A Prospective Case Series Examining the Use of a Large-Head Metal-on-Metal Total Hip System

摘要

To minimize wear-related failures and the risk of post-operative instability, large-head metal-on-metal (MoM) total hip replacement (THR) systems were introduced. However, concerns have been raised following high early failure rates of these implants. The purpose of the present study was to report the early clinical results of our center's experience using a large-head MoM THR system. From October 2005 to May 2010, 88 patients (53 males, 35 females- 89 hips) with a mean age of 59.7 ± 9.8 yr (range: 20 to 79) had the CONSERVE~® Total Hip with BFH~® (Big Femoral Head, diameter 36-54 mm) MoM and a modular femoral system (Profemur™) implanted by four surgeons. The mean body mass index was 29.5 ± 6.2 (range: 21.2 to 44.8). Post-operative follow-up consisted of physical examination, standard radiographs, and three patient-reported outcomes: Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), modified Harris Hip Score (HHS), and University of California at Los Angeles (UCLA) Physical Activity Scale. At mean follow-up of 30 months (range: 24 to 72), all outcomes from the whole cohort showed improvement (p ＜ 0.001). Mean WOMAC scores increased from 49.1 (pre-surgery) to 83.6 (follow-up) (pain), 44.5 to 73.2 (stiffness), 47.4 to 81.7 (function), and 47.5 to 81.4 (total). Mean modified HHS and UCLA activity scores improved from 54.0 to 82.4 and from 4.7 to 6.4, respectively. Nevertheless, nine cases required revision (mean = 31.9 months, range: 11 to 48) because of aseptic cup loosening (n = 6) or pseudotumor (n = 3). In the whole cohort, no patient had lucencies greater than 1.5 mm in three or more femoral zones. Three patients showed a radiographic lucency greater than 1 mm in one acetabular zone and one showed signs of cup migration greater than 5 mm and tilting greater than 5°. The mean cup inclination did not differ between patients requiring revision and those who retained their implant (43.3° versus 43.5°; p=0.91). Because a high revision rate of a large-head MoM THR was observed due to poor acetabular component fixation and adverse tissue reactions, use of this implant should be restricted to conversion of a failed resurfacing arthroplasty with a well-ingrown cup and in the absence of an adverse local tissue reaction.