In previous studies, we have demonstrated a fibrocartilaginous membrane around hydroxyapatite-coated implants subjected to micromovement in contrast to the fibrous connective tissue which predominates around similarly loaded Ti-coated implants had four times stronger fixation than did continuously loaded Ticoated implants (p < 0.01) but there was no equivalent difference between the two groups of HA-coated implants. The amount of bone ingrowth was greater into immobilised HA-coated implants than into

No abstract

No abstract

Intimate contact at the bone-porous surface interface is not always achievable in noncemented prosthetic implantation. We investigated the effect of hydroxyapatite (HA) coating on skeletal attachment in noninterference fit 4 weeks after implantation in 6 mature dogs. The pushout test of HA-coated implants surrounded by a 1-mm gap showed a twofold increased shear strength and fivefold increased shear stiffness compared with titanium alloy (Ti) coated implants. The fixation of Ti implants was reduced by two thirds when inserted in a gap as compared with press fit, whereas HA-coated implants in gap showed anchorage close to implants in press fit. Only minor differences were found between HA and Ti implants in press fit. Histomorphometric analysis showed a significant increase in bone in direct contact to HA-coated implant as compared with Ti implants inserted both in gap and press fit. The study indicates that tightness of surgical fit is an important factor for sufficient fixation of the implant. However, our results demonstrate that hydroxyapatite coating almost eliminates the negative influence of noninterference fit between bone and unloaded implant.The quantity of bone ingrowth into porous-coated implants depends, among other factors, on the interference fit obtained with the surrounding bone (Albrektsson and Albrektsson 1987, Cameron et al. 1976, Carlsson et al. 1988a, Harris et al. 1983, Sandborn et al. 1988). In the clinical situation, however, direct apposition of implant to bone is not always achievable Engh 1984, Engh et al. 1987 Schimmel and Huiskes 1988). Lack of optimal flatness after bone cutting, implant design deficiencies, and anatomic variations may result in gaps between the implant surface and surrounding bone Albrektsson 1987, Larsen andRyd 1990).Calcium phosphates in the form of granules have been employed to fill in gaps between bone and implant with no demonstrable effect on bone ingrowth at early time periods (Eschenroeder et al. 1987, Russotti et al. 1986. Recently, deposition of dense hydroxyapatite (HA) on titanium alloy (Ti) by plasma spraying technique has been shown to improve the HA-metal substrate interface shear strength , Thomas et al. 1987. HA coating provides earlier bone ingrowth compared with Ti (Geesink et al. 1988, Saballe et al. 1989a, b, c, Thomas et al. 1987.We examined the effect of HA coating on skeletal attachment of unloaded porous titanium implants inserted in noninterference fit compared with press fit insertion. Material and methodsExperimental design. Six skeletally mature labrador dogs of both sexes weighing 28 (22-31) kg comprised the material. Ti-and HA-coated implants were inserted in press fit or in noninterference fit in the distal femoral condyles. The dogs were killed after 4 weeks and the results were evaluated by the mechanical push-out test and histomorphometric analysis.Bone-density measurements. To investigate bone density at implantation site, CT scanning of the distal femora was performed 1 week before surgery as previously described (Saballe ...

No abstract