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RehabMeasures Instrument

Western Ontario and McMaster Universities Osteoarthritis Index

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Purpose

The WOMAC is a widely used self-administered health status measure used in assessing pain, stiffness, and function in patients with OA of the hip or knee. The WOMAC has also been used to assess back pain, rheumatoid arthritis, juvenile rheumatoid arthritis, systemic lupus erythematosus, and fibromyalgia.

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Instrument Details

Acronym WOMAC

Area of Assessment

Activities of Daily Living
Functional Mobility
Gait
General Health
Pain
Quality of Life

Assessment Type

Patient Reported Outcomes

Administration Mode

Paper & Pencil

Cost

Not Free

Cost Description

Varies depending on research study

Diagnosis/Conditions

  • Arthritis + Joint Conditions
  • Pain Management

Key Descriptions

  • Widely used self-administered health status measure assessing pain, stiffness, and function in patients with OA of the hip or knee.
  • The WOMAC measures three separate dimensions:
    1) Pain (5 questions)
    2) Stiffness (2 questions)
    3) Function (17 questions)
  • The original WOMAC is available in two formats, Visual Analog Scales and Likert-boxes, with similar metric properties.

Number of Items

24

Equipment Required

  • Pen or pencil
  • Copy of Outcome Measure

Time to Administer

12 minutes

Required Training

Reading an Article/Manual

Age Ranges

Adolescent

13 - 17

years

Adult

18 - 64

years

Elderly Adult

65 +

years

Instrument Reviewers

Initially reviewed by Khiem Bui, SPT, Dale Hamilton, SPT, Gary Johnson, SPT, Michael Murray, SPT, Andrew Newman, SPT, Jonathan Samuelson, SPT, Lorna Troost, SPT,  and Briarly White, SPT in November 2013.

Body Part

Lower Extremity

ICF Domain

Body Function
Activity
Participation

Measurement Domain

Activities of Daily Living
General Health

Professional Association Recommendation

Recommendations for use based on acuity level of the patient:

Van der Wees (2001)

  • APTA has no specific recommendations regarding the WOMAC, though the president released a letter/position statement August 2012 on CMS’s proposal for G-Code classification procedures arguing for severity level to be determined by therapists using patient response to multiple standardized measures selected for individualized appropriateness, both performance measures and patient report measures; the WOMAC was one of the example measures used to illustrate the point. 

Recommendations for entry-level physical therapy education and use in research:

Whitehouse (2007)

  • Alternative scale and scoring exist. It is proposed that where 1 or 2 items are missing, the average value for the sub-scale is substituted in lieu of these missing values. The reduced WOMAC function scale provides an alternative which will limit the number of missing values, and hence the number of invalid WOMAC scores. This has important implications when considering power studies for smaller studies, and the impact of questionnaire choice on compliance and duplication of data, as well as data completion, collection and analysis. A valid score could be calculated for the reduced-scale, but not for the full-scale questionnaire. Items with high frequencies of missing values were removed from the scale, so the number of missing values was reduced and the influence of each item on the score increased proportionately (from 6% to 14% per item). Hence, the impact of missing items was larger for the reduced scale questionnaire. 

Pua (2008)

  • Although larger sample sizes are needed to establish many of the findings in a convincing way, it would appear appropriate, in the interim, to at least include the LEFS alongside the WOMAC-PF in future clinical studies. 

Davis (2009)

  • This study provides evidence of construct validity and responsiveness of the measures as compared to the longer WOMAC Likert 3.0 PF subscale suggesting that these short measures are viable and maintain their psychometric quality for use in joint replacement, particularly when respondent burden and feasibility are of concern. This study supports the conclusion that WOMAC PF subscale includes redundant items that provide little additional information as the correlations amongst the three measures of PF were high (range 0.85-0.90), irrespective of the hip or knee sample, suggesting that the measures are providing similar information. 

Soohoo (2007)

  • The WOMAC may be more sensitive to change than the SF-36 when it comes to non-operative treatment of the hip. 

