title: Do patient-specific guides improve coronal alignment in total knee arthroplasty?
abstract: BACKGROUND
  Coronal alignment may impact clinical outcome and survivorship in TKA. Patient-specific instrumentation has been developed to restore mechanical or kinematic axis and potentially reduce component malpositioning. Although it is clear these instruments add cost, it is unclear whether they improve alignment.
  
  
  OBJECTIVE
  We determined whether the mean coronal alignment after TKA performed with conventional versus patient-specific instrumentation better restored the mechanical and kinematic axes and whether there were more outliers with one of the two methods.
  
  
  METHODS
  We retrospectively evaluated 150 primary TKAs performed for osteoarthritis: Group 1 (n = 50) conventional instrumentation; Group 2 (n = 50) patient-specific instrumentation restoring the mechanical axis; Group 3 (n = 50) patient-specific instrumentation restoring the kinematic axis, and measured femorotibial angle, hip-knee-ankle angle, and the zone of the mechanical axis from scout CT images taken 0 to 6 weeks postoperatively.
  
  
  RESULTS
  The mean femorotibial angle differed between the groups: Group 1 had the greatest varus mean alignment and most varus outliers. The mean hip-knee angle was similar between Groups 1 and 2, with Group 3 having greater valgus mean alignment and the most valgus outliers. For the zone of the mechanical axis, Groups 1 and 2 had similar percentages of outliers (40% versus 32%), whereas Group 3 had a greater number of outliers (64%) that were valgus.
  
  
  CONCLUSIONS
  TKAs with patient-specific instrumentation restoring the mechanical axis had a similar number of outliers as conventional instrumentation with both groups having more varus outliers than TKAs with patient-specific instrumentation restoring kinematic axis, which had more valgus outliers. Therefore, additional studies are needed to determine whether patient-specific instrumentation improves clinical function or patient satisfaction and whether their routine use can be justified in primary TKA.
  
  
  METHODS
  Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
authors.affiliation: Department of Orthopaedic Surgery, Washington University School of Medicine, One Barnes-Jewish Hospital Plaza, 11300 West Pavilion, Campus Box 8233, St Louis, MO 63110, USA. nunleyr@wustl.edu
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Nunley
authors.forename: Bradley S
authors.initials: BS
authors.lastname: Ellison
authors.forename: Jinjun
authors.initials: J
authors.lastname: Zhu
authors.forename: Erin L
authors.initials: EL
authors.lastname: Ruh
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Howell
authors.forename: Robert L
authors.initials: RL
authors.lastname: Barrack
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation* / Q000379:methods; D001696:Biomechanical Phenomena; D017760:Bone Malalignment / Q000517:prevention & control; D005260:Female; D005269:Femur / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D006801:Humans; D021621:Imaging, Three-Dimensional; D007719:Knee Joint / Q000000981:diagnostic imaging; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000601:surgery; D017060:Patient Satisfaction; D017755:Prosthesis Fitting; D025321:Surgery, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D013977:Tibia / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed