Abstract
Individual joint deviations are often identified in the analysis of cerebral palsy (CP) gait. However, knowledge is limited as to how these deviations affect the control of the locomotor system as a whole when striving to meet the demands of walking. The current study aimed to bridge the gap by describing the control of the locomotor system in children with diplegic CP in terms of their leg stiffness, both skeletal and muscular components, and associated joint stiffness during gait. Twelve children with spastic diplegia CP and 12 healthy controls walked at a self-selected pace in a gait laboratory while their kinematic and forceplate data were measured and analyzed during loading response, mid-stance, terminal stance and pre-swing. For calculating the leg stiffness, each of the lower limbs was modeled as a non-linear spring, connecting the hip joint center and the corresponding center of pressure, with varying stiffness that was calculated as the slope (gradient) of the axial force vs. the deformation curve. The leg stiffness was further decomposed into skeletal and muscular components considering the alignment of the lower limb. The ankle, knee and hip of the limb were modeled as revolute joints with torsional springs whose stiffness was calculated as the slope of the moment vs. the angle curve of the joint. Independent t-tests were performed for between-group comparisons of all the variables. The CP group significantly decreased the leg stiffness but increased the joint stiffness during stance phase, except during terminal stance where the leg stiffness was increased. They appeared to rely more on muscular contributions to achieve the required leg stiffness, increasing the muscular demands in maintaining the body posture against collapse. Leg stiffness plays a critical role in modulating the kinematics and kinetics of the locomotor system during gait in the diplegic CP.
Highlights
Cerebral palsy (CP) is an irreversible and non-progressive disorder caused by brain injury before, during or shortly after birth [1]
During terminal stance no significant differences in leg stiffness were found
The leg stiffness and related variables proposed in the current study provide a measure for assessing the control of the lower extremities as a whole in supporting the body against collapse during gait, which would be very helpful in the assessment of the effects of the pathology and the efficacy of relevant treatment methods in a clinical setting
Summary
Cerebral palsy (CP) is an irreversible and non-progressive disorder caused by brain injury before, during or shortly after birth [1]. During growth, impaired motor control often develops with secondary abnormalities such as bony deformities and changes in the joint and muscle. Depending on the level of involvement, children with CP may have different gait deviations, including increased hip flexion, increased knee flexion, decreased ankle dorsiflexion [1, 3], increased knee extensor moments [4], and increased hip extensor moments [5] during stance phase. Treatments may have different effects on these gait deviations. Interpreting the measured gait deviations and their changes in response to treatment can be very challenging [6]. A measure for assessing the control of the lower limb as a whole during gait would be very helpful in the assessment of the effects of the pathology and the efficacy of the treatment in a clinical setting
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