Ankylosing Spondylitis and the Spine

A condition guide by Mr Mohammed Madi, Consultant Orthopaedic & Spinal Surgeon.

Ankylosing spondylitis is a chronic inflammatory arthritis that particularly affects the spine and the joints where the spine meets the pelvis. Over time, the inflammation can cause the spine to stiffen and, in some people, to fuse, sometimes into a forward-stooped posture. It is led and managed by rheumatology, and modern treatment has genuinely transformed the outlook. From a spinal-surgery point of view, however, there is one message that overrides all others, and I want to put it right at the front: a spine that has fused becomes rigid and brittle, and it can break with surprisingly little force. Any person with ankylosing spondylitis who develops new spinal pain after even a minor injury is typically assessed urgently, because it may be a serious fracture. This guide explains the condition, its effect on the spine, and that all-important safety point.

Ankylosing spondylitis — now understood as part of a wider family called axial spondyloarthritis — is an immune-driven inflammatory condition that mainly affects the axial skeleton: the sacroiliac joints at the back of the pelvis, and the spine. It usually begins in late adolescence or early adulthood, with most people having their first symptoms before the age of thirty, and it has a strong association with a genetic marker called HLA-B27. It has traditionally been diagnosed more often in men, although the wider spondyloarthritis spectrum affects women just as often, and women are more likely to have an early form that does not yet show on plain X-rays. The hallmark of the condition over time is that the inflammation can lead to new bone formation, gradually stiffening and, in some, fusing the spine.

In plain terms: ankylosing spondylitis is an inflammatory arthritis of the spine and pelvis that causes stiffness and, over years, can fuse the spine. It is managed by rheumatology, but a fused spine is fragile and needs special care.

The exact cause is not known, but it results from a combination of genetic predisposition and the immune system. The genetic marker HLA-B27 is found in the great majority of people with the condition, but it is neither necessary nor sufficient — most people who carry it never develop the disease. The central problem is inflammation at the entheses, the points where ligaments and tendons attach to bone, and in the sacroiliac joints. Over time, the body's response to this chronic inflammation is to lay down new bone. This can bridge between the vertebrae with bony spurs called syndesmophytes and, when extensive, gradually fuse the segments of the spine together — which on an X-ray can give the classic appearance of a length of bamboo.

The hallmark symptom is a particular kind of back pain that we call inflammatory back pain, and it is quite different from ordinary mechanical back pain. It comes on gradually, usually before the age of forty; it lasts more than three months; it is associated with marked morning stiffness lasting more than half an hour; it characteristically eases with activity and exercise rather than with rest; and it often wakes the person in the second half of the night, easing once they get up and move. There may be alternating pain in the buttocks. Over time come progressive stiffness and loss of spinal movement, reduced expansion of the chest, and fatigue, which can be a prominent and wearing symptom. Beyond the spine, the condition can be associated with a painful, red, light-sensitive eye (acute anterior uveitis, which needs same-day eye assessment), with psoriasis, with inflammatory bowel disease, and with inflammation of tendons and other joints.

As fusion advances, the spine can lose its normal lower-back curve and develop a progressive forward curve of the upper back, leaving the person stooped and bent forward. In more severe cases this becomes a fixed deformity that makes it hard to stand upright or to look ahead — in the worst cases the gaze is directed downward, which is profoundly disabling for everyday life, eating and walking safely. Reduced movement of the spine and chest wall adds to the functional difficulty. This loss of posture and balance is one of the reasons that staying active and maintaining good posture, through exercise, is so important from the very start.

I make no apology for emphasising this, because it is the single most important thing on this page. A spine that has fused into a rigid column behaves very differently from a normal, flexible one. It becomes brittle and acts like a single long bone, so that even a minor, low-energy injury — a simple fall from standing, a trip, or a low-speed knock — can cause a fracture. These fractures are often unstable, frequently running right across the fused spine, and they carry a high risk of injury to the spinal cord, with a real chance of neurological harm. They are also easily missed, both because the pre-existing stiffness and deformity mask the new injury and because they can be hard to see on an ordinary X-ray. For all these reasons, the rule is simple and firm: in anyone with ankylosing spondylitis, new or changed spinal pain after even trivial trauma is typically treated as a fracture until proven otherwise, and it needs urgent assessment with a CT scan, and an MRI if there is any concern about the cord — a plain X-ray alone is not enough and can be falsely reassuring.

