Background: Acromiohumeral interval (AHI) is a measurement method to determine the superior migration of the humeral head in patients with rotator cuff tears.
Hypothesis/Purpose: The purpose of this study was to compare the AHI measurement in supine shoulder and upright shoulder radiographs, as well as magnetic resonance imaging (MRI), as well as to report the sensitivity, specificity, and accuracy in detecting full thickness rotator cuff tears.
Study Design: Diagnostic study.
Methods: From July 2020 to May 2021, evaluation of 86 shoulder radiographs in both supine & upright Grashey views compared with the MRI of the affected shoulder. Measurements of the AHI obtained from both radiographs and MRIs was determined by two independent orthopaedic surgeons. The intraclass correlation of the AHI measurement was tested. The difference between the AHI in each view was determined.
Result: The 86 shoulders were divided into 3 groups that included; 1) non-full thickness tear (50%), 2) full thickness (FT) tear 3 cm (33.7%), and 3) FT tear > 3 cm (16.3%). The mean difference of AHI noted was significantly lower in the supine radiographs than with the upright (1.34-1.37 mm.). The mean difference of the AHI was significantly lower in the MRI than the upright (1.62-1.87 mm.). AHI obtained from the supine radiographs and MRI had no significant differences. The area under the curve (AUC) of the upright and supine AHI in the diagnosis of the FT tears were at 0.649 and 0.642 accuracy. Upright AHI 7.09 mm. had 27.9% sensitivity and 100% specificity in diagnosing FT tears with 64% accuracy (p<0.001). The upright AHI cut off value of 9.52 mm. had 60.5% sensitivity, 67.4% specificity, and 64% accuracy (p=0.01). The supine AHI 6.56 mm. had 32.6% sensitivity, 100.0% specificity, and 66.3% accuracy (p<0.01). Supine AHI cut off value of 7.42 mm. had 41.9% sensitivity, 86.0% specificity, and 64.0% accuracy (p=0.004). The inter- and intra-rater reliability of AHI measurement in 3 views were of substantial to almost perfect agreement (0.668-0.824).
Conclusion: The AHI in supine radiographs were significantly lower than upright shoulder radiographs in all groups as divided by severity of the rotator cuff tear and was comparable with the MRI. For AHI ≤ 7 mm. in upright shoulder radiographs remains as a good diagnostic test of full thickness rotator cuff tears, while this value was not relevant for use as the cut point in the supine radiographs and MRI shoulders.
Level of evidence: Level III; Diagnostic study
Clinical Relevance: The AHI measurement in supine and upright radiographs are reliable and reproducible. The AHI ≤ 7 mm. in upright shoulder radiographs remains as a good diagnostic test of full thickness rotator cuff tears, while this value was not relevant for use as the cut point in the supine radiographs and MRI shoulders.