Pain Perception: Putting context into pain

Emotion, stress and past injury experience are vital clues to successful rehab. Scott Smith explains.

Most patients come to see sports therapy practitioners because they are in pain; others because they have had pain and want to know what they can do to prevent a recurrence. And so, not surprisingly, as practitioners we tend to focus on the mechanisms that have caused the pain: whether, for instance, certain structures are hypermobile or hypomobile, and how the body is compensating for this. What we are less good at is taking into account the possible effects of any previous experience of injury, in particular the potential damage done by the stress/emotional strain that accompanies injury and/or the degree of neuroplasticity (change to the nervous system) that results from pain. In fact, the level of pain experienced is a poor guide to the degree of tissue damage: pain perception can operate alarmingly independently of the severity of mechanical injury.

This is because pain relates to context. The pain an athlete feels will be closely linked to their perception of its cause. So if an athlete with low back pain is told by his health professional that he has a massive bulging lumbar disc (and is shown pictures of this), he will probably feel more unpleasant pain than if he had been told that bulging discs are reasonably common and not always painful.

I have seen patients who had similar MRI scans where one was presenting with intense pain, while the other was walking around with only mild discomfort. And when the pain level is low, the athlete will correspondingly perceive their tissue damage as being far less threatening to their training, their performance or future livelihood.

We all learn how to respond to pain early on in our lives. Have you ever seen an infant hurt themselves and then look at their parents before starting to cry? If the parents indicate that the child should be experiencing pain, the child will receive this stimulus and learn from it.

In general, pain is a useful and healthy signal. Thus the runner who has increased their mileage too quickly may start to develop Achilles pain. This allows them to realise (sometimes only after prompting from their therapist) that they have incorrectly increased their workload and need to modify it.

But the message of pain is not always so obvious. Take the athlete who is nearing competition and has not unwisely changed their workload, but who suddenly develops soreness in an old injury site. What processes are occurring here? You cannot underestimate the effect of emotional stress on the musculoskeletal system. There are other things going on.

Pain and the brain

Without delving too deeply into neurophysiology, there are three components to the pain experience (the pain cycle):

• Reception of pain stimuli: this occurs in the peripheral nerves and is detected by nociceptors or pain receptors;
• Transmission of pain signals: from the peripheral nerve to the spinal cord and up to the brain for interpretation;
• Perception of these pain signals: this is the balance between the information from the periphery and the resulting interpretation from the brain. This is where we decide how we feel about the pain and what we are going to do about it. The brain allows input from various areas relating to emotion, memory of previous pain, sympathetic nervous system responses, immune system responses and so on. So if we believe there is a threat to our health then we will feel pain.

Stresses and trauma, including past injury, can prompt changes in the nervous system that will alter its behaviour. In the peripheral nervous system (which provides information to the spinal cord about the muscles/joints etc) these changes include:

• More receptors activated;
• Receptors more easily excited;
• Receptors firing off spontaneously;
• Normally quiet receptors becoming ‘inappropriately’ receptive, making it more likely that stress/emotion will cause pain.

The central nervous system may undergo central sensitisation. This is where the spinal cord has greater excitability to all degrees of input from the peripheral nervous system. Normal stimuli (touch or movement) can be interpreted as pain, and moderately painful stimuli can be interpreted as extremely painful.

The higher centres of the central nervous system in the brain are also susceptible to change. This is where the centres responsible for emotion, memory, the autonomic nervous system and motor responses are situated. There is always an emotional component to our experience of pain: how an athlete will interpret this depends on previous injuries, when they occurred and the extent of the time away from competition. If an athlete is returning to an arena where they previously sustained an injury, the combined influence of memory and emotion may well cause them to feel the old injury site start to ache or feel tight – even though there is nothing wrong with the body part.

Decode and damp down

The therapist therefore has the tricky task of forming an opinion about the patient’s pain in relation to the objective level of tissue damage. In making this assessment, here are some points to consider:

Time since injury. If sufficient time has elapsed since the injury for inflammation, scarring and remodelling of the tissues to have occurred, yet the patient is still in pain, then broader questions have to be addressed.

