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

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.

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.

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).

The type of pars defect are associated with bone union after the smiley face rod method, but have little effect on postoperative symptoms.