Articular cartilage adjacent to full thickness defects are subjected to excessive shear strains under compressive loading

Objective Full-thickness cartilage defects are commonly found in symptomatic knee patients, and are associated with progressive cartilage degeneration. Although the risk of defect progression to degenerative osteoarthritis is multifactorial, articular cartilage defects change contact mechanics and the mechanical response of tissue adjacent to the defect. The objective of this study was to quantify changes in intra-tissue strain patterns occurring at the defect rim and opposing tissue in an experimental model mimicking in vivo cartilage-on-cartilage contact conditions. Methods Macroscopically intact osteochondral explants with smooth surfaces were harvested form the femoral condyles of 9 months old bovine knees. Two groups were tested; reference group with intact cartilage (n=8) and defect group with a full thickness cylindrical defect (diameter 8 mm) in one cartilage surface from each pair (n=8). The explants with defect articular surface and the opposing intact cartilage were compressed at ?0.33 times body weight (350N) during cycles of 2s loading followed by 1.4s unloading. In plane tissue deformations were measured using displacement encoded imaging with stimulated echoes (DENSE) on a 9.4T MRI scanner. A two-sample t-test was used to assess statistical significance (p