After straightening the leg behind the knee tendon pain consider muscle strain, muscle injury, lumbar intervertebral disc herniation, etc., to take the braking rest, drug therapy, physical therapy, surgical treatment. 1. Muscle strain: consider frequent flexion and extension of the knee caused by popliteal strain, need to rest, avoid strenuous exercise, you can line massage, relax the local muscles, you can also take oral relaxation tablets or elongation capsules. 2. Muscle injury: If the pain is caused by trauma, at least 5-7 days of recuperation, to avoid bending the knee joint, early local ice packs, external Yunnan Baiyao aerosol, oral Sanqi injury tablets or bones and tendons capsule. Use safflower oil externally. 3. Lumbar disc herniation: nerve compression radiating to the leg can cause symptoms, you can perform lumbar traction, acupuncture, mid-frequency pulse electro-physiotherapy, oral lumbar pain Ning capsule, minimally invasive surgical treatment if necessary. The tendon behind the knee after straightening the leg pulls the pain of a variety of possible causes, need to go to the hospital to clarify the cause of treatment, specific medication should be under the guidance of a doctor.