title: No condylar lift-off occurs because of excessive lateral soft tissue laxity in neutrally aligned total knee arthroplasty: a computer simulation study.
abstract: OBJECTIVE
  Condylar lift-off can induce excessive polyethylene wear after total knee arthroplasty (TKA). A computer simulation was used to evaluate the influence of femoral varus alignment and lateral collateral ligament (LCL) laxity on lift-off after single-design TKA. It was hypothesised that proper ligament balancing and coronal alignment would prevent lift-off.
  
  
  METHODS
  The computer model in this study is a dynamic musculoskeletal program that simulates gait up to 60° of knee flexion. The lift-off phenomenon was defined as positive with an intercomponent distance of >2 mm. In neutrally aligned components in the coronal plane, the femoral and tibial components were set perpendicular to the femoral and tibial mechanical axis, respectively. The femoral coronal alignment was changed from neutral to 5° varus in 1° increments. Simultaneously, the LCL length was elongated from 0 to 5 mm in 1-mm increments to provide a model of pathological slack.
  
  
  RESULTS
  Within 2° of femoral varus alignment, lift-off did not occur even if the LCL was elongated by up to 5 mm. However, lift-off occurred easily in the stance phase in femoral varus alignments of >3° with slight LCL slack. The contact forces of the tibiofemoral joint were influenced more by femoral varus alignment than by LCL laxity.
  
  
  CONCLUSIONS
  Aiming for neutral alignment in severely varus knees makes it difficult to achieve appropriate ligament balance. Our study suggests that no lift-off occurs with excessive LCL laxity alone in a neutrally aligned TKA and therefore that varus alignment should be avoided to decrease lift-off after TKA.
  
  
  METHODS
  Case series, Level IV.
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto, 606-8507, Japan. kuriyama@kuhp.kyoto-u.ac.jp.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Kuriyama
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto, 606-8507, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Ishikawa
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto, 606-8507, Japan.
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Nakamura
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto, 606-8507, Japan.
authors.forename: Moritoshi
authors.initials: M
authors.lastname: Furu
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto, 606-8507, Japan.
authors.forename: Hiromu
authors.initials: H
authors.lastname: Ito
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto, 606-8507, Japan.
authors.forename: Shuichi
authors.initials: S
authors.lastname: Matsuda
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D005260:Female; D005269:Femur / Q000601:surgery; D005684:Gait / Q000502:physiology; D006801:Humans; D007593:Joint Instability; D007717:Knee / Q000601:surgery; D007719:Knee Joint / Q000601:surgery; D007720:Knee Prosthesis; D017844:Lateral Ligament, Ankle / Q000601:surgery; D008297:Male; D013977:Tibia / Q000601:surgery
keywords: Computer simulation; Condylar lift-off; Femoral varus alignment; Lateral collateral ligament laxity; Total knee arthroplasty