Sciatica and Lumbar Nerve Pain

Why the leg hurts when the problem is in the back

The nerves that supply the legs leave the spinal canal through openings in the lower back, then travel down through the buttock and into the leg. Irritate one of those nerve roots where it exits and the brain reports pain along the whole territory that nerve supplies, not at the place the trouble actually is.

That is why sciatica feels like a leg problem. It also explains why treating the leg rarely helps.

Two things irritate the nerve, and they usually happen together. One is mechanical pressure, most often from a herniated disc fragment sitting against the root. The other is chemical: the material inside a disc is inflammatory when it escapes, and an inflamed nerve hurts even where the pressure is modest. The chemical component tends to settle before the fragment shrinks, which is why pain often improves well before a repeat MRI looks any different.

The pattern identifies the level

Each lumbar nerve root supplies a fairly predictable strip of skin and a particular group of muscles. So where the pain and numbness run, and which movement is weak, points at which root is involved before any imaging is ordered.

Pain down the back of the thigh into the calf and the sole, with a reduced ankle reflex, points somewhere different than pain along the outside of the calf into the top of the foot with difficulty lifting the toes. A careful examination narrows it to a level or two, and the MRI is then being used to confirm a specific question rather than to go looking.

This matters because most adult lumbar spines show something on an MRI. A film read without a clinical question attached produces a list of findings, and the most eye-catching finding is not always the one causing the symptoms.

What is worth trying first

Most sciatica settles without an operation, and the first weeks are about controlling symptoms while that happens.

Staying active within tolerance, rather than resting in bed, is the single most useful instruction. Physical therapy aimed at the specific pattern, anti-inflammatory medication where it suits the patient, and time do most of the work.

An epidural steroid injection has two roles. It can reduce inflammation around an angry nerve root enough to restore sleep and function while recovery happens. It is also diagnostic: meaningful temporary relief from an injection placed at one level is evidence that the level is the right one, which is useful information if surgery is later considered.

When surgery enters the conversation

An operation for sciatica is aimed at the leg pain, and the best candidates are the patients whose story, examination and imaging all point at the same nerve root.

Progressive weakness changes the timeline. A foot that is getting harder to lift is not a reason to keep waiting.

Leg pain that remains disabling after a fair trial of non-operative care, in a patient with a matching structural cause on imaging, is the common scenario. The usual operation is a microdiscectomy, removing the fragment pressing on the nerve through a small opening. For selected patients the same decompression can be done through an endoscope.

The red flags above are the exception to all of this. Loss of bladder or bowel control with numbness around the groin needs assessment the same day.

When it is not actually sciatica

A fair number of patients arrive having been treated for sciatica for months or years without improvement, and the reason is that the pain was never coming from a nerve root.

The sacroiliac joint produces deep buttock pain that can run into the back of the thigh and gets mistaken for sciatica routinely. Hip arthritis produces groin and thigh pain. Both are examined differently and treated differently.

Getting this right at the start is worth more than any single treatment that follows it.