Page 61 - Maximizing the efficacy of ankle foot orthoses in children with cerebral palsy

immobilize the ankle in zero degrees. We presume that this was the effect of an offset between the foot markers and the position of the bony landmarks. More specifically, the foot markers (placed on the shoe) were not replaced between the trials, while the insole wedges lifted the foot inside the shoe.
Also comparable to our results, the tuned AFO-FC in the Jadamma study[12] resulted in an increased internal peak knee extensor and ankle plantar flexion moment, whereas the peak hip moment remained unchanged. While we did expect to see these changes at the ankle and knee joints, the unchanged internal hip moment between conditions was in contrast to our hypothesis. In our study, subjects may have positioned the thigh such that the ground reaction force was aligned close to the hip joint at midstance, independent from shank kinematics, therewith showing similar internal hip joint moments between heel height conditions at this stage. Although AFO-FC heel height manipulations and the resulting changes in joint angles and moments found in Jagadamma’s studies[11,12] were smaller compared to our study, the nature of their effects was similar. Hence, our study confirms the responsiveness of the SVA to changes in AFO-FC heel height, though providing a more systematic change of heel height and, additionally, analyzing the effect of adjusting footplate stiffness.
Since literature on the effect of footplate stiffness on joint angles and moments is lacking, our results might best be compared to a study on the effect of different AFO footplate lengths[20]. Similar to the non-significant decrease in knee flexion angle as a result from the stiff footplate in our study, Fatone and colleagues[20] found a non- significant decrease in knee flexion angle while walking with the full-length footplate. The increase in the internal ankle plantar flexor moment as a result of the stiff footplate is also in agreement with that study[20], and may be explained by the ground reaction force shifting forward early in stance. On the contrary, Fatone’s study[20] showed a non- significant increase in the internal peak knee extensor moment in early stance while walking with a full-length footplate, compared to the three-quarter footplate. Yet, as they found that subtle changes in sagittal AFO-FC alignment had relatively less effect on the knee moments during stance compared to changes in the length of the footplate, Fatone et al.[20] suggested that adjustments in footplate length should be used to control the knee joint moments during stance. The interaction effect of heel height and footplate stiffness on the internal knee extensor moment found in our study, emphasizes the importance of considering footplate characteristics within AFO-FC tuning. In this context, tuning using footplate stiffness characteristics should however preferably be done using the ground reaction force, as the stiff footplate showed no effect on SVA.
III
The shank-to-vertical angle
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