Introduction
Studies have shown intervertebral discs, facet joints and sacroiliac joints to be potential sources of low back pain. Whilst there is a wealth of evidence regarding the diagnosis and treatment of intervertebral disc and facet joint pain, sacroiliac joint (SIJ) pain is more of a controversial issue and presents a challenge to clinicians. This article aims to provide an overview of SIJ pain, its presentation, diagnosis and treatment.
Prevalence
Although SIJ dysfunction has widely been acknowledged to be a cause of low back pain (LBP), its prevalence has not been well studied. Early studies used either clinical examination or radiological imaging techniques to make the diagnosis. In a retrospective review, using mainly physical examination, Bernard and Kirkaldy-Willis (1987) reported a 22.5% prevalence rate in 1293 patients with LBP. Schwarzer et al. (1995) performed fluoroscopically guided SIJ injections in 43 patients with chronic LBP below the L5/S1 level. Using pain relief as the sole diagnostic criteria, the prevalence rate was 30%. However, this fell to 16% when the diagnostic criteria required pain relief, a positive provocation test during joint distension and computed tomography abnormalities. Later studies using various examination, imaging and injection techniques, either alone or in combination, have reported the prevalence rate to be 10-38% in LBP patients (Manchikanti 2001, Laslett 2003, Irwin 2007, Van der Wurff 2006).
Anatomy
The SIJ is a true arthrodial joint with unique characteristics not found in other diarthrodial joints. In addition to hyaline cartilage, fibrocartilage is present, and there is discontinuity of the posterior capsule. Stability is aided by the irregular articular surfaces but primarily maintained by the many adjacent ligaments. Several muscles influence SIJ stability and motion, most notably the latissimus dorsi, gluteus maximus, biceps femoris and piriformis (Vleeming 1995, Slipmann 2001, Cohen 2005, Forst 2006). The innervation of the SIJ remains a controversial subject. Histological analysis has shown nerve fibres within the joint capsule and adjoining ligaments. The lateral branches of the L4-S3 dorsal rami appear to innervate the posterior SIJ (Bernard 1987), whilst other studies suggest the anterior joint may be innervated by all or part of the L2-S2 ventral rami (Solonen 1957, Ikeda1991).
Function / Biomechanics
The SIJ rotates in all three axes and functions to transmit and dissipate truncal load to the lower extremeties. Compared to the lumbar spine, axial load and torsion is poorly tolerated by the SIJ. These two motions may cause SIJ injury, with the weaker anterior joint capsule at particular risk (Dreyfuss 2004). SIJ pain can be divided between intra-articular and extra-articular causes. Intra-articular causes include chondromalacia, micro/macro fractures, arthritis and infection. Extra-articular sources, which are more common, include injury to the capsule or ligaments, fractures and myofascial pain. In addition, various factors that alter the load across the SIJ may predispose a person to develop SIJ pain. These include gait abnomalties, leg length discrepancy, prolonged vigorous exercise, scoliosis and lumbar fusion to the sacrum (Marymont 1986, Schuit 1989, Herzog 1994, Schoenberger 1964, Katz 2003).
| Diag 1. SIJ injection under fluoroscopic guidance with contrast agent outlining the left sacroiliac joint. |
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| Diag 2. CT guided SIJ injection. |
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The relationship between lumbar fusion and SIJ pain is unclear. Onsel et al. (1992) used bone scintigraphy after lumbar fusion to demonstrate an increased uptake in the SIJ. However Frymoyer et al. (1978) showed that neither biomechanical nor anatomical changes were more common in patients who underwent fusion compared to those who had only decompression procedures. A more recent study using finite element analysis reported an increase in motion and strain across the SIJ in patients with fused lumbar segments (Ivanov 2009). Lumbar spine surgery has also been suggested to cause SIJ pain by weakening the SIJ ligaments, causing post-surgical hypermobility or by violating the joint cavity during iliac crest harvest (Ebraheim 2000).
Pregnancy is another well described cause of SIJ pain. The mechanism is thought to involve a combination of hormone-induced ligamentous laxity, an exaggerated lordosis of the lumbar spine, weight gain and the mechanical trauma of parturition (Albert 2001, Berg 1998).
Other specific causes of SIJ pain include sero-negative and HLA-B27-associated spondyloarthropathies, pyogenic infections, malignancy and traumatic aetiologies such as athletic injuries, repetitive strain, and pelvic fractures (Baquie 1997). A retrospective analysis by Chou et al. (2004), looking at 54 patients with SIJ pain confirmed by injection, showed the cause to be trauma in 44%, idiopathic in 35% and repetitive stress in 21%.
Clinical Findings
Diagnosing SIJ pain is a challenge. SIJ pain is commonly referred to a rectangular pattern approximately 3×10 cm just inferior to the posterior superior iliac spine (Fortin 1994). Many physical examination tests having been described (Cohen 2004). The two best known tests involve distraction of the SIJ (Gaenslen's and Patrick's tests). However, most studies have shown clinical history and physical examination to be poor diagnostic tools in identifying SIJ pain (Slipman 1998, Dreyfuss 2001). Similarly, radiological studies cannot accurately diagnose SIJ pain. Radionuclide bone scan has reported specificities of 89 – 100% but sensitivities of 13-46% (Maigne 1998, Slipman 1996). Elgafy et al. (2001) reported that CT scans had a 57.5% sensitivity and 69% specificity.
| Diag 3. Plain film radiograph of right SIJ fusion. |
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