Ultrasound Imaging of Subtalar Joint Instability for Chronic Ankle Instability

Abstract

The purpose of this study was to develop the assessment of subtalar joint instability with chronic ankle instability (CAI) using ultrasonography. Forty-six patients with anterior talofibular ligament (ATFL) abnormalities and a history of ankle sprain were divided into CAI (21.2 ± 5.9 y/o, 7 males and 17 females) and asymptomatic groups (21.0 ± 7.4 y/o, 9 males and 12 females) on the basis of subjective ankle instability assessed using the CAIT and the Ankle Instability Instrument Tool (AIIT). Twenty-six age-matched feet participated in a control group (18.9 ± 7.0 y/o, 9 males and 17 females). Ultrasound measurements of the width of the posterior subtalar joint facet were obtained at rest and maximum ankle inversion (subtalar joint excursion; STJE). The differences in STJE among the three groups were assessed by one-way ANOVA. The relationship between STJE and subjective ankle instability was assessed using Spearman's correlation tests. The STJE value was significantly greater in the CAI group (2.3 ± 0.8 mm) than in the asymptomatic (1.0 ±0.4 mm) and control groups (0.8 ±0.2 mm) (p < 0.001, effect size: 0.64). STJE had significant negative correlations with CAIT (r = -0.71, p < 0.01), and significant positive correlations with AIIT (r = 0.74, p < 0.01). The cut-off value to distinguish between the CAI and asymptomatic groups was 1.7 mm using the ROC curve.

Keywords: chronic ankle instability; subtalar joint; ultrasonography.

Figure 1

Study flow diagram. CAI: chronic ankle instability, USI: ultrasound imaging, ATFL: anterior talofibular ligament.

Figure 2

Ultrasonography image of the subtalar joint (A) A probe is placed on the antero-inferior aspect of the lateral malleolus. Next, a probe is fixed proximally, and its distal end is slid posteriorly at about 30 degrees to capture the subtalar joint. (B) ultrasound image, P: peroneal tendon, T: talus, J: subtalar joint, C: calcaneus.

Figure 3

Measurement of the subtalar joint width (STJ width) (A) STJ width in a rest (B) STJ width in maximum inversion. The width of the talus and calcaneus (arrows) is measured at rest (A) and at maximum inversion of the calcaneus (B) by electronic calipers.

Figure 4

Receiver operating characteristic curve. ROC curve of STJE, with the cut-off value set at 1.7 mm.