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What is the root cause of shoulder pain?

The shoulder is an amazing joint, when you think about all the directions in which it can move. The shoulder joint not only keeps the upper arm in place, but it allows the arm to perform its many functions, while giving it the freedom to move in a variety of ways: rotate, swing, lift and descend. However that flexibility comes with a downside, as the shoulder's complex array of muscles and bones can be prone to a variety of injuries and the anatomical configuration that bestows such free range of movement can also make the joint vulnerable to instability.

Anatomical diagram of the shoulder joint

Unfortunately, for some people, some parts of the shoulder can become compromised and be a source of pain. This pain can have many origins, from repetitive injury, an accident, or even sleeping habits. It can be difficult to pinpoint the cause of some shoulder pain as the joint has so many moving parts, but there are a number of common conditions that are known to be a reason for discomfort.

They include:

Fractures of the arm or clavicle

These are fairly easy to diagnose, and generally pretty painful, so most people who break one of these bones get themselves to a hospital fairly rapidly. Treatment will depend upon the severity of the fracture. With a broken clavicle, recovery generally involves keeping the entire joint still to give the ends of the bone plenty of time to knit. A broken clavicle can be incredibly painful because it literally lies across the torso and there is nothing to keep it in place when broken, except a sling and remaining very still. Doing this is necessary for recovery but this kind of immobility can then lead to the phenomenon known as frozen shoulder.

The frozen shoulder

Also called adhesive capsulitis, this complaint generally occurs when the tissue around the shoulder swells, thickens and tightens. This can cause a lot of pain, by pressing on nerves and giving the humerus less space in which to move. As a result, the shoulder can be persistently stiff, with reduced movement. It may become difficult to perform general tasks such as driving, putting away the shopping, getting dressed or even sleeping. People who sleep on their sides or stomachs can sometimes aggravate shoulder conditions.

The symptoms of a frozen shoulder can encompass a wide range of discomfort, and the condition generally proceeds in three stages. In the first or “freezing” stage, the shoulder starts to get stiff and sore, particularly when reaching for something and often while sleeping. This phase can last for several months.

In the next phase, when the shoulder has “frozen”, it becomes stiffer, although the pain may not increase. In this phase, which can last up to a year, muscles may begin to waste away a little through lack of use.

In the final, “thawing” phase, the pain may decrease, along with the stiffness and it is possible that sufferers can regain some of their shoulder movement.

Many cases of frozen shoulder occur in people over 40, but risk factors include keeping the joint still for long periods of time, such as when recovering from a fracture. Diabetes is another risk factor, as is heart and lung disease or an overactive thyroid.

Any movement or action that irritates the shoulder or increases pain should be considered a likely cause of injury, and be eliminated where possible, or at least minimised to allow healing. The shoulder cannot be put into a cast, so rest is often the best way in which to give shoulder problems a chance to heal. When pain is severe, surgery can be suggested, but this should be a last resort. In many cases the shoulder hurts because of something we've done it to it, so the first step is to reduce the aggravation.

Issues with the rotator cuff

To understand shoulder pain means being aware of the rotator cuff: the group of muscles and tendons that surround the shoulder joint and allow lots of movement, while keeping everything in place. The tendons are like cords that join muscles to bones. Tendon are usually surrounded by a sheath or a bursa (sac) that is filled with fluid so the tendon can move smoothly.

If the tendon becomes inflamed it is known as tendonitis, which is painful, as is bursitis (bursa inflammation). These conditions can be caused by repetitive movements or overuse, such as a lot of lifting or throwing. An injury can also cause the tendons or bursa to become irritated. Even sleeping with your head on your upper arm or shoulder can cause irritation to the joint and the sensitive tissues that keep all the elements sliding easily over each other.

With a rotator cuff problem, pain can be aggravated by moving the arm in a certain direction, lifting it above the head, pain during the night or pain on the side and front of the shoulder.

If a tendon slips out of place and repeatedly rubs against bone, that can cause irritation and pain. Any kind of tear in a tendon or muscle will cause quite acute pain. Tears can become more common with age as the tendons become weaker.

If a physician refers to “rotator cuff syndrome”, they simply mean that one of the muscles or tendons in the rotator cuff has been torn.

Lack of stability

The top of the humerus (upper arm bone) has a ball that fits into the socket of the shoulder blade. If, for some reason, this ball and socket joint is not moving the way it should, this can lead to lack of stability in the shoulder joint. It can feel as though the joint is catching or slipping. If the ball comes out of the socket completely it is called a shoulder dislocation, which can be extremely painful. The arm will probably also appear to be out of alignment. Movement will probably be limited and the surrounding muscles could spasm.

A dislocation could occur gradually (an atraumatic dislocation), or more commonly it is caused by an accident (traumatic dislocation). An atraumatic dislocation could be the result of a repetitive action, such as throwing a ball, and may require modification of the behaviour or action that led to the injury. A traumatic dislocation will require treatment, and in both types of dislocation resting the joint will be necessary for healing.

Milder shoulder instability can have many symptoms, some of them vague. These can include pain, numbness, tingling, weakness and sounds of popping or clicking.

The other joint

Apart from where the ball of the humerus fits into the socket of the shoulder blade (scapula), there is another joint which can be a cause of pain. The acromioclavicular (AC) joint is at the top of the shoulder, where the clavicle and the highest point of the scapula meet.

Possible problems with the AC joint include dislocation, tearing a ligament, or osteoarthritis. Any of these could cause pain in or on top of the joint, in addition to limiting its movement. With a severe dislocation, the joint will be visibly affected.

Problems with this joint tend to occur in men, particularly when they are between the age of 20 and 50, and those who play contact sports such as rugby or boxing. Falls are often a major factor in these types of injuries, such as skiing accidents, or being thrown from a motorcycle.

Preventative measures

Become aware of your shoulder joint and any pain that may be a signal that something is causing irritation. Poor posture, particularly hunching over a computer, can lead to problems with the shoulder joint. The way you sleep, particularly as you get older, can be another factor, as are repetitive tasks.

Very active people who engage in a lot of sporting activity, are also at risk and should take all sensible precautions to avoid accidents and any forceful impact on the joint that could dislocate it or tear any component of the rotator cuff.

It may not seem like it at first, but over a period of time, pain can be your friend. Pay attention to vague pain, particularly if it increases, as it could be trying to tell you something, and alert you to behaviours that can be modified to keep your shoulder joint in fine, flexible and pain free health.