Shoulder Instability: The In’s and Out’s

The shoulder is one of the most fascinating joints in the human body. It is the most mobile joint that we have and gives us so much freedom of movement. However, with this freedom comes at the cost of some potential instability. Shoulder instability can have many causes ranging from congenital factors leading to overall joint laxity, repeated overhead movement or the classic example of a traumatic shoulder injury/dislocation. Many times after the latter there can be lingering or chronic sensations of shoulder instability.  


The Shoulder Joint

The shoulder joint, or glenohumeral joint, is the connection point for our arm into our trunk. The joint is made up of the head of the humerus (upper arm bone) and the part of the scapula (shoulder blade) called the glenoid. This connection is not exact as only about 25% of the head of the humerus is in contact with the shoulder blade at any given time. So to form a more stable “shoulder socket” the body surrounds the rim of the glenoid with the labrum and the whole joint with many ligaments to form a stable capsule. In order to increase even more stability in the shoulder joint we have 4 rotator cuff muscles (infraspinatus, supraspinatus, teres minor and subscapularis) that attach their tendons into this shoulder capsule. These rotator cuff muscles serve mostly as dynamic stabilizers. The muscles fire to restrict any excessive movement of the shoulder and keep the humeral head in alignment with the glenoid. Normally, all these components work with the larger deltoid muscles and muscles that surround the scapula to create a stable joint when the arm and/or shoulder blade are moving.


When people experience a large force to the arm or shoulder that exceeds the capacity of the shoulder capsule, rotator cuff muscles or larger muscles to accept load within its available range, the shoulder is likely to dislocate. Most commonly the shoulder will move forward and down—termed an anteroinferior dislocation. This can cause injury and intense stretch to the muscles, ligaments and other structures that normally stabilize the shoulder. 


Injuries to structures surrounding the shoulder can fall in a vast range. If all emergency pathologies are avoided patients can be left with injury to the ligaments, rotator cuff muscles or labrum. A study completed by Rowe and Zarins showed 85% of patients that experienced a traumatic shoulder dislocation have a tear of a portion of the labrum called a Bankart Lesion which decreases congruence in the shoulder joint. While surgery is indicated in some scenarios, many patients do not require surgery and conservative management through PT is indicated in a high percentage of cases.


Due to injury to surrounding shoulder structures the patient can be left with hypermobility in the shoulder joint and subsequent pain and/or a sensation of shoulder instability. The relative laxity and injury in the joint may also cause the body to create compensations throughout muscles surrounding the shoulder and scapula which is found in 64% of patients. These compensation patterns can cause even further compensations throughout movement and ultimately restrict pain free movement throughout the shoulder joint and create chronic shoulder instability.


Rehab Process: What to Expect 

Current strategies to combat chronic shoulder instability focus on progressive loading of the rotator cuff, deltoid and scapular musculature. Most people will have discomfort and shoulder instability in positions of shoulder elevation, horizontal abduction and external rotation (imagine making a goal post with your arm and this is that position). Where in these motions the person begins to feel instability or discomfort will vary from patient to patient, so gradually working into comfortable ranges on an individualized basis will be important in the rehab process. It is also crucial to maintain joint and tissue health in the surrounding areas, specifically at the elbow, neck, thoracic spine (upper back/rib cage), and in the neural structures that go down one’s arm.


Early Phase: 

  • Initially many patients will be immobilized in a sling to restrict movement and allow the injury to heal. However, recent literature has not shown that outcomes are similar between patients that are immobilized and those that are not, so we may be moving away from a lengthy or any immobilization phase post shoulder dislocation. 
  • Restoring pain free PROM 
  • Pain free active-assisted ROM 
  • Gentle isometric contractions of rotator cuff musculature.
  • Light activation of the scapular (shoulder blade) musculature.
  • Thoracic spine, neck, and elbow joint health exercises
  • Nervous system glides
  • All of this has the goal of increasing muscle activation in muscles that will help stabilize the shoulder, but there is also evidence that light isometrics and muscle activation have a profound effect on pain modulation and enhancement of the healing process within joint structures


Intermediate Phase

  • Will demonstrate good static stability of the shoulder in a neutral position. 
  • Focus in regaining full pain-free active ROM  
  • Progress strengthening of the rotator cuff, scapular and surrounding shoulder musculature in higher ranges of motion working toward stability in overhead position.
  • Rhythmic stabilization in different ranges of motion and closed chain exercises may be added later in this phase.
  • The goal here is to restore muscular balance throughout the shoulder to enhance stability and avoid compensation.


Advanced Phase 

  • As the shoulder becomes more stable in progressively higher ranges of motion the focus turns to more advanced movements.
  • This includes continuing to progress toward completing stability drills in points of apprehension and/or in overhead positions.
  • This phase will also work toward more aggressive upper body strengthening with larger combined movements
  • Late in this phase exercises to return to activity drills such as throwing are incorporated into the program.


Shoulder instability can be a frustrating condition because of how much we rely on the motion through this joint on a day-to-day basis. It is important to note that the shoulder is supposed to be mobile and for that reason may take time to fully rehab back to pre-injury function that may include progression to and from the different rehabilitation phases. However, that does not mean that there has to be instability and pain in the long-term. The body has structures in place to create resiliency in our joints, so it is important that we take advantage of this and train those structures in order to create the most healthy joint possible and return to pain free motion and activity to pre-injury levels.


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Jaggi A, Alexander S. Rehabilitation for Shoulder Instability – Current Approaches. Open Orthop J

2017;11:957-971. Published 2017 Aug 31. doi:10.2174/1874325001711010957

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glenohumeral instability. N Am J Sports Phys Ther. 2006;1(1):16-31.

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