Comparison of bone remodelling around short stem and conventional straight stem in total hip replacement: a prospective randomized radiographic and dual-energy X-ray absorptiometric study.

Objective: The aim of study was to evaluate periprosthetic bone mineral density (BMD) changes of proximal femur, osseointegration and clinical outcomes after implantation of short-stemmed and conventional straight-stemmed prostheses.

Methods: This prospective, randomized study included 50 patients with unilateral total hip replacement. The patients were randomized into 2 cohorts: patients with a cementless short stem Metha (n=25) and patients with a cementless conventional straight stem Bicontact evaluated as the control (n=25). Periprosthetic BMD changes were measured using a DEXA performed at one-week, 3-monts, 6-months and 1-year follow up. Clinical evaluation with Harris hip score (HHS) and radiographic assessment were performed through a 1 year follow up.

Results: Compared to 1-week postoperative assessment, there were differences in BMD changes between the groups at the final follow-up in all ROIs, with statistical significances in ROI 1, 2, 3, 6 and 7. The loss of periprosthetic BMD in all ROIs around straight stems at each time-point was observed. There was a tendency towards a regain of BMD in all ROIs at 1-year follow-up compared to the 3-months postoperative assessment with the short stems. Less pronounced bone loss was observed around the short stems that the straight stems in ROI 1 (‒2.9 % % vs ‒16.2 %), 5 (‒4.7 % vs ‒8.9 %) and 7 (‒8.6 % vs ‒20 %). The periprosthetic BMD exceeded baseline values in the short stem cohort in ROI 2 (+4.4 % vs ‒5 %), 3 (+5.6 % vs ‒2.5 %) and 6 (+4.3 % vs ‒10 %). All stems had a radiographically stable fixation. Stress shielding-related bone resorption was markedly lower in the short stem cohort. The HHS score was comparable between the two cohorts.

Conclusion: The implant-specific stress shielding altered the proximal loading condition for both stems; however, the results of this study suggest a more physiological strain distribution with the short stems versus the straight stems (Tab. 3, Fig. 3, Ref. 25).