A review of joint and muscle load simulation relevant to in‐vitro stress analysis of the hip

Model analysis of the hip has become an important research technique in the assessment of implant performance in Total Hip Replacements (T.H.R.). In the literature to date, however, there is an absence of suitable criteria to aid in the selection of representative joint and muscle loading conditions relevant to such analyses. Consequently, the interpretation of information regarding the loading of the hip joint varies greatly between studies. The objective of this study, therefore, is to review the procedures used to establish these forces and to outline how they may be appliedto in-vitro modeltesting of the proximal femur and the pelvis. The muscles active at the hip joint are categorised with respect to their positions and primary actions. The magnitudes of the muscle and joint loads, as estimated by force determination studies employing in-vitro, in-vivo and mathematical modelling techniques, are reviewed. Applications illustrating the load simulations applied to the model analysis of an implanted Exeter femoral prosthesis and the in-vitro testing of cementless acetabular cups are also presented. While there is reliable information regarding the joint reaction between the femur and the acetabulum, it is difficult to represent accurately the muscular loading, due to the conflicting information presented in the literature. It is possible, however, to apply this information to load simulations in a limited manner in an attempt to predict trends in behaviour which are representative of the in-vivo situation.