Disability in chronic low back pain : psychometric properties of ADL- and work-related instruments

Chronic low back pain (CLBP) is one of the most common health problems in Western society, and due to the considerable impact on daily functioning, sickness absence and work disability, it is also a heavy financial burden on society. In Rehabilitation Medicine, several treatment programs have been developed to improve participation in society by reducing activity limitations. The main focus is on the limitations and restrictions in the performance of domestic activities in daily living (ADL). Since low back pain is the primary cause of work absence, with huge costs, the impact on functioning at work needs to be considered in rehabilitation, also. Due to differences in area of functioning (at home or at work) both ADL and work-related instruments should be used to assess the effectiveness of treatment. To obtain evidence about the usefulness of instruments in Rehabilitation Medicine, the psychometric properties of the instruments should be acceptable. Important psychometric properties are reliability and validity. Reliability refers to the extent to which a measurement is consistent and free from errors. The most common measures of reliability are test-retest reliability and inter-observer reliability. Consistency involves the extent to which repeated measures in individuals remain stable over time, under the same circumstances in the absence of treatment. Errors influence the extent of stability over time in the absence of treatment. The validity of an instrument is the ability to measure what it is intended to measure. Besides content-, construct- and criterion-related validity, responsiveness is an important form in measuring treatment effectiveness. Responsiveness refers to the ability to detect clinically important changes in the construct being measured. No clarity exists in literature about responsiveness. Different external criteria are used to determine whether a patient has achieved a clinically important change in functional status, due to the absence of a gold standard to measure clinically important change. It is known that the choice of external criteria influences responsiveness measures. Several questionnaires have been developed to assess the limitations of CLBP patients to perform ADL activities. The Roland Morris Disability Questionnaire is one of the most frequently used questionnaires in rehabilitation practice. The Dutch language version of the RMDQ (RMDQ-Dv) proved to be valid and responsive; however the reliability was not investigated. Furthermore, the consequences of using different external criteria on the responsiveness of the RMDQ-Dv were not investigated also. Assessment of work limitations is a relatively new phenomenon in rehabilitation; therefore, work-related instruments have hardly been developed and introduced in daily practice. In other disciplines, several instruments were developed and are used to assess work limitations. In the Netherlands, the Work & Handicap Questionnaire (WHQ) was developed by the Netherlands Organization for Applied Scientific Research (TNO) within the scope of a vocational handicap research program. The Functional Information System (FIS) and the Functional Ability List (FAL) were developed in Dutch Social Insurance Medicine as standardized forms to determine capability to work. Until 2000 the FIS was used, nowadays the FAL is used. The social insurance physicians use the results of history taking and physical examination to fill out the standardised form about limitations in the performance of work-related activities. The ‘Isernhagen Work Systems Functional Capacity Evaluation’ (IWS FCE) is a battery of standardized tests designed to assess a person’s functional performance related to work-related activities in a laboratory setting. In these work-related instruments, different assessment perspectives are distinguished for the assessment of work limitations: patient’s self-report, physician’s report based upon history taking and physical examination and performance results based upon functional testing. Several studies showed that the assessed limitations inferred from different perspectives will correlate weakly; the extent of differences between the assessed limitations of the three perspectives, however, has not been investigated. The aim of this thesis was to investigate the reliability of the mentioned instruments in CLBP patients in Rehabilitation Medicine, to determine the responsiveness of the RMDQ-Dv and to determine the differences in limitations inferred from self-report, clinical examination and functional testing. The main research questions in this thesis were: ADL-related instrument - What is the reliability and stability of the Dutch language version of the Roland Morris Disability Questionnaire? - What is the responsiveness of the Dutch language version of the Roland Morris Disability Questionnaire using different external criteria? Work-related instruments - What is the reliability of the Work & Handicap Questionnaire, the Functional Information System, the Functional Ability List, and the Isernhagen Work Systems Functional Capacity Evaluation? - What are the differences in limitations inferred from self-report, clinical examination and functional testing?