The old misalignment of the tendon behind the bend of the leg may be caused by overwork, knee arthritis, muscle degeneration and laxity. 1. overwork: when the muscles of the leg after long-term use of exertion, will lead to the accumulation of local lactic acid, stimulate the nerve, due to muscle fatigue, for the tendon restriction weakened, may lead to tendon dislocation of the situation. 2. Knee osteoarthritis: when knee osteoarthritis occurs, there will be localized inflammatory cell infiltration and tissue edema, which will compress the tendon as well as the nearby nerves, leading to reflex displacement and misalignment. 3. Muscle degeneration and laxity: with age, muscle atrophy, muscle strength is weakened, will cause muscle laxity, muscle and tendon and the nearby joints of the pulling effect is weakened, so that it can not effectively limit the activities of the tendon, at this time may lead to the situation of the tendon after the leg bends dislocation. The tendon behind the leg bend is always misaligned may also have other reasons, such as plant function nerve disorder, trauma, etc., should consult a doctor in time, a clear diagnosis, targeted treatment.