Lumbar intradiscal pressure and whole-body vibration - first results

Objective. To contribute to the scientific background for the assessment of the health risk at the lumbar spine from whole-body vibration. Design. Experimental study. Background. Many workers have monitored the vibration at spinal locations o n the skin or using skeleton mounted devices in order to assess the vertebr al response when sitting. They have shown that resonance occurred in the 4- 7 Hz range. Considering the different structures of the intervertebral join t, it seemed interesting to assess their behaviour separately, using intran uclear pressures at the lumbar discs monitored simultaneously with the vert ebral accelerations. Methods. Seven unembalmed cadavers were submitted to 5 min. whole-body rand om vibration, in four seated postures (erect or as in a car, both with or w ithout a lumbar support). Power spectral density functions were estimated a t each lumbar level and each posture and the dominant frequency identified. The energy of the pressure signal was also estimated in the 0-25 Hz band. Analysis of variance was then performed to study the effects of subject, di sc level, and posture. Results, Energy of the intranuclear pressure variation decreased when leani ng the backrest backwards. The effect of the lumbar support depended on the discal level and on posture. The shape of the power spectral density funct ion suggested the existence of a cyclic loading of the nucleus pulposus, wh ile more complex phenomena were observed at the vertebral body. Conclusions. The response of the lumbar spine cannot be assessed by examini ng only vertebral acceleration at one level.