title: The Inadequacy of Short Knee Radiographs in Evaluating Coronal Alignment After Total Knee Arthroplasty.
abstract: BACKGROUND
  Prior studies have associated coronal alignment after total knee arthroplasty (TKA) with implant survivorship. Results have been based on either the femorotibial angle (FTA) on a short knee film or the hip-knee-ankle angle (HKA) on a full-length radiograph. The purpose of this study was to determine if the FTA on short knee radiographs can accurately predict the true HKA alignment after TKA.
  
  
  METHODS
  Two orthopedic surgeons measured the FTA, HKA, medial proximal tibial angle, and lateral distal femoral angle in 262 patients who had both short and full-length standing radiographs before and/or after primary TKA. Overall coronal alignment was considered neutral if the FTA was between 2.4° and 7.2° on short knee x-rays or if the HKA was between -3° and 3° on full-length films.
  
  
  RESULTS
  Preoperatively, 13.9% (26/187) of knees had a neutral FTA on short films, but 50% (13/26) of those were in varus or valgus on full-length films. Postoperatively, 51.4% (106/206) of knees had a neutral FTA on short films, but 27.4% (29/106) of those knees were in varus or valgus on full-length films. When comparing alignment classifications (neutral, varus, or valgus) based on the short vs full-length images, 13.9% (26/187) of patients had discordant classifications on preoperative imaging, and 33.0% (68/206) had discordant classifications on postoperative imaging.
  
  
  CONCLUSIONS
  A significant proportion of patients were misclassified as varus, valgus, or neutral based on the FTA when compared to the HKA. Short knee x-rays serve as an inaccurate proxy for full-length films when assessing coronal alignment after TKA.
authors.affiliation: Department of Orthopedic Surgery, Washington University School of Medicine, St Louis, Missouri.
authors.forename: Andrew
authors.initials: A
authors.lastname: Park
authors.affiliation: Department of Orthopedic Surgery, Washington University School of Medicine, St Louis, Missouri.
authors.forename: Jeffrey B
authors.initials: JB
authors.lastname: Stambough
authors.affiliation: Department of Orthopedic Surgery, Washington University School of Medicine, St Louis, Missouri.
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Nunley
authors.affiliation: Department of Orthopedic Surgery, Washington University School of Medicine, St Louis, Missouri.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Barrack
authors.affiliation: Department of Orthopedic Surgery, Washington University School of Medicine, St Louis, Missouri.
authors.forename: Denis
authors.initials: D
authors.lastname: Nam
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000843:Ankle Joint / Q000000981:diagnostic imaging; D019645:Arthroplasty, Replacement, Knee; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000601:surgery; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000601:surgery; D035002:Lower Extremity / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D011184:Postoperative Period; D013977:Tibia / Q000000981:diagnostic imaging / Q000601:surgery
keywords: Alignment; Full Length Radiographs; Mechanical Alignment; Short Radiographs; Total Knee Arthroplasty