抄録
Background: Despite the subcoracoid impingement which occurs between coracoid tip and lesser tuberosity of humeral head being known well as an etiology of the anterior shoulder motion pain, the detail of the mechanism is still unclear. We studied the quantitative image evaluation using kinematic analysis of 1.2T-open MRI.
Methods: 20 volunteer's shoulders in 20 asymptomatic individuals (18 men and 2 women, mean age of 34.7 ± 13 years ) were included in this study. The subject was placed in supine position with the arm in 90 degrees of forward flexion. Five sequential images of MRI in the transverse plain were evenly taken during segmental rotation from neutral position to 90 degrees of internal rotation. The distance and image findings between the coracoid tip and the lesser tuberosity and the diameter of the humeral head were evaluated on DICOM viewer.
Results: No individual felt shoulder pain during this study. Thickened subscapularis muscle which contacts with coracoid became less with contraction. The average shortest distance between the coracoid tip and the lesser tuberosity was 10.6mm (5.0-15.8mm). All cases showed space, which was occupied mainly by adipose tissue, between the coracoid tip and the anterior surface of subscapularis. Although all cases showed some amount of space without any direct contact between the coracoid tip and the humeral head, the distance varied appreciably in each individual.
Conclusion: Smooth tendon gliding along with scapula movement by contraction of scapula muscle is an important function for painless kinematics despite close distance to coracoid. A minute change in joint centralization may produce impingement.
