Psychological determinants of problematic outcomes following Total Knee Arthroplasty

PAINÒ 143 (2009) 123–129

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Psychological determinants of problematic outcomes following Total Knee Arthroplasty Michael Sullivan a,*, Michael Tanzer b, William Stanish c, Michel Fallaha d, Francis J. Keefe e, Maureen Simmonds f, Michael Dunbar c a

Department of Psychology, McGill University, 1205 Docteur Penfield, Montréal, Que., Canada H3A 1B1 Department of Surgery, McGill University, Montréal, Qc, Canada c Department of Surgery, Dalhousie University, Halifax, NS B3H 3A7, Canada d Department of Surgery, Université de Montréal, Montréal, Qc H1T 2M4, Canada e Duke Pain Prevention and Treatment Research Program, Duke University, Durham, NC 27710, USA f School of Physical and Occupational Therapy, McGill University, Montréal, Qc H3G 1Y5, Canada b

a r t i c l e

i n f o

Article history: Received 30 July 2008 Received in revised form 6 January 2009 Accepted 17 February 2009

Keywords: Arthritis TKA Pain catastrophizing Fear of movement Depression Surgical outcomes Pain

a b s t r a c t The primary objective of the present study was to examine the role of pain-related psychological factors in predicting pain and disability following Total Knee Arthroplasty (TKA). The study sample consisted of 75 (46 women, 29 men) individuals with osteoarthritis of the knee who were scheduled for TKA. Measures of pain severity, pain catastrophizing, depression, and pain-related fears of movement were completed prior to surgery. Participants completed measures of pain severity and self-reported disability 6 weeks following surgery. Consistent with previous research, cross-sectional analyses revealed significant correlations among measures of pre-surgical pain severity, pain catastrophizing, depression and pain-related fears of movement. Prospective analyses revealed that pre-surgical pain severity and pain catastrophizing were unique predictors of post-surgical pain severity (6-week follow-up). Pain-related fears of movement were predictors of post-surgical functional difficulties in univariate analyses, but not when controlling for pre-surgical co-morbidities (e.g. back pain). The results of this study add to a growing literature highlighting the prognostic value of psychological variables in the prediction of post-surgical health outcomes. The results support the view that the psychological determinants of post-surgical pain severity differ from the psychological determinants of post-surgical disability. The results suggest that interventions designed to specifically target pain-related psychological risk factors might improve post-surgical outcomes. Ó 2009 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.

1. Introduction Arthritis is the leading cause of disability in North America. Osteoarthritis (OA) is the most common form of arthritis, affecting approximately 21 million people in the United States and three million people in Canada. Patients with severe OA of the knee who experience significant pain and pain-related disability, or joint deformity may be considered candidates for Total Knee Arthroplasty (TKA) [13,49,55,63]. TKA improves function and yields significant pain relief for the majority of patients who undergo the procedure [20,36,60]. There are indications, however, that 15–30% of patients may continue to experience significant pain following surgery [2,18,36,43,54, 57,62]. The number of patients reporting ongoing symptoms of pain decreases through the first year post-surgery, yet as many * Corresponding author. Tel.: +1 514 398 5677; fax: +1 514 343 4896. E-mail address: [email protected] (M. Sullivan).

as 20% of patients report moderate to severe pain one year postsurgery [2,31]. Studies have shown that, for many patients, pain persists following TKA, in spite of objective indicators of surgical success [8,31,45]. Considerable research has accumulated indicating that medical status variables alone cannot fully account for symptoms of pain and disability associated with OA [33,39–41]. Biopsychosocial models have been put forward suggesting that a complete understanding of pain-related outcomes will require consideration of physical, psychological and social factors [40,77,81]. Research has supported the view that psychological factors play a significant role in the experience of pain and disability associated with arthritis [33,37,41,42]. In other domains of research, variables such as pain catastrophizing, pain-related fears of movement, and depression have been identified as risk factors for prolonged pain and disability [50,67,82]. High levels of pain catastrophizing predict ongoing pain, and more severe disability in individuals with

0304-3959/$36.00 Ó 2009 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.pain.2009.02.011

