Summary

A novel anatomical fibre-reinforced polycarbonate urethane (PCU) total medial meniscus implant shows encouraging results in a sheep model.

Abstract

Aim

No proven long-term joint-preserving treatment options exist for patients with irreparable meniscal damage. The ovine stifle joint is a well-established knee joint model for pre-clinical research in reconstruction or replacement of the cruciate ligaments, partial and 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 the structure and function of the native meniscus, at 3 months after implantation in the ovine model in comparison 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 a total meniscectomy using an epicondylar osteotomy approach. Transosseous tunnels were drilled from the distal anterolateral aspect of the tibia to the anterior and posterior native medial meniscus root sites, allowing textile straps extending from the implant anterior and posterior horns to be pulled down and fixed at the distal aperture with interference screws. The contralateral stifle joints acted as non-operated controls. Clinical observations, including lameness and pain scores, were performed regularly throughout the study. Following 3 months from implantation, implant integrity and wear, and histological condition of the synovium and cartilage were evaluated.

Results

All animals were fully weight-bearing with absent to mild lameness and pain scores on the Sheep Grimace Scale (SGS) within 1 week of surgery, and with no lameness or pain at 3 months after implantation. Implant integrity was confirmed post 3-month implantation for all implants (n=7) with no evidence of tears and minimal signs of localised wear evidenced by surface discolouration. 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 proximal/internal aperture of the posterior tunnel (n=6), and to a lesser extent at the anterior tunnel (n=2), causing implant extrusion posteriorly. Complete healing and integration of the anterior strap at the proximal aperture was noted, and to a lesser extent on the posterior horn. Mild signs of articular cartilage degeneration were noted at 3 months for the implanted stifles in comparison to the non-operated controls.

Conclusion

Our findings show that the reinforced implant body can withstand short-term physiological loading in sheep with minimal implant wear, and restore knee biomechanics and function. Further modifications are warranted at the implant strap extension-transosseous tunnel proximal boundary in order to reduce the risk of fraying and subsequent extrusion. This study highlights the effectiveness of a fibre-reinforced PCU meniscus implant as a potentially new treatment option for complete meniscus replacement in symptomatic patients.