Early histologic appearance of human patellar tendon autografts used for anterior cruciate ligament reconstruction

Nine patients underwent second-look arthroscopy and biopsy between 3 and 8 weeks after anterior cruciate ligament (ACL) reconstruction using autogenou s patellar tendon. All nine biopsies were taken from the central region of the graft. Every biopsy revealed viable cells in two different patterns. As early as 3 weeks after ACL reconstruction, there were areas that were very similar to patellar tendon control specimens with low nuclear counts, matu re collagen, and elongated, metabolically quiescent nuclear morphology. Oth er areas were hypercellular and associated intimately with neovascular inva sion. Vascularity of the grafts was present as early as 3 weeks after recon struction and increased in prevalence over the next 5 weeks. All specimens had areas of acellularity and degeneration. From these data, the authors co nclude that the transplantation of nonvascularized, autogenous patellar ten don is characterized by early viability of the graft both from original fib roblasts and by new cells that arise from neovascularity that is present as early as 3 weeks after ACL reconstruction.