The shoulder is the most mobile joint in the human body, with a complex arrangement of structures working together to provide the movement necessary for daily life. Unfortunately, this great mobility comes at the expense of stability.
Shoulder instability develops in two different ways: traumatic (injury related) onset or atraumatic onset. Understanding the differences is essential in choosing the best course of treatment. Generally speaking, traumatic onset instability begins when an injury causes a shoulder to develop recurrent (repeated) dislocations. The patient with atraumatic instability has general laxity (looseness) in the joint that eventually causes the shoulder to become unstable.
Traumatic shoulder instability is most common in young, athletic people. The younger and more active the patient is when the first dislocation occurs, the more likely it is that recurrent instability will develop. For example, if the first dislocation occurs during the teenage years, there is a 70% chance that recurrent instability will develop. However, people over 40 with a first dislocation have less than a 10% risk of developing chronic instability. Treatment strategies should be designed to suit each patient’s age and lifestyle.
The shoulder is the most mobile joint in the human body, with a complex arrangement of structures working together to provide the movement necessary for daily life. Unfortunately, this great mobility comes at the expense of stability. Several bones and a network of soft tissue structures (ligaments, tendons, and muscles), work together to produce shoulder movement. They interact to keep the joint in place while it moves through extreme ranges of motion. Each of these structures makes an important contribution to shoulder movement and stability. Certain work or sports activities can put great demands upon the shoulder, and injury can occur when the limits of movement are exceeded and/or the individual structures are overloaded.
What is traumatic shoulder instability?
Traumatic shoulder instability begins with a first dislocation that injures the supporting ligaments of the shoulder. The glenoid (the socket of the shoulder) is a relatively flat surface that is deepened slightly by the labrum, a cartilage cup that surrounds part of the head of the humerus. The labrum acts as a bumper to keep the humeral head firmly in place in the glenoid. More importantly, the labrum is the attachment point for ligaments stabilizing the shoulder. When the labrum is torn from the glenoid, the support of these ligaments is lost. The development of recurrent instability depends upon the type and amount of damage that is done to the labrum and the supporting ligaments.
The most common dislocation that leads to traumatic instability is in the anterior (forward) and inferior (downward) direction. A fall on an outstretched arm that is forced overhead, a direct blow on the shoulder, or a forced external rotation of the arm are frequent causes of this type of dislocation. Much less common is a posterior (backward) dislocation, which is usually related to a seizure disorder or electrocution, events in which the muscular forces of the shoulder cause the dislocation.
What are the signs and symptoms of a dislocation?
If the shoulder is dislocated, it is usually very apparent:
To return the dislocated arm to its socket (called a reduction) usually requires a visit to the emergency department, where expert assistance can be found. Some individuals with recurrent dislocations eventually become experienced at reducing the arm themselves.
How is a dislocation and traumatic shoulder instability diagnosed?
As a rule, a sudden dislocation is quite evident. The patient usually holds the arm against the side, since any attempts at motion cause pain. A large crease under the acromion and a bulge in the armpit are clues to the direction of the dislocation. However, when the shoulder spontaneously relocates into its proper position, the diagnosis can be more difficult. Patients may only report the feeling of having the shoulder "slip" before the spontaneous reduction occurred.
A qualified individual usually can relocate the humerus at the site of the injury occurrence. Once the reduction is performed, there is immediate pain relief. Without medications, some patients may be unable to relax the shoulder muscles enough to allow the reduction to take place. Often, these patients must go to the emergency department to get the reduction accomplished.
How is a dislocation and traumatic shoulder instability treated?
The initial reduction of a dislocation can be quite difficult. Contractions of the shoulder muscles can trap the humeral head against the glenoid. Gentle traction, and at times, medication may be needed to accomplish the reduction. Once the shoulder is reduced, a sling is used for a few days to protect it, and relieve discomfort. Physical therapy may help the patient regain motion in the joint.
Initial treatment for recurrent instability of the shoulder centers on physical therapy. Strengthening the rotator cuff muscles and periscapular muscles (those around the scapula) gives stability to the joint. The goal of physical therapy is to help the muscles provide stability to the shoulder that the torn ligaments can no longer supply. The therapy for recurrent instability should be carefully designed for each patient since this condition often causes apprehension about certain arm positions or exercise maneuvers. Very often, physical therapy can help regain lost motion, reduce apprehension, and restore shoulder function.
Surgery is usually recommended if recurrent instability cannot be controlled with physical therapy and activity modification. The goal of surgery is to return stability to the shoulder with the least loss of motion. All shoulder procedures designed to stabilize the shoulder involve some loss of motion. The current procedures for anterior shoulder instability attempt to restore the normal anatomy without over tightening the ligaments. In certain instances, such as in young persons who have a higher risk of re-dislocation and in contact athletes who plan on continuing to participate in sports that put their shoulders at risk, surgery may be performed after the first dislocation.
Patients who have a first dislocation, and do not develop recurrent instability, will often regain full motion from a four to six week course of physical therapy.
Patients who do develop recurrent instability have a longer rehabilitation course and should concentrate on strengthening the shoulder muscles. Daily exercises in a home program may be recommended to help prevent instability events.
Following either arthroscopic or open operative repair and stabilization:
A teenager has a first dislocation event. What is the likelihood that recurrent instability will develop?
Older research suggests that up to 90% of teenagers will develop recurrent instability after a first dislocation. More recent studies put that number closer to 70%. It is clear, however, that the younger a person is when the first injury occurs, the greater the risk is that recurrent instability will develop.
What is the point of doing physical therapy for the rotator cuff if the labrum and ligaments are torn?
The rotator cuff muscles and the periscapular muscles are important in maintaining shoulder stability. The more ineffective the ligaments are at supporting the shoulder, the more important muscular strength becomes for the control of the shoulder. Strengthening the muscles around the shoulder may provide enough stability to prevent recurrent dislocations and eliminate the need for surgery.
Should an open or arthroscopic surgery be performed?
The decision to have an open or arthroscopic repair depends on many factors. The cause of the instability, the total number of dislocations, and which technique the surgeon uses are important considerations when choosing the method of reconstruction. A thorough discussion with the surgeon of the treatment options is essential. Regardless of the technique used, the rehabilitation following surgery is the same.
Is a laser used to make the shoulder more stable?
Thermal capsulorraphy (heat treatment of the shoulder capsule) is a new technique developed to achieve shoulder stability. Newer techniques involve a radio frequency probe instead of a laser to shrink the capsule. This type of treatment continues to evolve, and its results are still being evaluated.
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