Does lumbar disk degeneration increase segmental mobility in vivo? Segmental motion analysis of the whole lumbar spine using kinetic MRI

STUDY DESIGN: This is a retrospective analysis of lumbar segmental motion using Kinetic magnetic resonance imaging (KMRI). OBJECTIVE: The aim of the study was to investigate lumbar segmental motion in functional (ie, standing weight-bearing flexion and extension) positions and examine the effects of lumbar disk degeneration on lumbar segmental motion. SUMMARY OF BACKGROUND DATA: Various biomechanical studies using cadaveric specimens have demonstrated the effects of disk degeneration on lumbar motion. However, the studies did not determine the effect of disk degeneration on segmental motion in the functional, living spine. METHODS: Segmental range of motion (ROM) was calculated and disk degeneration was graded in patients who had undergone KMRI in weight-bearing neutral, 60 degrees of flexion, and 20 degrees of extension. Patients (n=262) were categorized as having normal disks (n=94), single-level degeneration at L4-L5 (n=28) or L5-S1 (N=71), or double-level degeneration at L4-L5-S1 (N=69). Angular ROM, contribution (%) of each segment to total lumbar motion, and contribution of motion from upper (L1-L3) and lower (L4-S1) lumbar levels were compared. RESULTS: Mean ROM of the lumbar spine in the normal group was 41.3±13.3 degrees. The L4-L5 degeneration group (36.1±12.4 degrees) and the L4-L5-S1 degeneration group (37.1±12.5 degrees) showed significantly decreased total lumbar ROM compared with the normal group. The ROM in upper lumbar segments was significantly larger than that in the lower segments in the normal group and similar in the degeneration groups. The contribution of L5-S1 to total lumbar motion was the smallest of all segments, and no significant difference was found between all groups. CONCLUSIONS: In functional positions assessed utilizing weight-bearing KMRI, segmental motion at levels with degenerated disks was decreased. The contribution of upper lumbar segments to the total lumbar motion was not smaller than that of the lower segments. The L5-S1 level showed the smallest ROM in lumbar motion.