Condition-specific Western Ontario McMaster Osteoarthritis Index was not superior to region-specific Lower Extremity Functional Scale at detecting change

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Abstract

Objective

We determined whether the sensitivity to change of the Western Ontario McMaster Osteoarthritis Index (WOMAC) physical function (PF) subscale, a condition-specific measure for persons with osteoarthritis of the hip or knee, was superior to a lower extremity region-specific measure, the Lower Extremity Functional Scale (LEFS), in persons with osteoarthritis of the hip or knee undergoing total joint arthroplasty.

Methods

The WOMAC and LEFS were administered to 102 patients with osteoarthritis preoperatively, within 16 days of surgery, and >20 days after the first postoperative assessment. These time points enabled the assessment of deterioration and improvement. Two timed performance measures (40 m walk test and the timed-up-and-go test) were also assessed. Change was quantified by the standardized response mean (SRM).

Results

WOMAC PF SRMs were not greater than the LEFS SRMs. Performance measures' times increased significantly over the deterioration interval and decreased over the improvement interval. The WOMAC PF and LEFS demonstrated significant improvement over the second assessment interval; only the LEFS showed significant deterioration over the first assessment interval. WOMAC PF scores seem to be strongly influenced by pain.

Conclusion

The findings do not support the hypothesis that the WOMAC PF subscale is superior to the LEFS in detecting change.

Introduction

A popular method of classifying self-report health status measures applies three categories: generic measures, condition- or disease-specific measures, and patient-specific measures. Generic measures assess multiple domains or health concepts such as physical health, mental health, pain, vitality, and social well-being. Examples of generic health status measures include the SF-36 [1] and the Sickness Impact Profile [2]. Condition- or disease-specific measures have a narrower focus: They assess aspects of well-being most relevant to the condition of interest. Examples of condition-specific measures include the Arthritis Impact Measure [3] and the Western Ontario McMaster Osteoarthritis Index (WOMAC) [4]. Patient-specific measures contain items that are generated by individual patients; only the method of eliciting items and scoring responses are common among patients. Examples of patient-specific measures include the MACTAR [5] and Patient Specific Functional Scale [6], [7].

In addition to these classes of measures, the region-specific measure has emerged [8], [9], [10], [11], [12]. Region-specific measures are intended to be applicable to a spectrum of conditions within a specific anatomic region. Region-specific measures have become popular in the orthopedic field, and examples include the Roland-Morris Questionnaire (low back) [9], Disabilities of the Arm, Shoulder and Hand (DASH) (upper extremity) [11], Neck Disability Index (cervical spine) [10], and Lower Extremity Functional Scale (LEFS) (lower extremity) [12]. Region-specific measures are attractive to practitioners working with a varied caseload because a single measure can be used to assess a spectrum of conditions. For example, rather than using four condition-specific measures to assess the outcome of patients with hip fracture, knee osteoarthritis, anterior cruciate lesion, and ankle sprain, a single region-specific measure could be applied. However, a thoughtful practitioner is likely to consider a region-specific measure only if its ability to detect change is similar to that of the preferred condition-specific measure.

Although a body of evidence exists supporting the superiority of condition- and patient-specific measures to detect change compared with generic measures [12], [13], [14], [15], [16], [17], there is a paucity of information comparing condition-specific and region-specific measures. The work of Beaton et al. [18] provides the closest approximation of a study comparing a condition specific to a region-specific measure. These investigators compared the DASH's ability to detect change to two more specific region-specific measures, the Brigham, which was conceived for patients with carpal tunnel, and the Shoulder Pain and Disability Index, which was developed for patients with shoulder pain. The sample consisted of 200 patients with wrist, hand, or shoulder problems. The authors found that the DASH's ability to detect change was equal to or better than the more specific region-specific measures.

Given the lack of information concerning the relative ability of condition and region-specific measures to detect change, we chose to pursue this topic in the current investigation. The primary purpose of this study was to determine whether the sensitivity to change of the WOMAC's physical function (PF) scale [4], [19], [20] was significantly superior to that of the LEFS [12], [21], [22]. We chose to investigate these two measures because much is known about their measurement properties [12], [19], [21], [22], [23], [24], [25] and because the WOMAC has been validated on several conditions, including osteoarthritis [26] and hip and knee total joint arthroplasty [24], [27]. A secondary purpose was to suggest an explanation, by way of post-hoc analyses, for an unexpected finding associated with the results for this study's primary purpose.

Section snippets

Sample

Data for this study are from a larger, ongoing longitudinal study designed to describe recovery profiles in patients post total hip (THA) or knee arthroplasty (TKA). The sample consisted of patients with a diagnosis of osteoarthritis (OA) scheduled to undergo primary, unilateral THA or TKA. Patients contributed data to the present study if they provided informed consent and were able to complete the WOMAC and LEFS and the performance measures (40-m self-paced walk test and timed-up-and-go test)

Sample and demographics

The average age and body mass index (BMI) for the 102 patients in this study were 63 years (1st, 3rd quartiles: 55, 70 years) and 29.4 kg/m2 (1st, 3rd quartiles: 26.5, 34.1 kg/m2), respectively. Fifty patients were women, and differences did not exist in age or BMI for the two genders. Fifty-three patients had TKA, 28 of whom were women. The median interval between surgery and the first postoperative assessment was 8 days (1st, 3rd quartiles: 7, 10 days). The median interval between the first

Discussion

The goal of this study was to determine whether the sensitivity to change of the WOMAC PF, a condition-specific measure, was greater than that of the LEFS, a region-specific measure. The study sample consisted of patients with OA who underwent THA or TKA. The intent of the study design was to create a framework that allowed the investigation of the measures' abilities to detect deterioration and improvement in lower extremity functional status. We conceptualized difficulty with lower extremity

Acknowledgments

We thank Dr. Jean Wessel for her suggestions concerning an early version of this manuscript. This work was supported by the Orthopaedic and Arthritic Foundation.

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