Explant analysis of two rhine cervical discs

Purpose
Cervical disc replacement aims to preserve cervical spine motion and reduce the risk of adjacent segment disease. The Rhine cervical disc is a non-articulating, viscoelastic implant designed to replicate the natural biomechanics of the cervical spine. To date, no explant analyses of this device have been published. This study presents the explant analysis of two Rhine cervical discs retrieved from a 41-year-old female patient who had undergone two-level cervical total disc replacement, C4-C5 and C6-C7, for myeloradiculopathy.

Methods
The implants were removed approximately one year after the surgery due to increasing neck discomfort, recurrent neurological symptoms, and radiographic evidence of osteolysis. Explant analysis was performed on both implants to assess their physical condition and any associated tissue reactions.

Results
Both explants were intact, however, notable findings included plastic deformation of the viscoelastic cores, particularly in the upper disc. The direction of shear deformation differed between the explants, anterior in the upper disc and posterior in the lower disc, suggesting asymmetric loading conditions. In addition, osteolysis was observed predominantly at the posterior aspect of the lower disc one year after implantation.

Conclusion
These observations highlight deformation of the viscoelastic core in Rhine cervical discs. Whether this finding relates to surgical factors such as implant sizing and positioning, or to implant design itself, improper sizing and malpositioning may contribute to excessive shear forces, core deformation, and poor clinical outcomes. These factors are all important in implant survival and should be carefully considered. The deformation observed in the cores of the explants is consistent with viscoelastic polymer limitations reported in the literature for other viscoelastic cervical discs.