Facet joint contact pressure is not significantly affected by ProDisc cervical disc arthroplasty in sagittal bending: a single-level cadaveric study

BACKGROUND CONTEXT: Total disc arthroplasty is a motion-preserving spinal procedure that has been investigated for its impact on spinal motions and adjacent-level degeneration. However, the effects of disc arthroplasty on facet joint biomechanics remain undefined despite the critical role of these posterior elements on guiding and limiting spinal motion. PURPOSE: The goal was to measure the pressure in the facet joint in cadaveric human cervical spines subjected to sagittal bending before and after implantation of the ProDisc-C (Synthes Spine Company, L. P, West Chester, PA, USA). STUDY DESIGN: A biomechanical study was performed using cadaveric human cervical spines during sagittal bending in the intact and implanted conditions. METHODS: Seven C2-T1 osteoligamentous cadaveric cervical spines were instrumented with a transducer to measure the C5-C6 facet pressure profiles during physiological sagittal bending, before and after implantation of a ProDisc-C at that level. Rotations of the index segment and global cervical spine were also quantified. RESULTS: The mean C5-C6 range of motion significantly increased (p=.009) from 9.6 degrees +/- 5.1 degrees in the intact condition to 16.2 degrees +/- 63.6 degrees after implantation. However, despite such changes in rotation, there was no significant difference in the facet contact pressure during extension between the intact (64 +/- 30 kPa) and implanted (44 +/- 55 kPa) conditions. Similarly, there was no difference in facet pressure developed during flexion. CONCLUSIONS: Although implantation of a ProDisc-C arthroplasty device at the C5-C6 level increases angular rotations, it does not significantly alter the local facet pressure at the index level in flexion or extension. Using a technique that preserves the capsular ligament, this study provides the first direct measurement of cervical facet pressure in a disc arthroplasty condition. (C) 2012 Elsevier Inc. All rights reserved.