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

We found that cortical distance along the femoral calcar is directly correlated with the model of the stem implanted ('standard' or 'varus') and with the head diameter. This cortical distance indicates optimal collar size, which would grant maximum calcar coverage without prosthetic overhang. Collar size should be proportional to the size of the operated hip, and should be larger for 'varus' stem models than for 'standard' stem models.