Randomized Comparison Between 3 Surface Treatments of a Single Anteverted Stem Design

Eighty patients (84 hips) randomly received an anteverted cobalt-chromium stem (Lubinus SP2; Waldemar Link, Hamburg, Germany) with matte, polymethyl methacrylate-coated, or polished surface (uncollared). Radiostereometry was used to study migration and wear; and the bone mineral density was studied with dual-energy x-ray absorptiometry at 6 months, 1 year, 2 years, and 5 years. The polished stems had subsided 0.1 to 0.2 mm more at 6 months and 0.3 to 0.4 mm more at 5 years than the matte and precoated versions (P < .0001) and subsided mainly inside the cement mantle. The rotations of the stem and the migration and wear of the cemented cup did not differ between the 3 groups. After 1 and 2 years, the polished stems had lost significantly less bone mineral in Gruen zones 1, 2, 6, and 7 (P = .004 to .03); but this difference had disappeared after 5 years. The period of improved bone remodeling around the polished version coincided with the early period of increased subsidence, suggesting that stem motions inside the mantle resulted in a favorable loading of the proximal femur. Our observations suggest that alternative shapes could be possible on future polished femoral stem designs.