Influence of hindfoot alignment on postoperative lower limb alignment in medial opening wedge high tibial osteotomy.

ABSTRACT

INTRODUCTION: We have experienced unexpected under-correction after medial opening wedge high tibial osteotomy (MOWHTO). Although the tibia was corrected accurately, the postoperative mechanical axis (MA) was less than 57%. The purpose of this study was to evaluate the relationship between hindfoot alignment and postoperative lower limb alignment, and to reveal whether hindfoot alignment affects lower limb alignment after MOWHTO. Our hypothesis was that hindfoot alignment influences the postoperative MA in MOWHTO. MATERIALS AND METHODS: This study was a retrospective comparative study. The study cohort comprised 43 knees in 43 patients who underwent MOWHTO and had standing long-leg anteroposterior view and hindfoot alignment view radiographs taken preoperatively and at 3 months postoperatively. To evaluate the hindfoot alignment, the absolute value of the ankle joint line orientation relative to the ground was added to the absolute value of the hindfoot angle. We defined a postoperative MA of 57-67% as acceptable correction (A group) and a MA of < 56% as under-correction (U group). The two groups were analyzed to identify factors that affected postoperative limb alignment. RESULTS: The preoperative hindfoot alignment angle was significantly larger in the U group than the A group. The preoperative hindfoot alignment angle was a significant predictive factor of the postoperative MA, and the cut-off value that distinguished under-correction from acceptable correction was 15.9 degrees. CONCLUSION: Abnormal hindfoot alignment is one of the causes of under-correction after MOWHTO. Attention should be paid to the preoperative ankle joint line orientation relative to the ground and hindfoot angle. If the preoperative hindfoot alignment angle is ≥ 15.9 degrees, surgeons should reconsider the operative procedure and correction angle. LEVEL OF EVIDENCE Therapeutic level III, retrospective study.