This in vivo histological study using an ovine model evaluated the 90-day healing of unilateral segmental meniscal allograft transplantation.
Fresh-frozen medial menisci were transplanted to replace the right medial meniscus of six female sheep. Tissue healing was evaluated using semi-quantitative, descriptive methods. Formalin-fixed meniscal, distal femur and proximal tibia tissues were evaluated using Rodeo (cellularity/collagen), Ishida (reparative bonding), Collagen I IHC (collagen I), and Mankin (cartilage organization) scores at the medial femoral condyle (MFC) and medial tibial plateau (MTP). Meniscocapsular evaluations were performed at the: (a) peripheral junction; (b) posterior sector-native meniscus junction; (c) anterior sector-native meniscus junction; (d) posterior horn internal control; and (e) anterior horn internal control.
Three animals were euthanized at 39 ± 2.6 days post-surgery because of their knee condition. These animals had moderate Rodeo scores, low Ishida scores, and high Collagen I staining scores indicating moderately high fibrocartilaginous changes, mild or minimal healing and high collagen I content. Cartilage scores were low in the MFC and moderately high in the MTP, indicating mild MFC cartilage changes and moderately high MTP cartilage changes. Full-term (90 day) euthanized animals (n = 3) displayed improving Rodeo scores with mean scores of 3.3 and 3.6 at junctions (B) and (C), respectively. Ishida scores displayed similar improvements at all sectors. Collagen I staining revealed strong (grade 5) levels in all sections, with mean collagen I scores of 5, 5 and 4 for the peripheral (A), posterior (B) and anterior (C) junctions, respectively. Improved healing was observed at each segmental meniscus sector in terminally euthanized animals.
Segmental meniscal allograft transplantation displayed partial healing to remnant meniscal tissue. Further study is needed to better delineate the time needed for complete healing and the joint-loading progression that may enhance it.