The shoulder with a complex arrangement of structures working together is the most mobile joint in the human body. But this great mobility comes at the expense of stability. Atraumatic instability is a condition in which the shoulder starts to slip part way out of joint without having had a significant injury. Atraumatic instability may arise from a variety of causes. Certain shoulders may be more susceptible to atraumatic instability. Atraumatic shoulder instability is generally treated with rehabilitation using stabilizing exercises and surgery is only very rarely required.

The other type of instability is Traumatic instability of the shoulder and this is a common condition, which, especially in young patients, is associated with high recurrence rates. In this type of instability the anterior dislocation due to trauma is the most common type, corresponding to more than 90% of the cases. Posterior shoulder instability occurs less frequently, only accounting for less than 5% of traumatic shoulder dislocations. Atraumatic instability commonly results from repetitive overhead movements or congenital joint features. Atraumatic shoulder instability is not related to injury or trauma to the shoulder. It is the result of stretching of the shoulder capsule (a ligament that protects the muscles and ligaments of the shoulder) over a period of time.

Atraumatic instability could be either structural or positional instability which is muscle patterning usually seen in younger patients. Atraumatic instability is an acquired instability that could be brought on by repetitive microtrauma, which places undue stress upon the soft tissues; or rapid, forceful movements that contribute to the overall laxity of the joint. This is a common problem in athletes, particularly throwers, weight trainers, swimmers, golfers, tennis players and gymnasts, where they develop symptoms of instability due to overload and fatigue in the stabilizing muscles of the shoulder.

The two main types of atraumatic instabilities are Congenital Instability which is due to laxity of structures in the shoulder which may be present since birth and Chronic Recurrent Instability caused by repetitive extreme external rotation with the humerus abducted and extended. Congenital instability may be the result of bone anomalies, increased amount and composition of collagen and elastin, hypoplastic glenoid or increased retroversion of glenoid. The top symptoms of atraumatic shoulder instability can be feelings of looseness or instability of the shoulder or recurring (repeated) subluxation or partial dislocation. Shoulder instability can be tested with the help of an anterior apprehension test, or crank test.

Treatment strategies for atraumatic shoulder instability are devised to suit each patient’s age and lifestyle. The goal of the rehabilitation program may vary greatly based on the onset and mechanism of injury. If physical therapy does not improve shoulder stability, the doctor may recommend surgery. The goal of surgery for atraumatic shoulder instability is to tighten the ligaments that have been overstretched in order to reduce the risk of recurrent dislocations. Sometimes this type of surgery can be done arthroscopically and it is called a capsular shift. The recurrence rates of shoulder instabilities vary based on age, activity level and arm dominance and in collision sport athletes the rate of recurrence is pegged between 86-94%.

Q&As on Atraumatic Shoulder Instability

1. How is atraumatic shoulder instability diagnosed?

Atraumatic instability is now understood as a condition or syndrome that may result from various causes rather than a single one. We use the abbreviation “AMBRII” for multidirectional shoulder instability to keep in mind the many facets of this condition. Multidirectional laxity and bilateral findings characterise the atraumatic instability. Rehabilitation to regain complete control of one’s muscles is the mainstay of treatment. Reconstructing the capsule-coracohumeral ligament system and tightening the inferior capsule would be essential if surgery were to be recommended.

2. What is the type of atraumatic shoulder instability?

Atraumatic instabilities are more likely to have many directions of instability since they often come from the loss of middle stability. A compliant capsule and weak muscles in the flat glenoid are pathogenetic variables that may cause instability anteriorly, inferiorly or both anteriorly and posteriorly. Many underlying contributing variables may be developmental, even if the start of atraumatic instability may be triggered by a brief period of inactivity or a slight injury. The propensity for atraumatic instability is thus likely to be bilateral and family.

3. How is atraumatic shoulder instability treated non-surgically?

The non-operative treatment of atraumatic instability has two components:

  • Improving compressor muscles’ strength and
  • Humeroscapular balance training

First, the muscles must be developed to their full power and range of motion in order to compress the head of the humerus into the glenoid concavity. A regular workout routine may generally control the rotator cuff muscles’ weakness or inadequate endurance. The second exercise session focuses on recovering stability via neuromuscular control of the humeroscapular postures. A surgical repair may be considered if a significant and extended effort with the training regimen fails to improve shoulder function.

4. How is atraumatic shoulder instability treated surgically?

The doctor could suggest surgery if physical therapy cannot improve shoulder stability. Surgery for atraumatic shoulder dislocation aims to tighten the overstretched ligaments to lessen the possibility of recurring dislocations. This procedure is sometimes arthroscopic. Arthroscopy is a minimally invasive operative procedure that makes numerous very small (about one centimetre long) incisions to insert specialised tools and a camera connected to a thin, flexible tube. However, if the shoulder is very loose, making a tiny incision on the front of the shoulder may be necessary to correct the instability. The procedure is known as a capsular shift.

5.How long is the recovery after atraumatic shoulder instability surgery?

Within three to six months after starting therapy, you should be able to resume routine activities if you have undergone surgical treatment for atraumatic shoulder instability. After surgery, you must leave your arm immobile for several weeks in a sling before starting range-of-motion exercises with a trained physical therapist. Once your strength and range of motion have fully returned and you are pain-free, you may resume playing.

With persistent, recurrent usage of the shoulder, atraumatic shoulder dislocation might happen again. This is why it’s crucial to focus shoulder strengthening workouts throughout your sports career.

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