Biomechanical Study of Cervical Disc Arthroplasty Devices Using Finite Element Models

TLDR: The present study demonstrates the influence of different CDA designs on the anterior and posterior loading patterns at the index and adjacent levels and validates key clinical observations: CDA procedure is contraindicated in cases of facet arthropathy; and CDA may be protective against adjacent segment degeneration.

Abstract: Various types and designs of artificial discs for cervical disc arthroplasty (CDA) have been introduced to overcome the disadvantages of the conventional anterior cervical discectomy and fusion (ACDF). The purpose of this study was to evaluate the effects of different CDA designs on the range of motion (ROM), intradiscal pressure (IDP), and facet force variables with different types of FDA-approved CDA devices under normal physiological loading conditions. A validated three-dimensional finite element model (FEM) of the intact cervical spinal column (C2-T1) was used in the present study. The intact spine model was modified and used for postoperative FE models simulating CDAs implanted at the C5-C6 intervertebral disc space. The normal surgical procedures were used in the simulations. The hybrid loading protocol (intact spine loading: 2 Nm) with a compressive follower force of 75 N was applied at the superior end of the spine. The inferior endplate of C7 vertebra was constrained in all directions. Flexion, extension, and lateral bending loading conditions were simulated in all models: intact spine and models with different CDA devices. At the index level, all CDAs except the Bryan disc showed an increase in motion, and the range of motions at the adjacent levels decreased in flexion, extension, and lateral bending modes. The largest increase in motion occurred during lateral bending. The Bryan disc reduced the segmental motion at the index level under flexion, extension, and lateral bending, and had compensatory increases in motion at the adjacent levels. The intradiscal pressure reduced at the adjacent levels with Mobi-C and Secure-C devices. The Bryan and Prestige LP devices showed increases in the intradiscal pressure at the adjacent levels due to the reduced index level motion (Bryan disc) and the metal-on-metal design (Prestige LP). The facet force increased at the index level in all CDAs, with the highest force with Mobi-C, and this was attributed to its unrestrained design. The facet force generally decreased at the adjacent levels with CDAs, except for the Bryan disc, due to reduced index level motion, and the Prestige LP in lateral bending, likely due to its metal-on-metal design. The present study demonstrates the influence of different CDA designs on the anterior and posterior loading patterns at the index and adjacent levels. In addition, the study validates key clinical observations: CDA procedure is contraindicated in cases of facet arthropathy; and CDA may be protective against adjacent segment degeneration.