Shoulder pain is extremely common and often disabling, and up to 70% of people will experience shoulder pain in their life. The shoulder is a complex structure and is composed of three bones: the scapula (shoulder blade), the clavicle (collarbone) and the humerus (upper arm bone). There are also three joints in the shoulder: the glenohumeral joint between the humeral head and the glenoid cavity of the scapula, the acromioclavicular joint between the scapula and the clavicle, and the sternoclavicular joint between the sternum and the clavicle. The glenohumeral joint is a ball-and-socket joint and is the most mobile joint in the body. However, this ability to produce extreme ranges of motion also means that the joint is less stable and more prone to injury. Additional stability of this joint is provided by a fibrous joint capsule surrounding the humerus and by the four tendons of the rotator cuff.
Common causes of shoulder pain can be divided anatomically into rotator cuff disorders, glenohumeral joint disease, and acromioclavicular joint disease. Of these the most common are injuries to the rotator cuff.
The rotator cuff muscles are the supraspinatus, infraspinatus, subscapularis and teres minor. The tendons of these muscles attach onto the humerus, and are commonly injured especially with heavy lifting and repetitive movements performed above shoulder level. Inflammation of the tendon may cause shoulder pain, but generally does affect strength or range of motion. The tendons may also become partially or completely torn, and in this case there may be loss of strength or decreased range of motion in the shoulder. In younger people, tears usually occur as a result of an associated traumatic event. In older people, tears usually occur due to intrinsic age-related degeneration of the tendon or arthritic bone spurs which wear on the tendon. Management of rotator cuff injuries depends on the severity of the injury. Severe tears which affect the full thickness of the tendon may require surgical repair, and traumatic ruptures in younger people are more likely to require surgical repair for full recovery. However, even with full thickness tears, 70-80% of patients respond well to non-operative management. Non-operative management centers employ physical therapy with a focus on strengthening the muscles of the shoulder girdle. Non-steroidal anti-inflammatory medications (NSAIDs) and/or corticosteroid injections into the shoulder joint are also generally used to treat pain and inflammation.
Disorders of the glenohumeral joint also commonly cause shoulder pain. In these cases the pain may come from osteoarthritis within the joint itself, or from inflammation and tightening of the capsule surrounding the joint called adhesive capsulitis (frozen shoulder). Pain from osteoarthritis within the glenohumeral joint may progress over many years and is felt with any motion of the shoulder joint. This may be managed non operatively with a combination of physical therapy, topical or oral NSAIDs and corticosteroid injections. In severe cases, a shoulder replacement surgery may be needed. Pain from an adhesive capsulitis may onset slowly or the condition may develop after trauma or immobilization of the shoulder. The hallmark of this condition is a severe limitation in range of motion beginning with a restriction in external rotation of the shoulder. Time to full recovery is lengthy, and generally takes over a year even with early treatment. Treatment for adhesive capsulitis involves progressive, gentle range of motion exercises, which may be done at home or under the direction of a physical therapist. Corticosteroid injections into the glenohumeral joint are helpful in providing pain relief. Injection of saline to distend the joint capsule and vigorous manipulation are also sometimes performed to break the adhesions between the capsule and the humerus, although there is minimal evidence that this improves range of motion.
The acromioclavicular joint in the shoulder is also a common cause of shoulder pain. Pain from damage to this joint is most often experienced over the front of the shoulder where the acromion (a section of the scapula) meets the clavicle, and may worsen when the affected arm is moved across the body. The most common cause of pain in this joint is osteoarthritis which may occur from degenerative, post traumatic or inflammatory processes. Treatment for this includes avoiding repetitive cross-body movements, NSAIDs, and physical therapy to improve strength and range of motion in the shoulder girdle. Corticosteroid injections into this joint provide short term pain relief in over 90% of cases, and in some people may continue to provide relief at up to 5 years.
The shoulder girdle is a complex structure which allows for extreme mobility of the upper extremity. However, the price for this mobility is decreased stability and an increased risk of injury when compared to other joints. Most people will experience shoulder pain in their life, and a correct diagnosis of the pain source as well as proper medical treatment and physical rehabilitation are critical for recovery.
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