Waiting for total knee replacement surgery: factors associated with pain, stiffness, function and quality of life

1471-2474-10-52 1471-2474 Research article Waiting for total knee replacement surgery: factors associated with pain, stiffness, function and quality of life Desmeules François francois.desmeules@uresp.ulaval.ca Dionne E Clermont cdionne@uresp.ulaval.ca Belzile Étienne etienne.belzile@mail.chuq.qc.ca Bourbonnais Renée renee.bourbonnais@rea.ulaval.ca Frémont Pierre pierre.fremont@crchul.ulaval.ca

Population Health Research Unit (URESP), Research Centre of the Laval University Affiliated Hospital (CHA), Quebec, QC, Canada

Department of Social and Preventive Medicine, Faculty of Medicine, Laval University, Quebec, QC, Canada

Department of Rehabilitation, Faculty of Medicine, Laval University, Quebec, QC, Canada

Laval University Hospital (CHUQ), Quebec, QC, Canada

Community Health Care Centre (CSSS) de la Vieille Capitale, Quebec, QC, Canada

BMC Musculoskeletal Disorders 1471-2474 2009 10 1 52 http://www.biomedcentral.com/1471-2474/10/52 19457252 10.1186/1471-2474-10-52 29 10 2008 20 5 2009 20 5 2009 2009 Desmeules et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background

Recent evidences show that education and rehabilitation while waiting for knee replacement have positive effects on the patients' health status. Identification of factors associated with worse pain, function and health-related quality of life (HRQoL) while waiting for surgery could help develop pre-surgery rehabilitation interventions that target specifically these factors and prioritize patients that may benefit the most from them. The objectives of this study were to measure pain, stiffness, function and HRQoL in patients at enrolment on waiting lists for knee replacement and to identify demographic, clinical, socioeconomic and psychosocial characteristics associated with these outcomes.

Methods

This study is part of a broader study measuring the effects of pre-surgery wait in patients scheduled for knee replacement. From 02/2006 to 09/2007, 197 patients newly scheduled for total knee replacement were recruited from the waiting lists of three university hospitals in Quebec City, Canada. Pain, stiffness and function were measured with the Western Ontario and McMaster Osteoarthritis Index (WOMAC) and HRQoL was measured with the SF-36 Health Survey. Stepwise multiple regression analysis was used to assess the strength of the associations between the independent variables and the WOMAC and SF-36 scores.

Results

The scores of all eight HRQoL physical and mental domains of the SF-36 were significantly lower than aged matched Canadian normative data (p < 0.05). Contralateral knee pain, higher psychological distress, higher body mass index (BMI) and the use of a walking aid were significantly associated with worse function (p < 0.05) and contributed to 22% of the variance of the WOMAC function score (multiple r = 0.47). A higher BMI, the use of a walking aid, contralateral knee pain and advanced age were significantly associated with worse physical function (p < 0.05) and contributed to 17% of the variance of the SF-36 HRQoL physical functioning score (multiple r = 0.41).

Conclusion

Patients waiting for knee replacement have poor function and HRQoL. Characteristics that were found to be associated with these outcomes could help develop pre-surgery rehabilitation program and prioritize patients that may benefit the most from them. Such programs could include interventions to reduce psychological distress, therapeutic exercises targeting both knees and weight loss management.

Background

Knee replacement surgery is a common surgical procedure that allows for an effective reduction of pain and adequate restoration of function for the vast majority of patients suffering from advanced knee osteoarthritis or other forms of arthritis. 1 In the last decades, the growing needs of the population have made this procedure, along with hip replacement, the second most popular orthopaedic surgery. 2 In Canada, in 2006, the rate of knee replacements reached 106.9/100 000 persons, in sharp progression from the past decade. 3 This sharp rise in demand has translated into growing waiting lists. Governments have tried to tackle this problem, and with the allocation of new funding and the development of new policies, more patients are being operated. 4 But wait times remain a problem; recent Canadian data show that, depending on the province, the median pre-surgery wait time range from 112 to 291 days and still today an important proportion of patients are not operated within six months, the maximum acceptable waiting time benchmark established in Canada. 56

Waiting for knee replacement surgery represents a significant burden for patients as they experience great pain, suffer functional limitations and loss of health-related quality of life (HRQoL) for many months. Some authors have suggested that long delays for surgery could result in patient's deterioration in terms of pain, functional limitations and HRQoL and may have negative impacts on post-surgery outcomes. 789 To lighten the burden of patients waiting for knee replacement, some authors have suggested that reducing wait time is not the only strategy. Some actions should target the reduction of pain and the improvement of function and HRQoL of patients while they are on waiting lists. 10 Two recent studies have shown that education and rehabilitation while waiting for total joint replacement (also called prehabilitation) have positive effects on the patients' health status and could lead to better outcomes postoperatively. 1112 Until recently prehabilitation was believed to have little effect,13 but these two studies included a full therapeutic exercises program and were carried out for a longer period of time resulting in more positive outcomes. Therefore, if prehabilitation interventions were efficacious for this population, there is a need to identify factors associated with worse pain, function and HRQoL while waiting for surgery, as it may help develop interventions that target specifically these factors and prioritize patients that may benefit the most from them. To our knowledge, only one Australian study has identified factors associated with increased pain and functional limitations or loss of HRQoL precisely at the inclusion on surgical waiting lists. This study concluded that women had worst function than men and those with lower socioeconomic status had worst HRQoL when entering waiting lists for hip or knee replacement surgery. 14 Other studies have found that factors such as advanced age, female gender, low income, low formal education, long disease duration, high body mass index (BMI), more comorbidities and high use of non-steroidal anti-inflammatory drugs (NSAIDs) were associated with worse pain, function and HRQoL in patients waiting for joint replacement. However, these factors were measured at the time of surgery or during pre-surgery waiting but not at enrolment on the pre-surgery waiting lists. 1516171819

The objectives of the current study were to measure pain, stiffness, function and HRQoL in patients at enrolment on waiting lists for total knee replacement surgery and to identify demographic, clinical, socioeconomic and psychosocial characteristics associated with these outcomes.

