[Standardized ultrasound examination for classification of instability of the acromioclavicular joint]

Anteroposterior X-ray views of both acromio-clavicular (AC-) joints with 10 kg weights in each hand are generally accepted for the diagnosis of Tossy I to III AC-joint separations. An analogue diagnosis can be made by standardized ultrasound examination. Ten individuals without AC-instability (Tossy I), eleven with Tossy II- and eight with Tossy III-instability were examined both radiographically and by B-mode ultrasound. AC-joint width was uniformly calculated by using an index (AC-index = AC-joint width of uninjured side/AC-joint width of injured side). The sonographically measured mean AC-index for Tossy I-stability was 1.0; sonographically 0.49 and radiographically measured 0.5 for Tossy II-injury; and sonographically 0.21 and radiographically measured 0.2 for Tossy III-instability. Statistical analysis resulted in significant differences for all mean AC-indices of the three groups (p < 0.0001). We conclude that ultrasound examination of AC-joint instability is as reliable as radiographic measurement. Standard X-rays of the shoulder remain mandatory to exclude fractures only. The decision for operative stabilisation of the AC-joint can be based on the side-effect free and cost-effective ultrasound examination of the grade of AC-joint instability (AC-index < 0.3 equivalent Tossy III).