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. CONCLUSION: 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.
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. CONCLUSION: 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: Richard D Rames; Michael Mathison; Zachary Meyer; Robert L Barrack; Denis Nam Journal: Knee Surg Sports Traumatol Arthrosc Date: 2017-03-15 Impact factor: 4.342
Authors: Edgar A Wakelin; Linda Tran; Joshua G Twiggs; Willy Theodore; Justin P Roe; Michael I Solomon; Brett A Fritsch; Brad P Miles Journal: J Orthop Surg Res Date: 2018-10-30 Impact factor: 2.359