Methods

Settings

This study is part of a broader study measuring the effects of pre-surgery wait in patients scheduled for total knee replacement. From 02/2006 to 09/2007, patients were recruited from the waiting lists of the departments of orthopaedic surgery of three university hospitals in Quebec City, Canada (CHUL, HSFA and HDQ).

Participants

Every week, patients newly enrolled on the waiting lists were contacted over the phone by a research nurse. To be eligible for the study, patients had to meet the following criteria: 1-Aged = 40 years; 2-Newly enrolled on the orthopaedic waiting lists for primary unilateral total knee replacement; 3- Residents of the province of Quebec and beneficiaries of the provincial universal health insurance coverage (Régie de l'Assurance Maladie du Québec – RAMQ); 4- Understand and speak French. Patients were excluded if they presented severe cardiac condition, degenerative disease or mental disorder. Patients with a previous contralateral knee or a hip replacement were also excluded. Those who suffered a major trauma to the knee in the previous year or were operated urgently within 30 days of being put on the waiting list were also excluded.

Data collection

Data were collected through the review of the subjects' medical files and structured telephone interviews conducted within three weeks of the enrolment on waiting lists. The interviews lasted about 45 minutes. Daily attempts were made during weekdays and week-ends to contact new patients.

The first dependent variable was the Western Ontario and McMaster Osteoarthritis Index (WOMAC), which measures pain, stiffness and functional limitations related to the knee. 20 The 5-point Likert version was used. The WOMAC scores were transformed in order to obtain a range from 0 to 100, where a score of 100 indicated no pain, no stiffness or any functional limitations. This transformation allowed for an easier comparison with the SF-36. The WOMAC has been found to have very good reliability, convergent construct validity and responsiveness, and has been used extensively in patients suffering from knee osteoarthritis or undergoing knee replacement. 2122

The second dependent variable addressed HRQoL, measured with the Medical Outcomes Study 36-Item Short Form Health Survey (SF-36), a generic questionnaire on health status and HRQoL related to eight dimensions of health. 23 It allows for the calculation of two component scales: the physical component scale (PCS) and the mental component scale (MCS) as well as a specific scale for each of the eight health dimensions considered. The scores range from 0 to 100 where a score of 100 indicates optimal HRQoL. The use of the SF-36 has been extensive in population suffering from osteoarthritis24 and in particular in patients undergoing knee replacement. 232526272829 The reliability, validity and responsiveness of this self-administered questionnaire have been well established. 3031

Anthropometric data were collected through the review of the subjects' medical files after enrolment on the orthopaedic waiting lists and allowed the calculation of the BMI (in kg/m²). Data were typically taken from the pre-operative consultation about 6 weeks before surgery. Patients were also asked about their weight and height at the time of enrolment on the waiting list during the interview. The intraclass correlation coefficient between both measurements was very high (ICC = 0.95; 95% CI: 0.94 – 0.96).

Marital status, household living status, and clinical variables such as duration of symptoms and use of a walking aid were documented during the interview. Pain in the contralateral knee was assessed using the five questions of the WOMAC pain scale. For analyses, the score was dichotomized (presence or absence of contralateral knee pain). Using the medical files, comorbidities were documented with, the Cumulative Illness Rating Scale (CIRS). 32 This index measures the burden of chronic illness with a score that ranges from 0 to 56. This tool has been found to be reliable and valid in various settings. 333435 Formal education, employment status, household income and social support were measured with questions drawn from the questionnaire of the 1998 Quebec Health Survey. 36 The validated and reliable social support measurement tool has three sections referring to the size of the social network, satisfaction with social life and social integration. 37 Because of time constraint, only the questions regarding the size of the social network were used. For analyses, the social support score (range: 0–150) was dichotomized around the median score. Psychological distress was established with the modified version of the Psychological Symptom Index (PSI), that measures depression and anxiety (range: 0–42). 38 Its French translation has been previously validated by Préville et al. (1992) and has been found highly reliable. 3940

Analyses

Descriptive statistics were used to summarize the subjects' characteristics, WOMAC and SF-36 scores. Ninety-five percent confidence intervals (95% CI) were built around the mean WOMAC pain, stiffness and function score. Means and 95% CI of the SF-36 eight domain scores and the physical (PCS) and mental (MCS) component summary scores were compared to Canadian age-matched normative data using student t-tests.

