Clinical anatomy of the meniscus in animal models: pros and cons.

Nowadays, despite the possibility to use in vitro or computer models in research, animal models are still essential. Different animal models are available for meniscal repair investigation. Although a unique perfect model for the structure of the human's knee does not exist, the choice of the proper animal model is crucial for a correct research. The principal animal models in the meniscal repair are sheep, goats, pigs and dogs. Each of these has pros and cons for their utilization. Analysing each pro and con is essential for optimizing the choice of the animal model, which depends on the experimental question, avoiding unnecessary waste of resources and minimizing the animal suffering, according to the Russell and Burch's three "Rs" principles (Reduce, Refine and Recycle). In this concise review, we resume the meniscus anatomical features of the main large animals, to help choose the most suitable animal model for subsequent studies on meniscal repair.

Decorin age-related variations in the distribution of pig extracellular matrix meniscus.

Menisci act like shock absorbers and transmit load across the tibiofemoral joint by increasing congruency during movements or body weight load. This leads to decreasing the resultant stress on the articular cartilages. The meniscus has a dense extracellular matrix (ECM) composed of water, different types of collagens, and proteoglycans, such as decorin, aggrecan and biglycan. Decorin (DCN) regulates collagen fibrillogenesis acting on collagen fibrils diameter and fibrils orientation to achieve the proper assembly of its network. This work investigates the spatial disposition of this fundamental protein in pig meniscus' matrix by immunohistochemistry and western blot analysis. DCN shows an increasing trend, moving from neonatal to adult pig menisci. Adult meniscus, in porcine species, is the only one that could be considered fully mature and functional, and, even if an increasing trend is seen, no precise phenotypical switch points are seen in the age stages considered in this study.

Characterization of different in vitro culture conditions to induce a fibro-chondrogenic differentiation of swine adipose-derived stem cells.

Meniscus repair is still a challenge for orthopaedic surgeons as this tissue has a scarce healing potential due to the limited vascularization and to the lack of progenitor cells. Lately, several tissue engineering strategies combining cells and scaffolds have been developed. Adipose-derived stem cells (ASCs) represent a novel cell source for meniscus repair as they are easy to harvest, and they possess an intrinsic chondrogenic potential. The aim of our study was to analyze and compare the chondrogenic differentiation of swine ASCs cultured in vitro with different supplemented media. We isolated ASCs from swine adipose tissue and we placed in pellet cultures supplemented with either Bone Morphogenetic Protein (BMP)-2 and Transforming Growth Factor (TGF)-ß3 or with Bone Morphogenetic Protein (BMP)-7 and Transforming Growth Factor (TGF)-ß1. Samples were analyzed after 7, 14 or 21 days of culture by biochemical, histological and gene expression analysis. Our preliminary results show that BMP-2 and TGF-ß3 are stronger inducers of chondrogenesis.

Histological changes of the meniscus following an osteochondral lesion.

In the last few years, different tissue engineering strategies have been developed for the repair of osteochondral lesions. When the osteochondral scaffold is implanted on the femoral condyle, the meniscus might be affected by the implant and might undergo a progressive degeneration. The aim of our study is to analyze the morphological changes of the meniscus following an osteochondral lesion and the implant of a biphasic scaffold. A critical osteochondral defect was generated in the medial femoral condyle of mature sheep. Three defects were left untreated, the remaining lesions were divided into three groups and treated with a biphasic substituted formed by collagen type I and Wollastonite or Wollastonite/Hydroxyapatite. Animals were sacrificed after 6 months and menisci were isolated and analyzed by arthro-CT, macroscopic evaluation and histology. The results demonstrated that the osteochondral lesion negatively affects meniscus morphology and that the osteochondral substitute only partially mitigates the meniscus degeneration.