Features that warrant urgent assessment include new or worsening spinal pain after any injury, however minor, in someone with ankylosing spondylitis. Seek emergency assessment for any new weakness or numbness in the limbs, problems walking, or disturbance of bladder or bowel control, which may indicate pressure on the spinal cord or an unstable fracture. And seek same-day eye assessment for a painful, red, light-sensitive eye.

Diagnosis is led by rheumatology and draws on the pattern of symptoms, particularly inflammatory back pain, together with examination of spinal movement and posture, and a set of investigations. These include the HLA-B27 test and inflammatory markers in the blood (which can be normal even in active disease, so a normal result does not exclude the condition); X-rays of the sacroiliac joints and spine, which can show the characteristic changes; and an MRI of the sacroiliac joints, which can detect active inflammation early, before changes appear on X-ray, allowing the early, non-radiographic form to be recognised. For any deformity, full-length standing X-rays show how the alignment and balance of the spine have been affected.

The most important principle is that controlling the underlying inflammation well is the best way to protect the spine and prevent deformity, and modern treatment has changed the outlook dramatically. The cornerstone, alongside medication, is regular, structured exercise and physiotherapy — to maintain posture, mobility and function. I cannot overstate this: in this condition, rest is not the answer, and movement genuinely helps. Anti-inflammatory medicines are the first-line drug treatment. Where the disease remains active despite these, the modern biologic therapies — drugs that block specific parts of the inflammatory process, such as TNF inhibitors and IL-17 inhibitors — can bring the inflammation under control, ease symptoms, improve function, and may slow the progression of spinal damage. Not smoking, looking after cardiovascular health, and regular assessment of bone strength are also important parts of care.

Surgery is reserved for specific structural problems and is specialised, higher-risk work in this group of patients. The priority is the urgent stabilisation of spinal fractures in the fused spine, which usually require fixation over several levels because of the long lever arms of a rigid spine. For someone with a severe, fixed kyphotic deformity that prevents them from standing upright or looking ahead, a specialised corrective operation called an osteotomy — carefully cutting through the fused bone to bring the spine back into a more upright, balanced position — can restore the ability to look at the world at eye level. This is major, highly specialised surgery, reserved for carefully selected people and carrying significant risks, but in the right person it can be transformative. Surgery is also occasionally needed to relieve pressure on the spinal cord.

The outlook is variable, but it is far more hopeful than it once was. With modern biologic medicines and regular exercise, many people maintain good function and a full, active life, and severe disability has become less common. A minority do develop significant deformity or disability, and the condition is associated with some other health risks, including cardiovascular disease, thinning of the bones and the eye inflammation already mentioned, all of which are watched for and managed. Throughout, the combination of good inflammation control, dedicated exercise, and vigilance about the fracture risk gives the best long-term result.

"It's just ordinary back pain." No — inflammatory back pain has a distinct pattern and deserves proper assessment, because early diagnosis allows effective treatment.

"Rest is best." The opposite is true — exercise and movement improve symptoms and protect posture, while prolonged rest worsens stiffness.

"A normal blood test or X-ray rules it out." Not so — inflammatory markers can be normal, and early disease may show only on MRI.

"New pain after a small knock is nothing to worry about." Potentially dangerous — in a fused spine this can be a serious, unstable fracture.

"Nothing can be done about the stiffening." Modern treatment can control the inflammation, ease symptoms and help limit deformity.

Ankylosing spondylitis is an inflammatory arthritis of the spine and pelvis that causes a characteristic inflammatory back pain and, over time, can stiffen and fuse the spine, sometimes into a stooped posture. It is led by rheumatology, and the foundation of treatment is regular exercise together with anti-inflammatory and, where needed, biologic medicines, which can control the disease and protect posture. From the spinal-surgery standpoint, the overriding message is that a fused spine is brittle and fractures easily, so new pain after any injury is typically assessed urgently. Surgery has a role in stabilising fractures, correcting severe fixed deformity, and relieving any pressure on the cord. With good control and vigilance, most people do well.

This page is for general education only and is not a substitute for individual medical advice. If a patient has ankylosing spondylitis, urgent assessment is warranted for assessment for any new or changed spinal pain after even a minor injury, and emergency assessment for any new weakness, numbness, walking difficulty, or bladder or bowel disturbance.

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This information is for general patient education and is not a substitute for an individual consultation. Always seek personalised advice from a qualified spinal specialist.