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  • Definition
    • injury to the acromioclavicular (AC) joint with disruption of the AC ligaments with or without coracoclavicular (CC) ligament disruption
  • Epidemiology
    • incidence
      • common injury making up 9% of shoulder girdle injuries
    • demographics
      • more common in males and athletes
  • Pathophysiology
    • mechanism
      • direct blow to the shoulder
      • often sustained while falling onto the shoulder
  • 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
  • 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 
  • 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 q
    • 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

Rockwood Classification
AC ligament
CC ligament
Reducibility  Treatment
Type I
AC tenderness; no AC instability 
Type II
AC horizontal instability
AC joint disrupted; increased CC distance < 25% of contralateral
Type III

increased CC distance 25-100% of contralateral
reducible controversial
IIIA     AC vertical instability, no horizontal  stability
IIIB     AC vertical + horizontal instability
Type IV
skin tenting, posterior fullness
lateral clavicle displaced posterior through trapezius on the axillary lateral XR
not reducible surgery
Type V
severe shoulder droop, does not improve with shrug
increased CC distance > 100% of contralateral
not reducible surgery
Type VI
rare; associated injuries; paresthesias
inferior dislocation of lateral clavicle, lying either in subacromial or subcoracoid position
not reducible surgery

Differential Diagnosis
  • 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
  • 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
        • 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 with ORIF 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 
  • ORIF with CC screw fixation (Bosworth screw)  
    • has fallen out of favor 
    • approach 
      • proximal aspect of anterolateral approach to the shoulder 
    • 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
      • requires second surgery for plate removal
    • complications
      • acromial erosion
      • hook pullout
  • CC ligament reconstruction with coracoacromial (CA) ligament (Modified Weaver-Dunn)
    • approach
      • proximal aspect of anterolateral approach to the shoulder
      • 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
      • proximal aspect of anterolateral approach to the shoulder
      • 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
  • 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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