A Novel Fluoroscopic Method for Assessing Rotational Malalignment of the Tibia.

Abstract

OBJECTIVE\nTo evaluate the accuracy and reliability of a novel fluoroscopic technique for assessing tibial rotation and compare it to a previously described fluoroscopic method.\n\n\nMETHODS\nA multiplanar circular ring external fixator was secured to the tibial diaphysis of five cadaveric lower extremity specimens. Using deformity correction software, the frame and tibia were programmed to randomly rotate 5, 10, 15, 20, 25, and 30 degrees of internal and external rotation. Following each rotation, two blinded, independent observers measured the degree of tibial rotation using two different fluoroscopic methods: the previously described mortise method and the novel intermalleolar method. A total of 65 measurements were made by each observer. Accuracy and inter-observer reliability were calculated.\n\n\nRESULTS\nBoth intermalleolar and mortise methods had a mean absolute rotational difference from the true torsion of 3 degrees (SE 1, range 0-10 degrees intermalleolar versus 0-18 degrees mortise). We found that 98.5% (128/130) of measurements using the intermalleolar method were less than 10 degrees from the true rotation, compared to 93.8% (122/130) using the mortise method. Both the intermalleolar and mortise methods had excellent inter-observer reliability (ICC 0.99 and 0.96, respectively).\n\n\nCONCLUSION\nMeasuring tibial rotation fluoroscopically using the intermalleolar method is both accurate and reliable. Compared to the previously described mortise method, it has similar accuracy and provides a value that approximates the true tibial rotation. Also, it can be employed reliably and effectively intraoperatively to identify tibial malrotation and assist in intraoperative rotational corrections.