This ability to move makes the joint inherently unstable and also makes the shoulder the most often dislocated joint in the body.
The head of the humerus (upper arm bone) sits in the glenoid fossa, an extension of the scapula, or shoulder blade. Because the glenoid fossa (fossa = shallow depression) is so shallow, other structures within and surrounding the shoulder joint are needed to maintain its stability. Within the joint, the labrum (a fibrous ring of cartilage) extends from the glenoid fossa and provides a deeper receptacle for the humeral head. The capsule tissue that surrounds the joint also helps maintain stability. The rotator cuff muscles and the tendons that move the shoulder provide a significant amount of protection for the shoulder joint.
Dislocations of the shoulder occur when the head of the humerus is forcibly removed from its socket in the glenoid fossa. The shoulder can be dislocated in many different directions, and a dislocated shoulder is described by the location where the humeral head ends up after it has been dislocated. Ninety percent or more of shoulder dislocations are anterior dislocations, meaning that the humeral head has been moved to a position in front of the joint. Posterior dislocations are those in which the humeral head has moved backward toward the shoulder blade. Other rare types of dislocations include luxatio erecta, an inferior dislocation below the joint, and intrathoracic, in which the humeral head gets stuck between the ribs.
Dislocations in younger people tend to arise from trauma and are often associated with sports or falls. Older patients are prone to dislocations because of gradual weakening of the ligaments and cartilage that supports the shoulder. Even in these cases, however, there still needs to be some force applied to the shoulder joint to make it dislocate.
Anterior dislocations often occur when the shoulder is in a vulnerable position. A common example is when the arm is held over the head with the elbow bent, and a force is applied that pushes the elbow backward and levers the humeral head out of the glenoid fossa. This scenario can occur with throwing a ball or hitting a volleyball. Anterior dislocations also occur during falls on an outstretched hand. An anterior dislocation involves external rotation of the shoulder; that is, the shoulder rotates away from the body.
Posterior dislocations are uncommon and are often associated with specific injuries like lightning strikes, electrical injuries, and seizures. On occasion, this type of dislocation can occur with minimal injury in the elderly, and often the diagnosis is missed the first time the patient presents for evaluation of shoulder pain.
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Dislocations hurt. When the humerus is pulled out of the socket, cartilage, muscle, and other tissues are stretched and torn. Shoulder dislocations present with significant pain, and the patient will often refuse to move the arm in any direction. The muscles that surround the shoulder joint tend to go into spasm, making any movements very painful. Usually, with anterior dislocations, the arm is held slightly away from the body, and the patient tries to relieve the pain by supporting the weight of the injured arm with the other hand. Often, the shoulder appears squared off since the humeral head has been moved out its normal place in the glenoid fossa. Sometimes, it may be seen or felt as a bulge in front of the shoulder joint.
As with other bony injuries, the pain may provoke systemic symptoms of nausea and vomiting, sweating, lightheadedness, and weakness. These occur because of the stimulation of the vagus nerve, which blocks the adrenaline response in the body. Occasionally, this may cause the patient to faint or pass out (vasovagal syncope).
When a patient presents with a shoulder dislocation, pain control and joint relocation are primary considerations. However, it is still important for the health-care provider to take a careful history to understand the mechanism of injury and the circumstances surrounding it. In addition, information about medications, allergies, time of the last meal, and past medical history may be asked to prepare for a potential anesthetic administration to help relocate, or reduce, the shoulder dislocation. It will also be important to know if this is the first shoulder dislocation or whether the joint has been previously injured.
Pain and muscle spasm accompany dislocated joints, and a shoulder dislocation is no different. When the joint is disrupted, the muscles surrounding it are stretched and go into spasm. The patient will experience significant pain and will often resist the smallest movement of any part of the arm.
Physical examination of the shoulder will begin with inspection to look for "squaring off," or a loss of the normal rounded appearance of the shoulder caused by the deltoid muscle. In thinner patients, the humeral head may be palpated or felt in front of the joint.
The health-care provider may examine the blood and nerve supply to the arm since injuries may occur to arteries and nerves when the shoulder is dislocated. The brachial plexus, the axillary artery, and axillary nerve are located in the armpit and are relatively unprotected. Complications of shoulder dislocation can include artery and nerve damage.
Plain X-rays may be taken to confirm the diagnosis of shoulder dislocation and to make certain there are no broken bones associated with the dislocation. Two common fractures are the Hill-Sachs deformity, a compression fracture of the humeral head, and a Bankart lesion, a chip fracture of the glenoid fossa. While these may be present, they do not hinder the relocation of the shoulder. Other fractures of the humerus and scapula may make shoulder reduction more difficult.
Since the body is 3-D and X-rays are 2-D, at least two X-rays are taken to be able to accurately assess where the humeral head is located in relationship to the glenoid. Extra X-ray views also better assess the bones, looking for fracture.
In certain circumstances, (often on the athletic field) if a health-care provider is present at the time of injury, an attempt may be made to reduce or relocate the shoulder immediately without X-rays being taken. Using manipulation described below, before the muscles have a chance to go into spasm, it is possible to relocate the shoulder. Imaging of the injured shoulder (X-ray or MRI) would then be considered at a later time.
