Case Series With Histopathologic and Radiographic Analyses Following Failure of Fresh Osteochondral Allografts of the Talus.

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BACKGROUND: Fresh osteochondral allografting of the talus is one treatment option for large chondral defects. Following positive early term results, failure rates of up to 35% have been reported. A retrieval study was performed to characterize failed talar allografts.

METHODS: Failed fresh osteochondral allografts of the talus were retrieved on revision. Cases of deep infection were excluded. After tissue fixation, samples were decalcified, embedded, and stained with Safranin-O/Fast Green, osteocalcin, tumor necrosis factor alpha (TNF-α), CD4, CD8, and CD68. Slides were graded according to the modified Mankin scoring system or severity scale. Medical record review was performed.

RESULTS: Eight allografts (7 patients) were retrieved from patients, following an average term of implantation of 31 months (range, 12-58). There were 3 types of allografts in this series (hemidome, n=5; segmental, n=2; bipolar, n=1). Reasons for transplantation were post-traumatic arthritis or osteonecrosis; reasons for revision were graft failure/collapse, nonunion, progressive arthritis, and/or pain. Prior to revision, all grafts exhibited collapse and subchondral lucencies. At the graft host interface, Safranin-O staining demonstrated substantial loss of sulfated glycosaminoglycans, Osteocalcin immunostaning was nearly absent, CD68 (indicating osteoclast activity) was predominantly exhibited, and CD4+ helper T cells as well as CD8+ cytotoxic T cells and NK cells-cell types commonly implicated in allogeneic organ transplant rejection-were found in high concentrations. TNF-α was present throughout the graft.

CONCLUSION: A histopathologic analysis of 8 retrieved, failed talar allografts was performed. Graft failure appeared to be primarily biologic, with an extensive loss of viable cartilaginous and osseous tissue at the graft-host interface. This study provides the first evidence of a potential CD4+ and CD8+ lymphocyte-mediated failure mechanism in fresh osteochondral allografts that were revised following collapse.

LEVEL OF EVIDENCE: Level IV, case series.





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