Left leg pain may be muscle strain, osteoarthritis, synovitis, lumbar disc herniation, pear-shaped muscle syndrome. 1. Muscle strain: If the pain in the left leg is aggravated by walking or exertion, consider muscle strain, which can be alleviated by rest. 2. Osteoarthritis: if the knee joint pain, joint swelling, joint movement is limited, consider osteoarthritis, X-ray can be a clear diagnosis. 3. Synovitis: If there is obvious joint swelling, joint pain and joint effusion, consider synovitis. 4. Lumbar disc herniation: If the whole leg hurts with numbness, consider lumbar disc herniation. 5. Piriformis syndrome: pain in the buttocks, and pain and numbness radiating to the lower limbs. So the left leg pain needs to look at the specific location, go to the hospital to take a film to check a clear diagnosis.