Posteroanterior stiffness in the lumbosacral spine - The correlation between adjacent vertebral levels

Study Design. A descriptive design of posteroanterior stiffness in the lumbosacral spine. Objectives. To measure posteroanterior stiffness between L1 and S1 to establish the pattern of stiffness in individuals with no history of low back pain. Summary of Background Data. In clinical examination for low back pain, manual assessment of abnormal stiffness is used to determine the site of the pain-producing lesion. However, there is little objective evidence of the variation in stiffness between levels in normal spines or of the factors that determine posteroanterior stiffness. Method. Posteroanterior stiffness was measured with a specially developed measuring device at each of the six vertebral levels between L1 and S1. Force-displacement relations were computed for each vertebral level. The gradient of the linear part of the force-displacement relation was used as a coefficient of stiffness, and the amount of displacement between 5 N and 30 N of applied force (D5-30) was used as a measure of the length of the toe region. Results. Overall there was a significant linear trend of increasing stiffness from L1 to S1. Ninety percent of the difference scores for adjacent level comparisons were less than 3.6 N/mm. There was considerable variation in the patterns of stiffness found in different individuals. The stiffness coefficient and D5-30 correlated significantly with skinfold thickness measurements and body mass index. Conclusion. A linear trend of increasing stiffness was found between L1 and S1, but this pattern was influenced by variables related to body type (adiposity).