Scapulohumeral Rhythm

A description of how the scapula and humerus work together to get the arm over the head. This pattern is known as scapulohumeral rhythm or glenohumeral rhythm.
I made the model myself from cardboard and images from Wikimedia commons:
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[@user-is9cv1vb8s]

Fantastic video - and with the help of a sound engineer, it would immensely boost views. Brilliant video, thank you for posting 🙏🏻

[@hargunkhanna4566]

Awesome video! Really helped me understand shoulder rhythm

[@Dr.B_OT]

Great to hear!

[@BeeSaucySkateboarding]

"Im just gonna take my humerus off and set it to the side." Made me laugh I pictured u actually doing it

[@Dr.B_OT]

😁 Glad you liked it!

[@stevenb5778]

Questions: at 1:23 how do they call that SC joint elevation when it is tilting downwards? Also, when I lift my arm into abduction, are you saying my clavicle drops low? I feel as if my clavicle doesn't even move. At what point of glenohumeral abduction does the scapula kick in? And according to the 2:1 ration rule; if the arm is at 180 degrees does that mean the glenuhumeral joint is doing 120 degrees and the scapular is doing 60? For 150 degrees it's 100 degrees glenohumeral and 50 degrees scapular? Why not?

[@Dr.B_OT]

I am holding the proximal end of the clavicle in my right hand (the part that articulates with the sternum at the SC joint). Elevation refers to how the distal end moves relative to the proximal end. The proximal end of your clavicle does not drop during shoulder abduction (it is attached to your sternum). The distal end of the clavicle elevates with shoulder abduction, mostly during the first 90 degrees of abduction. The scapular upward rotation (at the acromioclavicular joint) really kicks in above 90 degrees of shoulder abduction. You are right - according to the 2:1 "guideline" (not sure I'd call it a "rule" as it is somewhat variable), 180 degrees of shoulder abduction would mean approximately 120 degrees of GH joint abduction + approximately 60 degrees of scapulothoracic upward rotation (which in itself is comprised of approximately 30 degrees of AC joint upward rotation + approximately 30 degrees of SC joint elevation). At less than 180 degrees of shoulder abduction, however, the 2:1 ratio does not necessarily apply, because it is not consistent through the whole arc of abduction. Initially in shoulder abduction, the GH joint does all of the work, then the SC joint starts to help, and after that the AC joint makes its contribution to shoulder abduction. Different joints contribute at different rates in different parts of the arc.

[@stevenb5778]

Wow, yeah I appreciate the response! But you say, "At less than 180 degrees of shoulder abduction, however, the 2:1 ratio does not necessarily apply..." I question if that was an error, because any issue with shoulder abduction is under 180 degrees. Thanks!@@Dr.B_OT

[@Dr.B_OT]

Good follow-up question, Steven. Here's the deal: from 0 to 20 or 30 degrees of shoulder abduction, all of that motion happens at the glenohumeral (GH) joint. From about 30 to 90 degrees of shoulder abduction, about twice as much of the abduction motion happens at the GH joint as happens through scapular upward rotation. Above 90 degrees of shoulder abduction, GH joint movement and scapular upward rotation contribute about equally to the abduction movement. So the relative contribution of the GH joint and scapular upward rotation differs in different parts of the abduction arc. Overall, once you have full (180 degrees) shoulder abduction, about twice as much came from GH joint movement as came from scapular upward rotation, thus the 2:1 ratio overall. Hope that helps!

[@studysection5819]

Sir sc joint is 1st elevated then posteriorly rotated

[@Dr.B_OT]

That is correct! The posterior rotation comes from tension in the coracoclavicular ligament as the AC joint is upwardly rotated.

[@goobiehome3235]

great video! made the shoulder complex rhythm not so complex.

[@Dr.B_OT]

:) I try to make the complex simple!