title: Reliability testing of the patellofemoral joint reaction force (PFJRF) measurement during double-legged squatting in healthy subjects: a pilot study.
abstract: BACKGROUND
  Anterior knee pain or patellofemoral pain syndrome (PFPS) is supposed to be related to patellofemoral joint reaction forces (PFJRF). Measuring these forces may therefore provide reliable evidence for conservative treatments to correct probable malalignment in subjects with PFPS. The aim of the present study was to examine the reliability of PFJRF measurements during double-legged squatting in healthy subjects.
  
  
  METHODS
  Using a motion analysis system and one forceplate, PFJRF of 10 healthy subjects were assessed during double-legged squatting. Data were collected from superficial markers taped to selected landmarks. This procedure was performed on the right knees, at three different knee flexion angles of 30, 45 and 60° during three separate double-legged squats. Subjects were then requested to repeat this test procedure on two separate test sessions at different occasions. The PFJRF was calculated using a biomechanical model of the patellofemoral joint.
  
  
  RESULTS
  The data reveal an increase in PFJRF values (from mean, SD of 425.2, 35.5N to 1075.4, 70.1N)with an increase in the tibiofemoral joint angle during double-legged squatting. The CV (coefficient of variation) values during within and between session tests, revealed the high repeatability and reproducibility of PFJRF measurements, while the ICC (intra class correlation coefficient) values showed the low reliability of these measurements.
  
  
  CONCLUSIONS
  The low reliability of PFJRF measurements suggests that the PFJRF measurement during double-legged squatting should be performed with caution with improving the method of kinetic measurement of the patellofemoral joint in healthy subjects.
authors.affiliation: Department of Physiotherapy, Faculty of Rehabilitation Sciences, Isfahan University of Medical Sciences, PO Box 164, Isfahan 8174673461, Iran. mostamand@rehab.mui.ac.ir
authors.forename: Javid
authors.initials: J
authors.lastname: Mostamand
authors.forename: Dan L
authors.initials: DL
authors.lastname: Bader
authors.forename: Zoë
authors.initials: Z
authors.lastname: Hudson
mesh_terms: D000328:Adult; D018771:Arthralgia / Q000175:diagnosis* / Q000503:physiopathology*; D001696:Biomechanical Phenomena / Q000502:physiology; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods* / Q000592:standards*; D008297:Male; D008954:Models, Biological; D009043:Motor Activity / Q000502:physiology*; D057071:Patellofemoral Joint / Q000502:physiology*; D010865:Pilot Projects; D012016:Reference Values; D015203:Reproducibility of Results; D055815:Young Adult