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Acute low back pain: pain-related fear and pain catastrophizing influence physical performance and perceived disability

Swinkels-Meewisse, Ilse E.J.a,b,*; Roelofs, Jeffreya; Oostendorp, Rob A.B.c,d; Verbeek, André L.M.e; Vlaeyen, Johan W.S.a,f

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doi: 10.1016/j.pain.2005.10.005
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Abstract

1. Introduction

In the past decades, disability due to low back pain (LBP) has become an increasing socio-economic problem (Maniadakis and Gray, 2000; van Tulder et al., 1995). The individual and societal impact of chronic LBP and the knowledge that LBP has a less favorable natural course than formally believed (Hestbaek et al., 2003; Pengel et al., 2003), has made the prevention of chronicity a major issue in public health decision making. The influence of psychological factors seems increasingly important in the transition from acute to chronic LBP (Croft et al., 1995; Keefe et al., 2004; Klenerman et al., 1995; Linton, 2000; Pincus et al., 2002; Williams et al., 1998). In particular, pain-related fear and pain catastrophizing are believed to be important factors for disability. A number of studies have shown that pain-related fear is a strong predictor of self-reported disability in both acute and chronic LBP (Crombez et al., 1999; Fritz and George, 2002; Klenerman et al., 1995; Sieben et al., 2002; Swinkels-Meewisse et al., 2003a, in press; Vlaeyen et al., 1995b; Waddell et al., 1993). Several studies support the notion that in patients with chronic LBP pain-related fear is significantly associated with restricted physical performance (Al Obaidi et al., 2000; Crombez et al., 1999; Geisser et al., 2000; Vlaeyen et al., 1995a). However, the influence of pain-related fear as a predictor of poor physical performance in acute LBP has yet to be investigated.

Pain catastrophizing refers to an exaggerated negative interpretation of pain, which might occur during actual or anticipated pain experience (Sullivan et al., 2001). Pain catastrophizing is shown to be associated with increased levels of pain intensity and disability in chronic pain population as well as in the open population (Buer and Linton, 2002; Peters et al., 2005; Picavet et al., 2002; Severeijns et al., 2001, 2002; Sullivan et al., 1998, 2002; Turner et al., 2000, 2002). There is some evidence to suggest that pain catastrophizing influences disability via pain-related fear as presented in a cognitive-behavioral model of chronic pain (Crombez et al., 1998; McCracken and Gross, 1993; Murphy et al., 1997; Vlaeyen et al., 1995a). Studies investigating cognitive-behavioral interventions attempting to modify pain-related fear and/or catastrophizing are generally in favor of this hypothesis (Spinhoven et al., 2004; Sullivan and Stanish, 2003; Vlaeyen et al., 2002a). Research concerning the relation between catastrophizing, pain-related fear and disability has mostly been performed in populations with chronic pain disorders, using perceived disability as the outcome measure. However, to the authors' best knowledge, there are no studies investigating the association between catastrophizing and pain-related fear on the one hand, and physical task performance and perceived disability on the other hand, in a population of patients with an episode of acute LBP. Therefore, the main aim of the current study is to investigate which factors are associated with the performance of a physical task in a sample of persons with an episode of acute LBP. A second goal is to study which factors are associated with more general perceived disability. It is hypothesized that both pain catastrophizing and pain-related fear are stronger predictors of performance and perceived disability than pain severity or socio-demographics.

2. Methods

2.1. Study sample and methodology

Between March and December 2004, general practitioners and physiotherapists in the southeast region of The Netherlands recruited 96 individuals experiencing an acute episode of LBP. An episode of acute LBP was defined as LBP with a duration of at most 4 weeks with a pain free period of at least three months preceding the current episode. Inclusion criteria were: age between 18 and 65 with non-specific LBP independent of irradiation. Criteria for exclusion were: illiteracy; specific LBP (e.g. tumors, trauma, infection, and inflammatory disorders); presence of malignancies; operations in the lumbar area; or pregnancy. During the first consultation for LBP, the general practitioner or physiotherapist requested the patients to participate in the study. Persons who agreed to participate were contacted within 2 days to make an appointment. All measurements were performed at the patient's home to ensure ecological validity. During the home visit, the participants signed the informed consent and completed a set of questionnaires in the presence of the researcher. After completion of the questionnaires the physical task was explained to the participant in a standardized way (see physical task). At the end of the visit, patients were given a booklet with information concerning LBP, thanking them for their participation. Participants did not receive incentives in turn for their participation. The Advisory Committee on Ethics of the Maastricht University approved the experimental protocol of this study.

