How does posture affect coupling in the lumbar spine?

There is evidence to suggest that abnormal coupling patterns in the lumbar spine may be an indicator of low-back problems. To quantify the normal coupling patterns, fresh cadaveric human lumbar spine specimens (L1-S1) were used. A pure axial torque or lateral bending moment of 10 N-m (in five equal steps) was applied to the specimen, in five spinal postures, and three-dimensional motions were measured at the five vertebral levels. The results indicated that the coupling patterns changed significantly with the intervertebral level. For example, in neutral posture, the left axial torque produced coupled lateral bending, which varied from approximately 2 degrees right lateral bending at L1-2, to approximately 0 degrees at L3-4, and to approximately 2.5 degrees left lateral bending at L5-S1. Additionally, there was coupled flexion of approximately 1 degrees to 2 degrees at all levels. Application of left lateral bending moment resulted in approximately 1.7 degrees of coupled right axial rotation at all levels, except at L1-L2, where it was 0 degrees. Additionally, there was coupled flexion of 0.7 degrees to 2 degrees at all levels. For example, at the L2-3 level, the left axial torque produced coupled right lateral bending that ranged from approximately 0.5 degrees at full extension to approximately 2.5 degrees at full flexion. There was also accompanying coupled flexion of approximately 0.4 degrees to 1.7 degrees. Application of left lateral bending moment at the L2-3 level produced axial rotation of approximately 2.5 degrees, which did not vary with the posture, while the other coupled motion varied from approximately 1.7 degrees flexion at full extension posture to approximately 0.8 degrees extension at full flexion posture.