What Is the Sacroiliac Joint and Why Does It Hurt?
The sacroiliac joint is a strong joint where the sacrum (which forms the base of the spine) meets the pelvic (iliac) bone; it moves very little but carries large loads. It works like a bridge transferring the load from the upper body to the legs. Pain arises when this joint's ligaments are strained, when its movement becomes unbalanced, or when it becomes inflamed. Pregnancy, a fall or trauma, a leg-length difference, the extra load placed on the joint after a spinal fusion operation, and some rheumatic diseases can all trigger sacroiliac pain.
Why Is It So Often Confused With a Disc Herniation?
Sacroiliac pain typically gives a sensation low and to one side of the back, in the buttock, sometimes radiating to the back of the thigh; this radiation creates confusion because it resembles the leg pain of a disc herniation. There is an important difference, though: sacroiliac pain usually does not descend below the knee and does not cause the numbness or weakness of nerve-root compression. Sitting, rising from a seated position, climbing stairs and turning onto the painful side increase the pain. Seeing a herniation in the back on MRI can be misleading; that herniation may be silent while the true source is the sacroiliac joint. The location and behaviour of the pain must therefore be assessed carefully.
Diagnosis: Provocation Tests and Diagnostic Injection
Examination is to the fore in diagnosing sacroiliac dysfunction: when several provocation tests that stress the joint from different directions (such as FABER, compression and distraction) are positive, the diagnosis is strengthened. Imaging (X-ray, MRI, CT) is used to show structural changes in the joint and to rule out rheumatic disease or other causes, but imaging alone does not establish the diagnosis. One of the most reliable confirmation methods is a diagnostic injection into the sacroiliac joint under imaging guidance: if the pain regresses markedly with a local anaesthetic, a sacroiliac source is strongly supported.
Treatment: Mostly Without Surgery
Treatment of sacroiliac joint dysfunction is, in the great majority, non-surgical. The first step is physiotherapy (strengthening the hip and back muscles that stabilise the joint), pain-relieving/anti-inflammatory medication, and addressing correctable causes such as a leg-length difference. If these are insufficient, sacroiliac joint injections are given under imaging guidance; in recurrent cases, radiofrequency ablation of the nerves supplying the joint can provide relief. In carefully selected, very resistant cases with a clear diagnosis, sacroiliac fusion (minimally invasive stabilisation of the joint) may come up, but this is a rare decision requiring careful patient selection.
Realistic Expectations
Sacroiliac pain is a manageable condition once the correct diagnosis is made, but finding the right source is often the hardest part — which is why many patients confused with a disc herniation or a hip problem can be treated wrongly for years. The aim of treatment in most patients is to reduce the pain markedly and make daily activity possible; methods such as injection and radiofrequency give time-limited relief and can be repeated when needed. The honest approach is to confirm the source on evidence first, then to proceed starting from the least invasive method.