PubMed · 1657051
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B R Frueh. 1991. Bone implants after enucleation.. https://doi.org/10.1111/j.1442-9071.1991.tb00336.x
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A model membrane system was used to investigate the ability of specific membrane constituents to modulate the precipitation of calcium phosphate. Intraliposomal precipitation was induced in phosphate-encapsulated liposomes composed of 7:2:1 molar mixtures of phosphatidylcholine (PC), dicetyl phosphate (DCP), and cholesterol (Chol) by ionophore-supported (X-537A) Ca2+ uptake. Extraliposomal precipitation occurred when these reactions were initiated in metastable external solutions. In this case, the endogenously formed crystals penetrated through the enclosing lipid bilayers and seeded the external solution phase. Transmission electron microscopy (TEM) was used to monitor the effect of acidic phospholipids [phosphatidic acid (PA), phosphatidylserine (PS), phosphatidylinositol (PI), phosphatidylglycerol (PG)] on the precipitation reactions when these molecular species were incorporated into the liposome membranes. Compared with the precipitation reactions in 7PC:2DCP:1Chol liposomes containing no acidic phospholipids, calcium phosphate formation in the presence of monoester phosphate (PA) and amino- (PS) phospholipids was inhibited. Analyses of the lipid-mineral interactions in PA-containing (10 mol%) liposomes revealed close physical contact between the small crystals of apatite and the inner lipid bilayers; there was only minimal extraliposomal precipitation. A few small crystals adhered to the external surfaces of the liposomes. In PS-containing liposomes, lipid-mineral interactions were dependent upon the DCP content of the lipid membrane. Discrete clusters of crystals formed within the interior aqueous compartment when intraliposomal precipitation was initiated in 7PC:2DCP:1Chol liposomes doped with up to 10 mol% PS. There was no evidence for specific associations between these crystals and the enclosing lipid bilayers.(ABSTRACT TRUNCATED AT 250 WORDS)
Biologic attachment of load-bearing orthopedic implants has developed as a response to long-term problems associated with polymethylmethacrylate cement fixation. Although early clinical results of uncemented hip and knee implants have been encouraging, histologic studies of retrieved implants have shown a distinct lack of bone apposition and ingrowth. Hydroxyapatite (HA) coatings applied to metallic implant substrates have been shown to enhance biologic fixation. These results have led to the clinical investigation of the use of HA-coated total hip replacements.