STUDY DESIGN

A biomechanical study of facet joint pressure after total disc replacement using cadaveric human cervical spines during lateral bending and axial torsion.

OBJECTIVE

The goal was to measure the contact pressure in the facet joint in cadaveric human cervical spines subjected to physiologic lateral bending and axial torsion before and after implantation of a ProDisc-C implant.

SUMMARY OF BACKGROUND DATA

Changes in facet biomechanics can damage the articular cartilage in the joint, potentially leading to degeneration and painful arthritis. Few cadaveric and computational studies have evaluated the changes in facet joint loading during spinal loading with an artificial disc implanted. Computational models have predicted that the design and placement of the implant influence facet joint loading, but limited cadaveric studies document changes in facet forces and pressures during nonsagittal bending after implantation of a ProDisc. As such, little is known about the local facet joint mechanics for these complicated loading scenarios in the cervical spine.

METHODS

Seven osteoligamentous C2-T1 cadaveric cervical spines were instrumented with a transducer to measure the C5-C6 facet pressure profiles during physiological lateral bending and axial torsion, before and after implantation of a ProDisc-C at that level. Rotations at that level and global cervical spine motions and loads were also quantified. RESULT.: Global and segmental rotations were not altered by the disc implantation. Facet contact pressure increased after implantation during ipsilateral lateral bending and contralateral torsion, but that increase was not significant compared with the intact condition.

CONCLUSION

Implantation of a ProDisc-C does not significantly modify the kinematics and facet pressure at the index level in cadaveric specimens during lateral bending and axial torsion. However, changes in facet contact pressures after disc arthroplasty may have long-term effects on spinal loading and cartilage degeneration and should be monitored in vivo.