In an attempt to explain how and why some individuals with musculoskeletal pain develop a chronic pain syndrome, Lethem et al. (Lethem J, Slade PD, Troup JDG, Bentley G. Outline of a fear-avoidance model of exaggerated pain perceptions. Behav Res Ther 1983;21:401±408) introduced a so-called`fear-avoidance' model. The central concept of their model is fear of pain.`Confrontation' and`avoidance' are postulated as the two extreme responses to this fear, of which the former leads to the reduction of fear over time. The latter, however, leads to the maintenance or exacerbation of fear, possibly generating a phobic state. In the last decade, an increasing number of investigations have corroborated and re®ned the fear-avoidance model. The aim of this paper is to review the existing evidence for the mediating role of painrelated fear, and its immediate and long-term consequences in the initiation and maintenance of chronic pain disability. We ®rst highlight possible precursors of pain-related fear including the role negative appraisal of internal and external stimuli, negative affectivity and anxiety sensitivity may play. Subsequently, a number of fear-related processes will be discussed including escape and avoidance behaviors resulting in poor behavioral performance, hypervigilance to internal and external illness information, muscular reactivity, and physical disuse in terms of deconditioning and guarded movement. We also review the available assessment methods for the quanti®cation of pain-related fear and avoidance. Finally, we discuss the implications of the recent ®ndings for the prevention and treatment of chronic musculoskeletal pain. Although there are still a number of unresolved issues which merit future research attention, pain-related fear and avoidance appear to be an essential feature of the development of a chronic problem for a substantial number of patients with musculoskeletal pain. q

Research studies focusing on the fear-avoidance model have expanded considerably since the review by Vlaeyen and Linton (Vlaeyen J. W. S. & Linton, S. J. (2000). Fear-avoidance and its consequences in chronic musculoskeletal pain: a state of the art. Pain, 85(3), 317--332). The fear-avoidance model is a cognitive-behavioral account that explains why a minority of acute low back pain sufferers develop a chronic pain problem. This paper reviews the current state of scientific evidence for the individual components of the model: pain severity, pain catastrophizing, attention to pain, escape/avoidance behavior, disability, disuse, and vulnerabilities. Furthermore, support for the contribution of pain-related fear in the inception of low back pain, the development of chronic low back pain from an acute episode, and the maintenance of enduring pain, will be highlighted. Finally, available evidence on recent clinical applications is provided, and unresolved issues that need further exploration are discussed.

Psychological factors play a significant role not only in chronic pain, but also in the etiology of acute pain, particularly in the transition to chronic problems. Specific types of psychological variables emerge and may be important in distinct developmental time frames, also implying that assessment and intervention need to reflect these variables. Still, psychological factors account for only a portion of the variance, thereby highlighting the multidimensional view. Because the methodologic quality of the studies varied considerably, future research should focus on improving quality and addressing new questions such as the mechanism, the developmental time factor, and the relevance that these risk factors have for intervention.

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This article reviews the role of psychological factors in the development of persistent pain and disability, with a focus on how basic psychological processes have been incorporated into theoretical models that have implications for physical therapy. To this end, the key psychological factors associated with the experience of pain are summarized, and an overview of how they have been integrated into the major models of pain and disability in the scientific literature is presented. Pain has clear emotional and behavioral consequences that influence the development of persistent problems and the outcome of treatment. Yet, these psychological factors are not routinely assessed in physical therapy clinics, nor are they sufficiently utilized to enhance treatment. Based on a review of the scientific evidence, a set of 10 principles that have likely implications for clinical practice is offered. Because psychological processes have an influence on both the experience of pain and the treatment outcome, the integration of psychological principles into physical therapy treatment would seem to have potential to enhance outcomes.

The results underscore that psychological variables are related to outcome 6 months later, and they replicate and extend earlier findings indicating that the Orebro Screening Questionnaire is a clinically reliable and valid instrument. The total score was a relatively good predictor of future absenteeism due to sickness as well as function, but not of pain. The results suggest that the instrument could be of value in isolating patients in need of early interventions and may promote the use of appropriate interventions for patients with psychological risk factors.

Potent psychosocial risk factors associated with future sick absenteeism were identified. Because the total score was related to outcome, the instrument may have use in screening patients with acute or subacute spinal pain in clinical situations.

The large individual variations in response to a similar nociceptive stimulus, as well as the development of persistent pain after an acute pain episode have puzzled researchers and clinicians alike. The Fear-Avoidance model has been introduced as a theoretical model to guide pain research and management, describing the cascade of events following pain that is perceived as threatening [5].