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<p>Definitions of the abbreviations of the markers are given in Table.</p

Leg and Joint Stiffness in Children with Spastic Diplegic Cerebral Palsy during Level Walking

<div><p>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.</p></div

Means (SD) of the initial values, total changes and normalized total changes of the inter-marker distances for each of the marker pairs of the mandible.

<p>The ‘group mean’ shows the mean of the normalized total changes over the whole group of markers. (unit: cm) Definitions of the abbreviations of the markers are given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0096540#pone-0096540-t001" target="_blank">Table 1</a>.</p

(a) Amount, (b) monthly change, and (c) percentage of change of the volume of the mandible over the monitoring period.

<p>(a) Amount, (b) monthly change, and (c) percentage of change of the volume of the mandible over the monitoring period.</p

Effective GRF and effective leg length.

<p>Stick figure of a lower limb during stance phase of gait showing the definitions of the effective GRF (thin vector, Fe(t)) and effective leg length (<i>L</i>_<i>e</i>(t)). The former is defined as the component of the measured GRF (thick vector) along the line joining the center of pressure (COP) and the hip joint center. The latter is defined as the distance between the COP and the hip joint center.</p

Means (standard deviations) of the time-averaged angles and moments of the hip, knee and ankle in the sagittal plane over each of the sub-phases of the stance phase of gait for children with CP and the control group.

<p>An asterisk indicates a significant group difference (<i>p</i> < 0.05). %BW*LL indicated the moments normalized to the body weight and leg length.</p

Means (standard deviations) of the temporal-spatial parameters of gait for children with CP and the controls.

<p>Statistical results using an independent-samples t-test are shown. An asterisk indicates a significant group difference (<i>p</i> < 0.05).</p

Percentages of change of inter-marker distances of the left side of the mandible over the monitoring period for the (a) anteroposterior, (b) superoinferior, (c) anteroinferior, and (d) mediolateral marker groups.

<p>Definitions of the abbreviations of the markers are given in Table.</p

Skeletal and muscular components of the leg stiffness <i>(K</i>_<i>l</i>).

<p>φ(t) is the angle between the longitudinal axis of the shank and the line joining the COP of the GRF; <i>K</i>_<i>s,l</i> (<i>t</i>) is the skeletal component in <i>K</i>_<i>l</i> (<i>t</i>); <i>K</i>_<i>m,l</i> (<i>t</i>) is the muscular component in <i>K</i>_<i>l</i> (<i>t</i>); <i>K</i>_<i>s</i>(<i>t</i>) is the skeletal stiffness; and <i>K</i>_<i>m</i>(<i>t</i>) is the muscular stiffness.</p

The experimental setup for the CBCT scan of a typical subject.

<p>The experimental setup for the CBCT scan of a typical subject.</p