Histologic Analysis of an Exact-Fit, Autogenous, Osteochondral Transplantation Model
Abstract & Commentary
Synopsis: Macroscopic analysis of autogenous osteochondral transplants revealed a smooth surface integrated with the surrounding native cartilage, but the histologic findings of implanted cartilage differed from normal articular cartilage.
Source: Makino T, et al. Histologic analysis of the implanted cartilage in an exact-fit osteochondral transplantation model. Arthroscopy. 2001;17(7):747-751.
Focal chondral defects pose an especially difficult problem because of the limited ability of cartilage to self-repair. Theoretically, osteochondral autograft transplantation offers the potential to restore the articular surface with hyaline cartilage that is well approximated to the surrounding native articular cartilage. Clinical and animal studies have demonstrated good congruity of the articular surface following autogenous osteochondral transplantation. However, the histology of osteochondral grafts has not been described in detail.
The gross appearance and histology of exact-fit osteochondral transplantation was characterized in 16 skeletally mature, female, Japanese white rabbits. Using the Osteochondral Autograft Transfer System (OATS, Arthrex Inc, Naples, Fla), a full-thickness osteochondral plug was harvested from the femoral condyle. The plug was completely removed and precisely reinserted to its original site in the femoral condyle. Four rabbits were sacrificed at 2, 4, 12, and 24 weeks, and the implanted autografts were evaluated.
Macroscopically, a slight gap around the graft was visible at 2 weeks that was replaced with granulation tissue but still detectable at 4 weeks. The plug surface had good congruity with the surrounding normal cartilage at 12 and 24 weeks. At 2 and 4 weeks, the implanted graft had thicker cartilage, an increased number of chondrocytes, and larger intracytoplasmic vacuoles compared to the normal cartilage. Although the architecture was discernable, the middle and deep zones contained clusters of round and polygonal hypertrophic chondrocytes at 12 and 24 weeks.
In an exact-fit model, the osteochondral transplant showed good congruity with the surrounding articular cartilage. However, the histologic appearance of the implanted graft revealed thicker cartilage and an increased number of abnormal chondrocytes, which more closely resembles immature articular cartilage.
Comment by Brian J. Cole, MD, MBA
Makino and associates did an excellent job in describing the macroscopic and microscopic appearance of exact-fit autogenous osteochondral transplants over 24 weeks. Because this is an exact-fit model, the study represents an ideal scenario even more precise than the clinical situation. Recently, we have seen a few patients treated with multiple small plugs presenting with reoccurring symptoms and arthroscopic findings of plug degeneration. While this has encouraged us to use a fewer number of larger sized plugs for the treatment of smaller chondral lesions (ie, < 2 cm2), comparisons of multiple-plug mosaicplasty to a single-plug osteochondral autograft procedure may help to clarify the superiority of one technique over another. Makino et al believe that the immature histologic appearance of the implant cartilage may have consequences for the viability of the graft over longer time periods, but this remains to be determined. Clearly, more work will need to be done to clarify the biochemical characteristics of the cartilage and bone associated with these findings. Despite its simplicity and intuitive appeal, osteochondral autografting is a procedure that will require further investigative efforts.
Dr. Cole, Assistant Professor, Orthopaedic Surgery, Rush Presbyterian Medical Center, Midwest Orthopaedics, Chicago, is Associate Editor of Sports Medicine Reports.
Author Acknowledgments: Dr. Cole would like to thank Shane Nho, MS, for his help in preparing the manuscript.
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