The medial collateral ligament runs down the inner aspect of the knee. Pellegrini-Stieda syndrome refers to an injury and calcification of the medial collateral ligament where it attaches to the thigh bone.
The inside of the knee is a complex of one large ligament, the MCL and and parts of the thickening joint capsular. Both function as the main valgus stabilizer of the knee, especially in 30 degrees of knee flexion
This most commonly occurs following a direct injury to the site, such as being hit on the inside of the knee, or following an overstretching injury that causes the knee to bend inwards overstretching the medial collateral ligament.
Management of this condition involves rest from aggravating activities and strengthening the knee muscles.