The effects of ankle foot orthoses on energy recovery and work during gait in children with cerebral palsy

Abstract

Background: Studies suggest that 50% of children with cerebral palsy are prescribed ankle foot orthoses. One of the aims of ankle foot orthosis use is to aid in walking. This research examined the effects that ankle foot orthoses have on the energy recovery and the mechanical work performed by children with cerebral palsy during walking.

Methods: Twenty-one children with spastic diplegia walked with and without their prescribed bilateral ankle foot orthoses. Ten of the subjects wore articulated (hinged) orthoses and 11 subjects wore solid orthoses. Three dimensional kinematic data were collected and between and within group repeated measures ANOVAs were applied to the dependent measures.

Findings: The results were similar for both groups. There was an increase in stride length, energy recovery, and potential energy and the kinetic energy variation. There was no change in the mechanical work performed to walk or the normalized center of mass vertical excursion. Unfortunately, the increase in energy recovery did not alter the external work, as it was offset by increased variation in the potential and kinetic energies of the center of mass. There was a great deal of variability in the measured work, with both large increases and decreases in the work of individual subjects when wearing orthoses.

Interpretation: These results suggest that current ankle foot orthoses can reduce the work to walk, but do not do so for many children with cerebral palsy. This research suggests that ankle foot orthosis prescription could be aided by measuring the mechanical work during walking.

Figure 1

The mean energy curves for BF and AFO conditions of all subjects. The dotted lines are KE and solid lines are PE. Thick lines are the BF condition and thin lines are the AFO condition. AFO use increased the variation of both energies and moved the relative phase closer to the ideal of 180°.

Figure 2

Fourier coefficients of (A) the PE and (B) the KE for BF and AFO conditions. FIH and FEH are indicated. FIH differed between conditions for PE. *P<0.001.

Figure 3

A histogram of the frequency of Positive, No Change, and Negative effects of AFO use on dependent measures. No Change was defined as any change of less than 10% of the no brace values. Positive and Negative were defined as changes of more than 10% that would lead to a reduction or increase in work, respectively. For the relative phase a change of 10° was used to group the subjects.