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Objectives: Preoperative tibial and femoral osteotomy planning using three-dimensional (3D) patient-specific instrumentation (PSIs) has been gaining popularity in deformity correction surgery. However, the variability between advanced imaging modalities and conventional two-dimensional (2D) radiographs for measuring limb alignment and corrective osteotomy angle remains unknown. Though CT is generally considered the gold standard for osseous imaging, radiographs remain the most common means for assessing preoperative coronal and sagittal alignment. Emerging data suggest there may be inaccuracies with this technique. In particular, multiple studies have found that sagittal slope measurements can vary greatly depending on modality used. The present study aims to characterize alignment measurements within a cohort of patients undergoing corrective osteotomy and to assess differences in preoperative planned alignment and correction angles between an advanced 3D imaging modality (Bodycad, Quebec, CA) and conventional 2D radiographs. Methods: Preoperative computed tomography (CT) scans of consecutive patients undergoing high tibial osteotomies (HTOs) and/or distal femoral osteotomies (DFOs) between January 1 st , 2016, and December 1 st , 2022 with preoperative x-ray and CT scans were retrospectively reviewed using advanced 3D PSI software. Equivalent 2D radiographs were independently analyzed using conventional imaging software. Manual 2D radiograph measurements, including hip-to-ankle weightbearing axis and posterior tibial slope were compared to 3D PSI measurements and variances were analyzed calculating Root Mean Square Error (RMSE). Results: A total of 97 patients (47 female, 50 males) with a mean age of 37 years (range, 15.8 to 60 years) were included in the final analysis. Fifty percent of the cohort had a lateral posterior tibial slope (LPTS) that was greater than medial posterior tibial slope (MPTS). Mean absolute posterior slope difference (aPTSD) did not vary significantly according to osteotomy type. For manual measurements, interclass correlation coefficients among raters was excellent (0.97, 95% CI 0.944, 0.988) in the coronal plane, while interclass correlation coefficient for the sagittal plane was poor. Mean hip-to-ankle corrective angle using conventional 2D radiographs was 6.02° (range, 0.45° to 19.62°), versus 7.31° on Bodycad (range, 3.25° to 10.63°) (p=0.022). Conclusions: Preoperative corrective osteotomy angles between advanced imaging software and conventional radiographs measurements are significantly different, with 3D CT predicting a significantly higher overall correction angle for all parameters. Despite excellent interrater reliability for coronal plane measurements using radiographs, reliability for slope measurements was poor. Surgeons should be mindful when using conventional 2D radiographs for osteotomy planning, which may underestimate correction angles and inaccurately assess preoperative sagittal alignment.
Ryan et al. (Mon,) studied this question.