title: No difference in patellar tracking between symmetrical and asymmetrical femoral component designs in TKA.
abstract: OBJECTIVE
  Poor knee extension function after total knee arthroplasty (TKA) is associated with factors including articular geometry and alignment. Femoral trochlear geometry has evolved from symmetrical to become more prominent proximal-laterally, with the groove aligned proximal-lateral to distal-medial. This study in vitro tested the hypothesis that a modern asymmetrical prosthesis would restore patellar tracking and stability to more natural behaviour than an older symmetrical prosthesis.
  
  
  METHODS
  Six knees had their patellar tracking measured optically during active knee extension. Medial-lateral force versus displacement stability was measured at fixed angles of knee flexion. The measurements were repeated after inserting each of the symmetrical and asymmetrical TKAs.
  
  
  RESULTS
  Significant differences of patellar lateral displacement stability, compared to normal, were not found at any angle of knee flexion. The patella tracked medial-laterally within 2.5 mm of the natural path with both TKAs. However, for both TKAs near knee extension, the patella was tilted laterally by approximately 6° and was also flexed approximately 8° more than in the natural knee.
  
  
  CONCLUSIONS
  The hypothesis was not supported: The more anatomical component design did not provide more anatomical patellar kinematics and stability.
authors.affiliation: Biomechanics Group, Department of Mechanical Engineering, Imperial College London, London, SW7 2AZ, UK.
authors.forename: J E
authors.initials: JE
authors.lastname: Stoddard
authors.forename: D J
authors.initials: DJ
authors.lastname: Deehan
authors.forename: A M J
authors.initials: AM
authors.lastname: Bull
authors.forename: A W
authors.initials: AW
authors.lastname: McCaskie
authors.forename: A A
authors.initials: AA
authors.lastname: Amis
mesh_terms: D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation*; D001696:Biomechanical Phenomena; D005269:Femur; D006801:Humans; D007719:Knee Joint / Q000502:physiology* / Q000601:surgery; D007720:Knee Prosthesis; D010329:Patella / Q000502:physiology* / Q000601:surgery; D016059:Range of Motion, Articular; D012399:Rotation