Children with cerebral palsy have larger Achilles tendon moment arms than typically developing children

Area of Science:

• Biomechanics
• Orthopedics
• Pediatric Rehabilitation

Background:

• The effectiveness of plantarflexor muscles in generating plantarflexion moments is influenced by Achilles tendon moment arm (ATMA) geometry.
• Reduced plantarflexion function in children with cerebral palsy (CP) is often attributed to muscle impairments, with less focus on ATMA geometry.
• Accurate ATMA estimation is vital for reliable musculoskeletal modeling in gait analysis.

Purpose of the Study:

• To compare 3D in-vivo ATMA estimates across adults, children with CP, and typically developing (TD) children.
• To evaluate the accuracy of ATMA estimates derived from linearly scaled musculoskeletal models against in-vivo measurements.
• To investigate the potential role of ATMA geometry in the reduced plantarflexion function observed in children with CP.

Main Methods:

• Utilized MRI scans from 8 children with CP, 11 TD children, and 9 healthy adults.
• Estimated 3D in-vivo ATMA using a validated method.
• Generated linearly scaled ATMA estimates from a lower limb musculoskeletal model scaled to individual tibia length.

Main Results:

• Normalized in-vivo 3D ATMA was significantly larger in children with CP (17.2% ± 2.0 tibia length) compared to TD children (15.2% ± 1.2) and adults (12.5% ± 0.8).
• Linear scaling of musculoskeletal models significantly underestimated in-vivo ATMA estimates across all groups, with discrepancies up to 34.7%.
• These findings highlight significant differences in ATMA geometry between children with CP and their typically developing peers.

Conclusions:

• Children with CP exhibit larger normalized 3D ATMA compared to TD children.
• This larger ATMA may contribute to the reduced plantarflexor function observed in CP.
• The study suggests that ATMA geometry should be considered in understanding CP-related gait impairments and in planning surgical interventions.