title: Variations in ankle registration using two different anatomic landmarks: a radiographic study.
abstract: OBJECTIVE
  To quantify the average deviation in tibial mechanical axis registration when registering the ankle centre using (a) the extreme medial and lateral points and (b) the most distal points, of the respective malleoli, and to identify whether body mass index (BMI) had any significant effect on mechanical axis registration error.
  
  
  METHODS
  The preoperative standing hip-knee-ankle radiographs of 40 patients who underwent navigated TKR at our institution were reviewed. The divergence from the anatomic ankle centre in degrees and millimetres was compared when using the Extremes Midpoint and the Distal Midpoint techniques.
  
  
  RESULTS
  No significant divergence was measured with either the Extremes Midpoint (0.2° lateral, SD = 0.5°; 1.1 mm lateral, SD = 2.6 mm) or the Distal Midpoint (0.2° lateral, SD = 0.6°; 1.7 mm lateral, SD = 2.3 mm) techniques. BMI had no significant effect on these differences.
  
  
  CONCLUSIONS
  Both the Extremes Midpoint and the Distal Midpoint techniques offer accurate registration of the ankle centre. BMI does not seem to affect the registration of the ankle centre with either technique. The findings of this study will help knee surgeons when choosing an ankle registration technique. These results may also lead to more accurate knee replacement navigation systems.
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 E 70th St., New York, NY, 10021, USA, eduardosuero@gmail.com.
authors.forename: Eduardo M
authors.initials: EM
authors.lastname: Suero
authors.forename: Mustafa
authors.initials: M
authors.lastname: Citak
authors.forename: Charles
authors.initials: C
authors.lastname: Claps
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Pearle
authors.forename: Christopher
authors.initials: C
authors.lastname: Plaskos
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D059925:Anatomic Landmarks / Q000000981:diagnostic imaging*; D000843:Ankle Joint / Q000000981:diagnostic imaging*; D019645:Arthroplasty, Replacement, Knee; D005260:Female; D006621:Hip Joint / Q000000981:diagnostic imaging; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000601:surgery; D008297:Male; D008875:Middle Aged; D011187:Posture; D011859:Radiography