What Is the Sacroiliac Joint, and Why Does It Hurt?
The sacroiliac joint lies between the sacrum (the triangular bone above the tailbone, the lowest part of the spine) and the ilium bones on either side of the pelvis; there is one on each side of the body. This joint is supported by very strong ligaments and normally moves very little; its main task is to safely transmit the load of the upper body to the legs while standing and walking. Sacroiliac joint pain arises from excessive or insufficient movement, irritation or inflammation of this joint. Triggers include a fall or trauma, repetitive strain, ligament laxity during pregnancy and after childbirth, a leg-length difference, mechanical changes after hip-spine surgery and some inflammatory rheumatic diseases. The key concept is this: this is not a condition that compresses the spinal nerves, but a mechanical/inflammatory pain arising from the joint itself.
Symptoms and Why It Is Often Confused
Sacroiliac joint pain is typically felt in the lower-side of the back, in the hip-tailbone region and sometimes in the groin; the patient often describes the pain by pointing 'right here' over the joint. The pain can increase with prolonged sitting, rising to stand, climbing stairs, loading one leg and lying on the affected side. It can sometimes radiate from the hip to the back of the thigh, but sciatic-type pain running below the knee, reaching the toes, with marked numbness or weakness — as in a disc herniation — is generally not expected. The reason this picture is often confused is that the symptoms largely overlap with disc herniation, facet joint syndrome and hip-joint problems. So in some patients followed for years as having 'a disc herniation', the true source can be the sacroiliac joint.
Diagnosis: Differential Assessment and a Joint Block
The diagnosis of sacroiliac joint pain does not rest on a single test; it is a careful process of differential diagnosis. The first step is a detailed examination aimed at excluding whether the pain comes from the disc, facet or hip joint. On examination, several provocation (stress) tests of the SI joint being positive together supports the diagnosis. Imaging (MRI, and CT or X-ray where needed) both shows inflammatory/degenerative changes in the joint and helps exclude another cause of pain; however, imaging findings alone do not prove that the pain comes from that joint. The most valuable confirmation method is an image-guided diagnostic sacroiliac joint block: after a local anaesthetic is delivered into the joint, a marked temporary reduction in pain strongly supports the SI joint as the true source.
Treatment: Injections and Physiotherapy First, Fusion Rare
Treatment of sacroiliac joint pain is stepwise and largely non-surgical. The first step is a conservative approach: pain/anti-inflammatory medication, activity modification, correction of a leg-length difference where present and, especially, targeted physiotherapy-exercise programmes that balance the pelvis-hip-trunk muscles; in some patients a supportive SI belt can help. When these are insufficient, an image-guided sacroiliac joint injection (steroid + local anaesthetic) both reduces pain and confirms the diagnosis. In recurrent pain, interventional methods such as radiofrequency directed at the nerve branches supplying the joint can be considered. Surgery (sacroiliac fusion) is a rare option that comes onto the agenda only when all conservative and interventional options have been exhausted, in selected and resistant cases whose diagnosis has been clearly confirmed by blocks.
Realistic Expectations and an Honest Assessment
The honest picture in sacroiliac joint pain is this: when the diagnosis is correct, most patients experience marked relief with conservative and interventional methods, without surgery. However, when there is an underlying mechanical/degenerative basis, it can be a condition that recurs from time to time; the duration of effect of injections varies from person to person and can be repeated when needed. No method is a guaranteed permanent solution; the aim is to control the pain, preserve function and avoid unnecessary intervention. The most critical point is the correct diagnosis: clarifying that the pain truly comes from the sacroiliac joint both prevents pointless back operations and directs treatment to the right target. Our approach is individual for each patient: to provide the most benefit with the least intervention.