The V angle compliments radiographic assessment of acute acromioclavicular joint dislocations by differentiating between Rockwood types III versus V and by considering dynamic horizontal translation in coronal radiographs

Abstract

AbstractPurposeAcromioclavicular joint (ACJ) dislocations are usually graded radiographically according to Rockwood, but differentiation between Rockwood types III and V may be ambiguous. The potentially clinically relevant horizontal instability is barely addressed in coronal radiographs. It was hypothesized that a new radiologic parameter (V angle) would complement ACJ diagnostics on anteroposterior radiographs by differentiating between cases of Rockwood III and V while also considering the aspect of dynamic horizontal translation (DHT).MethodsNinety‐five patients with acute ACJ dislocations (Rockwood types III and V) were included retrospectively between 2017 and 2020. On anteroposterior views (weightbearing: n = 62, non‐weight‐bearing: n = 33), the coracoclavicular (CC) distance and the newly introduced V angle for assessing scapular orientation were measured bilaterally. This angle is referenced between the spinal column and a line crossing the superior scapular angle and the crossing point between the supraspinatus fossa and the medial base of the coracoid process, reported as the side‐comparative difference (non‐injured side *minus* injured side). DHT on Alexander views was divided into stable, partially unstable or completely unstable.ResultsThe V angle on the injured side alone (mean 50.0°; 95% confidence interval (CI), 48.6°–51.3°) showed no correlation with the side‐comparative CC distance [%] (r = − 0.040; n.s.). Thus, the V angle on the non‐injured side was considered, displaying a normal distribution (n.s.) with a mean of 58.0° (95% CI, 56.6°–59.4°). The side‐comparative V angle showed a correlation with the side‐comparative CC distance (r = 0.83; p < 0.001) and was able to differentiate between Rockwood types III (4.7°; 95% CI, 3.9°–5.5°; n = 39) and V (10.3°; 95% CI, 9.7°–11.0°; n = 56) (p < 0.001). A cut‐off value of 7° had a 94.6% sensitivity and an 82.1% specificity (area under curve, AUC: 0.954; 95% CI, 0.915–0.994). The side‐comparative V angle was greater for cases with complete DHT (8.7°; 95% CI, 7.9°–9.5°; n = 78) than for cases with partial DHT (4.8°; 95% CI, 3.3°–6.3°; n = 16) (p < 0.001). A cut‐off value of 5° showed a sensitivity of 84.6% and a specificity of 66.7% (AUC 0.824; 95% CI, 0.725–0.924).ConclusionThe scapular‐based V angle on anteroposterior radiographs distinguishes between Rockwood types III and V as well as cases with partial or complete DHT.Study designDiagnostic study.Level of evidenceLevel II.