Heintjes (2008)

  • The WOMAC showed moderate to high responsiveness with adolescents and high responsiveness with young adult populations in general practice with complaints of knee pain.

Considerations

Escobar (2007)

  • The MCID for TKR is around 15 on WOMAC, while with the SF-36 of at least 10 points. These values should not be considered as absolute thresholds. 

Tubach (2005)

  • MCID is different for different scores on the exam: The higher the baseline score, the larger the MCII. Patients who have a severe symptom need a higher level of change to consider themselves clinically improved than those with less severe symptoms.

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Musculoskeletal Conditions

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Standard Error of Measurement (SEM)

Hip OA:

Pua (2008; n = 100; mean age = 62 (10) years)

  • SEM = 3.3 (on a scale of 0-50) 

 

Knee OA: 

Williams (2007; n = 2012: 2 month n = 159; 6 month n = 153; 12 month = 142; mean age = 63.9 years)

  • SEM : 2 months = 5.1; 6 months = 5.4; 12 months = 6.7 (on a scale 0-100) 

 

Hip/Knee OA:

Stratford (2007; n = 474; mean age 63.5 (10.3) years)

  • SEMIC = 1.48
  • SEMTCT = 1.69 (on a scale 0-100). 

 

TKR: 

Greco (2010; n = 63; mean age = 41.5 years) 

  • SEM = 3.9 at 6 months (on a scale of 0-50)
  • SEM = 5.5 at 12 months (on a scale of 0-50) 

Escobar (2007; n = 364; mean age = 71.6 years) 

  • SEM at 6 months post TKR = 8.08 (pain subscale), 10.50 (stiffness subscale), 4.73 (physical function subscale) (on a scale of 0-50) 

 

THR:

Quintana (2005; n = 469; mean age = 69.4 years (8.8); Charlson comorbidity index 1 = 29%, CCI 2 = 9.6%)

  • At 6 months: Pain = 7.71, function = 4.30, stiffness = 10.10 (on a scale 0-100). 

 

POAD:

Davidson (2011; = 83; mean age = 27 years)

  • Pain = 2.37; Function = 3.91; Stiffness = 0.84

Minimal Detectable Change (MDC)

Hip OA:

Pua (2008)

  • Physical performance MDC95 = 9.1points (on a scale of 0-50) 

 

Knee OA: 

Williams (2007) 

  • MDC95 at 2 months = 14.1 (on a scale of 0-100)
  • MDC95 at 6 months = 15.0 (on a scale of 0-100) 
  • MDC95 at 12 months = 18.5 (on a scale 0-100) 

 

Hip and Knee OA:

Stratford (2007)

  • MDC90 of pain= 3.94 (on a scale 0-100). 

 

TKR:

Greco (2010)

  • MDC95 = 10.9 at 6 months (on a scale of 0-50)
  • MDC95 = 15.3 at 12 months (on a scale of 0-50) 

Escobar (2007) 

  • MDC% at 6 months = 66.18% for pain subscale, 76.92% for physical function subscale and 43.41% for stiffness subscale (on a scale of 0-100%). 
  • MDC% at 2 years = 70.34% for pain subscale, 78.43% for physical function subscale and 51.40% for stiffness subscale (on a scale of 0-100%). 

 

THR:

Quintana (2005)

  • MDC90 of pain = 21.38; function = 11.93; stiffness = 27.98 (on a scale 0-100). 

 

POAD:

Davidson (2011)

  • MDC90 of pain = 5.51; function = 9.10; stiffness = 1.96 (on a scale 0-100).

Minimally Clinically Important Difference (MCID)

Knee OA: 

Williams (2007) 

  • MCID at 2 months (method 1 = 4.0; method 2 = 8.8)
  • MCID at 6 months (method 1 = 6.6; method 2 = 6.8)
  • MCID at 12 months (method 1 = 1.6; method 2 = 12.0) (on a scale 0-100). 