2.2. Physical task

The physical task consisted of lifting a bag with 7kg from the floor, on and off a table and on the floor again (table height was approximately 75cm). A maximum of standardization was pursued by using the same bag and explaining the task on a standardized way. Participants were free in the way they performed the lifting task, but the bag had to be lifted with two hands simultaneously, without pauses. The total lifting time (maximum time=300s) and the number of lifting bouts were recorded. This physical task was chosen because of its ecological value in daily activities. Both men and women are considered having sufficient experience in performing various lifting tasks in daily life. Furthermore, the task was expected to be sufficiently threatening for individuals with back pain, irrespective of their level of pain-related fear.

2.3. Measures

2.3.1. Demographic variables

A questionnaire was completed covering various socio-demographical characteristics (i.e. age, gender, education level, sick-leave, and sport activities), and questions regarding the current and/or preceding back pain episodes (i.e. duration, irradiation, onset, and numbers of preceding episodes).

2.3.2. Pain intensity

Current pain intensity was measured on a horizontal 100mm visual analogue scale (VAS) anchored with the words ‘no pain’, on the left side and ‘worst imaginable pain’, on the right side. Furthermore, maximum and mean pain intensity for the previous 2 days were measured with a VAS.

2.3.3. Functional status

A Dutch version of the Roland Disability Questionnaire (RDQ; Beurskens et al., 1996; Roland and Morris, 1983) was used to measure the functional status in LBP. The RDQ is a 24-items questionnaire with a dichotomous scoring format; yes (=item is applicable), or no (=item is not applicable). Total scores can vary from 0 (no disability) to 24 (severe disability). Reliability and validity of the measure were established (Roland and Morris, 1983; Stratford et al., 2000).

2.3.4. Pain-related fear

A Dutch version of the Tampa Scale for Kinesiophobia (TSK; Miller et al., 1991; Vlaeyen et al., 1995a) was used. The TSK is a 17-item self-report questionnaire measuring fear of movement or (re)injury. Items are scored on a four-point Likert scale ranging from ‘strongly disagree’ (score=1) to ‘strongly agree’ (score=4). Items 4, 8, 12, and 16 are reversibly scored. In a population of acute LBP patients, the TSK exists of two subscales: a harm subscale (TSK-harm, items 3, 5, 6, 9, 11, and 15), reflecting the beliefs that there is something seriously wrong with the body, encompassing both the danger and injury items; and an activity avoidance subscale (TSK-activity avoidance, items 1, 2, 7, 10, 13, 14, and 17), indicating the beliefs that avoiding exercise or activities might prevent an increase of pain (Swinkels-Meewisse et al., 2003a). The reliability of the TSK in a population with an acute LBP episode, as measured with the internal consistency and test–retest stability, varies between α=0.70 and 0.80, and r=0.78 and 0.79, respectively (Swinkels-Meewisse et al., 2003b).

2.3.5. Pain catastrophizing

A Dutch version of the Pain Catastrophizing Scale (PCS) was used (Sullivan and Bishop, 1995). The PCS exists of 13 items and was developed to measure exaggerated negative thoughts that might occur during actual or anticipated pain experience. Items are scored on a five-points scale ranging from 0 (totally disagree) to 4 (totally agree). Beside the overall scale (range 0–52), three subscales can be obtained: a rumination subscale, a helplessness subscale, and a magnification subscale (Van Damme et al., 2002). The Dutch version of the PCS is a valid and reliable measurement instrument (Van Damme et al., 2002).

2.3.6. Threat control

To investigate the threat value of the lifting task, five pictures of the photographs series of daily activities (PHODA) were shown (Kugler et al., 1999). These pictures were chosen because in a previous study, they discriminated well between high and low fearful subjects (Peters, unpublished data). According to data from this unpublished previous study, the five pictures might arbitrarily be divided in two pictures with highly feared activities (VASthreat≥60), one photograph with a moderately feared activity (40≤VASthreat<60), and two with low feared activities (VASthreat<40). Patients were asked to score on a 100mm VAS how concerned they were that the shown activity would (re)injure their back. Furthermore, before actually performing the physical task, the participants were asked to rate their concern of re/injuring their low back regarding the current lifting task on a VAS. It was hypothesized that the physical task would be moderately threatening in persons with an acute episode of LBP.

