Influence of Loading Conditions and the Superficial Tangential Zone in Contact Models of Articular Surfaces

Engineering tissue to repair articular surface defects remains a challenge. Normal zonal characteristics of articular cartilage throughout its thickness, particularly the superficial tangential zone (STZ), and normal material properties have not been reproduced in vitro in scaffolds nor in vivo in repairing defects. Without sufficient quality, such transplanted scaffolds in vivo may be doomed mechanically from the outset. The importance of the STZ in normal function [1–3] and deficient behavior of repair tissue [4–5] is well documented in the literature. Studies have modeled higher tensile properties in the STZ via transverse isotropy [6–9] or tension-compression nonlinearity [10] to better predict experimental results. Models incorporating an STZ with strain-dependent permeability [11–13] have indicated protection of underlying repairs. Permeable and impermeable rigid contact models [12] have been thought to bracket in vivo conditions. Recent efforts have been to create more complex models to better represent in vivo conditions [13]. This finite element study compares permeable and impermeable rigid contact models with a more realistic model to determine if the added complexity is warranted.