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M. Sullivan et al. / PAINÒ 143 (2009) 123–129

musculoskeletal conditions [10,23,51,70]. Pain catastrophizing has also been shown to predict post-surgical pain [29,58]. Pain-related fears of movement have been shown to be significant determinants of disability associated with low back pain. Depressive symptoms have also been implicated as factors contributing to the transition from acute to chronic pain [14,19,65,73]. Pain catastrophizing, pain-related fears of movement, and depressive symptoms may be overlapping or unique risk factors for problematic TKA outcomes. To date, research has yet to simultaneously examine the role of pain catastrophizing, pain-related fears of movement and depressive symptoms as risk factors for problematic recovery following TKA. From a clinical perspective, such research is important because it could help identify which of these factors should be key targets for psychosocial interventions designed to improve TKA outcomes. From a theoretical perspective, the predictive value of biopsychosocial conceptualizations will increase as research begins to address more directly how different model-relevant constructs summate or interact to give rise to pain-related outcomes. In the present study, patients scheduled for TKA were assessed one week prior to surgery and then again 6-weeks post-surgery. Analyses examined the value of pre-surgical measures of pain catastrophizing, pain-related fears of movement and depressive symptoms in the prediction of post-surgical pain severity and physical function. 2. Methods

2.2.3. Pain catastrophizing The Pain Catastrophizing Scale [PCS; 72] consists of 13 items describing different thoughts and feelings that individuals may experience when they are in pain. The PCS yields a total score and subscale scores for rumination, magnification and helplessness. The PCS total and PCS subscales have been shown to have good to high internal consistency (Cronbach’s [17] alphas: total = .87, rumination = .87, magnification = .66, helplessness = .78), and to be associated with heightened pain, and disability [68–70,72]. In the present study, Cronbach’s [17] alphas were .94 (PCS Total), .88 (rumination), .83 (magnification), and .89 (helplessness). 2.2.4. Pain-related fears of movement The Tampa Scale for Kinesiophobia [TSK; 47] is a 17-item questionnaire that assesses pain-related fear of movement. The TSK has been shown to be internally reliable (coefficient alpha = .77) [46,80]. The TSK has been associated with various indices of behavioural avoidance and disability in patients with a variety of health conditions including OA [16,59,70]. 2.2.5. Depressive symptoms The Patient Health Questionnaire-9 (PHQ-9) was used as a measure of depressive symptom severity. The PHQ-9 is a 9-item questionnaire that asks respondents to indicate the frequency with which they experience each of the nine symptoms considered in the diagnostic criteria for Major Depression [66]. The PHQ-9 has been shown to be a valid and reliable measure of depressive symptoms in patients with a variety of medical conditions [27,34,48].

2.1. Participants The study sample consisted of 75 (46 women, 29 men) individuals who had been scheduled for TKA at one of three hospitals in Eastern Canada. The mean age of the sample was 68.6 years with a range of 48 to 91 years. The majority of the samples were married (85%) and had completed at least 12 years of education (90%). Forty-five patients had TKA of the right knee and 30 had TKA of the left knee. 2.2. Measures 2.2.1. Pain and function The Western Ontario and McMaster University Osteoarthritis Index (WOMAC) was used to assess clinical health status relevant to TKA outcomes [4]. The WOMAC is a self-administered instrument that yields a total score and subscale scores for (1) Pain, (2) Stiffness, and (3) Physical Function. For the purposes of the present study, only the subscale scores for pain and physical function are reported. Scores on the Pain and Function subscales were converted to a 0–100 scale to facilitate cross-scale and cross-study comparison [6,9]. Higher scores reflect worse pain and function. Since the conversion to 100-point scales simply involves multiplication by a constant, the psychometric properties of the instrument are not affected. The WOMAC has been shown to be a valid and reliable index of health functioning associated with OA, and has been shown to be sensitive to changes in function subsequent to TKA [3–5]. 2.2.2. Co-morbidities Common co-morbid conditions that can influence TKA outcomes include hypertension, osteoarthrosis of other joints, diabetes mellitus, chronic obstructive pulmonary disease (COPD), and history of tobacco use. Co-morbidity was assessed with the Charlson Co-morbidity Index [CCI; 15]. On this measure, respondents are asked to indicate the presence and severity of 13 different health conditions. The number of different health conditions endorsed by the respondent is summed to yield a total score [15].

