Magnetic resonance imaging analysis of the subacromial space in the impingement sign positions.
Level 4 - case-series / case-control
Small observational imaging study in healthy volunteers without a clinical comparison group
PubMed 12469085 · doi:10.1067/mse.2002.127095
What was done
Ten subjects with normal shoulders (mean age, 32 years) underwent magnetic resonance imaging to measure anatomic structures and changes in the subacromial space as the arm was moved from rest to 160 degrees of forward flexion during Neer and Hawkins impingement sign maneuvers.
What was found
The acromiohumeral interval was smallest with the arm at the side (mean, 6.4 mm) and progressively increased as the arm elevated from 90 degrees to 160 degrees (mean, 7.7-14.2 mm). The rotator cuff was never found in contact with the anterior acromion. The rotator cuff insertion was closest to the anteroinferior acromion at 90 degrees of flexion (Hawkins sign position), not at full elevation (Neer sign position).
Why it matters
The findings help clarify the mechanical basis of clinical impingement tests, demonstrating that subacromial proximity occurs primarily at 90 degrees of flexion rather than full elevation.
Limits
The study included only 10 healthy participants and no symptomatic patients. Passive positioning in an MRI scanner does not reproduce active dynamic muscle forces, and standard deviations or statistical significance tests were not reported in the abstract.