Tubach (2005; = 265 with “good” response to treatment; age 64.6 (10.2)) 

  • Minimal clinically important improvement (MCII): -7.9 (with a 95% CI: -8.8 to -5). 
  • Low Baseline (scores less than or equal to 35.3): - 2.6 (with a 95% CI: -4.4 to -0.5). 
  • Intermediate (scores 35.4 to 51.4): -14.8 (with a 95% CI: -17.0 to -12.0). 
  • High (scores >51.5): -15.1 (--18.9 to --10.0) (on a scale 0-100). 

 

Hip OA:

Tubach (2005, = 67 with “good” response to treatment) Initial assessment with f/u after 4 weeks; Levels for Absolute change as well as baseline initial scores of low, intermediate, and high initial severity. 

  • Minimal clinically important improvement (MCII) -9.1 (with a 95% CI: -10.5 to -7.5). 
  • Low Baseline (scores less than or equal to 35.3): -5.3 (with a 95% CI: -6.5 to -3.8). 
  • Intermediate (scores 35.4 to 51.4): -11.8 (with a 95% CI: -13.0 to -10.4). 
  • High (scores >51.5): -20.4 (-22.5 to -18.11) (on a scale 0-100). 

 

TKR:

Greco (2010) 

  • MCID = 11.5 at 6 months (on a scale of 0-50) 
  • MCID = 11.5 at 12 months (on a scale of 0-50) 

Escobar (2007) 

  • MCID% at 6 months = 66.18% for pain subscale, 68.75% for physical function subscale and 59.71% for stiffness subscale (on a scale of 0-100%). 
  • MCID% at 2 years = 63.84% for pain subscale, 64.43% for physical function subscale and 66.57% for stiffness subscale (on a scale of 0-100%). 

 

THR:

Quintana (2005): 

  • MCID for stiffness = 25.91; pain = 29.26 (on a scale of 0-100).

Cut-Off Scores

Knee OA: 

Williams (2007)

  • ROC Analysis at 2 months = 0.70 (0.62, 0.79) 
  • ROC Analysis at 6 months = 0.72 (0.64, 0.80)
  • ROC Analysis at 12 months = 0.70 (0.61, 0.79)

Test/Retest Reliability

THR and TKR:

Whitehouse (2007)

  • Full pain:
    • Excellent test-retest reliability (ICC = 0.77) - measured with Spearmans Rho
  • Full function:
    • Excellent test-retest (ICC = 0.79) – measured with Spearmans Rho. 

 

TKR:

Greco (2010)

  • Excellent test-reliability (ICC 0.91) – measured at 6 months
  • Excellent test-reliability (ICC 0.86) – measured at 12 months 

 

Hip OA:

Pua (2008)

  • Excellent test-retest reliability (ICC = 0.90)

Basaran (2010)

  • Excellent test-retest reliability (ICC 0.77-0.94)

 

Knee OA:

Basaran (2010)

  • Excellent test-retest reliability (ICC 0.80-0.98) 

Williams (2007)

  • Excellent test-retest reliability [ICC at 2 months = .90(.76, .95); 6 months = .88 (.76, .94); 12 months = .81 (.63, .91)] 

 

Hip and Knee OA:

Stratford (2007)

  • Excellent, test-retest reliability (ICC 0.77)

Internal Consistency

Hip OA:

Basaran (2010, n = 44; mean age 64.7 ± 9.3)

  • Excellent internal consistency: (Cronbach alpha = 0.95) 

 

Knee OA:

Basaran (2010, n = 73; mean age 59.6 ± 9.6)

  • Excellent internal consistency: (Cronbach alpha = 0.95) 

 

Hip and/or Knee OA: 

Brooks (2004, n = 125)

  • Excellent internal consistency (mean Cronbach alpha = 0.98)

Stratford (2007)

  • Excellent, internal consistency (Cronbach alpha of pain = 0.84) 

 

TKR:

Escobar (2007, n = 364; mean age 71.6 ± 6.7)

  • Excellent internal consistency: (Cronbach alpha = 0.81 (pain), 0.93 (functional limitation), 0.81 (stiffness) 

 

THR:

Kapstad (2010, mean age = 69± 10) 

  • Pain (N = 203)
    • Excellent internal consistency (Cronbach alpha = .87)
  • Stiffness (N = 203)
    • Excellentinternal consistency (Cronbach alpha = .84)
  • Physical function (N = 202)
    • Excellent internal consistency (Cronbach alpha = .96)

Quintana (2005)

  • Excellent internal consistency: Cronback alpha = 0.83 (pain), 0.93 (function), 0.81 (stiffness).