2.2.6. Analgesic consumption A variety of analgesics were used for pain control post-operatively. Two separate indices of 48-h analgesic consumption were derived: total NSAID consumption (aspirin equivalent units) and total opioid consumption (morphine equivalent units). For NSAIDS, the following conversions were applied: aspirin 650 mg = acetominophen 650 mg = ibuprofen 200 mg = naproxen 125 mg [30]. For opioids, the following conversions were applied: IV morphine 1 mg = oxycodone 1.5 mg = hydromorphone .15 mg; PO morphine 6 mg = oxycodone 3 mg = hydromorphone .75 mg [1]. 3. Procedure Patients who were scheduled for TKA at one of three collaborating hospitals were invited to participate in the research. Patients were informed that the research was concerned with the physical, psychological and social determinants of recovery following surgery. They were invited to sign a consent form as a condition of participation. Participants received $25 as compensation for completing the questionnaires. The research was approved by the Research Ethics Boards of the McGill University Health Centre, the Hôpital Maisonneuve-Rosemont and the Capital Health Authority of Nova Scotia. Participants completed questionnaires at the time of their pre-surgical evaluation (one day prior to surgery), and at the time of their 6-week post-surgical follow-up. Surgeries were performed by seven surgeons from three different hospitals. Surgery was performed under spinal (n = 44) or general anesthesia (n = 31). Thirty-two patients also received a femoral block. The same approach to surgery was used by all surgeons. A midline incision with para-medial arthrotomy was performed. Intramedullary alignment guides were used for femoral and tibial cuts. The posterior cruciate ligament was left or resected at the discretion of the surgeon. Bicondylar femoral and tibial components were implanted and cemented. Resurfacing of the patellae was at the discretion of the surgeon. A polyethylene liner was inserted between the metallic femoral and tibial prostheses. Post-operatively,

M. Sullivan et al. / PAINÒ 143 (2009) 123–129

patients were given systemic prophylactic antibiotics and prophylactic anticoagulant to decrease deep venous thrombosis risk. Anterior–posterior (AP) and lateral knee radiographs were taken and reviewed before patient was transferred to a floor for continued care. The radiographs were reviewed to ensure that the prosthesis was inserted properly and that alignment was correct. Compression dressings were removed the day after surgery and continued passive range of motion was applied. Patients were instructed to weight bear as tolerated. At 6-week follow-up, radiographic analysis indicated that all implants were in good mechanical alignment (2–7° of femoral-tibial valgus) with satisfactory implant placement. None of the study patients had evidence of ligament instability on follow-up examination. By clinical standards, all patients in the study sample were considered surgical successes. 3.1. Data analytic approach Initial analyses addressed whether scores on predictor variables or outcome variables varied as a function of surgeon or hospital. No significant differences were found. As such, surgeon and hospital are not included in the predictive analyses. No significant differences on outcome measures were found as a function of type of anesthesia. One patient developed infection post-surgery. Analyses were conducted with and without this patient. The pattern of results was not affected and the patient was retained in the predictive analyses. Descriptive statistics were computed on sample characteristics and questionnaire scores. Pearson correlations were used to assess the concurrent and prospective relations among study variables. Bonferroni correction was used to control for alpha inflation. Multiple regression analyses were used to assess the value of pre-surgical psychological variables in predicting post-surgical pain and function. In predictive analyses, initial scores on measures of pain and function were used as covariates. In the regression results reported, all tolerance coefficients were greater than .60 such that no problem of multicollinearity was indicated. 4. Results 4.1. Sample characteristics As shown in Table 1, age distribution, BMI and WOMAC pain and function scores were similar to those reported in previous reTable 1 Sample characteristics.

