The shoulder girdle, is an incomplete bony ring formed by the clavicle and scapula on each side of the body, joined anteriorly by the manubrium of the sternum.¹ The bones of the shoulder girdle articulate with each other and partake in the formation of 4 joints that include:

The sternoclavicular joint - formed between the sternum and clavicle.
The acromioclavicular (AC) joint - formed between the scapula and the clavicle.
The glenohumeral (shoulder) joint - formed between the scapula and humerus.
The scapulothoracic joint - formed between the scapula and the posterior thoracic cage1

What is scapulohumeral rhythm?

Scapulohumeral Rhythm is the synchronized movement between the scapula, humerus and the clavicle during shoulder elevation. Active 180°of shoulder elevation comprises 60° of scapular upward rotation and 120° of elevation of the humerus.

What happens to the clavicle during elevation?
As active elevation occurs, the clavicle rotates posteriorly along with elevation of the lateral end of the clavicle.

How do we assess the movements of the clavicle?
Watch these clips to know more:

How to assess the clavicle: ELEVATION:

How to assess the clavicle: PROTRACTION:

How to assess the clavicle: ROTATION:

Source:
1. Gordana Sendic MD, Shoulder girdle, Kenhub.com
2. From the lecture ‘Management of the shoulder girdle’ by Ian Horsley