The scapulothoracic joint is the articulation between the scapula and the thorax. It is not a true joint, but rather the broad contact between the inner surface of the scapula and the rib cage. The scapula is able to slide relative to the rib cage to allow for elevation and depression, along with protraction/retraction, rotation and shoulder abduction. When the arm moves relative to the body, approximately two-thirds of this motion is at the glenohumeral joint and one-third at the scapulothoracic joint. Three relatively common conditions seen at the scapulothoracic joint are scapular winging, in which the scapula is not correctly stabilized (due to dysfunction of the serratus anterior/ long thoracic nerve or of the trapezius/spinal accessory nerve), snapping scapula syndrome (a grating sensation, often from overuse and scapulothoracic bursitis), and so-called scapulothoracic dyskinesis, in which abnormal scapula motion causes shoulder pain. It is also possible, with high energy trauma, to have a traumatic disruption of the scapulothoracic joint, a so-called scapulothoracic dissociation.
Structure and Function
The scapulothoracic joint is not a true synovial articulation, but rather is the broad contact between the scapula and the thorax. The only ligamentous connection of the scapula to the body is via the clavicle: the medial clavicle is attached to the sternum, whereas its lateral end is attached to the scapula at the acromion.
The scapula is able to move in multiple directions. The motions include: elevation (as in shrugging the shoulders) and depression, protraction (moving medial border medially) and retraction; and rotation (Figure 1a-1c modified from https://radiopaedia.org/cases/scapulothoracic-joint-movements?lang=us).
Figure 1a: The 4 basic straight motions of the scapula: elevation (purple) depression (red) protraction (yellow) and retraction (green).
Figure 1b: Medial rotation of the scapula (right scapula rotates clockwise as seen from the rear, medial side up)
Figure 1c: Lateral rotation of the scapula (right scapula rotates counter-clockwise as seen from the rear, lateral side up)
Motion of the scapula of course affects the position of the glenoid fossa, and in turn influences shoulder function. If the scapula does not move properly, the glenoid fossa will not be oriented for optimal contact with the humeral head. Also, about one-third of the arc of shoulder motion is at the scapulothoracic joint, and thus full range of motion of the shoulder requires normal scapular motion.
Scapulothoracic bursitis is caused by overuse of the shoulder. Chronic inflammation leads to fibrosis, which in turn can produce a snapping sensation. Snapping can also be the result of masses such as an osteochondroma or rib cage abnormalities (as may be seen with scoliosis).
A patient with a scapulothoracic disorder may present with shoulder pain, especially with overhead activities, or with focal scapular complaints such as audible or palpable crepitus.
Figure 2: Medial winging of the left scapula. (Courtesy of Khadilkar SV, et al. nn Indian Acad Neurol http://www.annalsofian.org/text.asp?2016/19/1/108/175435)
Lateral scapular winging is caused by dysfunction of the trapezius and thus the serratus anterior works unopposed. This is usually an iatrogenic injury during neck surgery.
“Pseudo-winging” of the scapula can be seen without neuromuscular disease, either if a mass pushes the scapula off the posterior aspect of the chest wall, or if patients learned to avoid painful positions by moving their scapula abnormally.
Plain x-rays will help detect osseous abnormalities. Snapping may be due to a mass, and if seen on x-ray, CT scans can be used for further definition. MRI may identify bursitis and soft-tissue masses.
An EMG may confirm the presence of a nerve injury that is responsible for winging.
Scapulothoracic disorders are thought to be rare, but may be under-diagnosed. That is, shoulder pain may be incorrectly attributed to primary disorders of the glenohumeral joint, when in fact scapulothoracic dysfunction is the true cause.
Scapulothoracic dyskinesis is usually found in athletes.
If snapping is present, the differential diagnosis is whether a mass is present or not. Imaging usually resolves this.
Scapular dyskinesis is often a diagnosis considered for a patient with shoulder pain that is not responding to treatment. It rarely is the diagnosis considered first, but rather is arrived at as a “diagnosis of exclusion”. It should be suspected in any patient with non-specific shoulder pain especially if the medial scapula is prominent at rest.
Winging is usually the product of dysfunction of the nerves, thus its presence should prompt a close examination to exclude any other neurological finding.
Two other points, not quite “red flags” but perhaps are related to the general topic of vigilance, are worthy of notice: First, it is easy to miss a scapulothoracic diagnosis if the patient is insufficiently disrobed (or if the scapula is not palpated in lieu of direct visualization. As such, a shoulder examination with a fully clothed patient is a red flag for a possibly missed diagnosis. Second, the lung is near the scapula. Thus, if one is performing a bursal injection, it is critical to stay parallel to the undersurface of the scapula to avoid giving the patient a pneumothorax.
Treatment Options and Outcomes
Medial winging usually resolves over time as well, as it is caused by chronic compression. Lateral winging has a worse prognosis, as it usually caused by overt trauma to the nerves.
Risk Factors and Prevention
Scapulothoracic dysfunction is usually caused by overuse, especially in sports such as baseball with repetitive, high velocity throwing. Occupations such as carpentry or wallpaper hanging, with repetitive overhead actions are also risk factors for this condition.
Scapulothoracic dyskinesis can be thought of as “SICK” scapula, which can remind the examiner of three associated findings: Scapular malposition, Inferior medial border prominence, Coracoid pain and malposition, leading to dysKinesis of scapular movement.
Snapping scapula, Scapular winging, Scapulothoracic dyskinesis
Recognize scapular winging on examination.