title: Quadriceps strength asymmetry predicts loading asymmetry during sit-to-stand task in patients with unilateral total knee arthroplasty.
abstract: OBJECTIVE
  This study aimed to examine interlimb differences in muscle strength and sit-to-stand (STS) kinetics in persons who underwent unilateral total knee arthroplasty (TKA) and to determine whether knee pain, quadriceps or hip abductor weakness contributes to altered STS performance. It was hypothesized that the operated limb would have weaker muscles, lower mechanical loading and that operated knee pain and muscle strength symmetry would predict loading symmetry between limbs during STS.
  
  
  METHODS
  One hundred and forty-two patients, 6 or 12 months post-unilateral TKA, underwent 3D motion analysis (VICON) of the STS task and isometric strength testing of the quadriceps and hip abductors. Knee pain was also quantified using a question from the Knee Outcome Survey-Activities of Daily Living Scale.
  
  
  RESULTS
  The operated limb had weaker quadriceps (P < 0.001), lower hip (P = 0.004) and knee extension moments (P < 0.001), and lower vertical ground reaction forces (P < 0.001). Operated knee pain and quadriceps strength symmetry were related to symmetry in knee extension moment (P < 0.04), and vertical ground reaction forces (P < 0.02) 6 months after surgery, while quadriceps strength symmetry was related to symmetry in vertical ground reaction forces (P = 0.03), 1 year after surgery.
  
  
  CONCLUSIONS
  Patients with unilateral TKA unload the operated limb and shift the mechanical load to the joints of the contralateral limb even 1 year after surgery. Knee pain and quadriceps strength asymmetry may play a role in the asymmetrical loading during STS post-TKA. Clinicians should consider addressing these modifiable impairments to resolve the loading asymmetry.
  
  
  METHODS
  III.
authors.affiliation: Rehabilitation Sciences Department, College of Applied Medical Sciences, King Saud University, P.O. Box 10219, Riyadh, 11433, Saudi Arabia. alialnahdi@ksu.edu.sa.
authors.forename: Ali H
authors.initials: AH
authors.lastname: Alnahdi
authors.affiliation: Department of Physical Therapy, University of Delaware, Newark, DE, USA.
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Zeni
authors.affiliation: Department of Physical Therapy, University of Delaware, Newark, DE, USA.
authors.forename: Lynn
authors.initials: L
authors.lastname: Snyder-Mackler
mesh_terms: D000203:Activities of Daily Living; D000368:Aged; D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength; D018908:Muscle Weakness / Q000503:physiopathology*; D011184:Postoperative Period; D011187:Posture; D052097:Quadriceps Muscle / Q000503:physiopathology*; D016474:Weight-Bearing
keywords: Altered loading; Knee replacement; Muscle weakness; Quadriceps strength