Effect of circumferential plasma-spray porous coating on the rate of femoral osteolysis after total hip arthroplasty

Background: Osteolysis of the femur has been a serious problem associated w ith some designs of total hip-replacement implants; it frequently leads to failure of the femoral component. We evaluated the effect of a circumferent ial plasma-spray porous coating on the rate of osteolysis in a study that i ncluded two groups of hips, each of which received an implant with the same design except for the extent of the porous coating. Our goal was to determ ine the possible role of circumferential porous coating in protecting the b one-implant interface from osteolysis. Methods: A series of consecutive primary total hip replacements performed,v ith insertion of the Mallory-Head implant without cement was divided into t wo study groups, The first 126 hips (Group 1) were treated with a femoral s tem that had a noncircumferential plasma-spray porous titanium coding, The next ninety hips (Group 2) were treated with a circumferentially coated ste m of the same design, The average duration of radiographic follow-up was 7. 8 years in Group 1 and 7.5 years in Group 2. Results: The average rate of polyethylene wear was similar for the two grou ps (0.187 millimeter per year in Group 1 and 0.189 millimeter per year in G roup 2). The prevalence of osteolysis in Group 1 (40 percent; fifty of 126 hips) was significantly higher than that in Group 2 (10 percent; nine of ni nety hips) (p < 0.001). Osteolysis remote from the joint space (distal to z ones 1 and 7) was found in 11 percent (fourteen) of the hips in Group 1 but in none of those in Group 2 (p = 0.0004). The average total area of osteol ysis in Group 1 (5.0 square centimeters) was significantly larger than that in Group 2 (2.9 square centimeters) (p < 0.05), Conclusions: A circumferential plasma-spray titanium porous coating on the femoral component of a total hip-replacement prosthesis inserted without ce ment appears to provide an effective barrier preventing wear debris from ga ining access to the endosteal surface of the femur and the greater trochant er. This finding supports the hypothesis of the so-called effective joint s pace, which predicts that wear debris from the joint bearing can migrate, d riven by intracapsular pressures, to all areas to which joint fluid has acc ess and thus can result in osteolysis. The reduction of the prevalence of o steolysis and the elimination of osteolysis from the zones remote from the joint space by the use of a circumferential plasma-spray porous coating ind icates that the femur was effectively sealed off from the joint space, We b elieve that the durability and longevity of the femoral component should be enhanced by the use of such a coating.