Reduced acromiohumeral distance and increased critical shoulder angle: implications for primary care clinicians

Objectives: The literature indicates that reduced acromiohumeral distance (AHD) and increased critical shoulder angle (CSA) are associated with large and massive rotator cuff (RC) tears which may not be amenable to a successful repair. The purpose of this study was to examine the overall accuracy of these two radiographic features in diagnosing significant RC pathology. Methods: This was a diagnostic study of patients with shoulder pain. To examine the overall accuracy of the measurements, the area under the Receiver Operating Characteristic curves (AUC) were calculated. The validity indices (sensitivity, specificity and likelihood ratios) examined the predictive value of specific cutoff categories of AHD<6 mm and the CSA >35°. Results: Data of 200 consecutive patients; mean age: 59(11), 117 males were used for analysis. There was a weak inverse correlation (r = 0.46) between the AHD and CSA. The AUCs for presence and size of RC tear and different stages of fatty infiltration of supraspinatus and infraspinatus muscles varied from fair to excellent for AHD and poor to good for CSA. Specificity was high for the cutoff categories of both AHD and CSA (>90%). The positive LRs were large for AHD and small to moderate for CSA. Conclusion: The AHD and CSA were reliably measured in the true AP radiographic view. Both radiographic features (AHD<6mm and CSA>35°) were able to confirm the presence of a major RC pathology. However, the AHD<6 mm, an acquired radiologic abnormality secondary to failure of the RC muscles/tendons had better measurement properties. This information is of value to primary care physicians, sports medicine specialists and advanced practice physiotherapists in their clinical decision making.