The leg drop pendulum test in spastic cerebral palsy: the addition of active elements to a passive, nonlinear, second order model

Abstract

This paper reports on ongoing work in the modelling of the leg drop pendulum test as a means of assessment in spastic cerebral palsy. In a previous paper, the author demonstrated that a passive model, while adequate for modelling normal limbs, is not adequate for modelling the limb of a subject with spastic cerebral palsy. This paper extends the previous work by presenting the results of an active model which was optimized to fit data taken from three subjects. The result of the optimization process demonstrates several important points. First, the model with active elements gives a better fit to real data than any combination of the previous passive model elements. Second, the addition of active elements, which are physiologically justifiable, allows the removal of passive elements from the previous model which were not physiologically justifiable. One of the more unique features of this work is the subjects: a set of identical triplets, two of whom have varying degrees of spastic cerebral palsy and one who is without a disability. As a result, the author had a "control" available from which a "normal" model could be derived. The paper presents a model based on passive elements derived from the "normal" triplet combined with active elements that cause the model to respond to the leg drop pendulum test in the same way as do the limbs of the two disabled subjects.