Medial opening-wedge high tibial osteotomy (MOWHTO) in patients with varus knee osteoarthritis (OA) causes changes to ankle and hindfoot alignment. However, the compensatory ability of the ankle and hindfoot varies according to the severity of ankle OA. The purpose of this study was to investigate whether the changes in ankle symptoms and ankle and hindfoot alignments differ following MOWHTO according to the severity of preoperative ankle OA.
The data of 130 patients who were followed for at least 4 years were reviewed. Patients were classified into 2 groups according to their severity of ankle OA (Group 1: modified Kellgren-Lawrence (KL) grade 0–1 and group 2: KL grade 2 or more). Four radiographic parameters were examined to evaluate ankle alignment: tibial plafond inclination (TPI), talar tilt (TT), talar inclination (TI), and tibia surface angle (TSA). The hindfoot alignment was evaluated using the varus–valgus angle of the calcaneus (VVA). A visual analogue scale (VAS) was used to evaluate ankle pain. The patient-reported outcome measures (PROMs) of the knee joint used the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score.
In group 2, the change in TI after MOWHTO was significantly greater and the changes in TPI, TT, VVA were all significantly smaller than in group 1 (all p < 0.05). Ankle pain VAS scores were more severe in group 2 than in group 1 both pre- and postoperatively (all p < 0.05), and group 2 reported that ankle pain worsened postoperatively (p < 0.05). In both groups, knee WOMAC scores improved, and there were no differences between groups pre- or postoperatively (all p > 0.05). A multivariate regression analysis demonstrated that a small VVA change (odds ratio: 0.775, p = 0.027) and severe OA grade of the ankle joint preoperatively (KL grade 2, 3, 4 vs. KL grade 0, 1) (odds ratio: 4.241, p = 0.046) predicted increased ankle pain VAS scores following MOWHTO.
Although the PROM for the knee joint improved irrespective of the presence of ankle OA, ankle pain worsened following MOWHTO in patients with ankle OA. Inadequate compensatory change in hindfoot alignment increased ankle pain in these patients.