This study is a randomized controlled trial to investigate a novel treatment for patients with painful knee osteoarthritis. The study will recruit patients who have osteoarthritis isolated to the medial compartment of the knee. Half of the patients will participate in a gait retraining program to alter their foot placement during walking; the other half will be assigned to a self-directed walking group. Gait retraining will be subject-specific and will depend on a key feature of each subject's baseline gait, namely which peak (early or late) in the bi-modal knee adduction moment (KAM) profile is larger. The retraining will involve changing the foot progression angle, which is the angle the foot makes relative to the forward direction. The intervention will involve either increasing internal foot rotation (toe-in) or increasing external foot rotation (toe-out). Previously, toe-in has been shown to reduce only the first peak, whereas toe-out has been shown to reduce only the second peak. Because of the personalized intervention, we expect all retrained subjects will be able to reduce the (larger) peak KAM and to reduce knee pain. Based on previous studies, we expect that approximately 80% of subjects in the gait retraining group will need to increase toe-in, and 20% of subjects will need to increase toe-out. Gait retraining will be done using a vibration feedback device taped to the lower leg as each subject walks on a treadmill. Body segment kinematics will be captured and ground reaction forces will be measured. During each step, subjects will receive vibration feedback informing them how they should change their foot progression angle during the next step. Real-time feedback facilitates training since an individual knows immediately whether their foot placement was correct or not, and they are informed via the feedback signal whether or not to change their foot angle during the next step. The gait retraining consists of once a week sessions for six weeks. The training uses a fading feedback approach, where the percentage of each weekly session during which feedback is used is decreased from week to week until no feedback is used by the last training session. At that point the new gait pattern is internalized and that new pattern then represents the new “natural” gait pattern for each individual. Throughout the six-week training period subjects will be encouraged to practice their new gait for at least ten minutes per day. After the six-week training, subjects will continue to use their new gait. Subjects will undergo gait lab checks at weeks 21, 31 and 41 and monitoring of foot progression angle under free-living conditions using “smart” shoes during weeks 8, 31 and 52 to assess retention, with refresher training if necessary. Their last assessment will be at 52 weeks. Participants in the control group will receive an educational pamphlet developed by the Arthritis Foundation that describes the benefits of regular walking for those with arthri...