What is chronic pain?

This is pain that continues for longer than three months and it is not normally associated with damaged tissues. We know that all the body’s tissues, even broken bones, are usually healed after six months.

Healthcare professionals believe that this type of pain persists for longer than the usual three-month healing period. This is because the nerves originally carrying the pain messages have developed a ‘memory’ for pain and send persistent unhelpful ‘faulty’ messages about pain. These messages are not a signal that the body is damaged or not healed.

PAIN PUZZLES

Puzzle 1: Some athletes injured in sports events, or soldiers injured in battle, do not notice or feel pain at the time they are injured.

Puzzle 2: People who have had a limb removed can still experience pain in the limb that is no longer there. This is called ‘phantom limb pain’.

Puzzle 3: A person has trodden on a sharp nail. It looks as if it has gone into his foot. The person is in great distress and pain. The foot x-ray shows that the nail has actually broken off in the sole of his boot and has not entered his foot. The person was in severe pain because he thought it had gone into his foot.

These puzzles show that the body’s pain systems are much more complex than people used to realize. They show pain can be linked to the meaning of the event or situation.

Acute and chronic pain systems

These two systems work very differently and it helps to understand them both.

The acute pain system

This is designed to help the body protect itself from damage or harm. For example, if you lift a very hot pan off the stove or have a very hot drink, the heat can cause pain in your hands or mouth. The pain may make you stop what you are doing, as it may cause injury. For example, you may put down the pan, or sometimes even drop it, to avoid being injured by the painful heat.

Acute pain nerve fibres take the pain message from the injury as fast as possible through the spinal cord to the pain centres in the brain. This is a survival mechanism designed to protect the body so the nerves need to send messages quickly to that part of the body to do something immediately, e.g. remove the hand from the hot pan. These are called ‘A’ nerve fibres (standing for ‘acute fast pain message system’). You can think of this system as being similar to dialling straight through to the emergency services for immediate action.

The chronic pain system

This system works differently from the acute pain system. It sends messages to the pain centres in the brain via another type of pain nerve fibre – ‘C’ fibres (standing for ‘chronic pain system’). These fibres send messages very slowly and repeatedly to several pain centres in the brain.

The brain may interpret these persistent pain messages to mean that the pain problem is still happening and is not finished or healed. Alternatively, the ‘C’ fibres may develop a ‘memory’ for pain experiences, and continue to send pain messages for many months or years after an injury, when healing is complete. These fibres are like a set of traffic lights stuck on red, which cannot switch onto green.

The ‘C’ fibre nerve endings can become very sensitive to movement, hot and cold sensations and chemical changes (like inflammation within the body system). Sometimes if the pain area is touched or moved, they send off many, many pain messages to the brain. The nerves seem to magnify the pain feelings or intensity, or cause other sensations like numbness or tingling.

So there seem to be many problems at different places – in the nerve endings, the nerve fibres and the pain centres in the brain. The important point is that feeling chronic pain does not mean there is any harm or damage happening in the body. These are unhelpful ‘faulty’ messages about pain or body sensations, which the pain centres in the brain treat as if they were accurate.

In addition, scar tissue from healed tissues can become tight and stiff. The pain nerves may be wrapped within this tissue. When moving this part of the body, the lack of flexibility (especially in muscles, tendons or joints) can increase pain messages.

There is some good news. It is possible to increase flexibility in stiff, tight tissues and thereby reduce the pain and its consequences. Gradually stretching and strengthening helps the nerve fibres become less sensitive to movement, enabling you to be more active and in less pain.

The best that doctors and physiotherapists can do is to try to help the person to control the pain, possibly by using medications and other treatments (see Chapter 5). However, this may only change the pain experience a little or in the short term. Doctors and pain scientists still don’t know enough about chronic pain systems and how to switch off the ‘C’ fibre pain messages. This means it is difficult to change:

•   the memory of pain in the ‘C’ fibres and the pain centres in the brain

•   the increased sensitivity in these nerve endings

•   With acute pain or during a setback, it is sensible to reduce many activities for two or three days, especially if there is a lot of bruising or swelling.

•   Most active sports people reduce their sports activities and have longer rest periods. Then, after two or three days, they gradually start to do more, steadily pacing and planning their increased activities (see Chapter 8).

•   Rest, especially complete rest in bed, is now believed to cause more problems than it solves, except in certain situations, such as cases of severe multiple injuries, e.g. after a car accident.