Ultrasound’s limitations in investigating dynamic ligamentous ankle anatomy

Abstract

The distal tibiofibular joint, or tibiofibular syndesmosis, is supported by the anterior and posterior inferior tibiofibular ligaments, tibiofibular interosseous membrane and ligament, and inferior transverse ligament. As a component of the ankle complex, the tibiofibular syndesmosis exhibits little mobility, with the fibula translating not only laterally (Harris 1991), but also posteriorly, with external rotation (Malhotra et al. 2019), during ankle dorsiflexion to accommodate the foot’s internal rotation and talar wedging. The mobility of the tibiofibular syndesmosis is relevant in both clinical and evolutionary contexts; disruption of the syndesmosis results in a high ankle sprain, one of the most recalcitrant orthopedic injuries (Gerber et al. 1998), and flexibility of the syndesmosis is thought to be critical to arboreal resource acquisition via tree climbing (Venkataraman, Kraft, and Dominy 2013). While Mei‐Dan et al. (2009) argued dynamic ultrasound investigation of the anterior inferior tibiofibular ligament could be used to diagnose distal tibiofibular syndesmotic injury after analyzing 47 professional athletes, to our knowledge no studies have sought to quantify basic normal variation of the tibiofibular interosseous ligament in non‐professional athletes (i.e., most people). We hypothesized the length of the tibiofibular interosseous ligament measured via ultrasound would be greater during closed‐packed dorsiflexion than closed‐packed standing in adults lacking a prior history of an ankle injury. Data were collected after obtaining informed consent from a mixed‐sex and mixed‐ancestry population of young adults (n = 78), via ultrasounding the distal tibiofibular joint during standing with the knee in closed‐packed position, measuring the tibiofibular interosseous ligament within the tibiofibular clear space, then measuring the same structure within the tibiofibular clear space during squatting with the ankle in closed‐packed position. We found approximately 25% of subjects’ tibiofibular interosseous ligaments decreased in length as measured by ultrasound – which we attribute to registration error inherent to the non‐reproducibility of consistent ultrasound probe placement throughout the ankle’s range of movement. These results cast doubt on the utility of ultrasound in investigating dynamic ligamentous ankle anatomy, consistent with the findings of Prakash (2018), and likely a consequence of the fibula’s complex pattern of motion relative to the tibia during ankle movement.Support or Funding InformationThis work was supported by the Arkansas College of Osteopathic Medicine.