Causes of left leg pain behind the knee tendon and inability to walk include knee ligament and joint capsule injury, exfoliation osteochondritis dissecans, etc. The treatment includes medication, physical therapy or surgery. 1. Knee ligament and joint capsule injury: pain in the tendon behind the knee when the knee is fully extended and flexed. If the swelling and pain are serious, Meloxicam or Indomethacin can be taken, along with topical medication Yunnan Baiyao Aerosol, blood-activating and pain-relieving creams, etc. Acupuncture and infrared physiotherapy can also be used as appropriate treatments. 2. Exfoliative osteochondritis dissecans: when the knee joint is flexed, there can be pressure and pain on the anterior medial epicondyle of the femoral condyles, and the treatment includes reducing the activities and surgical fixation of the bone block. In addition to the above diseases, hypocalcemia, knee meniscus injury and other diseases can also cause the above symptoms, according to different diseases should choose reasonable treatment. If the above symptoms do not improve, it is recommended to go to the hospital for examination and regular treatment under the guidance of the doctor. It is recommended that the above medications be used under the guidance of a doctor or pharmacist to avoid adverse reactions.