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BACKGROUND: Short stems in total hip arthroplasty (THA) have the potential to improve periprosthetic bone preservation compared to conventional stems due to a more anatomical distribution of biomechanical force. This study is a follow-up study of a randomised controlled trial using ultra-short and conventional stems in THA with the aim to investigate the long-term changes in periprosthetic bone mineral density (BMD) at 6 and 10 years post-THA.

METHODS: A cohort of 51 patients with hip osteoarthritis were randomized to either an ultra-short stem (n = 26) or a conventional stem (n = 25) group. Periprosthetic BMD was measured at 6- and 10-years post-surgery. Primary endpoint was BMD changes in Gruen zones 1 and 7. Lumbar spine, L1-4, BMD was used as an indicator of overall bone loss. Clinical outcome scores and BMD changes in Gruen zone 1-7 were used as secondary endpoints.

RESULTS: 37 hips, 17 ultra-short stems and 20 conventional stems, were followed up until 10 years. At 6- and 10-years post-THA, the ultra-short stem group had less periprosthetic BMD reduction compared to the conventional stem group in Gruen zone 1; mean differences (%) were -17.6 (CI, -23.4--10.6) and -18.3 (CI, -28.0--9.0), respectively (p < 0.001). There was similar BMD loss in Gruen zone 7 and zones 1-7 between groups. Compared to overall bone loss, the ultra-short stem group lost less BMD than the conventional group. Adverse events and clinical outcomes did not differ between groups.

CONCLUSIONS: Over a 10-year follow-up, THA using an ultra-short stem exhibited significantly reduced periprosthetic BMD loss in Gruen zone 1 compared to the conventional stem but this did not result in better clinical results. The observed preservation of bone density suggests potential long-term advantages of the ultra-short stem in minimising stress shielding and maintaining periprosthetic bone quality.

TRIAL REGISTRATION: ClinicalTrials.gov registration (number NCT01319227).