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Introduction 
  • Epidemiology
    • incidence
      • Common injury making up 9% of shoulder girdle injuries
    • demographics
      • more common in males
  • Pathophysiology
    • mechanism
      • direct blow to the point of the shoulder
      • seen while falling onto the shoulder
Anatomy
  • AC Joint
    • anatomy
      • the AC joint is a diarthrodial joint 
    • stability and ligaments
      • acromioclavicular ligament
        • provides horizontal stability
        • has superior, inferior, anterior, and posterior component
      • coracoclavicular ligaments (trapezoid and conoid)
        • provides vertical stability
        • trapezoid insert 3 cm from end of clavicle
        • conoid inserts 4.5 cm from end of clavicle in the posterior border
        • base of coracoid fracture can mimic a CC ligament disruption
    • capsule, deltoid and trapezius act as additional stabilizers
  • Complete AC joint anatomy 
Presentation
  • Symptoms
    • pain
  • Physical exam
    • palpate for lateral clavicle or AC joint tenderness
    • observe for abnormal contour of the shoulder compared to contralateral side
    • check for stability
      • AP stability assesses AC ligaments
      • vertical stability assesses CC ligaments
Imaging
  • Radiographs
    • bilateral AP
      • compare displacement to contralateral side
        • measured as distance from top of coracoid to bottom of clavicle
      • 1/3 penetration on AP to visualize AC joint
    • axillary lateral 
      • required to diagnose Type IV (posterior)
    • zanca view 
      •  performed by tilting the x-ray beam 10° to 15° toward the cephalic direction and using only 50% of the standard shoulder anteroposterior penetration strength. q
    • weighted stress views 
      • no longer used
      • helps differentiate Type II from Type III
Classification

Rockwood Classification of AC Joint Injuries
 
AC lig.
CC lig.
Reducibility
Displacement / Radiographs
Tx
Illus.
Xray
Type I
sprain
normal
-
none
sling
 
Type II
torn
sprain
reducible
AC joint is disrupted with a slight vertical separation and there is a slight increase in the CC interspace of <25%
sling
 
Type III
torn
torn
reducible
CC distance of 25-100% of other side
controversial
Type IV
torn
torn
not reducible
lateral end of the clavicle is displaced posterior through trapezius as seen on the axillary X-ray
surgery
 
Type V
torn
torn
not reducible
CC distance > 100% of other side (clavicle herniated through deltotrapezial fascia, resulting in subcutaneous distal clavicle)
surgery
Type VI
torn
torn
not reducible
rare injuries with the distal clavicle lying either in a subacromial or subcoracoid position (infero-lateral under conjoined tendon)
surgery
 


Differentials
  • Coracoid fracture
    • has superiorly displaced distal clavicle, but normal CC distance (normal is 11-13mm) 
Treatment
  • Nonoperative
    • ice, rest and sling for 3 weeks 
      • indications
        • Type I and II 
        • Type III in most individuals
          • good results when clavicle displaced <2cm
      • rehab
        • early ROM
        • regain functional motion by 6 weeks
        • return to normal activity at 12 weeks
      • complications
        • AC joint arthritis
        • chronic subluxation and instability
  • Operative
    • CC interval fixation (within 3-4wk) using either AC fixation or CC fixation
      • indications
        • Type III in laborers / elite athletes and those with cosmetic concerns
        • chronic Type III
        • Type IV, V, VI
          • when clavicle displaced >2cm
      • contraindications
        • patient unlikely to comply with postoperative rehabilitation
        • skin problems over fixation approach site
      • rehabilitation
        • sling immobilization without abduction for 6 weeks
        • no shoulder ROM for 6 weeks
        • generally return to full activity after 6 months 
    • Tissue graft reconstruction (>3-4wk)
      • indicated for chronic tears (>3-4wk)
      • results
        • stronger than Weaver Dunn
Surgical Techniques
  • ORIF with Bosworth CC screw fixation  (CC fixation)
    • approach
      • proximal aspect of anterolateral approach to the shoulder
    • technique
      • superior to inferior screw from distal clavicle into coracoid
    • pros & cons
      • rigid internal fixation
      • danger of screw being too long and damage to critical structure below coracoid
      • routine screw removal at 8-12wk is advised to prevent screw breakage 
        • because of normal movement between clavicle and scapula
    • complications
      • hardware irritation 
      • hardware failure at level of screw purchase in coracoid
  • ORIF with CC suture fixation (CC 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 & cons
      • no risk of hardware failure or migration
      • 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
  • ORIF with hook plate  with subsequent plate removal (AC fixation)
    • approach
      • exposure of distal and middle clavicle
    • technique
      • use of standard hook plate over superior distal clavicle
    • pros & cons
      • rigid fixation
      • generally require second surgery for plate removal
    • complications
      • acromial erosion
      • hook pullout
  • CC ligament reconstruction (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
      • combined with internal fixation
    • pros & 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
      • wrist incision for palmaris harvest
    • technique
      • figure-of--eight passage of graft from distal clavicle to coracoid
      • reinforce with internal fixation
    • pros & cons
      • graft reconstruction more closely recreates strength of native CC ligament
      • standard risks of allograft use or autograft harvest
      • lack of internal fixation risks failure of soft tissue repair
  • Primary AC joint fixation
    • approach
      • can be done percutaneously
    • technique
      • smooth wire or pin fixation directly across AC joint
    • pros & cons
      • hardware irritation
    • complications
      • high incidence of pin migration 
      • generally not performed due to high complication rates

Complications

  • Residual pain at AC joint in 30-50%
  • AC arthritis 
    • more common with surgical management than with nonop
  • CC screw breakage/pullout
 

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