Age BMI Comorbid Surgery duration 48 h Aspirin eq 48 h Morphine eq Pain Pre Function Pre Pain Post Function Post PCS TSK PHQ-9

Women

Men

p

Total

68.1 (10.2) 30.5 (5.7) 2.4 (1.2) 95.5 (12.2) 529.27 (2433.8) 44.4 (19.0) 60.9 (13.9) 66.0 (12.1) 44.1 (14.0) 44.2 (13.7) 15.4 (12.5) 29.2 (9.1) 5.6 (4.4)

69.5 (9.2) 29.0 (4.5) 2.5 (1.2) 101.3 (16.1) 5226.6 (2165.7) 42.0 (16.7) 58.5 (13.7) 64.2 (10.6) 50.8 (18.1) 46.4 (12.9) 18.0 (11.0) 28.5 (7.0) 4.2 (4.3)

ns ns ns ns ns ns ns ns ns ns ns ns ns

68.6 (9.6) 29.7 (5.2) 2.4 (1.2) 97.7 (14.0) 5267.1 (2319.0) 43.4 (18.1) 59.9 (13.7) 65.1 (11.6) 46.6 (15.8) 45.0 (13.3) 16.2 (11.9) 29.0 (8.3) 5.0 (4.4)

Note: N = 75. BMI = body mass index; Comorbid = number of comorbid health conditions; 48 h Aspirin eq = analgesic consumption first 48 hours post-op, aspirin equivalent mgs; 48 h Morphine eq = analgesic consumption first 48 hours post-op, morphine equivalent mgs; Pain Pre = WOMAC Pain Score, pre-surgery; Function Pre = WOMAC Physical Function Score, pre-surgery; Pain Post = WOMAC Pain Score, post-surgery; Function Post = WOMAC Physical Function Score, post-surgery; PCS = Pain Catastrophizing Scale; TSK = Tampa Scale for Kinesiophobia; PHQ9 = Patient Health Questionnaire-9.

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search on patients undergoing TKA [7,56]. The average patient reported having two co-morbid health conditions. The most frequently reported co-morbid health conditions were high blood pressure (71%), back pain (50%), and heart disease (15%). The presence or absence of high blood pressure and heart disease did not influence scores on post-operative pain and function. The presence of back pain was associated with more impaired post-operative function, t(73) = 2.0, p < .05, but was unrelated to post-operative knee pain. PCS scores were higher than those that have been reported in previous studies of patients undergoing TKA [64]. The distribution of depression scores suggests that the average patient was experiencing mild symptoms of depression. According to the suggested cut-off for clinically meaningful depressive symptomatology (e.g., PHQ-9 > 15), 4/75 patients scored in the moderate-severe range of depression. As expected, there were significant decreases in pain ( 13.3), t(74) = 7.2, p < .001, and functional difficulties ( 20.0), t(74) = 11.7, p < .001 from the pre-surgical to post-surgical evaluation. 4.2. Concurrent relations among psychological variables, pain and function: pre-surgery Table 2 presents the pre-surgical concurrent relations between psychological variables and health status variables. In order to control for alpha inflation, Bonferonni corrected alpha was set at .005. Consistent with previous research in individuals with arthritic conditions, measures of pain catastrophizing, pain-related fears, and depression were significantly correlated with measures of pain and function [33,38,42,64]. In addition to the correlations presented in Table 2, age was inversely correlated with pre-surgical pain, r = .38, p < .01, and BMI, r = .46, p < .01. 4.3. Prospective relations between pre-surgical psychological variables and post-surgical outcomes Table 3 presents the correlations between pre-surgical psychological measures and post-surgical measures of pain and function. Bonferonni corrected alpha was set at .005. Pre-surgical scores on measures of pain catastrophizing, pain-related fears, and depression were significantly correlated with post-surgical measures of pain and function. Of the three PCS subscales, the magnification subscale showed the highest correlations with post-surgical pain and function. As expected, post-surgical measures of pain and function were also significantly correlated with pre-surgical measures of pain and function. BMI, number of co-morbidities, dura-

Table 2 Concurrent relations among pre-surgical variables.

1. 2. 3. 4. 5. 6. 7. 8.

Pain Pre Function Pre TSK PHQ-9 PCS tot PCS rumin PCS magni PCS helps

1

2

3

4

5

6

7

.67** .32** .48** .44** .40** .40** .42**

.37** .49** .49** .40** .44* .55**

.44** .50** .46** .46** .58**

.45** .36** .43** .53**

.90** .88** .96**

.69** .78**

.82**

Note: N = 75. Pain Pre = WOMAC Pain Score, pre-surgery; Function Pre = WOMAC Physical Function Score, pre-surgery; Pain Post = WOMAC Pain Score, post-surgery; Function Post = WOMAC Physical Function Score, post-surgery; TSK = Tampa Scale for Kinesiophobia; PHQ-9 = Patient Health Questionnaire-9; PCS tot = Pain Catastrophizing Scale Total Score; PCS rumin = rumination subscale of the PCS; PCS magni = magnification subscale of the PCS; PCS helps = helplessness subscale of the PCS. ** p < .005.

