesions, an axial view will show the scapula anterior to the clavicle indicating a type 4 injury. Complete AC joint dislocation may result in a coracoid fracture which is diagnosed with the Stryker view.10 CT can offer more precise evaluation of bone – fractures and degenerative changes, while MRI is more valuable for the evaluation of capsuloligamentous structures and surrounding tissue.11

Supplemental assessment tools

The utility of diagnostic musculoskeletal ultrasound (US) is rapidly growing. For the AC joint, US offers high resolution imaging of the AC joint capsule and ligamentous structure as well as the cortical edges of the acromion and clavicle. While performing exam maneuvers such as cross arm adduction, joint space widening can be examined in real time with dynamic visualization for possible AC separation. Cortical irregularity can be seen, which would suggest an arthritic process.11

Early prediction of outcomes

Severity of injury plays a key role in outcome. For those requiring surgical stabilization, most patients with non-labor occupations typically return to work within 6 months, however 8.8% of manual laborers who required surgery did not return to work at two years follow up in a recent retrospective study.12   


AC joint separation is more common in contact sport athletes. Occupations and sports that require repetitive overhead lifting have a higher prevalence of AC joint arthritis.13 It is also more common in patients with spinal cord injury, with a prevalence of 50-71%.14

Social role and social support system

Impairment in ADLs are common with AC joint injury, due to restricted shoulder ROM, with dominant hand sided injuries causing further limitation. Family support coupled with robust rehabilitation plans are extremely important. Physicians should communicate closely with the rehabilitation team, including physical therapists and athletic trainers, to improve patient outcomes.

Professional issues

Controversy surrounds the management of type 3 injuries where there is disagreement between the effectiveness of surgical versus non-surgical treatment. First and foremost, using evidence-based counseling, joint decision making with the patient and collaboration with surgical colleagues are of the utmost most importance.

Rehabilitation Management and Treatments

Available or current treatment guidelines

The Rockwood Classification System can guide clinicians between non-operative and operative treatment (Table 1).1 A four-phase rehabilitation program has been described for treatment of non-operative AC joint injuries.15 These guidelines are discussed in more detail below.

Clinicians have also suggested a more practical approach for AC joint rehabilitation following the “PASS” pneumonic – pain control, decreasing apprehension with movements, and addressing anterior chest wall stiffness to improve scapular control. The goal of PASS therapy is to provide less-rigid protocols to encourage a more personalized rehabilitation process. Further research is needed to validate this approach.16

At different disease stages

Rehabilitation of Grade I or II injuries:15

  • Phase I: Ice, immobilization, pain control. Begin passive and active ROM with a focus on internal and external shoulder rotation. Advance when near 75% of baseline ROM, decreased pain and increased deltoid and trapezius strength.
  • Phase 2: Rotational ROM with abduction and flexion. Increase strength training (avoid pressing exercises) and advance as tolerates.
  • Phase 3: Advanced strengthening movements, including press exercises. Phase 4: Progress to activity or sport specific exercises.

Important Considerations:17

  • Grade I: Immobilization is not always required given intact capsule but may be used briefly to decrease pain. 
  • Grade II: Pain is expected to be longer given ligamentous injury.
  • Grade III: With AC and CC ligamentous disruption, some dynamic stability via the delto-trapezial fascia remains. Operative treatment is controversial.
  • Grade IV, V, and VI: Operative management is generally recommended. Conservative management may be recommended for Grade III-IV injuries in elderly patients or poor surgical candidates.4

Goals of immobilization include pain relief, joint stability, and prevention of further injury by supporting the humerus, preventing downwards traction of the shoulder girdle and scapula. Distal and lateral clavicular bracing is favored to avoid direct pressure over the AC joint.17 Commonly used bracing includes the Kenny-Howard brace (worn for 6-8 weeks to allow ligaments to heal), RJ bandage,4 or the Lerman platform brace (lesser degree of AC joint reduction).17 Caution must be used with braces to avoid skin irritation or breakdown, nerve compression (including anterior interosseous nerve), or improper fit.17

Coordination of care

It is important to coordinate care between surgeons, radiologists, physiatrists, therapists, and the patient. Determination of management (operative versus non-operative) should include all team members to ensure successful outcomes. For athletes, it is important to include the coaching and athletic training staff.17  

Patient & family education

Patients should actively participate in the rehabilitation process to guide progression through the various phases of rehabilitation. In athletes, it is important to educate the patient and coaching/athletic trainer staff regarding the risks and benefits of any local anesthetic or steroid injections requested for earlier return to play.17 

Measurement of Treatment Outcomes including those that are impairment-based, activity participation-based and environmentally-based.

