Extension creep in the lumbar spine.

This in vitro study was designed to examine extension creep of the lumbar spine under conditions of sustained loading. By means of a weight and pulley circuit, loads simulating lumbar extension and flexion were applied to 25 male lumbar spines removed at postmortem. Sagittal ranges of movement and the amount of creep occurring in a 20-min period at the limit of extension were recorded. The data were classified into three age group categories representing young adults, the middle-aged and the elderly. The results indicated that extension creep behaviour was similar to that of flexion creep previously reported. The elderly lumbar spines appeared to have a greater range of extension creep than those of the young and middle-aged groups, but analysis of variance showed that the difference in creep between age groups was not significant. The viscoelastic behaviour of the spinal ligaments, zygapophyseal joint capsules and intervertebral discs during extension are sufficient to produce a characteristic creep-recovery curve, but perhaps the important role that the zygapophyseal joints play in limiting extension is sufficient to prevent significant change in creep behaviour with increasing age. RELEVANCE:--This study provides information on the biomechanical responses of the lumbar spine to sustained end range extension loading. Results suggest that in the living, even brief periods of sustained extension loading may cause significant extension creep.