Tibial implants: biomechanical and histomorphometric studies of hydroxyapatite-coated and uncoated stainless steel and titanium screws in long-term ovariectomized sheep

This study was designed to evaluate osteointegration of HA-coated and uncoa ted titanium and stainless steel screws in the cortical bone of long-term ( 24 months) ovariectomized sheep (OVX group), in comparison with Sham-aged s heep (control group). The screws were tested biomechanically (extraction to rque) and histomorphometrically (affinity index: Al) 12 weeks after their i mplantation in tibia! diaphyses. Tibial cortical bone parameters showed sig nificant differences between the groups, showing a reduction of the selecte d parameters in the OVX group. ANOVA showed significant effects for both ma terial and ovariectomy factors on obtained extraction torque (material: F=1 59.26, p < 0.0005; ovariectomy: F=20.04, p < 0.0005) and AI data (material: F=8.04, p < 0.001; ovariectomy: F=7.17, p < 0.05). In both groups the extr action torque for coated screws of both materials was significantly higher than for uncoated screws, and uncoated titanium had a better extraction tor que than uncoated stainless steel. In the OVX group, the HA-coated stainles s steel and titanium AI data were significantly higher than uncoated Al dat a. In conclusion, the biomechanical and histomorphological results obtained suggest employing HA-coated screws in the presence of osteopenic cortical bone.