Study variables Several measures of functional capacity and pain are used. The primary outcome is the Western Ontario and McMaster Universities Osteoarthritis Index of severity of osteoarthrosis symptoms (WOMAC version 3.1). This self-administered questionnaire assesses pain, disability and joint stiffness using 24 items with 5-point Likert scales. Other outcomes included the Brief Pain Inventory (short form), which is administered to assess pain intensity and pain-related functional impairment (physical and emotional). More specifically, four items assess the intensity of current pain and pain at its least, worst, and average during the past day on scales from 0 ("no pain") to 10 ("pain as bad as you can imagine"). Seven more items measure pain-related functional interference in different domains (general activity, mood, walking ability, normal work, relations with other people, sleep, and enjoyment of life) rated from 0 ("does not interfere") to 10 ("interferes completely"). Participants will also rate their pain with the Wong-Baker Faces Pain Rating Scale, a series of 6 faces anchored at 0 for "no hurt" and 5 for "hurts worst". After being instructed that each face is for a person who feels happy because he has no pain or sad because he has some or a lot of pain, participants chose the face that best describes how they feel. Participants also rate their pain with a simple descriptive intensity scale with 7 adjectives (no pain, mild pain, moderate pain, severe pain, very severe pain, and worst pain possible), a numeric distress scale with anchors 0 for "no pain" and 10 for "unbearable pain", and a visual analogue scale with the words "no pain" and "pain as bad as could possibly be" at the left and right ends of the line, respectively. The Timed Up-and-Go Test will be used to evaluate functional capacity. Participants start in a sitting position (with hands resting on the arms of an armchair of standard height), stand up, walke 3 meters, turn around, and walk back to sit down on the chair again. The timing starts when the participant's back comes off the chair, and stops when their buttocks touch the seat of the chair.