High tibial osteotomy (HTO) is a surgical procedure used to treat early unicompartmental tibiofemoral osteoarthritis. HTO is typically performed on younger and more active patients with the goal of unloading the diseased cartilage and potentially delaying total knee arthroplasty. According to long-term studies, total knee replacements are required in more than 25% of knees 10 years after an HTO. Revisions of the HTO are typically related to poor patient selection, failure of surgical technique, and/or progression of the osteoarthritis. Total knee replacement after a failed HTO can be complicated by many of the following features: undercorrection, overcorrection, loss of correction, patella baja, arthrofibrosis, intra-articular fractures, nonunion, infection, peroneal nerve dysfunction, compartment syndrome, and/or thromboembolic disease. The surgery is more complex because of the presence of previous skin incisions, hardware, and an enlarged surgical exposure. Before performing a total knee arthroplasty after a failed HTO, the surgeon must understand the principles of HTO, possible complications, and the reasons for revisions.