Acromial arch shape: assessment with MR imaging

To test the hypothesis that acromial shape is comparable on supraspinatus outlet view radiographs and parasagittal magnetic resonance (MR) images.

Supraspinatus outlet view radiographs of a dried scapula were obtained in the neutral position and with various degrees of caudal, cranial, anterior, and posterior angulation. Sagittal MR images of 41 asymptomatic and 39 symptomatic shoulders were reviewed and compared with outlet view radiographs from the 39 symptomatic cases. Acromial shape was assessed with published classification schemes.

Minor variations in angulation produced changes in apparent acromial shape and thickness on the radiographs. MR imaging from a lateral to a more medial section changed the shape or thickness grade in 39 of 41 asymptomatic shoulders. There was poor correlation between findings at radiographic and MR assessment of acromial shape in the symptomatic group.

Apparent acromial shape is sensitive to minor changes in radiographic technique and MR section viewed.