M. Sullivan et al. / PAINÒ 143 (2009) 123–129

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Table 3 Prospective relations between pre-surgical and post-surgical variables. Pain Post **

Pain Pre Function Pre PCS tot PCS rumin PCS magni PCS helps TSK PHQ-9 BMI Co-morbidities Surgery duration (min) 48 h Aspirin 48 h Morphine

.43 .30 .46** .38** .47** .42** .31 .26 .05 .11 .05 .13 .06

Table 5 Regression analysis predicting post-surgical physical function (WOMAC function).

Function Post **

.37 .29 .32 .17 .37** .35** .38** .24 .16 .05 .04 .08 .01

Note: N = 75. Pain Pre = WOMAC Pain Score, pre-surgery; Function Pre = WOMAC Physical Function Score, pre-surgery; Pain Post = WOMAC Pain Score, post-surgery; Function Post = WOMAC Physical Function Score, post-surgery; PCS tot = Pain Catastrophizing Scale Total Score; PCS rumin = rumination subscale of the PCS; PCS magni = magnification subscale of the PCS; PCS helps = helplessness subscale of the PCS; TSK = Tampa Scale for Kinesiophobia; PHQ-9 = Patient Health Questionnaire-9; 48 h Aspirin eq = analgesic consumption first 48 hours post-op, aspirin equivalent mgs; 48 h Morphine eq = analgesic consumption first 48 hours post-op, morphine equivalent mgs. ** p < .005.

tion of surgery, and post-surgical analgesic intake were not significantly correlated with post-operative pain and function. 4.4. Predicting post-surgical pain and function Separate hierarchical regressions were computed to assess the value of pre-surgical measures of catastrophizing, pain-related fears, and depression in the prediction of post-surgical pain and function. In each regression, age and sex were entered in the first step. In the second step of the analyses, the pre-surgical score on the dependent variable (i.e. pain or function) was entered. In the third step of the analyses, co-morbid back pain (absent, present) was entered. Finally, the three psychological variables were entered. As shown in Table 4, age and sex were entered in the first step of the analysis but the contribution of this step failed to attain statistical significance (p = .07). However, in the final regression equation, sex did emerge as a significant predictor of post-surgical pain where women reported more intense pain than men. Pre-surgical pain accounted for 17% of the variance in post-surgical pain, before entering the psychological variables. Co-morbid back pain did not contribute to the prediction of post-operative knee pain. The PCS, Table 4 Regression analysis predicting post-surgical pain severity (WOMAC pain).

Step 1 Age Sex Step 2 Pain Pre Step 3 Back pain Step 4 PCS TSK PHQ-9

Beta

R2change

.01 .20*

.06

2.3 (2, 72)

.28

.17

16.5 (1, 71)**

.11

.01

.7 (1, 70)

.28* .07 .01

.08

2.8 (3, 67)*

*

Fchange

Note: N = 75. Pain Pre = WOMAC Pain Score, pre-surgery; PCS = Pain Catastrophizing Scale; TSK = Tampa Scale for Kinesiophobia; PHQ-9 = Patient Health Questionnaire9. Values in parentheses are degrees of freedom. Beta weights are from the final regression equation. * p < .05. ** p < .01.

Step 1 Age Sex Step 2 Function Pre Step 3 Back pain Step 4 PCS TSK PHQ-9

Beta

R2change

Fchange

.09 .09

.02

1.0 (2, 72)

.13

.07

6.1 (1, 71)**

.23*

.05

4.2 (1, 70)*

.12 .24  .04

.09

2.5 (3, 68) 

Note: N = 75. Function Pre = WOMAC Physical Function Score, pre-surgery; PCS = Pain Catastrophizing Scale; TSK = Tampa Scale for Kinesiophobia; PHQ9 = Patient Health Questionnaire-9. Values in parentheses are degrees of freedom. Beta weights are from the final regression equation.   p = .06. * p < .05. ** p < .01.

