Intermittent and Constant Osteoarthritis Pain

Abstract

The Intermittent and Constant OsteoArthritis Pain (ICOAP) scale is a specialized self-report questionnaire designed for the comprehensive pain assessment of individuals suffering from Osteoarthritis (OA) primarily affecting the hip and/or knee joints. A key feature of the ICOAP is its capacity to differentiate between and measure both intermittent pain (pain that comes and goes) and constant pain (persistent background pain).

This instrument is particularly effective for patients whose pain experience is highly variable. The scale instructs respondents to account for any pain reduction achieved through the use of medication when providing their scores, ensuring the assessment reflects the current experienced pain state. The ICOAP is a critical tool for detailed evaluation of OA pain in clinical and research settings.

Keywords

ICOAP, Osteoarthritis, Constant Pain, Intermittent Pain, Pain Measurement, Lower Extremity, Hip Pain, Knee Pain, Questionnaire, Rheumatology.

Authors

Hawker GA, French MR, Brocklehurst R, et al. (Original Development, 2008); Maillefert JF, et al. (Dutch Version Adaptation and Validation, 2009).

Purpose

The primary purpose of the ICOAP is to provide a nuanced and clinically relevant measurement of pain in individuals diagnosed with Osteoarthritis, moving beyond traditional single-item or unidimensional pain scales. It specifically aims to capture the variability inherent in OA pain, which often fluctuates significantly in intensity and presence throughout the day or week, particularly in the hip and knee joints.

By separately quantifying intermittent pain and constant pain, the scale offers clinicians and researchers a powerful tool for monitoring disease progression, evaluating the efficacy of pharmacological or physical interventions, and tailoring treatment strategies to address the specific type of pain experienced by the patient. It is particularly useful in clinical trials where sensitivity to change in distinct pain characteristics is crucial for outcome measurement.

Construct

The ICOAP measures the subjective experience of pain severity associated with Osteoarthritis, focusing on the sensorimotor domain of pain perception. The core construct is the multidimensional nature of chronic musculoskeletal pain, specifically distinguishing between two distinct pain dimensions: the intensity and frequency of pain that is always present (constant pain) and the intensity and frequency of pain that occurs only during specific activities or times (intermittent pain).

This differentiation acknowledges that constant background pain and activity-related breakthrough pain are often governed by different biological mechanisms and may respond differently to treatment. The scale thus provides specific scores reflective of these two underlying dimensions of the OA pain experience, categorized under sensory functions and pain domains.

Validity

Initial studies establishing the psychometric properties of the ICOAP demonstrated strong evidence of validity. Content validity was ensured through extensive literature review and expert consultation to confirm that the items comprehensively cover the domain of OA pain variability. Construct validity was supported by factor analysis, which typically confirms the hypothesized two-factor structure (Constant Pain and Intermittent Pain).

Furthermore, strong convergent validity has been observed through high correlations between ICOAP scores and scores on established measures of pain and function, such as the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain subscale, especially in populations with moderate to severe OA of the hip or knee. Discriminant validity is also supported, as the ICOAP shows lower correlations with measures of unrelated constructs, confirming it measures the intended specific pain dimensions.

Reliability

The ICOAP demonstrates robust internal consistency and test-retest reliability across various language adaptations. Measures of internal consistency, typically assessed using Cronbach’s alpha, consistently yield scores above the acceptable threshold of 0.70 for both the Constant Pain and Intermittent Pain subscales, indicating homogeneity among items within each dimension.

Test-retest reliability, assessed by administering the scale to stable patients over a short interval (e.g., 1–2 weeks), shows high Intraclass Correlation Coefficients (ICCs). This confirms that the instrument provides stable measurements over time, provided the patient’s clinical status has not changed significantly, making it suitable for longitudinal monitoring.

Factor Analysis

The original development and subsequent validation studies of the ICOAP consistently support a clear, two-factor structure when subjected to exploratory factor analysis (EFA) and confirmatory factor analysis (CFA). The two factors identified are the Constant Pain subscale and the Intermittent Pain subscale. These two factors are theoretically distinct yet moderately correlated, reflecting the overlapping yet differentiated nature of pain types in Osteoarthritis.

This robust factor structure is critical as it justifies the separate scoring and interpretation of the two dimensions, allowing for a more granular understanding of the patient’s pain profile compared to unidimensional scales that aggregate all pain types into a single score. This specialized approach is essential for targeted intervention planning.

Instrument

Test Type: Self-report Questionnaire

Format: Likert-type scale items, typically involving frequency and intensity ratings over a defined recall period.

Language Available: Original English, Dutch (Nederlandse versie), and numerous other validated translations (e.g., French, Spanish, Chinese).

Population Group: Clinical populations diagnosed with Osteoarthritis of the hip and/or knee (Conditions: Musculoskeletal system).

Age Group: Adults and Older Adults.

Population Details: Patients experiencing variable pain related to OA in the lower extremity.

Test Methodology: Assesses the severity and frequency of pain over a specific recall period, instructing respondents to account for medication effects. Focuses on sensory functions and pain.

Keywords

Chronic Pain, Rheumatology, Constant Pain, Intermittent Pain, Pain Variability, Hip Osteoarthritis, Knee Osteoarthritis, Pain Management, Psychometrics.

Authors

Author ORCID Identifier: Not specified in the source material.

Affiliation Email addresses: Contact information typically associated with the lead author’s institutional affiliation (e.g., G.A. Hawker, University of Toronto).

Correspondence Address: Correspondence generally directed to the Division of Rheumatology, University of Toronto, Canada, or the corresponding author of the specific validation study.

Permissions & Fee and Test Year

The original scale was developed and published in 2008 by Hawker GA, et al. The Dutch version was validated in 2009. The scale is generally available for non-commercial academic research use, often requiring appropriate citation. Specific permissions for commercial applications or clinical use outside of research may necessitate contacting the original authors or copyright holders.

Reference’s

The primary references for the ICOAP include the development and validation papers, as well as the original source materials:

1. Hawker GA, French MR, Brocklehurst R, et al. The development and preliminary psychometric properties of the Intermittent and Constant OsteoArthritis Pain (ICOAP) measure. Osteoarthritis Cartilage. 2008;16(12):1573-1580.
2. Maillefert JF, et al. Cross-cultural adaptation and validation of the Dutch version of the Intermittent and Constant OsteoArthritis Pain (ICOAP) questionnaire. Joint Bone Spine. 2009;76(3):288-292.
3. The original PDF Manual (Toelichtingsformulier) can be downloaded here: ICOAP Explanation Form PDF.
4. The original PDF Measurement Instrument (Meetinstrument) can be downloaded here: ICOAP Measurement Instrument PDF.

Items of the Intermittent and Constant OsteoArthritis Pain

IMPORTANT: The following scale items must be preserved in their original language and must not be changed in any way. Specific items are found within the linked measurement instrument PDF, but generally cover the following domains:

• Frequency and intensity of constant, baseline pain (Constant Pain Subscale).
• Frequency and intensity of intermittent, activity-related or breakthrough pain (Intermittent Pain Subscale).
• The impact of pain on daily function and mood.