Posterior dynamic stabilisation systems were developed to provide stabilisation to pathologic or hypermobile spinal segments while maintaining the healthy biomechanics of the spine. Numerous novel dynamic devices incorporate the temperature and moisture dependent material polycarbonate urethane due to its mechanical properties and biocompatibility. In this study, standardised pure moment in vitro tests were carried out on human lumbar spines to evaluate the performance of a device containing polycarbonate urethane. An environmental chamber with controlled moisture and temperature was included in the set-up to meet the requirements of testing under physiological conditions. Three test conditions were compared: (1) native spine, (2) dynamic instrumentation and (3) dynamic instrumentation with decompression. The ranges of motion, centres of rotation and relative pedicle screw motions were evaluated. The device displayed significant stiffening in flexion-extension, lateral bending and axial rotation load directions. A reduction of the native range of motion diminished the stiffening effect along the spinal column and has the potential to reduce the risk of the onset of degeneration of an adjacent segment. In combination with decompression, the implant decreased the native range of motion for flexion-extension and skew bending, but not for lateral bending and axial rotation. Curve fittings using the sigmoid function were performed to parameterise all load-deflection curves in order to enhance accurate numerical model calibrations and comparisons. The device caused a shift of the centre of rotation in the posterior and caudal direction during flexion-extension loading.

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