title: Polyethylene wear after total hip arthroplasty: the effect of a modular femoral head with an extended flange-reinforced neck.
abstract: The use of modular components in total hip arthroplasty has been thought to contribute to accelerated polyethylene wear. Specifically, a modular femoral head with a flange extension and a longer neck may cause increased wear. The purpose of the current study was to evaluate the effect of a flange extension on polyethylene wear. Ninety-one patients who had had a total of 100 primary total hip arthroplasties were evaluated after an intermediate duration of follow-up. All of the acetabular components consisted of a hemispherical titanium-alloy fiber-mesh porous-coated shell with a nonelevated modular polyethylene liner; they were inserted without cement and with use of supplemental screws through the dome after so-called line-to-line reaming. All of the femoral components consisted of a modular head with a diameter of twenty-eight millimeters and either a long neck (with a flange extension) or a short or medium neck (without a flange extension). The study group comprised sixty-two patients (sixty-six hips) who had had radiographic evaluation that was adequate to allow the valid measurement of polyethylene wear. Thirty-two hips were in men, and thirty-four were in women. The mean age of the patients was fifty-six years, the mean weight was seventy-three kilograms, and the mean duration of follow-up was 6.1 years (range, four to eight years). The rate of polyethylene wear in the eleven hips in which the femoral component had a flange extension was significantly greater than that in the fifty-five in which the femoral component did not have a flange extension (mean, 0.17 compared with 0.11 millimeter per year; p = 0.009). Multivariate analysis showed that the presence of a flange extension was associated with increased polyethylene wear to a greater degree (F = 2.86) than were all other variables that were measured, including a younger age (F = 1.72), a more vertical angle of the acetabular component (F = 0.49), a heavier weight (F = 0.14), male gender (F = 0.11), and a smaller initial thickness of the polyethylene (F = 0.02). These data support an association between the presence of a modular femoral head with a flange extension and an accelerated rate of polyethylene wear. The presumed mechanism is an increase in peripheral, or so-called rim, impingement of the flange-reinforced neck on the acetabulum due to a decrease in the ratio between the diameters of the femoral head and neck.
authors.affiliation: Division of Orthopaedic Surgery, Scripps Clinic, La Jolla, California 92037, USA.
authors.forename: A G
authors.initials: AG
authors.lastname: Urquhart
authors.forename: D D
authors.initials: DD
authors.lastname: D'Lima
authors.forename: E
authors.initials: E
authors.lastname: Venn-Watson
authors.forename: C W
authors.initials: CW
authors.lastname: Colwell
authors.forename: R H
authors.initials: RH
authors.lastname: Walker
mesh_terms: D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation*; D005260:Female; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008875:Middle Aged; D011095:Polyethylenes; D011446:Prospective Studies; D011474:Prosthesis Design; D011475:Prosthesis Failure
chemical_list: D011095:Polyethylenes