The recovery time for a sprained knee is as follows: 1. If there is only a knee ligament injury or soft tissue contusion, the ligament continuity is intact and requires a month of cast braking before recovery; 2. If there is a ligament rupture, such as a lateral collateral ligament rupture, cruciate ligament rupture or meniscus injury, recovery takes about three months. Surgery is needed to reconstruct the ligament integrity, and then a brace is fixed for about one month after surgery, and the brace can be removed and functional exercise can be performed only after one month.