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In vivo evaluations of biomechanical changes of calf muscle fascicles and Achilles tendon in children with cerebral palsy.

F GAO PHD 1, D GAEBLER-SPIRA 2, 3, L ZHANG 2, 3

1. The University of Texas at Tyler, Tyler, TX;
2. Rehabilitation Institute of Chicago, Chicago II;
3. Northwestern University, Chicago, II, USA

Background/Objectives: It is not clear how the calf muscle and Achilles tendon change in cerebral palsy, which may play significant roles in spasticity, reduced ankle range of motion and motor impairment of children with cerebral palsy. The objectives of this study were to examine the biomechanical changes of the calf muscle fascicles, Achilles tendon and the ankle simultaneously in children with CP. It was hypothesized that the biomechanical properties of the fascicles (length, pennation angle, and muscle thickness), tendon (length and cross-sectional area) and ankle joint (resistance torque) were not significantly different between the CP and control groups.

Design: Cross-sectional study.

Participants and Setting: Eight children with CP (four hemiplegia and four diplegia; weight: 34 ± 8.7 kg; height: 142.7 ± 14.3 cm; age: 11.1 ± 2.7 year, shank length: 33.1 ± 1.6 cm; modified ashworth scale: 2.0 ± 0.53) and eleven age and gender matched healthy subjects without any neurological and muscular disorder served as controls (weight: 50.9 ±12.5 kg; height: 158.7 ± 6.9 cm; age: 12.6 ± 2.3 year; shank length: 35.7 ± 2.9 cm).

Materials/Methods: For both groups, B-mode ultrasonography was used to evaluate architecture of the medial gastrocnemius muscle including fascicle length, pennation angle and muscle thickness at various ankle (30 and 15 degree plantar flexion and 0 and 10 degree dorsi-flexion) and knee (full extension, 30, 60 and 90 degree flexion) positions. At each position, the length and cross sectional area of the Achilles tendon were evaluated using ultrasonography and the ankle joint resistance torque was also measured.

Results: Compared to the controls, children with CP had significantly shorter muscle fascicles, smaller muscle thickness, longer Achilles tendon and smaller tendon cross-sectional area across most of the test conditions (P<0.05). The pennation angle and the passive resistance torque at comparable ankle positions were not significantly different between the two groups.

Conclusions/Significance: In summary, the gastrocnemius muscle fascicles become shorter and muscle becomes thinner. In contrast, the Achilles tendon becomes longer and smaller in cross-sectional area. These muscle-tendon changes indicate a proximal shift of the muscle-tendon junction. The changes in tendon properties could be due to adaptation to the changes of the calf muscle. Rehabilitation such as passive stretching and movement training may potentially loosen and elongate muscle fascicles and reverse these changes for improved motor functions.

 
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