Achilles tendon moment arm length is smaller in children with cerebral palsy than in typically developing children
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Barbara M Kalkman1, Lynn Bar-On2, Francesco Cenni2
1Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK.
Insights
Children with cerebral palsy (CP) have a smaller Achilles tendon moment arm (MA_AT) length, impacting ankle function. This measurement can be predicted using anthropometric data like tibia length.
Area of Science:
- Biomechanics
- Pediatric Orthopedics
- Neuromuscular Function
Background:
- Muscle and whole-body function in children with cerebral palsy (CP) depend on internal and external moment arms.
- The Achilles tendon moment arm (MA_AT) is crucial for determining the mechanical advantage of the calf muscles at the ankle.
Purpose of the Study:
- To investigate differences in Achilles tendon moment arm (MA_AT) length between children with CP and typically developing (TD) children.
- To determine if anthropometric measurements can predict MA_AT in these populations.
Main Methods:
- A case-control study involving 16 children with CP and 20 TD children.
- MA_AT was calculated using calcaneus displacement at 20° plantarflexion.
- Seven anthropometric variables were measured and correlated with MA_AT.
Main Results:
- Normalized MA_AT was significantly smaller (15%, ~7mm) in children with CP compared to TD children (p=0.003).
- Tibia length was a strong predictor of MA_AT, explaining 79% of variance in children with CP and 72% in TD children.
- All measured anthropometric variables showed predictive capability for MA_AT.
Conclusions:
- Children with CP exhibit altered Achilles tendon moment arm geometry.
- MA_AT is predictable from anthropometric data, offering potential for clinical assessment.
- Understanding MA_AT is vital for surgical planning and improving ankle mechanical advantage in CP.
Abstract:
When studying muscle and whole-body function in children with cerebral palsy (CP), knowledge about both internal and external moment arms is essential since they determine the mechanical advantage of a muscle over an external force. Here we asked if Achilles tendon moment arm (MAAT) length is different in children with CP and age-matched typically developing (TD) children, and if MAAT can be predicted from anthropometric measurements. Sixteen children with CP (age: 10y 7m±3y, 7 hemiplegia, 12 diplegia, GMFCS level: I (11) and II (8)) and twenty TD children (age: 10y 6m±3y) participated in this case-control study. MAAT was calculated at 20° plantarflexion by differentiating calcaneus displacement with respect to ankle angle. Seven anthropometric variables were measured and related to MAAT. We found normalized MAAT to be 15% (∼7mm) smaller in children with CP compared to TD children (p=0.003). MAAT could be predicted by all anthropometric measurements with tibia length explaining 79% and 72% of variance in children with CP and TD children, respectively. Our findings have important implications for clinical decision making since MAAT influences the mechanical advantage about the ankle, which contributes to movement function and is manipulated surgically.
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