The effect of partial vs. full hydroxyapatite coating on periprosthetic bone quality around the canine madreporic femoral stem.

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.