A Radiological Study for Assessing Syndesmosis Malreduction: Its Validity and Limitation

This study assessed the diagnostic utility of different X-ray radiological methods on syndesmosis malreduction. Thirteen fresh ankle specimens were used to make a syndesmotic separation model. The specimen was fixed in the anatomic position and in malreduction positions, including internal rotation 10° (IR10°), IR20°, external rotation 10° (ER10°), and ER20°. The tibiofibular clear space (TCS), tibiofibular overlap (TFO) on the anteroposterior view, and anteroposterior ratio (A/P ratio) on the lateral view were measured. When the syndesmosis was fixed in IR20°, the sensitivity of the TCS, TFO, and A/P ratio for malreduction diagnosis was 92.3% (12/13), 69.2% (9/13), and 100%, respectively. When the syndesmosis was fixed in IR10° malreduction, the sensitivity of the TCS, TFO, and A/P ratio for malreduction diagnosis was 38.4% (5/13), 38.4% (5/13), and 84.6% (11/13); in ER10°, 30.7% (4/13), 76.9% (10/13), and 69.2% (9/13); and in ER20°, 92.3% (12/13), 100% and 92.3% (12/13). In the anatomic reduction, the false-positive rate of the TCF, TFO, and A/P ratio was 7.6% (1/13), 7.6% (1/13), and 0%, respectively. The TFO and A/P ratio exhibited differences between all malreduction groups and the anatomic group. However, the TCS measurements had no statistical difference between the anatomic position and IR10° malreduction (p = .109). On the AP view, the TCS and TFO measurements are not sensitive enough to detect the syndesmosis malreduction. The A/P ratio on the lateral view exhibits better diagnostic utility for syndesmosis malreduction.