POLYETHYLENE WEAR IN CASES USING FEMORAL STEMS OF SIMILAR GEOMETRY, BUT DIFFERENT METALS, POROUS LAYER, AND MODULARITY

Ln this report, 83 total hip arthroplasties in 75 patients with femora l stems of similar geometry but different metals, porous surfaces, and femoral head-neck; design were compared at a mean follow-up of 66 mon ths (range, 40-104 months). One type of acetabular component and polye thylene were implanted in all hips. The femoral stem was monoblock in 25 hips, and in 58 it had a modular head-neck piece; 70 stems had chro me-cobalt heads, and 13 heads were titanium. Equally satisfactory clin ical results were obtained with either type of femoral implant (i.e., modular and monoblock). The calculated average annual linear polyethyl ene wear was significantly higher for the titanium stems with a plasma -spray porous surface and chrome-cobalt head on a Morse taper than the chrome-cobalt, beaded,monoblock stems (0.22 mm/year vs 0.07 mm/year, P < .0001). The prevalence of periprosthetic osteolysis was higher for these modular sterns (15.7% vs 0%), but this difference was not stati stically significant (P = .09). Gross corrosion was present on the tap er surfaces of an autopsy-retrieved femoral implant with a modular cob alt-chrome head on a titanium stem. Particles of chromium 3-orthophosp hate were present at the taper rim and in the periarticular tissues.