Research ArticleCEREBRAL PALSY

A lower-extremity exoskeleton improves knee extension in children with crouch gait from cerebral palsy

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Science Translational Medicine  23 Aug 2017:
Vol. 9, Issue 404, eaam9145
DOI: 10.1126/scitranslmed.aam9145
  • Fig. 1. Lower-extremity exoskeleton study description.

    (A) Image illustrating exoskeleton components on a study participant. To ensure accurate kinematic comparison between conditions, marker clusters were placed on limb locations free from interference with the exoskeleton and were not removed between conditions. EMG electrodes were placed over the vastus lateralis (vastus lat.) and semitendinosus (semitend.). (B) Timeline of the six visits, including two data collection assessments and practice visits. (C) Time spent walking over ground with the exoskeleton by each participant. (D) Schematic of gait cycle phases and the timing for the three modes of knee extension assistance: stance and swing (blue), stance only (red), and swing only (green). (E) Kinematic outcome measures included knee angle at initial contact (θ initial contact), peak knee angle during midstance (θ midstance), and total knee excursion. Knee angle data of a representative participant (P7) at baseline and with the exoskeleton and reference data from typically developing children and young adults from our clinical laboratory database are shown. EMG outcome measures included the integrated muscle activity (area under the EMG percent gait cycle curve) during stance [area under the curve (AUC) stance] and swing (AUC swing), normalized by the peak value of each muscle during baseline.

  • Fig. 2. Effect of exoskeleton assistance mode on crouch.

    Reduction in crouch, measured as increased knee extension angle compared to baseline walking during early (θ initial contact) and midstance (θ midstance) for the three assistance modes: stance and swing, stance only, and swing only. The darker and lighter bars depict group mean (n = 7) values of the more- and less-affected limbs, respectively. Error bars denote 1/2 SD; the large error bars indicate the large interparticipant variability (fig. S1). Significant differences between conditions are indicated (post hoc paired t tests with Bonferroni correction, P < 0.05).

  • Fig. 3. Biomechanical effects of exoskeleton extension assistance.

    (A) Knee angles across the gait cycle (GC) for each participant’s more- and less-affected limbs during exoskeleton walking under stance and swing assist (colored lines) and at baseline (thin black lines). Measured exoskeleton torques across the gait cycle (black dashed lines) for each limb, normalized by body mass, are plotted relative to the right axis. Bar charts below show the mean reduction in crouch during exoskeleton walking at midstance (left) and initial contact (right) for each individual. Vastus lateralis (B) and semitendinosus (C) EMG activity across the gait cycle for each participant’s more- and less-affected limbs during exoskeleton walking (colored lines) and baseline (thin black lines); EMG activity was scaled to baseline. Bars below are the mean change in EMG during exoskeleton walking relative to baseline during stance (left) and swing (right). For all bar plots, participants are presented from left to right by least-to-most improvement in crouch for their more-affected limbs. The darker and lighter bars depict the more- and less-affected limbs, respectively, and error bars denote 1/2 SD. Lines across the bar charts indicate group-level significant mean (avg.) changes from baseline for more-affected (dark shade) and less-affected (light shade) limbs (θ midstance for less-affected limbs: one-sided Wilcoxon signed-rank test, P < 0.05; all other comparisons: paired t tests, P < 0.05). All gait cycle plots are individual means ± 1 SD in shaded regions; darker and lighter lines depict more- and less-affected limbs, respectively.

  • Fig. 4. Improvement in crouch does not correlate with spasticity or strength.

    Mean reduction in crouch at midstance during exoskeleton walking plotted versus clinical measure of spasticity (modified Ashworth score; left) and body mass–normalized strength (MVIC, maximum voluntary isometric contraction; right) for the knee extensor (diamond) and knee flexor (circle) muscles. Pearson’s product-moment correlation analysis revealed no significant relationships between crouch reduction and spasticity (knee extensors, P = 0.77; knee flexors, P = 0.80) or strength (knee extensors, P = 0.41; knee flexors, P = 0.59).

