title: How precise is the identification of the center of the femoral head during total knee arthroplasty?
abstract: OBJECTIVE
  Identification of the center of the femoral head in the coronal plane is essential during total knee arthroplasty. We evaluated a new method for localization of the center of the hip, thereby detecting the neutral mechanical axis using inter-femoral head center distances (X) measured from a radiograph. Our proposed method was compared with 3 commonly used methods using landmarks that are estimated to be 2 finger-breaths medial to the anterosuperior iliac spine (method A), 2.5 cm perpendicular to the mid-inguinal point (method I), and 1.5 cm lateral to the femoral artery (method F).
  
  
  METHODS
  114 patients undergoing total knee arthroplasty were prospectively enrolled in the study. Four landmarks were marked and conventional anterior-posterior pelvic radiographs were taken. On the radiograph, the distance between the estimated FHC and the neutral mechanical axis was measured.
  
  
  RESULTS
  The median value (mm) of the measured distance was 9 in A, 7 in I, 8.5 in F, and 5 in X. When an error of more than 3° from neutral alignment was defined as an outlier, 15% of measurements in A, 6% of measurements in I, 14% in F, and 2% in X would fall in the outlier zone.
  
  
  CONCLUSIONS
  The method detecting the neutral mechanical axis using inter-femoral head center distances (X) showed the least variability and the lowest percentage of outliers.
authors: Department of Orthopedic Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors: Jai-Gon
authors: JG
authors: Seo
authors: Young-Wan
authors: YW
authors: Moon
authors: Sang-Hoon
authors: SH
authors: Park
authors: Ho-Min
authors: HM
authors: Kang
authors: Sang-Min
authors: SM
authors: Kim
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation* / Q000379:methods*; D001827:Body Height; D015992:Body Mass Index; D015986:Confounding Factors, Epidemiologic; D004867:Equipment Design; D005260:Female; D005270:Femur Head / Q000033:anatomy & histology* / Q000473:pathology; D006621:Hip Joint / Q000033:anatomy & histology; D006801:Humans; D007719:Knee Joint / Q000473:pathology; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D015203:Reproducibility of Results; D055105:Waist Circumference