Overlapping Allografts Provide Superior and More Reliable Surface Topography Matching Than Oblong Allografts: A Computer-Simulated Model Study

Abstract

Background: Osteochondral allograft transplantation is 1 treatment option for focal articular cartilage defects of the knee. Large irregular defects, which can be treated using an oblong allograft or multiple overlapping allografts, increase the procedure’s technical complexity and may provide suboptimal cartilage and subchondral surface matching between donor grafts and recipient sites. Purpose: To quantify and compare cartilage and subchondral surface topography mismatch and cartilage step-off for oblong and overlapping allografts using a 3-dimensional simulation model. Study Design: Controlled laboratory study. Methods: Human cadaveric medial femoral hemicondyles (n = 12) underwent computed tomography and were segmented into cartilage and bone components using 3-dimensional reconstruction and modeling software. Segments were then exported into point-cloud models. Modeled defect sizes of 17 × 30 mm were created on each recipient hemicondyle. There were 2 types of donor allografts from each condyle utilized: overlapping and oblong. Grafts were virtually harvested and implanted to optimally align with the defect to provide minimal cartilage surface topography mismatch. Least mean squares distances were used to measure cartilage and subchondral surface topography mismatch and cartilage step-off. Results: Cartilage and subchondral topography mismatch for the overlapping allograft group was 0.27 ± 0.02 mm and 0.80 ± 0.19 mm, respectively. In comparison, the oblong allograft group had significantly increased cartilage (0.62 ± 0.43 mm; P < .001) and subchondral (1.49 ± 1.10 mm; P < .001) mismatch. Cartilage step-off was also found to be significantly increased in the oblong group compared with the overlapping group ( P < .001). In addition, overlapping allografts more reliably provided a significantly higher percentage of clinically acceptable (0.5- and 1-mm thresholds) cartilage surface topography matching (overlapping: 100% for both 0.5 and 1 mm; oblong: 90% for 1 mm and 56% for 0.5 mm; P < .001) and cartilage step-off (overlapping: 100% for both 0.5 and 1 mm; oblong: 86% for 1 mm and 12% for 0.5 mm; P < .001). Conclusion: This computer simulation study demonstrated improved topography matching and decreased cartilage step-off with overlapping osteochondral allografts compared with oblong osteochondral allografts when using grafts from donors that were not matched to the recipient condyle by size or radius of curvature. These findings suggest that overlapping allografts may be superior in treating large, irregular osteochondral defects involving the femoral condyles with regard to technique. Clinical Relevance: This study suggests that overlapping allografts may provide superior articular cartilage surface topography matching compared with oblong allografts and do so in a more reliable fashion. Surgeons may consider overlapping allografts over oblong allografts because of the increased ease of topography matching during placement.