Effect on Tissue Differentiation and Articular Cartilage Degradation of a Polymer Meniscus Implant

Abstract

Background Replacement of the meniscus by an implant could potentially avoid cartilage degeneration. Hypothesis An implant of degradable polycaprolacton-polyurethane should act as a temporary scaffold enabling regeneration of a new meniscus by slow degradation of the polymer and simultaneous in-growth and differentiation of tissues into the typical cartilage-like tissue of the meniscus. Study Design Controlled laboratory study. Methods In 13 dogs’ knees, the lateral meniscus was replaced with a porous polymer implant (6 and 7 for 6- and 24-month follow-up, respectively); in 7 knees only a meniscectomy was performed. In 6 knees, no surgery was performed. After 6 and 24 months, the implants and the articular cartilage were histologically evaluated. Compression-stress tests were performed on implant biopsy specimens. Results The implants were fully integrated into the tissue without formation of a capsule. The foreign body reaction did not exceed grade I. Differentiation from fibrous- to cartilage-like tissue was pronounced after 24 months. Viable cells were particularly absent after 24 months in central parts of the most anterior part of the scaffold. The mechanical properties of the implants were intermediate between the scaffold before implantation and native meniscus tissue and were not different between 6 and 24 months. After both 6 and 24 months, small areas of the implant were not covered with tissue. Cartilage degeneration was not prevented. Conclusion A final remodeling of tissue into neomeniscus tissue could not take place since the original structure of the polymer was still present after 24 months. The implant did not prevent cartilage degradation. Several factors are discussed that may be responsible for this. Clinical Relevance Although clinical application of a polymer implant for the replacement of the entire meniscus is not supported by this study, the authors strongly believe in the concept, but further improvements in the implant and surgical technique are needed before such an implant can be recommended for human clinical use.

Synthetic meniscus replacement: a review

“…However, the materials were not strong enough to resist the (shear) forces in the knee joint and collagen type and orientation were not meniscus-like, possibly because of a lack of scaffold degradation at 24 months. The combination of these factors might have resulted in the lack of chondroprotectiveness of these polymer implants [32]. Following these results this type of polyurethane scaffold seemed to be more suitable as a partial meniscal substitute, to be used with a remaining peripheral meniscal rim.…”

“…Six months after implantation in dogs, fibrous tissue had formed in the periphery of the scaffold, but cartilaginous tissue was found in the central region [31]. Compressive properties of the implant increased up to evaluation at 24 months post-implantation and were not different from native meniscus properties [32]. However, the materials were not strong enough to resist the (shear) forces in the knee joint and collagen type and orientation were not meniscus-like, possibly because of a lack of scaffold degradation at 24 months.…”

“…The Actifit® implant originally was developed to serve as a full meniscus replacement. Based on the results of a dog study a partial implant was considered to be a more suitable application since as a total meniscus replacement the implant could not resist the shear forces in the knee joint and cartilage damage could not be prevented [31,32]. When implanted in a bovine partial meniscal defect, however, the Actifit® implant promoted fibrous tissue ingrowth into the defect site while not damaging the articular cartilage [33].…”

Polímeros como Biomateriais para o Tecido Cartilaginoso

“…Todavia, faz-se necessário saber que, o sucesso da regeneração do TCa com o uso arcabouços poliméri-cos está correlacionado diretamente com as interações destes materiais com as células circunjacentes no sítio de implantação (WELSING et al, 2008), as quais definirão o tipo de resposta tecidual apresentada após a implantação. Nota-se, assim, que a formação de um novo TCa depende da biocompatibilidade dos polímeros e dos seus subprodutos; das características físico-químicas do arcabouço pós-implantação (SCHNEI-DER et al, 2011); e da velocidade de degradação do material (LIU; MA, 2004), a qual deve ser compatível com sua função no organismo.…”

“…A formação de TCa com influxo de células, em sincronia com a degradação do biomaterial, foi observada em arcabouços de PCL (MARTINEZ-DIAZ et al, 2010) e PLGA (CHANG et al, 2012) na cartilagem articular de coelhos; e em arcabouços de poliuretano à base de policaprolactona (PCLPU), em lesões do menisco de cães (WELSING et al, 2008) e coelhos (HANNIK et al, 2012), com a presença de algumas células gigantes multinucleadas ao longo da superfície dos poros, o que não inviabiliza a utilização destes materiais, pois este tipo de resposta tecidual é inerente à implantação dos biomateriais nos tecidos vivos (ANDERSON et al, 2008).…”