Discussion

• AC joint is situated between the clavicle and acromion;
• acromion has two ossification centers which fuse at age 22 yrs;
• it permits motion in three planes:
  • AP gliding of acromion during protraction & retraction of scapula;
  • tilting of acromion during abduction & adduction of arm;
  • rotation of the clavicle;
  • rotation occurs during abduction & adduction of shoulder.

Anatomy

• innervation: provided by the suprascapular and lateral pectoral nerves
• ref: The suprascapular nerve and its articular branch to the acromioclavicular joint: an anatomic study
•  joint is reinforced by two sets of ligaments:
  • AC ligament
    • directed horizontally, and functionally the AC joints control horizontal stability;
    • palpable shallow depression between end of clavicle & acromion;
    • superior AC lig is most important ligament in stabilizing AC joint for normal daily activities;
  • coracoclavicular ligaments:
    • stronger, vertically directed contains conoid and trapezoid ligaments help to control vertical stability;
    • coracoclavicular lig are suspensory ligaments of upper limb;
    • conoid:
      • is the most important ligament for support of the joint against significant injuries and superior displacement;
      • cone shaped which extends between the conoid tubercle on the posterior clavicle and the base of the coracoid;
    • trapezoid:
      • resists AC joint compression;
      • begins anteriorly and laterally to the conoid ligament on the clavicle and inserts on the coracoid process;
    • reference: Biomechanical study of the ligamentous system of the acromioclavicular joint.
  •     - Sternoclavicular joint:
    • see Sternoclavicular Joint injury in the adolescent;
    • inherently more stable than AC joint; because of this stability & its more protected medial location;
    • it is injured less frequently than the acromioclavicular joint.

Management of Specific Injuries

• Acromioclavicular Joint joint arthrosis / distal clavicle excision
  • The influence of distal clavicle resection and rotator cuff repair on the effectiveness of anterior acromioplasty.
• Acromioclavicular Joint joint septic arthritis:
  • Septic arthritis of the acromioclavicular joint - a report of four cases
  • Septic arthritis of the acromioclavicular joint.
  • Sonographic detection, evaluation and aspiration of infected acromioclavicular joints.
    
  • Primary septic arthritis of the acromio-clavicular joint: case report and review of literature
• Acromioclavicular Joint Joint Separation
  

Exam

• palpate the AC joint during flexion and extension of shoulder;
• distract the arm as it is placed in adduction
• significant prominence of the distal clavicle indicates unstable AC injury;
• BvR test for DJD: resisted shoulder upward flexion with arm hyperadducted;
• ref: Clinical evaluation of acromioclavicular joint pathology: sensitivity of a new test

Radiology

• classification of Acromioclavicular Joint separation
• acromioclavicular joint stresses views
  • grade I injuries remain nondisplaced;
  • type I and type II injuries can be differentiated on stress radiographs;
  • w/ pt standing, 10 lb weight is secured to affected upper limb;
  • w/ grade II injury, suspended  wt displaces AC joint articulation, which increases distance between clavicle & acromion;
• zanca view
• scapular outlet view
• reference: Radiological evaluation of the acromioclavicular joint.

References

• The acromioclavicular joint in rheumatoid arthritis.
• Osteolysis of the distal part of the clavicle in male athletes.