The shoulder is the most flexible joint in the body. It allows for a range of movements of the hands, however makes it the most unstable joint of the body. It is a ball and socket joint where the head of the upper arm bone (humerus) articulates to the shallow cavity in the shoulder blade (glenoid). The labrum is the fibro-connective tissue surrounding the glenoid cavity and increases its depth and surface area to provide a better fit for the half-spherical head of the long arm bone. A group of ligaments forms a capsule around the shoulder joint and plays a very important role in providing stability to the otherwise unstable shoulder joint. The stability is further enhanced by the group of tendons and muscles that join the head of the humerus to the deeper muscles.
The ball of the shoulder joint sometimes comes out of the socket partially, which is called subluxation; or completely which is called dislocation. Once this occurs, it damages and loosens the supporting capsule of tendons and ligaments around the shoulder joint making the problem more and more recurrent. This condition is termed as chronic shoulder instability.
Depending on whether the shoulder pulls out in one direction or many directions instability is classified as unidirectional and multidirectional shoulder instability.
Some people are born with loose shoulder capsule making them prone to shoulder instability. The shoulder capsule may also loosen due to repetitive overhead activities as in certain sports such as racket sports and swimming. Shoulder instability due to loose shoulder capsule is referred to as multidirectional shoulder instability, which results in shoulder coming out of the socket in more than one direction.
Severe injury or trauma to the shoulder may lead to shoulder dislocation and an injury to the labrum. Even a fall from the cycle or from the stairs can cause shoulder dislocation. Depending on the position of the tear in the labrum, the shoulder instability occurs in either the anterior, posterior, or inferior direction. It cannot occur in superior direction because of the presence of bony extension of the shoulder blade, the acromion, on top of the humeral head.
People realize that they have unstable shoulder when the shoulder dislocates or when they have a persistent feeling that their shoulder is loose and may come out of the socket. People with shoulder instability experience pain with certain movements of the shoulder. Shoulder ball when misaligned or comes out of the socket results in severe pain and swelling.
Diagnosis of shoulder instability is usually done based on the symptoms, medical history, and physical examination. The X-ray and MRI (Magnetic resonance imaging) scan are done to assess whether the dislocation has caused any damage to bones or soft tissue respectively.
Shoulder dislocation or subluxation results in severe pain in the shoulder. Therefore, the patient should be taken to the orthopedist immediately. The orthopedist will put the arm back in the socket. To give rest to the affected shoulder, a sling would be put for that arm. Medications are given to provide relief from pain and reduce swelling. After the sling is removed some exercises that strengthen the shoulder muscles are advised.
The person can live with shoulder instability but have to avoid activities that may lead to shoulder dislocation. Surgery is advised when the shoulder instability interferes with the daily life or if the instability is due to the shoulder injury.
Surgery can be an open surgery or an arthroscopic procedure.