Four months after the left knee injury, stiffness in extension is mostly suggestive of adhesion or ankylosis of the joint, you can first systematic rehabilitation, if you can’t solve the problem, you can consider surgical release. 1. Systematic rehabilitation: generally four months after the best time for functional exercise, first passive knee flexion and extension, and then active flexion and extension training, at this time the rehabilitation generally need to be stronger, and the effect is not good, if there is still no improvement in two weeks, we need to consider surgical treatment. 2. Surgery: For patients who cannot recover through systematic rehabilitation, surgery is needed to loosen the adhesion, and then systematic rehabilitation and functional exercise after surgery. Adhesion and ankylosis of the knee joint is a common complication of knee injuries, which requires timely rehabilitation and functional exercises, and should be carried out according to the doctor’s instructions.