title: Transepicondylar axes for femoral component rotation might produce flexion asymmetry during total knee arthroplasty in knees with proximal tibia vara.
abstract: BACKGROUND
  Adequate rotation of the femoral component in total knee arthroplasty is mandatory for prevention of numerous adverse sequelae. Therefore, we investigate whether there is the distal femoral deformity in knees with tibia vara. The purpose of this study was to evaluate the reliability of the transepicondylar axis as a rotational landmark in knees with tibia vara.
  
  
  METHODS
  We retrospectively reviewed and selected 101 osteoarthritic knees with proximal tibia vara and 150 osteoarthritic knees without tibia vara for inclusion in this study. The transepicondylar axis (TEA), anteroposterior (AP) axis and posterior condylar (PC) line were measured using the axial image from magnetic resonance imaging axial images. We compared the external rotation angle of the TEA relative to the PC line between groups in order to investigate the presence of distal femoral anatomical adaptation in the tibia vara group.
  
  
  RESULTS
  The TEA in the tibia vara group had 6.1º of external rotation relative to the PC line, which was not significantly different from the 6.0º of external rotation in the non-tibia vara group. The line perpendicular to the AP axis in the tibia vara group had 6.1º of external rotation relative to the PC line, which was not significantly different from the 5.4º of external rotation in the non-tibia vara group. Distal femoral geometry was unaffected by the tibia vara deformity.
  
  
  CONCLUSIONS
  The use of transepicondylar axes in determining femoral rotation may produce flexion asymmetry in knees with tibia vara.
  
  
  METHODS
  Level III.
authors.affiliation: Joint & Arthritis Research, Department of Orthopaedic Surgery, Himchan Hospital, Seoul, Korea.
authors.forename: Il Seok
authors.initials: IS
authors.lastname: Park
authors.affiliation: Rothman Institute, NJ, USA.
authors.forename: Alvin
authors.initials: A
authors.lastname: Ong
authors.affiliation: Joint & Arthritis Research, Department of Orthopaedic Surgery, Himchan Hospital, Seoul, Korea.
authors.forename: Chang Hyun
authors.initials: CH
authors.lastname: Nam
authors.affiliation: Joint & Arthritis Research, Department of Orthopaedic Surgery, Himchan Hospital, Seoul, Korea.
authors.forename: Nong Kyum
authors.initials: NK
authors.lastname: Ahn
authors.affiliation: Joint & Arthritis Research, Department of Orthopaedic Surgery, Himchan Hospital, Seoul, Korea.
authors.forename: Hye Sun
authors.initials: HS
authors.lastname: Ahn
authors.affiliation: Joint & Arthritis Research, Department of Orthopaedic Surgery, Himchan Hospital, Seoul, Korea.
authors.forename: Su Chan
authors.initials: SC
authors.lastname: Lee
authors.affiliation: Joint & Arthritis Research, Department of Orthopaedic Surgery, Himchan Hospital, Seoul, Korea. Electronic address: kwangamj@gmail.com.
authors.forename: Kwang Am
authors.initials: KA
authors.lastname: Jung
mesh_terms: D000368:Aged; D059925:Anatomic Landmarks; D019645:Arthroplasty, Replacement, Knee; D060750:Bone Anteversion / Q000150:complications; D016022:Case-Control Studies; D005260:Female; D005269:Femur / Q000033:anatomy & histology* / Q000601:surgery; D006801:Humans; D007720:Knee Prosthesis; D008279:Magnetic Resonance Imaging; D008297:Male; D020370:Osteoarthritis, Knee / Q000601:surgery; D017755:Prosthesis Fitting / Q000379:methods*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012399:Rotation; D013977:Tibia / Q000002:abnormalities* / Q000601:surgery
keywords: Flexion gap; Magnetic resonance imaging; Rotational axis; Tibia vara; Total knee arthroplasty