Published in:
22-09-2023 | SHOULDER
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
Published in: Knee Surgery, Sports Traumatology, Arthroscopy | Issue 12/2023
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Purpose
Acromioclavicular 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).
Methods
Ninety-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.
Results
The 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).
Conclusion
The scapular-based V angle on anteroposterior radiographs distinguishes between Rockwood types III and V as well as cases with partial or complete DHT.
Study design
Diagnostic study.
Level of evidence
Level II.