Tibiofibular syndesmosis in asymptomatic ankles: initial kinematic analysis using four-dimensional CT

AIM: To evaluate the reliability of ankle syndesmotic measurements and their changes during active motion using four-dimensional computed tomography (4DCT) examination in asymptomatic ankles. MATERIALS AND METHODS: 4DCT was performed on both ankles of patients with signs and symptoms of unilateral ankle instability. Ankles from the asymptomatic side of 10 consecutive patients were included in this analysis. Five ankle syndesmotic measurements were adopted from the available literature and performed by two fellowship-trained foot and ankle surgeons: (1) syndesmotic anterior distance (SAD); (2) syndesmotic posterior distance (SPD); (3) syndesmotic translation (ST); (4) syndesmotic tibiofibular angle (STFA); and (5) ankle tibiofibular angle (ATFA). A Monte Carlo simulation was also performed to obtain exact p-values with 99% confidence intervals. RESULTS: Excellent interobserver reliability was observed among the two readers for four out of five measurements (intra-class correlation coefficients [ICC]: 0.767–0.995, p<0.001–0.020). The ICC values for SAD were not statistically significant (ICC=0.548 and 0.569 for dorsi and plantarflexion respectively, p=0.1). Among the five measurements, only ST measurements had significant changes during active motion (median [interquartile range] for change: –0.70 mm [–1.6–0.10]; p=0.012). Of the above measurements, only the ST measurements demonstrated a negative linear association with the tibiocalcaneal angle during active motion (beta=–2.5, p=0.04). CONCLUSIONS: Reliable quantitative kinematic assessment of ankle syndesmosis can be performed using 4DCT examination. Syndesmotic measurements remain unchanged during ankle motion except for the syndesmotic translation, which tends to decrease during plantar flexion.