The effect of foot deformities on the interplay of forces within the foot: An analysis of multi-segment foot joint moments in cerebral palsy.

BACKGROUND

Foot deformities are common in cerebral palsy (CP) and are likely caused by a disturbed interplay of forces in the foot. Evaluation of foot joint moments would therefore be highly relevant. However, kinetic foot models have not previously been applied to children with CP.

RESEARCH QUESTION: What is the difference in multi-segment foot joint moments between children with CP with foot deformities and children with typically developing (TD) feet?

METHODS

Children with spastic paresis were retrospectively included and compared to TD children. All children underwent clinical gait analysis, including a kinetic multi-segment foot model based on the Amsterdam Foot Model marker set. Internal joint moments of the ankle and midfoot (Chopart, Lisfranc) joints were calculated for each group.

RESULTS

67 feet of 40 children with spastic paresis (26 neutral, 25 planovalgus, 11 cavovarus, 5 equinovarus feet), and 15 feet of 15 TD children were included. Internal foot joint moments in children with CP with a cavovarus or equinovarus deformity showed an early ankle plantarflexion peak and increased valgus moments, increased Chopart plantarflexion and eversion moments, and increased Lisfranc abduction moments compared to TD feet. Planovalgus feet demonstrated early ankle plantarflexion and increased varus moments, increased Chopart adduction and reduced Lisfranc abduction moments compared to TD feet.

SIGNIFICANCE: The direction of the differences found in cavovarus, equinovarus and planovalgus feet indicates that the internal joint moments are generally opposite to the malalignment of the foot. This indicates that external joint moments, which are caused by external forces and can be assumed to be opposite and equal to the internal moments, may contribute to further development of the deformity. Hence, the forces that cause deterioration of foot deformity in CP may not only be a result of muscle actions, but also of altered external loading due to abnormal foot alignment. This highlights the importance of early interventions to realign the foot to prevent deterioration of a foot deformity.