Sorry its been so long since I’ve posted – I must try and get into the habit again. Particularly as I’ve had my 200th follower sign up this week.
This post is prompted by an e-mail from Rene van Ee in Nijmegen in the Netherlands. He wrote asking my opinions about using gait indices in amputees. We’re working on collaborative research with Headley Court in Surrey with some of the recent amputees from conflicts in Iraq and Afghanistan so the issue is quite pertinent to us at the moment as well.
The GGI, GDI and GPS/MAP are all essentially measures of deviations from the average healthy gait pattern. It is assumed that big deviations represent a poor quality gait and small deviations represent a high quality gait. The fundamental question is “Does this apply to amputees?”
In big picture terms, and particularly from a cosmetic point of view, I think the answer is almost certainly “yes”. We want amputees with reasonably “normal” gait patterns and big deviations from this can probably be seen as a bad thing. Many amputees, particularly young and otherwise fit soldiers with state of the art prostheses, however, walk extremely well nowadays. In this category, and particularly if you start considering the biomechanics, then the answer becomes less clear. The best way for a trans-femoral amputee to walk may not be to mimic “normal” walking as closely as possible.
My gut feeling is thus that any of the indices (they all measure deviation from normal in one way or another) will probably be useful measures of gait quality within the less able amputees but may become less useful with the better amputees. Our application is with some military amputees with very high levels of function so this is a big issue for us.
There is an argument that the human body has evolved for the joint to move in particular patterns during walking and that moving through other patterns may be detrimental. In this case measuring the deviation of the sound joints from normal may have some merit. I’d see this as a real advantage of the MAP. It allows you to see the different levels of deviation at the different joints. After that you could take the (RMS) average of the sound joints and create an index that effectively measures how well the movements of the anatomical joints mirror normal walking.
As an engineer, however, I’d expect abnormal joint loading to be at least as important as abnormal joint movement so maybe applying similar techniques to joint kinetics is more appropriate. There’s nothing to stop anyone extending the MAP to kinetics as well as kinematics. Adam and Mike have already proposed this for the GDI (Rozumalski & Schwartz,2011).
The problem with all these ideas is that they are quite complex and dependent on accepting a particular justification for any type of analysis. What I particularly like about the GPS and MAP are their simplicity and this just gets lost. There’s nothing wrong – it just doesn’t really appeal to me.
There is another way of looking at this that might have some merit. We tend to think of the control group used for the indices as “normal” walkers but an alternative would be to think of them as “optimal” walkers. In the healthy population it seems reasonable to just think of the “normal” gait pattern as optimal. It is quite possible that there is an optimal gait for amputees (if there is then there are probably several depending on the level of amputation). If you could select the optimal walkers out at each level then you could base a GPS/MAP/GDI/GGI style comparison against their data rather than against healthy “normal” walkers.
Of course you’d have to come up with some way of identifying the “optimal” walkers at each level. This might require some consideration of whether “optimal” varies with prosthetic componentry as well as amputation level. Perhaps I’ll leave that as a challenge for my readers.
Rozumalski, A., & Schwartz, M. H. (2011). The GDI-Kinetic: a new index for quantifying kinetic deviations from normal gait. Gait Posture, 33:730-732.