Participation in this study will last about 3 to 9 months. All eligible participants will wear the same knee brace for a 2-week run-in period during which they will record when they wear the brace and any pain medication used. Next, participants will be randomly assigned to wear one of two knee braces for 6 weeks and a minimum of 4 hours each day. This will be followed by 6 weeks of wearing no knee brace, and then by 6 weeks of wearing whichever knee brace they did not wear during the first 6-week period. There will be a total of nine study visits. The first study visit will screen for eligible participants and will include an interview, knee evaluations, x-rays, and a urine pregnancy test. The second and sixth study visits will include knee evaluations, brace fittings, and instructions on how to correctly wear and adjust the brace. Most of the other study visits will consist primarily of interviews and functional tests. During the first and third 6-week periods, participants will maintain a log to record how long they wear their braces and any pain medication used. Participants will also wear an accelerometer, which will keep track of how many steps they take.