Construct Validity

Hip OA: 

Pua (2008) 

  • Excellent construct validity with SF-36 Physical function (PF) (= 0.73)
  • Excellent construct validity with SF-36 Bodily pain (BP) (r = 0.64)
  • Adequate construct validity with Gait speed test (r = 0.32)
  • Adequate construct validity with Step test (r = 0.38)
  • Adequate negative construct validity with Timed stair test self-paced (= 90) (r = -0.46)
  • Adequate negative construct validity with Timed stair test fast paced (n = 90) (= -0.48) 

Basaran (2010)

  • Excellent negative construct validity with SF-36 Physical Function (PF) (r = -0.73)
  • Excellent negative construct validity with SF-36 Bodily Pain (BP) (r = -0.67) 

Bijsterboch (2010)

  • Adequate positive construct validity with Doyle pain index (n = 260) (r = 0.51)
  • Adequate positive construct validity with Doyle functional index (n = 260) (r = 0.49) 

 

Knee OA:

Basaran (2010

  • Excellent negative construct validity with SF-36 Physical Function (PF) (r = -0.73)
  • Excellent negative construct validity with SF-36 Bodily Pain (BP) (= -0.67) 

 

Hip and/or Knee OA:

Bruce (2004; n = 271; mean age = 65.7 (0.6) years; disease duration = 14.1 (0.7) years)

  • Excellent construct validity of WOMAC pain subscale to HAQ pain (r = 0.76)
  • Excellent construct validity of WOMAC function subscale to HAQ DI (r = 0.79)
  • Adequate construct validity of WOMAC function subscale to TKS (r = 0.49)
  • Excellent construct validity of WOMAC function subscale to patient global (r = 0.75)
  • Excellent construct validity of WOMAC pain subscale to patient global (r = 0.76)
  • Excellent construct validity of WOMAC stiffness subscale to patient global (r = 0.61) 

Brooks (2004)

  • Excellent construct validity of WOMAC total scale with COAT total scale (r = 0.92)
  • Excellent construct validity of WOMAC pain scale with COAT pain scale (r = 0.853)
  • Excellent construct validity of WOMAC stiffness scale with COAT stiffness scale (r = 0.844)
  • Excellent construct validity of WOMAC function scale with COAT difficulties scale (r = 0.890) 

 

THR:

Davis (2009)

  • Excellent construct validity of WOMAC pain subscale (PS) to HOOS-PS (= 0.70)
  • Excellent construct validity of WOMAC pain subscale to WOMAC physical function (PF) (= 0.80)
  • Excellent construct validity of WOMAC pain subscale to WOMAC PF-exclusions (r = 0.80) 

Kapstad (2010)

  • Excellent positive construct validity of WOMAC (PS) to BPI (PS) (r = .66)
  • Poor positive construct validity of WOMAC stiffness scale and BPI stiffness scale (r = .26)
  • Adequate positive construct validity between WOMAC function and BPI function (r = .57) 

 

TKR:

Davis (2009)

  • Excellent construct validity of WOMAC pain subscale to HOOS-PS (r = 0.73)
  • Excellent construct validity of WOMAC pain subscale to WOMAC PF (= 0.80)
  • Excellent construct validity of WOMAC pain subscale to WOMAC PF exclusions (= 0.78)

Content Validity

Hip and/or Knee OA:

Bruce (2004)

  • Authors determined the language on certain function scale items (e.g. “bending to floor” or lack of conjunction in items such as “getting on/off toilet”) to be ambiguous and thus open to variable interpretations, which has been previously reported to negatively impact reliability and sensitivity to change relative to more precisely worded items. Lawshe content validity ratios were not calculated.

