Measurement of the acromiohumeral interval on standardized anteroposterior radiographs: A prospective study of observer variability

Background: An acromiohumeral interval narrower than 6 mm has been considered pathologic and strongly indicative for rotator cuff tears by numerous authors. This prospective study assessed interobserver and intraobserver variability in the radiographic measurement of the acromiohumeral interval. Material and methods: Five board-certified orthopedic surgeons independently reviewed 58 blinded, standardized anteroposterior shoulder radiographs. The acromiohumeral interval was measured in millimeters. The 5 investigators classified each image a second time in random order. Results: After the same 58 radiographs had been evaluated by the 5 investigators at both examination time points, no significant differences were noted in the interobserver and intraobserver measurements (P<.05). The respective maximum interobserver and intraobserver differences were 4 and 3 mm (range, 0-4 mm). Conclusion: The assessment of the acromiohumeral interval using standardized anteroposterior radiographs is a reliable and reproducible method of measurement.