What is it and why is it important?
To help us understand this better, here is the definition of pain by the International Association of the Study of Pain (IASP):
“Pain is defined as an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.”
This definition of pain by the IASP consists of two very important concepts.
Part 1. Pain can be an unpleasant sensory and emotional experience.
Examples of unpleasant sensory experiences include touching an object that is too hot or too cold, burns, getting a paper cut, getting pinched, excessive pressure or tissue injury.
Examples of unpleasant emotional experiences leading to pain include an increase in stress, expecting pain, or worrying that there is a problem with a body part.
Part 2. Pain can occur because of actual tissue damage or potential tissue damage.
For this blog we are going to focus on acute pain. We all know the story, running down the pitch about to score the winning goal/try and ping there goes my hamstring. In my case it was doing the splits at a friend’s 30th on uneven ground but that’s a story for another day.
The amount of pain we experience does not necessarily correlate with the severity of injury. Have you ever cut your arm or leg and didn’t notice it until someone told you that you were bleeding? Then there was an increase in pain? Have you noticed that paper cuts are so painful for something so small? One reason for this is that the degree of pain is partially related to the context of pain. If our brain considers something to be dangerous then there may be more pain. Dr. Henry Beecher found that soldiers who had severe injuries required much less morphine than civilians with the same type of injury.
Acute pain serves a clear biologic purpose: to call on our bodies’ adaptive measures to stop the pain and protect the injured tissues. Inputs derived from damaged tissues help to mobilise the body’s protective reactions as well as the bodies’ healing systems.
For the purpose of this blog we will call acute pain, nociceptive pain
Nociceptive messages have 2 roles:
1 - inform the subconscious brain systems in order to promote a coordinated healing response
2 - inform consciousness via the medium of pain in order to change behaviour
If the conscious and unconscious parts of the brain are otherwise occupied with survival or are focused on something very enjoyable they are likely to take little notice until later. I have included a few examples of situations where people have ignored pain; it is hard to choose a favourite between
Manteo Mitchell running with a broken leg during the 400m relay heats at the 2012 London Olympics
or, good old Buck Shelford and his crown jewels: Five Kiwi moments of playing on while injured
If we don’t change our behaviour in response to pain then pain hasn’t worked!
You may well be asking yourself the question how can this be the case? If you think back to your high school biology you may vaguely recall the sympathetic nervous system which is one part of the autonomic nervous system. The sympathetic nervous system is not under volitional control and produces adrenaline and cortisol ‘fight or flight response’. This can produce descending inhibition of pain in the short term and allow us to perform superhuman feats as above. (this can allow our brains to block out some of the pain to perform..
So what do we, as physiotherapists, look for to identify nociceptive pain?
1. The strongest predictor of nociceptive pain is pain localised to the area of injury/ dysfunction.
2. Clear, proportionate mechanical/anatomical behaviour of the pain relating to aggravating and easing factors.
3. Pain is usually intermittent and sharp with movement/mechanical provocation and may be followed by a more constant dull ache or throb at rest.
4. Usually rapidly resolving or resolving in accordance with tissue healing/pathology recovery times
5. Responsive to simple analgesia/NSAIDs
6. Pain of recent onset
7. Pain in association with other symptoms of inflammation such as swelling, redness or heat.
1. Clear consistent and proportionate mechanical/anatomical pattern of pain reproduction on movement/mechanical testing of target tissues
2. Localised pain on palpation
3. Absence of/or expected proportionate findings of (primary and or secondary) hyperalgesia or allodynia explain
4. Antalgic (pain relieving - compensatory) postures/movement patterns (limp)
That’s all well and good but that doesn’t explain the pain.
The pain can be termed mechanical nociceptive – this is where nerve endings may be mechanically distorted by scar tissue or abnormal pressure from tissues. Movement increases the distortion of nerve endings, causing increased pain. This in turn is closely related to ischaemic (lack of blood flow) and inflammatory pain.
Ischaemic nociceptive – ischaemia alters the physical and chemical environment which results in increased excitation and sensitisation of nerve endings.
Ischaemic tissues become more acidic, lacking in oxygen and rich in inflammatory chemicals such as prostaglandins, bradykinin and potassium ions.
These have a particularly potent contribution to painful contracting muscles that have a poor or inadequate blood supply.
Persistent provocation over time with prolonged postures may confuse this simple on/off presentation as nociceptors become increasingly sensitised by the ischaemically related chemical soup, and central mechanisms begin to play a greater role. So holding your injured leg bent or limping everywhere can generate another type of pain
Inflammatory nociceptive – inflammatory processes in the injured or diseased tissues change. This can cause a change in their sensitivity causing the nerve endings to be more sensitive and fire off more easily response properties and the threshold for firing decreases, and some even fire spontaneously.
A link to stimulus still exists but now just a small amount of movement or gentle pressure may evoke pain and take time to settle.
Patients with inflammatory nociceptive pain often feel worse in the morning, with pain and stiffness, and may respond favourably to NSAIDs. Gentle passive or active movements often helps to relieve discomfort and feelings of stiffness
Movement may ease mechanical pressures caused by inflammatory fluids. Too vigorous a movement will increase pain, but often not until the next morning.
Pain is important to the healing process as it makes us changes are behaviour. With an acute injury we need to let the healing process play out and then restore normal movement and function. Recognising the type of factors contributing to nociception allows us to provide the optimal management.
Written by Allan Kershaw