Radiographic Analysis of Lumbar Motion in Relation to Lumbosacral Stability

STUDY DESIGN: This in vivo study was performed to examine active lumbar motion without any support. OBJECTIVES: To establish the behavior of segmental flexibility according to the degree of whole lumbar motion and to clarify the correlation between bony characteristics of the lumbosacral junction and stability in the segment. SUMMARY OF BACKGROUND DATA: In previous studies, the full mobility of the lumbar segments has been investigated. The details of motion commonly seen with the activities of daily living have not been clarified. It has been reported that the iliolumbar ligaments have an influence on lumbosacral stability and that the relative thickness of the transverse process of L5 could indicate the functional strength of the iliolumbar ligaments. However, the effects of the iliolumbar ligaments on the lumbosacral range of motion have not been studied in vivo. METHODS: Ninety adults, aged 20-39 years, were requested to perform motion commonly associated with activities of daily living, defined as moderate motions of the lumbar spine. The subjects then were asked to perform maximal motion of the lumbar spine. The segmental ranges of motion, segmental flexion, and extension at every level of the lumbar spine were calculated by using functional radiographs. The correlation between the relative thickness of the transverse process of L5 and the motion seen at the lumbosacral junction was also determined. RESULTS: The greatest segmental range of motion was found at L2-L3 in moderate motion and at L4-L5 in maximal motion. It shifted gradually from the upper to lower lumbar levels with the increase in total lumbar motion. With an increase in lumbar spine motion, maximum segmental flexion shifted from L2-L3 to L3-L4, then to L4-L5. Segmental extension changed only at L5-S1, increasing with total lumbar spine motion. There was an inverse statistical correlation between lumbosacral motion and relative thickness of the L5 transverse process. CONCLUSIONS: The greatest segmental flexibility induced by the moderate lumbar motion, usually seen with the activities of daily living, occurred more in the upper segments of the lumbar spine, especially in flexion. Further, the iliolumbar ligaments regulate lumbosacral motion especially flexion.