Outcome measures commonly used to assess ACJ injuries include:

  • Disabilities of the Arm, Shoulder, Hand (DASH) Score
  • American Shoulder and Elbow Surgeons (ASES) Score
  • Constant Score
  • Simple Shoulder Test (SST) Score
  • University of California Los Angeles (UCLA) Shoulder Score

Other general quality of life tools include the 36-Item or 12-Item Short Form Health Survey (SF-36 and SF-12, respectively).18  

Translation into Practice:  practice “pearls”/performance improvement in practice (PIPs)/changes in clinical practice behaviors and skills

While corticosteroid injections can be useful for pain relief following traumatic AC joint injuries, there may be a deleterious effect on natural healing and inflammatory response, however, most believe they are reasonable when done sparingly.1,19 Others suggest they may negatively alter perceptions of pain and worsen long-term outcomes.20 Careful consideration of risks and benefits is important prior to any procedure.

In degenerative ACJ disease, diagnostic and therapeutic joint injections are more widely accepted.2 Ultrasound guidance can improve the accuracy of these injections. Treatment should also include a therapy program to improve ROM while strengthening periscapular and RTC structures.2

Cutting Edge/ Emerging and Unique Concepts and Practice

  • Arthroscopic CC ligament reconstruction using a semitendinosus graft is becoming a commonly employed surgical technique4
  •  A single tendon, simultaneous reconstruction of the AC and CC ligaments may provide greater stability when compared to isolated CC reconstruction21
  • Prolotherapy (15% dextrose solution) may be an effective treatment option for ACJ arthropathy or moderate-to-severe acromial enthesopathy22
  • Autologous adipose-derived mesenchymal stem cell therapy is a new treatment option for ACJ OA but requires further research to support its use and long term effects23

Gaps in the Evidence-Based Knowledge

Controversies and gaps in the evidence-based knowledge

  • There remains significant controversy regarding whether Grade III injuries are best treated with non-operative or operative management4,17
  • Conservative and surgical treatments are both effective for ACJ OA, and there is a lack of evidence illustrating the superiority of one technique over the other24


