Technical note: measuring the coracoclavicular distance with ultrasound--a new technique

The distance between the clavicle and the coracoid process of the scapula is frequently assessed during the radiographic investigation of the acromioclavicular joint. This study defines an ultrasound technique (5 MHz real time linear array) for measuring the coracoclavicular distance, and determines its reliability and validity. A new ultrasonic technique was performed on 49 healthy subjects who had volunteered to participate in the study, having given signed, informed consent. The measuring endpoints for the coracoclavicular distance were the superior border of the clavicle and the superior border of the coracoid process. Three replicate scans were performed on each shoulder. The ultrasound measurements for 19 of the subjects were compared with the measurement obtained from a normal shoulder radiograph (which had previously been requested on clinical grounds). The data were subjected to analysis of variance (ANOVA) and the limits of agreement method of analysis. The mean difference between the radiograph and ultrasound measurements was 0.38 mm. The limits of agreement (95% confidence intervals) were -0.57 (-0.97, -0.17) and 1.33 (0.93, 1.73). Intraoperator and interoperator reliability were evaluated with a multifactor ANOVA and gave p = 0.7 for intraoperator reliability and p = 0.5 for interoperator reliability. The mean of the coefficients of variation for the two operators was 1.84%. The average range for repeated trials (same operator, same subject) was 1.35 mm. The maximum differences in the averages for each operator was 1.2 mm. The ultrasound technique described is a reliable, accurate and valid technique for evaluating the coracoclavicular distance and may usefully supplement the routine radiographic examination of the shoulder in patients presenting for radiographic examination of the acromioclavicular joint.