The joint between the sacrum and the pelvis — the sacroiliac joint, SI joint for short — is often overlooked in low back pain and sometimes blamed too readily. It lies deep, is barely mobile and is hard to assess on imaging. This page explains how we tell whether the pain really comes from there, what helps, and when — rarely — a fusion of the joint comes into consideration.
In SI joint syndrome, the diagnosis is the real work. No single test and no image proves it; only several examination manoeuvres together and a targeted anaesthetic block of the joint make it dependable. Treatment is almost always without an operation.
What is it?
On each side, the sacroiliac joint connects the sacrum with the ilium of the pelvis. It is not a joint for moving but for carrying: through its interlocking surfaces and very strong ligaments, the weight of the trunk is transferred to the legs, with only a few degrees of play. In SI joint syndrome the pain arises from this joint or from its ligaments — through wear, overload, loosening or malalignment. The popular term “SI joint blockage” describes a feeling of stiffness; an actually jammed joint position cannot as a rule be demonstrated.
To be distinguished from it is sacroiliitis, an inflammation of the joint in the context of inflammatory rheumatic diseases such as axial spondyloarthritis. It causes similar pain, but is treated differently and belongs in rheumatological hands.
What symptoms occur?
Typical is a one-sided pain deep down at the small of the back, below the belt line, over the joint itself; many of those affected can point to the spot with one finger. It radiates into the buttock, into the groin or into the back of the thigh, rarely as far as below the knee. It is made worse by getting up from sitting, by climbing stairs, by turning over in bed, by standing on one leg and after long periods of sitting or driving. Numbness, tingling along a strip and loss of strength are not part of it — they point to an irritated nerve root, that is to sciatica.
It sounds different when the pain occurs above all at night and in the early hours of the morning, with stiffness that improves with movement, and begins in younger people: then an inflammatory cause must be considered.
Causes
Common is an overload without a clear trigger, with wear of the joint surfaces or after a fall onto the buttocks. Differences in leg length, a scoliosis and hip conditions change the load on the joint; in pregnancy and after the birth, the ligaments loosen for hormonal reasons. SI joint syndrome is also observed after a fusion of the lower lumbar spine, because the joint then has to take over more movement. Less often, an inflammation, a fatigue fracture of the sacrum in osteoporosis or a general hypermobility of the joints lies behind it.
How is it diagnosed?
At the beginning stands the exclusion of the neighbours: the disc, the spinal canal, the vertebral joints and the hip cause similar pain and are checked as part of the examination. Then follow the provocation tests — examination manoeuvres with which we deliberately put the joint under tension, for example by pressure on the blades of the pelvis, pressure on the thigh with the hip bent, or extension of one leg. A single positive test says little; if several of the manoeuvres reproduce the familiar pain, the probability rises considerably. In SI joint syndrome the nervous system is unremarkable.
X-ray and MRI usually show little that is specific in SI joint syndrome; their job is to rule out other things — fracture, tumour, hip osteoarthritis, herniated disc — and, where inflammation is suspected, to demonstrate sacroiliitis. Blood tests then belong to it as well. The most informative single step is regarded to be the diagnostic infiltration: under X-ray or CT guidance, a local anaesthetic is injected into the joint. If the pain clearly eases for the duration of its effect, that speaks for the joint. This test too can mislead, which is why it is repeated when far-reaching decisions are at stake — it is one building block, not a proof.
Warning signs
An SI joint syndrome is not an emergency. Low back pain does, however, have to be assessed promptly if fever, unintended weight loss, a cancer in the past history, a fall with known osteoporosis or pain at rest at night are added — and immediately in the case of numbness in the perineal area, a new bladder or bowel problem or an increasing paralysis. More on this on the page Warning signs.
Conservative treatment
In SI joint syndrome, treatment without an operation is the normal case and, for the great majority, also the way to the goal. It starts with whatever is overloading the joint.
- Physiotherapy and your own training — strengthening the buttock, abdominal and deep back muscles, which stabilise the pelvis; stretching shortened hip muscles; mobilisation of the joint and of the lumbar spine. Manual therapy can release things in the short term, but does not replace the training.
- Compensating for contributing loads — a shoe raise for a relevant difference in leg length, a pelvic belt in pregnancy and in the weeks after the birth, treatment of a hip condition.
- Painkillers — anti-inflammatory medicines for a limited time at the lowest effective dose, so that movement remains possible. Warmth, if it does you good.
- Infiltration of the joint — an anti-inflammatory medicine into the joint under image guidance can ease the pain for weeks to months and bridge the time needed to build up muscle; a lasting effect is not established. It may come into consideration if the diagnostic anaesthetic block has made the joint likely as the cause.
