Measurement of pressures in the nucleus and within the annulus of the human spinal disc: due to extreme loading.

Specially developed intervertebral and intradiscal pressure transducers are used to map the pressures in the nucleus pulposus and within the annulus fibrosus of the human spinal discs, to the point of fracture of the segmental units. The results show that for normal discs, pressures in the nucleus and in the annulus are linearly related to each other and to the applied compressive loads. Mechanical strains which develop around the periphery of the vertebral body are also linear with the applied compressive loads, when the partial vertebral column is loaded to the point of bony fracture. Failure of the intervertebral discs at the point of fracture occurred through the vertebral body endplates and the annulus fibrosus remained intact.