title: The effects of kinematically aligned total knee arthroplasty on stress at the medial tibia: A case study for varus knee.
abstract: OBJECTIVE
  Little biomechanical information is available about kinematically aligned (KA) total knee arthroplasty (TKA). The purpose of this study was to simulate the kinematics and kinetics after KA TKA and mechanically aligned (MA) TKA with four different limb alignments.
  
  
  METHODS
  Bone models were constructed from one volunteer (normal) and three patients with three different knee deformities (slight, moderate and severe varus). A dynamic musculoskeletal modelling system was used to analyse the kinematics and the tibiofemoral contact force. The contact stress on the tibial insert, and the stress to the resection surface and medial tibial cortex were examined by using finite element analysis.
  
  
  RESULTS
  In all bone models, posterior translation on the lateral side and external rotation in the KA TKA models were greater than in the MA TKA models. The tibiofemoral force at the medial side was increased in the moderate and severe varus models with KA TKA. In the severe varus model with KA TKA, the contact stress on the tibial insert and the stress to the resection surface and to the medial tibial cortex were increased by 41.5%, 32.2% and 53.7%, respectively, compared with MA TKA, and the bone strain at the medial side was highest among all models.
  
  
  CONCLUSIONS
  Near normal kinematics was observed in KA TKA. However, KA TKA increased the contact force, stress and bone strain at the medial side for moderate and severe varus knee models. The application of KA TKA for severe varus knees may be inadequate.Cite this article: S. Nakamura, Y. Tian, Y. Tanaka, S. Kuriyama, H. Ito, M. Furu, S. Matsuda. The effects of kinematically aligned total knee arthroplasty on stress at the medial tibia: A case study for varus knee. Bone Joint Res 2017;6:43-51. DOI: 10.1302/2046-3758.61.BJR-2016-0090.R1.
authors.affiliation: Department of Orthopedic Surgery, Kyoto University, Graduate School of Medicine, 54 Shogoinkawaharacho, Sakyo-ku, Kyoto 606-8507, Japan shnk@kuhp.kyoto-u.ac.jp.
authors.forename: S
authors.initials: S
authors.lastname: Nakamura
authors.affiliation: Department of Orthopedic Surgery, Kyoto University, Graduate School of Medicine, 54 Shogoinkawaharacho, Sakyo-ku, Kyoto 606-8507, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Tian
authors.affiliation: Department of Orthopedic Surgery, Kyoto University, Graduate School of Medicine, 54 Shogoinkawaharacho, Sakyo-ku, Kyoto 606-8507, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Tanaka
authors.affiliation: Department of Orthopedic Surgery, Kyoto University, Graduate School of Medicine, 54 Shogoinkawaharacho, Sakyo-ku, Kyoto 606-8507, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Kuriyama
authors.affiliation: Department of Orthopedic Surgery, Kyoto University, Graduate School of Medicine, 54 Shogoinkawaharacho, Sakyo-ku, Kyoto 606-8507, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Ito
authors.affiliation: Department of Orthopedic Surgery, Kyoto University, Graduate School of Medicine, 54 Shogoinkawaharacho, Sakyo-ku, Kyoto 606-8507, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Furu
authors.affiliation: Department of Orthopedic Surgery, Kyoto University, Graduate School of Medicine, 54 Shogoinkawaharacho, Sakyo-ku, Kyoto 606-8507, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Matsuda
keywords: Computer simulation; Contact stress; Finite element analysis; Kinematic alignment; Total knee arthroplasty