Association of Pars Defect Type with Clinical Outcome after Smiley Face Rod Methods for Terminal-Stage Spondylolysis

Abstract

Introduction: The smiley face rod method is an effective treatment for symptomatic terminal-stage spondylolysis. However, the risk factors for treatment failure are unknown. We investigated the association of pars defect type with the treatment outcomes of this method. Methods: We retrospectively examined data from 34 patients (18.0±6.7 years) with terminal-stage spondylolysis who underwent surgery using the smiley face rod method. The mean follow-up period was 44.9±21.4 months. The patients were divided into 2 groups: pars defect without bone atrophy or sclerosis (group A; 18 patients), and with bone atrophy and sclerosis (group B; 16 patients). We evaluated and compared the visual analog scale (VAS) score for back pain, bone union rate, and time to return to preinjury athletics level between the groups. Fisher exact and paired t tests were used to compare the variables between groups. The VAS score between the groups was compared using a 2-factor repeated-measures analysis of variance. Results: Within groups, the VAS score was significantly different over time (p<0.001). The VAS scores between groups were not significantly different. Patients in group A had a significantly higher bone union rate per pars at 6 months (group A, 65.7%; and group B, 37.5%, p=0.028) and 24 months after surgery (group A, 97.1%; and group B, 75.0%, p=0.011). All patients returned to their respective sports, and no significant differences were observed in the time to return to preinjury athletics level between the groups (p=0.055). Conclusions: The type of pars defect are associated with bone union after the smiley face rod method, but have little effect on postoperative symptoms.