In general, unilateral leg pain may be caused by trauma, lumbar disc herniation, pyriformis syndrome and other reasons. 1. Trauma: such as falling, external impact, weight bearing and other reasons can cause unilateral leg muscles, ligaments and even bone damage, causing local edema, bleeding, resulting in unilateral leg pain and swelling. 2. Lumbar intervertebral disc herniation: due to the degenerative changes of lumbar intervertebral disc (composed of nucleus pulposus, annulus fibrosus and cartilage plate), while the annulus fibrosus is partially or completely broken, the nucleus pulposus protrudes to stimulate or compress the nerve root and the cauda equina, which is a syndrome of injury. The main manifestations are lumbago, sciatica, unilateral leg pain and numbness. 3. Piriformis syndrome: a syndrome in which the sciatic nerve is compressed in the region of the piriformis muscle, manifesting as pain in the buttocks of the affected side and radiating pain in the lower limbs, and painful claudication or even walking difficulty when the pain is severe. There are many other causes of unilateral leg pain, such as thromboembolic vasculitis. It is recommended to consult a doctor in time to clarify the diagnosis and carry out targeted treatment.