title: Subsidence of SB Charité total disc replacement and the role of undersizing.
abstract: OBJECTIVE
  A possible complication after total disc replacement (TDR) is subsidence, presumably caused by asymmetric implantation, implant undersizing or reduced bone quality. This study aims to quantify the degree of subsidence of an SB Charité TDR, and investigate whether undersizing is related to subsidence.
  
  
  METHODS
  A custom developed software package (Mathworks) reconstructed 3D bone-implant geometry. A threshold for subsidence was determined by comparing penetrated bone volume (PBV) and rotation angles. Inter- and intra-observer reproducibilities were calculated. Subsidence was correlated to undersizing.
  
  
  RESULTS
  High inter- and intra-observer correlation coefficients were found for the method (R > 0.92). Subsidence was quantified as PBV 700 mm(3) combined with a rotation angle >7.5°. A reduced risk of subsidence was correlated to >60 and >62 % of the bony endplate covered by the TDR endplate for L4 and L5, respectively.
  
  
  CONCLUSIONS
  A reproducible method to determine undersizing was developed. Thresholds were determined related to a reduced risk of subsidence.
authors.affiliation: Department of Orthopaedic Surgery, Maastricht University Medical Center and Research School CAPHRI, P. Debyelaan 25, P.O. Box 5800, 6202 AZ, Maastricht, The Netherlands, i.punt@mumc.nl.
authors.forename: Ilona
authors.initials: I
authors.lastname: Punt
authors.forename: Marc
authors.initials: M
authors.lastname: van Rijsbergen
authors.forename: Bert
authors.initials: B
authors.lastname: van Rietbergen
authors.forename: Keita
authors.initials: K
authors.lastname: Ito
authors.forename: Lodewijk
authors.initials: L
authors.lastname: van Rhijn
authors.forename: André
authors.initials: A
authors.lastname: van Ooij
authors.forename: Paul
authors.initials: P
authors.lastname: Willems
mesh_terms: D000328:Adult; D001175:Arthrography / Q000379:methods / Q000592:standards / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D055959:Intervertebral Disc Degeneration / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D017116:Low Back Pain / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D015588:Observer Variation; D009929:Organ Size; D011475:Prosthesis Failure / Q000009:adverse effects*; D017755:Prosthesis Fitting / Q000379:methods* / Q000592:standards / Q000706:statistics & numerical data; D012372:ROC Curve; D012189:Retrospective Studies; D012399:Rotation; D059145:Total Disc Replacement / Q000009:adverse effects / Q000379:methods*