Characteristics of Fresh Lumbar Spondylolysis Occurring below the Age of 9 Years.

Introduction: This study aimed to compare two groups (9 years or younger [U-9] and 10 years or older [O-10]) of patients with fresh lumbar spondylolysis and elucidate their characteristics. Methods: This study enrolled 51 elementary school students diagnosed with fresh lumbar spondylolysis through magnetic resonance imaging between March 2015 and March 2022. Study 1 included 10 and 46 patients in the early- and late-grade groups, respectively. Patient characteristics at disease onset (sex, presence or absence of spina bifida occulta [SBO] in the affected vertebra, vertebral level, unilaterality or bilaterality of lesions, presence of a contralateral terminal stage, and disease stage) were compared between the two groups. Meanwhile, Study 2 included 34 patients with confirmed successful or failed bone union. The bone union rates in both groups were compared, and the factors affecting bone union in the entire study cohort were examined. Results: In Study 1, the proportions of SBO, bilateral, and advanced stage cases were significantly higher in the U-9 group than in the O-10 group. In Study 2, the bone union rate was significantly lower in the U-9 group than in the O-10 group. Conclusions: The proportions of SBO, bilateral, and advanced stage cases were significantly higher in the U-9 group than in the O-10 group. The bone union rate was significantly lower in the U-9 group than in the O-10 group.