Spina bifida occulta of S1 is not an innocent finding.

One thousand two hundred patients (600 women and 600 men) aged 18 to 72 years were referred for computed tomographic examination of the lumbosacral spine (L3-S1) after low-back pain or sciatica. Patients with spinal abnormalities other than spina bifida occulta (SBO)-S1 and findings other than posterior herniation of intervertebral disc were not included in this study. All of the patients underwent conventional radiographs of the lumbosacral spine. The incidence of SBO-S1 was higher in younger age groups and decreased with age. Patients with SBO-S1 showed a higher incidence of posterior disc herniation, which increased with age. This can be explained by instability of the base of the lumbar spine caused by SBO-S1, which produces a predisposition to posterior disc herniation. The results were statistically significant.