TSK and PHQ-9 were entered in the final step of the regression and contributed significant variance to the prediction of post-surgical pain beyond the variance accounted for by age, sex and presurgical knee and back pain. Examination of the beta weights from the final regression equation indicated that, of the three psychological variables, only the PCS (beta = .28, p < .05) contributed significant unique variance to the prediction of post-surgical pain. Controlling for all other variables in the regression equation, sex, pre-surgical knee pain and pain catastrophizing accounted for 4%, 8% and 8% of the variance in post-surgical pain, respectively. Table 5 shows the results of the regression analysis for the prediction of post-surgical function. Pre-surgical WOMAC function scores accounted for 7% of the variance in post-surgical WOMAC function scores. Co-morbid back pain accounted for 5% of the variance in post-surgical WOMAC function scores. The three psychological variables were entered in the final step of the analysis but failed to contribute significantly to the prediction of post-surgical WOMAC function scores. Examination of the beta weights for the final regression equation revealed that the predictive value of the TSK was marginally significant, p = .06. 5. Discussion The present findings add to a growing body of literature suggesting that certain psychological variables might predispose individuals to adverse pain-related outcomes following surgical intervention. The results of the present research are consistent with previous studies showing that higher levels of pre-surgical pain and functional difficulties predict post-surgical pain and functional difficulties [26,31]. The results are also consistent with previous research showing that women experience more intense post-surgical pain than men [25,61]. The present research extends previous findings in showing that pain catastrophizing predicts post-surgical pain to the same degree as pre-surgical pain. Furthermore, the contribution of pain catastrophizing to the prediction of post-surgical pain was independent of the contribution of pre-surgical pain. Pain-related fears made a near-zero contribution to the prediction of post-surgical pain. Pain-related fears of movement were found to predict post-surgical functional difficulties following TKA in univariate but not multivariate analyses. From a theoretical perspective, the findings are consistent with cognitive behavioural models of pain that suggest that negative appraisals (e.g., catastrophic thinking) of pain will influence the intensity and persistence of pain experience. Pain catastrophizing has been construed as a multidimensional construct comprising

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elements of rumination (i.e. excessive focus on pain sensations), magnification (i.e. heightened perception of the threat value of pain symptoms) and helplessness (i.e., beliefs that the control of pain is beyond one’s ability) [75]. In previous research, each of these dimensions has been shown to have an adverse impact on pain experience [11,21,79]. In addition to the psychological processes that link catastrophizing to adverse pain outcomes, there are indications that catastrophizing might also influence neurophysiological processes involved in pain modulation. High levels of pain catastrophizing have been associated with poorer response to opioids for both clinical and experimental pain [24,32,35]. It has been suggested that pain catastrophizing might interfere with descending pain-inhibitory systems and might facilitate neuroplastic changes in the spinal cord during repeated painful stimulation, subsequently promoting sensitization in the CNS [28]. The findings are also partially consistent with fear-avoidance models that have been developed to account for the development of pain-related disability. According to fear-avoidance models, pain-related fears will lead to activity avoidance or escape, and in turn, contribute to functional disability. Prolonged periods of inactivity then compound disability through deconditioning and heightened risk of developing co-morbidities (e.g., obesity and diabetes) [33]. The results of the present research highlight the importance of examining psychological predictors of post-surgical outcomes from a multivariate perspective. Like previous research, the present study revealed significant variance overlap among measures of catastrophic thinking, pain-related fears and depressive symptoms (20–25% shared variance). In spite of this degree of shared variance, the findings suggest that pain catastrophizing and painrelated fears of movement are differentially associated with postsurgical pain and function. Not only do these findings support the conceptual distinctiveness of pain catastrophizing and pain-related fears of movement, but they also have implications for the nature of interventions that might be considered for individuals scheduled for TKA. Many individuals with OA will continue to experience debilitating symptoms of pain following surgery. In the present study, at 6 weeks post-surgery, 30% of patients reported their pain at rest to be moderate or severe. Research suggests that approximately half of these patients might go on to develop chronic pain conditions [31,43,44]. Once symptoms of pain become chronic, available methods of managing pain, whether pharmacological or psychological, have only modest impact on suffering and function. Persistent pain symptoms have been identified as central determinants of disability, both pre- and post-TKA [26,52,78]. Persistent pain symptoms following TKA can contribute to a trajectory increasing distress and disability associated with discontinuation of life role activities, progressive decline toward a sedentary lifestyle, and social isolation [12,39]. If individuals at risk for post-surgical pain and disability can be identified before the problem becomes chronic, individual’s suffering might be prevented or reduced to a significant degree. The results of the present study suggest that measures of pain catastrophizing and pain-related fears of movement might be considered as screening measures for identifying patients at risk for problematic outcomes following TKA. Individuals identified at risk might then be considered for targeted interventions that might prevent the development of persistent pain and disability following surgery. Research suggests that pain catastrophizing and pain-related fears of movement can best be construed as modifiable risk factors for problematic health outcomes. Although pain catastrophizing and pain-related fears of movement have been shown to be stable in the absence of intervention, both variables have been shown to

