Stress distribution in fresh osteochondral allografts of different diameters and lengths under rolling loads: a finite element analysis

This study examined the biomechanical impact of fresh allograft bone-cartilage grafts of varying diameters and lengths on the cartilage surface (CS) and subchondral bone (SB) stress under rolling loads using finite element analysis (FEA), aiming to provide valuable insights for the clinical selection of graft sizes. Based on anatomical data of the normal adult male knee, a simplified 3D finite element model was established to simulate femoral medial condyle cartilage defects with diameters of 8–22 mm and to fill the defects with allografts of matching sizes. Subsequently, vertical and rolling loads were applied to simulate physiological loading conditions during the gait cycle of a normal person. Finally, the von Mises stress distribution on the CS and SB was analysed via FEA, comparing peak stresses and normal knee joint stresses to assess the biomechanical compatibility of different graft sizes and their impact on the local stress environment. Regardless of SB length, CS stress increased progressively as graft diameter increased under rolling load conditions. The highest CS stress ratio was observed with a 20 mm graft diameter, showing an approximately 23% increase compared with that seen with normal cartilage. These findings suggest that graft diameter plays a substantial role in determining postoperative biomechanical behaviour. Grafts of different diameters and lengths significantly affect postoperative stress distribution in the cartilage and SB. A 20 mm graft elicited the highest relative CS stress within the examined parametric range, whereas a 14 mm graft reduced CS stress but generated elevated subchondral stress. When the graft diameter exceeded 14 mm with a 5 mm SB length, the stress concentration was lower.