Association of pars defect type with clinical outcome after smiley face rod methods for terminal-stage spondylolysis

Background 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). The visual analog scale (VAS) score for back pain, bone union rate, and time to return to preinjury level athletics were evaluated and compared between the groups. Fisher’s exact test and a paired t test were used when comparing the groups. VAS score between the groups were analyzed using a 2-factor repeated-measures analysis of variance. Results Within groups there were significant differences over time for VAS score (p p = 0.028) and 24 months after surgery (97.1% and 75.0%, p = 0.011). All patients returned to their respective sports, and no significant differences were observed with time to return to preinjury level athletics between the groups (p = 0.055). Conclusion These results suggested that the defect of pars sclerosis is associated with bone nonunion, but has little effect on postoperative symptoms.