Lower periprosthetic bone loss and good fixation of an ultra-short stem compared to a conventional stem in uncemented total hip arthroplasty

Abstract

Background and purpose — We hypothesized that an ultra-short stem would load the proximal femur in a more physiological way and could therefore reduce the adaptive periprosthetic bone loss known as stress shielding.

Patients and methods — 51 patients with primary hip osteoarthritis were randomized to total hip arthroplasty (THA) with either an ultra-short stem or a conventional tapered stem. The primary endpoint was change in periprosthetic bone mineral density (BMD), measured with dual-energy x-ray absorptiometry (DXA), in Gruen zones 1 and 7, two years after surgery. Secondary endpoints were change in periprosthetic BMD in the entire periprosthetic region, i.e. Gruen zones 1 through 7, stem migration measured with radiostereometric analysis (RSA), and function measured with self-administered functional scores.

Results — The periprosthetic decrease in BMD was statistically significantly lower with the ultra-short stem. In Gruen zone 1, the mean difference was 18% (95% CI: −27% to −10%). In zone 7, the difference was 5% (CI: −12% to −3%) and for Gruen zones 1–7 the difference was also 5% (CI: −9% to −2%). During the first 6 weeks postoperatively, the ultra-short stems migrated 0.77 mm more on average than the conventional stems. 3 months after surgery, no further migration was seen. The functional scores improved during the study and were similar in the 2 groups.

Interpretation — Up to 2 years after total hip arthroplasty, compared to the conventional tapered stem the ultra-short uncemented anatomical stem induced lower periprosthetic bone loss and had equally excellent stem fixation and clinical outcome.

MS conducted the study with patient inclusion, follow-up examinations, and collection and analysis of all data. He also wrote the manuscript. OS designed the study, supervised data collection, and helped with data analysis and manuscript preparation. OM, TA, HB, TE, and AS also helped with manuscript preparation.

The study was supported by grants from the following foundations: Ulla and Gustaf Ugglas Stiftelse, Åke Wibergs Stiftelse, Loo and Hans Ostermans Stiftelse, the Sven Norén Foundation, the regional agreement on medical training and clinical research (ALF) between Stockholm County Council and Karolinska Institutet, and the DePuy Johnsson and Johnsson Foundation for Clinical Research. DePuy Johnsson and Johnsson and the senior author (OS) signed a standard legal study agreement that economic support was granted unconditionally to perform the study and that DePuy Johnsson and Johnsson would have no influence on the study design, data analysis, or publication.

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