title: No influence of coronal laxity and alignment on lift-off after well-balanced and aligned total knee arthroplasty.
abstract: OBJECTIVE
  In vivo fluoroscopic analyses have revealed the kinematics after total knee arthroplasty (TKA), including femoral condylar lift-off. This study asked whether differences in static varus-valgus laxity or coronal limb alignment after TKA affect lift-off under weight-bearing conditions. It was hypothesised that there is a correlation between coronal laxity or alignment and lift-off during walking.
  
  
  METHODS
  The current study analysed nineteen subjects undergoing cruciate-retaining TKA performed by the measured resection technique. The varus-valgus laxity at knee extension was measured using a 150 N stress radiograph. The mechanical axis was measured using a full-standing radiograph. Continuous radiological images were taken while the subject walked on a treadmill, and the images during single-leg stance were analysed to determine the lift-off using a 3D-to-2D image-to-model registration technique.
  
  
  RESULTS
  The average angle in varus/valgus stress was 6.8 ± 1.8°/6.6 ± 2.1°. No statistically significant differences were observed between the varus and valgus laxity. The average amount of lift-off was 0.7 ± 0.4 mm. The static varus-valgus laxity (n. s.) or the differences in the laxities (n. s.) on the stress radiograph did not influence lift-off. The weight-bearing ratio was achieved within the middle third of the knee in 90 % of subjects. Two outliers with valgus alignment (68 ± 1 %) demonstrated no significant difference in lift-off in comparison with the majority of the subjects (46 ± 9 %).
  
  
  CONCLUSIONS
  The static coronal laxity and alignment did not influence the lift-off under dynamic weight-bearing conditions after well-balanced and aligned cruciate-retaining TKA. Measured resection technique can produce sufficient coronal stability and alignment without significant lift-off during walking.
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan, hamachan@ortho.med.kyushu-u.ac.jp.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Hamai
authors.forename: Hiromasa
authors.initials: H
authors.lastname: Miura
authors.forename: Ken
authors.initials: K
authors.lastname: Okazaki
authors.forename: Takeshi
authors.initials: T
authors.lastname: Shimoto
authors.forename: Hidehiko
authors.initials: H
authors.lastname: Higaki
authors.forename: Yukihide
authors.initials: Y
authors.lastname: Iwamoto
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D005260:Female; D005269:Femur / Q000601:surgery; D006801:Humans; D021621:Imaging, Three-Dimensional; D007593:Joint Instability / Q000000981:diagnostic imaging / Q000503:physiopathology*; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D011859:Radiography; D016138:Walking / Q000502:physiology; D016474:Weight-Bearing