Stepwise multiple regression analysis was used to assess the strength of the associations of the independent variables considered with the WOMAC and SF-36 scores. All three sub-scales of the WOMAC were used as dependent variables in separate models. For the SF-36, separate models were built with the physical and mental summary scores as dependent variables, as well as with the three more responsive health domain scores related to physical health: physical functioning, role-physical and bodily pain. 41 Age and gender were forced into all models. Confounding was defined as a change ≥ 10% in the regression coefficient of at least one independent variable of a model. 42 Significance levels for independent variable selection were set at 0.10 for initial model entry and at 0.05 to remain in the final model. When dependent variables showed non-normal distributions, the scores were transformed into ranks. 43 Residual plots, outliers and multicollinearity of final models were also assessed. Using simple linear regression models, assuming a type I error (α) of 0.05, power (1-β) of 0.80 and standard deviations of 25 (%) for the WOMAC score and of 45 (%) for the SF-36, sample sizes of 52 and 161 subjects would be needed to detect a 10% change in the WOMAC and the SF-36 scores, respectively. 72844 A 10% change in these scores is considered clinically significant. 4546 Statistical analyses were performed with the SAS software version 9.1 for Windows (SAS Institute Inc, Cary, NC, USA).

Ethics

The information and consent forms were read over the phone and verbal consent was sought. The information and consent forms were then mailed to the patient and all participants signed and returned the consent form. This procedure allowed for timely data collection right at the enrolment on the orthopaedic waiting list. The study was approved annually by the Research Ethics Boards of all three hospitals.

Results

Participants

Figure 1 presents the flow of patients considered and recruited for this study. Overall, 588 patients were enrolled on the waiting lists during the recruitment period. Thirty-two patients could not be contacted within three weeks of their inclusion on the waiting list and were excluded. Forty-five patients refused to participate before eligibility could be assessed. Once the remaining patients were assessed, 291 were found not eligible: 182 had a previous knee or hip replacement, 57 were operated within a month and 52 were excluded on other criteria. This left us with 220 eligible subjects, of whom 197 accepted to participate. The 45 patients who refused to participate before eligibility was assessed were included in the calculation of the overall eligibility proportion, (220+32)/(588-45) = 0.464 and in the calculation of the participation proportion, 197/(220 + (45 × 0.464)) = 81.8%.

Figure 1

Flowchart of patients' recruitment

Flowchart of patients' recruitment. * Eligibility status unknown (considered in calculation of participation proportion).

Subjects' characteristics

Table 1 presents selected characteristics of the participants. Subjects had a mean age of 67 ± 9.8 years. The majority was composed of women (64%) that were married or living in common law (63%). The mean BMI was 31.0 kg/m², indicating a high frequency of obesity defined at ≥30 kg/m²). 47 Psychological distress was low, with a mean score of 6.9/42 when compared to the Quebec population mean (16.23 ± 14.94). 48

Table 1

Characteristics of the study participants at enrolment on the waiting lists for total knee replacement (n = 197)

Variables

n (%)

Mean (SD)

Demographics

Age (years)

67 (9.8)

Gender

Female

126 (64)

Male

71 (36)

Marital status

Single, separated, divorced or widowed

72 (37)

Married or common law

125 (63)

Living situation

Living alone

45 (23)

Not living alone

152 (77)

Clinical characteristics

BMI* (kg/m²)

31.0 (6.3)

Comorbidities** (/56)

6.2 (2.3)

Duration of symptoms (years)

8.5 (8.8)

Contralateral knee pain ^†

Yes

53 (27)

144 (73)

Use of a walking aid

Yes

74 (38)

123 (62)

Socioeconomic characteristics

Educational level (part or complete)

High school or less

112 (57)

College or university

85 (43)

Employment status

Retired

128 (65)

Employed

39 (20)

Not working or sickness benefit

30 (15)

Household income ^‡

< $30 000/year

61 (36)

≥ $30 000/year

107 (64)

Psychosocial characteristics

Psychological distress (/42)

6.9 (6.5)

Social support ^§

Low

92 (47)

High

105(53)

* Body mass index

** Cumulative illness rating scale (CIRS); n = 177

^†Established from the WOMAC pain score for the contralateral knee

^‡n = 168

^§Social support was dichotomized around the median score: Low (≤ 80) and High (> 80)

WOMAC pain, stiffness and function

Participants presented important pain, stiffness and loss of physical function as measured by the WOMAC: the mean pain score was 47.5 (95% CI: 44.9 – 50.1), the stiffness score was 42.8 (95% CI: 39.8 – 45.8) and the function score was 47.1 (95% CI: 45.1 – 49.2).

SF-36 health-related quality of life

Summary measures of the SF-36 are presented in Table 2. Participants scored significantly lower (p < 0.05) in all eight domains of the SF-36 than the age matched adults of the general Canadian population. 49 Likewise, for the two component summary scales, the subjects' scores were significantly lower (p < 0.05) than the Canadian means.

Table 2

Health-related quality of life of the study participants and comparison with Canadian normative data (n = 197)

Mean score^†(SD)

95% CI

SF-36 Canadian normative data ^‡

(Mean and SD)

95% CI

SF-36

Physical functioning

24.3 (17.9)*

21.8 – 26.8

75.7 (22.2)

74.9 – 76.5

Role-physical

39.3 (25.6)*

35.7 – 42.9

76.2 (36.5)

74.9 – 77.5

Bodily pain

27.5 (11.7)*

25.8 – 29.1

74.0 (23.9)

73.1 – 74.8

General health

37.1 (10.4)*

35.6 – 38.6

73.5 (18.4)

72.8 – 74.1

Vitality

39.5 (13.4)*

37.6 – 41.4

67.7 (18.1)

67.0 – 68.3

Social functioning^§

40.9 (15.2)*

38.8 – 43.0

87.0 (19.8)

