EFFECTS OF POROUS COATING, WITH AND WITHOUT COLLAR SUPPORT, ON EARLY RELATIVE MOTION FOR A CEMENTLESS HIP-PROSTHESIS

In theory, porous or rough coatings could be used to reduce early post -operative relative motion about cementless hip prostheses. To investi gate this theory, we used detailed, non-linear finite element analysis to compare early relative motion about a well-fit Anatomical Medullar y Locking (AML) prosthesis for different amounts of porous coating (fu ll, proximal 2/3, and no coating), both with and without collar suppor t. Details of the model included quantitative computed tomography-deri ved (QCT-derived) geometric and material properties for the bone, and a no-tension interface condition at all bone-prosthesis interfaces, wi th Coulomb friction (mu = 1.73) over coated surfaces and zero friction elsewhere. Predicted values of relative motion for this well-fit devi ce were in the range of approximately 1-550 mum. The distribution of r elative motion was relatively insensitive to the amount of porous coat ing but was sensitive to collar support, while the magnitude of relati ve motion was sensitive to the porous coating and collar support. In a ddition, a reduction in the porous coating caused larger increases in relative motion when there was no collar support, indicating an intera ction between the effects of porous coating and collar support. For ex ample, distal twist increased (full vs 2/3 partial coating) by 38% wit h collar support and by 58% without collar support. These data suggest that porous coating, or other surface treatments which result in a hi gh coefficient of friction at the bone-prosthesis interface, may well be used to control the magnitude of early relative motion, particularl y when there is no collar support,