Spondylolisthesis (a slipped vertebra)

Spondylolisthesis is when one vertebra slides forward over the one below it. Nearly always it happens in the lower back, most often at the two lowest vertebrae. The word looks alarming, and someone reading it for the first time on a radiology report usually pictures a spine coming apart. The reality is different: in most people the slip is small, stays the same for years and turns up by accident, on a scan taken for something else entirely. This page is about when that finding means nothing, when it explains the pain, and when it must not be left alone.

What is actually slipping

A vertebra is not held in place by the disc alone. Behind it sits a bony arch with a pair of projections that hook onto the neighbouring vertebrae and stop the body of the bone from travelling forward. The slip begins when that rear catch stops holding.

It fails by two quite different routes, and almost everything else follows from which one it was.

• A crack appears in the arch — a tiny stress fracture caused by repeated backward bending. This happens in teenagers and young athletes, and it has a section of its own below.
• The small joints and ligaments simply wear out. This happens after the age of fifty, more often in women; the arch is intact, but the joints flatten and become loose and the disc settles. This is the commonest version by far.

Less often the slip comes from the shape a person was born with, from a serious injury, from previous spinal surgery, or from a disease that weakens the bone.

The size of the slip is described in quarters: the vertebra has moved a quarter of its own width, or a half, and so on. The first two grades account for the vast majority of cases. And one thing worth saying straight away: the grade on the image maps poorly onto how a person actually feels. A small slip can ache for years; a striking one can cause nothing at all.

What it feels like

The typical pain is low back pain — dull, spread across the back rather than in one spot, sometimes with a sense that the lower back is sagging. It behaves in a recognisable way, and that behaviour is what raises the suspicion:

• worse standing and on a long walk, easier sitting down;
• worse when you arch backwards: reaching for a top shelf, painting a ceiling, leaning back in a chair;
• easier when you bend forward — people find it noticeably easier to walk round a shop leaning on a trolley, or to ride a bicycle, than to stand still in a queue;
• it spreads into the buttocks and the backs of the thighs, and the hamstrings feel short and tight.

If the slip narrows the space where a nerve root runs, a second kind of pain appears: shooting down one leg below the knee, with numbness or pins and needles. There is another pattern too — the legs grow heavy and numb after a few hundred metres of walking and you have to stop, but sitting down or bending forward settles it within a minute and you can carry on.

And the commonest presentation of all: no symptoms whatsoever. A great many slips keep a person company in silence for a whole lifetime.

Back pain in a teenager is not growing pains

This section is for parents of sporty children. In sports where the back arches backwards over and over — artistic gymnastics, acrobatics, diving, wrestling, weightlifting, dance, rowing — the arch of the lowest lumbar vertebra takes hit after hit and can crack. It is a stress fracture, no different in principle from the ones runners get in the foot.

What it looks like: pain in the lower back, usually on one side, coming on during or after training, sharply worse on arching backwards and on standing on one leg while arching. The child starts avoiding certain moves and complains of a pulled back that has not gone away for weeks.

Low back pain in a teenager that lasts more than two weeks, or that gets in the way of training, is a reason to see a doctor rather than wait. It cannot be put down to growing: there is no such thing as growing pains in the lower back, and back pain in children far more often has a specific cause than it does in adults.

Why the timing matters so much: a fresh crack, given a rest from the loading that caused it, often heals in a few weeks or months, sometimes with a brace, and the story ends there. A missed one turns into a permanent defect, and the vertebra begins its slow slide forward — this time for good. The difference between those two outcomes is a couple of months and one appointment.

When this becomes an emergency

A handful of signs mean that the bundle of nerves at the very bottom of the spinal canal is being squeezed. They are rare, but when they appear the clock runs in hours, and delay leaves lasting disability.

