Explant analysis of two rhine cervical discs

Area of Science:

• Spine biomechanics
• Biomaterials science
• Orthopedic surgery

Background:

• Cervical disc replacement aims to maintain spine motion and prevent adjacent segment disease.
• The Rhine cervical disc is a non-articulating, viscoelastic implant designed to mimic natural cervical spine biomechanics.
• No previous explant analyses of the Rhine cervical disc have been published.

Purpose of the Study:

• To perform an explant analysis of two Rhine cervical discs.
• To assess the physical condition of the explants and associated tissue reactions.
• To investigate potential causes of implant failure and poor clinical outcomes.

Main Methods:

• Explant analysis of two Rhine cervical discs retrieved from a patient one year after C4-C5 and C6-C7 total disc replacement.
• Assessment of implant physical condition, including core integrity and deformation.
• Evaluation of associated tissue reactions, including osteolysis.

Main Results:

• Both explants were intact but showed plastic deformation of their viscoelastic cores.
• Asymmetric shear deformation was observed, differing between the upper (anterior) and lower (posterior) discs.
• Osteolysis was predominantly noted at the posterior aspect of the lower disc.

Conclusions:

• Viscoelastic core deformation in Rhine cervical discs is a significant finding.
• Improper implant sizing and positioning may lead to excessive shear forces, core deformation, and adverse clinical outcomes.
• The observed core deformation is consistent with known limitations of viscoelastic polymers in other cervical disc designs.