The purpose of the initial treatment of a dislocated shoulder is to reduce the dislocation and return the humeral head to its normal place in the glenoid fossa. There are a variety of methods that may be used to achieve this goal. The decision as to which one to use depends upon the patient, the situation, and the experience of the clinician performing the reduction. Regardless of the technique used, the hope is to be able to efficiently reduce the dislocation with a minimum of anesthesia required. Most often, a closed reduction is attempted and is successful; that is, no incision or cut is made into the joint to assist in returning the bones to their normal position. The term "open reduction" refers to performing surgery to repair the dislocation.
In rare circumstances, the shoulder cannot be reduced using closed reduction techniques because a tendon, ligament, or piece of broken bone gets caught in the joint, preventing return of the humeral head into the glenoid. When closed reduction fails, an operation or open reduction is considered to treat the shoulder dislocation. This requires that the orthopedic surgeon care for the patient in the operating room.
Depending upon the amount of pain and spasm present, medication may be needed to sedate and comfort the patient prior to and during the reduction procedure.
Patients receiving intravenous medications need to have their vital signs monitored before, during, and after the shoulder relocation just as if they were in the operating room. In some circumstances, for example a patient with underlying lung or heart illnesses, the presence of an anesthesiologist or nurse anesthetist may be appropriate during the relocation. Intravenous narcotics and muscle relaxants are used in combination to relieve pain, relax muscles, and help promote amnesia of the events. Common pain medications used include morphine, hydromorphone (Dilaudid), and fentanyl. Midazolam (Versed), diazepam (Valium), or lorazepam (Ativan) may be used as a muscle relaxant.
Anesthetics like ketamine or propofol are also commonly used to sedate the patient to allow shoulder reduction. Intra-articular (intra = within + articular = joint) injections of lidocaine into the shoulder joint itself may be used as local anesthesia.
In certain situations, dislocations may be reduced immediately. This is especially true in the sports medicine arena, where a health-care provider may reduce the dislocation on the field of play. This is a reasonable treatment alternative because the care provider was able to see the injury occur, examine the patient and come to the diagnosis, and then reduce the injury before muscles spasm sets in.
Many patients experience shoulder subluxation or partial dislocation. These are patients who have had previous dislocations and are aware that their shoulder has dislocated again and then spontaneously reduced. They may choose not to seek urgent or emergent care, but this situation should not be ignored. Once a shoulder dislocates, it becomes unstable and more prone to future dislocation and injury.
Shoulder dislocations may be complicated by fractures of the bones that make up the shoulder joint. Up to 25% of patients will have an associated fracture. Not included in these numbers are the Hill-Sachs deformity that may occur in up to 75% of anterior shoulder dislocations.
Nerve damage is a potential complication. Most often, the circumflex axillary nerve may be injured. The first sign of injury is numbness in a small patch distribution on the outside of the upper arm. This nerve often recovers spontaneously in a few weeks, but this is an important complication for the health-care provider to recognize since damage to the nerve may cause weakness of the deltoid muscle that helps move the shoulder.
Rotator cuff injuries are commonly seen in older patients who dislocate their shoulder. The diagnosis may be difficult to make initially and often is made in follow-up visits with the health-care provider.
Rare complications of shoulder dislocation include tearing of the axillary artery, the main artery that supplies blood to the arm and brachial plexus injury, in which the nerve bundle that attaches the arm nerves to the spinal cord is damaged. Both these structures are located in the axilla or armpit and are potentially damaged by the initial dislocation or by attempts to reduce the dislocation.
Doctors who perform this medical procedure
Orthopedist e Chairman of Clínica Espregueira Mendes
Graduated in Medicine in 1985 from Faculdade de Medicina da Universidade do Porto. In January 1994, he obtained the degree in Orthopedics and Traumatology with the final grade of 20,0 points – the highest grade possible. Since then, he is Specialist in Orthopedics and Traumatology by the Portuguese Medical Board.
In 1995, applied for the role of Hospital Assistant of Orthopedics and Traumatology of Hospital de São João, being accepted in first place with 20,0 points. In July 20th of 1995, received his PHD in Orthopedics and Traumatology from Faculdade de Medicina do Porto, being approved with unanimity, distinction and honors. His PHD thesis has the title: “Chronic Injuries of the Anterior Cruciate Ligament (ACL)”.
In October 1998, applied for the Direction of the Orthopedics and Traumatology service of Hospital São Sebastião and was nominated Director. Created from scratch the Orthopedics Service, part of a new management model of public hospitals with each director being responsible for an annual contract-program. In February 22nd of 2002, received the degree of Orthopedics Consultant of the Hospital Medical Career. From 2004 to 2008 he was the President of the Portuguese Society of Arthroscopy and Traumatology. In November 2005, was hired by Escola de Ciências da Saúde da Universidade do Minho has a guest associate professor, responsible for the area of Orthopedics and Traumatology.
In November 2005, he became the Director of Clínica Saúde Atlântica – Clínica do Dragão. He is the Chairman of Clínica Espregueira - FIFA Medical Centre of Excellence - ESSKA and ISAKOS official center. President of the European Society of Knee Surgery, Sports Trauma and Arthroscopy (ESSKA) from 2012 to 2014.
Languages: Portuguese and English.