The effect of rotation on intraoperative fluoroscopic evaluation of hindfoot alignment and how to help prevent error

Objective: Restoration of hindfoot alignment correlates with improved clinical and biomechanical outcomes after fracture care and reconstruction. Intraoperative assessment of alignment with fluoroscopy is challenging. This study was designed to determine the effect of rotation on the measurement of hindfoot alignment and to determine if any radiographic landmarks can be utilized to help surgeons identify appropriate rotation during intraoperative imaging. Methods: Ten unmatched cadaveric limbs that had been disarticulated at mid-tibia were used and placed supine in a radiolucent jig. Fluoroscopic images were obtained with the C-arm positioned at 45°. Images were obtained in sequential rotational adjustments from 12° of internal rotation to 12° of external rotation. The location of the fibula relative to the base of the fifth metatarsal was measured on images and recorded as an interval percentage overlap (0% to 50%, 50% to 100%, and greater than 100%). Hindfoot alignment was recorded by measuring the angle between the tibial and calcaneal axis. Results: Varus and valgus hindfoot alignment demon-strated a linear relationship to leg rotation (r² = 0.998, p < 0.001). In these uninjured cadaveric specimens, 8° to 15° of internal rotation relative to the medial border of the foot produced a normal valgus angle (0° to 5°). Using 50% to 100% overlap of the fibula over the fifth metatarsal base as a radiographic test was a reliable indicator of predicted measurement, with 89% sensitivity and 99% specificity. Conclusions: The measurement of hindfoot alignment changes with foot rotation. Use of the fibula overlap of the fifth metatarsal base may be a helpful tool to judge appropriate rotation intraoperatively.