Resurfacement of the weight-bearing surface in horses: What are the possibilities and outcomes in 2019? Running title: Long Term Outcome of Mosaicplasty in Clinical Cases

Introduction

Once destroyed, the adult weight-bearing joint cartilage never heals. There is no capacity for hyaline cartilage regeneration. On the less weight-bearing joint surfaces (e.g. the lateral femoral trochlea) a repair with fibrocartilage usually gives sufficient support, due to the less weight-bearing nature of the surface. On the other hand, hyaline cartilage damage on the weight-bearing joint surface will lead to degenerative changes, osteoarthritis and lameness.

Over the past 20 years, several techniques have been developed in human orthopaedic surgery in order to obtain a new gliding surface on the damaged weight-bearing joint surface. Without aiming at completeness, the techniques already used in clinical cases in equine joints will be summarised briefly.

Microfracture was developed by a human orthopaedic surgeon, J. R. Steadman in 1994. He described further development of the technique in 2003.¹ In the USA, more than 25,000 such operations are carried out on humans every year.² This technique was developed to enhance weight-bearing joint cartilage repair by taking advantage of the body’s own healing capacity. The result is still fibrocartilage on the surface, but in a more homogeneous arrangement. During microfracture, defects must be debrided down to the subchondral bone plate, removing the calcified cartilage layer followed by penetration of the bony surface with a surgical awl at 3- to 4-mm intervals. McIlwraith and his co-workers published a controlled study treating full-thickness 1-cm² defects with microfracture + bone marrow-derived mesenchymal stem cells on the weight-bearing joint surface of the medial femoral condyle (MFC). They found a significant increase in repair tissue firmness and a trend for better overall repair tissue quality.³  However, hyaline cartilage quality could not be achieved. [...]