34th Annual Scientific Meeting proceedings

When dealing with cartilage defects, one must distinguish between two types of defects: (1) those resulting from osteochondritis dissecans (OCD) in juvenile dogs and (2) degenerative defects, which arise from some form of mechanical disease, inducing accelerated wear of hyaline joint cartilage over time. The latter mostly occurs in older dogs; however, excessive forms of hip or elbow dysplasia, for example, can cause wear of a joint even before the patient reaches maturity. A partial or total joint prosthesis is typically employed as a synthetic resurfacing technique for such lesions because the lesions are bipolar, necessitating bipolar resurfacing, with metal (e.g., CoCr) on one side and polyethylene as a liner on the opposing joint surface.

When considering resurfacing extensive OCD lesions, the typical patient is an immature dog, approximately 5 to 10 months old, with OCD affecting the shoulder, elbow, stifle, or tarsal joint. Traditional surgical treatment aims to promote fibrocartilage infill at the debrided lesion site, typically performed in a minimally invasive manner using arthroscopy. Unfortunately, for large lesions located within the high-pressure zones of affected joints, the functional outcome might be unsatisfactory. Synthetic unipolar resurfacing implants, designed to mimic the biomechanical characteristics of hyaline joint cartilage, have been used as an alternative for treating large OCD lesions. Typically, the articulating bearing surface is made out of polycarbonate polyurethane, while the socket is a titanium mesh, promoting bone on- and ingrowth for secure long-term anchorage of the implant. Peer-reviewed studies reporting the clinical outcomes of such synthetic reconstructions in the shoulder and the stifle joint are very promising.[1-3] However, OCD lesions affecting the talus are not amenable to such off-the-shelf implants, as their shape does not match the curvature of the talar ridge. For OCD lesions at the humeral trochlea, the same implants can be used, although there is a lack of peer-reviewed reports on their efficacy and safety.[4]

Patient-specific synthetic resurfacing, employing the same materials as the 'native' off-the-shelf implants, allows for more extensive application of unipolar synthetic resurfacing because the implant perfectly matches the native curvature of the defect, enabling anatomical reconstruction of large, complex lesions. However, achieving anatomical reconstruction of the diseased joint surface is not guaranteed by the matching anatomical shape of the PSI alone, as slight errors in positioning and angulation during implantation can result in mismatch and loss of anatomical fit. [5, 6] Therefore, only the combination of navigated implantation and the use of a PSI will allow for 'perfect' anatomical resurfacing.

This technology has been used for the reconstruction of large OCDs affecting the humeral head, the lateral and medial femoral condyle, and the talar ridge in clinically affected cases.[7-9]

The longest follow-up so far is 4.5 years, without any clinical evidence of implant wear or loosening in any of more than 25 cases of stifle OCD, involving patients from all around Europe, the UK, the USA, Canada, and Australia. So far, we have recorded three cases with complications, with two of them showing partial subsidence of the implant, but without clinical consequence. The third case showed partial delamination of the PU bearing cup, diagnosed on arthroscopy, which was attributed to the initially used pattern of trabecular mesh to allow anchorage of the PU to the titanium socket. Since the trabecular design was changed, no further implant-related complications have been reported. In this case, clinical function never reached full function. In all other cases, owners were pleased with the results, reporting full function.

In one case, the PSI was used to successfully manage aseptic loosening of a previous resurfacing with two adjacent synACART implants.

The number of shoulder and talar PSI cases is still too small to draw definitive conclusions. Nevertheless, efficacy and safety appear to be comparable to the stifle cases. Because the shape of the humeral trochlea matches nicely the shape of the off-the-shelf implants, PSI for elbow OCD has not been performed yet.

References

1. Danielski, A. and M. Farrell, Use of Synthetic Osteochondral Implants to Treat Bilateral Shoulder Osteochondritis Dissecans in a Dog. Vet Comp Orthop Traumatol, 2018. 31(5): p. 385-389.
2. Egan, P., et al., Treatment of Osteochondrosis Dissecans of the Canine Stifle Using Synthetic Osteochondral Resurfacing. Vet Comp Orthop Traumatol, 2018. 31(2): p. 144-152.
3. Murphy, S.C., P.M. Egan, and N.M. Fitzpatrick, Synthetic osteochondral resurfacing for treatment of large caudocentral osteochondritis dissecans lesions of the humeral head in 24 dogs. Vet Surg, 2019. 48(5): p. 858-868.
4. Preston, C., Elbow: Latest Clinical Experiences, in VA3-Meeting. 2018: Naples, FL, USA.
5. Kunz, M., et al., Image-Guided Techniques Improve the Short-Term Outcome of Autologous Osteochondral Cartilage Repair Surgeries: An Animal Trial. Cartilage, 2013. 4(2): p. 153-64.
6. Sebastyan, S., et al., Image-guided techniques improve accuracy of mosaic arthroplasty. Int J Comput Assist Radiol Surg, 2016. 11(2): p. 261-9.
7. Moser, J., et al., Fully Guided Synthetic Osteochondral Resurfacing of a Large Stifle OCD Lesion Using a Patient-Specific Implant and Drill Guides. VCOT Open, 2023. 06(01): p. e8-e13.
8. Schmierer, P.A. and P. Böttcher, Patient specific, synthetic, partial unipolar resurfacing of a large talar osteochondritis dissecans lesion in a dog. Vet Surg, 2023. 52(5): p. 731-738.
9. Sutalo, S., M. Kühn, and P. Böttcher, Patient-Specific Synthetic Osteochondral Resurfacing of an Extensive Shoulder OCD Lesion in a Dog. VCOT Open, 2024. 07(01): p. e11-e16.