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    3DMA reliability

    This post relates to Chris Kirtley’s comment “…it seems to me the field has not progressed much in that last 10 years” as well as a comment on poor reliability and clinical 3D gait analysis (Thread: “Best web-site for interaction with doctors engaged with human gait disorder”). It also follows on from my previous posts which presented and understanding of axes-misalignment, 3DMA methods and normative gait data. The later highlighted to me the lack of awareness of the reliability of different 3DMA methods. To put some perspective on the comparative reliability of different methods and the progress made over the last 20+ years in 3DMA I have presented the results of a systemic review from a 4th year student research project.

    Methods include traditional anatomical land mark based, KAD, Optimization methods and rigid fixation devices with and without functional joint centre methods. A summary Excel spread sheet is attached and can be found at:
    Google drive folder: 3DMA Reliability
    or excel file: ResultsTableSytematic Review brief.xlsx
    Google drive preview does not show any plots.

    Key points:

    1. Intra-session (same marker placement) reliability for the majority of studies was very poor and unacceptable for non-sagital rotations of the hip, knee and ankle. Acceptable intra-session reliability has been produced for a number of studies for a few joint angles, irrespective of type of method, but this is the exception.
    2. Large variability is seen within each type of study design across intra-session, inter session and inter-examiner results. Therefore no design can be considered reliable and is highly dependent on the implementation of the method.

    There is something fundamentally wrong with the processes undertaken to derive joint angle data for the majority of reliability studies. So much so that often the gait variability within session is far larger than the total variability expected between subjects during normal gait.
    Comparison of methods:

    1. Traditional marker based anatomical landmark (AL) based methods of the 80’s and 90’s (Kit Vaughan, mod-HH, VCM, PiG) were known to suffer from cross-talk (axes misalignment and non-linear errors) and poor reliability in the non-sagital knee joint angle data.
    2. The KAD was introduced (90’s ?) to help define thigh medio-lateral (knee flex/ext) axis alignment to improve reliability and reduce cross talk. However it had limited success with marginal improvements in reliability in gait kinematics over the traditional marker based methods. The influence of the examiner’s interpretation and implementation of the method and variability in KAD placement was still a limiting factor.
    3. Optimisation approaches of the 2000’s saw a variety of methods to align medio-lateral knee axes based on minimizing knee abd/add cross talk. Including PCA or best fit to an ideal knee abd/add curve during gait. Although only a few studied and varying in their results between approaches, these methods saw a significant improvement in reliability over KAD or traditional AL methods.

    From here the methods have gone backwards.

    1. The T3DGait (2007) saw a return to the anatomical landmarks and minimal marker numbers of the traditional AL methods.
    2. Function methods for joint centres (2010’s) have also seen a return, but have produced no improvement in reliability over traditional AL methods, adding time and complexity to the analysis for no benefit. Although both KAD and function methods are unreliable, it could argued that for inter-session studies you should stick with the KAD method as it has a more controlled approach producing less variability between reliability studies. The function method lacks a clearly defined protocol in terms of planes of movement, RoM, or controlling pelvic motion, potentially leading to larger variability in outcome measures between reliability studies.
    3. A resent addition is the IK model for gait analysis. Although there are no reliability studies, published comparative gait data, and knowledge of factors that affect reliability and validity, indicate that this is possibly the worst method presented for 3D gait analysis. Combining the worst in 3DMA including whole body global optimization, 1 df knee joint, RFD on the thigh and functional joint centers.

    These later methods have all ignored previous literature and work on axes misalignment and non-linear error (cross talk), with no attempt to assess or correct for axes mis-alignment.

    Something that has been long missing in the 3DMA literature is criteria against which to measure reliability outcome measures. This is part of the reason why every reliability study that I have read concludes that their methods are reliable and suitable for 3DMA gait analysis, when clearly they are not. This conclusion has been based on a vaguely chosen value (such as ICC or CMC >0.8) that has no relevance to gait curves and is applied to all joint angle data despite it being known that the ROM varies considerably between different joint df’s (from 6 to 60 degs.).

    I will end with an important consideration on the progress of 3DMA and a future trend. There was a huge leap in 3DMA technology in the mid 90’s which saw the emergence of the multi-camera, 3D tracking, real-time gait technology we see today. The 3DMA methods (marker sets, protocols etc.) have been left behind and have in recent years (in my opinion) gone backwards through a lack of critical thought, understanding and research into the underlying methods. There is currently another boom happening with wireless inertial sensors and their application to 3DMA. These come with claims of accuracy and reliability and are being promoted as tools for research and clinical gait analysis. In light of what I have presented in comparative reliability as well as previous posts on marker based methods, understanding of axes misalignment and normative gait data, these claims should be taken with caution. This is where I feel that 3DMA societies/groups and those conducting fundamental research into 3DMA methods need to step up to provide leadership in an area of 3DMA that is again changing rapidly with the introduction of new technology. If as Paul Devita says it wants to become the “breakthrough science of the 21st century”. To do this however requires a huge step forward in the science and current understanding of 3DMA methods, validity and reliability.

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