title: Knee motion variability in patients with knee osteoarthritis: The effect of self-reported instability.
abstract: BACKGROUND
  Knee osteoarthritis has been previously associated with a stereotypical knee-stiffening gait pattern and reduced knee joint motion variability due to increased antagonist muscle co-contractions and smaller utilized arc of motion during gait. However, episodic self-reported instability may be a sign of excessive motion variability for a large subgroup of patients with knee osteoarthritis. The objective of this work was to evaluate the differences in knee joint motion variability during gait in patients with knee osteoarthritis with and without self-reported instability compared to a control group of older adults with asymptomatic knees.
  
  
  METHODS
  Forty-three subjects, 8 with knee osteoarthritis but no reports of instability (stable), 11 with knee osteoarthritis and self-reported instability (unstable), and 24 without knee osteoarthritis or instability (control) underwent Dynamic Stereo X-ray analysis during a decline gait task on a treadmill. Knee motion variability was assessed using parametric phase plots during the loading response phase of decline gait.
  
  
  RESULTS
  The stable group demonstrated decreased sagittal-plane motion variability compared to the control group (p=0.04), while the unstable group demonstrated increased sagittal-plane motion variability compared to the control (p=0.003) and stable groups (p<0.001). The unstable group also demonstrated increased anterior-posterior joint contact point motion variability for the medial tibiofemoral compartment compared to the control (p=0.03) and stable groups (p=0.03).
  
  
  CONCLUSIONS
  The finding of decreased knee motion variability in patients with knee osteoarthritis without self-reported instability supports previous research. However, presence of self-reported instability is associated with increased knee motion variability in patients with knee osteoarthritis and warrants further investigation.
authors: Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA.
authors: Jonathan A
authors: JA
authors: Gustafson
authors: Department of Physical Therapy, University of Pittsburgh, Pittsburgh, PA, USA.
authors: Megan E
authors: ME
authors: Robinson
authors: Department of Physical Therapy, Physical Therapy Clinical and Translational Research Center, University of Pittsburgh, Pittsburgh, PA, USA.
authors: G Kelley
authors: GK
authors: Fitzgerald
authors: Department of Orthopaedic Surgery, Department of Bioengineering, Biodynamics Laboratory, University of Pittsburgh, PA, USA.
authors: Scott
authors: S
authors: Tashman
authors: Departments of Physical Therapy & Bioengineering, Human Movement Research Laboratory, University of Pittsburgh, Pittsburgh, PA, USA. Electronic address: Farrokhi@pitt.edu.
authors: Shawn
authors: S
authors: Farrokhi
mesh_terms: D000368:Aged; D005260:Female; D005684:Gait / Q000502:physiology; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging / Q000209:etiology; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009038:Motion; D009068:Movement; D020370:Osteoarthritis, Knee / Q000150:complications / Q000503:physiopathology*; D011859:Radiography; D057566:Self Report
keywords: Gait; Instability; Kinematics; Variability