Selecting a Cervical Disc Arthroplasty: Biomechanical Considerations

Abstract

Introduction: Cervical disc arthroplasty (CDA) is for motion preservation, and may replace anterior cervical discectomy and fusion (ACDF) for treatment of radiculopathy. Biomaterials/designs of CDA’s are evolving. ROM, Return-To-Duty, CDA’s risks in military personnel has not been addressed. This finite element (FEM) study of 5 CDA’s and ACDF was to optimize treatment for cervical spondylosis in military populations. Methods: Validated C2-T1 FEM, spine simulated. Intact spine modified at C5-C6 to simulate the ACDF and 5 types of CDA’s: 1 metal-on-metal (MOM) and 3 metal-on-polymer (MOP). Models fixed T1, load applied at C2. Follower load 75 N, bending moment 2 Nm under flexion, extension applied. Hybrid loading protocol using variable moment loading applied. Bending moment varied until ACDF, MOM and MOP models responded with same total C3-C7 ROM. The facet force (FF) and ROM were obtained at index and adjacent levels under each loading mode, and intradiscal pressures (IDP) determined. Results: Difference in CDA behavior of MOP and MOM was noted. The MOP had highest ROM in flexion, extension and highest FF in extension at index level. Conversely, MOM demonstrated highest adjacent IDP. Conclusion: ACDF demonstrate increased ROM all levels. ACDF minimizes ROM and FF at index but increases ROM, and IDP at adjacent levels. CDA’s kinematic behavior was reflective more on material type than design. For military pilots with CDA exposed to higher forces, slightly stiffer CDA - MOP may be preferable to minimize potential anterior extrusion. Military with “normal” activities, more mobile MOP CDA implants may be preferred.