The most common clinical cause of pain in a tendon in the leg is lumbar disc herniation. The herniated disc or nucleus pulposus compresses and irritates the nerve root, resulting in radiating pain or numbness in the muscles in the area innervated by the nerve root. If the nerve compression is prolonged, numbness, loss of muscle strength, and difficulty walking may occur. In this case, the first thing you should do is to improve the lumbar spine CT or lumbar spine MRI examination to clarify the segment of the lumbar disc herniation and the degree of herniation. The most common clinical condition is sacral nerve root compression. Most of them are lumbar five sacral disc herniation, which compresses sacral nerve root and causes pain in one tendon on the back side of the calf. If it is a tendon pain on the lateral side of the calf, it may be a herniated disc of the fourth or fifth lumbar vertebrae, which compresses the nerve root of the fifth lumbar vertebrae and causes radiating pain in the area of the posterior thigh, lateral calf, and dorsum of the foot. For the above conditions, most patients in the clinic, can be cured by conservative treatment options, and about 15% of patients may need surgery.