Histological appearance of the graft in AOC 18 + sheep. (A) Complete remodeling of cortical graft resulted in well-organized cortical bone with osteons displaying the classical concentric arrangement of the bone lamellae in close association with osteocytes. (B) Cortico-endosteal surface in a resting state, covered by a thin inactive osteoid seam (arrow) indicating that the remodeling process at this site was accomplished. (C) Structural restoration of the marrow cavity is evidenced by the presence of well-organized mature bone trabeculae undergoing remodeling (arrow). (D) The restoration of the bone marrow microenvironment can be confirmed by the presence of hematopoietic cells. Masson-Goldner trichrome stain; 5- μm -thick undecalcified sections. Magnification (A-C) 4× and (D) 20×. Histological appearance of the graft in AOC 18 - sheep. (A) Although an osseous union was accomplished at both interfaces with the host bone in CMA 18 + sheep, in CMA 18 - sheep, cartilage (ha) remnants and connective tissue (fvc) were still present at this location. This finding characterizes the incomplete incorporation of the graft. (B) Orifice corresponding to the perforation of the cortical graft incompletely filled with bone, suggesting that bone formation is not yet complete. (C) Despite the formation of highly vascular connective tissue in the inner portion the graft, there is no evidence of osteogenesis. (D) Compared with CMA 18 + sheep, the delay in the process of consolidation and remodeling of the allograft can be exemplified by the presence of residual cancellous graft (arrow) undergoing osteoclastic resorption (oc). Masson-Goldner trichrome stain; 5- μm -thick undecalcified sections. Magnification (A and B) 4×, (C and D) 10×.