Proximal femoral anatomy and collared stems in hip arthroplasty: is a single collar size sufficient?

Background Even if the benefits of collars are unclear, they remain widely used, in several femoral stem designs. This study aimed to determine whether collar size should be proportional to hip dimensions and morphology. The hypothesis was that the collar should be larger for greater stem sizes and for varus femoral necks. Methods Computed Tomography scans of 204 healthy hips were digitally analysed and manually templated to determine principle dimensions, appropriate stem size and model, as well as cortical distance at the femoral calcar (ideal collar size). Results Univariable analysis revealed that cortical distance was moderately correlated with mediolateral offset ( r = 0.572; p