Femur-referenced 3D-CT detects patellar height decrease and its correlation with correction magnitude after opening-wedge high tibial osteotomy: Comparison with conventional radiographic indices.

Abstract

This study aimed to evaluate changes in the positional relationship between the femur and the patella before and after medial opening wedge high tibial osteotomy (OWHTO) using three-dimensional computed tomography (3D-CT), and to compare these findings with conventional radiographic assessments. We hypothesized that femur-referenced 3D-CT would demonstrate greater sensitivity than conventional radiographic indices for detecting postoperative changes in patellar height and their association with correction magnitude, and that patellar height decreases after OWHTO. We retrospectively analyzed 18 knees in 17 patients who underwent OWHTO. Pre- and postoperative (1-year) evaluations included radiographic measurements (Caton-Deschamps index [CDI], femoral-patellar height index [FPHI], and patellar tilt) and 3D-CT-based assessments of patellar height and tilt using a femur-based coordinate system. Correlations between the change in hip-knee-ankle (HKA) angle and patellar height were investigated. Interobserver reliability was assessed using intraclass correlation coefficients (ICC). CDI significantly decreased postoperatively (from 0.84 to 0.78; p = 0.01), while FPHI showed no significant change (p = 0.12). In 3D-CT assessment, patellar height significantly decreased by 3.0 ± 1.5 mm (p < 0.01) and patellar tilt shifted laterally by 1.5° ± 2.1° (p < 0.01). A significant correlation was observed between the change in HKA angle and the decrease in 3D-patellar height (r = -0.50, p = 0.04), but not with CDI or FPHI. The ICCs for CDI, FPHI and 3D-patellar height were 0.88, 0.94, and 0.97, respectively. 3D-CT assessment revealed a significant average decrease in patellar height and a lateral opening tilt following OWHTO. 3D-CT was considered to provide a more detailed evaluation of the patellofemoral joint compared to conventional radiography. III, retrospective observational study.