The shoulder joint is capable of a wider and more varied range of motion than any other joint in the human body. This extraordinary flexibility has allowed human beings to do everything from swinging a sledgehammer to rocking a baby.
Unfortunately, because the shoulder is so flexible, it also tends to be unstable. And this instability contributes to a variety of problems that include:
- Partial dislocation (subluxation) means the shoulder joint is partially out of its socket.
- Complete dislocation means it's all the way out. Both partial and complete dislocation cause pain and unsteadiness in your shoulder.
- Shoulder Instability is the result of repeated shoulder dislocations.
The shoulder joint is composed of three bones:
- Clavicle (collarbone)
- Scapula (shoulder blade)
- Humerus (upper arm bone).
Two joints facilitate shoulder movement:
- The acromioclavicular joint is located between the acromion ( that part of the scapula that forms the highest point of the shoulder) and the clavicle.
- The glenohumeral joint, commonly called the shoulder joint, is a ball-and-socket type joint that helps move the shoulder forward and backward and allows the arm to rotate in a circular fashion or hinge out and up away from the body. (The "ball," or humerus is the top rounded portion of the upper arm bone; the "socket," or glenoid is a dish-shaped part of the outer edge of the scapula into which the ball fits.) The capsule is a soft tissue envelope that encircles the glenohumeral joint. It is lined by a thin, smooth synovial membrane.
The shoulder is a ball-and-socket joint. Most ball and socket joints are constructed of a large socket into which the ball fits nicely. This is a very stable type of joint. The shoulder joint, on the other hand, is made up of a ball which is larger than the socket. This is not a very stable type of joint.
Because the shoulder's ball-and-socket joint provides little inherent stability, it is highly dependent on the surrounding soft tissues such as the capsule, ligaments, and the muscles to hold the ball in place. The relative instabllity of the shoulder joint allows it to be highly mobile, thus allowing an individual to place the hand in numerous positions. It is, in fact, one of the most mobile joints in the human body.
The bones of the shoulder are held in place by muscles, tendons, and ligaments.
- Tendons are tough cords of tissue that attach the shoulder muscles to bone and assist the muscles in moving the shoulder. The rotator cuff is a structure composed of tendons that work along with associated muscles to hold the ball at the top of the humerus in the glenoid socket; it provides mobility and strength to the shoulder joint
- Ligaments attach shoulder bones to each other, providing stability. For example, the front of the joint capsule is anchored by three glenohumeral ligaments. Two filmy sac-like structures called bursae permit smooth gliding between bones, muscles, and tendons. They cushion and protect the rotator cuff from the bony arch of the acromion.
- Muscles are bundles of specialized tissue that attach to, and move bones via their tendons.
The rotator cuff consists of four muscles and several tendons that form a covering around the top of the upper arm bone (humerus). These muscles form a cover around the head of the humerus. The rotator cuff holds the humerus in place in the shoulder joint and enables the arm to rotate.
Symptoms may begin suddenly when the cause is an injury, or they may develop over time when the cause is joint laxity. Symptoms may include:
- The shoulder is quite painful.
- Motion is severely restricted.
- The shoulder appears to hang down and forward, with a large dimple evident under the acromion (in the area of the collar bone).
- The head of the humerus may be visible as a bump on the front of the shoulder, or in the armpit.
- Shoulder may feel loose.
- Shoulder may slip out of place.
- Numb feeling radiating from the shoulder down the arm.
Shoulder instability/dislocation develops in one of two ways:
- Traumatic onset. A bad injury to the shoulder can cause the shoulder to become unstable by stretching or tearing the ligaments of the shoulder.
Joint laxity (Atraumatic Laxity). This type of instability occurs in people who have a general looseness in the shoulder joint that causes the shoulder to be unstable. Some causes for shoulder joint laxity are:
- Anatomical abnormalities
Generalized laxity (known as hypermobility)
- Muscle weakness
Mechanism of a traumatic shoulder instability/dislocation:
The most common injuries that lead to traumatic instability are:
- A fall on an outstretched arm that is forced overhead.
- A direct blow to the shoulder.
- Forced external rotation of the arm.
Another cause of shoulder instability occurs in athletes who compete in sports that involve overhead activities. These athletes, such as volleyball players, swimmers, and baseball pitchers, stretch out the shoulder capsule and ligaments, and may develop chronic shoulder instability. While they may not completely dislocate the joint, they may have the feeling that the shoulder is about to dislocate. This may prevent them from playing these sports.
Treatment depends upon whether symptoms are due to a dislocated shoulder or shoulder instability.
Treatment of a dislocated shoulder:
When the shoulder is dislocated, the dislocation must be "reduced," or put back in place as quickly as is possible. In most cases, the maneuvers required to reduce the dislocation are done under anesthesia by a doctor in the emergency room. The shoulder should be supported until the injured person sees a physician.
Once the should dislocation is back in place, x-rays are taken to ensure it is, indeed, in the correct position, and also to evaluate for other injuries. Patients are placed in a sling to rest the shoulder and referred to their orthopedic surgeon for further management.
Additional treatment may be needed by patients who sustain a shoulder dislocation, since they are much more likely to suffer future shoulder dislocations. The reason is that when a shoulder dislocation occurs, ligaments within the shoulder are torn, and the shoulder joint becomes less stable. If ligament damage is present, the patient may need to consider surgical treatment to repair the dislocation, or to prevent future dislocations.
Treatment of shoulder instability:
Treatment of shoulder instability depends upon several factors, and almost always begins with physical therapy and rehab. If patients complain of a feeling that their shoulder is loose or about to dislocate, physical therapy, with specific strengthening exercises will often help maintain the shoulder in proper position. Other treatments sometimes used to treat shoulder instability include cortisone injections and anti-inflammatory medications.
If therapy fails, there are surgical options that can be considered. Depending upon the cause of the instability, the surgical treatments may differ.
If the cause of the shoulder instability is a loose shoulder joint capsule, then a procedure to tighten the capsule of the shoulder may be considered.
If the problem is due to a tearing of the ligaments around the shoulder then a procedure can be performed to fix the ligament.
People with shoulder pain have also found these products to be effective: