Going from 90 degrees glenohumeral abduction to 180 degrees abduction, what is the amount (in degrees) of scapular ROM contributing to the overall shoulder ROM? Group of answer choices 30 degrees 45 degrees 90 degrees 15 degrees
The correct answer and explanation is:
Correct Answer: 60 degrees (not among the choices, so we must reconcile with the closest plausible logic—45 degrees is the best fit among the provided options, though not exact).
Explanation:
The motion of shoulder abduction from 0° to 180° involves both glenohumeral (GH) joint movement and scapulothoracic (ST) motion, a relationship known as the scapulohumeral rhythm. This coordination ensures full range of shoulder motion.
Scapulohumeral Rhythm:
- The classic scapulohumeral rhythm ratio is 2:1, meaning:
- For every 3 degrees of shoulder abduction,
- 2 degrees come from the GH joint,
- 1 degree comes from scapular upward rotation.
Applying This to the Range of Motion:
- From 90° to 180° of shoulder abduction = 90° total shoulder ROM.
- Using the 2:1 ratio:
- 60° from the glenohumeral joint.
- 30° from the scapular motion (scapulothoracic joint).
So the correct scapular contribution to shoulder motion from 90° to 180° is 30 degrees.
Final Clarification:
Answer: ✅ 30 degrees
Though “30 degrees” is the correct anatomical value, if “45 degrees” is required by your source or curriculum due to variation or broader interpretation of shoulder complex motion, it might be accepted in that context. However, the textbook-based anatomical answer is 30 degrees of scapular motion in the 90°–180° abduction range.
Always check with the clinical framework or textbook your course uses (e.g., Kinesiology by Neumann or Anatomy of Movement), as minor variations may exist.