title: Can the frontal tibiofemoral alignment be assessed on anteroposterior knee radiographs?
abstract: BACKGROUND
  The aim of total knee arthroplasty is, amongst others, the reconstruction of a physiological axis of the leg with a tibiofemoral angle in the frontal plane of an average of 6°. The aim of this study is to clarify how much of the bone length on the femur and tibia has to be reproduced on anteroposterior (AP) knee radiographs in order to determine the leg's alignment after a total knee arthroplasty.
  
  
  METHODS
  We analyzed the postoperative hip-to-ankle (HTA) radiographs of 100 patients who had undergone a total knee arthroplasty at our institution.
  
  
  RESULTS
  There were strong correlations between the measured values on HTA and 20 cm bone length [lateral distal femur angle (LDFA) r = 0.887, medial proximal tibial angle (MPTA) r = 0.874, tibiofemoral angle (TFA) r = 0.888], but not between the measurements on HTA and 10 cm (LDFA r = 0.267, MPTA r = 0.102, TFA r = 0.161). There were significant differences between all measurements both on HTA and 20 cm and on HTA and 10 cm, with the exception of the LDFA between HTA and 10 cm (p = 0.085) and of the MPTA between HTA and 20 cm (p = 0.227). The intra- and inter-observer correlations were both high.
  
  
  CONCLUSIONS
  If preoperatively crude axis deviations are excluded, the tibiofemoral angle on AP knee radiographs can be determined with an accuracy of ±2.6° if at least 20 cm length of bone is reproduced (measured from the femoral and tibial joint line). Due to the high 95 % confidence intervals and bearing in mind that deviations greater than 3° may lead to inferior clinical results, however, it appears inappropriate to determine lower limb alignment with anteroposterior radiographs.
  
  
  METHODS
  Level 2.
authors.affiliation: Department for Orthopaedic Surgery, University of Ulm, Oberer Eselsberg 45, 89081, Ulm, Germany. sgroi.mirco@yahoo.de.
authors.forename: M
authors.initials: M
authors.lastname: Sgroi
authors.affiliation: Department for Orthopaedic Surgery, University of Ulm, Oberer Eselsberg 45, 89081, Ulm, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Faschingbauer
authors.affiliation: Department for Orthopaedic Surgery, University of Ulm, Oberer Eselsberg 45, 89081, Ulm, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Reichel
authors.affiliation: Department for Orthopaedic Surgery, University of Ulm, Oberer Eselsberg 45, 89081, Ulm, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Kappe
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D017760:Bone Malalignment / Q000000981:diagnostic imaging*; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging* / Q000601:surgery; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D013977:Tibia / Q000000981:diagnostic imaging* / Q000601:surgery
keywords: AP knee recording; Alignment; Full strut; Knee arthroplasty