Calcification of the medial and lateral collateral ligament AKA periarticular arthritis or calcific tendinitis is a rare disease that can cause acute knee pain. It is an entity in which hydroxyapatite calcific deposits cause inflammation.

Calcium hydroxyapatite deposition disease is one of the common causes of periarticular calcification. It usually presents as amorphous calcification in tendons, close to their site of insertion, but may also affect joint capsules and bursae.

It's a well-known pathology involving the shoulder joint (the rotator cuff tendons), however, it might also involve the hip, elbow, wrist, and knee joints (involving the MCL or LCL).

On imaging, it appears as calcifications involving the MCL or LCL. Calcification could be resorbed and might disappear on follow-up imaging.

Ddx for peri-articular and soft tissue calcifications including gout, CPPD disease, scleroderma, dermatomyositis, hyperparathyroidism, and dystrophic calcification secondary to trauma.