Keywords
Summary and introduction
The Intermittent and Constant Osteoarthritis Pain (ICOAP)
1
questionnaire for the knee (a version for the hip is also available) is a patient-reported pain measure which was developed to assess patients with knee osteoarthritis (OA). Constant and intermittent pain were regarded as relevant by OA patients in a focus group study2
. The development of this measure of pain intensity and impact on quality of life was part of a broader Osteoarthritis Research Society International (OARSI) and Outcome Measures in Rheumatology (OMERACT) initiative3
. The ICOAP is available in several languages1
, 4
, 5
, and is reliable and valid1
, 4
, 6
. The responsiveness of this measure was also previously demonstrated, but only in patients undergoing total joint replacement6
, 7
. Since physical therapy plays an active role in the conservative management of knee OA8
, the responsiveness of the ICOAP after physical therapy needed to be tested. The aim of the present paper was to evaluate the responsiveness of the ICOAP after physical therapy for knee OA. The responsiveness study demonstrated that the ICOAP subscales (constant and intermittent) and total pain score were able to detect changes over 4 weeks of physical therapy.Methods, results and discussion
Methods
Subjects
The sample comprised 109 consecutive patients with symptomatic knee OA, attending seven physical therapy outpatient clinics in Portugal during a 6-month period. Subjects were selected after obtaining informed consent and checking the inclusion and exclusion criteria. To be included in this responsiveness study, subjects had to: have a diagnosis of uni- or bilateral knee OA (validated by a physician) according to the clinical and radiographic criteria of the American College of Rheumatology
9
; to experience knee pain; to be aged 50 years or older; and to start an individually delivered physical therapy intervention for the knee with a probable duration of at least 4 weeks. Subjects were excluded if they: had received physical therapy interventions or intra-articular injections (for the knee) within the previous 30 days; had other disease of the bones and joints of the lower limb; neurological disease or any other disabling condition (e.g., back problems or widespread pain); or if they were not Portuguese-speaking. All physical therapy outpatient clinics obtained approval from their respective review boards.- Altman R.
- Asch E.
- Bloch D.
- Bole G.
- Borenstein D.
- Brandt K.
- et al.
Development of criteria for the classification and reporting of osteoarthritis. Classification of osteoarthritis of the knee. Diagnostic and Therapeutic Criteria Committee of the American Rheumatism Association.
Arthritis Rheum. 1986; 29: 1039-1049
Measurements
Measurements were carried out at the above-mentioned clinics. The entire sample was assessed during the first visit for a physical therapy intervention using the Portuguese ICOAP and a form detailing the characteristics of the patients (gender, age, body mass index, involved knee, duration of knee OA, and walking aids). The entire sample was assessed again 4 weeks later using the Portuguese ICOAP and Global Rating of Change Scale (GRCS). A 4-week interval was chosen because it corresponds to the typical duration of physical therapy treatments for knee OA in Portugal. No attempt was made to standardize the physical therapy treatments (mainly exercise and manual therapy). All measures were interviewer-administered by trained physical therapists.
The ICOAP
1
contains 11 items that are combined in two subscales: constant pain and intermittent pain. A score is separately produced for the constant pain subscale (0–20) and the intermittent pain subscale (0–24), and for total pain (0–44) according to the ICOAP user's guide, available on the OARSI website (http://www.oarsi.org/). Normalized scores for the two subscales and for the total pain score, from 0 (no pain) to 100 (extreme pain), were calculated by summing the response values of the included items, dividing this sum by the maximal possible score and multiplying this quotient by 100. The ICOAP has been cross-culturally adapted and validated for use in Portugal4
.The GRCS
10
is a 15-point Likert scale used to assess the patient-perceived deterioration or improvement following an intervention, ranging from −7 (a very great deal worse) to +7 (a very great deal better). The GRCS included a single question about change in disease-specific health status after 4 weeks of physical therapy for knee OA. The response burden for patients was minimal.Statistical analyses
The Wilcoxon test was used to compare pre- and post-treatment ICOAP subscales and total pain scores. The effect size of 4 weeks of physical therapy was evaluated using the standardized effect size (SES) and standardized response mean (SRM). The 95% confidence intervals (CI) were calculated based on 1000 bootstrap samples. The effect sizes were interpreted as large (≥0.80), moderate (≥0.50) or small (≥0.20). The Wilcoxon test was also used to compare SES and SRM among ICOAP subscales and total pain. A P value of 0.05 was taken as the reference level of significance.
