Differences in the Radius of Curvature Between Femoral Condyles Implications for Osteochondral Allograft Matching

Background: The radius of curvature (ROC) is an important variable related to potential cartilage incongruities in the transplantation of a large femoral osteochondral allograft. The anterior-posterior length (APL) of a condyle is used as a criterion for donor-graft acceptance. We hypothesized that there would be a linear correlation between the ROC and APL of a condyle, that the ROC and APL would differ significantly between the medial femoral condyle (MFC) and the lateral femoral condyle (LFC), and that a donor graft from the LFC would be suitable for an MFC defect. Methods: Knee magnetic resonance imaging scans of 147 patients with no cartilage defects were analyzed. Best-fit circles in the sagittal plane were determined at standardized locations on each condyle. Assuming the use of a 20-mm graft that was flush to the edges of the native cartilage, the central graft prominence was calculated for potential donor-host differences in the ROC. Results: There was a linear correlation between the ROC and APL. There were significant differences in the mean ROC and APL between the MFC and LFC. Based on calculations of the central graft prominence among all ROC combinations within the patient group, 100% of potential medial-to-medial, 97.8% of lateral-to-lateral, and 92.5% of lateral-to-medial transplantations would produce a central graft prominence of < 1 mm. On average, an allograft harvested from an LFC (mean ROC, 25.7 mm; mean APL, 69.8 mm) implanted into an MFC defect site (mean ROC, 31.9 mm; mean APL, 66.6 mm) would have a central graft prominence of 0.4 +/- 0.3 mm. Conclusions: Assuming a maximum central graft prominence tolerance of 11 mm, our findings demonstrate that matching the ROC or APL would not be necessary for potential medial-to-medial or lateral-to-lateral allograft transplants within this patient group. Implantation of an LFC donor allograft into an MFC defect is also supported by our findings.