How long it takes to fully bend a knee with a medial collateral ligament injury cannot be generalized. Recovery time is related to the degree of ligament injury, which is categorized into medial collateral ligament injury and medial collateral ligament rupture. 1. Medial collateral ligament injury: partial injury or strain of the superficial layer of the medial collateral ligament can be treated conservatively, the ligament usually recovers in about 4 weeks, and then you can start to do exercise sports. It takes about 3 months for the recovery time to return to normal range of motion and the knee joint can be fully flexed. 2. Medial collateral ligament rupture: complete rupture of the medial collateral ligament requires arthroscopic repair surgery of the medial collateral ligament, the complete healing time of 2~3 months, generally 4~12 weeks after the operation to do the exercise of bending the leg, 12 weeks to return to normal range of motion, the knee can be completely bent. The specific recovery time for medial collateral ligament injury varies from person to person, and it is recommended to follow the doctor’s instructions to exercise and recover according to the individual’s condition.