Participants • N=20 (10 male, 10 female)• Mean age = 13.1 ± 3.5 years• 17 hemiplegia, 3 diplegia • Gross Motor Function Classification System level I-II

Prosser LA laura.prosser@nih.gov, Bland DC, Bellini LA, Alter KA, Damiano DL damianod@cc.nih.gov Functional and Applied Biomechanics Section, Rehabilitation Medicine Department, NIH Clinical Center

INTRODUCTION

HYPOTHESIS

METHODS

RESULTS

DISCUSSION

REFERENCES

TA muscle architecture on the more affected side will be related to muscle strength and gait impairments in children with CP and unilateral foot drop.

Muscle architecture partially explains the degree of impairment in ankle strength and gait function in individuals with CP. Moderate relationships between architecture and function suggest additional factors affect functional ability in CP, including disruption in neural activation [2], muscle consistency [3], variations in fiber size and type [4], and selective voluntary motor control [5]. These data also support existing evidence that the more affected TA is significantly smaller than the less affected TA [1], and that muscle size is related to strength in children with CP [6].

Interventions focused on increasing TA size and strength may lead to improvements in gait. Future research should investigate the efficacy of training programs (i.e., resistance training, functional electrical stimulation, or intense motor practice) to lessen asymmetries, and thereby improve ankle function during gait.

1. Bandholm T, et al. Neurorehabilitation, 2009; 24(4): 299-306.2. Stackhouse SK, et al. Muscle Nerve, 2005; 31: 594-601.3. Booth CM, et al, Dev Med Child Neurol, 2001; 43: 314-20.4. Rose J, et al, J Orthop Res, 1994; 12:758-68.5. Fowler E, et al. Dev Med & Child Neurol 2010, 52: 264-9.6. Ohata. Physical Therapy, 2006; 86 (9): 1231-9.

Procedures• Participants were seated on an isokinetic dynamometer in 60º knee

flexion, and 0º ankle position. • Bilateral longitudinal and cross-sectional ultrasound images were

obtained at the thickest point of the TA muscle belly and analyzed with MIPAV software (Figure 2).

• Participants performed 3 maximum isometric contractions (MVIC) of dorsiflexor muscles on the more affected side. The peak force was used for analysis.

• 3D gait data were collected during trials of self-selected (SS) and “as fast as possible” (FAST) speeds and processed in Visual 3D (Figure 3).

As anticipated, TA muscle size was smaller on the more affected side than the less affected side. MT was 27.3% smaller and CSA was 34.8% smaller. PA was not different between sides (Figure 2). Gait measures were also significantly different between sides at both speeds for the majority of variables analyzed, including ICDf, DfMxSt, MTO, DfMxSw, DfMn, and velDf.

MT was related to CSA, strength (MVIC), step length, MTO and DfMxSw during self-selected walking and to step length, and velDf during fast walking. PA was not related to strength, gait function, or any other muscle architecture variable except for ICDf during the self-selected pace. CSA was related to strength, step length, DfTO, MTO, DfMxSw, and DfMn during self-selected walking, and to step length, DfMxSw, and DfMn during fast walking (Table 1).

4 7

Relationship of Tibialis Anterior Muscle Architecture to Gait Function in Children with Cerebral Palsy

This research year was funded by the Intramural Program of the NIH Clinical Center and

the Clinical Research Training Program, a public-private partnership supported jointly by

the NIH and Pfizer Inc (via a grant to the Foundation for NIH from Pfizer Inc).

Data Analysis• Outcome variables representing ankle function included:

• ICDF - Dorsiflexion angle at initial foot contact • DfMxSt - Maximun dorsiflexion angle in stance • DfTO - Dorsiflexion angle at toe off • MTO - Plantarflexion moment at toe off • DfMxSw - Maximum dorsiflexion angle in swing • DfMn - Mean dorsiflexion angle in swing • velDf - Ankle dorsiflexion velocity in swing • Step length

• Differences between more and less affected legs were analyzed with paired t-tests. Relationships between muscle architecture, gait, and strength were evaluated with correlation coefficients.

Figure 3: Mean ankle angle through gait cycle from a representative participant.

*

Figure 2. Representative longitudinal (top) and transverse views (bottom) of the tibialis anterior muscle on the more (left) and less (right) affected side.

The ankle is one of the most commonly affected joints in ambulatory children with cerebral palsy (CP). Common gait abnormalities include inadequate dorsiflexion during the swing phase of gait or “foot drop.” Ambulatory children with CP exhibit asymmetries in tibialis anterior muscle (TA, Figure 1) size between their more and less affected legs [1]. However, relationships between TA muscle architecture and gait have not been investigated. The purpose here was to examine the relationship of TA muscle thickness (MT), pennation angle (PA), and cross-sectional area (CSA) to ankle function during walking in children with unilateral foot drop.

MVIC Step

length ICDf DfMxSt DfTO MTO DfMxSw DfMn velDf

SS MT 0.59* 0.55* -0.01 -0.02 0.29 -0.63* 0.47* 0.36 0.38

PA 0.01 0.00 0.45* 0.13 -0.07 -0.34 0.01 0.11 -0.27

CSA 0.50* 0.48* 0.13 0.21 0.52* -0.70* 0.64* 0.60* 0.24

FAST MT 0.55* 0.10 -0.30 -0.04 -0.30 0.40 0.25 0.50*

PA 0.15 0.14 0.21 -0.27 -0.26 -0.26 -0.23 -0.13

CSA 0.45* 0.30 0.11 0.27 -0.25 0.61* 0.54* 0.41

*significant at α=0.05 level

Table 1. Relationships between measures of muscle architecture and function on

the more affected side

Figure 1. Tibialis anterior muscle.