This two groups, parallel design randomized controlled trial will compare patients with medial compartment knee OA and varus alignment receiving optimized non-surgical treatment plus High Tibial Osteotomy (HTO) to similar patients receiving optimized non-surgical treatment only. All participants will receive non-surgical treatment that will be individualized to the patient and include medications, physiotherapy and nutritional seminars. The non-surgical treatment will include supervised physiotherapy and nutritional seminars once per week for 12 weeks, will be accompanied and followed by a home program, and follow-up appointments for potential modification every three months for the duration of the study. Participants randomized to surgery will also undergo medial opening wedge HTO after 12 weeks of optimized non-surgical treatment. Both groups will follow the same schedule of clinic visits throughout the 24 month follow-up period. MRI-derived measures of articular cartilage morphology, biological markers of articular cartilage degradation and synthesis, gait biomechanics and patient-reported outcomes will be assessed at baseline, 12 and 24 months follow-up.