Spearman's correlation coefficients were used to correlate the change scores for the ICOAP subscales and total pain score with the GRCS score
11
. Since these measures assess overlapping but different constructs, it was hypothesized that the change scores for the ICOAP subscales and total pain should correlate at least fairly (negatively) with the GRCS score. Spearman's correlation coefficients were read as follows: excellent relationship if higher than 0.90; good if between 0.90 and 0.71; fair if between 0.70 and 0.51; weak if between 0.50 and 0.31; little or none if lower than 0.30. The presence of floor and ceiling effects compromises the responsiveness of a measure. Floor effects were considered to be present when more than 15% of the patients received the lowest possible score on pre-treatment ICOAP subscales and total pain12
. Ceiling effects were considered to be present when more than 15% of the patients received the highest possible score on pre-treatment ICOAP subscales and total pain score12
. Statistical analyses were performed using SPSS 18.0 for Windows.Results
Pre-treatment characteristics of the patients and post-treatment patient-perceived improvement are presented in Table I. A total of 109 patients were included in the responsiveness assessment. There were no missing data for any individual items of the ICOAP. Thus, a score could be obtained for ICOAP subscales and total pain for all patients. After physical therapy, 55 (55.5%) patients reported at least moderate improvement (score higher or equal to 4) on the GRCS.
Table IPre-treatment characteristics of the patients and post-treatment patient-perceived improvement (N = 109)
| Variables | Data |
|---|---|
| Pre-treatment | |
| Gender | |
| Female | 66 (60.6) |
| Age (years) | 68.0 ± 8.4 (50.0–80.0) |
| Body mass index (kg/m2) | 29.9 ± 4.5 (19.3–42.5) |
| Involved knee (knee with OA) | |
| Bilateral | 69 (63.3) |
| Duration of knee OA (years) | 10.1 ± 6.2 (1.0–30.0) |
| Walking aids | |
| No aids necessary | 62 (56.9) |
| Post-treatment | |
| GRCS (points) | |
| About the same (0) | 1 (0.9) |
| A tiny bit better (+1) | 5 (4.6) |
| A little bit better (+2) | 20 (18.3) |
| Somewhat better (+3) | 28 (25.7) |
| Moderately better (+4) | 21 (19.3) |
| Quite a bit better (+5) | 17 (15.6) |
| A great deal better (+6) | 13 (11.9) |
| A very great deal better (+7) | 4 (3.7) |
Quantitative variables: mean ± standard deviation (SD) (range); categorical variables: frequency (percentage).
The main responsiveness results are summarized in Table II.
Table IIResponsiveness of the ICOAP subscales and total pain (N = 109)
| ICOAP (points) | Pre-treatment Mean ± SD | Post-treatment Mean ± SD | Change Mean ± SD (range) | P | SES (95% CI) | SRM (95% CI) | Correlation with GRCS | Floor effect % | Ceiling effect % |
|---|---|---|---|---|---|---|---|---|---|
| Constant pain subscale | 55.9 ± 24.6 | 35.4 ± 19.5 | −20.5 ± 15.4 (0.0–−75.0) | <0.001 | 0.83 (0.71–0.95) | 1.33 (1.14–1.52) | −0.62 | 6.4 | 1.8 |
| Intermittent pain subscale | 63.1 ± 17.3 | 38.6 ± 16.5 | −24.5 ± 14.6 (0.0–−75.0) | <0.001 | 1.42 (1.27–1.57) | 1.68 (1.50–1.85) | −0.56 | 0.9 | 1.8 |
| Total pain | 59.8 ± 18.6 | 37.1 ± 16.6 | −22.7 ± 13.6 (0.0–−75.0) | <0.001 | 1.22 (1.08–1.35) | 1.67 (1.48–1.85) | −0.64 | 0.0 | 0.9 |
ICOAP is 0–100 points, best to worst; GRCS is −7 to +7 points, worst to best.
∗ Change = post-treatment score – pre-treatment score; improvement if change < 0.
