Cartilage thickness mismatches in patellar osteochondral allograft transplants affect local cartilage stresses

Abstract

Osteochondral allograft implantation is a form of cartilage transplant in which a cylindrical graft of cartilage and subchondral bone from a donor is implanted into a patient's prepared articular defect site. No standard exists for matching the cartilage thickness of the donor and recipient. The goal of this study was to use finite element (FE) analysis to identify the effect of cartilage thickness mismatches between donor and recipient cartilage on cartilage stresses in patellar transplants. Two types of FE models were used: patient‐specific 3D models and simplified 2D models. 3D models highlighted which geometric features produced high‐stress regions in the patellar cartilage and provided ranges for the parameter sweeps that were conducted with 2D models. 2D models revealed that larger thickness mismatches, thicker recipient cartilage, and a donor‐to‐recipient cartilage thickness ratio (DRCR) < 1 led to higher stresses at the interface between the donor and recipient cartilage. A surface angle between the donor‐recipient cartilage interface and cartilage surface normal near the graft boundary increased stresses when DRCR > 1, with the largest increase observed for an angle of 15°. A surface angle decreased stresses when DRCR < 1. Clinical Significance: This study highlights a potential mechanism to explain the high rates of failure of patellar OCAs. Additionally, the relationship between geometric features and stresses explored in this study led to a hypothetical scoring system that indicates which transplanted patellar grafts may have a higher risk of failure.

Subchondral Bone Alignment in Osteochondral Allograft Transplants for Large Oval Defects of the Medial Femoral Condyle: Comparison of Lateral versus Medial Femoral Condyle Donors

“…These variations in local stresses have been thought to be great enough to kill chondrocytes or inhibit graft integration, potentially leading to graft failure. 53 Several animal studies have provided a foundation for the idea that the subchondral bone is crucial for graft survival. In their in vivo sheep and goat models of femoral condyle OCA, Von Rechenberg et al 57 and Pallante-Kirchura et al 59 found that step-off at the subchondral bone level was a risk factor for subchondral cyst formation.…”

“…52 These differences have been shown to result in abnormal force attenuation and distribution, especially in the region near the graft:host interface. 53 The purpose of this study was to use surface contour mapping to determine whether using a contralateral LFC versus an ipsilateral MFC OCA graft plays a role in the ability of donor subchondral bone to align with the native condyle subchondral bone when treating large oval osteochondral defects of the MFC.…”