Correlation of Plain Radiographs and 3-Dimensional CT With Coronal and Sagittal Measurements in Patients Undergoing Corrective Osteotomies

Background: The patient-specific instrumentation (PSI) used during corrective high tibial osteotomies and distal femoral osteotomies is based on 3-dimensional computed tomography (3D CT). Plain radiographs are typically used preoperatively to determine the need for an osteotomy; however, it is unclear how well measurements on plain radiographs correlate with 3D CT. Purpose/Hypothesis: The purpose of this study was to evaluate the correlation between coronal and sagittal alignment measurements on plain radiographs and 3D CT. It was hypothesized that there would be high agreement in the measurement of the mechanical medial tibial width ratio (mMTWr) and the medial posterior tibial slope (PTS) between both modalities. Study Design: Cohort study (diagnosis); Level of evidence, 3. Methods: Patients who underwent hip-to-ankle CT as part of the preoperative workup before a corrective osteotomy from October 2020 to November 2023 were reviewed. Coronal (mMTWr) and sagittal alignment (medial PTS) were evaluated preoperatively by 2 raters on standing whole-leg radiographs and a lateral radiograph of the knee, respectively, and by semi-automated PSI software on 3D CT. Intraclass correlation coefficients (ICC) were calculated to assess interrater reliability for each measurement and to evaluate agreement between raters and the PSI software. Results: Complete data sets were obtained for 91 cases. The ICC between raters for preoperative mMTWR was 0.99. The ICC between the raters’ measurements and the PSI software measurements of mMTWr was 0.99. The ICC between raters for preoperative PTS was 0.82. The ICC between the raters’ measurements and the PSI software's PTS measurements was 0.63. Conclusion: This study found that coronal measurements performed on whole-leg radiographs and 3D CT were highly correlated, with near-perfect agreement, and that medial PTS measurements showed moderate agreement between modalities. These data suggest that measurements on plain radiographs are reproducible and accurate for evaluating coronal alignment and PTS preoperatively. Surgeons can confidently use plain radiographs to assess whether or not a patient is a candidate for a knee osteotomy.