Standardization of the functional syndesmosis widening by dynamic U.S examination

BACKGROUND Dynamic US examination is a convenient, accurate, inexpensive and reproducible diagnostic tool for assessing the integrity of the distal tibiofibular syndesmosis in ankle injuries. However normal values for physiological functional widening of the anterior tibiofibular clear space in healthy subjects has yet to be determined. The purpose of this study was to determine normal values for the syndesmosis clear space on ultrasound examination. METHODS We evaluated 110 healthy subjects. A dynamic U.S examination was performed in neutral (N), forced internal rotation (IR) and external rotation (ER) of the ankle. In each position the anterior tibiofibular clear space was measured at the level of the anterior inferior tibio-fibular ligament (AITFL). Height and calf length were also recorded. Results were analyzed in relation to age, activity, dominant leg and gender. RESULTS Mean age was 32 years (range 16-60). There were 59 males and 51 females. 60% were professional athletes. Mean height was 173 cm (range 149-192). Functional Mean position measurements for clear space opening were: N=3.7mm, IR=3.6mm and ER=4.0mm. In younger men and women the clear space was significantly wider in neutral (Men: Y=3.8, O=3.4 \ Women: Y=3.8, O=3.4) and with rotational force application (Men ER: Y=4.1, O=3.6 \ Women ER: Y=4.1, O=3.8) compared to older subjects (p<0.05). There was no correlation with activity, height or the leg length.Females had a higher syndesmosis widening ratio (ER/N) under stress than males (p<0.01) this tended to occur more commonly in active subjects. CONCLUSIONS Normal values for the syndesmosis clear space on ultrasound examination were determined as 3.78mm in neutral, 3.64mm in internal rotation and 4.08mm in external rotation. The clear space was shown to decrease with age both as an absolute measure and when rotational stresses are applied. Females tend to have a larger clear space and a greater functional widening.These findings provide a useful reference for radiologists and sports physicians when performing ultrasound assessment of ankle syndesmotic injuries and we encourage use of this modality.