Bilateral Glenohumeral-Acromioclavicular Composite Articulations Identified During Routine Cadaveric Dissection: A...

The acromion and lateral clavicle normally lie outside the glenohumeral joint capsule. During routine dissection of an 80-year-old female donor, bilateral glenohumeral-acromioclavicular composite articulations were identified. In each shoulder, the surface opposing the humeral head extended superiorly to include a variant acromion and lateral clavicle; the humeral heads appeared morphologically typical. In the more extensively dissected right shoulder, the lateral end of the clavicle was broad, flattened, and polished where it opposed the humeral head, with a gross appearance consistent with chronic repetitive contact; no clearly defined articular cartilage was apparent. The infraspinatus and teres minor retained their normal humeral attachments, while variant fibers from both muscles blended with the expanded posterior capsule. The supraspinatus passed through an osseous tunnel formed by the variant acromial process and adjacent superior glenoid region before reaching its humeral insertion. The tendon of the long head of the biceps brachii was absent from the joint cavity and appeared to originate within the intertubercular sulcus. Morphometric analysis demonstrated increased acromial dimensions, acromioglenoid distance, and glenoid anteroposterior diameter compared to reference data. These bilateral composite articulations may have altered shoulder stability, range of motion, and rotator cuff mechanics. Recognition of this configuration may help distinguish anatomical variation from acquired shoulder disease.