title: Measurement characteristics of a force-displacement curve for chronic patellar instability.
abstract: OBJECTIVE
  The clinical diagnosis of patellar instability is subjective, depending on the patient's apprehension. We hypothesized that a subjective diagnosis could be supported by a numerical evaluation of the slope, or compliance, of the early phase of a force-displacement curve.
  
  
  METHODS
  Cross-sectional control group comparison.
  
  
  METHODS
  A university-based sports clinic.
  
  
  METHODS
  Healthy volunteers (n = 21; 16-40 years old) and patients (n = 21; 15-34 years old) who had a clearly definable diagnosis of unilateral dislocation, followed by chronic anterior knee pain, and positive apprehension signs for more than 6 months, without patella alta or abnormal limb alignment.
  
  
  METHODS
  Lateral displacement and reactive forces were measured with a Patella Stability Tester.
  
  
  METHODS
  Sensitivity in detecting injured knees was defined, with the 95% confidence interval of healthy subjects determined as the normal range.
  
  
  RESULTS
  Compliance at 5 mm in displacement showed the highest reproducibility (plot difference of 4.7%) and the highest sensitivity (95%). Among injured knees, compliance was significantly correlated with the activity-related symptoms of the Kujala score (correlation coefficient, -0.61; P = 0.004). Compliance at 5 mm of displacement showed the highest sensitivity (95%) and significant correlation with the activity-related symptoms of the Kujala score among injured knees (coefficient of determination, 0.37; P = 0.004).
  
  
  CONCLUSIONS
  It is a novel finding that early compliance at 5 mm of displacement showed a correlation with the subjective diagnosis and symptoms.
authors.affiliation: Departments of Rehabilitation, Faculty of Medicine, Shimane University, Izumo, Shimane, Japan.
authors.forename: Norimasa
authors.initials: N
authors.lastname: Egusa
authors.forename: Ryuji
authors.initials: R
authors.lastname: Mori
authors.forename: Yuji
authors.initials: Y
authors.lastname: Uchio
mesh_terms: D000293:Adolescent; D000328:Adult; D002908:Chronic Disease; D003187:Compliance; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000175:diagnosis*; D007718:Knee Injuries / Q000175:diagnosis* / Q000503:physiopathology*; D008297:Male; D010329:Patella / Q000503:physiopathology*; D031222:Patellar Dislocation / Q000175:diagnosis* / Q000503:physiopathology*; D055815:Young Adult