When the leg is straightened by pain, it can be divided into the following two cases for corresponding treatment: First, the patient usually seldom participates in physical exercise, so the muscle tendon tension of the posterior thigh is higher, and when the lower limb is straightened, there will be muscle tendon stretching pain, adhere to daily leg stretching stretching, can be in 3-7 days pain relief, muscle tendon can make adaptive changes. Second, the knee joint degenerative disease, such as osteoarthritis, in the middle and late stages will appear after the knee joint capsule, and the back of the thigh muscle tendon tension, contracture, in the leg straightening can appear in the back of the thigh pain symptoms, in serious cases can appear knee joint straightening restrictions, should be carried out as soon as possible knee joint examination, usually found in the knee joint there are hyperplastic bone superfluous obstruction knee joint straightening, perform knee arthroscopic surgery or knee joint replacement surgery Removing the blocking factor and restoring the normal movement of the knee joint can remove the painful symptoms when the leg is straightened.