86.2 – 87.7

Role-emotional^§

69.8 (26.3)*

66.1 – 73.5

83.4 (32.8)

82.2 – 84.6

Mental health^§

53.4 (11.4)*

51.8 – 55.0

79.3 (15.0)

78.8 – 79.8

Physical component scale (PCS)^§

28.2 (6.4)*

27.3 – 29.1

47.2 (9.7)

46.8 – 47.6

Mental component scale (MCS)^§

42.9 (8.1)*

41.7 – 44.0

53.7 (8.3)

53.4 – 54.0

^†A higher score signs a better health-related quality of life

^‡Age matched normative data

^§n = 196

* Significantly lower (worse) than the Canadian normative data, p < 0.05

Multivariate Regression Analyses

Because no important differences were found in the selection of independent variables between the initial models and the models in which the dependent variables were transformed into ranks, the final models were built with untransformed scores. Age and sex were forced into all models and no other adjustments of confounding variables were necessary.

WOMAC pain, stiffness and function

Results of multivariate analyses on the WOMAC scores are presented in Table 3. Contralateral knee pain, higher psychological distress and higher BMI were significantly associated with worse knee pain (p < 0.05) and explained 11% of the variance of the WOMAC pain score (multiple correlation coefficient r = 0.33). Contralateral knee pain and higher psychological distress were significantly associated with more knee stiffness (p < 0.05). Longer duration of knee symptoms was significantly associated with less knee stiffness (p = 0.003). These three subjects' characteristics explained 11% of the variance of the WOMAC stiffness score (multiple r = 0.33). Contralateral knee pain, higher psychological distress, higher BMI and use of a walking aid were significantly associated with worse knee function (p < 0.05) and explained 22% of the variance of the WOMAC function score (multiple r = 0.47).

Table 3

Associations between the study participants' characteristics and the WOMAC scores (n = 197)

WOMAC SCORE ^†

β ^‡

95% CI

p value

Pain score (r²= 0.11)

Contralateral knee pain

- 7.65

- 14.56 – - 3.29

0.009*

Psychological distress

- 0.45

- 0.83 – - 0.07

0.020*

BMI^§

- 0.46

- 0.86 – - 0.05

0.026*

Stiffness score (r²= 0.11)

Contralateral knee pain

- 10.07

- 16.60 – - 3.54

0.003*

Duration of symptoms

0.53

0.18 – 0.87

0.003*

Psychological distress

- 0.55

- 1.00 – - 0.11

0.015*

Function score (r²= 0.22)

Contralateral knee pain

- 7.18

- 11.43 – - 2.93

0.001*

Psychological distress

- 0.53

- 0.82 – - 0.24

0.004*

BMI

- 0.42

- 0.72 – - 0.12

0.006*

Use of a walking aid

- 4.81

- 8.70 – - 0.94

0.015*

^†Stepwise multiple regression analysis. Age and gender were forced into all models.

^‡Multivariate unstandardized linear regression coefficients. For each unit of the participants' characteristics, there is in average a β increase (+) or a decrease (-) on the WOMAC score. A positive β has a positive effect on the participants' condition and a negative β has a negative effect.

* p < 0.05

^§BMI = Body mass index

SF-36 health-related quality of life

Results of multivariate analyses on the SF-36 scores are presented in Table 4. Higher BMI, use of a walking aid, contralateral knee pain and advanced age were significantly associated with worse HRQoL related to physical functioning (p < 0.05) and explained 17% of the variance of this score (multiple r = 0.41). Use of a walking aid, higher psychological distress and comorbidities were significantly associated with worse HRQoL due to physical role limitations (p < 0.05). Married subjects had significantly better HRQoL related to physical role limitations than single, separated, divorced or widowed subjects (p= 0.025). Together, these four characteristics explained 17% of the variance of the role-physical score (multiple r = 0.41). Use of a walking aid was the only characteristic associated with bodily pain and explained 5% of the variance of this score (multiple r = 0.22).

Table 4

Associations between the study participants' characteristics and the SF-36 health-related quality of life scores (n = 197)

SF-36 SCORE ^†

β ^‡

95% CI

p value

Physical functioning (r²= 0.17)

BMI^§

- 0.69

- 1.10 – - 0.29

<0.001*

Use of a walking aid

- 8.28

- 13.25 – - 3.31

0.001*

Contralateral knee pain

- 6.03

- 11.37 – - 0.69

0.027*

Age

- 0.26

-0.52 – - 0.01

0.049*

Role-physical (r²= 0.17)

Use of a walking aid

- 15.23

- 22.42 – - 8.06

<0.001*

Psychological distress

- 0.71

- 1.23 – - 0.18

0.008*

Marital status (Married or common law)

8.47

1.08 – 15.85

0.025*

Comorbidities

-1.46

- 2.95 – - 0.03

0.044*

Bodily pain (r²= 0.05)

Use of a walking aid

- 3.85

- 7.27 – - 0.44

0.027*

Physical component scale - PCS (r²= 0.08)°

Use of a walking aid

- 2.90

- 4.78 – - 1.02

0.003*

BMI

- 0.17

- 0.32 – - 0.02

0.030*

Mental component scale – MCS (r²= 0.42)°

Psychological distress

- 0.74

- 0.88 – - 0.60

<0.001*

Low social support

- 2.28

- 4.14 – - 0.41

0.017*

Contralateral knee pain

- 2.60

- 4.61 – - 0.59

0.011*

^†Stepwise multiple regression analysis. Age and gender were forced into all models.

