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According to Fitzgerald et al study in Pittsburgh, Pennsylvania, USA(14) who
estimated the prevalence of knee buckling in knee osteoarthritis patients at 63% and
assuming a confidence level of 0.05 and an accuracy of 0.01, the sample size was
determined 90.
The patients who were included in the study signed university-approved written informed
consent forms prior to participation and completed demographic data sheets. All
participants were allowed to be excluded at any time, if they did not want to continue the
study. One hundred and two patients were enrolled to study; 12 subjects did not fulfill the
inclusion criteria thus, the main participants were 90 patients (65 females, 25 males).
Data for each subject were collected during one testing session that lasted approximately
1.5 hours. During the session, subjects first completed a demographic and health history
questionnaire, a self?report measure of function, and rated the severity of knee pain and
knee instability. Following completion of the questionnaires, physical performance
measurements of function were administered.
Outcome measures were consisted of knee pain intensity by Visual Analogue Scale (VAS),
timed up and go test (TUG), six-minute walk test (6MWT) and Western Ontario and
McMaster Universities Osteoarthritis Index (WOMAC). Ebrahimzadeh et al assessed validity
and reliability of WOMAC and demonstrated its suitability for Persian speaking patients with
KOA (15).
A self-reported knee instability check list ,based on the study of Felson et al (2),was used to
appraise the episodes of buckling of the knee in the past 3 months. Persons reporting knee
giving way were additionally asked for the number of buckling in the previous 3 months;
whether these episodes concerned the left, right, or both knees and whether knee buckling
had resulted in a fall. We also asked what the patients were doing when their knee buckled
and they were asked to write the name of the activity.
Two functional tests were used for the assessment of performance status in patients with
KOA. In this study the following functional tests were used; three trails of the tests were
performed and the average of their results was recorded.

• The Timed “Up & Go” Test(TUG)
The TUG was used to provide a timed measure of balance and functional mobility in
the KOA patient. The test requires the patient to rise from a standard armchair, walk 3 m at a comfortable pace, walk back to the chair, and sit down. Timing begins when
the person starts to rise from the chair and ends when she returns to the chair and sits down .The time of TUG was recorded by a chronometer Fox 40 (Fox 40 Co, Canada) with 1/100 second precision (16).
• Six-Minute Walk Test (6MWT)
The 6MWT is a safe, easy to administer and good tolerated functional test for KOA patients which reflects activities of daily living. It is a measure of endurance. The primary measurement in 6MWT is the distance covered in 6 min. The 6MWT was completed in an enclosed corridor on a flat course 30 m in length. The object in this test was to walk as quickly as for six minutes around the track (16).

To evaluate the effect of buckling on physical function, we used WOMAC as a self-reported questionnaire consisting of 24 items divided into 3 subscales;
– Pain (5 items): during walking, using stairs, in bed, sitting or lying, and standing upright
– Stiffness (2 items): after first waking and later in the day
– Physical Function (17 items): using stairs, rising from sitting, standing, bending, walking, getting in / out of a car, shopping, putting on / taking off socks, rising from bed, lying in bed, getting in / out of bath, sitting, getting on / off toilet, heavy domestic duties, light domestic duties.
Each item is scored on a scale of 0 to 4 on the basis of the amount of difficulty experienced; the total score ranges from 0 to 96 (15).

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