gait analysis

Analysing analysis

What do we mean by clinical gait analysis? Most of you reading this blog will assume it requires a kinematic measurement system, a couple of force plates and possibly an EMG system. For the vast majority of clinicians across the world, however, it means looking at how their patients walk without even the benefit of a video camera. In my book I suggest that what we call clinical gait analysis should really be called instrumented clinical gait analysis. I then pointed out that this is rather cumbersome and that I’d use the term clinical gait analysis anyway!

OGA Rancho

The team at Rancho Los Amigos used the term Observational Gait Analysis as long ago 1989 when they published their Handbook. The photo below is the cover of the 4th edition from 2001. The most recent edition is an app for the iPhone which you can get download from iTunes (doesn’t seem to be any Android equivalent yet unfortunately). Brigitte Toro picked up on observational gait analysis (OGA) and introduced video-based observational gait analysis (VOGA) in a review article a few years ago now (2003). If we used these terms carefully there would be clear ground between them and clinical gait analysis which could be reserved for the instrumented approach.

I was, however, interested by the comments of Professor Phil Rowe from Strathclyde University speaking at one of the satellite events orbiting ESMAC in Glasgow this year and focussing on the word analysis. His point was that analysis is a process of thinking which requires some data.  It is thus not possible to perform a clinical gait analysis without some sort of instrumentation to provide those data. On this basis it would be inappropriate to refer to clinical observation of walking (either direct or through video recordings) as analysis. Perhaps clinical or observational gait assessment  are more appropriate terms (although we then end up with the same acronym, CGA). The surgeons in Melbourne also used to talk about gait by observation which seems another sensible alternative. As an engineer I quite like Phil’s line of reasoning and think a distinction between a true analysis of data and an observation of patterns is useful.

But maybe things aren’t so clear cut. Wikipedia defines analysis as the process of breaking down a complex topic into smaller parts to gain a better understanding of it. This definition doesn’t actually require any data.  It’s also true that whenever I’ve heard observational gait assessment being taught the focus has been on breaking down the overall gait pattern into smaller parts, either by plane or level, or both, to aid understanding. Maybe I’m being over-protective in trying to restrict the term analysis to instrumented processes. Any comments?

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Toro, B., Nester, C., & Farren, P. (2003). A review of observational gait assessment in clinical practice. Physiotherapy Theory and Practice, 19(3), 137-149.

Why do we so rarely test normalisation schemes?

Normalising gait data is so common that we may sometimes forget about why we are doing it. It’s getting on for 17 years since At Hof published his paper on non-dimensional normalisation (Hof, 1996). Slowly this approach is being becoming part of mainstream practice. What interests me, however, is how little testing to check that it actually works.

Normalisation is a technique to try and reduce the variability in data that comes when individuals of different sizes are being compared. A raw measure of joint moment in Newton-metres, for example, is likely to be greater in a heavier person simply because they are heavier. Measurements of joint moments across a range of people are likely to be vary considerably simply because those people are of different weights. By dividing all the measurements by bodymass and reporting measurements in N-m/kg we hope to reduce the variability. This should make it much easier to spot a subject who has abnormal moments because of the way they walk rather than how heavy they are.

At introduced a hypothesis that a particular way of normalising data to give non-dimensional values would reduce the variability in data. This is an extremely sensible approach but it is essentially a hypothesis. Given this it is interesting that there has been so little work to test the hypothesis. Ben Stansfield (2003) and colleagues in Edinburgh tested how non-dimensional normalisation affected a correlations between a range of temporal and spatial parameters with impressive results but didn’t actually address the even more basic question of how whether the normalisation reduces the variability with body size (which is what it is designed for as described above).

