Slippage of a spinous process hook during flexion in a flexible fixation system for the lumbar spine

This study was undertaken to measure the amount of slippage of a spinous pr ocess hook (that forms part of a flexible fixation system) during flexion. Human cadaveric lumbar spines (10) were fitted with the device. A rig was d esigned to apply flexural displacements to a spine using a materials testin g machine. Spherical markers were attached to the spine and hook. As a spin e was flexed a digital video camera was used to record the positions of the markers. The movements of the markers were measured using interactive comp uter software to assess any slippage of the spinous process hook. During fl exion the overall mean hook slippage was measured to be 0.10 mm (standard d eviation 0.04 mm). The mean hook slippage, for each of the 10 specimens, wa s in the range of 0.05-0.14 mm. The results imply that slippage of a spinou s process hook during flexion is small. (C) 2001 IPEM. Published by Elsevie r Science Ltd. All rights reserved.