  • Fig. 5. Change in biomechanical measures between first and last assessments.

    (A) Knee angle during midstance (θ midstance), knee angle at initial contact (θ initial contact), and step length for more-affected (dark shades) and less-affected (light shades) limbs and gait speed at the first and last assessment visits during baseline (black/gray) and exoskeleton stance and swing assist (dark/light blue) walking. Asterisks indicate significant differences between conditions during the first assessment (paired t tests, P < 0.05) in step length (more-affected limb, P = 0.025; less-affected limb, P = 0.039) and gait speed (P = 0.023). Differences between conditions at the last assessment are shown in Fig. 3 and fig. S3. (B) Change in vastus lateralis and semitendinosus activity during exoskeleton walking relative to baseline as measured by area under the curve. EMG data during the exoskeleton trials were normalized by the EMG from baseline walking within visits. All values plotted are group means (n = 7); error bars denote ±1/2 SD. Bold lines and P values indicate significant differences between visits (paired t tests, P < 0.05).

  • Table 1. Participant information.

    GMFCS, Gross Motor Function Classification System; MAS, modified Ashworth Scale for knee flexors of the more- and less-affected limbs; AFO, ankle-foot orthosis.

    Patient (ID)Age (years)GenderHeight (m)Body mass (kg)GMFCS levelMAS (more/less affected)Baseline conditionExoskeleton mass (kg)*
    P110Female1.4842.5II1+/1+AFO3.7
    P212Male1.7269.3I1/1Shod3.8
    P319Female1.4865.1II1/1Shod4.5
    P411Male1.3532.0II2/1+Shod3.0
    P56Male1.1120.0II0/0AFO3.1
    P611Female1.5640.8II1+/1+Shod3.6
    P75Male1.1520.6II1+/1AFO2.6

    *Exoskeleton mass is the combined total for both limbs.

    †P3 typically walks with crutches and was originally classified as GMFCS III; however, when prompted, she walked without assistance and was reclassified as GMFCS II.

    Supplementary Materials

    • www.sciencetranslationalmedicine.org/cgi/content/full/9/404/eaam9145/DC1

      Fig. S1. Effect of exoskeleton assistance mode on crouch by individual.

      Fig. S2. Biomechanical effects of walking with the null exoskeleton.

      Fig. S3. Effect of exoskeleton assistance on gait parameters.

      Fig. S4. Individual differences in crouch between first and last assessments.

      Fig. S5. Group-level change in biomechanical measures between first and last assessments during walking with the null exoskeleton.

      Table S1. Knee torque measurement by exoskeleton condition and muscle strength.

      Table S2. Individual subject-level data.

    • Supplementary Material for:

      A lower-extremity exoskeleton improves knee extension in children with crouch gait from cerebral palsy

      Zachary F. Lerner, Diane L. Damiano, Thomas C. Bulea*

      *Corresponding author. Email: thomas.bulea{at}nih.gov

      Published 23 August 2017, Sci. Transl. Med. 9, eaam9145 (2017)
      DOI: 10.1126/scitranslmed.aam9145

      This PDF file includes:

      • Fig. S1. Effect of exoskeleton assistance mode on crouch by individual.
      • Fig. S2. Biomechanical effects of walking with the null exoskeleton.
      • Fig. S3. Effect of exoskeleton assistance on gait parameters.
      • Fig. S4. Individual differences in crouch between first and last assessments.
      • Fig. S5. Group-level change in biomechanical measures between first and last assessments during walking with the null exoskeleton.
      • Table S1. Knee torque measurement by exoskeleton condition and muscle strength.

      [Download PDF]

      Other Supplementary Material for this manuscript includes the following:

      • Table S2 (Microsoft Excel format). Individual subject-level data.

      [Download Table S2]

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