Three-Dimensional Reconstruction of Foot in the Weightbearing Position From Biplanar Radiographs: Evaluation of Accuracy and Reliability

The initial assessment and postoperative monitoring of patients with various abnormalities of the foot in clinical routine practice is primarily based on the analysis of radiographs taken in the weightbearing position. Conventional x-ray imaging, however, only provides a 2-dimensional projection of 3-dimensional (3D) bony structures, and the clinical parameters assessed from these images can be affected by projection biases. In the present work, we addressed this issue by proposing an accurate 3D reconstruction method of the foot in the weightbearing position from low-dose biplanar radiographs with clinical index measurement assessment for clinical routine practice. The accuracy of the proposed reconstruction method was evaluated for both shape and clinical indexes by comparing 3D reconstructions of 6 cadaveric adult feet from computed tomographic images and from biplanar radiographs. For the reproducibility study, 3D reconstructions from the biplanar radiographs of the foot of 6 able-bodied subjects were considered, with 2 observers repeating each measurement of anatomic landmarks 3 times. Baseline assessment of important 3D clinical parameters was performed on 17 subjects (34 feet; mean age 27.7, range 20 to 52 years). The average point to surface distance between the 3D stereoradiographic reconstruction and the computed tomographic scan-based reconstruction was 1 mm (range 0mm to 6mm). The selected radiographic landmarks were highly reproducible (95% confidence interval <2.0 mm). The greatest interindividual variability for the clinical parameters was observed for the twisting angle (mean 87°, range 73° to 100°). Such an approach opens the way for routine 3D quantitative analysis of the foot in the weightbearing position.