Analysis of the Capsule and Ligament Insertions About the Acromioclavicular Joint: A Cadaveric Study

PURPOSE: The purpose of this study was to analyze the capsular and ligamentous insertions about the acromioclavicular (AC) joint to determine the amount of bone that can be removed without destabilizing the joint. METHODS: We dissected 28 cadaveric shoulders. The AC ligament insertions were measured under loupe magnification with a digital caliper on the acromial and clavicular sides on the anterior, posterior, superior, and inferior edges. We measured the distance to the coracoacromial (CA) and coracoclavicular ligaments. In addition, the axial and coronal angle of the AC joint was measured. RESULTS: The AC joint capsular insertion on the acromion begins, on average, 2.8 mm (range, 2.3 to 3.3 mm) from the medial acromion and begins on the lateral clavicle a mean of 3.5 mm (range, 2.9 to 3.9 mm) from the distal clavicle. The mean capsular width ranged from 1.6 to 2.9 mm. The mean distance from the medial acromion to the CA ligament insertion was 3.5 mm. The mean axial angle of the AC joint was 51 degrees , with a 12 degrees coronal angle. The mean distance from the lateral clavicle to the start of the trapezoid ligament was 14.7 mm, and that to the conoid ligament was 32.1 mm. CONCLUSIONS: An anatomic-based recommendation for safe AC joint resection is that 2 to 3 mm of the medial acromion and 3 to 4 mm of the distal clavicle can be resected without removing the AC capsular insertions. The trapezial and CA attachments are in close proximity to the AC capsular insertions. Medial resections greater that 15 mm will begin to take down the trapezoid ligament. Arthroscopic bone resection should be directed into the AC joint at approximately 50 degrees in the axial plane and 12 degrees in the coronal plane for safe symmetric resection. CLINICAL RELEVANCE: These anatomic measurements suggest that AC joint resections (5 to 7 mm) with 2 to 3 mm from the acromial side and 3 to 4 mm from the clavicular side will not disrupt the stabilizing ligaments of the AC joint after distal clavicle resection.