Structural analysis of meniscal allografts after immediate and delayed transplantation in rabbits

Purpose: To compare long-term performance of meniscal allografts transplanted immediately after meniscectomy and allografts transplanted 6 weeks after meniscectomy. Type of Study: Experimental study. Methods: Twenty-one rabbits were subjected to meniscectomy and divided into 3 groups of 7 animals. Immediate meniscal transplantation was performed in group A (6-week follow-up) and group B (1-year follow-up). Group C underwent delayed transplantation 6 weeks after meniscectomy. One animal in group B developed infective arthritis and was not included. Six nonoperated knees served as controls. Four other knees were subjected to a sham procedure. Menisci were examined macroscopically and histologically at 6 weeks (group A and 2 sham-operated animals) and 1 year (group 13, C, controls, and 2 sham-operated animals). Results: Capsular ingrowth was observed in all allografts. At 1 year, osteoarthritic changes in the delayed transplant group were more pronounced than in the immediate transplant group. Menisci in nonoperated controls and sham-operated knees appeared normal. No differences in shrinkage of allografts were observed between groups A and B. Group C showed significantly more shrinkage than allografts in both group A (P = .004) and group B (P = .005). Two allografts in group C were completely degenerated. Differences in architecture of the allografts were not found between groups A, B, and C. In both the peripheral and central areas of transplanted menisci, the number of cells was frequently increased because of repopulation even at 6-week follow-up. Conclusions: Delayed meniscal allograft transplantation causes distinct structural damage to menisci in comparison with immediate transplantation