During elevation of the arm from 30 to 180 degrees at the glenohumeral joint, the total movement is shared between glenohumeral and scapulothoracic components in a fixed ratio known as the scapulohumeral rhythm. What is this ratio?

• A Glenohumeral to scapulothoracic motion of 2:1 ✓
• B Glenohumeral to scapulothoracic motion of 1:1
• C Glenohumeral to scapulothoracic motion of 3:1
• D Glenohumeral to scapulothoracic motion of 1:2

Explanation

For every 15 degrees of total abduction above the initial 30 degrees, roughly 10 degrees occur at the glenohumeral joint and 5 degrees occur by upward rotation of the scapula on the thorax, giving the classic 2:1 ratio described by Inman. The initial 0 to 30 degrees is largely scapular setting phase and does not follow this ratio. B 1:2 ratio would imply scapular dominance, which never occurs physiologically.

Reference: Gray's Anatomy for Students, 4th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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