Acromioclavicular Disc

discus articularis acromioclavicularis

The acromioclavicular disc is a fibrocartilaginous intraarticular disc within the AC joint, present as a complete meniscus in 50% and as a wedge-shaped partial meniscus in the remaining cases. It degenerates early in life and is usually absent or vestigial after the fourth decade. When present, it separates the medial articular surface of the acromion from the lateral clavicular facet.

Region: Shoulder

Clinical Relevance

Clinical Notes

The AC disc degenerates rapidly and contributes to AC joint osteoarthritis, which begins earlier in life than glenohumeral arthrosis, commonly becoming symptomatic in athletes and manual workers in their 30s-40s. Horizontal adduction cross-arm test and direct joint palpation reproduce AC joint pain. Corticosteroid injection into the small AC joint space provides diagnostic confirmation and therapeutic benefit. Arthroscopic distal clavicle resection (ACJ arthroplasty) removes 5-7 mm of the clavicle end and eliminates the arthritic disc.

Pathology

Common Injuries & Conditions

AC Joint Arthrosis from Disc Degeneration

Early degeneration of the AC fibrocartilaginous disc produces AC joint arthrosis with superior shoulder pain reproduced by horizontal adduction, palpation directly over the joint, and the painful arc between 120-180 degrees, managed by injection and ultimately arthroscopic distal clavicle resection.