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Aseptic loosening remains the major problem facing arthroplasty longevity with particulates from component materials touted as the cause of periprosthetic osteolysis. Proposed mechanisms in aseptic bone loss include: increased resorption, increased differentiation of osteoclasts (and/or macrophages locally), and decreased osteoblastic bone formation. Leukotrienes participate in osteoclastic bone resorption. We investigated inhibiting leukotrienes synthesis, using ICI 230487, to ameliorate the effects of particulates on osteoclast pit formation and also assessed the effects of alendronate, a bisphosphonate, on pit formation. Three particulates were used: ultra high molecular weight polyethylene (UHMWPE), polymethylmethacrylate (PMMA) and hydroxyapatite (HA). Osteoclast resorption was increased with UHMWPE, PMMA, and HA particles. Interventions with alendronate and ICI 230487 reduced particulate-induced osteoclast resorption. Both ICI 230487 and alendronate reduced osteoclast numbers at higher doses. To assess the effect of particulates on osteoclast and macrophage differentiation, mouse bone marrow was cultured and stained for tartrate resistant acid phosphatase colonies (TRAP+, osteoclasts) and nonspecific esterase positive colonies (NSE+, macrophage precursors). Particulates increased both TRAP+ and NSE+ colony formation. These increases were inhibited by ICI 230487. Particulates also inhibited osteoblast function assessed by the development of mineralized nodules and alkaline phosphatase positive (AP+) colony area. ICI 230487 partly protected osteoblast function from this particulate effect. Blockade of leukotriene production may prove a useful therapeutic intervention for particulate-induced aseptic loosening by inhibiting resorptive activity, reducing the pro-inflammatory cell populations induced and recruited by these particulates, as well as ameliorating the negative effects of inflammatory mediators on osteoblast function., (Copyright 2001 John Wiley & Sons, Inc.)

While hydroxyapatite coatings have been shown to enhance osseointegration of metal prostheses, the optimal extent of the coating over the femoral stem component remains unclear. In this study, we investigated the effect of the application of hydroxyapatite to the proximal half of the femoral stem vs. full hydroxyapatite coating on the madreporic-surfaced femoral stems in a canine model over time. Total hip arthroplasties were performed on 22 dogs. Fifteen had half-HA coated stems, and seven had fully HA coated stems. The dogs were followed for 3 weeks, 3 months, or 1 year postoperatively. Micromotion near the femoral component was assessed at three levels along the medial aspect of the stems. Percent bone apposition, trabecular strut width, connectivity index, and cortical porosity measurements were performed at five levels and in four quadrants about the femoral stems. Micromotion was greater adjacent to the half-coated stems at 3 weeks postoperatively only. There was a trend to decreased micromotion from proximal to distal in both stem types. Both designs fixed proximally and tended to load share laterally more than in the other three quadrants. Fully HA coated stems induced greater percent bone apposition, wider trabecular struts, and more connectivity compared to half-HA coated stems., (Copyright 2000 John Wiley & Sons, Inc.)