Cell distribution and regenerative activity following meniscus replacement

Meniscus replacement is of clinical benefit, but universal efficacy remains elusive. A greater understanding of the biological activity within implanted allografts or synthetic scaffolds may assist the development of improved surgical strategies. Biopsies of fresh-frozen allograft (n = 20), viable allograft (n = 18) and polyurethane scaffolds (n = 20) were obtained at second-look arthroscopy. Histological evaluation of tissue morphology and cell density/distribution was performed using haematoxylin-eosin (H&E) staining. Immunohistochemistry was used to detect the presence of CD34 (on progenitor cells and blood vessels) and smooth muscle actin (SMA)-positive structures and aggrecan. Collagen presence was investigated using picrosirius red staining. Cell density in the deep zone of the meniscus replacement was significantly higher in polyurethane scaffolds versus allograft transplants (p < 0.01) and also significantly higher in viable allograft compared with deep-frozen allograft (p < 0.01). CD34 staining was significantly higher in polyurethane and viable allografts versus deep-frozen allograft (progenitor cells p < 0.05; blood vessels p < 0.01). There were no significant differences in SMA or aggrecan staining across groups. All three specimen types demonstrated strong presence of collagen type I. Both viable allograft and a polyurethane meniscal scaffold show enhanced morphological, cell-distribution and regenerative patterns over deep-frozen allograft following surgical implantation. Given the limitations in viable allograft availability, these findings support the continued development of synthetic scaffolds for meniscus replacement surgery.