Bendable osteochondral allografts for patellar resurfacing: A finite element analysis of congruence

Osteochondral allograft (OCA) transplantation provides a safe and effective treatment option for large cartilage defects, but its use is limited partly due to the difficulty of matching articular surface curvature between donor and recipient. We hypothesize that bendable OCAs may provide better curvature matching for patella transplants in the patellofemoral joint (PFJ). This finite element study investigates PFJ congruence for unbent and bendable OCAs, at various flexion angles. Finite element models were created for 12 femur-patella OCA pairings. Two grooves were cut in each OCA bony substrate, allowing the articular layer to bend. PFJs with either unbent (OCA) or permanently bent (BOCA) allografts were articulated from 40 to 70 degrees flexion and contact area was calculated. OCAs and BOCAs were then shifted 6 mm distally toward the tibia (S-OCA, S-BOCA) to investigate the influence of proximal-distal alignment on congruence. On average, no significant difference in contact area was found between native PFJs and either OCAs or BOCAs (p > 0.25), indicating that both types of allografts restored native congruence. This result provides biomechanical support in favor of an emerging surgical procedure. S-BOCAs resulted in a significant increase in contact area relative to the remaining groups (p < 0.02). The fact that BOCAs produced equally good results implies that bendable allografts may prove useful in future surgical procedures, with the possibility of transplanting them with a small distal shift. Surgeons who are reluctant to use OCAs for resurfacing patellae based on curvature matching capabilities may be more amenable to adopting BOCAs.