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decrease in response to intervention [71,74]. Although comparative studies have yet to be conducted, there are data to suggest that cognitive techniques might be most effective in reducing pain catastrophizing while behavioural (e.g., exposure) techniques might be most effective in reducing pain-related fears of movement [76,83]. The present research suggests that interventions that specifically target pain catastrophizing and pain-related fears of movement could be adapted for patients scheduled for TKA, and hold promise of reducing the degree to which patients will continue to experience significant pain and disability post-surgery. To date, preventative psychosocial interventions for OA patients have primarily taken the form of broad-based educational programs. Since education programs do not select individuals at risk, nor do they target specific prognostic factors for pain and disability, it is not surprising that they have yielded only modest impact on surgical outcomes [53]. There have been previous reports suggesting that depression might contribute to poor TKA outcomes, defined either in terms of pain, function or quality of life indices [25,26]. For example, Faller et al. [22] reported that pre-operative depression scores predicted post-operative scores of a measure of functional difficulties at 3 months and 12 months following TKA. In the latter study, the unique contributions of pain catastrophizing and painrelated fears of movement were not simultaneously assessed. In the present study, depression was associated with pain and function scores in univariate analyses (but not when correlations were Bonferonni corrected), and not in the multivariate analyses. Although the negative impact of depression needs to be considered in the treatment of all debilitating health conditions, depression might not make a unique contribution to problematic health outcomes following TKA. Roth et al. [64] recently reported the results of a study examining predictors of post-surgical pain in a sample of patients having undergone TKA. Cross-sectional analyses revealed significant relations between pain intensity and pain catastrophizing, but prospective analyses failed to show significant predictive value of pre-operative pain or pre-operative pain catastrophizing. A number of factors might account for these inconsistent findings. First, the level of catastrophizing of patients in the Roth et al. sample (Total PCS = 4.7) was considerably lower than that in the present study (Total PCS = 16.2). It is possible that high scores on pain catastrophizing were insufficiently represented in the Roth et al. study to reveal a prospective relation with post-surgical outcomes. Roth et al. also assessed pain in the first three days following TKA while the present study assessed TKA outcomes at 6-weeks postsurgery. It is possible that due to higher medication intake during the days immediately following surgery, relations between pain catastrophizing and pain intensity might have been obscured. More research is needed to specify the conditions that determine whether or not prospective relations between psychological variables and post-surgical outcomes will be observed. Caution must be exercised in the interpretation of the present findings. It is important to consider that cross-study discrepancies provide grounds for questioning the reliability or robustness of the findings. Sample sizes have been modest in most studies conducted to date on the psychological predictors of post-surgical outcomes. Confidence in the reliability of the findings awaits replication with a larger sample size. In addition, the present sample was followed up for only 6 weeks. While the findings point to the influence of catastrophic thinking and pain-related fears of movement on pain and function at 6 weeks post-surgery, it is unclear whether these relations would persist over a longer period of time. In many studies of orthopedic surgery outcomes, follow-up periods might be as long as two years. Since psychological factors likely have a dynamic relation with changing health status over time, longer follow-up periods might be needed to provide a

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