High rates of outliers in computer-assisted high tibial osteotomy with excellent mid-term outcomes.

PURPOSE: The primary aim was to evaluate the accuracy of navigation in opening wedge high tibial osteotomy (HTO). The secondary aim was to examine mid-term outcomes after HTO. METHODS: Inclusion criteria were patients with medial compartment knee osteoarthritis who underwent computer-assisted HTOs. Mechanical axis (MA), percentage MA (%MA), and change in posterior tibial slope (ΔPTS) were displayed on the navigation screen. Radiographic examinations included hip-knee-ankle (HKA) angle, medial proximal tibial angle (MPTA), joint line convergence angle (JLCA), and PTS. Preoperative and 5 weeks postoperative standing radiographs of the whole lower extremity and knee were used. Clinical evaluations were performed using American Knee Society knee score and function score both preoperatively and at last follow-up. Radiographic evaluations were performed by orthopedic surgeons. Intraoperative navigation after osteotomy and postoperative standing radiograph were compared. MA (HKA), %MA, and ΔPTS were compared. Outliers were defined as > 3° in MA, > 10% in %MA, and > 10° in ΔPTS. Outlier and non-outlier groups were compared. The rate of conversion to arthroplasty was examined. RESULTS: This study involved 38 patients (44 knees) and last follow-up was at a mean of 5 years (range, 1-9 years). Mean American Knee Society knee score and function score improved significantly from 59 to 69 preoperatively to 95 and 85 at last follow-up, respectively. Absolute values of mean errors for MA, %MA, and ΔPTS were 2.1°, 9.3%, 1.2°, respectively. Outlier rates were 18% in MA, 39% in %MA, and 5% in ΔPTS. No significant factors were found in MA and ΔPTS. In %MA, preoperative JLCA was significantly higher in the outlier group compared to the non-outlier group. No knees underwent conversion to total knee arthroplasty. No differences in outcomes were found between outlier and non-outlier groups. CONCLUSION: Although rates of outlier values in computer-assisted opening wedge HTO were high, mid-term outcomes were excellent. LEVEL OF EVIDENCE: IV.