Preoperative Hindfoot Alignment and Outcomes After High Tibial Osteotomy for Varus Knee Osteoarthritis
Authors: Yang Hong Yeol , Kang Joon Kyoo , Kim Ji Won , Yoon Tae Woong , Seon Jong Keun 
Published: February 2024

Update
This article was updated on May 15, 2024 because of previous errors, which were discovered after the preliminary version of the article was posted online. On page 898, in the section entitled “Materials and Methods,” the sentence that had read “The WBL ratio of the knee joint was defined as the point where the GA or MA passed through the width of the tibia and intersected a line from the center of the femoral head to the center of the calcaneus (for the GA) or talus (for the MA), with the medial edge defined as 0% and the lateral edge as 100%.” now reads “The WBL ratio of the knee joint was defined as the point where the GA or MA passed through the width of the tibia and intersected a line from the center of the femoral head to the lowest point of the calcaneus (for the GA) or the center of the talus (for the MA), with the medial edge defined as 0% and the lateral edge as 100%.” Likewise, in the legend for Figure 3 on page 899, the sentence that had read “Depiction of the ground mechanical axis (GA), defined as the line (represented by the solid red line) from the center of the femoral head to the ground reaction point at the center of the calcaneus, passing lateral to the traditional mechanical axis (MA; represented by the dashed red line).” now reads “Depiction of the ground mechanical axis (GA), defined as the line (represented by the solid red line) from the center of the femoral head to the ground reaction point at the lowest point of the calcaneus, passing lateral to the traditional mechanical axis (MA; represented by the dashed red line).” Finally, on page 903, “HKA” was changed to “HKA angle” in Table III.

Background:
The hip-to-calcaneus axis, previously known as the ground mechanical axis (GA), ideally passes through the center of the knee joint in the native knee. The aim of this study was to elucidate, with use of hip-to-calcaneus radiographs, changes in knee and hindfoot alignment and changes in outcomes following high tibial osteotomy (HTO).

Methods:
We reviewed the records for 128 patients who underwent HTO between 2018 and 2020. Patients were stratified into 2 groups, a hindfoot valgus group (n = 94) and a hindfoot varus group (n = 34), on the basis of their preoperative hindfoot alignment. The hindfoot alignment was evaluated with use of the hindfoot alignment angle (HAA). To evaluate lower-limb alignment, full-length standing posteroanterior hip-to-calcaneus radiographs were utilized to measure 4 radiographic parameters preoperatively and 2 years postoperatively: the hip-knee-ankle (HKA) angle, hip-knee-calcaneus (HKC) angle, and the weight-bearing line (WBL) ratios of the mechanical axis (MA) and GA.

Results:
The mean HAA improved significantly from 5.1° valgus preoperatively to 1.9° valgus postoperatively in the hindfoot valgus group (p < 0.001). In contrast, in the hindfoot varus group, the HAA showed no meaningful improvement in the coronal alignment of the hindfoot following HTO (p = 0.236). The postoperative mean HKC angle in the hindfoot varus group was 2° more varus than that in the hindfoot valgus group (1.0° versus 3.0°; p = 0.001), and the GA in the hindfoot varus group passed across the knee 8.0% more medially than that in the hindfoot valgus group (55% versus 63% from the most medial to the most lateral part of the tibial plateau). The hindfoot varus group had worse postoperative clinical outcomes than the hindfoot valgus group in terms of the mean Knee injury and Osteoarthritis Outcome Score for pain and American Orthopaedic Foot & Ankle Society Ankle-Hindfoot Score.

Conclusions:
Although our findings did not provide sufficient evidence to establish clinically relevant differences between the groups, they indicated that the group with a preoperative fixed hindfoot varus deformity had a higher rate of undercorrection and worse clinical outcomes, especially pain, following HTO. Therefore, modification of the procedure to shift the GA more laterally may be required for these patients.

Level of Evidence:
Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.