Passive dynamics of the knee joint in healthy children and children affected by spastic paresis.

OBJECTIVE The purposes of this study were (1) to evaluate how changes in biomechanical parameters affect segment dynamics in children and (2) to determine whether the biomechanical parameters were changed in children with spastic paresis. DESIGN In vivo measurements were collected of knee viscoelastic properties. Background. It is unknown if the inertial and viscoelastic properties of a human growing limb should be considered in motor performance. Also unclear are whether changes in passive dynamics might be responsible for abnormal control in human spastic paresis. METHOD Small oscillation techniques were used to measure moment of inertia of lower leg, stiffness and viscous damping of the knee joint. Eighty seven healthy children and 32 children with spastic paresis participated. RESULTS Moment of inertia, stiffness and the damping changed with the fifth power of child's height. Dynamic equation of motion parameters were a constant, independent of the child's height. Passive viscoelastic parameters were not changed in spastic patients. CONCLUSIONS Inertial and viscoelastic properties of a growing limb segment should not be considered in motor performance. Passive viscoelastic properties were not changed in patients with spastic paresis and, therefore, cannot be responsible for abnormal control in human spastic paresis. RELEVANCE There is no need to adapt control patterns in children (ages 6-18). Passive viscoelastic parameters cannot be used as a descriptor of spasticity.