The effect of the medial collar in total hip arthroplasty with porous-coated components inserted without cement. An in vivo canine study.

We performed an in vivo study in a canine model to compare the results of the use of a porous-coated collared femoral component with those of the use of a porous-coated collarless femoral component in total hip arthroplasties without cement. Our study focused on the comparative proximal strain pattern, bone ingrowth, and cortical porosity of the two types of prostheses. We used a trochanteric wire marker to measure subsidence. The use of the limb was assessed with gait analysis. Twelve weeks after the operation, the collarless components had significantly greater bone ingrowth proximally (p = 0.003) and were associated with significantly lower cortical porosity (p = 0.006). There were no differences between the groups with regard to either axial or hoop strain. While the group that had a collarless prosthesis had significantly less proximal-medial radiolucency (p = 0.03), there were no differences between the groups with regard to subsidence.