title: Normal Femorotibial Rotational Alignment and Implications for Total Knee Arthroplasty: an MRI Analysis.
abstract: BACKGROUND
  Rotational alignment of prosthetic components in total knee arthroplasty (TKA) is important to successful outcomes. Component malrotation is a known cause of revision and understanding normal rotational alignment may help recreate normal joint kinematics. To date, no large MRI study assessing femorotibial rotational alignment in nonarthritic knees has been undertaken.
  
  
  OBJECTIVE
  Is Insall's tibial axis a reliable rotational landmark against common femoral rotational axes in the nonarthritic patient population?
  
  
  METHODS
  We reviewed 544 knee MRI scans performed for suspected soft tissue pathology and identified Insall's tibial rotational axis as well as the femoral clinical trans-epicondylar axis (TEAc), femoral surgical trans-epicondylar axis (TEAs), posterior condylar articular axis (PCA), and a modified Eckhoff's cylindrical axis. The perpendiculars of these axes were superimposed on Insall's tibial axis, and the angular differences were measured.
  
  
  RESULTS
  Insall's axis was internally rotated to the TEAc by 1.4°, externally rotated to Eckhoff's cylindrical axis by 1.8°, externally rotated to the TEAs by 2.7°, and externally rotated to the PCA by 3.5°. The mean deviation from 0° (optimal alignment for each femoral axis) was significantly greater for the PCA relative to all other femoral axis.
  
  
  CONCLUSIONS
  Insall's axis is a reliable landmark for rotational positioning of the tibial component and may optimize femorotibial kinematics in fixed-bearing TKA.
authors.affiliation: Sydney Knee Specialists, 8/19 Kensington St, Kogarah, NSW 2217 Australia.
authors.forename: Gregory C
authors.initials: GC
authors.lastname: Wernecke
authors.affiliation: Sydney Knee Specialists, 8/19 Kensington St, Kogarah, NSW 2217 Australia.
authors.forename: Ian A
authors.initials: IA
authors.lastname: Harrris
authors.affiliation: Sydney Knee Specialists, 8/19 Kensington St, Kogarah, NSW 2217 Australia.
authors.forename: Bradley G
authors.initials: BG
authors.lastname: Seeto
authors.affiliation: Sydney Knee Specialists, 8/19 Kensington St, Kogarah, NSW 2217 Australia.
authors.forename: Darren B
authors.initials: DB
authors.lastname: Chen
authors.affiliation: Sydney Knee Specialists, 8/19 Kensington St, Kogarah, NSW 2217 Australia.
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: MacDessi
keywords: Insall axis; alignment; femoro-tibial congruity; knee; rotation; tibial component alignment