Improving postoperative radiographs for the parameter measurement of hexapod external fixator using an additional foot ring

Background It is challenging to determine the orthogonality of radiographs in daily clinical practice. The purpose of this study was to show the usefulness of an additional foot ring which might determine the orthogonality of postoperative radiographs for the parameter measurement of hexapod external fixator. Methods We retrospectively analyzed 81 consecutive trauma patients with tibial shaft fractures treated by the hexapod external fixator at our institution from September 2014 to July 2019. Starting in March 2016, the postoperative radiographs for parameter measurement were obtained under the control of an additional foot ring. The final data consisted of 47 patients in traditional radiographs (Group I) and 34 patients under the control of foot ring during the radiographic process (Group II). The demographic data, original postoperative deformities, residual deformities after final correction, number of repeated radiographs after the first postoperative radiographs, time to the satisfactory reduction achieved, and external fixation time in all patients were documented and analyzed. The Johner-Wruhs criteria were used for the final clinical outcomes evaluation at the last clinical visit. Results Satisfactory reduction and bone union were achieved in all patients. There were no statistical significances between the two groups in the demographic data, original postoperative deformities, residual deformities after final correction, external fixation time, and the final clinical outcomes (P > 0.05). The mean number of repeated radiographs after the first radiographs (1.4 times) and mean time to the satisfactory reduction achieved (3.3 days) in patients with an additional foot ring used were all less than those without foot ring (2.4 times, 5.3 days) (P < 0.05). Conclusions The additional foot ring is a practical device to ensure the orthogonality of postoperative radiographs for the hexapod external fixator parameter measurement. Radiation exposure, duration of deformity correction, and cost for patients might be reduced due to the less repeated radiographs with the wrong position.