title: Analysis of retrieved growth guidance sliding LSZ-4D devices for early onset scoliosis and investigation of the use of nitinol rods for this system.
abstract: METHODS
  Analysis of volumetric wear loss of retrieved growth guidance sliding devices LSZ-4D for treatment of early onset scoliosis and laboratory in vitro wear test for comparison of wear resistance of alloys Nitinol, Ti, and cobalt chromium (CoCr).
  
  
  OBJECTIVE
  To evaluate quantitatively the amount of wear debris from the sliding LSZ-4D device and to investigate the potential of using Nitinol for replacing Ti alloys in spinal instrumentation. To do that, wear resistance of Nitinol, Ti, and CoCr was compared.
  
  
  BACKGROUND
  There are little data regarding the amount of wear debris associated with growth guidance sliding devices for patients with early onset scoliosis and the wear resistance of superelastic Nitinol compared with Ti and CoCr.
  
  
  METHODS
  Volumetric wear loss was measured on LSZ-4D devices made from titanium alloy Ti6Al4V and each consisted of 2 rectangular section (6 × 4 mm) rods and 40 ± 8 fixture elements (20 ± 4 hooks and 20 ± 4 clips) retrieved from 3 patients (implantation period, 3.5-5.8 yr). Images of wear scars were taken on Bruker interferometer microscope and incorporated into MATLAB software. Wear resistance of Nitinol, Ti, and CoCr was studied using reciprocation pin-on-disk wear test in bovine serum at 37°C ± 1°C.
  
  
  RESULTS
  The volume wear rate of LSZ-4D device was found to be 12.5 mm per year from which 5 mm³ per year is the wear debris of the rod and 7.5 mm per year is the contribution of fixtures. Wear resistance of Nitinol is 100 times higher than that of Ti and comparable with that of CoCr.
  
  
  CONCLUSIONS
  Application of wear-resistant coatings on Ti components in growth guidance sliding devices for the treatment of early onset scoliosis will be useful. High wear resistance of Nitinol combined with its superelastic and shape memory properties could make application of Nitinol rods for spinal instrumentation beneficial.
authors.affiliation: *Kingston University London, Surrey, United Kingdom †"MATI"-RSTU, Moscow, Russia ‡University College London, London, United Kingdom §Russian University of Peoples' Friendship, Moscow, Russia; and ¶Royal National Orthopaedic Hospital, Middlesex, United Kingdom.
authors.forename: Elena
authors.initials: E
authors.lastname: Lukina
authors.forename: Mikhail
authors.initials: M
authors.lastname: Kollerov
authors.forename: Jay
authors.initials: J
authors.lastname: Meswania
authors.forename: David
authors.initials: D
authors.lastname: Wertheim
authors.forename: Peter
authors.initials: P
authors.lastname: Mason
authors.forename: Paul
authors.initials: P
authors.lastname: Wagstaff
authors.forename: Aleksandr
authors.initials: A
authors.lastname: Laka
authors.forename: Hilali
authors.initials: H
authors.lastname: Noordeen
authors.forename: Wai Weng
authors.initials: WW
authors.lastname: Yoon
authors.forename: Gordon
authors.initials: G
authors.lastname: Blunn
mesh_terms: D000293:Adolescent; D000497:Alloys; D001672:Biocompatible Materials; D002648:Child; D002858:Chromium Alloys; D020878:Device Removal; D005260:Female; D017276:Friction; D006801:Humans; D008297:Male; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D009984:Orthopedic Fixation Devices; D019736:Prostheses and Implants; D011474:Prosthesis Design; D012600:Scoliosis / Q000601:surgery*; D013499:Surface Properties; D014025:Titanium
chemical_list: D000497:Alloys; D001672:Biocompatible Materials; D002858:Chromium Alloys; C031462:titanium alloy (TiAl6V4); C013616:nitinol; D014025:Titanium