A biomechanical study of artificial cervical discs using computer simulation

Study Design. A virtual simulation model of the subaxial cervical spine was used to study the biomechanical effects of various disc prosthesis designs. Objective. To study the biomechanics of different design features of cervical disc arthroplasty devices. Summary of Background Data. Disc arthroplasty is an alternative approach to cervical fusion surgery for restoring and maintaining motion at a diseased spinal segment. Different types of cervical disc arthroplasty devices exist and vary based on their placement and degrees of motion offered. Methods. A virtual dynamic model of the subaxial cervical spine was used to study 3 different prosthetic disc designs (PDD): (1) PDD-I: The center of rotation of a spherical joint located at the mid C5-C6 disc, (2) PDD-II: The center of rotation of a spherical joint located 6.5 mm below the mid C5-C6 disc, and (3) PDD-III: The center of rotation of a spherical joint in a plane located at the C5-C6 disc level. Results. A constrained spherical joint placed at the disc level (PDD- I) significantly increased facet loads during extension. Lowering the rotational axis of the spherical joint towards the subjacent body (PDD-II) caused a marginal increase in facet loading during flexion, extension, and lateral bending. Lastly, unconstraining the spherical joint to move freely in a plane (PDD-III) minimized facet load build up during all loading modes. Conclusion. The simulation model showed the impact simple design changes may have on cervical disc dynamics. The predicted facet loads calculated from computer model have to be validated in the experimental study.