title: Femur bowing could be a risk factor for implant flexion in conventional total knee arthroplasty and notching in navigated total knee arthroplasty.
abstract: OBJECTIVE
  This study aimed to investigate the relationship between preoperative femoral axes and femoral implant position and to determine how femoral sagittal axes, including femoral anterior bowing, influence the femoral component position in total knee arthroplasty (TKA).
  
  
  METHODS
  The relationship between femoral axes (femoral anterior bowing, mechanical axis and the anterior cortical line, intramedullary axis) and implant position was compared in 50 conventional and 50 navigated TKAs. Outliers with more than a 3° margin of error in placement of the femoral component compared with the mechanical axis in the sagittal plane were calculated.
  
  
  RESULTS
  The femoral component flexion angle was 3.1° in the conventional group and 1.6° in the navigation group (p < 0.001). Anterior femoral bowing correlated positively with the angle between the mechanical axis and implant (r = 0.360, p = 0.010) in the conventional group and negatively with the angle between the anterior cortical line and flange of the femoral component (r = -0.355, p = 0.010) in navigated TKAs. Incidence of outliers was 48 % (24 patients) in the conventional group compared with 10 % (five patients) in the navigated group (p = 0.008).
  
  
  CONCLUSIONS
  Femoral anterior bowing was an influential factor for implant position and could be a risk factor for both femoral implant flexion in conventional TKAs and notching in navigated TKAs. The results of this study should be considered by surgeons when assessing the risk factors for femoral geometry before performing TKAs, as these results may help them to avoid an overly flexed or extended position of the femoral component, which would affect clinical long-term survival.
  
  
  METHODS
  Retrospective comparative study, Level III.
authors.affiliation: Department of Orthopedic Surgery, Yonsei University College of Medicine, 50 Yonsei-ro, Seodaemun-gu, Seoul, 120-752, Republic of Korea.
authors.forename: Jae Han
authors.initials: JH
authors.lastname: Ko
authors.affiliation: Department of Orthopedic Surgery, Yonsei University College of Medicine, 50 Yonsei-ro, Seodaemun-gu, Seoul, 120-752, Republic of Korea.
authors.forename: Chang Dong
authors.initials: CD
authors.lastname: Han
authors.affiliation: Department of Orthopedic Surgery, Yonsei University College of Medicine, 50 Yonsei-ro, Seodaemun-gu, Seoul, 120-752, Republic of Korea.
authors.forename: Kyoo Ho
authors.initials: KH
authors.lastname: Shin
authors.affiliation: AIC-CURE International Children's Hospital of Kenya, Kijabe, Kenya.
authors.forename: Levis
authors.initials: L
authors.lastname: Nguku
authors.affiliation: Department of Orthopedic Surgery, Yonsei University College of Medicine, 50 Yonsei-ro, Seodaemun-gu, Seoul, 120-752, Republic of Korea.
authors.forename: Ick Hwan
authors.initials: IH
authors.lastname: Yang
authors.affiliation: Department of Orthopedic Surgery, Yonsei University College of Medicine, 50 Yonsei-ro, Seodaemun-gu, Seoul, 120-752, Republic of Korea.
authors.forename: Woo Suk
authors.initials: WS
authors.lastname: Lee
authors.affiliation: Department of Orthopedic Surgery, Yonsei University College of Medicine, 50 Yonsei-ro, Seodaemun-gu, Seoul, 120-752, Republic of Korea.
authors.forename: Kwang Il
authors.initials: KI
authors.lastname: Kim
authors.affiliation: Department of Orthopedic Surgery, Yonsei University College of Medicine, 50 Yonsei-ro, Seodaemun-gu, Seoul, 120-752, Republic of Korea. kkpark@yuhs.ac.
authors.forename: Kwan Kyu
authors.initials: KK
authors.lastname: Park
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D017760:Bone Malalignment; D005260:Female; D005269:Femur / Q000502:physiology*; D006801:Humans; D007719:Knee Joint / Q000601:surgery; D007720:Knee Prosthesis; D008297:Male; D000072662:Margins of Excision; D008875:Middle Aged; D011183:Postoperative Complications; D016059:Range of Motion, Articular; D012189:Retrospective Studies; D012307:Risk Factors; D025321:Surgery, Computer-Assisted / Q000379:methods
keywords: Femur component; Navigation; Sagittal alignment; Total knee arthroplasty