Mapping of donor and recipient site properties for osteochondral graft reconstruction of subchondral cystic lesions in the equine stifle joint

Reasons for performing study: To improve osteochondral graft reconstruction of subchondral cystic lesions in the medial and lateral femoral condyles by matching the material properties of donor and recipient sites. Objectives: To measure biomechanical and biochemical parameters that influence the function and healing of osteochondral grafts used to reconstruct subchondral cystic lesions. Hypothesis: Suitable donor sites are available within the stifle joint for reconstructing the femoral condyles, despite considerable regional property variation. Methods: Fifty-six osteochondral cores were harvested from 6 distal femurs for initial studies that determined subchondral bone modulus of elasticity and ultimate stress. In a second study, 28 osteochondral cores were harvested from 6 distal femurs to measure cartilage aggregate modulus, thickness and sulphated glycosaminoglycan (sGAG) content. Using micro-CT imaging, subchondral bone mineral density and bone volume fraction were also measured. In both studies 2-dimensional contour plots using a bicubic interpolation method and normalised data were generated to allow visual comparison of joint surface characteristics. Statistical comparisons between donor and recipient site raw data were made using an ANOVA for repeated measures with a post hoc Tukey test. Results: Material properties of cartilage and bone vary considerably over the surface of the stifle joint but the central region of the medial condyle, where subchondral cystic lesions frequently occur, typically demonstrated bone strength and modulus values of the highest observed. Cartilage thickness and aggregate modulus were highest in the medial femoral condyle and axial aspect of the lateral condyle. Conclusions: Material properties of the grafts from the trochlear groove and axial aspect of the lateral trochlear ridge were the closest match for those found in the medial condyle, whereas properties of the lateral condyle were most similar to those found in the trochlear groove and axial aspect of the medial trochlear ridge.