In a previous article, I have written about how physiotherapists use metaphors and analogies to explain chronic pain. As discussed in that article, chronic pain is a complex affair and we as physiotherapists have to use these metaphors, analogies and models to understand the complexity as well as make patients realise the multiple factors influencing their pain patterns. In this article, I discuss the onion rings model of chronic pain which I have found to be an excellent metaphor to discuss the complexity of chronic pain.
The Onion Rings model of chronic pain has been around for a long time. Initially postulated by Prof. Loeser in the 1980s and more recently enhanced by Lorimer Moseley and David Butler in their ‘Explain Pain‘ book.
Based on the bio-psychosocial approach, the onion rings model explained that although pain is a nociceptive event, persistent pain leads to suffering and subsequent behaviours that are shaped by external psychosocial and other environmental factors.
So let’s explore this model a little bit.
At the centre of the onion is the nociception (the initial trigger which may have caused the acute painful event), though one must also consider neurobiological mechanisms such as neuropathic pain and nociplastic pain. But nociception in this model also represents internal construct.
The next ring is the attitudes and beliefs. This is really important as we do not exist or perceive pain in isolation. In my PhD research, this was a consistent theme that patients who have a positive attitude towards physiotherapy and believed that the exercise program would be helpful for them would generally adhere better and therefore achieve better outcomes vs. those who had negative perception of the physiotherapy program.
This can be applied to pain experience as well. How often we have seen individuals who have a highly positive outlook towards life come out of an event unscathed which might have brought others down? This is not to say that its all in the attitude or belief, but its an element which defines our perception of event and our response to it. Another important consideration about attitudes and beliefs is that these are based on subjective, internal past experiences which a person may deem to be relevant and important to them.
The next layer is suffering which refers to the personal experience of pain by that individual patient, what it means for them in their wider context. Dr Adriian Louw, when talking about this model and suffering gave an example of a marathon runner who trains all year long, bearing adverse weather conditions to prepare for a marathon. If that runner injures his ankle a week before the marathon, would it be appropriate to have a blase attitude towards that injury and just dismiss it as a grade 1 ankle sprain? The suffering experienced by that runner can augment the pain experience and therefore increase the pain response.
The next layer is the pain escape behaviour. This ring signifies the response of a person to pain which can again be based on their childhood experiences, their social learning as well as other contextual elements.
Which brings us to the final layer which is the social environments. We do not exist in isolation (unless quarantined!!) and are a product of our social and cultural environment. In some cultures, maintaining the stiff upper lip is considered the right approach whilst others are more open to publicly demonstrating your emotions. Other social elements such as stigma associated with pain, culture, social isolation, social norms and support available also influence our pain behaviours.
So what is the value of understanding of onion rings model and how we can use it in practice?
The onion rings model of chronic pain can be a useful tool to explain pain mechanism to the patients. It highlights that at the center of it is the pain neurobiology (physical factors which initiated pain), but that so many other factors influence our experience of pain, the meaning we attach to it and how our body therefore reacts to it.
But we can’t do this without listening to our patients, giving them the time to share their pain experience with us which will in turn allow us to relate their experiences to this model and make it relevant to their social contextual elements.