Face Validity

Hip and/or Knee OA: 

Bruce (2004)

  • Authors found that the 5 items of the WOMAC pain scale consist of function-based behaviors that suggest disability measure attributes versus purely pain, that they are general behaviors rather than those specific to hip or knee OA (e.g., squatting, full joint straightening). 
  • For the function scale, authors judged it questionable as to why a disease-specific scale for knee and hip OA would include more items assessing both upper and lower extremity function than lower extremity function specifically.

Floor/Ceiling Effects

Hip OA:

Pua (2008)

  • Excellent, no participants scored the lowest or highest possible scores on the WOMAC or LEFS, that is, floor and ceiling effects were not present for both measures. Moreover, less than 10% of the participants had initial WOMAC-PF or LEFS scores that did not allow sufficient detection of deterioration or improvement on the retest. This indicates that both measures possess adequate and relatively equivalent scale width. 

 

TKR:

Escobar (2007)

  • Adequate, WOMAC had minor floor and ceiling effect (less than 15% of patients in the worst or best possible score of each domain) before the intervention. The ceiling effect was increasing until 2 years while the floor was constant across time. 

 

General Knee Pain:

  • Adequate, the WOMAC subscores for pain and function showed acceptable ceiling effects ranging from 5.2% (traumatic) to 9.2% (non-traumatic) and from 6.9% (traumatic) to 14.2% (non-traumatic) respectively

  • Poor, the stiffness subscore showed an unacceptable ceiling effect of 40% for non-traumatic patients. 

 

THR:

Kapstad (2010)

  • On the WOMAC subscales at baseline, floor and ceiling effects were minor. One year after THR, the floor effect was larger on all three WOMAC subscales, but most marked on the pain and stiffness subscales.

Quintana (2005)

  • Poor floor effects at 6 months (pain = 25.20%, stiffness = 30.91) and 2 years (pain = 39.54%, stiffness = 46.91%)
  • Adequate floor effects for function at 6 months (4.86%) and 2 years (8.52%)
  • Excellent ceiling effects at 6 months (pain = 0.27%, function = 0.00% stiffness = 0.54%) and 2 years (pain = 0.33%, function = 0.00% stiffness = 0.33%).

Responsiveness

Hip and/or Knee OA:

Bruce (2004)

  • Small standardized effect size at average follow-up of 3.2 (0.10) years = -0.05 (physical function subscale), -0.10 (pain subscale), -0.15 (stiffness subscale)

Brooks (2004)

  • Moderate standardized effect size for WOMAC total scale from baseline to 12 weeks = 0.63
  • Standardized response mean for WOMAC total scale at 12 weeks = 7.73 

 

THR:

Whitehouse (2007)

  • Large long term effect size: 3 years, THR = 78.6 (SD = 18.9)

Davis (2009)

  • Standardized response mean for WOMAC PF: pre-surgery to 6 months post-surgery, THR = 1.7

Soohoo (2007)

  • Large effect size: minimum 5 month post-operative follow up, THR = -1.51 (global subscale), -1.53 (pain subscale), -1.02 (stiffness subscale), 1.37 (physical function subscale)

Soohoo (2007)

  • SRM: minimum 5 month post-operative follow up, THR = -1.49 (global subscale), -1.40 (pain subscale), -0.93 (stiffness subscale), -1.37 (physical function subscale) 

Kapstad (2010)

  • Large effect size: Baseline to 1 year, THR = -2.69 (pain subscale), -2.28 (stiffness subscale), -2.61 (functional subscale).

