title: Role of preoperative calculation of condylar twist angle (CTA) by CT scan in optimizing femoral component rotation during TKA.
abstract: BACKGROUND
  A perfect rotational alignment could be achieved if the implant rotation is individualized for each knee before operation. The anatomic transepicondylar axis (aTEA) is a standard reference for setting the femoral component rotation. Intraoperative localization of aTEA is difficult. However, aTEA could be readily identified on preoperative CT scans, and condylar twist angle (CTA) could be determined preoperatively. The femoral component can subsequently be implanted according to CTA. Therefore, perfect intraoperative rotational alignment can be easily achieved. The aim of the study was to evaluate the role of preoperative calculation of CTA by CT scan in optimizing femoral component rotation during TKA.
  
  
  METHODS
  We analyzed fifty-three total knee arthroplasty in 36 primary osteoarthritis patients, aged 49-78 years. CTA was measured on preoperative CT scan. Intraoperative equal magnitude of external rotation was set so that the femoral cut was parallel to aTEA. Postoperative CT scan was done to confirm the femoral component rotation.
  
  
  RESULTS
  Postoperatively, femoral component was parallel to aTEA with a mean error of 0.77°. In 34 knees (64.15%), surgical transepicondylar axis (sTEA) could also be determined; average angle between sTEA and aTEA was 4.65°. Femoral component in these knees was found to be parallel or externally rotated in relation to sTEA (mean 4.22°).
  
  
  CONCLUSIONS
  Preoperative calculation of CTA by CT scan helps to optimize the femoral component rotation during TKA.
authors.affiliation: Department of Orthopedics, Post Graduate Institute of Medical Education and Research, Dr. Ram Manohar Lohia Hospital, New Delhi, 110001, India. sharmadhruv340@gmail.com.|ESIC Medical College and Hospital, NH-3, NIT, Faridabad, Haryana, 132001, India. sharmadhruv340@gmail.com.
authors.forename: D
authors.initials: D
authors.lastname: Sharma
authors.affiliation: Department of Orthopedics, Post Graduate Institute of Medical Education and Research, Dr. Ram Manohar Lohia Hospital, New Delhi, 110001, India.
authors.forename: A
authors.initials: A
authors.lastname: Shukla
authors.affiliation: Department of Orthopedics, ESIC Medical College and Hospital, Faridabad, Haryana, India.
authors.forename: K
authors.initials: K
authors.lastname: Kumar
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging* / Q000601:surgery; D011300:Preoperative Care / Q000379:methods*; D011446:Prospective Studies; D012399:Rotation; D014057:Tomography, X-Ray Computed
keywords: CT scan; Condylar twist angle; Femoral rotation; TKA; Transepicondylar axis