Spine height and disc height changes as the effect of hyperextension using stadiometry and MRI.

STUDY DESIGN: In vivo biomechanical design using stadiometry and MRI to measure the height change due to (hyper)extension.

SUMMARY OF BACKGROUND DATA: Spine height is decreased under loads such as lifting, whole body vibration and sitting. Extension including increased lumbar lordosis reduces the load on the spine.

METHODS: The aim was to assess the effects of a supine hyperextended posture as a means of restoring the intervertebral disc height after loading and allowing rehydration of the discs. Ten healthy male subjects were tested. A hyperextension intervention was achieved by the means of an inflatable cushion placed under the lumbar spine. The spine height was measured using a stadiometer and MRI was used to assess disc height changes.

RESULTS: The spine height gain after 10 minutes of a supine hyperextended posture differed significantly between individuals but everybody gained height. MRI images of the lumbar spine were used to measure the disc height. All but one subjects gained height during the hyperextension. Images of the spine during hyperextended posture showed increased lumbar curve and an increased anterior height of each disc compared with the dimensions of the disc with the spine in neutral posture.

CONCLUSIONS: All subjects lost height during sitting. Both methods demonstrated a recovery of height due to hyperextension. Hyperextension could be considered as a prophylaxis against the height loss in occupational loading.