The importance of scapulo-thoracic motion.

 The motion of the arm in relation to the body takes place at two articulations, the glenohumeral joint and the scapulothoracic joint.

When we measure the motion of the shoulder, we usually measure the overall motion of the humerus in relation to the thorax (chest)

If we look carefully, however, we can see that while much of this motion takes place between the humerus and the scapula

a substantial portion takes place between the scapula and the thorax.

Thus, overall humero-thoracic motion is the result of the combination of humero-scapular motion (also known as glenohumeral motion) and scapulo-thoracic motion.

When patients and surgeons think of "shoulder problems", they commonly focus on the glenohumeral joint - the articulation between the shoulder blade's socket (glenoid) and the humeral head. These areas are easy to assess on physical exam, plain x-rays and MRIs.

However - as shown above - a substantial component of shoulder function is determined by the articulation of the shoulder blade on the chest wall: the scapulothoracic joint. This area is hidden with the patient's shirt on and is difficult to evaluate with x-ray or other types of imaging. On one hand, impaired scapulothoracic function can compromise the overall workings of the shoulder. On the other hand, enhanced scapulothoracic function can compensate for poor motion at the glenohujmeral joint. Because female patients typically have more lax joints than men, a stiff glenohumeral joint can be overlooked because of compensatory motion at the scapulothoracic joint.

The components of shoulder motion are wonderfully demonstrated in two videos produced by our late partner, Doug Harryman, including the now famous "pin brother" studies (video 1 and video 2).

While there are many ways to assess the relative contributions of glenohumeral and scapulothoracic motion to overall humerothoracic motion (including the Kinect and fluoroscopy), a clinically useful method is for the examiner to hold the scapula in its resting position while attempting to elevate the arm.

This reveals the amount of motion at the glenohumeral joint which can then be compared to the amount of arm elevation achievable when the scapula is not stabilized. The difference between these two measurements is the scapulothoracic contribution to shoulder motion.

The authors of The contribution of the scapula to active shoulder motion and self-assessed function in three hundred and fifty two patients prior to elective shoulder surgery found that scapulothoracic motion is an important component of active shoulder motion and function in both healthy shoulders and in those compromised by common pathologies. They concluded that rehabilitation directed at improving active scapulothoracic motion may improve the function of shoulders with loss of active glenohumeral motion. Three papers illustrate this principle: (1) Harryman's paper Residual motion and function after glenohumeral or scapulothoracic arthrodesis, (2) Scapulohumeral rhythm in shoulders with reverse shoulder arthroplasty measured with a new portable three-dimensional scapular kinematics assessment system, and (3) Scapulohumeral rhythm relative to active range of motion in patients with symptomatic rotator cuff tears

Scapulo-thoracic motion can be restricted because of muscle weakness (serratus anterior, trapezius, latissimus dorsi, rhomboids), abnormalities of the sternoclavicular and acromioclavicular joint, prior scapular or rib fractures, snapping scapula, tumors, and disuse (see link). Using four clinically palpable landmarks (1 inferior pole of scapula, 2 medial edge of the scapular spine, 3 the posterior corner of the acromion, and 4 the coracoid process), the position and motion of the scapula can be assessed and compared to the opposite side.

Comment: It can be concluded that active scapulothoracic motion can be a major contributor to the function of normal and pathologic shoulders. In shoulders with glenohumeral pathology (e.g. arthritis, rotator cuff tears) and in patients with anatomic and reverse total shoulder arthroplasties, simple exercises such as the "press plus" (see this link) can help activate the scapulothoracic musculature than may be in suboptimal condition and thereby substantially improve overall shoulder function.

Great thanks to our shoulder fellow, Mihir Sheth, who proposed this post and did much of the "spade work" on it.

You can support cutting edge shoulder research and education that are leading to better care for patients with shoulder problems, click on this link.

Follow on twitter: https://twitter.com/RickMatsen or https://twitter.com/shoulderarth
Follow on facebook: click on this link
Follow on facebook: https://www.facebook.com/frederick.matsen
Follow on LinkedIn: https://www.linkedin.com/in/rick-matsen-88b1a8133/

Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link).