† P value from Wilcoxon test comparing pre- and post-treatment scores.
‡ SES = |mean (change) ÷ SD (pre-treatment)|.
§ SRM = |mean (change) ÷ SD (change)|.
|| Bootstraps.
¶ Spearman's correlation coefficients (correlation of ICOAP change scores with GRCS scores).
The SES for the ICOAP scores was significantly different (intermittent pain subscale SES > total pain SES > constant pain subscale SES; P < 0.001). The intermittent pain subscale SRM was comparable to the total pain SRM (P = 0.916). These two SRM were significantly higher than the constant pain subscale SRM (P < 0.001).
The SES and SRM were also calculated within subgroups: patients with unilateral knee OA (N = 40) versus patients with bilateral knee OA (N = 69); patients with less than 5 years of duration of knee OA (N = 23) versus patients with 5 or more years of duration of knee OA (N = 86). All the ICOAP scores obtained SES and SRM values above the 0.80 cutoff in all the subgroups, with the exception of the constant pain subscale SES for the subgroups of patients with unilateral knee OA (0.78) and with less than 5 years of duration of knee OA (0.50).
Concise discussion
In this responsiveness study we provided evidence that the ICOAP was able to detect changes following physical therapy for knee OA.
As expected, pain improved with 4 weeks of physical therapy. In fact, the comparison of pre- and post-treatment ICOAP subscales and total pain showed statistically significant reduction in pain intensity and impact on quality of life.
In the total sample, large SES and SRM were found after 4 weeks of physical therapy. Additionally, with the exception of the constant pain subscale SES (moderate) for the subgroups of patients with unilateral knee OA and with less than 5 years of duration of knee OA, all the ICOAP scores obtained large SES and SRM in all the subgroups. This is consistent with the evidence that physical therapy is effective to reduce pain in knee OA
8
. Among the 12 randomized controlled trials (RCTs) of physical therapy interventions for knee OA included in a recent meta-analysis, the overall effect size (95% CI) on pain was 0.38 (0.22–0.54) for strength training, 0.34 (0.19–0.49) for exercise and 0.69 (0.41–0.97) for exercise and manual therapy13
. All these values are lower than those obtained in the current study. However, the RCTs included in the meta-analysis focused mainly on pain measured on the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain subscale, used different duration of treatment periods and included individual and group treatments13
. Gonçalves et al.14
reported similarly large SES (1.08) and SRM (1.28) for the Knee injury and Osteoarthritis Outcome Score (KOOS) pain subscale after 4 weeks of physical therapy treatments. Intermittent pain demonstrated higher responsiveness to physical therapy than constant pain. This may be due to the fact that intermittent pain is usually triggered by a specific activity or movement (e.g., walking) that can be targeted by physical therapy. Indeed, the intermittent pain subscale SES and SRM were significantly higher than the constant pain subscale SES and SRM, indicating that the two subscales are evaluating different aspects of the pain experience. This emphasizes the need to assess the effect sizes for each subscale separately. The ICOAP has been also shown to be a responsive outcome measure in total joint replacement. Davis et al.7
found SRM from 0.84 to 1.02, 6 months after total knee replacement. Ruyssen-Witrand et al.6
reported SRM from 0.45 to 0.65, 12 months after total knee replacement. In this last study, the ICOAP was self-administered which may have contributed to the lower SRM values. According to these authors, this mode of questionnaire administration may have introduced a misunderstanding bias6
.The pre-defined hypothesis for responsiveness was confirmed. The change scores for the ICOAP subscales and total pain following physical therapy presented negative fair correlations with the GRCS score. As expected, the change detected by the ICOAP subscales and total pain was correlated with the post-treatment patient-perceived improvement. Davis et al.
7
also reported evidence for responsiveness of the ICOAP as indicated by significant associations with change scores of other self-reported measures.The floor and ceiling effects were considered not to be present in the ICOAP subscales and total pain score. In particular, the ability of the ICOAP subscales and total pain score to detect improvements attributable to the physical therapy was not constrained by floor effects.
