A missing link in the evolution of THR: "discovery" of the lateral femur.

Using cadaveric studies and mathematical models that include consideration of the iliotibial band (ITB) as a "tension band," the authors have demonstrated that compression loading occurs throughout the entire lateral femoral cortex from the apophyseal line of the greater trochanter to the lateral femoral epicondyle at the knee. This model suggests that the magnitude of this load on the medial and lateral cortices is proportional to the medial displacement of these cortices from the ITB. The authors have further demonstrated that the "tension band" model is more consistent with actual bone morphology and function than existing models and is a strong argument for the incorporation of design concepts such as lateral extensions into total hip arthroplasty femoral components. Such extensions would permit use of lateral femoral cortical bone as an additional base of prosthesis support, distributing loads over a greater area of the proximal femur. This model, therefore, would theoretically reduce the areas of stress concentration in diaphyseal bone and stress shielding of the proximal femur, both of which appear to be deficiencies of present femoral stem designs.