terminology

Gait graphs for beginners

I’m teaching about gait to the undergraduate physios next week. Its the first lecture I’ve given at this level trying to emphasise the approach I’ve developed in the Why we walk the way we do videos. The colleague who’s delivering the previous lecture – which included a first introduction to gait graphs – wanted to use the same format as I use which started a conversation about what aspects of walking we’d like those graphs to emphasize.

Knee graph

I’m pretty keen on fixed aspect ratios and scaling so that you can forget about those issues when you are actually looking at data – so we’ve fixed that.  We wanted also wanted to reinforce the terminology for different phases that I’ve described in a previous post – so we’ve put those abbreviated names across the top.

I also like to represent the continuity of the gait cycle – it amazes me how many people I come across who don’t seem to realise that point on the far left of the graph is the same as the point on the far right hand side (give or take a little stride to stride variability). It’s also not uncommon to spot data in the literature where values of gait variables at 0% and 100% are different but not commented upon. Various people in the past have tried plotting more than a single stride to try and emphasize continuity. I know Jurg Baumann was an advocate of this but can’t find easily get my hands on a sample. At Hof also used it – his 2002 paper on the speed dependence of EMG profiles is an example – but it has never really caught on. In this format I’ve tried to capture the point by allowing the gait curves to fade away to nothing outside the graph. It’s a bit messy if you’ve got a whole array of graphs but I kind of like it in the context of an introduction at this level.

I’m also very keen on getting students to appreciate what the right leg is doing plotted on the same time scale as the left leg. I know this insenses people who are paranoid about the importance of symmetry in gait but it’s a hell of a lot easier to explain the biomechanics if you look at the data this way. It’s unconventional of course so I’ve chosen to represent this as a much fainter line.

There was another question mark over the hip angle. As gait analysts most of us assume that this should be measured relative to a pelvic axis represented by the line from PSIS to ASIS and thus biasing the hip graph towards flexion. In assessing gait by observation, however, physios almost always consider the angle with the vertical which might be more relevant for daily practice. In the end we decided to stick with the gait analysis approach and just make sure we explain this very clearly.

Anyone got any additional features they like to add?

.

Hof, A. L., Elzinga, H., Grimmius, W., & Halbertsma, J. P. (2002). Speed dependence of averaged EMG profiles in walking. Gait Posture, 16(1), 78-86.

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?

.

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

Re recycling terminology

My second post on this blog was a suggestion that, when you think about it in detail, there are some problems with the conventional terminology that clinical gait analysts use to divide the gait cycle into phases and that a very simple scheme based upon simple division of the gait cycle into single support, double support and swing might have some advantages. Here is a video I’ve developed to help gait analysts reflect on the issues.

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?

Recycling terminology

Do other people struggle with the conventional terminology for describing the phases of the gait cycle? I’m not sure how this arose but the earliest reference I know of is the first edition of Jacquelin Perry’s book [1].

The first phase is initial contact and lasts for just 2% of the gait cycle. It should really be described as an instant in the gait cycle not a phase. Loading response is also a misnomer. Any response is what happens after an event and even the most cursory glance at the vertical component of the ground reaction shows that loading is not complete until well after the end of the loading response phase.

Mid stance isn’t in the middle of stance – as Perry describes it  it is the phase leading up to the middle of stance. Terminal stance isn’t at the end of stance – it ends at opposite foot contact. I quite like the term pre-swing as it emphasizes the continuity of the gait cycle and how the final requirement of stance is to prepare for swing. Following this logic, however, there is a much stronger case for labelling the phase prior to foot contact as pre-stance as preparing the limb for loading is extremely important in late swing.

Another puzzle is why single support and swing, which are the same phases of gait but viewed from the perspective of one limb or the other are divided into a different number of sub-phases. Single support is divided into two phases whereas swing is divided into three. This makes any attempt to describe gait taking into accounting for the interaction between the limbs is unnecessarily complicated.

Some of the technical delineations for the phases are also based on the characteristics of normal walking and it may not be clear how to delineate the phases for different types of pathological gait. Terminal stance, for example, starts with heel rise. Where does terminal stance start for a patient who walks on their toes and never has their heel down in the first place.  Mid-swing is defined as ending when the tibia is vertical. Patients walking with a crouched gait pattern, however, may not have a vertical tibia at any stage of the gait cycle.

I’m not really a fan of trying to re-define the terms to be more logical. This only leads to confusion. Try looking at the literature on crouch gait. There are at least four well accepted definitions of crouch gait and thus, unless there is additional clarification, it is actually impossible to know what any given individual is referring to when they use the term.

Phases of gait

The terminology I prefer is illustrated above. Single support and swing are both divided  into three or equal duration phases. The terms early, middle and late  are different to the original initial, mid and terminal which helps avoid confusion. The three letter abbreviations can be useful where brevity is an asset.

1.   Perry, J., Gait Analysis1992, Thorofare: SLACK.