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 attaches to the conoid tubercle, which is posteromedial to the trapezoid tubercle inserts on clavicle 4.5cm medial to lateral edge most important for vertical stability trapezoid attaches to the trapezoid tubercle, which is anterolateral to the conoid tubercle 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 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 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