Is patient weight a risk factor for breakage of smaller cementless femoral stems in total hip arthroplasty? A prospective monocentric cohort study of 251 femoral stems at risk with a mean follow-up of six years.

Abstract

Background: In 2014, based on biomechanical test results, the use of cementless Meije Duo™ (Corin, Cirencester, UK) stems (sizes 1 and 2) was contraindicated for patients weighing more than 60 kg to mitigate the risk of fracture. There is no data regarding the in vivo behavior of such components, therefore we did a retrospective study aiming to evaluate the incidence of stem breakage or failure in these patients, considering weight and activity level, with a minimum follow-up of four years.

Hypothesis: There is no greater risk of implant breakage for patients not following the ISO 7206-4 standard.

Methods: This retrospective, single-center, multi-operator study was conducted at a specialized hip prosthetic surgery center. It included all consecutive patients who received an cementless Meije Duo™ femoral stem (sizes 1 or 2) between 2007 and 2014, with at least four years of postoperative follow-up. Weight changes, complication occurrence, and the need for surgical revision were evaluated, alongside radiographic assessments for stem subsidence or non-integration.

Results: A total of 251 stems were analyzed, with a mean follow-up of 88 months (range, 77-109). Primary THA was performed in 241 cases (96%) and 10 (4%) were revision surgeries. The mean age at surgery was 59.3 years (range, 53-66 years), and the average weight was 66.2 kg (range, 40-103 kg). One hundred and fifty-eight THAs (62.9%, 158/251) were over 60 kg at the time of surgery. No stem breakages were observed at the final follow-up. Seven adverse events occurred (3.2%), including two dislocations, one instance of non-osseointegration, one case of femoral stem subsidence at three months without stem revision, and three femoral stem revisions (1.2%) (1 instance of subsidence at one year, 1 mechanical pain at seven years, 1 non-osseointegration following a periprosthetic fracture at 5 months). A significant increase in patient weight was observed (p = 0.02): 60% of THAs (140/233) experienced weight gain, with an average increase of 5 kg (range: 0.5-33 kg). Sixteen patients (6.8%, 16/233) had an inclusion weight <60 kg but > 60 kg at the last follow-up. Finally, the Devane score remained stable or increased in 176 patients (77.2%, 176/228).

Discussion: No stem breakage was observed in this cohort of patients considered at risk. A postoperative increase in body weight was noted in several cases, with some patients exceeding the weight limits set by the ISO 7206-4 standard. While these findings do not directly question the validity of the standard, they suggest that weight at the time of implantation may not be the sole parameter to consider when assessing the risk of stem breakage.

Level of evidence: IV; retrospective study, therapeutic study.