Design modifications of the uncemented Furlong hip stem result in minor early subsidence but do not affect further stability

Abstract

Background and purpose — Even small design modifications of uncemented hip stems may alter the postoperative 3-D migration pattern. The Furlong Active is an uncemented femoral stem which, in terms of design, is based on its precursor—the well-proven Furlong HAC—but has undergone several design changes. The collar has been removed on the Active stem along with the lateral fin; it is shorter and has more rounded edges in the proximal part. We compared the migration patterns of the uncemented Furlong HAC stem and the modified Furlong Active stem in a randomized, controlled trial over 5 years using radiostereometry (RSA).

Patients and methods — 50 patients with primary osteoarthritis were randomized to receive either the HAC stem or the Active stem. The patients underwent repeated RSA examinations (postoperatively, at 3 months, and after 1, 2, and 5 years) and conventional radiography, and they also filled out hip-specific questionnaires.

Results — During the first 3 months, the collarless Active stem subsided to a greater extent than the collar-fitted HAC stem (0.99 mm vs. 0.31 mm, p = 0.05). There were, however, no other differences in movement measured by RSA or in clinical outcome between the 2 stems. After 3 months, both stem types had stabilized and almost no further migration was seen.

Interpretation — The Active stem showed no signs of unfavorable migration. Our results suggest that the osseointegration is not compromised by the new design features.

Recruitment of patients and operations was done by GF and MS. The data were analyzed by EW, GF, and MS. The paper was written by EW and reviewed by GF and MS.

We thank Håkan Leijon of the RSA laboratory in Lund, Skåne University Hospital, for help in computerizing the RSA pictures and data, and Phillipe Wagner, Statistician, RC Syd, Clinical Sciences, Skåne University Hospital for statistical advice.

JRI Ltd. sponsored the RSA examinations in this study, but did not take part in planning, data collection, analysis, interpretation of the results, or in writing of the manuscript. Otherwise, no benefits have been received or will be received from a commercial party related directly or indirectly to the subject of this article.