• Numbness in the groin, the genitals or the inner thighs — the area that touches a seat. It can feel as though the skin belongs to someone else, or as though there were paper or a pad down there.
• Trouble passing urine: you cannot start, you cannot feel the bladder filling or the urge to go, you cannot feel the flow, or urine leaks away.
• Loss of bowel control, or losing the sensation of opening your bowels.
• Weakness in the legs that is getting worse: the foot stops lifting and slaps the floor as you walk, or it becomes hard to rise from a chair or climb stairs.
• Numbness in both legs at once.
• Sudden loss of sensation around the genitals.

Any one of these means going to an emergency department immediately — within the hour, not later the same day. If getting there under your own steam is not realistic, call an ambulance; across Europe the single emergency number is 112.

Separately, see a doctor the same day, though not as an emergency, if the back pain started after a fall or a road accident, if it comes with a temperature, or if it wakes you at night and goes together with weight loss.

How it is found

The main investigation is a plain side-on X-ray of the lower back, and it needs to be taken standing up. Lying down partly reduces the slip, and the film can look almost normal. Two extra images, one bending forward and one arching back, are sometimes added to show whether the vertebra shifts to and fro — that changes what is done next.

If there is pain, numbness or weakness in a leg, an MRI scan is arranged: it shows not the bone but the nerves and how much room they have left. A CT scan is the best way to see the crack in the arch itself. In a teenager with the picture described above the imaging is not put off, because a fresh fracture is often still invisible on a plain X-ray.

During the examination the doctor will ask you to bend and arch, will test the strength, sensation and reflexes in your legs, and may run a hand down the spine — with a marked slip there is a step you can feel between the bony bumps.

What actually helps

The foundation is not rest but muscle. A back that has lost its bony catch is held by its muscular corset, and that is the one thing a person can improve by their own effort.

• Exercise therapy guided by a physiotherapist: the abdominal and low back muscles, the glutes, and hamstring stretching. It has to be regular and long-term — a habit rather than a course of ten sessions.
• What to drop from your training: deep backward arching, heavy squats and overhead presses, sharp twisting, lifting weights with straight legs. Walking, swimming, cycling and machine work within a comfortable range are all worth doing.
• Losing weight makes a noticeable difference to the pain if there is weight to lose.
• Pain relief. Start with paracetamol; if that is not enough, an anti-inflammatory painkiller for a short course. Choose it with a doctor or pharmacist, as that group of medicines has limits in stomach, kidney and heart disease.
• Steroid injections around the nerve root come up when the pain runs down the leg and stops you exercising. They calm the inflammation and buy a window of some weeks or months in which the exercise programme can get going.

What is not worth doing: lying down for more than two or three days at a stretch, waiting for it to knit itself together, and wearing a rigid brace all the time — in adults that weakens the muscles and makes things worse.

When surgery comes up

Surgery is for a minority. The conversation starts in three situations: pain in the back or leg that has not eased after several months of genuine effort and is interfering with work and sleep; weakness or numbness in a leg that is getting worse; a teenager whose slip keeps increasing from one image to the next. Signs of pressure on the nerve bundle are a separate matter — those are operated on urgently.

What the operation does comes down to two things: making room for the compressed nerves, and joining the slipped vertebra to its neighbour with screws, rods and a bone graft so that it can no longer move. It is done under general anaesthetic.

Recovery takes weeks to months, and leg pain usually settles better and faster than the pain in the back itself. As with any spinal operation there are risks, and they are worth going through in detail with the surgeon. It is worth knowing that outside the emergencies there is time to think it over: hurrying improves nothing here.

Online consultation

Three things suit a remote appointment well. The first is going through a radiology report you already have: the doctor can explain what the grade and the numbers mean, whether the finding needs anything beyond keeping an eye on it, and how often it should be reviewed. The second is building an activity plan: what to drop, what to keep, which physiotherapist to see and what to expect three months in. The third concerns teenagers — if a child who trains has been complaining of low back pain for more than two weeks, the doctor can say which imaging is needed and how quickly. The signs listed in the emergency section are not something to discuss online: they mean going to hospital straight away.

This material is for information only and does not replace medical advice.