2.4. Statistical analyses

Zero-order correlations between all measures were calculated. Univariate analysis of variance was used to investigate differences in dichotomous demographical and episode related variables with respect to pain-related fear, pain catastrophizing, perceived disability and lifting time. To investigate the extent to which pain-related fear and pain catastrophizing were associated with physical performance and perceived disability, hierarchical linear regression analyses were performed with lifting time and RDQ score as dependent variables. In the first step demographic variables and pain intensity were entered. In the second step, pain-related fear and pain catastrophizing were independently added. Outliers, defined as an extremely high score on PCS and/or TSK (mean+2SD) in combination with maximum lifting time (300s), were excluded from the sample.

3. Results

3.1. Descriptive data

Participants were 96 patients with a new back pain episode. Patients included by physiotherapists or general practitioners did not differ significantly on demographic variables, pain-related fear, pain catastrophizing, or outcome measures. Three participants were excluded from the analyses, one because of age (>65 years), one as a result of improper performance of the lifting task, and one because he/she was an outlier (i.e. TSK total score=52 and lifting time was 300s). Of the remaining 93 participants, the mean age was 44.8 years (SD=11.5) with 52% being female (n=48). 51.6% of the participants had a high education (more than 13 years education) and 50.5% of the patients were engaged in sport activities. Concerning the current LBP episode, the mean duration was 11.6 days (SD=7.6). Of this sample, 21% experienced a first episode of LBP, 56% had experienced 0–7 preceding episodes, and 23% had more than seven preceding episodes of LBP. There were no significant differences between persons with or without previous episodes on lifting time, pain-related fear, pain catastrophizing, perceived disability, or demographic variables. Moreover, 53.8% of the patients experienced radiating pain in the leg, and in 74.2% of the cases the LBP had a sudden onset. Table 1 shows the means, standard deviations and correlations between disability, current pain intensity, pain-related fear, pain catastrophizing, and lifting time. Both pain catastrophizing and pain-related fear were significantly associated with disability. Lifting time was normally distributed (Kurtosis=0.66; Skewness=−0.35) and correlated significantly with disability, pain-related fear, and pain catastrophizing, but the associations were modest. Pain intensity was modestly correlated with disability only. There was a significant difference in lifting time between men and women (mean difference: 40.7s, t=−2.57, P=0.012), and between high and low educated individuals (mean difference: 33.3s, t=−2.08, P=0.041), with men and highly educated persons having longer lifting times. There were no significant differences between dichotomous demographical or episode specific variables, and total scores on pain intensity, pain-related fear, pain catastrophizing, and disability.

T1-6
Table 1:
Mean, SD, and zero-order correlations between current pain intensity, disability, pain catastrophizing, pain-related fear, and lifting time

3.2. Threat control

The participants scored high (mean VASthreat: 75.6; SD: 23.2), moderate (mean VASthreat: 41.5; SD: 27.4), and low (mean VASthreat: 28.0; SD: 25.5) on the photographs of high, moderate, and low feared activities, respectively. As expected, patients scored moderately (mean VASthreat: 43.5; SD: 30.7) when asked to rate their concern about the lifting task used in the current study. The mean difference between high and low fearful participants on the VASthreat of the physical task was 29.0 (t=4.49, P<0.001). From these results, it may be concluded that the chosen physical task was sufficiently threatening and discriminated well between high and low fearful persons in this sample.

3.3. Prediction of physical performance

Hierarchical linear regression analysis with pain intensity, and pain-related fear as independent variables, controlling for the effects of demographic variables, indicated that performance of the physical task (i.e. lifting time) was significantly predicted by pain-related fear (β=−0.27, P=0.021). Educational level was the only demographic variable predicting lifting time (β=0.23, P=0.043). Regression analysis with pain catastrophizing as independent variable showed that education was the only significant variable associated with lifting time (education: β=0.26, 95% CI=0.03–0.47, P=0.024). Secondary analyses were performed to investigate the contribution of the subscales of the TSK in the association with lifting. Analysis with TSK-harm or TSK-activity avoidance showed that only TSK-activity avoidance was significantly associated with lifting time (β=−0.31; P=0.005), increasing the explained variance from 9 to 17.6% (F=8.33, P=0.005). Results of the remaining variables were almost identical. Table 2 shows the results of the analyses.

T2-6
Table 2:
Results of hierarchical regression analysis with lifting time as dependent variable and demographic variables, pain intensity and pain-related fear as independent variables

3.4. Prediction of perceived disability

Linear regression analysis, controlling for demographic variables, with pain intensity, and pain-related fear as independent variables indicated that perceived disability (i.e. RDQ) was significantly predicted by pain-related fear (β=0.35; P=0.003) and current pain intensity (β=0.27; P=0.012). Secondary analyses with TSK-harm and TSK-activity avoidance in the equation showed comparable results (see Table 3, step 2b and c). Regression analyses with pain catastrophizing in the equation revealed that both pain catastrophizing (β=0.40; P<0.001) and pain intensity (β=0.26; P=0.012) were significantly associated with perceived disability (see Table 4).

