Summary

This study investigates regional differences in the articular cartilage within lateral femoral condyle osteochondral allograft (OCA) donor tissue toward understanding the optimal locations from which to harvest OCA cores for transplantation.

Abstract

Introduction

Osteochondral allograft (OCA) transplantation is an effective treatment for large focal cartilage defects of the knee. Traditionally, orthotopic hemicondyle graft matching is performed to optimize recipient surface congruence. However, lateral femoral condyle (LFC) allograft tissue is more abundant than medial femoral condyle (MFC) allograft tissue and is sometimes used in a non-orthotopic fashion to treat MFC defects. Additionally, OCA cores may be harvested from a location on the allograft that does not correspond to the same location as the host defect. This study investigates regional differences in the articular cartilage within LFC donor tissue toward understanding the optimal locations from which to harvest OCA cores for transplantation.

Methods

Articular cartilage samples were obtained from human LFC hemicondyle allograft donor tissues (JRF Ortho, Englewood, CO) used clinically for OCA transplantation from December 2023 to July 2024. This work was exempt from institutional research board approval. After use, the remaining tissue specimens were collected, frozen wrapped in gauze soaked with protease inhibitor at -20°C, and then thawed at 4°C before analysis. Each specimen was separated into four regions (trochlea, anterior, central, and posterior condyle) from which samples were taken for histological, mechanical (compressive and tensile), and biochemical analysis. Tensile samples were trimmed to the top 1-mm of cartilage and evaluated in both the anterior-posterior (AP) and medial-lateral (ML) directions. Data are presented as mean±sd and analyzed with analysis of variance and Tukey’s post hoc testing at p<0.05 (n=4-6 per group).

Results

Tissue specimens were all from male donors aged 25.7±5.4 years. Time between tissue processing and surgery was 21.0±2.1 days. Histological evaluation demonstrated consistent hematoxylin & eosin staining among regions. Picrosirius red staining showed intense collagen staining throughout all sections, with an especially increased layer of intensity in the superficial layer of the anterior condyle. Safranin-O staining showed mildly increased glycosaminoglycan intensity in the anterior and central condyle sections. Mechanically, the compressive aggregate modulus of the central condyle (413.5±42.2 kPa) was 1.33 times that of the posterior condyle (309.8±47.0 kPa) (p=0.042). Ultimate tensile strength (UTS) displayed no significant differences across direction tested. However, the UTS of cartilage in the posterior condyle (19.8±5.6 MPa) was 1.78 times higher than that of the central region (11.1±4.2 MPa) (p=0.004). Quantification of collagen normalized to dry weight revealed that collagen content was 1.45 times higher in the anterior condyle (29.0±4.2%) compared to the trochlea (20.0± 2.1%) (p=0.001).

Conclusion

This study demonstrated regional differences in histological, mechanical, and biochemical properties within the articular cartilage of LFC allograft donor tissue intended for OCA transplantation. Biochemical analyses were consistent with histological analyses, with more intense picrosirius red staining in the anterior condyle consistent with the increased collagen content in that region. The higher aggregate modulus of the central condyle compared to the posterior condyle is consistent with decreased loading of the posterior condyle. Along with harvesting a donor core that will best restore recipient articular surface congruence, surgeons should also be aware of regional differences in donor tissue mechanics and matrix properties when harvesting cores from LFC allografts.