1 Department of Orthopaedics and Traumatology, University Hospital of Patras, Greece
2 Laboratory of Dynamics and Structures, School of Mechanical Engineering, National Technical University of Athens, Greece
Due to their theoretical advantages, hip systems combining modular necks and large diameter femoral heads have gradually gained popularity. However, among others, concerns regarding changes in the load transfer patterns were raised. Recent stress analyses have indeed shown that the use of modular necks and big femoral heads causes significant changes in the strain distribution along the femur. Our original hypothesis was that these changes may affect early distal migration of a modular stem. We examined the effect of head diameter and neck geometry on migration at two years of follow-up in a case series of 116 patients (125 hips), who have undergone primary Metal-on-Metal total hip arthroplasty with the modular grit-blasted Profemur®E stem combined with large-diameter heads (>36 mm). We found that choice of neck geometry and head diameter has no effect on stem migration. A multivariate regression analysis including the potential confounding variables of the body mass index, bone quality, canal fill and stem positioning revealed only a negative correlation between subsidence and canal fill in midstem area. Statistical analysis, despite its limitations, did not confirm our hypothesis that choice of neck geometry and/or head diameter affects early distal migration of a modular stem. However, the importance of correct stem sizing was revealed.
Keywords: Grit-blasted, large-diameter femoral head, metal-on-metal, modular neck, stem subsidence, Total Hip Arthroplasty.
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* Address correspondence to this author at the Department of Orthopaedics and Traumatology, University Hospital of Patras, Rion, Greece, Postal Code GR-26504, Greece; Tel: +302610999940; Fax: +302610994579; E-mails: email@example.com