Excursion of the Rotator Cuff Under the Acromion

Abstract

Nine fresh-frozen, human cadaveric shoulders were elevated in the scapular plane in two different humeral rotations by applying forces along action lines of rotator cuff and deltoid muscles. Stereophotogrammetry determined possible regions of subacromial contact using a proximity criterion; radiographs measured acromiohumeral interval and position of greater tuberosity. Contact starts at the anterolateral edge of the acromion at 0 degrees of elevation; it shifts medially with arm elevation. On the humeral surface, contact shifts from proximal to distal on the supraspinatus tendon with arm elevation. When external rotation is decreased, distal and posterior shift in contact is noted. Acromial undersurface and rotator cuff tendons are in closest proximity between 60 degrees and 120 degrees of elevation; contact was consistently more pronounced for Type III acromions. Mean acromiohumeral interval was 11.1 mm at 0 degrees of elevation and decreased to 5.7 mm at 90 degrees, when greater tuberosity was closest to the acromion. Radiographs show bone-to-bone relationship; stereophotogrammetry assesses contact on soft tissues of the subacromial space. Contact centers on the supraspinatus insertion, suggesting altered excursion of the greater tuberosity may initially damage this rotator cuff region. Conditions limiting external rotation or elevation may also increase rotator cuff compression. Marked increase in contact with Type III acromions supports the role of anterior acromioplasty when clinically indicated, usually in older patients with primary impingement.

Sonographic evaluation of subacromial space

“…Measurements were performed by the authors during sonographic exam. Flatow et al [5] assessed the normal X-ray subacromial space, quantifying it as being an average of 10-15 mm. Other authors measure subacromial space with an MRI [7] (values 8.2 mm in men and 7 mm in women at 30°degrees of abduction) and with intra-operative measurement obtained by artroscopy [8] (16 mm): the values of the subacromial distance measured were very different in relation to the method of evaluation.…”

“…Before or after sonography, all of the subjects underwent a X-ray examination of the shoulders using antero-posterior, trans-axillary and supraspinatus outlet views in order to study the morphology of the acromion and any osteoarthritic alterations of the acromioclavicular joint, as well as measure the subacromial space [5].…”

“…In 1994, Flatow et al [5] assessed the subacromial space of a normal X-ray, quantifying it as being an average of 10-15 mm.…”

Alterations in Shoulder Kinematics and Associated Muscle Activity in People With Symptoms of Shoulder Impingement

“…15,[17][18][19] Motions that bring the greater tuberosity in closer contact with the coracoacromial arch 20 are particularly problematic. These motions include excessive superior or anterior translations of the humeral head on the glenoid fossa, inadequate lateral (external) rotation of the humerus, and decreases in the normal scapular upward rotation and posterior tipping on the thorax, all occurring during humeral elevation.…”

Local pressures in the subacromial space

“…Flatow et al [4], with the use of stereo-photogrammetric analysis, demonstrated that acromion undersur- face and rotator cuff tendons are in closest proximity between 60°and 120°of elevation in cadaveric shoulders and that the main area of increased contact is the anteroinferior part of the acromion. However, they did not measure the pressure quantitatively.…”