The effect of a collar and surface finish on cemented femoral stems: a prospective randomised trial of four stem designs

Purpose The optimal design for a cemented femoral stem remains a matter of debate. Over time, the shape, surface finish and collar have all been modified in various ways. A clear consensus has not yet emerged regarding the relative merits of even the most basic design features of the stem. We undertook a prospective randomised trial comparing surface finish and the effect of a collar on cemented femoral component subsidence, survivorship and clinical function. Methods One hundred and sixty three primary total hip replacement patients were recruited prospectively and randomised to one of four groups to receive a cemented femoral stem with either a matt or polished finish, and with or without a collar. Results At two years, although there was a trend for increased subsidence in the matt collarless group, this was not statistically significant (p = 0.18). At a mean of 10.1 years follow- up, WOMAC scores for the surviving implants were good, (Range of means 89-93) without significant differences. Using revision or radiographic loosening as the end-point, survivorship of the entire cohort was 93% at 11 yrs, (CI 87-97 %). There were no significant differences in survivorship between the two groups with polished stems or the two groups with matt stems. A comparison of the two collarless stems demonstrated a statistically significant difference in survivorship between polished (100 %) and matt (88 %) finishes (p = 0.02). Conclusions In the presence of a collar, surface finish did not significantly affect survivorship or function. Between the two collarless groups a polished surface conferred an improved survivorship.