Histological Analysis of Tissue Ingrowth and Organization Following Implantation of a Novel Synthetic Acellular Meniscal Scaffold for the Treatment of Irreparable Partial Meniscus Tears and/or Partial (SS-27A)

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Introduction Histological analysis of biopsy tissue to assess tissue ingrowth and organization as it populates a novel, biodegradable, polyurethane meniscal scaffold designed for the treatment of painful irreparable partial meniscus tears and/or partial meniscal tissue loss. Methods This was a prospective, single-arm, multicentre clinical investigation in patients with an irreparable partial medial or lateral meniscal tear or partial meniscus loss. The scaffold is designed to support the body's own physiological pathways of tissue repair by providing a temporary three-dimensional matrix for cellular attachment and vascular ingrowth. A biopsy was obtained at 12 months (±1 month) after implantation of the Actifit scaffold in the 44 patients who had agreed to a relook arthroscopy with a biopsy. All biopsies were taken with an arthroscopic punch from the center of the inner free edge of the implanted scaffold meniscus according to a standardized protocol and fixed in 4%-buffered formol for at least 24 hours. Histochemical staining of the biopsy and cellular markers were used to enable visualization of specific cellular and extracellular structures. Results A total of, 52 patients (34 medial: 18 lateral) were treated with the polyurethane meniscal scaffold. The population recruited into the study were young (mean age, 30.8±9.4 years), and the majority (88%) had undergone 1 or 2 prior surgeries on the involved meniscus. The mean longitudinal length of the meniscal defect was 47.1±10.0 mm. All 44 biopsies showed fully vital material, with no signs of necrosis or cell death, illustrating biocompatibility and successful tissue ingrowth into the scaffold meniscus within the knee joint. Notably, in addition to a fibrous capsule, three distinctly different layers were observed: Layer 1: a superficial fibrotic vascularized, tissue layer, mainly consisting of fibroblasts and some fusiform fibrochondroblast-like cells. Layer 2: an avascular "transition" layer situated between the superficial "layer 1" and the deep "layer 3." Layer 2 consists of a mixture of cell types, of which fusiform cells with a morphology resembling fibrochondroblasts are most prominent. In some biopsies cells with a morphology resembling fibrochondroblasts of the polygonal subtype are prominent. The extracellular matrix is loosely organized with positive staining for collagen type I. Layer 3: a deep, avascular hypocellular layer consisting of cells with a morphology resembling fibrochondroblasts of the polygonal subtype with a matrix rich in fibrin. Conclusion No signs of tissue necrosis or cell death were observed and all biopsies showed complete re-population by cells and tissue that can be regarded as vital structures, illustrating the biocompatibility of the polyurethane scaffold. Importantly, the layered organization of biopsied scaffold meniscus, each with its own histological characteristics, is illustrative of an ongoing process of regeneration, maturation, and remodeling. Moreover, the above-described structures and their organization are similar to that of the native human meniscus. (Actifit Study Group: R. Verdonk, P. Beaufils, J. Bellemans, P. Colombet, R. Cugat, P. Djian, H. Laprell, P. Neyret, H. Paessler.)