A practice audit of CT-guided injections of pars interarticularis defects in patients with axial low back pain: A primer for further investigation

Objective: To assess whether computed tomography(CT)-guided injections of local anesthetic and corticosteroid into chronic lumbar pars interarticularis defects may identify and provide benefit to a cohort of patients where the pars defects act as a primary axial pain generator. Design: Retrospective practice audit. Setting: Single academic radiology pain management practice. Patients: 59 consecutive patients undergoing CT-guided injections of lumbar pars defects. Methods: Patients were assessed with a pain numerical rating scale (NRS, 0-10) and Roland-Morris disability questionnaire (R-M) prior to injection and at 2 weeks and 2 months follow-up. For categorical outcomes, successful pain relief response was defined as either ≥50% reduction in NRS or pain 0/10; functional response was defined as ≥40% reduction in R-M score. Continuous outcomes (mean NRS, R-M scores) were assessed for significant change following injection. Results: For categorical outcomes, 37.9% of patients were responders at 2 months' follow-up; 20.7 % had complete relief of index pain. For functional recovery, 34.5% were responders at 2 months. Using continuous outcomes, mean NRS was 5.4±2.1 prior to injection and 3.6±2.6 at 2 months (P<0.0001). Mean R-M score was 11.7±6.0 prior to injection and 9.0±5.4 at 2 months (P=0.001). There were no complications. Conclusions: This practice audit suggests that in patients with axial low back pain and chronic pars defects, the pars defects may be implicated as the primary axial pain generator in a small subgroup of patients. Local deposition of corticosteroids into the pars defect may provide significant pain relief in one out of three patients, and complete relief in one out of five patients. This data suggest there may be benefit to pursuing randomized controlled trials of pars injections comparing steroid injection with placebo.