Demographic, baseline and 6-month follow-up data from the FOOTSTEP trial. 164 patients aged over 50 years with moderate to severe symptomatic radiographic medial knee osteoarthritis. Intervention was flat flexible (n = 82) or stable supportive shoes (n = 82), worn for at least 6 hours a day for 6 months. All data presented in the results paper (Annals of internal medicine. 2021;174:462-471) available in XLSX format.