In vivo analysis of the circles measurement supports its use in evaluating acromioclavicular joint dislocations.

Background: Classification and treatment of acromioclavicular joint (ACJ) dislocations according to the Rockwood classification is controversial. The "circles measurement" on Alexander views was proposed to enable a clear assessment of displacement in ACJ dislocations. However, the method and its ABC classification were introduced on a Sawbones model based on exemplary Rockwood scenarios without soft tissue. This is the first in vivo study to investigate the circles measurement. We aimed to compare this new measurement method with the Rockwood classification and the previously described semiquantitative degree of dynamic horizontal translation (DHT).

Methods: A total of 100 consecutive patients (87 men and 13 women) with acute ACJ dislocations between 2017 and 2020 were included retrospectively. The mean age was 41 years (range, 18-71 years). ACJ dislocations on panoramic stress views were classified according to Rockwood type (type II, n = 8; type IIIA, n = 9; type IIIB, n = 24; type IV, n = 7; and type V, n = 52). On Alexander views, where the hand of the affected arm rested on the contralateral shoulder, the circles measurement and the semiquantitative degree of DHT (none, n = 6; partial, n = 15; or complete, n = 79) were assessed. Convergent and discriminant validity of the circles measurement (including its ABC classification according to displacement) with the coracoclavicular distance and Rockwood types, as well as the semiquantitative degree of DHT, was tested.

Results: The circles measurement showed a strong correlation with the coracoclavicular distance according to the Rockwood classification (r = 0.66, P < .001) and differentiated between Rockwood types according to the ABC classification, including types IIIA and IIIB. The circles measurement correlated with the semiquantitative method of assessing DHT (r = 0.61, P < .001). Measurement values were smaller in cases without DHT than in cases with partial DHT (P = .008). Cases with complete DHT had respectively larger measurement values (P < .001).

Conclusion: In this first in vivo study, the circles measurement allowed differentiation between Rockwood types according to the ABC classification in acute ACJ dislocations with a single measurement and correlated with the semiquantitative degree of DHT. On the basis of these validations of the circles measurement, its use for evaluating ACJ dislocations is recommended.