Background: High tibial osteotomy [HTO] is a surgical procedure for treatment of medial compartmental osteoarthritis combined with varus deformities of the knee in middle-aged patients. The goal of this procedure is to shift the weight-bearing axis from the medial compartment to the lateral compartment of the knee joint, resulting in a change of knee alignment from varus to valgus. Although changing the coronal plane is the main purpose of high tibial osteotomy, changes in axial rotation after the procedure has been documented in previous studies. Unintentional change in the axial plane following HTO has been proposed as one of the factors that influence overall gait mechanics and patellofemoral kinematics.

Objective: This study aimed to measure changes in the degree of rotation in the axial plane resulting from biplane medial opening wedge high tibial osteotomy [MOWHTO].

Materials and Methods: Nine patients with medial compartmental osteoarthritis combined with varus
deformity were enrolled in this study. Biplane MOWHTO with medial high tibia plate fixation was performed on all the patients by a single surgeon. The change in rotational profile of the tibia after surgery was determined by comparing the pre- and post-surgery angle between the proximal posterior tibial axis and the distal bimalleolar axis using CT scans. The data were analyzed using a paired t-test. Values of p<0.05 were considered statistically significant.

Results: A change in rotational profile after biplane MOWHTO was found in all patients. Eight patients showed external rotation and one patient showed internal rotation. However, the change in the degree of axial rotation was not significant.

Conclusion: Although not significant, minor changes in the degree of rotation were detected. Those changes suggest that an unintended rotation of the tibia could have occurred during biplane MOWHTO, especially changes in the external rotation patterns. Unintended rotation of the tibia is a factor that needs be considered during the opening of the osteotomy gap in high tibial osteotomy.

Keywords: HTO; Biplane; Medial opening wedge high tibial osteotomy; Rotation profile; External rotation