Post-meniscectomy syndrome is broadly characterised by intractable pain following the partial or total removal of a meniscus. There is a large treatment gap between the first knee pain after meniscectomy and the eligibility for a TKA. Hence, there is a strong unmet need for a solution that will relieve this post-meniscectomy pain. Goal of this first-in-man study was to evaluate the safety and performance of an anatomically shaped artificial medial meniscus prosthesis and the accompanying surgical technique. A first-in-man, prospective, multi-centre, single arm clinical investigation was intended to be performed on 18 post-medial meniscectomy syndrome patients with limited underlying cartilage damage (Kellgren Lawrence scale 0–3) in the medial compartment and having a normal lateral compartment. Eventually 5 patients received a polycarbonate urethane mediale meniscus prosthesis (Trammpolin® medial meniscus prosthesis; ATRO Medical B.V., the Netherlands) which was clicked onto two titanium screws fixated at the native horn attachments on the tibia. PROMs were collected at baseline and at 6 weeks, 3, 6, 12 and 24 months following the intervention including X-rays at 6, 12 and 24 Months. MRI scans were repeated after 12 and 24 months.Introduction
Methods
Meniscectomy, induces osteoarthritis. Options for repair of a damaged meniscus are an allograft meniscus, an implant made of natural scaffold materials (the collagen meniscus implant; CMI) or an implant made of polymers. Allograft menisci and the CMI are already clinically used for a considerably number of years. In this educational lecture the focus is on a comparison between the three implant types and the status of a tissue-engineered meniscus. The allograft meniscus is already used for at least ten years. It is intended for the younger patient with a previous total meniscectomy, with moderate cartilage degeneration and with a good alignment of the knee. The clinical outcome is based on function and pain scores. In this lecture the functional scores, the survival rate and the histology of allograft menisci will be highlighted. The CMI meniscus implant is intended for a different patient group. To enable implantation of the CMI the rim of the native meniscus should be intact. Patient series that should demonstrate the efficacy of this type of implant are still small and are mainly of the inventors of the implant. In general patients tolerated the implant well. Tissue ingrowth and remodelling into a fibro-cartilaginous tissue was found in animals and patients. Polymers may be a good alternative for the allograft and CMI implant. Previously they were used to guide vascularized new repair tissue through an ingrowth channel to the avascular lesion. We developed a porous polymer meniscus scaffold with properties to allow tissue infiltration and regeneration of a neomeniscus. It was implanted in dog knees and compared with total meniscectomy. The tissue infiltration and redifferentiation in the scaffold, the stiffness of the scaffold, and the articular cartilage degeneration were evaluated. Three months after implantation, the implant was completely filled with fibrovascular tissue. After 6 months, the central areas of the implant contained cartilage-like tissue with abundant collagen type II and proteoglycans in their matrix. The foreign-body reaction remained limited to a few giant cells in the implant. The compression modulus of the implant-tissue construct still differed significantly from that of the native meniscus, even at 6 months. Cartilage degeneration was observed both in the meniscectomy group and in the implant group. The improved properties of these polymer implants resulted in a faster tissue infiltration and in phenotypical differentiation into tissue resembling that of the native meniscus. However, the material characteristics of the implant need to be improved to prevent degeneration of the articular cartilage.
Type I and II collagen-based scaffolds, with and without attached chondroitine sulphate (CS), were implanted without additional chondrocytes into full-thickness defects in the trochlea of young adult rabbits. We hypothesise that the chemical composition of the matrix will have a direct effect on the speed of repopulation and the phenotypic expression of the subchondral repair cells. Evaluation of the repair process was performed with routine histology and with two quantitative histological grading systems, four and twelve weeks after implantation. Four weeks after implantation, type I collagenous scaffolds were completely filled with a cartilage-like repair tissue. By contrast, type II collagenous scaffolds showed a superficial zone of cartilaginous tissue, and in many defects chondrocyte-like cells at the interface of the implant material with the subchondral bone. In collagen type II filled lesions larger areas of the scaffolds were completely devoid of repair tissue. Control defects showed a repair reaction that was very similar to that observed in defects filled with a type I scaffold. After 12 weeks, the subchondral defect was largely replaced by bone and the differences between the scaffolds were less pronounced. The quantitative blind score of the sections confirmed that the scores of the control defect and of the collagen type I based scaffolds were slightly higher as compared to the type II based scaffolds. Irrespective of the type of scaffold, there was a trend that the scaffolds with CS scored slightly higher than those without CS. We conclude that different types of scaffold induce different repair reactions. Collagen types I based scaffolds seem superior to guide progenitor cells from a subchondral origin into the defect. Repair cells in collagen type II based scaffolds seem to assume a chondrocyte-like phenotype, which could have a negative effect on the mobility of the repair cells.