Some limitations of this study should be acknowledged. The sample used is not representative of the entire population of Portuguese patients with knee OA referred for physical therapy. In fact, only patients with knee OA receiving physical therapy interventions in outpatient clinics were recruited. No attempt was made to standardize the physical therapy treatments. However, the responsiveness characteristics obtained by the ICOAP in this study may be somewhat different for specific physical therapy interventions. Information on medication use was not obtained. All measures were interviewer-administered by physical therapists introducing the possibility of willingness to please bias. The extent to which the willingness to please bias may have influenced the absence of patient-perceived deterioration after physical therapy and the relatively high effect size for the ICOAP scores was, however, judged as minimal. The GRCS provided a means of measuring change in OA-specific health status. In turn, the ICOAP provided a means of measuring change in OA pain intensity and OA pain impact on quality of life. Although the measured constructs are closely related, they are not the same. Also, the GRCS was administered only at post-treatment, introducing the possibility of recall bias, whereas the ICOAP was administered at pre- and post-treatment to detect a change. More testing is required in order to assess this important psychometric property.
Nevertheless, we may conclude that the ICOAP demonstrated responsiveness to physical therapy for knee OA.
Author contribution
Gonçalves takes responsibility for the integrity of the work as a whole, from inception to finished article.
Conception and design: Gonçalves, Meireles.
Collection and assembly of data: Gonçalves, Meireles, Rosado.
Analysis and interpretation of the data: All authors.
Drafting of the article: Gonçalves.
Critical revision of the article for important intellectual content: All authors.
Final approval of the article: All authors.
Conflict of interest
None of the authors have any conflict of interest related to this work.
Acknowledgements
The authors would like to thank the staff from the physical therapy outpatient clinics. In addition, the patients who participated in this study also deserve our deep gratitude.
References
- Development and preliminary psychometric testing of a new OA pain measure – an OARSI/OMERACT initiative.Osteoarthritis Cartilage. 2008; 16: 409-414
- Understanding the pain experience in hip and knee osteoarthritis – an OARSI/OMERACT initiative.Osteoarthritis Cartilage. 2008; 16: 415-422
- OMERACT/OARSI initiative to define states of severity and indication for joint replacement in hip and knee osteoarthritis.J Rheumatol. 2007; 34: 1432-1435
- Cross-cultural adaptation and validation of the Portuguese version of the intermittent and constant osteoarthritis pain (ICOAP) measure for the knee.Osteoarthritis Cartilage. 2010; 18: 1058-1061
- Multi-language translation and cross-cultural adaptation of the OARSI/OMERACT measure of intermittent and constant osteoarthritis pain (ICOAP).Osteoarthritis Cartilage. 2009; 17: 1293-1296
- Psychometric properties of the OARSI/OMERACT osteoarthritis pain and functional impairment scales: ICOAP, KOOS-PS and HOOS-PS.Clin Exp Rheumatol. 2011; 29: 231-237
- Evaluating the responsiveness of the ICOAP following hip or knee replacement.Osteoarthritis Cartilage. 2010; 18: 1043-1045
- Physical therapy interventions for patients with osteoarthritis of the knee: an overview of systematic reviews.Phys Ther. 2008; 88: 123-136
- Development of criteria for the classification and reporting of osteoarthritis. Classification of osteoarthritis of the knee. Diagnostic and Therapeutic Criteria Committee of the American Rheumatism Association.Arthritis Rheum. 1986; 29: 1039-1049
- Measurement of health status. Ascertaining the minimal clinically important difference.Control Clin Trials. 1989; 10: 407-415
- A comparison of different indices of responsiveness.J Clin Epidemiol. 1997; 50: 239-246
- Individual-patient monitoring in clinical practice: are available health status surveys adequate?.Qual Life Res. 1995; 4: 293-307
- Strength training alone, exercise therapy alone, and exercise therapy with passive manual mobilisation each reduce pain and disability in people with knee osteoarthritis: a systematic review.J Physiother. 2011; 57: 11-20
- Cross-cultural adaptation and validation of the Portuguese version of the Knee injury and Osteoarthritis Outcome Score (KOOS).Osteoarthritis Cartilage. 2009; 17: 1156-1162
Article info
Publication history
Published online: July 26, 2012
Accepted:
June 21,
2012
Received:
December 5,
2011
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© 2012 Osteoarthritis Research Society International. Published by Elsevier Inc.
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