title: A biomechanical comparison between the single-axis and multi-axis total knee arthroplasty systems for the stand-to-sit movement.
abstract: BACKGROUND
  Compared to the design of a traditional multi-axis total knee arthroplasty, the single-axis arthroplasty studied has a fixed flexion/extension center of rotation in the femoral component. The influence of this characteristic on functional daily activity, i.e., stand-to-sit, is not well understood. The purpose of this study was to investigate the effect of different arthroplasty designs on knee kinematic and lower limb muscular activation for the stand-to-sit movement.
  
  
  METHODS
  Sixteen unilateral, posterior-stabilized knee arthroplasty participants (8 single-axis and 8 multi-axis) with excellent Knee Society scores performed 4 trials of the stand-to-sit test. Three-dimensional video analysis of whole body and joint kinematics and electromyography analysis of quadriceps and hamstrings were conducted. One-way ANOVAs were used for statistical analyses (alpha=0.05).
  
  
  RESULTS
  The multi-axis group showed some functional adaptations while sitting down. The single-axis group exhibited less arthroplasty limb quadriceps electromyography and hamstring co-activation electromyography than the multi-axis group. For the arthroplasty limb, single-axis demonstrated less abduction angular displacement and reached peak abduction earlier than the multi-axis arthroplasty limb. The estimated effect size for this study was 0.196.
  
  
  CONCLUSIONS
  The single-axis design requires less eccentric knee extensor muscle activation and exhibits greater medio-lateral stability than the multi-axis designs. Findings from this study could provide useful information to orthopedic knee surgeons and rehabilitative specialists.
authors.affiliation: Department of FNES, Queens College, 203 Fitzgerald Gym., Flushing, NY 11367, USA. hewang@forbin.qc.edu
authors.forename: H
authors.initials: H
authors.lastname: Wang
authors.forename: K J
authors.initials: KJ
authors.lastname: Simpson
authors.forename: S
authors.initials: S
authors.lastname: Chamnongkich
authors.forename: T
authors.initials: T
authors.lastname: Kinsey
authors.forename: O M
authors.initials: OM
authors.lastname: Mahoney
mesh_terms: D000222:Adaptation, Physiological; D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation / Q000379:methods; D001696:Biomechanical Phenomena / Q000379:methods; D004576:Electromyography / Q000379:methods*; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology* / Q000601:surgery*; D007720:Knee Prosthesis; D035002:Lower Extremity / Q000503:physiopathology; D008297:Male; D009068:Movement; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000503:physiopathology*; D011187:Posture; D020127:Recovery of Function / Q000502:physiology; D016896:Treatment Outcome