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Questions and Answers
What is the ratio of glenohumeral abduction to scapulothoracic upward rotation in scapulohumeral rhythm after 30 degrees of abduction?
What is the ratio of glenohumeral abduction to scapulothoracic upward rotation in scapulohumeral rhythm after 30 degrees of abduction?
What is the significance of Inman's classic 2:1 ratio in evaluating shoulder abduction?
What is the significance of Inman's classic 2:1 ratio in evaluating shoulder abduction?
What is the reason for variations in reported scapulohumeral rhythms across studies?
What is the reason for variations in reported scapulohumeral rhythms across studies?
Study Notes
- Scapulohumeral rhythm is a natural kinematic rhythm in the shoulder.
- It involves the timing between glenohumeral abduction and scapulothoracic upward rotation.
- After 30 degrees of abduction, the rhythm occurs at a ratio of 2:1.
- This means for every 3 degrees of shoulder abduction, 2 degrees occurs by GH joint abduction and 1 degree occurs by scapulothoracic joint upward rotation.
- A full arc of nearly 180 degrees of abduction is the result of a simultaneous 120 degrees of GH joint abduction and 60 degrees of scapulothoracic upward rotation.
- Published scapulohumeral rhythms vary across studies.
- Variations in the reported scapulohumeral rhythms reflect differences in measurement technique, subjects, speed and plane of motion, and external loading.
- Inman's classic 2:1 ratio remains a valuable axiom for evaluating shoulder abduction.
- Scapulohumeral rhythm is important in understanding the overall relationship between humeral and scapular movement.
- It is simple to remember and helps to conceptualize the full 180 degrees of shoulder abduction.
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