Fifty-four patients with genu varum and/or osteoarthritis scheduled for an opening wedge high tibial osteotomy (OWHTO) were randomized to receive bone grafting of the open defect with tri-calcium phosphate (TCP) granule (n=27) or allogenous bone chip (n=27). Outcomes of interest included the degree of bone union, pain score on a Visual Analogue Scale (VAS), median proximal tibial angle (MPTA), open wedge size, the Western Ontario and McMaster Universities (WOMAC) Osteoarthritis Index, hip-knee-ankle (HKA) angle, and range of motion (ROM). WOMAC and VAS pain scores were assessed at 6 months and 1 year post-operation, MPTA and HKA angle at 3 months and 1 year post-operation, and ROM at 1 year post-operation. The degree of bone union was assessed radiographically at 6 weeks, 3 months, 6 months, and 1 year post-operation. No statistical significant differences were observed between the TCP and allogenous bone chip groups in all outcomes, at all time-points (p>0.05 for all).