There are many causes of pain in the upper left thigh, the most common ones are lumbar spine lesions, local injuries, local inflammation, as follows: a. Lumbar spine lesions: if the patient has lumbar spine lesions, common lumbar disc herniation, lumbar spine slippage, intravertebral tumor, lumbar spinal stenosis, when the compression of the spinal nerve roots, it will lead to the existence of significant pain symptoms in the upper left thigh. Local injury: If the patient is subjected to external force, causing muscle and soft tissue injury, causing fracture of the femur, it will also lead to obvious pain symptoms on the left thigh, and a local plain X-ray examination is needed to make a clear diagnosis. Third, local inflammation: patients with hip synovitis, hip osteoarthritis, and femoral head necrosis will also lead to significant pain symptoms in the upper left thigh, and need to conduct an MRI examination of the hip joint, which can make a clear diagnosis.