Validación del proceso

3.4.3.1

Overview

The fear-avoidance model as a way to explain ongoing pain was first suggested by Lethem et al (129). In the last 20 years there has been extensive research into this concept

especially in LBP. Pincus et al (130) defines fear avoidance as a “fear of pain and

movement”. One of the central assumptions of this concept is that individuals will restrict their movements or activities because of a fear that they will cause pain or re-injury or might cause pain or re-injury (131, 132p211). This model proposes that if the avoidance of activity is sufficient and ongoing it will lead to disability. Vlaeyen et al (132p210) suggests that fear avoidance behaviour is a result of misinterpretation of the meaning of pain (catastrophisation). For example, pain is interpreted as being a sign of tissue damage even after the initial injury has healed. Misinterpretation of pain as threatening (catastrophic thinking) causes pain-related fear resulting in avoidance of movement and activity leading to disability (132p211, 133, 134p10)(See Figure 5). Misinterpretation may be fuelled by

88 factors such as previous pain experiences (132p210). This becomes a vicious cycle

maintained by the pain-related fear (133). When catastrophising does not occur there is no associated fear of pain or movement and an early resumption of normal activities will occur (133). It is also thought that the development of pain related fear results in hypervigilance and an excessive focus on pain related information (101).

Figure 5 The fear-avoidance model of chronic pain (101)

3.4.3.2

Fear avoidance beliefs as a prognostic factor

Fear avoidance beliefs are generally presented as a risk factor for disability although very little research exists in the area of WAD. There is a more extensive evidence base available when considering LBP. A systematic literature review was identified that investigated prognostic factors for recovery following acute LBP (130). This review concluded that there was little evidence to support the link between levels of fear avoidance early after the onset of LBP and prognosis. Pincus et al (130) state:

89 “In summary, the evidence from prospective cohort studies suggests that any causal link between fear avoidance and long-term measures of disadvantageous outcome is at best weak.”

Instead, it was suggested that fear-avoidance may play a role in maintaining disability in the later stages of pain (130). Avoidance behaviour may be normal coping behaviour

immediately after injury. Avoiding aggravating movements or activities and rest of the injured part is recommended in the management of acute soft-tissue injuries in the initial post injury phase (the first 72 hours) to reduce pain and facilitate tissue healing (135) . However, when avoidance behaviour continues beyond the initial post-injury phase it becomes problematic. Another possibility is that avoidance of activities is not only

attributable to a fear or pain or re-injury but that other psychological factors contribute to avoidance behaviour.

The review by Pincus et al (130) review included 9 studies of which 7 included a measure of fear of pain. Fear of pain measures were either the Tampa Scale of Kinesiophobia (TSK) (72) or the Fear-avoidance Beliefs Questionnaire (FABQ) (136). Three studies (137-139)

measured fear of pain within 3 weeks of injury and no relationship was seen between fear avoidance and outcome when it was measured early on. The remainder included

participants with LBP of varying duration from 3 days up to 6 months. Three of these studies demonstrated no link between baseline fear of pain and outcome (140-142). Only one study found an association between fear of pain and outcome (128).

Eleven other studies were identified that were not included in the review by Pincus et al (130). Consistent findings were reported that work related fear avoidance beliefs

90 (measured by the FABQ work subscale) were predictive of outcomes related to return to work (RTW) (125, 143-147). These findings contradict that of Pincus et al (130). One reason for this may be that the FABQ work subscale measures a very specific type of fear-

avoidance beliefs and this appears to have a greater predictive value than a more general measure of fear-avoidance beliefs.

The findings in relation to disability and pain outcomes were not consistent. Some studies presented mixed findings depending on the outcome measure used and the timing of follow up. For example, Pool et al (118) reported that fear avoidance beliefs were

predictive of disability at 12 week follow up but not at 1 year. George et al (148) found that fear avoidance beliefs predicted disability but not pain ratings. In total, seven studies reported findings that fear avoidance beliefs were predictive of outcome (118, 144, 145, 148-150) and 5 studies reported findings that they were not (118, 143, 148, 151, 152). All studies carried out multivariable analysis but differed in the factors included in the statistical models. For example, not all the models included a measure of emotional distress. Grotle et al (152) found that when distress was included in the model that fear avoidance was no longer predictive of outcome. This is in agreement with the review by Pincus et al (103) who concluded that distress/depression played an important role in the early stages of disability development.

3.4.3.3

Summary

Contradictory findings emerge regarding the role of fear avoidance as a risk factor for poor outcome in acute and sub-acute populations. The identified systematic literature review concluded that the link between fear avoidance beliefs and outcome was weak in LBP

91 (130). Subsequent research demonstrated consistent evidence that fear avoidance beliefs about work were predictive of RTW outcomes but the ability to predict pain and disability was much less clear. Research to date had focused heavily on LBP so further investigation into other conditions is warranted. Only two studies were identified in the systematic literature review (Chapter 1) that investigated fear avoidance in LWS and the findings were contradictory so further investigation was warranted.