Femur bowing could be a risk factor for implant flexion in conventional total knee arthroplasty and notching in navigated total knee arthroplasty
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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).
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.
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).
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.
Level of evidence
Retrospective comparative study, Level III.
KeywordsTotal knee arthroplasty Sagittal alignment Femur component Navigation
The authors thank Keun Jung Ryu, MD (Yonsei University, College of Medicine, Seoul, Korea), for his help with the statistics, Jeyoung Woo with graphic support and Hee Yeon Lee and Seojin Park with data organization. This study was supported by a faculty research grant of Yonsei University College of Medicine for 2015 (6-2015-0092).
Compliance with ethical standards
Conflict of interest
The authors have no conflicts of interest to declare.
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