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A shoulder dislocation is a significant shoulder injury. What exactly is injured when the shoulder dislocates? What is the typical treatment following a dislocation and is surgery necessary?
The shoulder is comprised of three bones: the humerus, scapula, and clavicle. The joint typically considered the shoulder joint is comprised of the humerus as it connects to the scapula. It is the head of the humerus that connects to the glenoid of the scapula, thus forming the glenohumeral joint.
The shoulder joint gets a majority of its stability from the soft tissue structures that surround the glenohumeral joint. The rotator cuff provides for dynamic stability as these four muscles contract to help center the humerus on the glenoid.
Another soft tissue structure called the joint capsule also helps to provide shoulder stability. Although this tissue does not contract, it helps to provide additional support to the very mobile shoulder joint.
What is a Shoulder Dislocation?
A shoulder dislocation is technically when the head of the humerus slides out away from its connection with the glenoid with the head of the humerus remaining out of the socket. In comparison, a shoulder subluxation is when the head of the humerus slides out away from the glenoid but quickly slides back into place.
Most commonly the direction in which the head of the humerus moves is anterior and inferior. This simply means the humerus slides forward and down, moving into the region of the armpit. Although a shoulder can dislocate in the posterior direction, the anterior and inferior dislocation is by far the most common.
What Tissues Are Injured?
A number of different structures can become injured when a shoulder dislocates. Injuries to the soft tissue that helps support the joint and the bones of the shoulder joint itself can become injured.
The most common soft tissue that is injured is the joint capsule. The inferior or bottom part of the capsule can become significantly stretched or more likely torn secondary to the stress of the humeral head.
Another soft tissue structure, called the glenoid labrum, can also become injured. The labrum is like the cartilage of the shoulder. The labrum is attached to the glenoid of the scapula and functions to help improve the stability of the joint. When the shoulder is dislocated, the head of the humerus can cause a tear in the inferior aspect of this labrum. The specific term for this injury is called a bankart lesion.
In addition to soft tissue injuries, the bones themselves can become injured from the shoulder dislocation. Some times as the head of the humerus is moving downward, it can hit the edge of the glenoid. This can cause an injury to the head of the humerus called a Hill-Sachs lesion. This lesion is basically a divot in the head of humerus.
In addition to the humerus becoming injured, the glenoid can also sustain an injury. Most commonly the inferior aspect of the glenoid can sustain a fracture from the force of the humeral head hitting it as the shoulder dislocates.
Mechanism of Injury
How does a dislocation typically happen? Most often a first time dislocation will occur secondary to trauma.
A fall on an outstretched arm or, more commonly, reaching out to the side with the arm slightly rotated can cause a shoulder dislocation.
Recurrent dislocations can occur even without trauma. Reaching out to the side, moving the shoulder in a throwing motion, or even turning over in bed can cause a shoulder that has previously dislocated to pop out of joint.
Signs and Symptoms
As with any traumatic shoulder injury,
shoulder joint pain
is first noticed. The shoulder will have a sensation of being out of joint. Occasionally a feeling of tingling or numbness will radiate down the arm. In addition, the arm will be unable to move and you’ll most likely want to position the arm close to the body.
In addition to sever pain and an inability to move the shoulder, the shoulder will have an obvious deformity. The lateral aspect of the shoulder will look flat compared to the opposite side as the head of the shoulder is no longer in the correct position.
Shoulder Dislocation Treatment
Following a dislocation, the shoulder first must be relocated or put back into place. This should be done by a doctor or other trained health care professional. Preferably an x-ray should be done prior to relocating the shoulder in order to determine if a fracture has occurred. The shoulder is generally relocated by applying a distraction force to the joint to allow the head of the humerus to slide back into place.
Once the shoulder is relocated follow up diagnostic tests including x-rays and at times an MRI are generally performed. These tests are utilized to evaluate the presence of a fracture and to what extent the soft tissue has been damaged. This information can be utilized to determine if surgery is necessary.
Following relocation the shoulder is put into a sling for a minimum of two weeks. The extent of tissue injury will often dictate the length of immobilization. Shoulders do have a tendency of becoming stiff with immobilization thus range of motion exercises are initiated early in the healing.
Following immobilization physical therapy is generally performed. Range of motion exercises in addition to strengthening exercises will be part of the program. Because the shoulder relies on muscle strength for its stability, restoring shoulder strength is essential prior to resuming function. Full recovery following a shoulder dislocation generally requires 3-4 months.
When Is Surgery Necessary?
Whether or not surgery is indicated can in part be based on the extent of the injury. If a bankart lesion and/or glenoid fracture occurs, significant soft tissue damage most likely has also taken place. In this instance the likelihood of recurrent instability is high, making additional dislocations more likely. Many orthopedic physicians will recommend physical therapy first prior to recommending surgery. However, the extent of the damage may make having surgery first a reasonable option.
Surgery following a dislocation often involves addressing a number of issues. If damage to the glenoid has occurred a bankart repair will be performed. In addition, in order to provide for additional stability to the joint an anterior capsular shift is also performed. This procedure is done in order to provide for more stability and minimize the chance of recurrent dislocations.
• Shoulder dislocations involve the head of the humerus ‘popping out’ away from the glenoid.
• Most dislocations occur secondary to trauma with the humerus moving anterior and inferior.
• Soft tissue damage including the capsule and the labrum in addition to bony fractures can occur.
• Treatment starts with relocation of the shoulder, immobilization, and physical therapy.
• In some cases surgery to repair the labrum and provide for shoulder stability is required to minimize the incidence of recurrence.
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