Shoulder Instability

Shoulder Instability


Shoulder injuries are frequently caused by athletic activities that involve excessive, repetitive, overhead movements, such as swimming, tennis, and weightlifting. Injuries can also occur due to day to day activities such carrying your child or groceries, or even long-distance driving using one arm.

Some people tend to neglect the pain and push through it which only aggravates the condition and may possibly cause more damage to the quality of movement performed by the individual. People also may underestimate the extent of their injury because of steady pain will become almost normal to them as they will develop altered movement patterns over time, which eventually will end up with shoulder instability.

Shoulder instability can be categorized into three types according to the reason behind it:

  1. Atraumatic: due to the reasons mentioned above or muscle imbalance due to acquired poor postural habits.
  2. Traumatic:  due to a fall, dislocation or labrum damage.
  3. Neurological dysfunction: i.e. hemiplegia.


In this article, you will learn more about shoulder instability in general and the relation between the scapula to the shoulder quality of movement.

The scapula is a triangular bone at the back of your shoulder known as the “shoulder blade”. Its only attachment to the rest of the skeleton is through the collarbone at the acromioclavicular joint. Therefore, the bone is primarily held in place by the attached and surrounding muscles. At the outer edge of the scapula a shallow socket where the humeral head sits forming the shoulder joint (glenohumeral joint). Proper positioning and movement of the scapula is critical for full and normal shoulder range of motion. We tend to use the acronym SICK to refer to an injury resulting from overuse and fatigue of the muscles that stabilize and provide motion for the scapula. which stands for:



  • Scapular malposition
  • Inferior medial border prominence
  • Coracoid pain and malposition  
  • dysKinesis of scapular movement


A SICK scapula will result in Scapular Dyskinesis which is an alteration in the normal position or motion of the scapula during scapulohumeral movements. It occurs in many injuries involving the shoulder joint and often is caused by injuries that result in the inhibition or disorganization of activation patterns in scapular stabilizing muscles. It may increase the functional deficit associated with shoulder injury by altering the normal scapular role during coupled scapulohumeral motions. Scapular dyskinesis appears to be a nonspecific response to shoulder dysfunction because no specific pattern of dyskinesis is associated with a specific shoulder diagnosis. The majority of scapular dyskinesis cases are the result of loss of muscular coordination. The trapezius, rhomboid and serratus anterior muscles must be properly synchronized in their action for smooth scapular motion during arm movement.


On the other hand, an article was published in September 2018 by Ansanello Netto et all, about the scapular muscle and the traumatic shoulder instability. the researcher used isokinetic machine to evaluate the efficiency of the shoulder protractor and retractors muscles between two groups, normal individuals and subjects with traumatic anterior glenohumeral instability. the results were lower peak force of protraction and retraction during isometric and fast speed tests in the group of glenohumeral instability. The researcher concluded by “People with traumatic anterior glenohumeral instability present muscle weakness of scapular protractors and retractors. Considering the importance of the scapulothoracic muscles for the dynamic stability of the glenohumeral joint, strengthening of these muscles is recommended for rehabilitation of traumatic anterior glenohumeral instability.”


The moral of the story is regardless of the cause of the shoulder injury, the scapular muscles are crucial to be addressed during the rehabilitation plan to fix the mechanics of the shoulder joint and regain normal range and function.



Ahmed K.


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