- Switching off the joint nerves (radiofrequency denervation) — the small nerve branches at the back of the joint are switched off with a probe using heat. This may come into consideration if an anaesthetic block has clearly helped; the evidence is inconsistent, and the effect is limited in time.
- Multimodal pain therapy — for symptoms lasting months, a combined treatment of exercise, pain medicine and psychological support. Where the cause is inflammatory, rheumatological treatment takes priority.
When an operation is considered
Rarely — and only when several conditions come together: the diagnosis is secured by the examination and by an image-guided anaesthetic block of the joint with clear, repeatable relief of pain; other causes in the lumbar spine and the hip have been ruled out; there is no inflammatory disease; treatment without an operation has been carried out consistently for about six months and has not helped sufficiently; and the symptoms restrict everyday life considerably. Another, rare reason is a genuine instability of the joint after an injury to the pelvis. The wish for a quick solution is not a reason, because the joint cannot be “unfused” again.
Surgical options
The procedure is the fusion of the sacroiliac joint (SI joint screw fixation, arthrodesis). We offer this procedure. Its aim is to end the remaining residual movement in the joint, so that it consolidates with bone and drops out as a source of pain. The mobility of the back changes hardly at all as a result, because the joint is almost immobile in any case.
- ProcedureUnder general anaesthetic and lying face down or on the side, a channel is created through a short skin incision at the side of the buttock under X-ray guidance, where appropriate with navigation, leading through the ilium across the joint and into the sacrum. In it, screws or triangular titanium implants are anchored, which bridge the joint. The procedure is comparatively short, the hospital stay usually a few days.
- RisksAs with any operation, infection, bleeding, thrombosis and the risks of anaesthesia. Specific to this procedure: a malposition of the implants with irritation or injury of the nerve roots that run beside the sacrum — with sensory disturbance, pain or weakness in the leg —, a fracture of the ilium, a later loosening, a failure of the bone to fuse, and persisting pain despite a technically successful fusion, for instance because the joint was after all not the sole source. The opposite side, the hip and the lower lumbar spine can be loaded more heavily afterwards. Which of these is to the fore in your situation, we discuss before the procedure.
- AftercareGetting up on the day of the operation or the day after; for a few weeks partial weight-bearing of the operated leg with forearm crutches, then a build-up of load and physiotherapy. The bony fusion takes months and is checked with X-ray or CT images. How long you are unfit for work depends on your occupation.
To put it in perspective: in the two randomised trials, those operated on reported considerably less pain and less limitation after two years than those treated conservatively. Both trials were not blinded and were funded by the manufacturer of the implants; long-term data over many years are scarce. We tell you this so that you set your expectations correctly. Open procedures with bone grafting are larger operations and are the exception today.
Alternatives
The most important alternative is to stay with treatment without an operation and to carry it out consistently: training, compensating for contributing loads, an infiltration or denervation if needed, and multimodal pain therapy for persisting symptoms. If you have been advised elsewhere to have a fusion, you can obtain a second opinion from us.
What to expect
In most people, SI joint syndrome improves with targeted training over weeks to months, even though relapses occur with overload. After pregnancies, the symptoms usually settle as the ligaments recover. What you can do yourself: strengthen the buttock and trunk muscles for the long term, avoid one-sided loads and long periods of sitting, keep the pelvis level when getting up and lifting. After a fusion it is about a patient build-up of load until the joint has fused. New symptoms on the opposite side or in the hip are a reason to come back and be seen.
Frequently asked questions
Can an “SI joint blockage” be manipulated back into place?
Manual manoeuvres can release the symptoms in the short term. According to present knowledge, an actually jammed joint position is not “reset” in the process; the effect rests more on muscle and pain responses. What helps in the long run is whatever takes load off the joint: training.
Can SI joint syndrome be seen on MRI?
Usually not. Signs of wear at the joint are common and do not explain the pain; an unremarkable MRI does not rule out an SI joint syndrome. The MRI is important in order to rule out inflammation, fractures and causes in the lumbar spine.
Sciatica or SI joint — how do I tell the difference?
Sciatica runs along a strip into the lower leg or the foot, often with tingling or weakness, and becomes stronger on coughing and bending forwards. SI joint pain sits deep at the small of the back on one side, usually stays above the knee and makes itself felt on getting up, climbing stairs and turning over in bed. The two can only be separated reliably at the examination.
How certain is the diagnosis before a fusion?
Never entirely. That is why, before an operation, we require several concordant provocation tests, a repeated image-guided anaesthetic block with clear relief, and the exclusion of all other causes — and we take the time for it.
Do I need a referral?
No. It is useful, because it brings us the previous history. Bring any existing images and reports with you, including reports about earlier injections and their effect; everything else is on the page Your first appointment.