Thickness of fibrous capsule after implantation of hydroxyapatite in subcutaneous tissue in rats

The-present study evaluates in rats the histomorphometrical thickness of fi brous capsules that surround hydroxyapatite (HA) disks after implantation. HA disks were implanted into the subcutaneous tissue of 79 rats for 1 day t o 20 months. Decalcified histological sections stained with hematoxylin and eosin were examined. Fibrous capsule thickness (FCT) was measured using:an objective micrometer. On the fourteenth day, primary fibrous capsules form ed around implants. From that time point FCT increased with time of implant ation. Within a given sample, FCT differed from one portion of the fibrous capsule to another, depending on which site faced the disks. FCT was thicke st at the upper and lower portions of the disks, thinner at the lateral por tions and thinnest at the upper and lower ring-shaped portions. Two possibl e explanations for the above findings are discussed in this paper: (1) The area of contact between disk and tissue differs. (2) Chemical stimulation o f implanted material caused by demineralization and remineralization may re sult from the varying thicknesses of fibrous capsules. FCT from upper and l ower portions of HA disks increased by over 200% in the first 10 months and steadily increased about 20% over the next 10 months. Many studies have co ncluded that HA is useful for reconstructive surgery, so the long-term effe cts of FCT need further study. (C) 1999 John Wiley & Sons, Inc.