Davis (2010)

  • SRM: 6 months post-op, THR = 1.20 (pain subscale) 

Blanchard (2003; n = 90; mean age = 68.13 (8.15) years; mean hip disease duration = 6.48 (7.27) years)

  • At follow-up of mean 3.82 months pre to post-THA, large effect size = 2.92 (total scale), 2.72 (pain), 2.02 (stiffness), 2.73 (function)
  • SRM = 2.45 (total), 2.37 (pain), 1.79 (stiffness), 2.34 (function)
  • Guyatt’s statistic = 11.95 (total), 6.69 (pain), 6.27 (stiffness), 16.96 (function)
  • Paired-sample t-test = 23.25 (total), 22.47 (pain), 17.41 (stiffness), 22.24 (function)

Quintana (2005)

  • Large effect size at 6 months (pain = 2.10, function = 2.34, stiffness = 1.61)
  • Large effect size at 2 years (pain = 2.24, function = 2.58, stiffness = 1.81) 

 

TKR:

Whitehouse (2007)

  • Large long term Effect size:3 months, TKR = 70.0 (SD = 18.8) 
  • Large long term Effect size:12 months, TKR = 73.8 (SD = 20.6)

Davis (2009)

  • Standardized response mean for WOMAC PF: pre-surgery to 6 months post-surgery, TKR = 1.5

Greco (2010)

  • Large effect size: 6 months, TKR = 0.96 
  • Large effect size: 12 months, TKR = 1.19

Escobar (2007)

  • Effect size: 6 months post TKR = 1.71 (pain subscale), 1.13 (stiffness subscale), 1.58 (physical function subscale). 
  • Effect size at 2 years post TKR = 1.86 (pain subscale), 1.32 (stiffness subscale), 1.69 (physical function subscale)

Escobar (2007)

  • SRM 6 months post TKR = 1.46 (pain subscale), 0.90 (stiffness subscale), 1.31 (physical function subscale). 
  • SRM 2 years post TKR = 1.55 (pain subscale), 1.03 (stiffness subscale), 1.32 (physical function subscale)

Escobar (2007)

  • Guyatt’s Responsiveness statistic 6 months post TKR = 1.20 (pain subscale), 0.56 (stiffness subscale), 1.16 (physical function subscale). 
  • Guyatt’s Responsiveness statistic 2 years post TKR = 1.74 (pain subscale), 0.62 (stiffness subscale), 0.77 (physical function subscale)

 

General Knee Pain:

Heintjes (2008)

  • Moderate to Large effect size: average of 1 year follow up = 0.84 (global pain subscale), 0.92 (pain subscale), 0.62 (stiffness subscale), 0.77 (physical function subscale)

Heintjes (2008)

  • SRM average of 1 year follow up = 0.83 (global pain subscale), 0.96 (pain subscale), 0.66 (stiffness subscale), 0.75 (physical function subscale)

Heintjes (2008)

  • Guyatt’s Responsiveness statistic average of 1 year follow up = 1.27 (global pain subscale), 0.92 (pain subscale), 0.87 (stiffness subscale), 1.27 (physical function subscale) 

 

POAD:

Davidson (2011)

  • Large effect size: pain = 1.49; function = 0.94; stiffness = 0.97)

Bibliography

Basaran, Sibel, Guzel, Rengin, Seydaoglu, Gulsah, & Guler-Uysal, Fusun. (2010). Validity, reliability, and comparison of the WOMAC osteoarthritis index and Lequesne algofunctional index in Turkish patients with hip or knee osteoarthritis. Clinical rheumatology, 29(7), 749-756.

Bijsterbosch, J, Wassenaar, MJE, le Cessie, S, Slagboom, PE, Rosendaal, FR, Huizinga, TWJ, & Kloppenburg, M. (2010). Doyle Index is a valuable additional pain measure in osteoarthritis. Osteoarthritis and Cartilage, 18(8), 1046-1050. 

Blanchard, Chris, Feeny, David, Mahon, Jeffrey L, Bourne, Robert, Rorabeck, Cecil, Stitt, Larry, & Webster-Bogaert, Susan. (2003). Is the health utilities index responsive in total hip arthroplasty patients? Journal of clinical epidemiology, 56(11), 1046-1054.

