Introduction

A large preoperative joint line convergence angle (JLCA) is a risk factor for overcorrection in high tibial osteotomy (HTO) for varus knee. Tibial plateau shape is one of the important factors for predicting change in JLCA. This study sought to clarify the relationship between JLCA and tibial bone morphology.

Methods

We assessed 93 knees in 80 patients with osteoarthritis (OA) or osteonecrosis of the knee who underwent HTO between January 2017 and April 2020 at our institution. Patients were assessed radiographically pre- and postoperatively on full-length weightbearing radiographs. All procedures were performed by 4 specialist knee surgeons using a TriS™ locking plate (Olympus Terumo Biomaterials, Japan), and there were no major differences in surgical technique. Tibial plateau shape was classified into three types based on the slope of the medial and lateral articular surfaces as follows: flat, depressed, or convex (pagoda). The flat type was defined as the slope of the medial and lateral articular surfaces measuring within 3 degrees. Measured radiological parameters were femorotibial angle (FTA), medial proximal tibial angle (MPTA), hip knee ankle angle (HKA), and JLCA. We calculated the difference in each radiological parameter between pre- and postoperative full-length weightbearing radiographs (#FTA, #MPTA, #HKA, and #JLCA). Correlations between radiological parameters were analyzed according to tibial plateau shape. Statistical analysis was performed using the Wilcoxon or Kruskal-Wallis test and the Chi-square test. Correlations were determined using a simple linear regression model. Significance was set at p < 0.05.

Results

The distribution of the groups was flat type in 40 knees, depression type in 35 knees, and pagoda type in 18 knees. There were no differences among all types in age, sex, preoperative OA grade, or pre- and postoperative radiological parameters (FTA, MPTA, HKA, and JLCA). We found moderate correlations of #JLCA with #FTA, #MPTA, and #HKA in the pagoda type (r=-0.57,0.45, and 0.57 respectively), with no significant correlation observed in the other two types. In addition, there were moderate correlations of #JLCA with preoperative FTA and HKA in the pagoda type (r=-0.56 and 0.57, respectively).

Discussion

Some of the results presented in this study were intuitive. For the pagoda type, the weight-bearing line might move laterally in a seesaw manner. It was also interesting that no significant differences were found for the other two types. One of the limitations of this study was that patients-reported outcomes were not considered.

Conclusion

In treatment of the pagoda type with HTO, #JLCA was predictable to some extent, but careful preoperative planning was required for cases with severe varus deformity.