Sacroiliac Joint Pain

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.

Diag 2. CT guided SIJ injection.

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.

Diag 4. Axial MRI section of right SIJ fusion

Diag 5. Plain film radiograph showing bilateral SIJ fusions and lumbar fusion.

Controlled diagnostic injection blocks are often regarded as the most reliable method of confirming the SIJ as a pain generator; however, the validity of such injections is unproven. SIJ injections are challenging to perform accurately and are prone to significant false positive and false negative rates. Injections should never be performed blindly (Rosenberg 2000), but even with fluoroscopic guidance, Fortin et al. (1994) noted a 90% contrast extravasation rate and 40% of the subjects experienced lower limb numbness, implying that there was an inadvertent block of the lumbrosacral nerve roots. CT guidance may be beneficial in patients with joints that are difficult to enter. A systematic review in 2009 found that the false-positive rate of single, uncontrolled, sacroiliac joint injections is 20% to 54% (Rupert 2009).

Treatments
Although there are no prospective controlled studies to support their role, physiotherapy, osteopathic or chiropractic manipulation have been reported to reduce SIJ symptoms. This is most likely by way of addressing spinal mal-alignment and altered gait mechanics (Osterbauer 1993). Any underlying pathologies should also be addressed (e.g. leg length discrepancy). Pelvic belts that reduce SIJ rotation in the saggital plane have been advocated for pregnant women, as have exercise-induced pelvic stabilisation programmes (Mooney 2001, Vleeming 1992).

Intra-articular injection of steroid and local anaesthetic are both diagnostic and therapeutic. Most studies using radiologically guided injections report good levels of pain relief lasting up to 1 year. Double blind studies looking at extra-articular injections also show a significant benefit (Katz 2003, Fisher 2003, Luukkainen 2002).

Radiofrequency denervation was introduced with the aim of providing prolonged pain relief. Methods include targeting the nerve supply to the SIJ or creating lesions within the SIJ itself, with the former achieving superior outcomes (Yin 2003). Some studies have suggested the ventral portion of the SIJ to be the major pain source in up to 70% of sufferers (Schwarzer 1995). However radiofrequency denervation does not target this area, which is a major drawback of the technique.

Other interventions include intra-articular injection of hyaluronic acid and prolotherapy (the injection of drugs that induce fibroblastic hyperplasia). Prolotherapy is hypothesised to work by strengthening and desensitising the supporting ligamentous structures around the SIJ. The few studies which support their use are controversial and of questionable design (Srejic 1999, Ongley 1987). The disadvantages of prolotherapy treatment include the requirement of repeated injections, post injection pain and variable results.

Patients who do not respond to conservative or injection therapy should be considered for surgical intervention. Surgical SIJ fusion is primarily indicated for instability or fractures; however, success has also been reported for degenerative joint disease (Simpson 1987, Dabezies 1989, Waisbrod 1987). Khurana et al. (2009) recently reviewed 15 patients who underwent percutaneous SIJ fusion. Thirteen had a good to excellent outcome. The other 2 had improved SF-36 scores but persisting back pain which the authors suggested was due to lumbar pathology.

Conclusion
SIJ pain is an under-diagnosed cause of low back pain. Studies have estimated the SIJ to be a pain generator in 10-38% of patients with axial lumbar back pain. Failure to recognise SIJ pain and treat it accordingly will result in unsatisfactory outcomes. Diagnosis and treatment remain a challenge to the clinician. There is moderate evidence to support the use of SIJ injection blocks, but only limited evidence for provocative manoeuvres in the diagnosis of SIJ pain (Rupert 2009). Treatment should firstly aim to correct any secondary mechanical causes (e.g. leg length discrepancy or altered gait patterns) and encompass conservative measures. Intra- and peri- articular injection of local anaesthetic and steroid have been shown by most but not all studies to improve symptoms by up to 10 months. There is limited evidence to support radiofrequency denervation or surgical fusion as treatment modalities. Although these treatment modalities may benefit chronic SIJ pain sufferers who are resistant to other treatments, further research into their efficacy is required.

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