Contact models of repaired articular surfaces: influence of loading conditions and the superficial tangential zone

Abstract

The superficial tangential zone (STZ) plays a significant role in normal articular cartilage's ability to support loads and retain fluids. To date, tissue engineering efforts have not replicated normal STZ function in cartilage repairs. This finite element study examined the STZ's role in normal and repaired articular surfaces under different contact conditions. Contact area and pressure distributions were allowed to change with time, tension-compression nonlinearity modeled collagen behavior in the STZ, and nonlinear geometry was incorporated to accommodate finite deformation. Responses to loading via impermeable and permeable rigid surfaces were compared to loading via normal cartilage, a more physiologic condition, anticipating the two rigid loading surfaces would bracket that of normal. For models loaded by normal cartilage, an STZ placed over the inferior repair region reduced the short-term axial compression of the articular surface by 15%, when compared to a repair without an STZ. Covering the repair with a normal STZ shifted the flow patterns and strain levels back toward that of normal cartilage. Additionally, reductions in von Mises stress (21%) and an increase in fluid pressure (13%) occurred in repair tissue under the STZ. This continues to show that STZ properties of sufficient quality are likely critical for the survival of transplanted constructs in vivo. However, response to loading via normal cartilage did not always fall within ranges predicted by the rigid surfaces. Use of more physiologic contact models is recommended for more accurate investigations into properties critical to the success of repair tissues.

Finite element study of a tissue-engineered cartilage transplant in human tibiofemoral joint

“…Modelling the opposing cartilage layer as a deformable material would give a more accurate representation of the mechanics in the knee. Owen and Wayne (2011) showed that loading with a deformable cartilage layer results in increased contact area and decreased axial deformation and pore pressure compared with a rigid impermeable indenter; thus our results overestimate the axial deformation and pore pressure. However, the same study also demonstrated that radial and axial stresses and strains are similar in models of repair cartilage with a rigid impermeable indenter or with a deformable cartilage layer.…”

“…However, the same study also demonstrated that radial and axial stresses and strains are similar in models of repair cartilage with a rigid impermeable indenter or with a deformable cartilage layer. Furthermore, Owen and Wayne's (2011) results suggest that the rigid impermeable indenter may allow for reasonable comparisons between models in some instances. For example, the pore pressure is the highest in their 'NORMBOT' and lowest in their 'REP' models, regardless of how the indenter is modelled.…”

“…Another simplification with regard to modelling tibial cartilage was that tensioncompression nonlinearity was not included in the constitutive model. It is well known that collagen fibres contribute to higher tensile stiffness of AC and several computational models have successfully incorporated collagen fibres (Soulhat et al 1999;Wilson et al 2005b;Shirazi et al 2008;Ateshian et al 2009;Li et al 2009;Shirazi and Shirazi-Adl 2009;Owen and Wayne 2011).…”

The role of the superficial region in determining the dynamic properties of articular cartilage

“…A biomechanical failure of the collagen network in the STZ is postulated in many hypotheses as related to the development of osteoarthritis 14,59,60 Computational models have also been used to demonstrate how a viable superficial zone is critical to achieving long term survival in repairing articular cartilage 61,62 . This study demonstrates that although this layer is less stiff than the remainder of the tissue in compression, it plays a key role in elevating the dynamic material properties of the tissue.…”

Analysis of the Unilateral Contact Problem for Biphasic Cartilage Layers With an Elliptic Contact Zone and Accounting for Tangential Displacements

“…[2,3,11,13]). Many analytical solutions to the problem of contact interaction of articular cartilage surfaces in joints are available.…”