Paper 43: Correction accuracy of coronal plane alignment modifying osteotomies using patient-specific instrumentation

Objectives: High tibial osteotomy (HTO) and distal femoral osteotomy (DFO) are powerful tools for correcting coronal malalignment of the lower extremity, and are effective, joint-preserving treatment strategies for addressing early tibiofemoral compartment osteoarthritis in young patients. Historically, these procedures have been performed freehand using intraoperative fluoroscopy, after extensive presurgical planning based on preoperative imaging. More recently, the advent of 3D CT-based patient-specific instrumentation (PSI) has been associated with decreased intraoperative fluoroscopy, improved safety and possibly improved accuracy in a cadaveric model.1 The purpose of this study was to assess correction accuracy of coronal plane modifying osteotomies using PSI in a consecutive series of patients.
Methods: All patients who underwent single-level coronal plane correction osteotomy (HTO or DFO) with PSI (Bodycad, Quebec City, Canada) performed by two fellowship trained orthopaedic surgeons at a tertiary orthopaedic center between October 2020 and September 2024 were eligible for study inclusion. Patients who underwent sagittal plane correction osteotomies, dual level osteotomies, or had documented intraoperative hinge fractures were excluded. All included patients underwent preoperative and postoperative long-standing alignment radiographs at a minimum of 3 months postoperatively. Patients without complete imaging were excluded. Preoperative and postoperative 3D CT-based measurements of medial tibial width ratio (MTWR) and joint line congruency angle (JLCA) were obtained from the PSI preoperative plan. Preoperative and postoperative radiographic measurements of MTWR and JLCA were performed by two independent raters. Means +/- standard deviations and medians with ranges were used as descriptive statistics for normally and non-normally distributed variables, respectively. Intraclass correlation coefficients (ICCs) were used to assess both interrater and intermethod reliability for MTWR and JLCA. Wilcoxon signed-rank tests were used to compare the MTWR between 3D CT data and radiographic measurements. Cutoffs of +/-2.5%, +/-5% and +/-10% relative to the planned postoperative 3D CT MTWR were used to assess correction accuracy (Fig 1).
Results: 130 patients met study inclusion criteria. Patient characteristic data are found in Table 1. Median age was 40 years (range: 16-59) and 52% of patients were female. Ninety patients (69%) underwent HTO and 40 patients (31%) underwent DFO. The ICC score for interrater reliability on preoperative radiographs was 0.99 (95% CI: 0.99-0.99) for MTWR and 0.92 (95% CI: 0.88-0.95) for JLCA. The ICC score between preoperative 3D CT data and measured values on preoperative radiographs was 0.99 (95% CI: 0.98-0.99) for MTWR and 0.50 (95% CI: 0.36-0.62) for JLCA. There was no significant difference in preoperative MTWR measured on 3D CT compared to preoperative radiographs (difference in means = 0.4% (95% CI: -0.2% -1.0%), p=0.25). Similarly, there was no significant difference in postoperative MTWR planned on 3D CT compared to postoperative radiographic measurement (difference in means = 1.1% (95%CI: -0.5% - 2.7%, p=0.09). The ICC score for the preoperative to postoperative change in MTWR planned on 3D CT and measured on radiographs was 0.97 (95% CI: 0.95-0.98) (Fig 2A). Subgroup analysis demonstrated similar findings for DFO and HTO patients, with ICC scores for preoperative to postoperative changes in MTWR planned on CT and measured on radiographs of 0.86 (95% CI: 0.49-0.97) for DFOs and 0.95 (95% CI: 0.91-0.97) for HTOs (Fig 2B & 2C). When comparing final MTWR measured on postoperative radiographs with the planned 3D CT MTWR, 24.2%, 49.5% and 88.4% of patients had a measured MTWR on postoperative radiographs within 2.5%, 5%, 10% of the planned 3D CT MTWR, respectively (Fig 3A). Subgroup analysis of osteotomy type demonstrated similar results, with 25.0%, 52.9% and 91.2% of HTO patients (Fig 3B) and 22.2%, 40.7% and 81.5% of DFO patients meeting the 2.5%, 5% and 10% accuracy cutoffs, respectively (Fig 3C).
Conclusions: These results demonstrate a high degree of interrater reliability for radiographic measurements of MTWR and JLCA. MTWR demonstrated a high degree of intermethod reliability between radiographic measurements and 3D CT data, whereas JLCA demonstrated much lower intermethod reliability. This discrepancy in JLCA is likely related to the non-weight bearing nature of the CT scan versus weight-bearing radiographs. Thus, the MTWR appears to be a highly reliable method for communicating coronal plane correction, as this value is normalized to each patient's tibia and avoids measurement limitations associated with abnormalities in the anatomic axis of the femur and/or tibia. Additionally, the planned degree of correction was highly reliable between the radiographic and CT data. The PSI method for coronal plane osteotomy was highly accurate in achieving the desired correction in coronal plane alignment, with 24.2%, 49.5% and 88.4% of patients' final radiographic coronal alignment falling within 2.5%, 5% and 10% of the preoperative 3D CT plan. Furthermore, this accuracy was maintained for both HTOs and DFOs. HTOs may be slightly more accurate than DFOs, with a higher percentage of patients meeting each of the accuracy cutoffs and a higher ICC score between planned and measured coronal correction, which may be related to the osteotomy cut being closer to the joint line in HTOs compared to DFOs. Overall, this study demonstrates 1) a high degree of concordance between preoperative radiographic measurements of MTWR and 3D CT data and 2) a high degree of accuracy in obtaining the desired coronal correction and final MTWR using PSI for coronal plane osteotomies.References: 1. Carey EG, et al. Orthop J Sports Med. 2025 Jan 28;13(1).