Oxygen normalisation

Adapted from Schwartz et al., 2006

Mike Schwartz and I (Schwartz et al., 2006) adopted the approach for normalising oxygen cost and rate/consumption. The traditional approach was simply to divide Oxygen cost by mass and when we tested this we found that the data was over-normalised. Raw measurements (mmO2/m) increase with increasing weight. Measures normalised by bodymass (mmO2/kg-m) actually decrease with increasing mass (see Figure below). Deriving a non-dimensional equivalent results in data that show no systematic variation with mass, height or age. When we did this paper I think we assumed that other people might investigate other normalisation schemes in a similar manner but, to my knowledge there have been no such studies.

Two obvious candidates for such studies are joint moments and powers. Dividing either by mass alone (as is almost universal practice in clinical gait analysis) only partially normalises the data. Hof recommends that moment should be normalised by leg length as well as mass (and this is common practice in some strands of research particularly studies of the knee adduction moment). It really is quite amazing that over three decades after David Winter popularised the use of joint moments in clinical gait analysis (Winter & Robertson, 1978) no-one yet has performed a definitive study to identify the optimum normalisation scheme for the data.

Hof, A. (1996). Scaling gait data to body size. Gait and Posture, 4, 222-223.

Schwartz, M. H., Koop, S. E., Bourke, J. L., & Baker, R. (2006). A nondimensional normalization scheme for oxygen utilization data. Gait Posture, 24(1), 14-22.

Stansfield, B. W., Hillman, S. J., Hazlewood, M. E., Lawson, A. M., Mann, A. M., Loudon, I. R., & Robb, J. E. (2003). Normalisation of gait data in children. Gait Posture, 17(1), 81-87.

Winter, D., & Robertson, D. (1978). Joint torque and energy patterns in normal gait. Biological Cybernetics, 29, 137-142.

What’s in a name?

We’ve recently advertised for a “Clinical Gait Analyst”. Perhaps I shouldn’t have been surprised but we’ve had expressions of interest from all sorts of people that obviously have quite a different idea of what clinical gait analysis is to the one that I’ve got. To me a clinical gait analyst is someone who works in a clinical gait analysis service. They capture data using a 3-d optoelectronic measuring system (or equivalent) which may incorporate synchronous force plate or EMG measurements. Many also provide an interpretation of this, generally drawing on additional information from a quantitative physical examination. If clinically qualified they may provide clinical recommendations based on the analysis.

“Gait analysis” is, quite appropriately, used in many other contexts. Google up “gait analysis” and there is a good chance that the first hits will refer to a combination of video recording of running and expert advice to help you choose an expensive pair of running shoes. Another group of gait analysts will look at your running and suggests ways of improving your style to improve your times or prevent injury. Getting more clinical many orthotists, prosthetists, podiatrists and physiotherapists base much of their working lives on observational gait analysis. Some will take video recordings but many will simply look at how their patients are walking as a basis for clinical recommendations. On the more technical side there are a number of people interested in gait for a variety of reasons with little or know interest in clinical applications. There is another group of people who perform gait analysis for clinical research. They perform a variety of analyses on grouped data to try and learn more about a disease condition or intervention but don’t offer any results or interpretation for individual patients.  Gait analysis is also proposed as a biometric technique for security purposes. It’s not restricted to humans – Google up “canine” or “equine gait analysis” and you might be surprised by the number of hits.

None of us has a monopoly of such a generic term as “gait analysis” or even “clinical gait analysis” but I do think there is a need for something that refers specifically to what I do (perhaps as far as most readers of this blog are concerned to what we do). Trying to claim that only someone that does what I do is involved in gait analysis is ridiculous and mildly insulting to other practitioners. Perhaps we need a more specific term for what we do.

Some people use “3-d gait analysis” but taking a coronal and sagittal plane video, or even just watching someone walk from different angles is three dimensional. “Instrumented gait analysis” has also been used  but there are a wide range of instruments – a single force plate for example. The best I can come up with while writing this article is “Comprehensive Clinical Gait Analysis” (CCGA). To me this captures the aim of getting a reasonably complete picture of the way someone is walking (even if its rare that anything like a complete picture actually emerges!). Anyone have any other ideas?