Signs of increased sensitivity to normal sensation such as touch.For instance, the lumbar spine patient who feels pain just on light palpation of the lumbar tissues is experiencing ‘allodynia’, a sign of changes in central nervous system processing;

Negative test results. If reliable objective mechanical tests are negative (for instance, upper limb tension tests are normal while the patient reports neural symptoms), ask questions;

Adverse response to small changes in temperature.An example would be when cold-weather training causes an old injury to start aching even though nothing is wrong with the tissues. Ask questions;

Raised level of emotional stress. As an important competition looms, for instance, the athlete’s sensitivity to an injury site can increase;

Number of helpers. The size of the entourage accompanying the patient into the physio’s consulting room can be inversely proportional to the seriousness of the injury – and with some patients, the additional company seems to magnify their pain;

Response to treatment. This can be influenced by previous treatment the patient has had or their understanding of treatment. A recent patient of mine who had ruptured his posterior cruciate ligament was doing really well with his rehab until he met a friend who’d had the same injury and told my patient that he, too, would need surgical repair. It was not until my client received positive reinforcement from the surgeon (telling him that the rehab process should alleviate his symptoms and return him to his previous level of competition) that his pain subsided and rehab was successful.

The course of pain over time

By attending to broader contextual issues and with good management, the therapist can reduce this magnified pain response. Indeed, the patient comes to the therapist with expectations, and the level of confidence that they have in the ‘expert’ will in itself make a tremendous difference to their response to treatment. Even the certificates and plaques that professionals display on the walls of our clinics are part of that process of establishing our clients’ confidence in us. Here are some more measures you might deploy to help reduce pain:

Positive reinforcement about the injured tissue; for example, that it is mechanically sound and objective tests are normal;

Explain the pain cycle: as Moseley et ⁽¹⁾ have demonstrated with low back pain sufferers, by explaining the way pain works, you can help diminish the patient’s pain levels and reduce their anxiety about what they are feeling;

Use movement therapy (whether that is manipulation or mobilisation) not just for mechanical effect but also to reduce pain levels by damping down the nervous system’s centralised sensitivity. Passive movement of injured tissue can help speed the brain’s winding down of pain responses;

Advise the client about self-care; eg, to stretch an old injury site just before a competition, not simply to warm up but also to act as reassurance that no harm will come to that limb because it is feeling good, working well and is properly prepared;

Be ready to revise the pace of your graduated rehab programme. Your main aim will be to allow healing tissue to strengthen and regain extensibility at a safe and efficient rate of progress, but the client’s previous injury experience and preconceptions about pain may interfere. Their brain may be instructing the body to slow the process down if it perceives that the speed of rehab may in fact exacerbate the damage;

Reduce the threat of further injury: probably the most important factor here is environment. The rehab environment should feel safe and not related to the scene of the injury. But as healing progresses you will gradually need to introduce stress/pressure to simulate the sporting environment (see below).

Finally, devise preventive or proactive work that can help the athlete minimise their associations with pain:

• Mental rehearsal of movements that have previously injured body parts – using good technique. Thus, a high jumper who has hurt her back because she is extending too much through the lumbar spine can visualise performing her jump using the stabilising muscles to protect her back;
• Change exercise position: perform the rehab process in different positions that stimulate different thought processes, eg vary quad/gluteal exercises against a wall and on a leg press machine to try and break any negative thought processes attached to a specific movement or exercise pattern;
• Add differing degrees of balance challenges/different surfaces: again, the idea here is to re-educate the brain about an acceptable normal range of movement patterns and bio-feedback;
• Design situations of emotional stress into the rehab, eg the injured rugby player who has sustained a medial ligament injury will need to progress to stepping off that leg when pressured from a would- be tackler. The challenge here is certainly physical, but also hugely psychological;
• Add distractions, simulating the playing environment with noise etc;
• Use visual inputs to reinforce the value of the rehab: the positive effect of specific exercises can be enhanced by showing the client the beneficial changes to their body. For instance, use of real-time ultrasound in retraining the transversus abdominis muscle can convince the patient of its attachment into the deep parts of the lumbar spine. Imagery is very important as a reinforcement tool.

Summary

As therapists, we need to understand what our interventions are doing, not just at a mechanical level but also at a pain level. Otherwise it is impossible to fathom why a straightforward prescription to a straightforward problem may be having no effect on a particular patient. When the textbook formula fails to work, the therapist needs to modify their intervention to get a better result.

It is likely that good therapists already practise many of these interventions. The point here is to use them methodically not just as aids to mechanical recuperation, but also to retrain neural responses and perceptions in order to inhibit pain pathways and reinforce normal movement control, bearing in mind that your client’s pain may have less to do with their current injury than a number of other factors in their personal sporting and injury background.

Scott Smith is an Australian physiotherapist. He works at Albany Creek Sports Injury Clinic in Brisbane, specialising in running and golf injuries. He is currently working with Australian Rules football teams in Brisbane

Illustrations by Viv Mullett

References

1. Moseley GL, Hodges PW, Nicholas MK, ’A randomised controlled trial intensive neurophysiology education in chronic back pain’ Clinical Journal of Pain 2003