Abstract
Introduction: Alendronate is a pyrophosphate analogue of bisphosphonate that has been shown to inhibit osteoclastic bone resorption. Bone formation and remodeling are necessary to establish initial fixation of uncemented implants, especially those coated with bioactive surfaces, such as HA. Because the process of bone remodeling that culminates in new bone formation is thought to be initiated by osteoclastic bone resorption, it is appropriate to test the influence of osteoclast inhibiting medications on bone apposition to hydroxyapatite (HA)-coated implants. The purpose of this study was to determine the influence of alendronate on early bone apposition and remodeling around HA-coated canine total hip implants.
Methods: Twelve canines underwent staged bilateral total hip arthroplasty with surgeries 20 weeks apart. The femoral component was a titanium alloy stem with a proximal macro-textured surface and a plasma-sprayed HA coating. Modular cobalt-chromium alloy heads were used with cemented, all-polyethylene acetabular components. Six of the dogs received oral alendronate therapy from surgery to sacrifice; the other 6 dogs were untreated controls. The animals were sacrificed 4 weeks after the second surgery. Sections from matched implant sites (proximal, middle, and distal) were histologically analyzed. The linear extent of bone apposition, HA coating thickness, and the total amount of cortical and cancellous bone were measured with the use of an interactive image analysis system.
Results: There were no significant differences in radiographic or histologic findings between the two groups at either 4 or 24 weeks. Although the extent of HA coating decreased with time in both groups, no significant influence of alendronate was identified on either the extent of bone apposition, the extent or thickness of the HA coating, or the average cortical or trabecular bone area around the implants.
Conclusions: Many patients who are receiving alendronate for osteoporosis or other disorders may also qualify for uncemented total joint arthroplasty. Although bone formation is generally thought to be initiated by, and coupled with bone resorption, our results suggest that alendronate has no significant influence on attaining immediate fixation or in short term bone remodeling around HA-coated total joint implants.
The abstracts were prepared by Professor Jegan Krishnan. Correspondence should be addressed to him at the Flinders Medical Centre, Bedford Park 5047, Australia.
