Korean Journal of Metals and Materials (대한금속재료학회지)

The Korean Institute of Metals and Materials (대한금속재료학회)
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Failure Analysis of Ti alloy Screws in Fixing Fractured Spines

척추교정 티타늄 앵커나사 파단 손상원인 분석

  • Choe, Byung Hak (Department of Advanced Metal and Materials Engineering, Gangneung-Wonju National University) ;
  • Kim, Moon Kyu (Department of Neurosurgery, Gangneung Asan Hospital, University of Ulsan College of Medicine) ;
  • Kim, Seong Eun (Special Alloys Group, Korea Institute of Materials Science) ;
  • Shim, Yoon Im (KBSI Gangneung Center, Gangneung-Wonju National University) ;
  • Lee, Young Jin (Department of Advanced Metal and Materials Engineering, Gangneung-Wonju National University) ;
  • Jeong, Hyo Tae (Department of Advanced Metal and Materials Engineering, Gangneung-Wonju National University) ;
  • Choi, Won Yeol (Department of Advanced Metal and Materials Engineering, Gangneung-Wonju National University)
  • 최병학 (강릉원주대학교 신소재금속공학과) ;
  • 김문규 (울산대학교 강릉아산병원 신경외과) ;
  • 김승언 (한국기계연구원 부설재료연구소) ;
  • 심윤임 (한국기초과학지원연구원) ;
  • 이영진 (강릉원주대학교 신소재금속공학과) ;
  • 정효태 (강릉원주대학교 신소재금속공학과) ;
  • 최원열 (강릉원주대학교 신소재금속공학과)
  • Received : 2011.04.27
  • Published : 2011.12.25
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Abstract

Failure analyses of the screws in spinal fixation devices were carried out. The fractured screws were retrieved from a patient who had spinal surgery in the thoracic vertebrae from number 10 to 15. The failure occurred one month after the removal of the braces. Microstructures and fracture surfaces were examined by optical and scanning electron microscopy. The microstructures of the screws corresponded to annealed Ti-6Al-4V bar. However, in the vicinity of the screw surface, there was an insufficient number of fine precipitates. Fracture surfaces showed typical fatigue failure modes. Regarding the fact that no machining defects were detected, fatigue crack initiation might have been caused by the lack of precipitates near the screw surfaces. Only the fourth of five fixed screws was severely stress-concentrated by the action of the spinal bones, while the stress of the 4th screw was decreased to half of its acceptable level when the screw was supplemented by one more, which might have been fixed in the 6th vertebra under the 5th position by the switching of its position. The stress simulation was conducted by ANSYS with 3D CAD of PRO/E in order to understand the stress concentration behavior and to provide an effective spinal surgery guide.

Keywords

Acknowledgement

Supported by : 한국가스공사

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