Updated: 1/23/2023

Acromioclavicular Joint Injury

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  • summary
    • An acromioclavicular joint injury, otherwise known as a shoulder separation, is a traumatic injury to the acromioclavicular (AC) joint with disruption of the acromioclavicular ligaments and/or coracoclavicular (CC) ligaments.
    • Diagnosis is made with bilateral focused shoulder radiographs to assess for AC and CC interval widening.
    • Treatment is immobilzation or surgical reconstruction depending on patient activity levels, degree of separation and degree of ligament injury.
  • Epidemiology
    • Incidence
      • common injury making up 9% of shoulder girdle injuries
    • Demographics
      • more common in males and athletes
  • Etiology
    • Pathophysiology
      • mechanism
        • direct blow to the shoulder
        • often sustained while falling onto the shoulder
  • Anatomy
    • Osteology
      • diarthrodial joint
        • articulation of the scapula (medial acromion) and the lateral clavicle
        • oblique orientation of joint surface
      • contains a fibrocartilaginous intraarticular disc between the osseous elements
        • analogous to the meniscus of the knee
        • involutes with age, disintegrates by age 40
    • Motion
      • primarily gliding motion
      • rotational motion is minimal
        • clavicle rotates 40-50° posteriorly with shoulder elevation
        • only ~8° rotation through the AC joint, due to synchronous scapuloclavicular motion
    • Stability
      • static
        • joint capsule
        • acromioclavicular (AC) ligaments
          • controls horizontal motion and anterior-posterior stability
          • has superior, inferior, anterior and posterior components
            • posterior and superior AC ligaments are most important for stability
        • coracoclavicular (CC) ligaments
          • controls vertical motion and superior-inferior stability
          • two ligaments
            • conoid
              • medial
              • inserts on clavicle 4.5cm medial to lateral edge
              • most important for vertical stability
            • trapezoid
              • lateral
              • inserts on clavicle 3cm medial to lateral edge
      • dynamic
        • anterior deltoid
        • trapezius
  • Presentation
    • Symptoms
      • pain
        • usually over AC joint
        • can also be referred to the trapezius
    • Physical exam
      • lateral clavicle or AC joint tenderness
      • abnormal contour of the shoulder compared to contralateral side
      • stability assessment
        • horizontal (anterior-posterior) stability evaluates AC ligaments
          • cross-body adduction
          • horizontal instability (ISAKOS type 3B) may indicate need for more aggressive treatment
        • vertical (superior-inferior) stability evaluates CC ligaments
      • AC joint exacerbation tests
        • O'Brien's test
          • superficial pain localized to AC joint is suggestive of AC joint pathology
            • deep pain is suggestive of a SLAP lesion
        • crossbody adduction 
  • Imaging
    • Radiographs
      • required views
        • bilateral anteroposterior (AP) view of AC joints
          • compare displacement to contralateral side
            • measured as distance from top of coracoid to bottom of clavicle
          • use 1/3 penetration on AP to visualize AC joint
        • axillary lateral view
          • required to diagnose Type IV (posterior)
        • zanca view
          • performed by tilting the x-ray beam 10-15° cephalad and using only 50% of the standard shoulder AP penetrance
      • additional veiws
        • cross-body adduction view (Basmania)
          • scapular Y performed with cross-body adduction stress
        • weighted stress views
          • usually no longer used
          • may help differentiate Type II from Type III
      • findings
        • fractures can mimic AC separations
          • base of coracoid fracture
          • Neer type 2A distal clavicle fracture
            • ligaments remain attached to distal fragment as proximal (medial) fragment displaces
  • Classification
      • Rockwood Classification
      • Type
      • AC ligament
      • CC ligament
      • Exam
      • Radiographs
      • Reducibility
      • Treatment
      • Illus.
      • XR
      • Type I
      • Sprain
      • Normal
      • AC tenderness
      • No AC instability
      • Normal
      • Reducible
      • Sling
      • Type II
      • Torn
      • Sprain
      • AC horizontal instability
      • AC joint disrupted
      • Increased CC distance < 25% of contralateral
      • Reducible
      • Sling
      • Torn
      • Torn
      • AC joint disrupted
      • Increased CC distance 25-100% of contralateral
      • Reducible
      • Controversial
      •  IIIA
      • AC vertical instability
      • No horizontal stability
      •  IIIB
      • AC vertical instability
      • Horizontal instability
      • Type IV
      • Torn
      • Torn
      • Skin tenting
      • Posterior fullness
      • Lateral clavicle displaced posterior through trapezius on the axillary lateral XR
      • Not reducible
      • Surgery
      • Type V
      • Torn
      • Torn
      • Severe shoulder droop, does not improve with shrug
      • Increased CC distance > 100% of contralateral
      • Not reducible
      • Surgery
      • Type VI
      • Torn
      • Torn
      • Rare; Associated injuries; paresthesias
      • Inferior dislocation of lateral clavicle, lying either in subacromial or subcoracoid position
      • Not reducible
      • Surgery
  • Differential
    • Coracoid fracture
      • base of coracoid fracture can mimic a CC ligament disruption
      • has superiorly displaced distal clavicle, but normal CC distance (normal is 11-13mm)
    • Distal Clavicle Fracture (Neer 2A)
      • can mimic AC separations as well, as ligaments remain attached to distal component
    • Pediatric medial clavicle physeal injury
    • Pediatric distal clavicle physeal injury
  • Treatment
    • Nonoperative
      • brief sling immobilization, rest, ice, physical therapy
