Biomechanics of Cervical Disc Arthroplasty—A Review of Concepts and Current Technology

Another example of a prosthesis with 3 articulating components with 2 bearings is the Mobi-C cervical artificial disc. The bearing (joint) formed by the mobile core with the superior prosthetic endplate is spherical. The core forms a planar bearing with the inferior prosthetic endplate. Endplate angular motion (blue arrow) will result in a corresponding translation of the core (red arrow).

The Secure-C disc prosthesis has a mobile core that forms a spherical (ball-and-socket) bearing with the superior prosthetic endplate and a cylindrical bearing with the inferior prosthetic endplate with the long axis of the cylinder aligned in the coronal plane (Source: Globus Medical).

Prostheses with 2 components that articulate to form a spherical (ball-and-socket) joint. (A) ProDisc-C (Source: Centinel Spine). (B) Discover (Source: DePuy Synthes Spine). (C) PCM (Source: NuVasive).

Prostheses with 2 components that articulate to form (A) a saddle joint (Source: Stryker Spine), (B) a ball-in-trough joint (Source: Medtronic), and (C) 3 noncongruent ball-and-socket joints (Source: Dymicron, Inc).

A class of nonarticulating discs with compressible cores. (A) Bryan disc (Source: Medtronic), (B) M6-C disc (Source: Orthofix Spine), (C) CP-ESP disc (Source: FH Orthopedics Inc.), and (D) Rhine disc (Source: Stryker Spine).

Axial rotation range of motion test of C5-C6. (A) View of right facet showing full overlap during right rotation, (B) left facet showing minimal facet overlap during right rotation, and (C) right rotation showing coupled right lateral bending. Transparent C5 body shows decreased facet overlap on left (D) left rotation showing coupled left lateral bending. Note increased facet overlap on left.

Axes of rotation in a healthy C5-C6 segment: (A) flexion-extension COR, (B) lateral bending axis of rotation shown in sagittal projection, and (C) intersection of lateral bending axis with the midcoronal plane. COR, center of rotation.

(A) Kinematic signature of a cervical spine segment in flexion-extension. (B) Effect of decompressive surgery on the kinematic signature showing increased laxity (decreased stiffness) around the neutral posture, resulting in larger range of motion.

Axes of rotation in a reconstructed C5-C6 segment implanted with a single spherical bearing prosthesis: (A) flexion extension COR, (B) lateral bending axis of rotation shown in sagittal projection, and (C) intersection of lateral bending axis with the mid-coronal plane. COR, center of rotation.

Examples of kinematic signatures of a cervical spine segment in flexion extension: intact (native) and after CDA using an M6-C disc prosthesis. CDA, cervical disc arthroplasty.