The sciatic nerve is the largest and longest nerve in your body, running from your lower spine all the way down to your feet. At its widest point, near the buttock, it averages about 20 millimeters across, roughly the width of your thumb. It controls movement and sensation in most of your lower body, and when it’s compressed or irritated, it produces the radiating leg pain commonly known as sciatica.
Where It Starts and Where It Goes
The sciatic nerve forms from a bundle of nerve roots that exit the lowest segments of your spine, in the lumbar and sacral regions. These individual roots merge into a single thick nerve that exits the pelvis through an opening called the greater sciatic foramen, passing just beneath a deep buttock muscle called the piriformis.
From there, it travels diagonally down through the buttock, crossing over several small muscles before diving beneath the hamstring on the back of the thigh. As it descends, it sends off branches that control the hamstring muscles and part of the inner thigh muscle. When it reaches the back of the knee, in a hollow area called the popliteal fossa, the sciatic nerve splits into its two terminal branches: the tibial nerve and the common fibular (peroneal) nerve. These two branches continue downward and are responsible for nearly all movement and feeling in the lower leg and foot.
What It Controls
The sciatic nerve handles two jobs: making muscles move and relaying sensation back to the brain.
On the motor side, it powers the hamstrings (the group of muscles on the back of your thigh that bend your knee and help extend your hip). It also contributes to the adductor magnus, a large inner-thigh muscle. Once the nerve splits at the knee, its branches control the muscles of the calf, shin, and foot. Virtually every movement below the knee, from pointing your toes to lifting your foot while walking, depends on signals traveling through the sciatic nerve or one of its branches.
On the sensory side, the nerve and its branches provide feeling to the outer lower leg, the top of the foot, the sole, and the toes. The only major area of the lower leg it doesn’t cover is the inner shin and inner ankle, which are supplied by a different nerve. So if you stub your toe, feel gravel under your foot, or notice a breeze on your calf, that information is traveling up through branches of the sciatic nerve to reach your brain.
Why It Causes So Much Pain
Because the sciatic nerve is so long and passes through several tight spaces, it’s vulnerable to compression at multiple points. The result is sciatica: pain that typically radiates from the lower back or buttock down the back of the leg, sometimes all the way to the foot.
The most common cause is a herniated disc in the lumbar spine. When the soft interior of a spinal disc pushes outward, it can press directly on one of the nerve roots that form the sciatic nerve. The disc material also releases inflammatory chemicals that irritate the nerve, which is why the pain can be intense even when the physical compression is modest. Lumbar spinal stenosis, a narrowing of the spinal canal that tends to develop with age, is another frequent culprit. Less commonly, the piriformis muscle in the buttock can tighten or spasm and squeeze the nerve where it passes underneath.
Sciatica pain varies widely. Some people feel a sharp, burning sensation shooting down the leg. Others describe a deep ache, numbness, tingling, or weakness in the foot. Symptoms are almost always on one side. Sitting for long periods, coughing, or bending forward often makes it worse.
How Sciatica Is Diagnosed
Doctors typically start with a physical exam that includes a straight leg raise test. You lie on your back while the examiner lifts your straightened leg. If this reproduces your radiating leg pain, it suggests compression of a lower lumbar nerve root. The test has a diagnostic accuracy of about 81%, with a sensitivity of 77% and specificity of 81%, meaning it catches most true cases while correctly ruling out most non-cases. It’s a useful screening tool, though imaging like an MRI is often needed to confirm exactly what’s pressing on the nerve.
Treatment and Recovery
Most sciatica caused by a herniated disc improves with conservative treatment within a few weeks to months. The most important early step is staying active. Bed rest used to be standard advice, but current guidelines recommend against it because inactivity tends to prolong symptoms rather than relieve them. Continuing with normal activities as much as pain allows leads to better outcomes.
For pain management, anti-inflammatory medications taken at the lowest effective dose for the shortest time are a first-line option. Physical therapy plays a central role, helping to reduce nerve compression through targeted stretching and strengthening exercises, particularly for the core and hip muscles. Some people benefit from neuropathic pain medications if symptoms are severe, though certain drug classes, including opioids and oral steroids, are not recommended for routine sciatica management according to current clinical guidelines from the UK’s National Institute for Health and Care Excellence.
Surgery becomes an option when conservative treatment fails after several months, or when nerve compression is causing progressive weakness or loss of function. The most common procedure removes the portion of disc or bone that’s pressing on the nerve.
Symptoms That Need Emergency Attention
Rarely, severe compression of the nerve roots at the base of the spine causes a condition called cauda equina syndrome. Warning signs include sudden difficulty urinating or controlling your bowels, numbness spreading across both inner thighs and the buttock area (sometimes described as “saddle numbness”), and rapidly worsening leg weakness. This is a surgical emergency. The nerve damage can become permanent within hours, so these symptoms warrant an immediate trip to the emergency room.