INTRODUCTION
Most cases of spina bifida occulta (SBO) are asymptomatic, but SBO is known to be associated with lumbar spondylolysis. Since there are few reports on the effects of SBO on sacral morphology in adolescents, the present study was designed to investigate this relationship.
METHODS
One hundred patients (mean age 14.9 ± 2.0 years, 44% female) who underwent lumbosacral CT imaging due to low back pain were included. Spina bifida occulta (SBO), lumbosacral transitional vertebra (LSTV), lumbar spondylolysis (L5), iliac crest height, fusion status of the first to fifth sacral vertebrae, morphology of the first sacral superior articular process, and facet tropism were assessed. The iliac crest height was classified into six levels: Type 1 (below the sacral endplate), Type 2 (between the L5 endplate and the sacral vertebra), Type 3 (between the inferior margin of the L5 vertebral body and the L5 endplate), Type 4 (between the midpoint and inferior margin of the L5 vertebral body), Type 5 (between the superior and midpoint of the L5 vertebral body), and Type 6 (above the L5 vertebral body). Statistical analysis was performed to assess the association between each factor and SBO. Facet tropism was considered positive if there was a difference of 1 standard deviation or more between the right and left facets.
RESULTS
Among all patients, SBO was present in 46%, LSTV in 6%, and fifth lumbar spondylolysis in 36%. The mean iliac crest height was 4.14 ± 1.1 cm. Women had an earlier onset of sacral fusion. The morphology of the superior articular process of the first sacral vertebra was 55.1 ± 8.9° in the axial view and 95.5 ± 6.1° in the sagittal view. Facet tropism was present in 16% in the axial plane and 14% in the sagittal plane. SBO was significantly more common in females, and sacral fusion was significantly delayed in these patients. No significant difference was found in iliac crest height. SBO was more frequently associated with L5 spondylolysis, and facet tropism was significantly more common in the sagittal plane.
DISCUSSION
Although the association between SBO and L5 spondylolysis has been reported previously, the pathogenesis of SBO remains unclear. The present study suggests that SBO is associated with delayed sacral vertebral fusion and may contribute to facet tropism in the sagittal plane. Furthermore, in combination with previous reports on biomechanical factors, it is proposed that facet tropism in the sagittal plane may play a role in the development of L5 spondylolysis.