title: Reproducibility of intra-operative measurement of the mechanical axes of the lower limb during total knee replacement with a non-image-based navigation system.
abstract: OBJECTIVE
  The restoration of a normal mechanical axis of the lower limb following total knee prosthesis (TKP) depends on the accuracy of the intra-operative measurement of the femoro-tibial angle. We have studied the reproducibility of intra-operative measurement of the coronal mechanical femoro-tibial axis with the OrthoPilot (Aesculap, Tuttlingen, Germany) non-image-based navigation system.
  
  
  METHODS
  A consecutive series of 20 TKP (Aesculap SEARCH Evolution prosthesis) implanted by the same surgical team of two senior orthopedic surgeons was analyzed. They used a non-image-based navigation system that allows the mechanical axes of the femur and tibia to be defined with a kinematic analysis. The operating surgeon and assistant surgeon performed the kinematic analysis twice and once, respectively, and measured coronal mechanical femoro-tibial angles in maximal extension and at 90 degrees flexion without varus or valgus stress.
  
  
  RESULTS
  The mean intra-observer variation in the measurement of the coronal mechanical femoro-tibial angle in maximal extension was 0.1 degrees (SD = 0.7 degrees). The mean intra-observer variation in the measurement of the coronal mechanical femoro-tibial angle at 90 degrees of knee flexion was 0.2 degrees (SD = 0.6 degrees). The mean inter-observer variation in the measurement of the coronal mechanical femoro-tibial angle in maximal extension was 0.1 degrees (SD = 0.7 degrees). The mean inter-observer variation in the measurement of the coronal mechanical femoro-tibial angle in maximal extension was 0.0 degrees (SD = 0.6 degrees). There were no significant differences and a high correlation between all paired intra- and inter-observer measurements.
  
  
  CONCLUSIONS
  This system allows high reproducibility of the intra-operative measurement of the mechanical axes of the lower limb by a non-image-based kinematic registration of the hip, knee and ankle centers.
authors.affiliation: Centre de Traumatologie et d'Orthopédie, Illkirch, France. jean-yves.jenny@evc.net
authors.forename: Jean-Yves
authors.initials: JY
authors.lastname: Jenny
authors.forename: Cyril
authors.initials: C
authors.lastname: Boeri
authors.forename: Frédéric
authors.initials: F
authors.lastname: Picard
authors.forename: François
authors.initials: F
authors.lastname: Leitner
mesh_terms: D019645:Arthroplasty, Replacement, Knee; D003198:Computer Simulation; D006801:Humans; D007720:Knee Prosthesis; D007866:Leg / Q000033:anatomy & histology*; D016343:Monitoring, Intraoperative / Q000295:instrumentation*; D015203:Reproducibility of Results