Sciatica is radiating pain in your lower back, hips, and thighs. The pain begins in the bottom part of the back, then shoots down one leg. It usually stops just below the knee. Sciatica isn’t a condition itself but a unique pain that usually starts because of damage or changes to the spine.

Sciatica is named for the sciatic nerve, the main nerve in the lower back. While sciatica can happen because of sciatic nerve irritation, in most cases, the irritation actually happens in the nerve roots.

The leading causes of nerve root irritation are:

• Herniated discs
• Spinal stenosis
• Degenerative disc disease
• Bone spurs
• Facet synovial cysts
• Scar tissue buildup following back surgery
  
  

Sciatic nerve irritation is most commonly caused by piriformis syndrome. This syndrome begins with buttock muscle spasms that affect the nearby sciatic nerve.

Another possible cause of sciatic nerve irritation is ischiofemoral impingement, a narrowing between the femur (thigh bone) and the lower back part of your hip bone. This happens in the buttocks, triggering sciatic nerve irritation.

Posterior femoral cutaneous nerve entrapment, which shows up in a branch of your sciatic nerve, can cause pain that shoots down your thigh. Unlike most sciatica pain, pain from this type of nerve entrapment usually stops in the upper leg.