Shoulder pain can stem from many causes. In some cases, shoulder pain is localized, meaning that it is confined to a specific area. In other cases, pain may be more widespread, affecting areas throughout the shoulder and even into the neck, back or arm.

Shoulder pain varies depending on the nature of the injury, degenerative process or abuse that is the source of the pain. Common causes of shoulder pain include:

• Dislocation. Shoulder injuries of this type are the most common major dislocations in the body. In most cases, a dislocation occurs when some force (such as a fall or sports injury) pulls the shoulder outward or an extreme rotation of the shoulder pulls the ball of the humerus (long bone of the arm extending from the shoulder to the elbow) out of the shallow socket. Dislocation often occurs when a backward pull on the arm overwhelms the muscles.

A partial dislocation in which part of the ball remains against the socket is known as a subluxation. A few patients may experience minor subluxation followed by reduction itself. Subluxation, sometimes painful, can also result from neurovascular conditions such as stroke.

Shoulders can dislocate in several directions – forward, backward or downward. Dislocation usually causes pain that may be intensified when accompanied by muscle spasms. Swelling, numbness, weakness and bruising are common, as are associated ligament (tough, fibrous tissue connecting bones or cartilage at a joint or supporting an organ) or tendon (tough, inelastic fibrous tissue that connects muscle with its bony attachment) damage and – less frequently – nerve damage.

• Separation. Occurs in the area where the collarbone (clavicle) and the shoulder blade (scapula) meet. Ligaments that hold the joint together may become partially or completely torn, causing the outer end of the clavicle to slip so that it does not properly join with the scapula. Blows to the shoulder or falling with an outstretched hand are the most common causes of shoulder separations.
  
  People who suffer a shoulder separation experience pain and tenderness, usually over the acromioclavicular (AC) joint between the acromion and the clavicle especially when the shoulder is moved. In some cases, a bump may form in the middle of the shoulder over the acromioclavicular joint. The AC joint can be palpated by moving fingers over the collarbone from medial (near the center of the body) to lateral (away from the center of the body). 
  
  
• Torn rotator cuff. The rotator cuff is made up of the muscles and tendons that connect the humerus to the shoulder blade. Tendons in the rotator cuff are normally strong, but they can become inflamed and tear as a result of overuse, wear and tear associated with aging or an accident such as a collision. Sports that require repeated overhead motion (e.g., pitching in baseball) and occupations that require heavy lifting are primary sources of rotator cuff tears. Usually patients may have difficulty raising their arm above the shoulder (90 degrees). Small tears may go unnoticed.
  
  
• Tendinitis, bursitis and impingement syndrome. These three closely related conditions can occur separately or in combination. They are sometimes grouped under the heading of an injured rotator cuff. The three conditions are:
  
  
• • Tendinitis. Inflammation of a tendon. In the shoulder, tendinitis is most likely to affect the tendons of the rotator cuff or biceps as a result of pinching from surrounding structures.
    
    
  • Impingement syndrome. When tendinitis affects the rotator cuff, the inflamed and thickened tendon may become trapped under the acromion. This squeezing of the rotator cuff is called impingement syndrome.
    
    
  • Bursitis. Inflammation of the bursae. These sacs protect the shoulder and help make movement more fluid. However, they can become inflamed either separately or in tandem with tendinitis and impingement syndrome.
    
    
  Repetitive motions involving the arms, or wear and tear over many years can irritate or wear down tendons, muscles and surrounding tissues. Sports involving overuse of the shoulder and jobs that require excessive overhead reaching are sources of these disorders. In addition, they may be caused by diseases such as rheumatoid arthritis.
  
  Tendinitis, bursitis and impingement syndrome may cause a slow onset of discomfort or pain in the upper shoulder. The pain also may travel to down the arm to the elbow and forearm. Some patients report difficulty sleeping on the shoulder. In addition, tendinitis and bursitis often cause pain when the arm is lifted away from the body or overhead. Strong pain may be felt if the arm or shoulder is pushed forcefully up, forward or backward. Patients with these conditions often have limited shoulder mobility.
  
  
• Fracture. A partial or total crack through a bone, frequently as the result of a fall or blow to the shoulder. Fractures often involve the clavicle or the neck of the humerus, which is the area just below the ball. Although a fracture may not be a major injury, it usually results in severe pain accompanied by redness and bruising.

• Arthritis of the shoulder. A degenerative disease caused by either wear and tear of the cartilage (osteoarthritis) or inflammation of one or more joints (rheumatoid arthritis). Ankylosing spondylitis, a form of arthritis that primarily affects the spine, can also cause shoulder pain. Arthritis also can affect supporting structures, including muscles, tendons and ligaments. People with arthritis of the shoulder experience pain – typically over the AC joint - and decreased shoulder mobility.
  
  
• Osteophytes (bone spurs). These are often caused by degenerative changes such as osteoarthritis. Bony projections can restrict the shoulder’s range of motion and cause pain.
  
  
• Frozen shoulder. Also known as adhesive capsulitis, this condition causes pain that severely restricts the patient’s ability to move the shoulder. Patients may be unable to raise their arm without feeling significant pain, and stiffness and pain may worsen at night. Injuries are a common source of frozen shoulder, but it also can result from rheumatic diseases and shoulder surgery. Hallmarks of this condition include inflammation, abnormal bands of tissue between the joint surfaces and a lack of synovial fluid (which normally provides lubrication to the gap between the humerus and its socket). People with diabetes, stroke, lung disease, rheumatoid arthritis and heart disease are at greater risk for frozen shoulder.
  
  
• TMJ disorder. This condition primarily affects the temporomandibular joints of the jaw but can cause pain in the shoulders, ears, neck, back and elsewhere..
  
  
• Pinched nerve. Nerves can be compressed throughout the body. Examples that affect the shoulder include impingement of the axillary nerve in the armpit, which can result from use of crutches, and subscapular nerve entrapment, an uncommon condition caused by restriction of the subscapular nerve. A herniated disc in the neck can cause pain running down the shoulder and arm.
  
  
• Heavy packs. Hefty or poorly positioned backpacks used by schoolchildren and oversized purses, briefcases or luggage used by adults can injure the shoulders and back.
  
  
• Thoracic outlet syndrome (TOS). A name given to several unrelated disorders, some of them controversial and ill-defined, that affect blood vessels and nerves in the region between the base of the neck and the armpit. Symptoms can include shoulder, neck and arm pain and weakness. True neurologic TOS, caused by atypical anatomic features that are present at birth, is rare and can be treated surgically, according to the National Institutes of Health. Other forms of TOS can be treated symptomatically.
  
  
• Whiplash. An injury to the soft tissues of the neck resulting from a sudden jerking of the head. In addition to neck pain, whiplash may cause shoulder pain, back pain and headaches.
  
  
• Polymyalgia rheumatica. A chronic inflammatory disease marked by muscle pain and stiffness around the neck, shoulders and hips.
  
  
• Cervical dystonia. A nerve disorder that causes severe muscle contractions in the neck and shoulder.
  
  
• Heart attack. Pain radiating from the chest to the shoulders, arms, neck or jaw may signal a heart attack (myocardial infarction). A heart attack can also cause shoulder pain without chest pain. Patients suspecting a heart attack are urged to seek immediate medical attention.
  
  
• Infection. Rarely, infection can be another source of pain and inflammation.
  
  
• Referred pain. Pain from the neck or other areas can be felt in the shoulder. Ectopic pregnancy (implanted outside the uterus) and certain conditions of the gallbladder, liver or diaphragm can be experienced as shoulder pain.