^‡Multivariate unstandardized linear regression coefficients. For each unit of the participants' characteristics there is on average a β increase (+) or a decrease (-) on the SF-36 score. A positive β has a positive effect on the participants' condition and a negative β has a negative effect.

* p < 0.05

^§BMI = Body mass index

° n = 196

For the physical component scale, use of a walking aid and higher BMI were significantly associated with worse physical HRQoL and explained 8% of the variance of this score (multiple r = 0.28). Higher psychological distress, low social support and contralateral knee pain were significantly associated with worse mental HRQoL and explained 42% of the variance of the mental component score (multiple r = 0.65).

Discussion

In this cross-sectional study, 197 patients were recruited at the time of enrolment on waiting lists for total knee replacement to measure pain, stiffness, function and HRQoL and to identify demographic, clinical, socioeconomic and psychosocial characteristics associated with these outcomes. We found that subjects reported important pain, stiffness and loss of function. HRQoL was also significantly impaired in these subjects, compared to the Canadian norms, for all the domains and components measured. These findings likely reflect the surgical indication of the subjects' condition. Interestingly however, mental aspects of HRQoL were also impaired. This finding may have implication regarding prehabilitation interventions for these patients, since it suggests that it might be beneficial to include mental health interventions to better help these patients. It is coherent with previous evidence that show that good mental health is a protective factor of functional decline in subjects suffering from knee osteoarthritis. 50

We believe that one very interesting finding of our study is that contralateral knee pain is associated with worse pain, stiffness, function and HRQoL related to the knee scheduled for replacement surgery. Although no studies have formally identified this kind of association, from a clinical point of view, it seems logical that patients suffering from both knees have a worse condition. Only one study by Merle-Vincent (2007) has looked at that specific factor but the authors did not find a significant association. 18 Clearly, further research is needed to evaluate the effects of bilateral knee pain on patient's status and outcomes while waiting, as well as after knee replacement surgery. However, this phenomenon may have important clinical implication, as conservative treatment in patients waiting for knee replacement could realistically target both knees to maximize patients' status.

Psychological distress was low in this cohort of patients waiting for knee replacement surgery. Nonetheless, it was significantly associated with worse pain, stiffness, function and HRQoL. Other studies have outlined the important role of psychological distress on the health status of patients suffering from knee pain or undergoing knee replacement surgery. 1417 High BMI was also significantly associated with worse pain, function and HRQoL. Other studies have found that BMI is a risk factor for the incidence and progression of knee osteoarthritis 51 and that it is also related to post-operative outcomes. 1528 In terms of treatment, weight-loss therapy and exercise have been found to be beneficial for this population and could be an important component of a prehabilitation program. 52

Low social support was significantly associated with worse mental HRQoL in our study. This finding is compatible with the results published by Ethgen et al. (2004), who found a significant association between social support and mental and physical aspects of HRQoL in subjects suffering from knee osteoarthritis. These authors recommended that physical health interventions should also add a social support component to improve health outcomes in these patients. 53 In our study, subjects married or living in common-law had a better HRQoL compared to single, separated, divorced or widowed subjects. Further adjustment of this regression model with social support did not change the strength of the association between marital status and the role-physical component of HRQoL. Therefore, we believe that this association is more likely to be related to the help of the spouse on coping skills than to an effect of social support. 54

Contrary to what other studies found, sociodemographic factors were not related to pain, stiffness, function or HRQoL in our study. This may results from the fact that in this cohort of Canadian patients, access to surgery is equitable as it is not diminished in subjects of lower socioeconomic backgrounds nor that workers are fast tracked to see the surgeon. 141655

Although the association between longer duration of symptoms and knee stiffness found in our study was small, it is unclear why subjects with longer duration would show less stiffness. Maybe it results from a response shift and possible adaptation to the chronic condition of knee osteoarthritis or arthritis. 56 However this would potentially reflect also in the other sections of the WOMAC, an effect we did not observe.

Several factors were significantly associated with increased pain, stiffness, loss of function and loss of HRQoL in the study subjects. One of the strengths of our study is that many of these independent factors have a consistent effect across the scales of the WOMAC or the SF-36, which further supports the validity of our results. Other strengths include a high participation proportion (81.7%), thorough and relevant independent variables selection and no indication of selection bias (there were no significant differences between participants and eligible non participants on age and gender (data not shown). The regression models were adjusted for age and gender and further adjustments with other potential confounding factors only marginally changed the strength of the associations and were therefore not kept in the final models.

This study used a cross-sectional design and therefore caution is warranted when interpreting our results. Hypothesis related to the causality of the different independent variables on patients' health status need to be validated prospectively. Nonetheless, we believe our results provide valuable information regarding the patients' condition right at their enrollment on pre-surgery waiting list for knee replacement.

Another limitation was that the main outcome measures were self-reported and we did not include performance-based measures. The WOMAC and the SF-36 have been found to be valid instruments; still, it has been reported that performance-based measures provide distinct impressions of pain and function that complement self-reported measures. 57 Therefore, the associations or strength of associations between patients' characteristics and performance-based measures could be different from the findings of our study. Although we found a significant association between low social support and worse mental HRQoL, the social support measure only reflected the size of the social network and not the two other components of social support. Therefore associations or strength of associations with the full validated social support measurement tool could be different. It is important to point out that this study focused on patients scheduled for primary unilateral knee replacement and excluded patients undergoing a revision or with a previous contralateral knee replacement or with a hip replacement, therefore results may differ for these patients.

