title: Implant Failure of Titanium Versus Cobalt-Chromium Growing Rods in Early-onset Scoliosis.
abstract: METHODS
  Retrospective case series of one institute database.
  
  
  OBJECTIVE
  To investigate the differences in the metallic strength of rods used for implant failure in the dual growing rod technique and evaluate clinical outcomes.
  
  
  BACKGROUND
  The dual growing rod technique in which implanted rods extend with the growth of the spine is a useful treatment for early onset scoliosis. However, many complications, particularly those associated with rods, exist. Especially, the implant failure of growing rod focused on metallic strength is unknown.
  
  
  METHODS
  Thirteen patients (42 lengthening surgeries) who underwent surgery by this technique at our hospital from 2007 were divided into a titanium rod plus titanium connector group (T group, n = 4, 26 lengthening surgeries) and cobalt-chromium rod plus titanium connection group (C group, n = 9, 16 lengthening surgeries). The incidence of implant failure and the site of fracture were retrospectively investigated.
  
  
  RESULTS
  Implant failure occurred in three patients in the T group, because of rod fracture in two patients and connector fracture in one. In the C group, implant failure occurred in six patients, because of rod fracture in one patient and connector fracture in seven. Fracture occurred twice in two patients. The rod fracture rate decreased with the use of cobalt-chromium rods but the rate of connector fracture increased. We performed a stress distribution analysis using the finite element method to clarify the mechanisms underlying implant failure in both groups. Regardless of the rod type, the greater load was placed on the distal rod. However, differences in the metallic strength caused the rod to fracture when titanium rods were used and connectors (weak metallic strength) to fracture when cobalt-chromium rods were used.
  
  
  CONCLUSIONS
  Rod fractures occurred more commonly with titanium rods and connector fractures with cobalt-chromium rods.
authors.affiliation: *Department of Orthopaedic Surgery, Division of Science of Functional Recovery and Reconstruction, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan †Department of Advanced Mechanics, Division of Industrial Innovation Sciences, Okayama University Graduate School of Natural Science and Technology, Okayama, Japan.
authors.forename: Kensuke
authors.initials: K
authors.lastname: Shinohara
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Takigawa
authors.forename: Masato
authors.initials: M
authors.lastname: Tanaka
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Sugimoto
authors.forename: Shinya
authors.initials: S
authors.lastname: Arataki
authors.forename: Kentaro
authors.initials: K
authors.lastname: Yamane
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Watanabe
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Ozaki
authors.forename: Takaaki
authors.initials: T
authors.lastname: Sarai
mesh_terms: D001852:Bone Lengthening; D002648:Child; D002675:Child, Preschool; D002858:Chromium Alloys / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D008297:Male; D019637:Orthopedic Procedures / Q000009:adverse effects* / Q000295:instrumentation* / Q000379:methods / Q000706:statistics & numerical data; D011183:Postoperative Complications; D011475:Prosthesis Failure; D012189:Retrospective Studies; D012600:Scoliosis / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D014025:Titanium / Q000627:therapeutic use*
chemical_list: D002858:Chromium Alloys; D014025:Titanium