Instability Problems of the Glenohumeral Joint
Multidirectional Instability versus Unilateral Instability
Oct 11, 2009
The glenohumeral joint is one of three joints that make up the shoulder complex. It is the largest of the three joints and also has the greatest range of motion. The other two joints include the sternoclaviular joint (articulation between the sternum and the clavicle) and the acromioclavicular joint (articulation between the acomion process of the scapula and the clavicle.
The shallow bony arrangement of the glenohumeral joint places the joint at risk for stability problems if any of the soft tissue structures (labrum, ligaments, joint capsule) are injured or congenitally lax. Instability type injuries mean that the head of the humerus has more movement than it should within the glenoid fossa.
An unstable glenohumeral joint means that the head of the humerus can shift further than it should in either one direction (unidirectional instability) or in multiple directions (multidirectional instability). Unidirectional instabilities can be in one of three directions: anterior, posterior, or inferior.
Unidirectional instabilities are most likely caused by damage to the soft tissue structures during either an acute injury (one time event such as a subluxation or dislocation) or from repeated microtears (chronic overuse injury). The most common unidirectional instability is in the anterior direction.
Anterior Unidirectional Instabilities
Anterior instability injuries are the result of some type of injury to the anterior glenohumeral ligaments, specifically the middle and inferior glenohumeral ligaments. If the original force is strong enough, the labrum and joint capsule can also be torn or damaged.
A specific injury to the anterior soft tissue structures is called a Bankart lesion. In a Bankart lesion, the inferior glenohumeral ligament is torn from the labrum or is torn along with a piece of the labrum (Examination of Orthopedic and Athletic Injuries, 3rd edition, 2010). This can occur as the head of the humerus shifts in an anterior direction during either a subluxation or dislocation but more commonly during recurrent injuries.
Posterior Unidirectional Instabilities
Posterior instability can occur from one single traumatic event, but more commonly results from repeated microtrauma. This type of instability is less common and is typically associated with blocking in football in which the head of the humerus is driven in a posterior direction while the arm is in a position flexed in front of the body.
While inferior instability injuries do exist, they are fairly rare.
Treatment of Unidirectional Instabilities
Unidirectional instabilities can initially be treated conservatively with rest and rehabilitation. Although ligaments and joint capsule tissue cannot return to their original length, they can scar down over time. However, this does leave the joint permanently lax. To make up for this laxity, the deep muscles surrounding the joint can be strengthened to provide some stability (Foundations of Athletic Training: Prevention, Assessment, and Management, 4th edition, 2009)..
If rehabilitation does not reduce the pain and strengthen the muscles to prevent further subluxations or dislocations, then surgery is most likely indicated.
Multidirectional Instabilities
Multidirectional instabilities are more likely congenital and result from loose connective tissue (ligaments and/or joint capsule). This means that the head of the humerus has the ability to shift more than a normal range within the glenoid fossa in more than one direction (anterior, inferior, posterior). This would also mean that the individual would be likely to have multidirectional instabilities in other joints of the body.
Treatment for this type of instability includes strengthening the deep muscles of the shoulder girdle and shoulder joint. The focus is on strengthening the muscles all around the joint rather than in just one direction. Stabilization exercises can also be done to train the muscles to contract and strengthen when force is applied in different directions.
The key in treating instability injuries of the glenohumeral joint is to differentiate between a unidirectional instability and a multidirectional instability. A thorough medical history can determine whether the instability was caused by an acute or chronic mechanism or whether the instability was the result of a congenital condition. A physician or sports medicine professional can evaluate the shoulder joint through the application of specific stability tests to determine which type of instability the glenohumeral joint has.
Once this is determined, conservative treatment should be undertaken to try to strengthen surrounding muscles enhancing stability. If conservative treatment is not successful, then surgery may be considered.
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