title: Accuracy of Individualized Custom Tibial Cutting Guides in UKA.
abstract: BACKGROUND
  Component malposition is one of the major reasons for early failure of unicompartmental knee arthroplasty (UKA).
  
  
  OBJECTIVE
  It was investigated how reproducibly patient-specific instrumentation (PSI) achieved preoperatively planned placement of the tibial component in UKA specifically assessing coronal alignment, slope and flexion of the components and axial rotation.
  
  
  METHODS
  Based on computer tomography models of ten cadaver legs, PSI jigs were generated to guide cuts perpendicular to the tibial axis in the coronal and sagittal planes and in neutral axial rotation. Deviation ≥3° from the designed orientation in a postoperative CT was defined as outside the range of acceptable alignment.
  
  
  RESULTS
  Mean coronal alignment was 0.4 ± 3.2° varus with two outliers. Mean slope was 2.8 ± 3.9° with six components in excessive flexion. It was noted that the implants were put in a mean of 1.7 ± 8.0° of external rotation with seven outliers.
  
  
  CONCLUSIONS
  PSI helped achieve the planned coronal orientation of the component. The guides were less accurate in setting optimal tray rotation and slope.
authors.affiliation: Department of Orthopedics and Rheumatology, University Hospital Marburg, Baldingerstrasse, 35043 Marburg, Germany.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Heyse
authors.affiliation: Department of Biomechanics, Hospital for Special Surgery, 535 East 70th Street, New York, NY USA.
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Lipman
authors.affiliation: Department of Biomechanics, Hospital for Special Surgery, 535 East 70th Street, New York, NY USA.
authors.forename: Carl W
authors.initials: CW
authors.lastname: Imhauser
authors.affiliation: Department of Biomechanics, Hospital for Special Surgery, 535 East 70th Street, New York, NY USA.
authors.forename: Scott M
authors.initials: SM
authors.lastname: Tucker
authors.affiliation: Department of Biomechanics, Hospital for Special Surgery, 535 East 70th Street, New York, NY USA.
authors.forename: Yogesh
authors.initials: Y
authors.lastname: Rajak
authors.affiliation: Adult Reconstruction & Joint Replacement Division, Hospital for Special Surgery, 535 East 70th Street, New York, NY USA.
authors.forename: Geoffrey H
authors.initials: GH
authors.lastname: Westrich
keywords: PSI; component alignment; individualized custom tibial cutting guides; unicompartmental knee arthroplasty