Localised Pain or Referred Pain?
Pain-where is it coming from?
Pain, at a physiological level, is stimulation of sensitive nerve endings (nociceptive) either by chemical or mechanical means.
This commonly occurs through injury and its purpose is to inform us of tissue damage.
These nerve endings are found everywhere in the body-bone, joints (including ligaments), cartilage, muscle, tendon, discs and neural structures. Also on our skin and internal organs. We will be more concerned with the ones that cause musculoskeletal pain.
Joints, muscles and neural structures are richly innervated (supplied by many nerves) and are common sources of pain.
Sometimes the source of pain gives rise to pain at that spot. Sometimes however the pain is perceived at a distant spot. This is called referred pain.
The best known example is someone experiencing a heart attack. Pain is commonly felt in the left arm and shoulder but the source is a blood flow disturbance of the heart.
Referred pain is not well understood but is thought to be due to common pathways of nerve endings that the brain is unable to distinguish between.
There are two types of referred pain. Radicular pain is caused by nerve irritation/compression that gives rise to sharp, shooting pain and paraesthesia (pins and needles/numbness) and perhaps muscle weakness.
A common example is sciatica-which is pain and paraesthesia down the back of the leg due to sciatic nerve injury. This is usually caused by lumbar spine(low back) disc pathology that impinges on the sciatic nerve as it exits the spinal cord. It can also be caused by irritation anywhere along its course. An example of this is piriformis syndrome where the piriformis muscle irritates the sciatic nerve.
Less common is arm pain due to brachial plexus nerve damage or irritation occurring at the cervical spine(neck).Disc pathology again is the usual cause.
The other type of referred pain is called somatic pain. It is not associated with paraesthesia and the nature of the pain is harder to localise and not as sharp as radicular pain.
Discs, joints, muscles and ligaments can cause this type of pain. In fact pain down the back of the leg is usually somatic referred pain and not sciatica.
Shoulder pain is commonly referred pain from the cervical spine joints. Treating the shoulder does little to help if it is not the cause-but mobilising (stretching) the neck does.
Trigger points in muscles feel like painful knots and often refer pain to other areas of the body. These are areas of tightness – structures do not need to be damaged to be causing pain.
Nerves, ligaments and joints also when tight can do the same-cause pain either locally or referred. Usually these structures are injured first and tightness follows. The longer the pain has been present the more likely surrounding structures will also be affected.
Understanding pain-what type of pain it is and where it is coming from-is crucial to a positive treatment outcome. Physiotherapists are expert in diagnosing injury and treatment of musculoskeletal disorders.
If you have pain that is not going away and or getting worse-see your physiotherapist.