Biomechanical behaviour of a prosthetic lumbar nucleus

The aim of this study is to determine the significance of an artificial nucleus implant for lumbar discs (PDN device) with special regard to the biomechanical properties of the spinal motion segment. From 11 human cadavers the lumbar segment L2/L3 was harvested, the lamina and the muscles were removed with care to preserve the anterior and posterior longitudinal ligaments. The segments were fixed on a special testing device mounted in universal testing machine (Zwick, Ulm-Germany). Physiological load with maximum of 7 Nm was applied in flexion/extension, right and left sidebending and right and left torsion. The movement of the measuring point (center of L2) was registered along three axes (sagittal, frontal and vertical axis). Three cycles of measurement were performed in all specimens: a) the intact segment, b) segment after nucleotomy, c) segment with 2 PDN devices. There was a statistically significant (p<0.05) increase in segmental mobility in all directions after nucleotomy with an increased mobility of the segment between 38 and 100 percent. After introduction of two PDN implants there was a restoration of segmental mobility for all movement-directions with no statistically significant difference compared with the intact situation before nucleotomy.