BACKGROUND: Functional anatomy and prevalence of lumbar spine conditions differ between males and females. For instance, females have greater lumbar lordosis than males and females are also at a greater risk for age-related spinal conditions, such as degenerative spondylolisthesis. If and to what extent lumbar mobility and intervertebral stability differ by sex, however, remains unclear. Given that intervertebral motion is used to diagnose spinal stability, a better understanding of how lumbar intervertebral segment mobility and stability differ by sex in patient populations is needed. METHODS: A retrospective analysis of lumbar intervertebral rotational (IVR) and translation (IVT) motion in the sagittal plane was conducted using dynamic fluoroscopy image analysis of age-matched males (n=350) and females (n=350) with non-traumatic symptoms and no prior spinal surgeries. Multivariate linear regression analyses were used to examine how intervertebral motion variables related to sex with age and BMI adjusted. RESULTS: The results suggest IVR in flexion was 9.1% less in females (21.5 degrees) than males (23.8 degrees) for L3-L4 (p=0.05) and L4-L5 (F: 22.7 degrees M: 24.7 degrees; p=0.03) and IVR in extension was greater in females (17.1, 18.1, 16.8 degrees) compared to males (16.2, 17.6, 15.9 degrees) for L2-L3, L3-L4, and L4-L5, respectively. For IVT, the greatest difference 0.5% (p<0.01) between the sexes occurred at L4-L5 with average translation in males indicating retrolisthesis and in females, spondylolisthesis. Sex differences in IVT at L4-L5 were significant in flexion, neutral posture, and extension for both our younger and older halves of our sample. CONCLUSIONS: The findings demonstrate that females have a greater range of lumbar intervertebral extension in the mid-lumbar disc segments, which may relate to greater lumbar lordosis. Females appear to be more affected by age-related reductions of lumbar intervertebral mobility. The reduction in rotational motion may coincide with the sex differences in translation. The results highlight the importance of accounting for age and BMI in studies of lumbar motion, as well as using valid and repeatable methods. To create clearer lumbar motion standards indicative of instability, future work should compare our results to similar intervertebral motion data from an asymptomatic population.

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