VIABILITY OF A SINGLE INFUSION OF ZOLEDRONIC ACID (ZOL) TO REDUCE IMPLANT FAILURE RATE IN THA – RESULTS FROM A RANDOMIZED, DOUBLE-BLIND, CONTROLLED TRIAL

Abstract

Despite great progress in implant design, materials and new implantation techniques aseptic loosening is still the most frequent cause of implant failure in THA, which was found to be increased especially in patients with osteonecrosis of the femoral head (ON-FH). While a direct link between aseptic loosening and periprosthetic bone loss still remains elusive, there is plentiful evidence for a close association with early migration of implant components. Although the beneficial effect of bisphonates on periprosthetic bone mass is well established, little is known to date about their effects on implant migration. This is an important issue, because successful prevention of early implant migration would provide strong evidence of a beneficial effect on the survival rate of THA. Previously, Krismer et al. found that a total migration of the cup of ≥ 1mm and a subsidence of ≥ 1.5mm 2 years after surgery was highly predictive for aseptic implant failure of THA within 8 to 10 years.

Fifty patients with end-stage ON-FH were consecutively enrolled to receive either 4mg of ZOL or saline solution (CTR) in a double-blind fashion. Radiographs standardized for EBRA-digital analysis were performed at each follow-up exam at 7 weeks, 6 months, 1 year, and yearly thereafter. The minimum follow-up period was 2 years (median follow-up: 2.8 years). Migration of the acetabular and femoral components was analyzed with the EBRA-digital software (University of Inns-bruck, Austria) independently by 3 investigators fully blinded to randomization.

Within the placebo group, distal migration of the stem (subsidence) steadily increased up to −1.2mm ± 0.6 SD at 2 years after THA without reaching a plateau phase (P< 0.001, Friedman ANOVA). Less but a nearly curvilinear migration pattern was found for the acetabular components, with a transverse migration of 0.6mm ± 1.0 SD and a vertical migration of 0.6mm ± 0.8 SD at 2 years (P< 0.001, Friedman ANOVA). Treatment with ZOL effectively minimized the migration of cups in both the transverse and vertical direction (0.15 mm ± 0.6 SD and 0.06 mm ± 0.6 SD, respectively, P< 0.05, ANOVA), and a trend to a decreased subsidence was also found for stem migration (−0.91 mm ± 0.51 SD; P=0.11, ANOVA). In addition, total cup migration exceeding 1mm at 2 years was significantly reduced by ZOL in 8 patients (12 vs 4 in CTR vs ZOL, respectively) as was also found in 6 patients for subsidence (≥ 1.5mm in 9 vs 3 patients in CTR vs ZOL, respectively) (P< 0.05, Fisher’s exact).

This is the first clinical trial reporting that a single infusion of ZOL suffices to improve initial implant fixation in THA. Based on best evidence available to date, this new concept shows great promise of improving the long-term outcome in THA and should be given attention in long-term trial.