Sciatica Is a Symptom, Not a Diagnosis
Here’s the first thing you need to understand about sciatica: it’s not actually a diagnosis. It’s a symptom. So many people think they can go and get a scan and someone says, “there it is — you’ve got sciatica.” That’s not how it works.
Sciatica just means pain travelling down the leg from an irritated nerve. It tells you what you’re feeling, but it doesn’t tell you why — and the why is the whole game. So in this article I’ll explain what causes sciatica, why it shoots down your leg, and the different things that can actually be behind it. As always, this is a guide to help you understand what’s going on, not a diagnosis.
Why It Can Come From Anywhere Along the Nerve
To understand what causes sciatica, you need to picture where the nerve runs. The sciatic nerve is the big one. It starts at the bottom of your spine, runs straight through your buttock, down the back of your thigh through the hamstring, down the calf, and all the way into your foot.
It’s a long nerve, travelling a long way through a lot of structures — and that’s the key to the whole thing. That nerve can be irritated, or compressed, at any point along its path. And wherever it gets irritated, it can create that same pain shooting down the leg. So the pain you feel isn’t necessarily coming from where you think — it’s coming from wherever, along that line, the nerve is being squeezed or irritated. That’s why the real question is never just “have I got sciatica?” It’s “where, and what, is irritating the nerve?”
The Four Most Common Causes
So let’s go through the usual culprits.
The most well-known one is a disc. Right at the top, where the nerve leaves the spine, a disc bulge can press on the nerve root. That’s the classic disc-related sciatica — irritation right at the source, sending pain all the way down.
The second is stenosis, which is a narrowing of the space where the nerve exits the spine. If that space narrows and crowds the nerve, you get the same result — sciatic pain down the leg.
The third is lower down, in the buttock — a tight piriformis muscle. The piriformis is a muscle deep in your glute, and the sciatic nerve runs right underneath it, sometimes through it. So if that muscle is tight and angry, it can clamp down on the nerve right there in the buttock and create sciatica, with nothing wrong with your disc at all.
And the fourth is further down again — the hamstring. The nerve runs right down through the back of the thigh, so if you’ve got tightness or adhesions in the hamstring — little areas where the tissue’s stuck and gripping around the nerve — that can tether and irritate it, and create sciatic pain too.
Same Pain, Four Different Causes
So look at what we’ve just covered. Disc, stenosis, piriformis, hamstring. Four completely different causes, in four different places, all creating the same symptom — pain down the leg.
And this is exactly why “you’ve got sciatica” tells you almost nothing. Two people can both have sciatica and have two completely different things causing it, needing two completely different approaches to fix it. So the aim of the game is never just to label it sciatica. It’s to find the underlying driver — the actual thing irritating that nerve.
Why Finding the Right Driver Is Everything
Because here’s the thing: if you treat the wrong one — if you chase the disc when it’s really a tight piriformis — you’ll get nowhere. Get the right driver, treat that, and that’s when the leg pain finally settles.
So to bring it together: sciatica is a symptom, not a diagnosis. It’s pain down the leg from an irritated sciatic nerve, and that nerve can be irritated anywhere along its path — the disc, the spine narrowing, the piriformis in the glute, or the hamstring. The job is always the same. Not “have you got sciatica” — but “what’s driving it.” Find that, and you’re on the road to actually fixing it, rather than chasing the pain around in circles.
Joe Sharp
BSc (Hons) Physiotherapy
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