clinical gait analysis

Clearing the air

Every so often I’m asked about why we tend to do clinical gait analysis barefoot and in AFOs (and shoes). One answer is that the barefoot condition tends to give a better indication of the full extent of a patient’s problems whereas walking in AFOs may be a better indication of how they function in everyday life. Another, however, is that sometimes walking in AFOs can help in identifying which particular impairments are having the most effect on gait. This was certainly the case when, a couple of weeks ago, I was reviewing one of the case studies we often use for teaching purposes but which exhibited features that I had not previously understood.

The analysis is of a seven year old girl with diplegic cerebral palsy (GMFCS III). She can take a few steps unaided but normally walks with a K-walker. We actually tested her in and out of the K-walker barefoot and in shoes and AFOs. the K-walker didn’t make that much difference to the kinematics with either condition so we’ll focus on the two unassisted walking conditions.

toe-walking-graphs

Perhaps the most obvious feature of the barefoot data is that she walks right up on her toes in considerable plantarflexion (feature c). The physical examination data shows that plantarflexor contractures (no passive dorsiflexion with knees extended beyond 10° plantarflexion ) can account for some of this but there are also signs of spasticity (from modified Tardieu and Ashworth tests). There is also, however, some suggestion of late (feature b) and reduced (feature a) knee flexion in swing. There is no clear explanation of this from the physical exam although there is a response to the Duncan-Ely test when performed quickly which might indicate some rectus femoris spasticity. Along with these specific findings the assessment indicates generalised weakness, persistent bilateral femoral neck anteversion and some mild tightness of the hip flexors.

The gait analysis with AFOs is quite different. The solid AFOs cast in a neutral position (which might have been assumed to be too aggressive given the physical examination) do appear to be holding the ankle in neutral  and substantially limit movement at the ankle (feature h).  The pelvis is a little more anteriorly tilted (feature d), possibly to move the centre of mass anteriorly as the new sagittal plane foot alignment will move the centre of pressure anteriorly (the steps were too short to get reliable kinetics). This would also exert a greater external extending moment at the knee which accounts for the hyperextension in late stance (feature g). The increased pelvic tilt leads to increased maximum hip flexion whereas the hyperextension pushes the knee back and maintains maximum peak hip extension. The overall effect is an increased range of movement at the hip (feature e). Perhaps most interestingly though, given that there is a question as to whether the rectus is spastic or not, is that peak knee flexion in swing is essentially normal (feature f). The slope of the knee graph through toe off is if anything a little steeper than normal. Such free flexion of the knee suggests that rectus spasticity is not a problem. Peak knee flexion is still delayed but this is clearly seen to be a consequence of the knee being too extended as it starts to flex in middle single support rather than of any stiffness. In summary, the data from the barefoot condition is inconclusive as to whether rectus femoris spasticity is contributing to the gait pattern but the data from the AFO condition provides quite strong evidence that it is not.

I hope that this has answered the question I posed at the beginning of this post but it does prompt another question – if there is no rectus spasticity then why is peak knee flexion so reduced in the barefoot condition?

I think the answer to this may lie in the observation that if a person is walking on their toes (and in plantarflexion) then it actually requires considerably less knee flexion for clearance in swing than in normal walking. In other words this girl may be showing reduced knee flexion in swing simply because she doesn’t need it when walking barefoot not because there is anything wrong with her knee function.In AFOs the ankle is held in neutral which makes clearance much more difficult and she has no option but to flex the knee more. It is interesting to note that when walking with shoes and AFOs she walks 20% slower than in bare feet and looks considerably less stable and fluent in her movements.

Rather than waste a lot of text in trying to explain why this occurs I’ve recorded a short video using Verne to illustrate that this is the case.

I go into the underlying concepts in relation to normal gait in this screen cast and have explored some of the other consequences of this for those walking in a more crouched gait pattern in this video blog.

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Gait analysis in the near future?

Last week we had a demonstration of new gait analysis software from Qualisys. It showed nearly automated capture of data from treadmill running and immediate export of data to a web-based report. It was really slick by comparison with other packages that I’ve seen, for which the developers require credit. Let’s hope it stimulates some competition amongst manufacturers to deliver truly user friendly systems. I still felt, however, that it is a long way from what should be possible given current technology.

It caused me to go back to a document a wrote for myself in 2009 trying to map out what  should happen in a clinical gait lab. It was my feeling that most of the technical elements described are currently available and all that is really required is for someone to stitch them all together. Here’s what I wrote:

The patient is welcomed at the door of the gait lab by a single gait analyst. The patient undresses to shorts and a t-shirt and the analyst attaches a number of markers quickly and easily to the patient. A small number of these have to be placed carefully but the others only need approximate locations.

The patient walks into the capture volume and stands still. The system detects they are standing still and captures the static trial. The patient performs the calibration exercises with or without assistance from the gait analyst (following a projection of what they are supposed to be doing on the wall of the laboratory). The system recognizes what they are doing and tells the gait analyst when sufficient calibration data has been captured.

Once this has happened the patient walks up and down several times.  Data capture is automatic and when sufficient data has been captured the system tells the gait analyst that this is the case. If data is required in another condition then the gait analyst tells the system this and the capture of walking data is repeated. The whole process takes about 15 minutes if one condition is required and another 10 minutes for any other conditions.

The quality of the data is continuously monitored. The system is only recalibrated when the system detects that this is required. Markers rarely fall off but if they do the system will tell the gait analyst who simply replaces them and the system automatically recalibrates for the slightly different marker position. Because there is redundancy in the system, it will continue to work even if one or two markers have fallen off. The system analyses the data and alerts the analyst immediately if there are any suspicious features (such as too much knee movement in the coronal plane).

All data is processed in real time and stored as required. The data is collated automatically into a report which is available immediately the tests are complete.

The system has been standardized so that essentially the same process takes place no matter where in the world the analysis is conducted and data from all sites is directly comparable.

I emphasize that all the elements to achieve this are already available. All we need is one (or all of the manufacturers) to cobble them together into a streamlined package. The system I saw last week was moving in the right direction but its still quite a long way from the final destination.

There’s a paragraph I’ve missed out that might be a bit more controversial and may take a little longer to develop:

… This report is based around a computer graphic animation of the subject walking with interpretation tools alerting the clinicians to specific features of the gait pattern and how these are linked to the patient’s underlying pathology. If the clinician wants then it will also make treatment suggestions. The entire report is written in a language that is comprehensible to a health professional with reasonable clinical experience but no specific training in 3-d gait analysis. There are no gait graphs in the report (although these are accessible should the clinician be old-fashioned enough to want to look at them).

Note I haven’t forgotten the physical exam – I’ve just assumed that this will have been conducted somewhere else beforehand, either immediately before at the same visit or on some previous occasion.