Summary

A novel anatomical fibre-reinforced polycarbonate urethane (PCU) total medial meniscus implant can withstand short-term physiological loading in an ovine model, highlighting its effectiveness as a potentially new treatment option for complete meniscus replacement in symptomatic patients.

Abstract

Aim

No proven long-term joint-preserving treatment exists for irreparable meniscal damage. The ovine stifle joint is a well-established knee joint model for pre-clinical research in cruciate ligament reconstruction/replacement, partial/total meniscus replacements, cartilage lesion repair and osteoarthritis treatment. This study aimed to evaluate the safety and performance of a novel anatomical fibre-reinforced polycarbonate urethane (PCU) total medial meniscus implant, designed to replicate native meniscus structure and function, at 3 months after implantation in an ovine model compared to non-operated controls.

Methods

Seven mature female North of England Mules (cross-bred sheep) were implanted with a fibre-reinforced PCU total medial meniscus replacement in the right stifle joint following total meniscectomy using an epicondylar osteotomy approach. Transosseous tunnels were drilled from the distal anterolateral aspect of the tibia to the native anterior and posterior medial meniscus root sites, allowing textile straps extending from the implant anterior and posterior horns to be passed and fixed at the distal aperture with interference screws (Quick-Start Screw, Innovate Orthopaedics Ltd). Contralateral stifle joints formed non-operated controls. Clinical observations, including lameness and pain scores, were performed regularly throughout. At 3 months from implantation, implant integrity and wear, histological cartilage condition and tissue-implant fixation integration were evaluated.

Results

All animals were fully weight-bearing with absent to mild lameness and pain scores on the Sheep Grimace Scale within 1 week of surgery, and with no lameness or pain at 3 months. Implant integrity was confirmed post 3-month implantation for all implants (n=7) with no evidence of tears and minimal signs of localised wear. Interference screw fixation at the distal bone tunnel apertures was secure and fully integrated with no signs of slippage. Indications of strap fraying were noted at the posterior proximal/internal aperture (n=6), and to a lesser extent at the anterior tunnel (n=2), causing implant extrusion posteriorly. Mild macroscopic cartilage degeneration was noted at 3 months for the implanted stifles compared to non-operated controls. Microscopically, cartilage condition in the implanted group was consistent with compressive and tribological effects of surgery and implantation. Complete healing of tissue around the strap at anterior proximal and, to a lesser extent, posterior proximal tunnel apertures was noted. Substantial deposition of relatively mature bone was observed around all fixation straps (n=14) with bony integration at the screws and tissue in-growth in the tunnels, and with no indication of inflammatory irritation.

Conclusion

Our findings show that the reinforced implant body can withstand short-term physiological loading in sheep with minimal implant wear, restoring biomechanical function. Further modifications at the proximal transosseous tunnel aperture have since been implemented to reduce strap fraying risk and subsequent extrusion. Longer-term evaluation against meniscectomy controls will further evidence the effectiveness of this meniscus replacement. Nonetheless, the tibial articular cartilage condition reported in this study was comparable to that of other meniscal devices at 3 months implantation that have since progressed to the clinic (Vrancken et al., 2015). These findings highlight the effectiveness of a fibre-reinforced PCU meniscus implant as a potentially new treatment option for complete meniscus replacement in symptomatic patients.