[3-dimensional biomechanical study of a new flexible lumbar intervertebral disk implant]

The aim of this study was to determine the significance of a new artificial nucleus implant for lumbar discs (polymethyl siloxane polymer, DR-PMSO) with special regard to the biomechanical properties of the spinal motion segment. The lumbar segments L1/L2 and L4/L5 were harvested from six calf cadavers. The segments were fixed on a special device mounted on a three-dimensional testing machine. Physiological load with a maximum of 7 Nm was applied in flexion/extension, right and left lateral bending, and right and left torsion. The movement of the measuring point (center of L1 and L4) was registered along three axes (sagittal, frontal, and vertical). Three cycles of measurements were performed on all specimens: (1) intact segment, (2) segment after nucleotomy, and (3) segment with PMSO. There was a statistically significant (p = 0.0313) increase in segmental mobility in all directions after nucleotomy with an increased mobility of the segment up to 30% for rotation and 50% for translation. After introduction of the PMSO implant, segmental mobility for all movement directions was restored with no statistically significant difference from the intact situation before nucleotomy. The disc material was found to be noncytotoxic according to current ISO 10993 standards.