T3-6
Table 3:
Results of hierarchical regression analysis with perceived disability as dependent variable and demographic variables, pain intensity and pain-related fear as independent variables
T4-6
Table 4:
Results of hierarchical regression analysis with perceived disability as dependent variable and demographic variables, pain intensity and pain catastrophizing as independent variables

4. Discussion

The present experimental study provides a first attempt to examine the role of pain-related fear and pain catastrophizing in the prediction of a physical task in a sample of individuals with an episode of acute LBP. Furthermore, we investigated to what extent pain-related fear and pain catastrophizing were associated with perceived disability. In predicting the performance of a lifting task, pain-related fear, as measured with the TSK, was the strongest predictor. However, both pain catastrophizing and pain-related fear, together with pain intensity were significantly related to perceived disability.

Studies investigating pain catastrophizing or pain-related fear as predictors of performance or perceived disability mostly used chronic pain samples investigating either the influence of catastrophizing or pain-related fear. There are few studies investigating both pain-related fear and pain catastrophizing in the prediction of perceived or actual disability. The study of Crombez et al. (1999) studied the role of both pain catastrophizing and pain-related fear (measured with the TSK) with performance as outcome measure. In line with the current study, their results indicated that pain-related fear was a better predictor of performance than were pain intensity or pain catastrophizing. However, the study of Crombez et al. used a small sample of chronic back pain patients (n=31) and the physical task (i.e. lifting a 5.5kg bag with the dominant arm and hold it as long as possible) differed from the lifting task used in the present study. Initially, we wanted to replicate the study of Crombez et al. (1999) and Vlaeyen et al. (1995a) using the same task but using a population of acute rather than chronic LBP patients and using a higher sample size. However, the results of a pilot study showed a clear ceiling effect of the lifting time. In addition to the ceiling affect, continually lifting a weight while standing still might be less ecologically valid than a more dynamic task. The current performance task (dynamically lifting a bag from the floor on and of a table) resulted in two possible outcome measures, i.e. number of lifts and lifting time. The authors have chosen lifting time as main performance measure because of the better comparability with previous studies (Crombez et al., 1999; Vlaeyen et al., 1995a) and because the data of the number of lifts were skewed.

Generally the results of the current study are in line with investigations using chronic pain patients (Al Obaidi et al., 2000; Burns et al., 2000; Heuts et al., 2004; Peters et al., 2005; Roelofs et al., 2004; van den Hout et al., 2001; Verbunt et al., 2003; Vlaeyen et al., 1995a) or in the open population (Buer and Linton, 2002). Prior studies in a sample of individuals with an episode of acute LBP found pain-related fear to be a significant predictor of perceived (future) disability (Swinkels-Meewisse et al., 2003a, in press). However, these investigations used self-report measures that are susceptible to shared method variance. This might also explain why, in the present investigation, pain catastrophizing significantly predicted perceived disability, whereas it lacked significance in predicting actual performance. Besides that, pain-related fear (resulting in avoidance behavior) is more proxy to actual performance of a moderately feared activity than is pain catastrophizing. Investigating disability using an actual performance measure seems to be more robust. Taking only pain catastrophizing into account, the results of this study are in contradiction with the investigation of Sullivan et al. (2002) who found pain catastrophizing to be significantly predictive of performance even after controlling for pain intensity, whereas in the current study neither catastrophizing nor pain intensity were significantly associated with performance. The difference might be accounted for by the difference in methodology and performance task. Sullivan et al. studied healthy sedentary students, inducing muscle soreness by a strenuous repeated lifting task.

