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Types of Shoulder Instability

Shoulders become unstable because of two major reasons. First reason is due to structural causes and the second cause is because of the development of unbalanced muscle recruitment around the shoulder. When the head of the upper arm bone is forced out of the shoulder socket following a sudden injury or from overuse a shoulder instability can occur.

The basic forms of shoulder instability are subluxations and dislocations. A subluxation is a partial or incomplete dislocation whereas a dislocation is when the head of the arm bone slips out of the shoulder socket. When there is a possibility for chronic instability, shoulder dislocations can happen frequently.

As per Stanmore classification system there are basically three types of shoulder instability based on the structural and non-structural components. According to this system the concept of instability is that it happens due to a combination of structural and neurological system disturbances. The three types are Structural Instability, Atraumatic Instability and Neurological dysfunctional or muscle patterning also known as Habitual non-structural Instability. This system of classification is used for posterior and anterior dislocations and also for subluxations, and complete dislocations.

Traumatic Instability is the most common glenohumeral dislocation and this occurs anteriorly mostly because of sporting accidents or falls especially when the upper extremity is in 90° abduction and external rotation. A posterior dislocation happens as because of seizures, shock and falls. Atraumatic instability happens due to extreme external rotation with the humerus abducted. This chronic instability is mostly associated with participation in sports such as gymnastics, tennis, swimming, and weight training.

Another type of shoulder instability is the Congenital Instability. The possible reasons are hypoplastic glenoid, decrease anterior-posterior diameter of glenoid, increased retroversion of glenoid, increased amount and composition of collagen and elastin or bony anomalies.

Based on the clinical presentation there can be three types of shoulder instability. Anterior Instability, Posterior Instability and Multidirectional Instability. The possible signs and symptoms of anterior instability can include clicking, pain, a dead arm sensation, posterior pain, possible subacromial or internal impingement signs and a positive result in an apprehension test, relocation test, and an anterior release test. In the case of a Posterior shoulder instability the signs could be possible subacromial or internal impingement, glenohumeral internal rotation deficit, pain, clicking and an increased joint accessory motion particularly in the posterior direction. In a multidirectional Instability there can be antero-inferior laxity along with global shoulder pain and a positive result on a sulcus test, a relocation test and on an anterior release test.

The Anterior shoulder instability when the head of the humerus excessively moves anteriorly (forward) within the glenoid (shoulder joint cavity is the most common form of shoulder instability and accounts for about 95% of all shoulder dislocations. Shoulder instability mostly occurs due to the lack of adequate strength and motor control of the shoulder girdle. Depending on the type of tissue that is injured, as many of which may be injured with shoulder instability the healing timelines for it will also differ.

For enquiry related to Shoulder Injuries, Sports Injuries and their treatment options, send a message to www.BangaloreShoulderInstitute.com/contact

Visit the youtube channel to watch videos by Dr Ayyappan V Nair on different shoulder, sports and other orthopaedic conditions and their treatment options – https://www.youtube.com/channel/UCJldz_Osg88qFYM99IEsjew

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