Leg pain after playing contrast agent mostly refers to the pain in the lower limbs after playing contrast agent in CT examination, and the possible causes are allergic reaction, osteoarthritis of knee joint, lumbar disc herniation, etc. 1. Allergic reaction: due to the body’s allergy to the contrast agent, causing the body’s perverse reaction, the immune cells attack the normal tissues, causing tissue damage can appear after the lower limb pain. 2. Knee osteoarthritis: If you are an elderly person, due to old age, obesity and other reasons, degenerative changes in the knee joint, joint cartilage degeneration osteomalacia can also appear knee pain, not necessarily the pain caused by playing contrast media. 3. Lumbar intervertebral disc herniation: because of old age, prolonged weight bearing, obesity and other reasons, resulting in intervertebral disc degeneration, nucleus pulposus protrusion compression of the nerve root, can also appear lower limb pain, playing the contrast agent due to changes in body position, emotional tension and other reasons may induce pain. Lower limb pain after CT examination with contrast medium, if the symptoms continue to be unrelieved, it is recommended to consult a doctor in a timely manner, under the guidance of the doctor’s treatment.