Abstract
Introduction
Ceramic femoral heads have proven to be more scratch resistant with better wettability and improved wear characteristics compared to metal heads in the laboratory setting. The objective of this study was to compare long-term survivorship and in vivo wear rates of ceramic and metal femoral heads against conventional polyethylene articulation in young patients.
Materials and Methods
Thirty-one matched pair of alumina and metal femoral heads against conventional polyethylene in young patients (≤ 65 years) were analyzed for wear and failures for mechanical reasons. The match was based on gender and age at the time of surgery. All procedures were performed between June 1989 and May 1992 by a single surgeon via posterolateral approach, using non-cemented RB (Ranawat-Bernstein) stems, HG II (Harris-Galante) cups, 4150 conventional polyethylene and 28mm femoral heads.
Hospital for Special Surgery (HSS) hip score was used for clinical analysis. Wear measurements were performed between the initial anteroposterior standing pelvis radiographs, at a minimum of one year after the index procedure to eliminate the effect of bedding-in period, and the latest follow-up. Two independent observers analyzed polyethylene wear rates using the computer-assisted Roman 1.70 software. In revision cases, the wear rates were calculated from radiographs prior to revision surgery. A pair student t test was performed to analyze the statistical difference. Two-tailed ρ values less than 0.05 were considered statistically significant.
Results
The mean age was 54.5 ± 8.5 at the time of surgery (range 23.3–65). Average clinical and radiographic follow-up were 17 ± 2.1 (range 12.8–20) and 14.1 ± 2.6 years (range 10–19.1) respectively. The mean HSS score in ceramic and metal groups were 30.4 ± 8 (range 24–56) and 36.6 ± 4.7 (range 20–40) respectively. The mean wear rate for the ceramic group and the metal group were 0.086 ± 0.046 mm/year and 0.137 ± 0.052 mm/year, respectively which was statistically significant (p < 0.001). There were no revisions in the ceramic group for osteolysis or loosening, however one patient required a strut graft for femoral osteolysis that was distal to the tip of the implant due to non-circumferential porous coating of the stem. There were 3 cup revisions in the metal group, all for acetabular osteolysis, and no stem lysis or loosening. The Kaplan-Meier survivorship for revision for mechanical failure in the ceramic and metal group was 100% and 90.3% respectively.
Discussion
The low mean wear rate of ceramic compared to metal in this study is consistent with previously published laboratory reports. There was no revision for loosening or osteolysis in the ceramic group, with 100% survivorship for revision due to mechanical failures, which demonstrates superior durability of this material compared to metal femoral heads. The strength of this study is that this the first long-term report comparing ceramic and metal femoral heads against conventional polyethylene using a matched pair analysis in young patients.
