Multivariable analysis of the relationship between pain referral patterns and the source of chronic low back pain.

BACKGROUND Discogenic, facet joint, and sacroiliac joint mediated axial low back pain may be associated with overlapping pain referral patterns into the lower limb. Differences between pain referral patterns for these three structures have not been systematically investigated. OBJECTIVE To examine the individual and combined relationship of age, hip/girdle pain, leg pain, and thigh pain and the source of internal disc disruption (IDD), facet joint pain (FJP), or sacroiliac joint pain (SIJP) in consecutive chronic low back pain (CLBP) patients. DESIGN Retrospective chart review. SETTING Community based interventional spine practice. PATIENTS 378 cases from 358 consecutive patients were reviewed and 157 independent cases from 153 patients who underwent definitive diagnostic injections were analyzed. METHODS Charts of consecutive low back pain patients who underwent definitive diagnostic spinal procedures were retrospectively reviewed. Patients underwent provocation lumbar discography, dual diagnostic medial branch blocks, or intra-articular diagnostic sacroiliac joint injections based on clinical presentation. Some subjects underwent multiple diagnostic injections until the source of their chronic low back pain (CLBP) was identified. MAIN OUTCOME MEASUREMENTS Based on the results of diagnostic injections, subjects were classified as having IDD, FJP, SIJP, or other. The mean age/standard deviation and the count/percentage of patients reporting hip girdle pain, leg pain, or thigh pain were estimated for each diagnostic group and compared statistically among the IDD, FJP, SIJP, and other source groups. Next, the 4 predictor variables were simultaneously modeled with a single multinomial logistic regression model to explore the adjusted relationship between the predictors and the source of CLBP. RESULTS The mean age was significantly different among the source groups. IDD cases were significantly younger than FJP, SIJP, and other source groups and FJP cases were significantly younger than other sources. The age by thigh pain interaction effect was statistically significant (P = 0.021), indicating that the effect of age on the source of CLBP depends on thigh pain, and similarly, that the effect of thigh pain on the source of CLBP depends on age. LIMITATIONS Retrospective study design. CONCLUSIONS The presence or absence of thigh pain possesses a significant correlation on the source of CLBP for varying ages, whereas the presence of hip/girdle pain or leg pain did not significantly discriminate among IDD, FJP, or SIJP as the etiology of CLBP. Younger age was predictive of IDD regardless of the presence or absence of thigh pain.