Knee Locking and Partial Ligaments Tear.

I had accident 3 weeks back and left knee was twisted. I didn't know initially because stiffness and locking started after 2 days. Cannot push knee all the way back while standing. When I try to push it back I always feel some resistance on the medial side. I had MRI and this is the analysis - 1. Grade I sprain of the anterior cruciate ligament. 2. Grade II degeneration in the posterior horn of the medial meniscus. 3. Lateral tracking of patella is seen with partial tear & attenuationof medial patellofemoral ligament. 4. Grade I sprain of the medial collateral ligament. 5. Mild joint effusion is seen, more in the suprapatellar recesses. All these injuries are first time for me. I want to know the right course of action. Why locking is happening when there is no meniscus tear. Can physiotherapy heal it or surgery is required.