Medial knee protrusion may be caused by degenerative hyperplasia of the medial knee joint, collateral ligament injury, bursitis and other reasons. 1. Degenerative hyperplasia of the medial knee joint: the hyperplasia may irritate the surrounding soft tissues, thus causing protrusion of the medial side of the knee, which is usually accompanied by pressure pain. 2. Collateral ligament injury: it may cause obvious swelling, bruising, pain, and hematoma formation and protrusion on the medial side of the knee. 3. Bursitis: This is an acute or chronic inflammation of the bursa. It may be caused by direct violent injury, pathogenic bacterial infection and other reasons. Due to the stimulation of inflammation, bursa edema and hyperplasia can occur, which leads to obvious protrusion, pain and pressure pain on the inner side of the knee. In addition, the protrusion of the inner side of the knee can also be seen in other diseases, it is recommended that the patient go to the hospital in time, to clarify the cause of the disease and follow the doctor’s instructions for treatment.