Current research efforts aim at enhancing osseointegration of cementless implants to improve early bone fixation.

Purpose: The aim of the present study was to investigate whether bone morphogenic protein (BMP) 2 had a positive effect on the osseointegration of hydroxyapatite coated implants.

Method: Hydroxyapatite (HA) implants were coated with BMP-2 and hyaluronic acid (HY) as the carrier or with HY alone. Uncoated HA-implants served as controls. The osseointegration of the implants was evaluated either by light microscopy or by pullout tests after 1, 2 and 4 weeks of unloaded implantation in the cancellous bone of 18 sheep.

Results: The BMP-2 coating significantly increased bone growth into the perforations of HA-implants. The proportion of bone-ingrowth at 4 weeks was 32% for the BMP-implants compared to 12% for HA implants. However, BMP-2 did not enhance the percentage of bone implant contact and interface shear strength values.

Conclusion: This study indicates that BMP-2 may help to increase bone growth across gaps of cementless implants in the early stages of bone healing improving fixation and decreasing the risk of loosening.

Introduction and Aims: Current research efforts aim at enhancing osseointegration of cementless implants to improve early bone fixation. The aim of the present study was to investigate whether bone morphogenic protein (BMP) 2 had a positive effect on the osseointegration of hydroxyapatite-coated implants in an animal model.

Method: Hydroxyapatite (HA) implants were coated with BMP-2 and hyaluronic acid (HY) as the carrier or with HY alone. Uncoated HA-implants served as controls. The osseointegration of the implants was evaluated by light microscopy and pullout tests after one, two and four weeks of unloaded implantation in the cancellous bone of 18 sheep.

Results: The BMP-2 coating significantly increased bone growth into the perforations of HA-implants. The proportion of bone-ingrowth at four weeks was 32% for the BMP-implants compared to 12% for HA implants. However, BMP-2 did not enhance the percentage of bone implant contact and interface shear strength values.

Conclusion: This study indicates that BMP-2 may help to increase bone growth across gaps of cementless implants in the early stages of bone healing improving fixation and decreasing the risk of loosening.

Current research efforts aim at enhancing osseointegration of cementless implants to improve early bone fixation.

The aim of the present study was to investigate whether bone morphogenic protein (BMP) 2 had a positive effect on the osseointegration of hydroxyapatite coated implants.

Hydroxyapatite (HA) implants were coated with BMP-2 and hyaluronic acid (HY) as the carrier or with HY alone. Uncoated HA-implants served as controls. The osseointegration of the implants was evaluated either by light microscopy and pullout tests after 1, 2 and 4 weeks of unloaded implantation in the cancellous bone of 18 sheep.

The BMP-2 coating significantly increased bone growth into the perforations of HA-implants. The proportion of bone-ingrowth at 4 weeks was 32% for the BMP-implants compared to 12% for HA implants. However, BMP-2 did not enhance the percentage of bone implant contact and interface shear strength values.

Conclusion: This study indicates that BMP-2 may help to increase bone growth across gaps of cementless implants in the early stages of bone healing improving fixation and decreasing the risk of loosening.

We carried out a histological study of a proximally hydroxyapatite (HA)-coated femoral component, retrieved after 9.5 years of good function. The HA coating had completely degraded. Bone was in direct contact with the titanium surface in all the areas which had been coated, with no interposing fibrous tissue. There were no signs of particles, third-body wear, adverse tissue reactions or osteolysis. Bone remodelling was evident by the presence of resorption lacunae; tetracycline labelling showed bone laid down six years after implantation.

The loss of the HA-coating had no negative effect on the osseo-integration of the stem. We conclude that the HA coating contributes to the fixation of the implant and that its degradation does not adversely affect the long-term fixation.

Introduction: After more than 10 years of clinical experience, hydroxyapatite (HA) coated orthopaedic implants are now an established, viable alternative to porous coatings for achieving good implant fixation. However, developments are continuing to improve the nature and adhesion of the HA coating.

Aim: To investigate the biological attachment characteristics of titanium and highly crystalline HA implant coatings in the metaphysis of an animal model.

Method: Titanium alloy implants with a coating of commercially pure titanium (Ti) or highly crystalline HA were evaluated by light microscopy and pullout tests after one, two and four weeks of unloaded implantation in the tibial and femoral metaphyses of 18 sheep.

Results: The interface shear strength pullout increased from approximately 29N/cm2 at one week to approximately 326N/cm² at two weeks. At four weeks the pull-out strength for Ti and HA coated implants was 1,004.87 ± 189.82N/cm2 and 1,043.26 ± 260.61N/cm2 respectively. The pullout strength increased significantly over time up to four weeks, but the difference between the coatings was not statistically significant at any time interval.

Histomorphometric analysis showed an increase of bone-implant contact between one and two weeks from 0 to 15% for Ti and 0 to 20% for HA coated implants. At four weeks Ti and HA implants showed 44% and 60% bone-implant contact respectively. There was a significant increase in bone-implant contact over time for both coatings. HA implants had significantly higher bone-implant contact at two and four weeks. Light microscopy revealed that bone grew into HA coated surfaces in the form of feet, spreading over the surface. Whereas for Ti the newly formed bone looked like a bridge linking the original bone with the implant surface.

Conclusion: The different growth patterns of bone into Ti and HA surfaces resulted in different bone-implant contact areas. Highly crystalline hydroxyapatite coatings enhanced the osseointegration in the early stages of bone healing. However there was a discrepancy between the mechanical and histological results. This may suggest that the mechanical failure does not occur at the implant-bone interface.