A new short uncemented, proximally fixed anatomic femoral implant with a prominent lateral flare: design rationals and study design of an international clinical trial

Abstract

BackgroundAnatomic short femoral prostheses with a prominent lateral flare have the potential to reduce stress-shielding in the femur through a more physiological stress distribution to the proximal femur. We present the design rationale of a new short uncemented, proximally fixed anatomic femoral implant and the study design of a prospective multi-centre trial to collect long-term patient outcome and radiographic follow up data.MethodsA prospective surveillance study (trial registry NCT00208555) in four European centres (UK, Italy, Spain and Germany) with a follow up period of 15 years will be executed. The recruitment target is 200 subjects, patients between the ages of 18 and 70 admitted for primary cementless unilateral THA will be included. The primary objective is to evaluate the five-year survivorship of the new cementless short stem. The secondary objectives of this investigation are to evaluate the long term survivorship and the clinical performance of the implant, the impact on the subjects health related Quality of Life and the affect of the prosthesis on bone mineral density. Peri- and postoperative complications will be registered. Clinical and radiographic evaluation of prosthesis positioning will be done post-operatively and at 3, 6, 12, 24, 60, 120 and 180 months follow up.DiscussionShortening of the distal stem can maximise bone and soft tissue conservation. New stem types have been designed to improve the limitations of traditional implants in primary THA. A new, uncemented femoral short stem is introduced in this paper. A long-term follow up study has been designed to verify stable fixation and to research into the clinical outcome. The results of this trial will be presented as soon as they become available.

Inter-subject variability effects on the primary stability of a short cementless femoral stem

“…There is still some debate on the use of short stems and their ability to achieve immediate postoperative stability (Renkawitz et al, 2008;Shah et al, 2009;Santori and Santori, 2010;Khanuja et al, 2011;Bieger et al, 2012). It is believed that young and active patients would benefit from their use.…”

“…A proximal lateral flare in shorter stems may reduce stress-shielding and produce a more physiological stress distribution. However, concerns exist about their primary torsional stability and such stems are not ideally suited to all patients due to the minimum area of healthy cancellous bone required for fixation (Renkawitz et al, 2008).…”

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

“…Design rationales for the ultra-short stem are an anatomical wedge shape, a prominent lateral flare, and absence of a diaphyseal stem. These features are claimed by the manufacturer to provide initial stability both vertically and rotationally and, together with a high horizontal neck resection, ensure load transfer to both the medial and the lateral aspects of the proximal femoral metaphysis (Walker et al 1999, Renkawitz et al 2008, Toth et al 2010). The macrotexture of the surface is stepped to increase ingrowth area and to transform tangential forces into compressive loads to the bone (Ghera and Pavan 2009).…”

CORR Insights®: Long-term Results and Bone Remodeling After THA With a Short, Metaphyseal-fitting Anatomic Cementless Stem

“…Despite the excellent reported results, the Immediate Postoperative Stability (IPS) stem (DePuy, Warsaw, IN) used by the authors, is no longer available, having been replaced by the Proxima (DePuy, Warsaw, IN) component, a newer generation design. The new implant has been described as incorporating the design philosophy of the previous device, while enhancing the fixation surface and removing the superfluous distal stem [11]. The potential benefits of these modifications are welcome, and other authors have presented sound rationale and in vitro evidence for the new generation implant [11,13,14].…”

“…The new implant has been described as incorporating the design philosophy of the previous device, while enhancing the fixation surface and removing the superfluous distal stem [11]. The potential benefits of these modifications are welcome, and other authors have presented sound rationale and in vitro evidence for the new generation implant [11,13,14]. However, even theoretically sound design changes that received regulatory approval may occasionally be prone to unexpected adverse events that become apparent only after unrestricted clinical use, as illustrated by a number of recent examples including symptomatic taper corrosion and catastrophic modular neck failures [1,10].…”