Three-Dimensional Kinematic Analysis of the Human Whole Lumbar Spine and Natural Lumbosacral Spondylolysis

The purposes of this in vitro study were to analyse the three-dimensional (3D) movements of the fresh whole human lumbar spines and natural L5 spondylolysis spine to clarify the instability of this lesion. The representative values of the movements of the human whole lumbar spine were presented. In flexion, the mean values showed an increasing range of motion from L1/2 to L5/S1, and L5/S1 had the greatest motion (10.0°). In extension, similar magnitudes of motions were seen at L1/2, L2/3, L3/4, and more motion took place at L4/5 (5.6°) and L5/S1 (7.8°). In axial rotation, the maximum range of motion was under 3°. The least motion took place at L5/S1 (1.3°). In lateral bending, similar magnitudes of motions were seen on the left and right sides. The greatest motion was seen at L2/3 (7.0°) and the least motion was seen at L1/2 (4.9°). The main motions of the lumbosacral junction in the natural L5 spondylolysis specimen were 14.8° in flexion, 9.0° in extension, 7.7° in left axial rotation, 7.5° in right axial rotation, 10.7° in right lateral bending, and 7.6° in left lateral bending. The lumbosacral movements of the L5 spondylolysis specimen were bigger than those of the normal specimens in all directions. Especially the rotational instability was remarkable in the natural L5 spondylolysis specimen.