Open wedge high tibial osteotomy (OWHTO) has been performed by orthopedic surgeons without filling the osteotomy gap. However, the osteotomy space dimensionand fixation methods suitable for this method are still controversial. We use the metaphyseal cancellous bone of tibia distal fragment; using a special technique to slide thecancellous bone into the osteotomy gap to provide better bone healing. This study was conducted to investigate the benefits of this method in terms of bone union. Thiswas designed as a prospective randomized controlled study. There are 17 patients in each group. Patients with an osteotomy gap of only 12 mm were included in the studyin preoperative planning. The Lysholm Knee Scoring Scale was used to assess the functional status of the patients. Hip Knee ankle (HKA) angle and tibial posterior slopeangle were measured during preoperative and control visits. Bone healing was assessed by trabecular and cortical continuity on anteroposterior and lateral radiographs.Reduced pain and recovery of functions confirmed the union. The mean union time was 14.3 ± 4.7 (12-22) weeks in the control group and 13.1 ± 3.9 (11-18) weeks in thegraft sliding group (P = 0.04). In the control group, the HKA angle was 10.8 ± 2.5 ° Varus preoperatively and 2.1 ± 1.4 ° valgus at second-year control visit. In the graftsliding group, preoperative HKA angel was found 11.3 ± 1.9 ° Varus and 2.7 ± 2.1 ° valgus at second-year control visit (p> 0.05). There was no statistically significantdifference between the groups in terms of Lysholm Knee Scale scores at preoperative and postoperative second-year control visits. The sliding cancellous bone of thetibial distal fragment into the osteotomy gap provided earlier bone union than the control group. There was no difference in functional results between the groups in thetwo-year follow-up results of the patients.