What's Old Is New Again: The Sacroiliac Joint as a Cause of Lateralizing Low Back Pain.

It has not been easy to identify mechanical failure of the sacroiliac joint (SIJ) with traditional imaging. The integrated model of function (Lee and Vleeming, 1998) suggests that under normal circumstances, form and force closure combined contribute to sacral nutation and "locking" the SIJ for optimal load transfer. This model is supported by clinical evidence and scintigraphic findings that contribute to successful therapy in 80% of cases. Single-photon emission computed tomography and x-ray computed tomography (SPECT-CT), a hybrid device, was used in a study of 1200 patients (64% female and 36% male patients with an average age of 42 years; range, 15-78 years) with a clinical diagnosis of SIJ incompetence (pelvic girdle pain syndrome). Standard clinical testing and an alternate series of tests were used as a reference standard for imaging. Symptoms were present for a mean of 43 months. Imaging finding were of increased uptake in the upper SIJ (S1-S2), with extension into the dorsal interosseous ligament and measurable by count profile. Associated findings of tendon enthesopathy reflected altered biomechanics around the pelvis. Ipsilateral adductor enthesopathy was found in 70% and contralateral hamstring enthesopathy in 60% of patients. SPECT-CT criteria for the diagnosis of SIJ incompetence were developed and validated. SPECT-CT is a valid and reproducible technique for the diagnosis of SIJ incompetence with high concordance and specificity compared to the reference standards. Findings are supportive of the integrated model of SIJ function proposed by Lee and Vleeming.