Overview of Shoulder Pain
Shoulder pain occurs in and around the shoulder joints. In some cases, pain in the shoulders can be difficult to distinguish from neck pain. The shoulders, which connect the arms to the trunk (torso), are the most moveable joints in the body. This high level of mobility can cause the joints to be relatively unstable. Shoulder pain often occurs as a result of disease or injury that affects structures in the shoulder joint (e.g., tendons, ligaments, muscles, bones).
The shoulders are made up of bones, cartilage, muscles, tendons, and ligaments. The upper arm bone (humerus), collar bone (clavicle), and shoulder blade (scapula), which are held together by bands of connective tissue called ligaments, make up the shoulder joints. The bones in the shoulders do not provide much stability to the joint and are held in place by muscles, tendons, and ligaments.
There are two joints in the shoulder. The glenohumeral joint is a flexible ball-and-socket joint formed by the scapula and the head of the humerus bone. This joint, which allows the shoulder to move forward and backward and the arm to move in a circular motion, is also called the shoulder joint.
The acromioclavicular joint is a gliding joint located on the top of the shoulder. This joint is formed by a part of the scapula called the acromion and the clavicle.
Articular cartilage cushions the shoulder joint and fibrous cartilage (called the labrum) helps to stabilize it. Sac-like structures called bursae (singular is bursa) are located within the shoulder joints. Bursae contain synovial fluid, which lubricates the joints and reduces friction between the bones and muscles, tendons, and ligaments.
Bones in the shoulder are attached to surrounding muscles by tendons (fibrous cords of tissue). The rotator cuff is a group of four tendons that connects muscles from the scapula and allows the shoulder to rotate and elevate. Inflammation of these tendons (rotator cuff tendonitis) is a common cause for shoulder pain.
Other common causes include arthritis, bursitis (inflammation of a bursa), and shoulder injury (e.g., dislocation, fracture).
Incidence and Prevalence of Shoulder Pain
According to the Centers for Disease Control and Prevention (CDC), approximately 13.7 million people in the United States required medical treatment for shoulder pain in 2003. Due to age-related issues, the incidence of shoulder pain increases with age. Some types of shoulder pain (e.g., rotator cuff problems) are more common in people older than 60 years of age.
Shoulder Pain Risk Factors and Causes
The major risk factor for shoulder pain is age. Overuse (e.g., through participation in sports or other recreational activities, occupation) increases the risk for injury and also for age-related changes in the shoulder joint (e.g., arthritis) that can result in pain. Conditions such as bursitis and tendonitis (e.g., rotator cuff tendonitis) can cause shoulder pain.
Injury is another common cause for shoulder pain. Participation in sports (e.g., baseball, swimming) and manual labor increases the risk for shoulder injury. Types of shoulder injury include the following:
- Dislocation (condition in which the head of the upper arm bone [humerus] is displaced from the shoulder joint; often caused by a fall on an outstretched arm or when the arm is pulled from behind)
- Fracture (crack in a bone; often accompanies shoulder dislocation and usually involves the humerus or collar bone)
- Separation (partial or complete tear of ligaments in the shoulder; often causes by a fall or a direct blow to the shoulder)
- Sprains (injury to ligaments in the shoulder)
- Strains (injury to shoulder muscles)
- Tears (e.g., torn rotator cuff; may occur in muscles, tendons, or ligaments)
Frozen shoulder (also called adhesive capsulitis) is a condition that causes shoulder pain and restrictive movement in the shoulder. Frozen shoulder is more common in women in their 40s and 50s, in people who have had other conditions (e.g., bursitis, tendonitis, heart attack), in patients who have chronic diseases (e.g., diabetes), and following surgery.
Shoulder pain also can occur following surgery (e.g., mastectomy, axillary node dissection). Rare causes include infection, nerve problems (e.g., pinched nerve in the cervical spine [neck]), and tumors.