Middle-aged athletes represent adults from the age of 35 to 60 years for the purposes of this discussion. The prevalence of knee osteoarthritis increases with age, and older people are staying active longer. The indications for opening wedge high tibial osteotomy (owHTO) continue to grow. owHTO correct malalignment to unload the medial joint in middle-aged athletes with a varus knee who want to return to high-impact activities. owHTO may be combined with cartilage preserving procedures, or with ligament reconstructions. We describe our preferred surgical technique and surgical implant with advanced guidance system to create predictable accurate results.