        • indications
          • type I and II
          • type III in most individuals
            • good results when clavicle displaced < 2cm
        • rehab
          • early shoulder range of motion
          • regain functional motion by 6 weeks
          • return to normal activity at 12 weeks
          • consider corticosteroid injections
        • outcomes
          • type III treated non-op had higher DASH scores at 6 weeks and 3 months, and equal function at 1 year with lower rate of secondary surgery (removal of hardware) compared to those treated operatively
        • complications
          • AC joint arthritis
          • chronic subluxation and instability
    • Operative
      • CC interval restoration (ORIF vs. Ligament Reconstruction)
        • indications
          • acute type IV, V or VI injuries
            • recent studies suggest no difference in functional outcomes between operative and nonoperative interventions for high grade injuries
          • acute type III injuries in laborers, elite athletes, patients with cosmetic concerns
          • chronic type III injuries that failed non-op treatment
            • historically it was thought acute injuries were treated with ORIF and chronic injuries were treated with CC ligment reconstruction
              • however, new studies have shown no difference in outcomes in types III injuries treated surgically after 6 weeks non-op treatment versus immediate surgery
        • contraindications
          • patient unlikely to comply with postoperative rehabilitation
          • skin problems over fixation approach site
        • techniques
          • ligament reconstruction with soft tissue graft
            • Modified Weaver-Dunn
              • distal clavicle excision with transfer of coracoacromial ligament to the distal clavicle to recreate CC ligament
            • autograft
            • allograft
          • fixation
            • suture
            • hook plate
            • CC screw (Bosworth)
            • cortical flip button (e.g Dog Bone)(+/- arthroscopic assistance)
            • K-wire
        • rehabilitation
          • sling immobilization for 6 weeks, no shoulder range of motion
          • return to full activity after 6 months
  • Techniques
    • ORIF with CC screw fixation (Bosworth screw)
      • has fallen out of favor
      • approach
      • technique
        • screw placement from distal clavicle to coracoid, superior to inferior
      • pros
        • rigid internal fixation
      • cons
        • danger of screw being too long and damage to critical structure below coracoid
        • routine screw removal at 8-12 weeks is advised to prevent screw breakage
          • due to normal motion between clavicle and scapula
      • complications
        • hardware irritation at level of screw purchase in coracoid
        • hardware failure at level of screw purchase in coracoid
    • ORIF with CC suture fixation
      • approach
        • proximal aspect of anterolateral approach to the shoulder
      • technique
        • suture placed either around or through clavicle and around the base of the coracoid
        • can also use suture anchors for coracoid fixation
      • pros
        • no risk of hardware failure or migration
      • cons
        • suture not as strong as screw fixation
        • requires careful suture passage inferior to coracoid due to proximity of crucial neurovascular structures
      • complications
        • suture erosion causing distal third clavicle fracture
        • hardware irritation
    • ORIF with AC pin fixation (Phemister Technique)
      • approach
        • can be done percutaneously
      • technique
        • smooth wire or pin fixation directly across AC joint
      • cons
        • hardware irritation
      • complications
        • high incidence of pin migration
        • generally not performed due to high complication rates
    • ORIF with AC hook plate fixation
      • approach
        • exposure of distal and middle clavicle
      • technique
        • use of standard hook plate over superior distal clavicle
      • pros
        • rigid fixation
      • cons
        • may require second surgery for plate removal if symptomatic
      • complications
        • acromial erosion
        • hook pullout
    • CC ligament reconstruction with coracoacromial (CA) ligament (Modified Weaver-Dunn)
      • approach
        • arthroscopic technique also described
      • technique
        • distal clavicle excision
        • transfer of coracoacromial ligament to the distal clavicle to recreate CC ligament
        • reinforce with internal fixation
      • cons
        • coracoacromial ligament only 20% as strong as normal CC ligament
        • lack of internal fixation risks failure of soft tissue repair
    • CC ligament reconstruction with free tendon graft
      • approach
        • can be performed arthroscopically-assisted
      • graft
        • autograft
          • palmaris longus
          • semitendinosus
        • allograft
          • tibialis anterior
      • technique
        • figure-of-eight passage of graft, looping around coracoid and fixation through clavicular tunnels
        • reinforce with internal fixation
      • pros
        • graft reconstruction more closely recreates strength of native CC ligament
      • cons
        • standard risks of allograft use or autograft harvest
        • lack of internal fixation risks failure of soft tissue repair
  • Complications
    • Residual pain at AC joint
      • 30-50%
    • AC arthritis
      • more common with surgical management than with nonoperative treatment
    • Hardware failure
      • CC screw breakage/pullout
    • Coracoid fracture
      • can occur with coracoid tunnel drilling
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(OBQ09.272) A 58-year-old right-hand dominant accountant falls off a bicycle 4 days ago and injured his left non-dominant shoulder. A radiograph is shown in Figure A. The axillary radiograph shows no antero-posterior translation. What is the most appropriate next step in treatment?

