Objective: The objective was to determine whether arm and radiographic beam positional changes affect the acromiohumeral interval (AHI) in radiographs of healthy shoulders.
Materials and methods: Controlling for participant's height and position as well as radiographic beam height and angle, from 30 right shoulders of right-handed males without shoulder problems four antero-posterior (AP) radiographic views each were obtained in defined positions. Three independent, blinded physicians measured the AHI to the nearest millimeter in 120 randomized radiographs. Mean differences between measurements were calculated, along with a 95% confidence interval.
Results: Controlling for observer effect, there was a significant difference between AHI measurements on different views (p< 0.01). All pair-wise differences were statistically significant after adjusting for multiple comparisons (all p values<0.01).
Conclusions: Even in healthy shoulders, small changes in arm position and radiographic beam orientation affect the AHI in radiographs.