Medial Ankle Stability Evaluation With Dynamic Ultrasound: Establishing Natural Variations in the Healthy Cohort.

Introduction: Destabilizing injuries to the deltoid ligament have relied on radiographic stress examination for diagnosis, with a focus on medial clear space (MCS) widening. Recently, studies have demonstrated the use of ultrasonography to assess deltoid ligament injury, but not the medial ankle stability. The purpose of this study was to assess the MCS via ultrasonography while weight-bearing and with a gravity stress test (GST) in the uninjured ankle as a means of establishing normative values for future comparison.

Methods: Twenty-six participants with no reported ankle injury in their premedical history were included. The MCS was examined using ultrasonography with the patient lying in a lateral decubitus position to replicate a GST with the ankle held in a neutral and plantarflexed position as well as while weight-bearing. The MCS was assessed in mm at the anteromedial and inferomedial aspect of the ankle joint.

Results: With weight-bearing, the average anterior MCS and inferior MCS were 3.6 and 3.3 mm, respectively. During the GST in neutral ankle position, the average anterior MCS was 4.1 mm, whereas the average inferior MCS was 4.0 mm. When measured during the GST in plantarflexed ankle position, the averages anterior MCS and inferior MCS increased to 4.4 mm. MCS values were notably higher with GST than with weight-bearing measurements (P < 0.001). MCS values were notably higher with the foot in a plantarflexed compared with a neutral position when doing GST (P < 0.001). No notable differences in MCS distance were found when comparing laterality (P > 0.05). Height had a notable effect on all MCS values (P < 0.05). Inter- and intra-rater reliabilities for ultrasonographic MCS measurements were all excellent (interclass correlation coefficient >0.75).

Discussion: Ultrasound can reliably measure the MCS of the ankle while doing dynamic stress manoeuvres. With the deltoid ligament intact, a GST increases MCS widening more than weight-bearing, and holding the ankle in plantarflexion while doing a gravity stress view, further increases this difference.

Levels Of Evidence: Diagnostic studies-investigating a diagnostic test: Level III.