We have studied the effect of hydroxyapatite (HA) coating in 15 ovariectomised and 15 normal rats which had had a sham procedure. Twenty-four weeks after operation, HA-coated implants were inserted into the intramedullary canal of the right femur and uncoated implants into the left femur. The prostheses were removed four weeks after implantation. Twelve specimens in each group had mechanical push-out tests. Sagittal sections of the other three were evaluated by SEM.The bone mineral density (BMD) of the dissected left tibia was measured by dual-energy x-ray absorptiometry. The difference in BMD between the control and ovariectomised tibiae was 35.01 mg/cm 2 (95% CI, 26.60 to 43.42). The push-out strength of the HA-coated implants was higher than that of the uncoated implants in both groups (p < 0.0001), but the HA-coated implants of the ovariectomised group had a reduction in push-out strength of 40.3% compared with the control group (p < 0.0001).Our findings suggest that HA-coated implants may improve the fixation of a cementless total hip prosthesis but that the presence of osteoporosis may limit the magnitude of this benefit. [Br] 1999;81-B:705-9. J Bone Joint Surg Received 26 May 1998; Accepted after revision 4 November 1998Many studies have used animal models to demonstrate the osteoconductive properties of bioactive ceramics, especially hydroxyapatite (HA). Recently, HA-coated implants have been used in total hip replacement (THR), and early clinical results suggest that HA-coated prostheses are an attractive alternative to standard methods of cementless arthroplasty.1-6 The animals used in basic studies on the properties of HA coating had a normal bone metabolism and bone mass. 4,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] In such animals, the formation and resorption phases of bone are tightly coupled, and bone mass is maintained. We believe, however, that many patients, especially women, who undergo THR, have uncoupling of the phases of bone remodelling and decreased bone mass. 22 Our aim was to confirm the efficiency of HA in osteoporotic conditions and we have studied the bone-implant attachment strength of HA-coated titanium implants in ovariectomised and normal rats. Materials and MethodsExperimental design and operative procedure. We used thirty 12-week-old female Wistar King rats weighing between 243 and 282 g. They were housed and tested at the Institute of Laboratory Animals, Faculty of Medicine, Kyushu University. All the rats were sedated with ether and anaesthetised by peritoneal administration of pentobarbital (40 mg/kg body-weight). They were then divided into two groups. One had bilateral ovariectomy using standard veterinary procedures and the other a sham operation which consisted of exposure and palpation of the ovaries without removal. At 24 weeks after this operation HA-coated and uncoated implants were inserted into the medullary canal of the right and left femora, respectively, in both groups, after reaming the intercondylar notch of each distal femur with a 1.5 mm dri...
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