Sacroiliac Joint Pain: A Comprehensive Review of Anatomy, Diagnosis and Treatment.
Cohen, Steven P. Sacroiliac Anesth Analg 2005;101:1440-1453.
SI Joint Key Points:
- Compared to the lumbar spine, SI joints can withstand a medially directed force 6 times greater but only half the torsion and 1/20th of the axial compression load.
- The long-term success rate for SI joint fusion appears to be in the range of 70%.
- The SI joint is a real yet underappreciated pain generator in an estimated 15% to 25% of patients with axial LBP.
Anatomy: The sacroiliac (SI) joint in the largest axial joint in the body, with an average surface area of 17.5cm².
Innervation: Innvervation of the SI joint remains a subject of much debate. The lateral branches of the L4-S3 dorsal rami are cited by some experts as composing the major innervations to the posterior SI joint. Other investigators claim that the L3 and S4 contribute to the posterior nerve supply.
Function and Biomechanics: Compared to the lumbar spine, the SI joints can withstand a medially directed force 6 times greater but only half the torsion and 1/20th of the axial compression load. These last 2 motions may preferentially strain and injure the weaker anterior joint capsule.
Prevalence: The largest SI joint study is by Bernard and Kirkaldy-Willis, who found a 22.5% prevalence rate in 1,293 adult patients presenting with LBP. Schwarzer et al. conducted a prevalence study involving 43 consecutive patients with chronic LBP. Using local anesthetic as the sole criterion for diagnosis, the prevalence of SI joint pain was found to be 30% (95% CI: 16-44%). Maigne et al. conducted a prevalence study in 54 patients using a series of blocks done with different local anesthesia. 18.5% (95% CI: 9-29%) were considered to have true SI joint pain. Based on these studies, the prevalence of SI joint pain in carefully screened LBP patients appears to be in the 15-25% range.
Mechanism of Injury: In a retrospective by Chou et al. assessing the inciting events in 54 patients with injection-confirmed SI joint pain, the authors found trauma was the cause in 44% of patients, 35% were idiopathic, and 21% were attributed to the cumulative effects of repeated stress.
Treatment: Generally, treatment of SI joint pain can be divided into 2 categories: those directed at correcting the underlining pathology and those aimed at alleviating symptoms. In patients with SI joint pain unresponsive to more conservative measures, several investigators have advocated surgical stabilization. The long-term success rate for SI joint fusion appears to be in the range of 70%.
Conclusions: The SI joint is a real yet underappreciated pain generator in an estimated 15% to 25% of patients with axial LBP.