Reproducing the hip center with a femoral neck-retaining implant.

Because of the recent trend for total hip arthroplasty in younger patients, more bone-preserving implants have been designed, based partly on the premise that maintenance of more bone stock would allow revision with standard primary implants. Another possible advantage of an implant that retains the femoral neck is that it may allow anatomical recreation of the center of the femoral head, femoral neck anteversion, anterior tilt, and caput-collum-diaphysis (CCD) angle, as well as femoral offset and leg length, without the use of modular implants. To determine whether the proximal femoral anatomy could be recreated, this study used computed tomography data and 3-dimensional modeling from 10 cadaver hips in 6 whole body specimens. Three femoral neck resection levels were investigated: 2 mm, 5 mm (recommended resection), and 10 mm from the base of the femoral neck. Results showed that the center of the femoral head, femoral neck anteversion, and CCD angle could all be recreated with available implant sizes, without modularity, within 2° and 1 mm on average. The addition of a modular neck provided no advantage in recreation of the hip center or other anatomical parameters. Use of a short metaphyseal femoral neck retaining-type of stem should allow restoration of anatomical parameters without the use of an exchangeable modular femoral neck.