The sciatic nerve is the largest nerve in the body. It consists of 5 nerves that emerge from the lower spine, and resembles a thick, flattened cord. It extends down the back of both legs and into the feet. The sciatic nerve can be as thick as a thumb at its fattest point. It provides sensory and motor functions to the legs and feet.
Trauma
The sciatic nerve can be damaged by injury at any point along its length. MayoClinic.com notes that trauma due to motor vehicle accidents, violence or falls can cause fractures that damage the nerve. An injury to bones of the lower spine, pelvis, legs or feet can cause injury to the nerve that results in pain or muscle weakness.
Degenerative Disc Disease
Cartilaginous discs that allow for cushioning and movement separate the vertebrae of the spine. Medline notes that these discs can sometimes rupture and put pressure on the nerve. The deterioration of intervertebral discs can also cause forward slippage of the vertebrae themselves, a condition called spondylolisthesis. This vertebral displacement can impinge upon the sciatic nerve where it exits the spinal column.
Tumors
A tumor within the spinal cord or its membranes, or in the sciatic nerve itself can affect the nerve and lead to injury or muscle dysfunction, according to MayoClinic.com. The American Academy of Orthopaedic Surgeons lists osteochondroma, or bone tumors, as another cause of sciatica. These could occur within the bones of the spine or pelvis.
Muscle Impingement
Piriformis syndrome is a condition wherein the piriformis muscle, which is located in the buttocks, can cause pressure on the sciatic nerve, resulting in unpleasant symptoms. This condition can be aggravated by sitting for prolonged periods, or by activities such as walking, running and climbing, according to the National Institute of Neurological Disorders and Stroke.
Spinal Stenosis
Stenosis is a term used to describe the narrowing of a passageway; this can sometimes occur in the spinal column. Since the sciatic nerve emerges through a number of passages in the lower lumbar spine, as well as the sacral bone, MayoClinic.com notes that stenosis in any of these openings can put pressure on the nerve roots and lead to pain all along the leg and into the foot.
Lifestyle
Medline warns that sometimes activities as seemingly benign as wearing high heels or sitting with crossed legs can put pressure on the sciatic nerve and cause pain and muscle weakness. Common peroneal nerve dysfunction refers to damage to a part of the sciatic nerve known as the peroneal nerve and it can be caused by improper footwear or posture when sitting. This condition manifests as numbness or muscle weakness to the lower leg and foot.
