The foundations of a biomedical approach to disease were laid by Virchow in the early 19th century (Virchow 1858). In this model one first examines the body for signs of abnormal pathology, infers the cause of the disease from the observations, applies a treatment and expects the signs of disease to improve. This works well for isolated pathology but it was incorrectly extrapolated from signs of disease to the cause of disability. A biomedical model of disability is predicated on there being a linear relationship between the cause of the illness, the pathology identified, the severity of the symptoms, the degree of functional limitation and the consequent disability. The simple cure was to address the root cause and everything else would improve of its own accord. However, things are not that simple. In everyday life we know of people who seem to be very disabled by relatively moderate illnesses and complaints and those who despite pain and/or physical impairment do not let it interfere with their ability to work or conduct their hobbies. As you meet patients you will no doubt become aware that some seem to “keep going” despite considerable problems whereas other seem defeated by the same condition and become very disabled and dependent on the help of others.

So what is it that makes people with similar conditions and similar levels of disease so different in their physical function and disability? In the most simple of concepts, it is what people understand and believe about their condition, the way they cope with the condition and their own perception of their ability to be able to do things despite their illness/impairment. The relative contribution of examination (clinical testing, MRI), physical findings (muscle strength, range of motion) or even physiologic tests in nonpain conditions (blood gases, cardiac function in cardiorespiratory disease) varies by condition but in most, nonclinical, mainly psychologic and social factors are important or pre-eminent in explaining the level of disability (Main et al 2008).

Unfortunately, over-reliance on a biomedical model of pain results in patients being classified as malingering or exaggerating their symptoms for secondary gain such as access to benefits or to avoid work or unpleasant circumstances. This does our patients a disservice. And it is not just the medical profession who do this. The same may happen if physiotherapists have an overly biomedical or biomechanical model of musculoskeletal pain.

In order to manage people better we must address the biomedical/biomechanical factors and the psychosocial.

It is important to note that this chapter refers to pain-related disability and not to the perception or reporting of pain as a sensation. This in itself is an interesting subject but here I will concentrate on disability resulting from pain.

Some of the most complete research comes from the musculoskeletal field, particularly low back pain. In this area, not only are we able to look at the factors which are most important in determining the degree of disability but longitudinal studies have demonstrated that psychosocial factors can predict the likelihood of disability over a year after onset. One of the reasons why psychosocial influences in musculoskeletal pain are so well researched is that we cannot externally corroborate a person’s pain, we only have their report to go on. The intensity of pain in chronic pain conditions has often been reported to explain relatively little about disability. Studies have demonstrated that pain explains, at best, about 24% of the disability of people attending physiotherapy for back pain (Woby et al 2007); in tertiary care centers like pain management programs, it might explain 8% or less of disability (Turner et al 2000).

Fig. 9.1.

The Glasgow Biopsychosocial model for low back pain.

A biopscyhosocial model for pain was developed by Waddell (2004) (see Fig. 9.1); at the core of the model is the perception of a sensation which is nociceptive or interpreted as potentially damaging. We then try to make sense of this sensation. Is it damaging? Do we need to be concerned? Our interpretation/cognitions about the sensation influence our emotional reaction to it; this is the affective component. This interpretation influences what we do about the pain – our pain or illness behavior. If we think it is nothing and it will go away by itself, we generally do little, are unconcerned and carry on. However, we might believe that it is a sign of damage and requires treatment and therefore will consult a healthcare practitioner. All our understanding of health and illness and our reactions to this are influenced by our prior experi-ence, learning and influences from the social environment, e.g. what is acceptable and unacceptable illness behavior for a particular problem (Main et al 2008). Illness behavior is everything we do with regard to a condition, including reporting pain, taking medication, vocalizing, body posture and movement, adopting a sick role and seeking economic benefits (sick pay, social security benefits) (Keefe & Dunsmore 1992).