ReviewThe reliability of three-dimensional kinematic gait measurements: A systematic review
Introduction
Three-dimensional kinematic gait measurements are used widely in clinical gait analysis services and clinical research. Despite the increasing number of gait laboratories, there is limited cohesive information regarding the reliability of kinematic gait measurements. Two recent reports [1], [2] highlighting between-laboratory differences in 3DGA measures have raised concerns from the wider orthopaedic community [3], [4]. This paper presents a systematic review and qualitative appraisal of the evidence describing the reliability of three-dimensional kinematic gait data (3DGA).
The reliability and validity of gait measurements should be known in order to be used appropriately [5]. As repeated gait measurements typically show some differences, these can be assumed to contain a proportion of error. This review addresses reliability, which is the extent to which gait measurements are consistent or free from variation. The term ‘error’ in this paper is used within the context of reliability and refers to the variation found across repeated measures. Knowledge and understanding of typical measurement variation is helpful to guide the use and interpretation of data.
Clinical gait analysis typically seeks to discriminate between normal and abnormal gait and to assess change in walking over time [6]. Repeated gait measurements can be used to evaluate the response to therapeutic interventions such as surgery, physiotherapy, medications and orthotics. Variability between ‘before’ and ‘after’ measurements may be due to treatment effects or measurement variation, or a combination of both. Knowledge of the error magnitude can enable clinical teams to minimise the risk of over-interpreting small differences as meaningful, [7] and to have greater confidence that the treatment effect exceeds the measurement error. Additionally, the use of measurements with low reliability in clinical research may lead to underestimation or failure to detect significant effect sizes; with too much noise (error) drowning out real effects [8].
The reliability or consistency of 3DGA can be examined in various ways. Typically multiple walking trials are collected within a single session. Variability between these trials can be regarded as ‘intrinsic variation’, and reflects the inherent variation within unimpaired individuals or those with pathology [7]. These intrinsic variations cannot be reduced, yet provide a baseline indication of variation independent of other error sources. Other measurement variation arises from extrinsic factors such as procedural errors [7]. Reliability of data obtained from different testing sessions conducted by the same assessor (inter-session or within-assessor) and by different assessors (inter-assessor) is susceptible to these extrinsic errors. Inconsistent marker placement is generally regarded as a key factor, although other factors such as inconsistent anthropometric measurements, variation in walking speed, data processing or measurement equipment errors may also contribute to data variation [9]. Reliability across sessions is of immediate relevance to clinical gait analysis practices; as observations are routinely and regularly repeated to measure patient performance over time, and different assessors may conduct tests for an individual patient. This aim of this review was to identify and critically evaluate the evidence describing the reliability of lower body kinematic gait data across repeated sessions.
Section snippets
Study identification and selection
The search strategy for this review began with retrieval of published reports indexed on health or biomechanics related electronic databases from MEDLINE (1970 to July 2007), EMBASE (1980 to July 2007), CINAHL (1982 to July 2007), RECAL Bibliographic Database (pre-1990 to July 2007) and Inspec (1970 to July 2007). The search was limited to literature reporting studies of human subjects with abstracts written in English. The search terms were customised to each database and included the
Results
The electronic searches and hand-search of references and selected conference proceedings yielded a total of 510 articles. Following the application of the inclusion/exclusion criteria, 23 studies were identified for inclusion in the systematic review; 15 full papers and 8 abstracts.
Details of the 23 identified studies are provided in Table 1. Within-assessor reliability was reported in 15 of the studies, and between-assessor in 10. Four of the studies were described as test–retest, as either
Discussion
The diversity of study participants, methods, biomechanical modelling techniques, statistical analyses and results precludes a simple conclusion about the reliability of 3DGA. Data from studies reporting reliability indices do however suggest that the majority of studies reported moderate to good reliability for sagittal and coronal plane variables, with the exception of pelvic tilt and knee varus/valgus in some reports. Likewise, estimates of error (S.D. or S.E.; Fig. 1) suggest most studies
Considerations and recommendations for future research
A number of limitations should be considered when interpreting the findings of this review. All papers were retained for inclusion regardless of study quality, in order to provide a comprehensive overview of available data. Statistical synthesis of the data was not performed. The findings of this review are limited to the published papers identified by the search strategies. Potential publication bias was not assessed and may have resulted in an over-estimation of reliability. Study quality was
Conflict of interest
Author RB has received research support funding from VICON. The other authors state there were no conflicts of interest.
Acknowledgements
This project was funded by a National Health and Medical Research Council Grant (ID 264597) to the Centre for Clinical Research Excellence in Gait Analysis and Gait Rehabilitation, Murdoch Childrens Research Institute, Melbourne, Australia.
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