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Abstract
Introduction Bisphosphonates have been proposed to delay or prevent loosening of joint replacement implants by reducing bone resorption. It is known, however, that implant motion prevents the bone anchorage necessary to maintain secure implant fixation.
Methods We used our experimental implant model with controlled motion to evaluate the relative effects of implant motion and bisphosphonate. We implemented our established 8-week experimental revision protocol to obtain a bony and soft tissue setting of revision joint replacement in 16 dogs. At 8 weeks, we had stabilized half of the implants. The other half of the implants continued pistoning. Half of the dogs were exposed to alendronate (oral).
Results Stabilization of the revision implant was more effective at improving fixation (higher shear strength) than administering alendronate. As expected, the fibrous membrane remained under unstable conditions, even with alendronate. With alendronate and stabilized implants, increased bone was observed near the sclerotic shell of the revision cavity, but it was reduced with alendronate when the implant was unstable.
Interpretation Our findings suggest that it may be difficult for alendronate administration alone to rescue implants that are already loose. In implants that have not progressed to loosening, alendronate may increase bone density at the border with the sclerotic shell, but the effect of this bone in delaying eventual loosening is not known.
Contributions of authors
KS: study design, experimental surgeries, data analysis and interpretation, and manuscript preparation. XC: study design, assistance with experimental surgeries, and administration of bisphosphonate. TJ: study design, data analysis and interpretation, and manuscript preparation. LK: study design, histomorphometric analysis, and manuscript preparation. JB: study design, assistance with experimental surgeries, data analysis and interpretation, and manuscript preparation.