Beyond Euler/Cardan analysis: True glenohumeral axial rotation during arm elevation and rotation.
Klevis Aliaj, K Bo Foreman, Peter N Chalmers and 1 others
PMID 33989999WHAT IT FOUND
True shoulder rotation is near zero during arm elevation, but standard calculations show up to 30° of rotation depending on the method used.
Clinicians should know that reported rotation values may be mathematical artifacts, not actual physical twisting of the bone.
Key findings
01True glenohumeral axial rotation did not differ from zero beyond 100° of elevation in the coronal plane, 83° in the scapular plane, and at all angles in the sagittal plane.
02At maximum elevation, the difference between true rotation and apparent rotation calculated via the xz’y” sequence was 25.7° for coronal abduction, 12.8° for scapular abduction, and -28.9° for forward elevation.
03Apparent axial rotation varies by the mathematical sequence chosen, whereas true axial rotation remains consistent across planes of elevation.
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTs
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What it does not show
The study included only 19 healthy adults, so findings may not apply to patients with shoulder pathology or post-surgical anatomy. The analysis focused on specific motion tasks (elevation and rotation); complex multi-planar movements common in daily life were not directly tested. The paper is a biomechanical analysis, not a clinical trial, so it does not evaluate patient outcomes or treatment efficacy.
Declared interests
The study was supported by the National Institutes of Health (NIH). No commercial conflicts of interest were reported.
The easy way to misread this
Do not assume that high apparent axial rotation values reported in previous literature represent actual physical rotation of the humerus. These values are often mathematical artifacts dependent on the calculation method used, not true bone movement.