Inter Observer Variability in the Specificity of Magnetic Resonance Imaging for External Impingement of the Shoulder—Is There Agreement among Radiologists?

Abstract

Purpose: External impingement in the shoulder is a condition characterised by tenderness in the antero-lateral aspect of the shoulder on arm elevation due to an absolute or relative decrease in the subacromial space. Magnetic resonance imaging (MRI) is frequently utilised to confirm the condition and rule out other differential diagnoses. We conducted a study to look at the inter observer variability in specificity of MRI scanning in impingement of the shoulder. Methods: Twenty-six shoulders aged between 20 and 34 who all presented with shoulder instability only were included in the study. Three experienced consultant musculoskeletal radiologists were then asked to comment on the presence or absence of impingement on reviewing their MRI scans. Results: Radiologist 1 (R1) diagnosed 7 shoulders with impingement and 19 shoulders without. Radiologist 2 (R2) observed that 13 shoulders had radiological signs of impingement and 13 did not, and radiologist 3 (R3) suspected impingement in 20 shoulders with 6 shoulders normal. For R1 and R2, the agreement was 0.58 with a kappa value of 0.16. Between R2 and R3, the agreement was also 0.58 with a kappa value of 0.16. Comparing R1 and R3, the agreement was 0.46 and the kappa value was 0.14. Across all three radiologists, there was agreement in 8 out of the 26 MRI scans (31%) but only in 4 out of the 26 (15.4%) did they all agree that impingement was not present. Conclusion: MRI should be used judiciously in the work up of patients with external impingement of the shoulder.