Reliability of sonographic measurements of anterior talofibular ligament band thickness

Introduction: Ankle sprains are common and the anterior talofibular ligament is typically injured. Ultrasound imaging can be used to diagnose the severity and extent of anterior talofibular ligament tears. However, the multi-banded nature of the anterior talofibular ligament is often underappreciated, and tears to individual bands can occur. When partially torn, the anterior talofibular ligament or its individual bands appear sonographically ‘thickened’. This research aimed to investigate the most reliable method of sonographically imaging and measuring the thickness of anterior talofibular ligament individual bands. Methods: Intra-observer reliability of sonographic anterior talofibular ligament thickness measurements was investigated using a repeated measures observational study. The effect of using short-axis imaging to identify anterior talofibular ligament banding, foot positioning during imaging and optimisation of sonographic factors on the reliability of anterior talofibular ligament band thickness measurements was examined. Results: Short-axis ultrasound imaging to identify anterior talofibular ligament banding configuration and ensure specific anterior talofibular ligament bands were consistently imaged and measured, and yielded excellent reliability (intra-class correlation coefficient = 0.97 and limits of agreement ± 0.26 mm). Further improvements were gained by imaging the anterior talofibular ligament bands and measuring them with the foot in a free-hanging position and optimising the sonographic focus (limits of agreement ±0.13 mm). Conclusion: Short-axis ultrasound imaging allows the anterior talofibular ligament banding configuration to be determined and ensure individual anterior talofibular ligament bands are assessed. Placing the foot in in a free-hanging (plantar flexed and inverted) position places the anterior talofibular ligament under tension, enhancing anterior talofibular ligament band assessment; furthermore, optimisation of the sonographic focus can allow the epiligament to be best assessed. These factors can enhance the reliability of anterior talofibular ligament band thickness measurements and identification of anterior talofibular ligament tears.