QID: 3085

Coracoclavicular ligament reconstruction



Acromioclavicular capsular reconstruction



Sling and early ROM exercises



Arthroscopic distal clavicle excision



Weaver-Dunn procedure



L 1 C

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(OBQ08.7) For Grade III AC joint separations, surgical treatment results in which of the following when compared to non-operative management?

QID: 393

Faster return to play



Increased range of motion



Increased functional rotator cuff strength



Decreased funtional rotator cuff strength



Higher complication rate



L 2 D

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(OBQ08.203) A football player sustains a suspected shoulder separation. In addition to a true AP and an axillary lateral, which of the following additional radiographic views is most appropriate to evaluate the AC joint?

QID: 589

Stryker notch view



West Point view



Supraspinatus outlet view



Velpeau view



Zanca view



L 2 D

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(SBQ07SM.49) A 35-year-old non-athlete sustains the injury shown in Figure A. An axillary radiograph is also obtained which is normal. Which of the following outcomes has been shown to be associated with reduction and stabilization compared to nonoperative treatment?

QID: 1434

Improved patient reported outcomes at 3 months



Return to pre-injury sporting activity within 1 year



Improved shoulder range of motion (ROM)



Improved strength and endurance



Improved cosmesis



L 3 D

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(SAE07SM.86) A 46-year-old woman fell from her bicycle and sustained the injury shown in Figure 24. Which of the following ligaments has been disrupted?

QID: 8748




Acromioclavicular and coracoclavicular






Coracoacromial and sternoclavicular






L 1 E

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(OBQ05.251) What is the preferred treatment for a symptomatic acute acromioclavicular separation where there is a 20% increase in the coracoclavicular distance on AP radiograph compared to the opposite uninjured side?

QID: 1137

Anatomic coracoclavicular ligament reconstruction



Acute repair of acromioclavicular capsule



Sling followed by early physical therapy



Reduction and retrograde pinning of the acromioclavicular joint



Distal clavicle excision



L 1 D

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