Supraspinatus tendon load during abduction is dependent on the size of the critical shoulder angle: A biomechanical analysis

Abstract

Shoulders with supraspinatus (SSP) tears are associated with significantly larger critical shoulder angles (CSA) compared to disease-free shoulders. We hypothesized that larger CSAs increase the ratio of joint shear to joint compression forces (defined as "instability ratio"), requiring substantially increased compensatory supraspinatus loads. A shoulder simulator with simulated deltoid, supraspinatus, infraspinatus/teres minor, and subscapularis musculotendinous units was constructed. The model was configured to represent either a normal CSA of 33˚or a CSA characteristic of shoulders with rotator cuff tears (38˚), and the components of the joint forces were measured. The instability ratio increased for the 38˚CSA compared with the control CSA (33˚) for a range of motion between 6˚to 61˚of thoracohumeral abduction with the largest differences in instability observed between 33˚and 37˚of elevation. In this range, SSP force had to be increased by 13-33% (15-23 N)

The morphometric anatomy of the delto-fulcral triangle: A 3D CT-based reconstruction study

“…6,8,11,[14][15][16][17][18][19] Anatomically, the three sides that create this triangle in the typical supraspinatus-outlet view are easily obtainable from both X-ray images and CT scans because the three osseous scapular landmarks are clearly visualised. Side 1 (AFLAC), arising from the antero-superior aspect of the coracoid process and ending at the lateral acromion, represented the ligamentous attachment of the coraco-acromial ligament that spans the area of the coraco-acromial arch, over which the deltoid muscle passes towards its humeral insertion at the deltoid tuberosity.…”

Predictors of Shoulder Degeneration in the KwaZulu-Natal Population of South Africa

“…Since the critical shoulder angle and acromion index are considered to be characteristic of subacromial pathology, there is much need for the evaluation of these biomechanical parameters as separate and interrelated predictors of shoulder degeneration in the South African population (Armfield et al, 2003;Moor et al, 2013;Bouaicha et al, 2014;Gerber et al, 2014;Spiegl et al, 2016). As the scapulo-humeral geometry related to these parameters present as static stabilisers, the relationship between the latter and the surrounding musculature determines the stability of the shoulder (Armfield et al;Moor et al, 2013;Gerber et al).…”

“…As the scapulo-humeral geometry related to these parameters present as static stabilisers, the relationship between the latter and the surrounding musculature determines the stability of the shoulder (Armfield et al;Moor et al, 2013;Gerber et al).…”

“…The critical shoulder angle, an analytical tool of an individual's scapular anatomy, quantifies the angle between the superior and inferior osseous glenoidal margins and the lateral-most aspect of the acromion (Moor et al, 2012;Bouaicha et al;Gerber et al;Daggett et al, 2015;Spiegl et al;Viehöfer et al, 2016). This novel radiological parameter provides reasoning for the occurence of glenohumeral osteoarthritis or rotator cuff tears by measuring both the lateral acromial extension and the glenoid slope (Moor et al, 2013;Gerber et al;Spiegl et al).…”

“…This novel radiological parameter provides reasoning for the occurence of glenohumeral osteoarthritis or rotator cuff tears by measuring both the lateral acromial extension and the glenoid slope (Moor et al, 2013;Gerber et al;Spiegl et al). As a result, Moor et al (2012) reported a critical shoulder angle of less than 30º to depict glenohumeral osteoarthritis, while that greater than 35º was reflective of degenerative rotator cuff tears.…”