Introduction: The long-term results of HTO depends on exact reconstruction of the weight bearing line. The lack of exact intraoperative real time control of the mechanical axis often results in postoperative malalignments. After preopertive planing and intraoperative measurement of the deformities, HTO is performed under navigation. The system shows the weight bearing line, the size of the osteotomy wedge and the tibial slope. Aim of the current study is to evaluate accuracy of intraoperative datas using the OrthoPilot in comparison to long standing radiographs including the center of the hip, knee and ankle joint.

Material and method: 54 patients with a mean age 49.7 years underwent HTO with navigation using the Ortho-Pilot. According to Ahlback’s staging 1 patient had I, 4 II, 21 III, 19 IV and 9 V osteoarthritis of the knee.

Results: The mean preoperative deviation of the mechanical axis was 6.0 varus (3 to 14) on the x-ray and was confirmed by the OrthoPilot. The mean postoperative mechanical axis was 1.7 valgus (2 varus to 5 valgus) on the x-ray and was confirmed by the OrthoPilot with 1.4 valgus (0 to 3 valgus). The mean postoperative femorotibial angle was 7.1 (2–11). Complications related to the navigation procedure was one hematoma of the distal pin track.

Conclusion: By using an intraoperative navigation system, the outcome of the preoperative planned procedure becomes more predictable and more precision of the alignment can be achieved in HTO. Long-term studies will have to be carried out to verify whether this will lead to a lasting benefit for the patient.