Conclusion

As seen in this cohort or elsewhere in other Canadian provinces or countries, patients will be waiting for many months, often for more than six months with severe pain, loss of function and poor HRQoL. 6 We acknowledge that actions should be taken to alleviate the burden of patients by reducing wait times but with the growing needs for this surgery, allocation of more resource for surgery alone is unlikely to reach its goal. We believe that other actions are needed to improve pain, function and HRQoL of patients while they are on waiting lists. Although more research is needed to evaluate the full effects of the characteristics identified in the current study, the results of the current study could help identify subjects most in need of prehabilitation and thus may be useful to prioritize patients. Pre-operative assessment already takes place a few weeks before surgery; some of the resource used there could be diverted to meet with patients at the enrollment on the orthopedic wait lists. Patients showing a high BMI, bilateral knee pain, lower social support, poorer HRQoL mental health or high psychological distress could be identified right away and enrolled on a prehabilitation programs while they wait. Further research is needed to evaluate the effects of prehabilitation interventions targeting this population of patients or these factors specifically and could lead to a new model of care for these patients.

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

This paper reports part of the doctoral dissertation in Epidemiology of FD, realized under the supervision of CED and the co-supervision of RB. FD participated in the design, coordination and collection of data. He performed the statistical analyses, led the interpretation of results and drafted the manuscript. CED participated in the design, coordination, interpretation of results and writing of the manuscript. EB participated in the design, coordination and writing of the manuscript. RB participated in the design and writing of the manuscript. PF participated in the collection of data and the writing of the manuscript. All authors read and approved the final version of the paper.

Acknowledgements

F Desmeules is supported by a training fellowship from the Canadian Institutes of Health Research (CIHR). CE Dionne is a senior Quebec Health Research Fund (FRSQ) scholar. The URESP research unit is funded by FRSQ through an infrastructure grant.

