[Sagittal plane rotational and translational motion of lumbar segments with decreascd intervertebral disc height].

Purpose: Employing a precise measurement protocol, it was investigated whether decreased height of lumbar discs is related to an increase of sagittal plane segmental motion or to a displacement of the cranial vertebra into a retrolisthesis position.

Methods: The height of the intervertebral discs, the dorsoventral displacement of the cranial vertebra and the range of sagittal plane rotational and transitional motion were measured for all segments of the lumbar spine from flexion-extension views of 30 patients. In each patient, at least one lumbar disc exhibited a significant height decrease. The measurement was performed using a new protocol compensating for distortion in central projection, off-centre position, axial rotation and lateral tilt of the spine. Measured data on retrolisthesis position, rotational and translational motion were compared with previously compiled age- and gender-appropriate normal data.

Results: In the cohort investigated there was no statistically significant relation between a decrease of disc height and segmental hypermobility with respect to sagittal plane rotation or translation. There was no relation between a decrease of disc height and a displacement of the adjacent cranial vertebra into a retrolisthesis position.

Conclusions: The results challenge the often postulated relation between low disc height and segmental hypermobility ("instability") and retrolisthesis position of the cranially adjacent vertebra.