Brooks, Lyndon O, Rolfe, Margaret I, Cheras, Phillip A, & Myers, Stephen P. (2004). The comprehensive osteoarthritis test: a simple index for measurement of treatment effects in clinical trials. The Journal of rheumatology, 31(6), 1180-1186. 

Bruce, Bonnie, & Fries, James. (2004). Longitudinal comparison of the Health Assessment Questionnaire (HAQ) and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Arthritis Care & Research, 51(5), 730-737.

Davidson, Darin, Yen, Yi-Meng, Jette, Alan M, Olarsch, Sippy, & Kim, Young-Jo. (2011). Responsiveness of the SF-36 and WOMAC Following Periacetabular Osteotomy for Acetabular Dysplasia. The Journal of Bone & Joint Surgery, 93(23), 2214-2218.

Davis, Aileen M, Perruccio, Anthony V, Canizares, Mayilee, Hawker, Gillian A, Roos, Ewa M, Maillefert, J-F, & Lohmander, L Stefan. (2009). Comparative, validity and responsiveness of the HOOS-PS and KOOS-PS to the WOMAC physical function subscale in total joint replacement for osteoarthritis. Osteoarthritis and Cartilage, 17(7), 843-847.

Davis, AM, Lohmander, LS, Wong, R, Venkataramanan, V, & Hawker, GA. (2010). Evaluating the responsiveness of the ICOAP following hip or knee replacement. Osteoarthritis and Cartilage, 18(8), 1043-1045.

Escobar, A, Quintana, JM, Bilbao, A, Arostegui, I, Lafuente, I, & Vidaurreta, I. (2007). Responsiveness and clinically important differences for the WOMAC and SF-36 after total knee replacement. Osteoarthritis and Cartilage, 15(3), 273-280.

Greco, Nicholas J, Anderson, Allen F, Mann, Barton J, Cole, Brian J, Farr, Jack, Nissen, Carl W, & Irrgang, James J. (2010). Responsiveness of the International Knee Documentation Committee Subjective Knee Form in comparison to the Western Ontario and McMaster Universities Osteoarthritis Index, modified Cincinnati Knee Rating System, and Short Form 36 in patients with focal articular cartilage defects. The American journal of sports medicine, 38(5), 891-902.

Heintjes, EM, Bierma-Zeinstra, SMA, Berger, MY, & Koes, BW. (2008). Lysholm scale and WOMAC index were responsive in prospective cohort of young general practice patients. Journal of clinical epidemiology, 61(5), 481-488. 

Kapstad, Heidi, Rokne, Berit, & Stavem, Knut. (2010). Psychometric properties of the Brief Pain Inventory among patients with osteoarthritis undergoing total hip replacement surgery. Health and quality of life outcomes, 8(1), 1-8.

Pua, Yong-Hao, Cowan, Sallie M, Wrigley, Tim V, & Bennell, Kim L. (2009). The Lower Extremity Functional Scale could be an alternative to the Western Ontario and McMaster Universities Osteoarthritis Index physical function scale. Journal of clinical epidemiology, 62(10), 1103-1111.

Quintana, JM, Escobar, A, Bilbao, A, Arostegui, I, Lafuente, I, & Vidaurreta, I. (2005). Responsiveness and clinically important differences for the WOMAC and SF-36 after hip joint replacement. Osteoarthritis and Cartilage, 13(12), 1076-1083. 

SooHoo, Nelson Fong, Vyas, Raj M, Samimi, David B, Molina, Ricardo, & Lieberman, Jay R. (2007). Comparison of the responsiveness of the SF-36 and WOMAC in patients undergoing total hip arthroplasty. The Journal of arthroplasty, 22(8), 1168-1173. 

Stratford, PW, Kennedy, DM, Woodhouse, LJ, & Spadoni, GF. (2007). Measurement properties of the WOMAC LK 3.1 pain scale. Osteoarthritis and cartilage, 15(3), 266-272. 

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