Why do the calcifications occur most commonly in the shoulder?
The supraspinatus tendon is prone to impingement. The tendon is poorly vascularized a few millimeters from its insertion into the humeral head. Therefore, its ability to recover from the repetitive trauma of impingement is poor at this site, resulting in ischemia and necrosis. This “critical zone” is prone to accumulating calcium salts (BCPs) causing calcific deposits in the tendon and bursa. Notably, other tendons that develop calcifications have a similar pathogenesis, with deposition at relatively avascular and traumatized sites in the tendon. Therefore, the calcification may be the result of chronic tendinitis as well as a driver of further tendon injury.
