Contact Stresses in the Human Hip: Implications for Disease and Treatment

Contact stresses in the hip articular surfaces relate in some way to normal maintenance as well as destruction of joints. In vivo determinations of cartilage-on-cartilage contact pressure histories have never been reported, and current technology does not allow such measurements without the potential for artifact: all experimental methods require introducing some material between the surfaces, and all numerical methods have yet to be fully validated. Nonetheless, a variety of distinct experimental and numerical approaches lead to estimates of contact stresses and surprisingly, despite the choice of technique, values for peak contact stresses lie within a range of one order of magnitude (i.e. 0.5–5.0 MPa) and usually closer. Pathological conditions increase this to the range of over 5.0 MPa, while surgical procedures designed to reduce peak pressures theoretically can achieve reductions. Two critical unresolved issues are 1.) What aspect of the contact stress history (e.g. contact stress gradients over time) in fact cause the biological responses? 2.) What level of contact stress history is tolerated by the cartilage? Future research will need to address these critical issues.