Causes / typical injury mechanism: Initially defined in weightlifters, distal clavicle osteolysis is commonly found in individuals performing repetitive upper extremity motions, both for work and for leisure. The mechanism is generally atraumatic and a sequela of repetitive stress to the acromioclavicular (AC) joint in the form of excessive traction. This was surmised from its close association with exercises such as bench presses, chest flys, and push-ups. 

The acromion and AC joint serve as the "roof" of the subacromial space. Due to this, bony changes can result in a compression of the subacromial space, contributing to diagnoses such as impingement syndrome, bursitis, biceps tendonitis, and rotator cuff tears. These diagnoses occur in tandem with distal clavicle / AC joint pathology up to 80% of the time, potentially further complicating a diagnosis in isolation.

Prevalence:

• Age – In most studies, the average age of onset is around 20-30 years. Prevalence is poorly defined due to the rarity of the condition.
• Sex / gender – Distal clavicle osteolysis is typically found in young adult males.

Classic history and presentation: The classic patient is a young male who enjoys weightlifting (eg, bench press, pull-ups, push-ups, and chest flys) who has tenderness at the distal clavicle at the AC joint.

Pathophysiology: Exercises such as bench presses, chest flys, and push-ups result in excessive traction to the AC joint, which subsequently results in microfracture of the clavicle or even complete cartilage loss in severe cases. It has also been indicated that the microtrauma may allow synovial fluid infiltration from the AC joint into the distal clavicle, preventing effective bony remodeling.