16.2.5 - Non-Degradable Polycarbonate-Urethane Focal Knee Resurfacing Implants: A 6-Month Caprine Animal Study
- P. Van Hugten (Maastricht, NL)
- P. Van Hugten (Maastricht, NL)
- R. Jeuken (Maastricht, NL)
- E. Asik (Helmond, NL)
- A. Roth (Maastricht, NL)
- C. Van Donkelaar (Eindhoven, NL)
- J. Thies (Geleen, NL)
- L. Van Rhijn (Maastricht, NL)
- P. Emans (Maastricht, NL)
Abstract
Purpose
Focal knee resurfacing implants (FKRIs) are typically intended to treat cartilage defects in middle-aged patients. Most FKRIs are metal-based, implying potential stress-shielding, hampering follow-up using MR imaging and potentially leading to degeneration of the opposing articulating cartilage due to the large mismatch in elastic modulus. To overcome these drawbacks, a bi-layered non-degradable thermoplastic polycarbonate-urethane (TPU)-based FKRI is proposed. We hypothesized that by approaching the elastic modulus of cancellous bone and articular cartilage with a bi-layerd design, the implants would osseointegrate and induce less damage to the articulating cartilage when compared to metal-based implants. The purpose of this study was to evaluate the performance of this implant in a caprine model.
Methods and Materials
TPU-based, mushroom-shaped implants composed of a Bionate® II 80A top-layer and a BCP-coated Bionate® 75D/zirconium oxide (40/60 wt%) composite stem were injection moulded. Bi-layered metal implants (cobalt-chromium and titanium) and sham-operated knees served as control (n=8 per group). Surgery was performed bilaterally in the stifle joints of Dutch milk goats. After a follow-up of six months, the opposing cartilage was evaluated histologically using the Modified Mankin Score (MMS; 0-25). Bone histomorphometry was performed to assess osseointegration. Implant positioning was assed using laser scanning.
Results
The tibial cartilage articulating with the metal and TPU-based implants had a mean MMS of 14.79±3.45 and 10.31±1.89 respectively (p<0.01). The MMS of the metal implant group was significantly higher than the sham-operated group (p<0.001), while no significant difference was observed between the TPU-based implants and sham-operated knees (p=0.94). No significant difference in the bone-to-implant-contact was observed between the metal and TPU implant groups (p=0.72). No significant difference in implant positioning was observed.
Conclusion
TPU-based implants show promise as joint preserving implants with satisfactory osseointegration and less articulating cartilage damage when compared to metal implants. Longer follow-up studies are warranted to evaluate the long-term effects of TPU-based FKRIs.
