Objective: Open wedge high tibial osteotomy (OWHTO) is an established procedure for medial knee osteoarthritis (OA). The use of a navigation system enables acquisition of an accurate correction angle and better clinical outcomes. However, the difference in the coronal alignment between the intraoperative navigation system and the postoperative radiograph in OWHTO is unknown. We defined this difference as the navigation correction loss (NCL). We examined the relationship between the stage of OA and NCL, soft tissue laxity, and clinical outcome.

Methods: Fifty seven patients (68 knees) who underwent OWHTO with a navigation system for OA were enrolled. Patients were divided into two groups by the Yokohama City University OA classification. Grade 1 or 2 were defined as the low grade OA group, and Grade 3 or more were defined as the progressive OA group. The low grade OA group included 42 knees and the progressive OA group included 26 knees, respectively. Soft tissue laxity was evaluated by the preoperative joint line convergence angle (JLCA), and the difference of it between preoperative and postoperative radiographs (⊿JLCA). Japan Orthopedic Association (JOA) score, American Knee Society score (KSS), and Function score (FS) were used for the evaluation of clinical outcome before and after OWHTO. We examined absolute values of NCL (｜NCL｜), JLCA, ⊿JLCA, and clinical scores between low grade and progressive OA groups.

Results: The mean hip-knee-ankle angle (HKA) in the intraoperative navigation was −3.8±1.8°, and postoperative radiograph was −4.6±2.5° (P＝0.008). The mean｜NCL｜in the low grade OA group was 1.8±1.5°, and that in the progressive OA group was 2.6±1.3° (P＝0.007). The mean preoperative JLCAs were 3.7±2.0° and 5.9±2.1°in the low grade and progressive OA groups, respectively (P＝0.001). No differences were found in preoperative clinical scores, but postoperative KSS had a difference between the low grade OA group (90.5±5.1) and the progressive OA group (86.3±8.5) (P＝0.033).

Conclusion: A navigation system is useful for OWHTO in terms of accurate correction and good clinical scores especially in low grade OA.