Factors affecting length of stay and need for rehabilitation after hip and knee arthroplasty Forrest G Fuchs M Gutierrez A Girardy J J Arthroplasty 1998 13 2 186 190 10.1016/S0883-5403(98)90097-3 9526212 Rheumatology: 10. Joint replacement of the hip and knee – when to refer and what to expect Brady OH Masri BA Garbuz DS Duncan CP Cmaj 2000 163 10 1285 1291 80338 11107466 Canadian Joint Replacement Registry (CJRR) 2007 Annual Report: Hip and Total Knee Replacements in Canada The Canadian Institute for Health Information Ottawa, Ont: CIHI 2008 Surgical Volume Trends, 2008 – Within and Beyond Wait Time Priority Areas The Canadian Institute for Health Information Ottawa, Ont: CIHI 2008 Towards establishing evidence-based benchmarks for acceptable waiting times for joint replacement surgery-Report 2 Noseworthy T Sanmartin C Bohm E Conner-Spady B DeCoster C Dumbar M Lorenzetti D McLaren L McGurran J Calgary: University of Calgary 2005 56 Wait Times Tables – A Comparison by Province, 2008 The Canadian Institute for Health Information Ottawa, Ont: CIHI 2008 Outcomes of total hip and knee replacement: preoperative functional status predicts outcomes at six months after surgery Fortin PR Clarke AE Joseph L Liang MH Tanzer M Ferland D Phillips C Partridge AJ Belisle P Fossel AH Arthritis Rheum 1999 42 8 1722 1728 10.1002/1529-0131(199908)42:8<1722::AID-ANR22>3.0.CO;2-R 10446873 Timing of total joint replacement affects clinical outcomes among patients with osteoarthritis of the hip or knee Fortin PR Penrod JR Clarke AE St-Pierre Y Joseph L Belisle P Liang MH Ferland D Phillips CB Mahomed N Arthritis Rheum 2002 46 12 3327 3330 10.1002/art.10631 12483739 The Development of an Orthopedic Waiting List Algorithm for Elective Total Hip and Total Knee Replacement Surgery Ashworth A Brulé C Day A Harrison M Hopman W Rudan J Canadian Health Services Research Foundation 2002 44 Rehabilitation services after total joint replacement in Ontario, Canada: can 'prehabilitation' programs mediate an increasing demand? Landry MD Jaglal SB Wodchis WP Cooper NS Cott CA Int J Rehabil Res 2007 30 4 297 303 10.1097/MRR.0b013e3282f14422 17975449 The effect of an educational program to improve health-related quality of life in patients with osteoarthritis on waiting list for total knee replacement: a randomized study Nunez M Nunez E Segur JM Macule F Quinto L Hernandez MV Vilalta C Osteoarthritis Cartilage 2006 14 3 279 285 10.1016/j.joca.2005.10.002 16309929 Effect of preoperative exercise on measures of functional status in men and women undergoing total hip and knee arthroplasty Rooks DS Huang J Bierbaum BE Bolus SA Rubano J Connolly CE Alpert S Iversen MD Katz JN Arthritis Rheum 2006 55 5 700 708 10.1002/art.22223 17013852 Pre-operative education for hip or knee replacement McDonald S Hetrick S Green S Cochrane Database Syst Rev 2004 1 CD003526 14974019 Severely compromised quality of life in women and those of lower socioeconomic status waiting for joint replacement surgery Ackerman IN Graves SE Wicks IP Bennell KL Osborne RH Arthritis Rheum 2005 53 5 653 658 10.1002/art.21439 16208653 Health-related quality of life and costs in patients with osteoarthritis on waiting list for total knee replacement Nunez M Nunez E Segur JM Macule F Sanchez A Hernandez MV Vilalta C Osteoarthritis Cartilage 2007 15 3 258 265 10.1016/j.joca.2006.07.011 16962795 Effects of socioeconomic status on patients' outcome after total knee arthroplasty Davis ET Lingard EA Schemitsch EH Waddell JP Int J Qual Health Care 2008 20 1 40 46 10.1093/intqhc/mzm059 18174221 Health-related quality of life in patients waiting for major joint replacement. A comparison between patients and population controls Hirvonen J Blom M Tuominen U Seitsalo S Lehto M Paavolainen P Hietaniemi K Rissanen P Sintonen H Health Qual Life Outcomes 2006 4 3 1373609 16423293 10.1186/1477-7525-4-3 Cross-sectional study of pain and disability at knee replacement surgery for osteoarthritis in 299 patients Merle-Vincent F Couris CM Schott AM Perier M Conrozier S Conrozier T Piperno M Mathieu P Vignon E Joint Bone Spine 2007 74 6 612 616 10.1016/j.jbspin.2007.01.038 17892964 The effect of co-morbidities on health-related quality of life in patients placed on the waiting list for total joint replacement Tuominen U Blom M Hirvonen J Seitsalo S Lehto M Paavolainen P Hietanieni K Rissanen P Sintonen H Health Qual Life Outcomes 2007 5 16 1831765 17362498 10.1186/1477-7525-5-16 A preliminary evaluation of the dimensionality and clinical importance of pain and disability in osteoarthritis of the hip and knee Bellamy N Buchanan WW Clin Rheumatol 1986 5 2 231 241 10.1007/BF02032362 3731718 A comparative study of telephone versus onsite completion of the WOMAC 3.0 osteoarthritis index Bellamy N Campbell J Hill J Band P J Rheumatol 2002 29 4 783 786 11950022 The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC): a review of its utility and measurement properties McConnell S Kolopack P Davis AM Arthritis Rheum 2001 45 5 453 461 10.1002/1529-0131(200110)45:5<453::AID-ART365>3.0.CO;2-W 11642645 The MOS 36-item short-form health survey (SF-36). I. Conceptual framework and item selection Ware JE Jr Sherbourne CD Med Care 1992 30 6 473 483 10.1097/00005650-199206000-00002 1593914 Monitoring health outcomes among patients with arthritis using the SF-36 Health Survey: overview Keller SD Majkut TC Kosinski M Ware JE Jr Med Care 1999 37 5 Suppl MS1 9 10.1097/00005650-199905001-00001 10335739 Comparison of a generic and a disease-specific measure of pain and physical function after knee replacement surgery Bombardier C Melfi CA Paul J Green R Hawker G Wright J Coyte P Med Care 1995 33 4 Suppl AS131 144 7723441 Health related quality of life outcomes after total hip and knee arthroplasties in a community based population Jones CA Voaklander DC Johnston DW Suarez-Almazor ME J Rheumatol 2000 27 7 1745 1752 10914862 The effect of age on pain, function, and quality of life after total hip and knee arthroplasty Jones CA Voaklander DC Johnston DW Suarez-Almazor ME Arch Intern Med 2001 161 3 454 460 10.1001/archinte.161.3.454 11176772 Determinants of function after total knee arthroplasty Jones CA Voaklander DC Suarez-Alma ME Phys Ther 2003 83 8 696 706 12882610 The burden of waiting for hip