Effects of Articular Cartilage Defect Size and Shape on Subchondral Bone Contact: Implications for Surgical Cartilage Restoration

Osteoarthritis (OA) progression involves the deterioration of articular cartilage, which, without surgical intervention, will not spontaneously stop. A number of factors influence this progression, two of which are cartilage defect size and subchondral bone changes that occur, such as sclerosis. Microfracture surgery generates mechanically inferior fibrocartilage repair tissue and succeeds in stopping OA progression in small defects, while ACI produces highly organized hyaline-like cartilage that has been shown to restore function and stop OA progression in large defects. The most frequently quoted threshold size to guide defect management is 2 cm2 although there is relatively little clinical or biomechanical data to support this. Therefore, the purpose of this project was to determine the effect of defect size and shape on subchondral bone contact. Experimental biomechanical loading on bovine knees was preformed and defect subchondral bone contact was measured for defects ranging from 5 mm to 25 mm in diameter. Defect shape was also examined using oval – shaped defect. Results indicate that the current 2 cm2 threshold for guiding management of articular cartilage defects may be too conservative, as major subchondral bone contact was not realized in defects below 2.87 cm2 in our study. Furthermore, it was determined that subchondral bone contact was consistently higher in defect on the lateral condyle compared to that of the medial condyle. Preliminary testing of oval defect also suggests that the medial to lateral width of a defect may be more important than the absolute widest dimension of the defect.