  1. Gilot G, Mutnal AB, Owens J. Ch. 15: Epidemiology, Clinical Evaluation, Imaging, and Classification of Acromioclavicular Joint Injuries.” Disorders of the Shoulder: Diagnosis and Management – Shoulder Trauma, Lippincott, Williams & Wilkins, 2014.
  2. Mall NA, Foley E, Chalmers PN, Cole BJ, Romeo AA, Bach BR. Degenerative Joint Disease of the Acromioclavicular Joint: A Review. Am J Sports Med. 2013 Nov;41(11):2684–92.
  3. Pallis M, Cameron KL, Svoboda SJ, Owens BD. Epidemiology of Acromioclavicular Joint Injury in Young Athletes. Am J Sports Med. 2012 Sep;40(9):2072–7.
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  6. Williams GR, Nguyen VD, Rockwood CA. Classification and radiographic analysis of acromioclavicular dislocations. Appl Radiol. 1989;18(2):29–34.
  7. Mazzocca AD, Arciero RA, Bicos J. Evaluation and treatment of acromioclavicular joint injuries. Am J Sports Med. 2007;35(2):316–29.
  8. Chang K-V, Wu W-T, Hsu P-C, Lew HL, Özçakar L. Clinical Tests of the Shoulder: Accuracy and Extension Using Dynamic Ultrasound. Am J Phys Med Rehabil. 2020 Feb;99(2):161–9.
  9. Chronopoulos E, Kim TK, Park HB, Ashenbrenner D, McFarland EG. Diagnostic value of physical tests for isolated chronic acromioclavicular lesions. Am J Sports Med. 2004 May;32(3):655–61.
  10. SACCOMANNO MF, DE IESO C, MILANO G. Acromioclavicular joint instability: anatomy, biomechanics and evaluation. Joints. 2014 Jul 8;2(2):87–92.
  11. Precerutti M, Formica M, Bonardi M, Peroni C, Calciati F. Acromioclavicular osteoarthritis and shoulder pain: a review of the role of ultrasonography. J Ultrasound. 2020 Jul 15;23(3):317–25.
  12. Porschke F, Schnetzke M, Studier-Fischer S, Gruetzner PA, Guehring T. Return to work after acromioclavicular joint stabilization: a retrospective case control study. J Orthop Surg. 2019 Feb 12;14:45.
  13. Chaudhury S, Bavan L, Rupani N, Mouyis K, Kulkarni R, Rangan A, et al. Managing acromio-clavicular joint pain: a scoping review. Shoulder Elb. 2018 Jan;10(1):4–14.
  14. Morgenroth DC, Gellhorn AC, Suri P. Osteoarthritis in the Disabled Population: A Mechanical Perspective. PM&R. 2012 May;4:S20–7.
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  16. LeVasseur MR, Mancini MR, Berthold DP, Cusano A, McCann GP, Cote MP, et al. Acromioclavicular Joint Injuries: Effective Rehabilitation. Open Access J Sports Med. 2021 May;Volume 12:73–85.
  17. Gilot G, Owens J. Mutnal AB. Ch. 16: Non-operative Management of Acromioclavicular Joint Injuries: Indications and Outcomes. Disorders of the Shoulder: Diagnosis and Management – Shoulder Trauma, Lippincott, Williams & Wilkins, 2014. In.
  18. Reintgen C, Gerlach EB, Schoch BS, Mamelson K, Wright TW, Farmer KW, et al. What Outcome Measures Are Reported in the Management of Acromioclavicular Joint Injuries? Orthop J Sports Med. 2020;8(1):2325967119892322.
  19. Nelson C. Anesthetic injections in football: an ethical dilemma. Sports Med Dig 2001; 23: 133.
  20. Snibbe JC, Gambardella RA. Use of injections for osteoarthritis in joints and sports activity. Clin Sports Med. 2005 Jan;24(1):83–91.
  21. Shin S-J, Campbell S, Scott J, McGarry MH, Lee TQ. Simultaneous anatomic reconstruction of the acromioclavicular and coracoclavicular ligaments using a single tendon graft. Knee Surg Sports Traumatol Arthrosc. 2014 Sep;22(9):2216–22.
  22. Hsieh P-C, Chiou H-J, Wang H-K, Lai Y-C, Lin Y-H. Ultrasound-Guided Prolotherapy for Acromial Enthesopathy and Acromioclavicular Joint Arthropathy: A Single-Arm Prospective Study: Ultrasound-Guided Prolotherapy for a Painful AC Joint. J Ultrasound Med. 2019 Mar;38(3):605–12.
  23. Freitag J, Wickham J, Shah K, Tenen A. Effect of autologous adipose-derived mesenchymal stem cell therapy in the treatment of acromioclavicular joint osteoarthritis. BMJ Case Rep. 2019 Feb;12(2):e227865.
  24. Soler F, Mocini F, Djemeto DT, Cattaneo S, Saccomanno MF, Milano G. No differences between conservative and surgical management of acromioclavicular joint osteoarthritis: a scoping review. Knee Surg Sports Traumatol Arthrosc. 2021 Jul;29(7):2194–201.

Author Disclosure

Kristian von Rickenbach, MD, MS
Nothing to Disclose

Mani Singh, MD
Nothing to Disclose

Nicholas Tsitsilianos, MD
Nothing to Disclose

Zainab Shirazi, MD
Nothing to Disclose