Objective To evaluate the clinical effect for ablation of posterior medial branch of the spinal nerve guided by C-arm X-ray machine in the treatment of lumbago caused by spondylolysis in adolescents. Methods A retrospective analysis was conducted on the clinical data of 30 adolescent patients with lumbar spondylolysis who were hospitalized in the department of spinal surgery of the First Affiliated Hospital of Guangxi University of Traditional Chinese Medicine from February 2022 to December 2022. Among them, 15 patients who underwent ablation of the posterior medial branch of the spinal nerve at the affected site under X-ray fluoroscopy were designated as the radiofrequency group. During the same period, 15 patients who received mixed injection of triamcinolone acetonide injection and lidocaine injection at the affected site, with comparable general data (such as gender and age) to the radiofrequency group, were included in the local block group. The general data of the two groups, as well as the Visual Analogue Scale (VAS) scores for lumbargo, Oswestry Disability Index (ODI) scores, and modified Macnab efficacy scores before and after treatment were recorded and compared. Results All patients successfully completed the surgery. There was a statistically significant difference in VAS scores between the two groups (Finter-group=1 501.11,P<0.001). The VAS scores of both groups showed a decreasing trend with the prolongation of time (Ftime=4 560.97,P<0.001), and there was an interaction effect between intervention measures and follow-up time (Finteraction=474.54,P<0.05). There was a statistically significant difference in ODI scores between the two groups (Finter-group=334.93,P<0.01). The ODI scores of both groups showed a decreasing trend with the prolongation of time (Ftime=276.93,P<0.01), and there was an interaction effect between group and follow-up time (Finteraction=115.41,P<0.001). In terms of the modified Macnab efficacy score, the radiofrequency group showed better efficacy than the local block group (P<0.05). Conclusion Ablation of the posterior medial branch of the spinal nerve guided by C-arm X-ray machine for lumbago caused by spondylolysis in adolescents is safe, effective, and conducive to rapid rehabilitation, making it worthy of clinical promotion.