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 o f the use of a porous-coated collarless femoral component in total hip arthroplasties without cement. Our study focused on the comparative p roximal strain pattern, bone ingrowth, and cortical porosity of the tw o types of prostheses. We used a trochanteric mire marker to measure s ubsidence. The use of the limb was assessed with gait analysis. Twelve weeks after the operation, the collarless components had significantl y greater bone ingrowth proximally (p = 0.003) and were associated wit h significantly lower cortical porosity (p = 0.006). There were no dif ferences between the groups with regard to either axial or hoop strain . While the group that had a collarless prosthesis had significantly l ess proximal-medial radiolucency (p = 0.03), there were no differences between the groups with regard to subsidence. CLINICAL RELEVANCE: The present study demonstrated greater bone ingrowth and less cortical po rosity with the use of collarless prostheses. This may be related to t he ability of these components to settle under repeated physiological loading during the early postoperative recovery period. In doing so, t he prosthesis may maintain a more optimum fit and thus, in the long te rm, may exhibit less relative motion with respect to the femoral canal . The amount of this subsidence appears to be slight and should not me asurably alter the position of the femoral component.