Validation of Foot Angular Measurements Using Intraoperative Simulated Weightbearing Fluoroscopic Images

Background: Weightbearing foot and ankle radiographs are essential because skeletal geometry changes under load. Radiographic measurements, which guide management decisions, have been validated using weightbearing radiographs. Simulation of weightbearing intraoperatively would be ideal and may improve the accuracy of deformity correction in foot and ankle surgery. This study aims to validate the accuracy of angular measurements on intraoperative simulated weightbearing fluoroscopic foot images. Methods: A prospective study of 50 patients with a mean age of 51.3 years undergoing elective foot surgery at a single institution was performed. A simulation of weightbearing was performed intraoperatively and fluoroscopic anteroposterior and lateral images were obtained. Six angular measurements were performed on the standard preoperative weightbearing radiographs and compared to the intraoperative simulated weightbearing fluoroscopic images, by 4 researchers at 2 intervals. Results: The mean differences for the hallux valgus angle (HVA), intermetatarsal angle (IMA), interphalangeal angle (IPA), 4-5 intermetatarsal angle (4-5 IMA), calcaneal pitch (CP), and talocalcaneal angle (TCA) were +0.02, −1.79, +1.13, −0.01, +4.80, and −1.41 degrees, respectively. Of the anteroposterior and lateral measurements, the HVA, IPA, 4-5 IMA, and TCA showed no statistically significant mean difference (paired t test), and inter- and intraobserver reliability was good to excellent. The IMA and CP showed a mean difference that was statistically significant; however, this mean difference was clinically negligible (IMA: −1.79 ± 1.68 degrees; CP: 4.8 ± 3.4 degrees). A good inter- and intraobserver reliability was found between researchers. Regression analyses showed strong correlations for the HVA, IMA, 4-5 IMA, and CP and fair correlations for the TCA and IPA. Conclusion: The study suggests the technique we use for intraoperative simulated weightbearing fluoroscopic imaging correlates with standard preoperative weightbearing foot radiographs and may facilitate a more accurate, real time assessment of alignment during foot deformity correction surgery. Level of Evidence: Level II, diagnostic.