In vivo analysis of coracoid and subacromial shoulder impingement mechanism during clinical examination.

Background: Understanding the mechanisms of shoulder impingement created by clinical tests is crucial to accurately evaluate the condition. The objective of this study was to relate mechanisms of subacromial and coracoid impingement occurring in positions of the shoulder during clinical examination, in quantitative and qualitative terms.

Methods: A 1.0T open magnetic resonance imaging system was used in 18 female and 19 male subjects, to determine the distances between the humeral head and the acromion or coracoid, and contact with the rotator cuff (RC). Measurements were taken with the shoulder in neutral, "Hawkins", "Neer", and 90° abduction/15° internal rotation (horizontal impingement test) positions. Additionally, impingement was classified based on the grade of RC contact with the acromion or coracoid.

Results: In the Hawkins position, distance between the supraspinatus and the coracoid was closest (14.5 ± 4.5 mm), while the coracohumeral distance (CHD) narrowed (p < 0.001). In the horizontal impingement test position, the minimum distance between the subscapularis and coracoid was found, whereas the CHD increased (27.4 ± 5.7 mm). In the Neer and Hawkins positions, the space between the greater tuberosity and acromion was significantly narrowed, which was also the case in the horizontal impingement test position compared to neutral position (p < 0.001).

Conclusion: Shoulder movements of forward flexion and internal rotation (Hawkins test) and abduction and internal rotation (horizontal impingement test) can lead to different coracoid impingement mechanisms during clinical examination. The Hawkins, Neer, and horizontal impingement tests lead to comparable narrowed acromiohumeral distances and subacromial contact of the RC.

Level Of Evidence: Therapeutic level III.