Shoulder pain can be caused by a minor injury, bad posture or an underlying health condition.

Conditions that can cause shoulder pain include:

• frozen shoulder 
• rotator cuff disorders
• shoulder instability 
• acromioclavicular joint disorders  
• a broken arm or broken collarbone

Frozen shoulder

Frozen shoulder, also known as adhesive capsulitis, is a painful persistent stiffness of the shoulder joint that makes it very difficult to carry out the full range of normal shoulder movements.

Frozen shoulder occurs when there is thickening, swelling and tightening of the flexible tissue that surrounds your shoulder joint. This leaves less space for your upper arm bone (humerus) in the shoulder joint, and makes movement stiff and painful.

You may find it difficult to carry out everyday tasks such as dressing, driving and sleeping comfortably. Some people are unable to move their shoulder at all.

The symptoms of frozen shoulder can vary greatly, but tend to advance slowly. They are usually felt in three stages spread over a number of months or years.

Read more detailed information about the symptoms of frozen shoulder.

Risk factors for frozen shoulder

Most cases of frozen shoulder occur in people over the age of 40.

The exact cause of frozen shoulder is not fully understood. However, there are several risk factors that make developing frozen shoulder more likely. These include: 

• shoulder injury or surgery – keeping your arm and shoulder still for long periods of time; for example, while you recover from an arm injury or arm surgery 
• diabetes – you are more likely to develop frozen shoulder if you have diabetes, but the exact reason for this is unknown 
• other health conditions – these include heart or lung disease, an overactive thyroid (hyperthyroidism) and Dupuytren's contracture (a condition that causes one or more fingers to bend into the palm of your hand)

Read more information about the causes of frozen shoulder.

Rotator cuff disorders

The rotator cuff is the group of muscles and tendons that surround the shoulder joint. Tendons are the tough, rubbery cords that link muscles to bones.

The rotator cuff keeps the joint in the correct position, allowing it to move in a controlled way.

Different types of rotator cuff disorder can cause different symptoms, but common features include:

• pain that is worse during activities that involve your arm being above shoulder level – for example, when brushing your hair
• pain when you move your arm in an arc away from your body 
• pain on the front and side of your shoulder
• pain at night

The different types of rotator cuff disorders and their slightly different causes are explained below.

Tendonitis and bursitis

Tendonitis is inflammation (swelling) of a tendon. Bursitis is inflammation of a bursa. A bursa is a small fluid-filled sac usually found over the joints and between tendons and bones.

Rotator cuff tendonitis and bursitis are usually the result of irritation and inflammation caused by a shoulder injury or overuse of the shoulder.

For example, these conditions may affect someone whose job involves a lot of overhead lifting, or an athlete who competes in throwing sports, such as the javelin or discus.

If there is any kind of injury to the shoulder joint, the tendons or bursa may become inflamed. This means there is less space within the joint for the tendons and muscles to move.

If the tendons, muscles or surrounding tissue become trapped between the bones in the shoulder, any repeated movement will irritate them. 

Tendonitis and bursitis often occur together. When the tendons or bursa are trapped between the bones it is often known as "impingement syndrome".

If the tendon is repeatedly scraped against the shoulder bones, it can gradually weaken and will sometimes tear.

Tears

A torn muscle or tendon will cause severe pain and possible weakness in your arm and shoulder. Some people may also feel a popping sensation when they move their shoulder.

Tendon tears are most common in people aged over 40. Tears that affect younger people are usually caused by an accident. In older people, tears are often caused by impingement syndrome.

It is estimated around half of people over the age of 60 may have partial or complete rotator cuff tears. This is because your tendons become weaker as you get older.

Rotator cuff syndrome

The term "rotator cuff syndrome" is used to describe any type of damage to tendons in the rotator cuff, including complete tears.

Shoulder instability

The shoulder joint is a ball and socket joint. The top of your upper arm bone (humerus) is the ball, which fits into the socket of your shoulder blade.

Shoulder instability occurs when the ball part of the shoulder joint does not move correctly in the socket. This can range from a slipping or "catching" feeling in your shoulder, to a full shoulder dislocation where the ball comes completely out of the socket.

The symptoms of shoulder instability can sometimes be vague. People with shoulder instability often describe symptoms that are similar to having a "dead arm", such as:

• tingling
• weakness
• numbness
• shoulder fatigue
• a clicking, locking or popping sensation

If the shoulder is dislocated (where the ball has come out of the socket), symptoms can include:

• severe pain 
• the arm being visibly out of position
• muscle spasms where the muscles contract painfully 
• limited movement

Types of shoulder instability

Shoulder instability can be either:

• traumatic – the shoulder is forced out of place by a sudden impact
• atraumatic – the shoulder gradually moves out of place over time

Traumatic shoulder instability is often the result of an accident.

Atraumatic shoulder instability tends to occur as a result of repetitive arm movements, such as throwing or swimming.

Shoulder instability usually occurs in people aged under 35.

Acromioclavicular joint disorders

The acromioclavicular joint is the joint at the top of your shoulder (not the ball and socket joint). Possible acromioclavicular joint disorders include:

• osteoarthritis – a condition that causes the joints to become painful and stiff, and is the most common cause of acromioclavicular joint disorders
• tearing or stretching the ligaments in the acromioclavicular joint – ligaments are the tough bands of connective tissue that link two bones together at a joint
• partially or completely dislocating your acromioclavicular joint

Symptoms of acromioclavicular joint disorder include:

• pain in the joint
• limited movement of the joint 
• pain on the top of the shoulder

If the acromioclavicular joint is dislocated, it may also look visibly out of position.

Risk factors for acromioclavicular joint disorders

Acromioclavicular joint disorders are more common in men and those between the ages of 20 and 50.

People who play contact sports such as rugby have an increased risk of developing acromioclavicular joint disorders.

They are also more likely to occur in people who have fallen on their shoulder – for example, during a skiing accident.