In our lab in Uppsala, Sweden, we are also working to some extend with gait analysis for children with cerebral palsy, and we expect this activity to increase in the future. We are using video cameras and a force plate. The use of walking aids is indeed complicating the measurement and analysis. Among other things it is important to make sure that the crutch or walker does not intefere with the force plate data. In other words the walking aids must not touch the force plate. If this condition is fulfilled, my opinion is that it is still valid to use the normal inverse dynamic model for the estimation of joint moments and power at lower extremety joints, as long as the walking aid only provide external forces to the upper extremeties. When the computation scheme starts from the force plate and the calculations proceed to the ankle, knee and hip joints, then the external forces from a crutch will be taken care of by the force plate data (If 10% of body weight is carried by the crutches, then the force plate data will be reduced by 10%). There are other problem that I think can be practically more important, like the problem of getting a child with walking difficulties to hit the force plate properly, especially if you hide the force plate by a math (which is of course desirable for other reasons). Another problem is that the joints of interest can be obscured by the walking aid, which complicates the kinematic data collection. An area where there is a need for modification of the used model is when an leg orthosis is used that directly influences the load transmitted by the joint. In such cases I do not have any good suggestions on how to estimate the load distribution unless the orthosis is instrumented. We sometimes use moment arms of the ground reaction force instead of talking about joint moments. By doing this we avoid the load distribution problem, and it is possible to assess the effect of a knee orthosis on the varus/valgus inclination in this way. We have seen dramatic decreases in the moment arm of the ground reaction force with respect to the knee joint in the frontal plane as a result of using a suitable orthosis as compared to walking without an orthosis. The hypothesis is then that it is favourable to have relatively small moments arms, since this is correlated with small external moments and thus probably to small joint loads. Concerning walking with crutches, we have also been doing measurements with the subject walking in a way so that only the crutch and not the feet are hitting the force plate. From such measurements we can see to what extent the crutch is actually used during walking. Such measurements have only been done on adult amputees. I will be glad to continue the communication with you, since we probably have many common interests. On thing that we are presently considering is measurement of postural stability of children with neurological problems. Do you have any experience in this area (The measurements will concerns sitting and standing on a force plate). Yours sincerely Haakan Lanshammar ************************************ * From: Haakan Lanshammar * hl@SysCon.uu.se * * Tel: 018-18 30 33 * Fax: 018-50 36 11 ************************************Dear Chris, I was involved in the technical aspects of similar studies here in Belfast. The surgeon who headed the project was an orthopaedic surgeon whose name is Kerr Graham. The aforementioned has since become Professor of Orthopaedic Surgery along the coast from you in Melbourne. Exactly where in Melbourne I don't know off hand. But it shouldn't be difficult to find out. He would be the man to talk to since he has used gait analysis (VICON system) routinely to plan corrective surgery in children as well as analysing the effects of muscle relaxant drugs to improve the gait in CP children (rather than surgical solutions) If you do manage to get hold of him please pass on my best wishes! Also, get back to me if you can't find him and I will get an exact address. I am fairly sure he would be most interested in your work and will prove to be a valuable "resource". Best wishes from a damp Ireland Joe Murphy ========================================================== | "JOSEPH.MURPHY"
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