and knee replacements in Ontario. Ontario Hip and Knee Replacement Project Team Williams JI Llewellyn Thomas H Arshinoff R Young N Naylor CD J Eval Clin Pract 1997 3 1 59 68 10.1111/j.1365-2753.1997.tb00068.x 9238608 Generic and condition-specific outcome measures for people with osteoarthritis of the knee Brazier JE Harper R Munro J Walters SJ Snaith ML Rheumatology (Oxford) 1999 38 9 870 877 10.1093/rheumatology/38.9.870 10515649 Predicting the outcome of total knee arthroplasty Lingard EA Katz JN Wright EA Sledge CB J Bone Joint Surg Am 2004 86-A 10 2179 2186 15466726 Rating chronic medical illness burden in geropsychiatric practice and research: application of the Cumulative Illness Rating Scale Miller MD Paradis CF Houck PR Mazumdar S Stack JA Rifai AH Mulsant B Reynolds CF 3rd Psychiatry Res 1992 41 3 237 248 10.1016/0165-1781(92)90005-N 1594710 Cumulative Illness Rating Scale was a reliable and valid index in a family practice context Hudon C Fortin M Vanasse A J Clin Epidemiol 2005 58 6 603 608 10.1016/j.jclinepi.2004.10.017 15878474 How to measure comorbidity. a critical review of available methods de Groot V Beckerman H Lankhorst GJ Bouter LM J Clin Epidemiol 2003 56 3 221 229 10.1016/S0895-4356(02)00585-1 12725876 A manual of guidelines to score the modified cumulative illness rating scale and its validation in acute hospitalized elderly patients Salvi F Miller MD Grilli A Giorgi R Towers AL Morichi V Spazzafumo L Mancinelli L Espinosa E Rappelli A J Am Geriatr Soc 2008 56 10 1926 1931 10.1111/j.1532-5415.2008.01935.x 18811613 Enquête sociale et de santé 1998 Daveluy C Pica L Audet N Courtemanche R Lapointe F Québec: Institut de la statistique du Québec 2e 2000 «Environnement de Soutien » Chapitre 25 Julien M Julien D Lafontaine P Enquête sociale et de santé 1998 Québec: Institut de la statistique du Québec 2e 1998 Further validation of a psychiatric symptom index in a normal population Ilfeld FW Jr Psychol Rep 1976 39 1215 1228 « Santé Mentale » Chapitre 16 Légaré G Préville M Massé R Poulin C St-Laurent D Boyer R Enquête sociale et de santé 1998 Québec: Institut de la statistique du Québec 2e 1998 La détresse psychologique: détermination de la fiabilité et de la validité de la mesure utilisée dans l'Enquête Santé Québec Préville M Boyer R Potvin L Perrault C G L Les cahiers de la recherche, 7, Enquête Santé Québec 87, Gouvernement du Québec, Ministère de la Santé et des Services Sociaux 1992 SF-36 Health Survey: Manual & Interpretation Guide Ware JE Jr Kosinski M Gandek B Lincoln, RI: QualityMetric Incorporated 1993 2000 Modern Epidemiology Rothman K Greenland S Philadelphia: Lippincott Williams & Wilkins 2 1998 Rank transformations as a bridge between parametric and nonparametric statistics Conover W Iman R Am Stat 1981 35 3 124 130 10.2307/2683975 Change in pain and function while waiting for major joint arthroplasty Kelly KD Voaklander DC Johnston DW Newman SC Suarez-Almazor ME J Arthroplasty 2001 16 3 351 359 10.1054/arth.2001.21455 11307134 Smallest detectable and minimal clinically important differences of rehabilitation intervention with their implications for required sample sizes using WOMAC and SF-36 quality of life measurement instruments in patients with osteoarthritis of the lower extremities Angst F Aeschlimann A Stucki G Arthritis Rheum 2001 45 4 384 391 10.1002/1529-0131(200108)45:4<384::AID-ART352>3.0.CO;2-0 11501727 Minimal perceptible clinical improvement with the Western Ontario and McMaster Universities osteoarthritis index questionnaire and global assessments in patients with osteoarthritis Ehrich EW Davies GM Watson DJ Bolognese JA Seidenberg BC Bellamy N J Rheumatol 2000 27 11 2635 2641 11093446 Obesity: preventing and managing the global epidemic. Report of a WHO Consultation. WHO Technical Report Series 894 WHO Geneva: World Health Organization 2000 [Psychological distress in a noninstitutionalized population of Quebec: normative results of the Quebec health survey] Boyer R Preville M Legare G Valois P Can J Psychiatry 1993 38 5 339 343 8348474 Canadian normative data for the SF-36 health survey. Canadian Multicentre Osteoporosis Study Research Group Hopman WM Towheed T Anastassiades T Tenenhouse A Poliquin S Berger C Joseph L Brown JP Murray TM Adachi JD Cmaj 2000 163 3 265 271 80287 10951722 Physical functioning over three years in knee osteoarthritis: role of psychosocial, local mechanical, and neuromuscular factors Sharma L Cahue S Song J Hayes K Pai YC Dunlop D Arthritis Rheum 2003 48 12 3359 3370 10.1002/art.11420 14673987 Body mass index associated with onset and progression of osteoarthritis of the knee but not of the hip: the Rotterdam Study Reijman M Pols HA Bergink AP Hazes JM Belo JN Lievense AM Bierma-Zeinstra SM Ann Rheum Dis 2007 66 2 158 162 10.1136/ard.2006.053538 16837490 Intensive weight loss program improves physical function in older obese adults with knee osteoarthritis Miller GD Nicklas BJ Davis C Loeser RF Lenchik L Messier SP Obesity (Silver Spring) 2006 14 7 1219 1230 10.1038/oby.2006.139 16899803 Social support and health-related quality of life in hip and knee osteoarthritis Ethgen O Vanparijs P Delhalle S Rosant S Bruyere O Reginster JY Qual Life Res 2004 13 2 321 330 10.1023/B:QURE.0000018492.40262.d1 15085904 Effects of spouse-assisted coping skills training and exercise training in patients with osteoarthritic knee pain: a randomized controlled study Keefe FJ Blumenthal J Baucom D Affleck G Waugh R Caldwell DS Beaupre P Kashikar-Zuck S Wright K Egert J Pain 2004 110 3 539 549 10.1016/j.pain.2004.03.022 15288394 The influence of income and race on total knee arthroplasty in the United States Skinner J Zhou W Weinstein J J Bone Joint Surg Am 2006 88 10 2159 2166 10.2106/JBJS.E.00271 17015592 'I suppose that depends on how I was feeling at the time': perspectives on questionnaires measuring quality of life and musculoskeletal pain Ong BN Hooper H Jinks C Dunn K Croft P J Health Serv Res Policy 2006 11 2 81 88 10.1258/135581906776318938 16608582 Modeling early recovery of physical function following hip and knee arthroplasty Kennedy DM Stratford PW Hanna SE Wessel J Gollish JD BMC Musculoskelet Disord 2006 7 100 1712335 17156487 10.1186/1471-2474-7-100

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