BIOMECHANICAL ANALYSIS OF DIFFERENT PRODISC-C ARTHROPLASTY DESIGNS AFTER IMPLANTATION: A NUMERICAL SENSITIVITY STUDY

Abstract

Ball-and-socket disc prostheses are the leading type of artificial disc replacement (ADR) and are typically used to treat degenerative cervical spine instability. Previous publications focused on the influence of different ProDisc-C design parameters in view of biomechanics. However, more beneficial data could be gathered if the implant was implanted prior to testing. Therefore, this study aimed to estimate the effect of different ProDisc-C arthroplasty designs and alignments when implanted at the C5-6 segment. This research can provide advice on the design of artificial discs as well as optimal placement. The geometry of the vertebrae was developed based on computed tomography (CT) images of a 32-year-old healthy male (170 cm height and 68 kg weight) with a slice thickness of 0.625 mm. A finite element (FE) model of intact C5–C6 segments including vertebrae and disc was developed and validated. A ball-and-socket artificial disc prosthesis model (ProDisc-C, Synthes) was implanted into the validated FE model. The curvature of the ProDisc-C prosthesis as well as the implanted position was varied. All models were loaded with a 74 N compressive force and pure moments of 1.8 Nm in flexion-extension, bilateral bending and axial torsion. The radius of the artificial disc influenced the ROM, facet joint force and capsule ligament tension only in flexion, while the position influenced these aspects in all loading conditions. The disc with a 6 mm radius had a greater ROM in flexion, and lower stress on the polyethylene (PE) insert without apparent stress concentrations, but it had a greater facet joint force and ligament tension compared to other radii. For all the designs, the implant position in the anterior–posterior direction had a significant influence on the disc biomechanics. Disc design and surgical procedure, such as implantation position, are important factors in postoperative rehabilitation, especially regarding the ROM in flexion/extension and implant stress. Thus, a suitable disc design should consider preserving an adequate range of motion (ROM) as well as a moderate facet joint force or stress, and proper implant positioning along the anterior–posterior direction should be monitored.