Efficacy of hydroxyapatite in pedicular screw fixation in canine spinal vertebra

Background: The success of orthopedic implants depends on strong anchorange of the device to skeletal tissue. Titanium alloys pedicular screw systems are widely used in spinal surgery. However, the host response to the titanium is not always favorable, and a fibrous layer may form at the skeletal tissue/device interface causing aseptic loosening of the device. Hydroxyapatite (HA)-coated implants exhibit osteoconductive properties. Superior bone ingrowth has been found for HA-coated implants inserted with an initial gap to surrounding cancellous bone. Objective: To carry out in-vivo study on uncoated and HA-coated titanium alloys in pedicular screw system and to investigate the effect of the different surfaces on bone ingrowth and osteointegration of bone implant interface in the vertebral bodies. Material and method: HA-coated and uncoated titanium pedicular screws were fixed in six adult dogs for 3, 4, and 6 months. Screw fixation strength was examined using pull-out tensile test. The bone formation was examined using scanning electron microscopy. Results: There was no difference of bone intergration between HA-coated titanium and uncoated titanium pedicular screw in the vertebral spine. The differences between HA-coated and uncoated pull-out strength were not statistically significant. Conclusion: The HA coating did not improve neither bone integration nor pull-out strength of unloaded-pedicular screw in vertebral body