Prosthesis design influences segmental contribution to total cervical motion after cervical disc arthroplasty

• Published in: European spine journal Vol. 29; no. 11; pp. 2713 - 2721
• Main Authors: Patwardhan, Avinash G., Havey, Robert M.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-11-2020; Springer Nature B.V
• Subjects: Arthroplasty; Intervertebral discs; Joint surgery; Kinematics; Medicine; Medicine & Public Health; Neurosurgery; Original Article; Prostheses; Prosthetics; Spine (cervical); Surgical Orthopedics; United States > US; Quality of motion; Total disc replacement; Cervical disc arthroplasty; Segmental motion fraction; Cervical
• ISSN: 0940-6719; 1432-0932
• DOI: 10.1007/s00586-019-06064-4

Introduction
We investigated a new metric for assessing the quality of motion of the cervical segments over the arc of extension-to-flexion motion after cervical disc arthroplasty (CDA). We quantified: (1) the amount of motion contributed by individual spinal segments to the total cervical spine motion, termed segmental motion fraction, and its variation throughout the arc of extension-to-flexion motion and (2) how cervical disc arthroplasty using two distinct prosthesis designs may influence the segmental motion contributions.
Materials and methods
We tested 16 human C3–T1 spine specimens under physiologic loads; first intact, after CDA at C5–C6, and then at C5–C6 and C6–C7. The M6-C (Orthofix, USA) and Mobi-C (Zimmer, USA) disc prostheses were used in eight specimens each.
Results and conclusions
The designs of the cervical disc prostheses tested significantly influenced the variation in segmental motion fraction as the spine underwent motion between the endpoints of extension and flexion. While the mean segmental motion contribution to the total cervical motion was not influenced by prosthesis design, the way the motion took place between the extension and flexion endpoints was significantly influenced. The M6-C artificial disc restored physiologic motion quality such that implanted segments continued to function in harmony with other segments of the cervical spine as measured before arthroplasty. Conversely, the Mobi-C prosthesis, while maintaining average motion contributions similar to the pre-implantation values, demonstrated large deviations in motion contribution over the extension-to-flexion arc motion in ten of 16 implanted segments. Such non-physiologic implant kinematics could cause excessive prosthesis wear and motion and stress shielding at adjacent segments.
Graphical abstract
These slides can be retrieved under Electronic Supplementary Material.