The sciatic nerve is the largest nerve in the body, running from the lower back to the foot. Sciatica causes pain in the lower back, hips and legs that is often characterised by a tingling or sharp "pins and needles" sensation down the leg.
Herniated disks are the most common cause of sciatica, according to Dr. Steven R. Garfin, professor and chair of the Department of Orthopaedics at the University of California, San Diego. Herniated disks typically occur in the lower back because this part of the spine carries the majority of the body’s weight. When a disk bulges out of place or herniates, it can press on the sciatic nerve, causing pain and tingling down the leg. Most herniated disks heal on their own, though some require surgical intervention.
Lumbar Spinal Stenosis
Lumbar spinal stenosis is characterised by a narrowing of the spinal canal in certain areas. When the lumbar region of the spinal canal constricts, it can place pressure on the sciatic nerve, causing pain that can radiate down the leg. Spinal stenosis is often a result of degenerative disk disease or arthritis. Treatment for the condition generally involves anti-inflammatory medications, epidural steroid injections, physiotherapy or a combination of these methods. In severe cases, doctors may remove a portion of the vertebra or disks in the narrowed area to relieve pressure on the sciatic nerve.
Degenerative Disk Disease
Degenerative disk disease is often simply a result of ageing. Osteoarthritis, smoking and spinal injuries can also contribute to chemical and structural changes in the disks. When disks start to wear thin, they can irritate the sciatic nerve or cause the vertebrae to slip out of place and pinch the sciatic nerve. The disease can lead to herniated disks and lumbar spinal stenosis, two of the major causes of sciatica.
The piriformis muscle runs from the lower back and extends to each thighbone. When the muscle tightens or spasms, it can create pressure on the sciatic nerve. Sciatic pain that results from piriformis syndrome can radiate down the back of the thigh, though it does not extend below the knee like other types of sciatic pain can. Piriformis syndrome is most common in individuals who frequently sit for extended periods of time or sustain a lower back injury from a car accident or a fall, according to the Mayo Clinic.