The shoulder is structurally and functionally complex as it is one of the most freely moveable areas in the human body due to the articulation at the glenohumeral joint. The high range of motion of the shoulder comes at the expense of decreased stability of the joint, and it is prone to dislocation and injury. The shoulder girdle is composed of the clavicle and the scapula, which articulates with the proximal humerus of the upper limb.
Four joints are present in the shoulder:
- sternoclavicular joint
- acromioclavicular joint
- scapulothoracic joint
- glenohumeral joint
Causes of Shoulder Pain
There are many causes of shoulder pain and not all of them are due to problems of the shoulder joints or associated structures.
Osteoarthritis (OA): a chronic disease often associated with joint pain and stiffness, reduced mobility and reduced quality of life.
Inflammation of the shoulder capsule
- Synovitis (or synovial inflammation) is when the synovium of a joint becomes inflamed (swollen).
- Adhesive capsulitis (also known as frozen shoulder) is a syndrome defined as idiopathic restriction of shoulder movement that is usually painful at onset. Secondary causes include alteration of the supporting structures of and around the shoulder, and autoimmune, endocrine or other systemic diseases. The three defined stages of this condition are the painful stage, the adhesive stage and the recovery stage.
Bursitis: inflammation of a bursa. A bursa is a small fluid-filled sac that acts as a cushion between bone and soft tissue (muscles, tendons and skin). A bursa (plural bursae) reduces friction and assists joint movement. In your shoulder the bursa that sits between the rotator cuff tendon and the bony tip of the shoulder (acromion) can become inflamed, most commonly with repetitive movements.
Injuries and sprains
- If the ligaments are injured or sprained, they can cause short-term pain. This may be the result of the humerus coming partially out of the joint socket (subluxation) or if the humerus comes completely out (dislocation).
- A labral tear can occur as a result of an injury (e.g. falling onto your outstretched arm) or repetitive actions.
- A direct blow to your shoulder can result in the acromioclavicular joint being sprained. This type of injury often occurs in people participating in contact sports who take a blow to the shoulder. It can also occur as a result of a fall.
- Tears to rotator cuff tendons may occur as a result of an injury (e.g. a fall, broken collarbone) or happen over a period of time as you age.
Neck and upper back: problems with the joints and associated nerves of your neck and upper back can also be a source of shoulder pain. The pain from your neck and upper back is often felt at the back of the shoulder joint and/or through to the outside of your upper arm.
Axillary nerve palsy: a neurological condition in which the axillary nerve has been damaged by shoulder dislocation. It can cause weak deltoid and sensory loss below the shoulder. Since this is a problem with just one nerve, it is a type of peripheral neuropathy called mononeuropathy.
Referred pain: shoulder pain may also be caused by problems affecting your abdomen (e.g. gallstones), heart (e.g. angina, heart attack) and lungs (e.g. pneumonia).