HERALD WEEKLY ISSUE 600: 25 January 2012

Pain - part 1
Ainslie graduated from the New Zealand School of Physiotherapy in 1974 and has been a Member of the New Zealand Society of Physiotherapists (NZSP now called Physiotherapy NZ) since 1975. She completed a Diploma of Educational Studies in 1980 and an Advance Diploma Physiotherapy specialising in paediatrics in 1990. She has been an associate member and later a Member of the New Zealand College of Physiotherapy since 1990. She has also served on the College Board and various NZSP branch committies over the years. Currently she is a Member of the NZ College of Physiotherapists with Advanced Practitioner status in Paediatrics, a Member of Physiotherapy New Zealand and also a member of the neurology and paediatric special interest groups. And holds a current NZ Annual Practising Certificate.

Pain is a protective mechanism of the brain. The pain experienced is not related to the injury. It is related to the brain’s perception of the danger the body is in. About 30% of people found after death to have severe joint damage have not experienced any pain from this during their lives. Equally about 30% of those who experienced severe pain in life had no visible damage to the tissues after death.
‘All pain is normal
‘We believe that all pain is normal and an excellent though unpleasant response to what your body judges to be a threatening situation. We believe that even if problems do exist in your joints, muscles, ligaments, nerves, immune system or anywhere else, it won’t hurt if your brain thinks you are not in danger’.
‘In exactly the same way, even if no problems whatsoever exist in your body tissues, nerves, or immune system, it will still hurt if your brain thinks you are in danger. It is as simple, and as difficult, as that ‘. ( David Butler in Course notes for Explain Pain Course in New Zealand November 2010)
The type and extent of the pain each individual’s experience is unique to that individual. There are general patterns that can be recognised.
There are many different aspects to chronic pain. Not all of them occur in everyone who has long standing or recurrent pain but there is usually more than one mechanism involved in the chronic or recurrent pain experience.
Changes in the Relationship Between Pain Onset and Tissue Damage
Before we have an injury we will experience pain or discomfort as a warning slightly before we reach the point at which tissues will be damaged. After the injury has occurred if tissue repair has not been complete there will be a new point at which tissues will be at risk. The point at which pain or discomfort are felt as a warning sign will also change. Usually pain will come on much sooner – well before the new point of tissue risk.
Muscle Spasm
Muscle spasm is commonly associated with pain as the body attempts to protect the damaged part from further damage by limiting movement. This is totally appropriate in the very early stages immediately after and injury involving damage to bones or muscles but is not helpful in many painful conditions. It may contribute to the pain experience.
Nerve Hypersensitivity
As part of the protective mechanism immediately after injury some nerves will become more sensitive to stimulus. Impulses are transmitted between nerves by a variety of different chemicals. For a chemical to enter a nerve there has to be the right ‘channel’. After injury the number and types of channels in the nerves supplying that area of the body will change. This is another protective mechanism that causes the body to be more sensitive to things that might cause further damage to the injured part. If we think that the part is still not fully healed or that there is further risk the hypersensitivity will remain after the injury has healed.
Nerve Tethering or Entrapment
Normally nerves move smoothly over and through the tissues surrounding them as we bend and stretch. Nerve tissue is not stretchy like muscles and needs to be very mobile. When we have an injury nerves sometimes become trapped by scar tissue. This may be a direct result of the injury and repair or may be secondary to a lack of movement while the injured part was repairing. The body will protect the nerve from stretching too much with pain and muscle spasm.
To get an idea of just how much movement occurs try holding a length of string or similar over the top of your knee when it is bent, then straighten your knee. You will notice several cm of surplus string when your knee is straight.
Muscle Weakness
Muscles will weaken very quickly when they are not being used normally because of pain. Pain will also prevent a muscle from contracting normally and it may appear to be weak as a result of the inhibition. Nerve damage may also cause weakness. When muscles are weak the affected part is not supported and protected properly and pain often results.
Joint Stiffness
This may be directly related to the injury or may be as a result of restricted movement of the joint or even a distant part of the body while the injury is healing. If it is many years since the original injury it may be the result of arthritic changes arising from the injury or from the uneven pull of the muscles around the joint causing uneven pressures on the bones. The body is in a constant state of absorbing and replacing cells and this occurs in response to the stresses and strains placed on the various structures.
The nutrition and health of the joint cartilage is dependent on the movement of the joint to stimulate the production of the joint fluid (synovial fluid) that carries the nutrients to the cartilage cells and lubricates the joint surfaces.

Herald Issue 554 09 March
- Norm exposes Trio of Doom
- Briefs from PM’s media conference Tuesday
- Tourism Industry ponders $5 million draft strategy
- Norman George resigns from Cook Islands Party
- Letter of Resignation from CIP
- Norman selfish says Prime Minister

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