Secondary analyses in the current study with the TSK subscales ‘harm’ and ‘activity avoidance’ in the equation yielded comparable results with previous studies using these TSK factors (Geisser et al., 2000; Swinkels-Meewisse et al., 2003a, in press). Geisser et al. studied the influence of the TSK subscales on the outcome of two functional tests in a sample of chronic back pain patients. Swinkels-Meewisse et al. investigated the TSK factors as predictors of perceived disability in a population with an episode of acute LBP. From the current study and previous literature one might conclude that the activity avoidance subscale is the strongest predictor of both self reported disability and performance. According to Vlaeyen's cognitive behavioral model (Vlaeyen et al., 1995b; Vlaeyen and Linton, 2000), it is proposed that fear plays a strong role in the initial development of disability whereas activity avoidance plays a significant role in maintaining chronic pain disability. Therefore, one would expect the harm subscale to be significantly related to functional activity in a acute sample, rather than the TSK-activity avoidance. This might raise some questions about the significance of the items on the TSK that measure ‘harm’. Although the construct validity of the total TSK was established, the validity of the subscales have yet to be investigated. A possible explanation of the activity avoidance factor being a more powerful predictor of functional activity than the TSK-harm subscale, might be that activity avoidance is more proxy to actual performance than are items regarding possible (re)injury. This means that activity avoidance moderated the association between fear of (re)injury (TSK-harm) and functional activities. However, this hypothesis has yet to be investigated.

In sum, the results of the current study are in line with existing literature concerning pain-related fear showing that pain-related fear is significantly associated with perceived disability and actual performance in chronic pain patients.

There are some limitations in the present study that need considering: first, the cross-sectional character of this study does not permit causal inferences regarding the associations found. To examine causality, one should manipulate pain-related fear and pain catastrophizing to study the effects on performance. Second, the measurements were performed at the patients' home. Although this might have resulted in a loss of standardization, the authors believe that the measurement favors ecological validity. To ensure standardization, each measurement the same bag was used and the task was explained in a standardized way. Participants were blinded for their scores on the physical task. Third, although gender, age, and sports activities were controlled for in the regressions, individual differences in muscle strength or body mass index, which likely influence task performance, were not controlled for. This might have influenced the results. Fourth, individuals (i.e. researchers or partners) in contact with patients might have beliefs that impact on the participant, unintentionally effecting performance or completion of questionnaires (Houben et al., 2005a,b). In order to diminish as much as possible interaction with other persons, measurements were performed without any significant others in the neighborhood, the researchers were blinded for the scores on the questionnaires, and they were asked not to respond to any pain behavior of the patient, and to give no feedback concerning the beliefs of the patient or the performance of the task. Fifth, the mean current pain intensity seems somewhat low compared with other studies on acute LBP patients (Fritz and George, 2002; Haas et al., 2002; Swinkels-Meewisse et al., 2003a; Wand et al., 2004). This low pain intensity might have caused the non-significant prediction of performance by pain intensity. Viewing the mean maximum pain intensity this relatively low current pain intensity might be the result of the favorable natural course of LBP in the first 4 weeks after onset (Pengel et al., 2003). Finally, the present study used a single physical task due to logistical reasons. This means that no conclusions can be substantiated concerning overall actual disability (Reneman et al., 2002), but together with the comparable results of studies using various physical tasks in chronic pain patients, the current study might indicate that pain-related fear is associated with actual disability.

The present study supports the finding that pain-related fear, as measured with the TSK, is present early in an episode of LBP (Buer and Linton, 2002; Fritz and George, 2002; Grotle et al., 2004; Swinkels-Meewisse et al., 2003a) and is a strongly associated with functional status in an acute LBP episode. This is in line with the cognitive-behavioral model of fear of movement/(re)injury (Vlaeyen et al., 1995a). This model conceptualizes the process of developing chronic disabling pain, ascribing a major role to catastrophic misinterpretations of painful sensations and pain-related fear. In patients with an acute LBP episode the TSK might be used as a screening instrument identifying persons with elevated pain-related fear scores. Fear-reducing information, education or interventions designed to reduce pain-related fear should be incorporated early, possibly preventing long lasting disability. Applying exposure-based interventions such as graded exposure, in individuals with elevated levels of pain-related fear have shown to positively affect patients beliefs and avoidance behavior, fostering increased activity and possibly preventing the transition to chronic LBP (Boersma et al., 2004; Jong et al., 2005; Vlaeyen et al., 2001, 2002a,b).

Acknowledgements

We thank the general practitioners and physical therapists for their assistance in including patients. The authors wish to thank Madelon Peters for her permission to use the PHODA data of chronic LBP patients and Raymond Swinkels, Kim Kugler, and Sven Balk for data-collection. Participation of Dr J. Vlaeyen was supported by The Netherlands Organization for Health Research and Development (ZONMW), grant no. 904-65-090.

We thank the reviewers for their careful reading of the manuscript and their thoughtful comments on an earlier draft.

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Keywords:

Acute low back pain; Pain-related fear; Pain catastrophizing; Performance; Disability

© 2006 Lippincott Williams & Wilkins, Inc.