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BACKGROUND:Half-ring sulcated external fixator is a bone external fixation device.Its structure is relatively simple,with multi-plane fixed,and small occupying space.So far,there are few experimental reports about construction of tibial defect model by it in large animals.OBJECTIVE:To validate the practicality and repeatability of half-ring sulcated external fixator in establishing tibial defect models in goats.DESIGN,TIME AND SETTING:The randomized controlled observation was performed at the Animal Laboratory of the Third Military Medical University from March 2005 to February 2007.MATERIALS:Nine healthy adult(Animal Center of Third Military Medical University);Half-ring sulcated external fixator,made by Professor Li of the Third Military Medical University;Osseous pin,ψ2.5 mm,Shanghai Medicai Instruments Co.,Ltd.METHODS:After animals were anesthetized,two needles were threaded in the same plane of cancellous bone about 1.5-2.0 cm above the superior articular surface of the tibia,named group 1.The angle between the two needles was 40°.One needle was threaded at the place of 3.0 to 5.0 cm under the group 1 and parallel with optional needle of the group 1,named group 2.Needles of group 4 were threaded at the cancellous bone that was 2.0 cm from the joint surface of inferior extremity of the tibia.One needle was threaded at the place of 3.0 to 5.0 cm from group 4 and parallel with optional needle of the group 4.The included angle between these two needles of group 2 and group 3 was 60°.There were totally 6 needles.Tibia was fixed by half-ring sulcated external fixator.According to the length of the tibia from X-ray,tibia and periosteum were amputated by wire saw between the two needles in the middle and inferior segment of the tibia to make segmental bone and periosteal defects of 20 percent of tibia.MAIN OUTCOME MEASURES:①Postoperative general state of the animals and effect of half-ring sulcated external fixator.②Self-repair of bone defects by X-ray and Lane-Sandhu scoring standards.RESULTS:Of the 9 selected goats,1 died of postoperative infection,and 1 developed pinhole infection and supplemented.All the others survived and were included in final analysis.The goats were awake within 2-6 hours after surgery and able to stand up to eat.The loosening nuts were screwed up.No external fixation failure or loosening was found.No skin was necrotic.Injured limb could touch the ground in 2 days,but could not bear load until 2 weeks.The goats could walk in three weeks with a slight limp,then moved freely without claudication in four weeks after the operation.At the 5th week after operation,the radiographs showed little periosteal reaction.At the 10th week after operation,sclerosis was found in the fracture ends,and medullary cavity started to close.Fifteen weeks after operation,the medullary cavity closed and periosteal reaction did not aggravate.Inaddition.Lane score was 0 at any time point.No bone formation was found in the histological examination at 5,10 and 15 weeks after operation,and Lane score was 0 at any time point.CONCLUSION:The goat model established in goat tibia with 20%defects by the half-ring sulcated external fixator shows no bone healing after 15 weeks by X-ray or histological exanimation,indicating this is a practical and repetitive method to establish animal models of large segmental defect for bone tissue engineering.