Optimal assessment for anterior talofibular ligament injury utilizing stress ultrasound entails internal rotation during plantarflexion

OBJECTIVESAn optimal load and ankle position for stress ultrasound of injured anterior talofibular ligament (ATFL) is unknown. Objectives of this study were to compare stress ultrasound and ankle kinematics from a 6 degree-of-freedom (6-DOF) robotic testing system as a reference standard for evaluation of injured ATFL and suggest cut-off values for ultrasound diagnosis.METHODSTen fresh-frozen human cadaveric ankles were used. Loads and ankle positions examined by 6-DOF robotic testing system were: 40 N anterior load, 1.7 Nm inversion and 1.7 Nm internal rotation torques at 30° plantarflexion, 15° plantarflexion, and 0° plantarflexion. Bony translations were measured by ultrasound and robotic testing system under the above conditions. After measuring intact ankle, ATFL was transected at its fibular attachment under arthroscopy. Correlations between ultrasound and robotic testing system were calculated with Pearson correlation coefficients. Paired t-tests were performed for comparison of ultrasound measurements of translation between intact and transected ATFL, and unloaded and loaded conditions in transected ATFL.RESULTSGood agreement between ultrasound measurement and that of robotic testing system was found only in internal rotation at 30° plantarflexion (ICC=0.77; 95% Confidence Interval 0.27-0.94). At 30° plantarflexion, significant differences in ultrasound measurements of translation between intact and transected ATFL (p < 0.01) were found in response to 1.7 Nm internal rotation torque, and non-stress and stress with internal rotation (p < 0.01) with mean differences of 2.4 mm and 1.9 mm respectively.CONCLUSIONBased on the data of this study, moderate internal rotation and plantarflexion is optimal to evaluate the effects of ATFL injury when clinicians utilize stress ultrasound in patients.