You have a "pinched nerve." A herniated disc and/or arthritis in your back can cause this. The discs are shock absorbers between each vertebra and are close to nerves, which originate in the spine and travel down the legs. If the disc is damaged, part of it may bulge, herniate or even burst free into the spinal canal, putting pressure on the nerve and causing leg pain, numbness or weakness. Bone spurs caused by arthritis can do the same things.