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 Ligaments stability static stability login to view 15 more bullets dynamic stability login to view 2 more bullets 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 login to view 2 more bullets vertical (superior-inferior) stability evaluates CC ligaments AC joint exacerbation tests O'Brien's test login to view 2 more bullets crossbody adduction Imaging Radiographs required views bilateral anteroposterior (AP) view of AC joints login to view 3 more bullets axillary lateral view login to view 1 more bullet zanca view login to view 1 more bullet additional veiws cross-body adduction view (Basmania) login to view 1 more bullet weighted stress views login to view 2 more bullets findings fractures can mimic AC separations login to view 3 more bullets 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 Type III 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 immobilization with early motion indications login to view 3 more bullets techniques login to view 1 more bullet rehab login to view 4 more bullets outcomes login to view 1 more bullet complications login to view 2 more bullets Operative open reduction and internal fixation (ORIF) indications login to view 6 more bullets contraindications login to view 2 more bullets techniques login to view 14 more bullets rehabilitation login to view 2 more bullets 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 login to view 1 more bullet 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 login to view 2 more bullets allograft login to view 1 more bullet 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