Evaluation of cylindrical interbody fusion devices in canine lumbar spine: Comparison of fixation stiffness in devices with and without hydroxyapatite coating
To establish intervertebral body fusion without the use of autogenous bone grafts, we tested special titanium cylindrical devices. The firmness of fixation of devices coated with hydroxyapatite (HA) (HA-D) or not coated (Ti-D) was compared in nine mongrel dogs. General anesthesia, was compared in nine mongrel dogs. General anesthesia, was conducted and the devices were implanted in the same animal through the peritoneum in two adjacent intervertebral spaces (between L3 and L6). The follow-up period was 2–72 weeks, and two animals at a time were evaluated at different periods during follow-up (groups I–IV). In each group, the entire lumbar segment of L3-7 was removed en bloc and examined histologically and radiologically with soft X-ray. In Group II (the earliest group), radiographs of the HA-D showed bone growth converging into the perforations of the device, indicating a firm bond between HA-D and vertebral bodies. No such bone growth was observed in the Ti-D. Histologically, the HA-D showed an intimate bond between the new osseous tissue and HA as early as in group I. In group III, marked ingrowth of bone was noted with both types of devices, although it was more marked with HA-D than Ti-D. Fibrous gaps between the metal and bone were present in Ti-D throughout the study period of 72 weeks. The HA-D allowed a firm bond between HA and ingrowth of ample amounts of bone inside the perforations, as well as a strong bond between HA and the vertebral bodies. When the HA-D was used for interbody fixation, early stable interbody fixation was achieved, indication that the hydroxyapatite-coated cylindrical device may be suitable for interbody fixation without the need for a bone autograft.
Key wordshydroxyapatite spinal fixation spinal instrument fusion cage
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