Original ArticleLongitudinal and cross-sectional validity of the DynaPort® Knee Test in adults with nontraumatic knee complaints in general practice
Introduction
Musculoskeletal conditions are a major burden on individuals, health systems, and social care systems, with indirect costs due to disability being predominant [1]. Although musculoskeletal pain, injury, and dysfunction affect all ages, the elderly are particularly targeted [2]. In general practice, knee complaints take second place after back pain in the prevalence of musculoskeletal disorders (48 per 1,000 patients per year), most presented as knee pain or function loss of the knee joint [3]. Pain and function are also important clinical outcomes in research projects and both can be measured subjectively or objectively. A Visual Analog Scale or a Likert scale can be used to measure pain subjectively. Function can be measured both subjectively and objectively on “impairment” and “disability” level. Several tests are available to measure the function of the knee joint on the “disability level,” including the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) [4], [5], the Medical Outcomes Study Short Form-36 (SF-36) [6], [7], and the Knee Society Score (KSS) [8]. The WOMAC and the SF-36 are self-report questionnaires whereas the KSS is a clinical rating scale. The KSS is subdivided in the KSS knee assessment score (built by ratings of pain, range of motion, and stability of the knee) and KSS function score (built by walking, climbing stairs, and use of walking aids).
In view of the risk of inter and intraobserver bias and the length of time needed for the more objective knee function measurement (like the KSS), most investigators prefer to use the patient-based assessment scales like the WOMAC and the SF-36 [9], [10], [11]. Because various studies report a moderate correlation between self-reports and performance-based tests and it is assumed that they measure different aspects of knee function [12], [13], [14], [15], [16], [17], it seems useful to deploy them next to each other.
The DynaPort® KneeTest (DPKT), an accelerometer-based system, was developed to objectively assess knee-related functional abilities in an unobtrusive, user-friendly way [18]. This test has proved to be a useful performance-based instrument for use in patients with knee osteoarthritis undergoing a total knee replacement, showing good reliability and validity [19], [20]. However, the validity of the DPKT for patients with knee complaints in general practice is not yet known. It remains to be tested to what extent such instruments validated in secondary care can be applied in the primary care setting.
Therefore, this study assessed the cross-sectional and longitudinal (= responsiveness) validity of the DPKT in adults with nontraumatic knee complaints in general practice.
Section snippets
Study design and study population
A subgroup of patients of the prospective HONEUR knee cohort was enrolled for this DPKT study. A detailed description of the HONEUR knee cohort had been published previously [21]. In brief, consecutive patients visiting their general practitioner with a first episode of knee complaints were enrolled in the study and followed for 1 year. New complaints were defined as complaints that were presented tot the GP for the first time. Recurrent complaints for which the GP was not consulted within the
Study population
For the DPKT there were 330 eligible patients of which 87 participated. Reasons for nonparticipating were unwillingness or inability to match a date or hour for the extra visits required for the measurements [21].
Of these 87 patients, the data of 86 persons were available for analysis and data of one person were lost due to technical problems. The study population included 44 women (51.2%) and the median age was 54 (range 18–81) years; additional baseline characteristics are given in Table 2.
Cross-sectional and longitudinal validity
The present study was performed to assess the cross-sectional and longitudinal validity of the DPKT in patients visiting their general practitioner with nontraumatic knee complaints.
To assess the cross-sectional and longitudinal validity, 12 hypotheses were tested (Table 1). Of the nine hypotheses concerning the cross-sectional validity, only three were confirmed, all of which concerned the DynaPort cluster score “rise and descent.” The remaining hypotheses concerning the KneeScore2 and the
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