Back and leg pain often come hand in hand, especially when caused by conditions such as sciatica. More often, back and leg pain are caused by injury or overuse during physical activities. As humans age, they may also experience back and leg pain due to conditions such as arthritis, though one may feel arthritis pain in one area without feeling pain in the other in some cases. Lumbar radiculopathy — chronic pain in the back and legs due to nerve compression — also commonly leads to pain in the legs and back, and this condition can be caused by several different conditions including a herniated disc in the spine.
Injuries account for most back and leg pain, as muscles, ligaments, tendons, and bones within the lower body can all become injured during day to day activities. Muscle strains, in which small fibers in the muscle tear, or ligament sprains, in which ligament fibers stretch and tear, often occur during physical activity and lead to pain in the affected area. When a muscle in the legs is strained, it is possible for that muscle to cause pain in other areas of the body, either because that muscle may have been connected to the hips, or because the other muscles in the body compensate for the injured muscle's failures.
Sciatica is a condition in which the sciatic nerve that runs from the lower back down the back of each leg becomes compressed, causing sharp or radiating back and leg pain. Sciatic pain may occur only in one leg or the other, or it may occur in the lower back or buttocks, or it may occur in all these areas. Sciatic nerve compression can happen when a particularly tight muscle clamps down on the nerve, or it may occur when a disc in the spine herniates, causing compression on the sciatic nerve.
A herniated disc occurs when the spinal disc ruptures, allowing the fluid to press against the nerves that run through the spine. While the sciatic nerve is one of the more common nerves affected by a herniated disc, it is by no means the only nerve that can be affected. The sciatic nerve will, however, most often lead to back and leg pain. A herniated disc can cause pain in the back without pressing on a nerve, and the legs may end up compensating for affected muscles in the back, thereby leading to pain in the legs as well.