title: Musculoskeletal mechanisms of paediatric idiopathic toe-walking
Creators: name: Harkness-Armstrong, C
Publisher: name: Liverpool John Moores University
Year: 2021

description: Children who idiopathically toe-walk (ITW) walk in equinus with no known pathological, neurological, or orthopaedic cause. Therefore, they are a particularly challenging population for clinicians, as persistent, untreated equinus can lead to secondary problems, such as a worsening of symptoms, fixed deformity, and fixed contracture. Consequently, children who ITW are often prescribed with clinical interventions which target the plantarflexor muscles. However, at present, there is no knowledge about the musculoskeletal mechanisms which may contribute to the pathology of these children and thus, no knowledge as to the effect that such interventions may pose to muscle function. Therefore, the main body of work presented within this thesis aims to improve our understanding of the musculoskeletal mechanisms of children who ITW, with a specific focus on (1) the architecture and passive lengthening properties of the gastrocnemius medialis muscle, (2) muscle strength and the in vivo operating lengths of the gastrocnemius medialis muscle during gait, and (3) the effective mechanical advantage of the plantarflexors. Firstly, the gait kinematics and kinetics of children who ITW and typically developing (TD) children are presented in chapter 2. Between-group differences were observed in the sagittal plane at the ankle joint only. No between-group differences were found in the frontal or transverse planes at the ankle joint, or in any cardinal plane for the knee and hip joints. Secondly, chapter 3 assesses the architecture and passive lengthening properties of the gastrocnemius medialis muscle and Achilles tendon. Children who ITW were shown to have longer muscle belly and fascicle lengths and a shorter Achilles tendon length than typically developing (TD) children, regardless of which common joint position that groups were compared. Chapter 4 then assesses the gastrocnemius medialis muscle strength and functional properties relative to the demands of gait. Children who ITW were strongest at more plantarflexed angles and at longer fascicle lengths than TD children. Both alterations coincide with the ranges used during gait, suggesting that the alterations present in children who ITW are well adapted to the characteristic demands of equinus gait. To calculate the effective mechanical advantage of the plantarflexors during gait in children who ITW, a new and novel method needed to be developed to calculate the Achilles tendon moment arm in extreme plantarflexed positions. Therefore, chapter 5 develops a new method that can account for tendon curvature in the calculation of the Achilles tendon moment arm length. This method was shown to not only be reliable in simulated toe-walking, but was also relatively simple to perform, which could facilitate the implementation of such measures into routine clinical practice. Finally, in chapter 6, the new method was implemented to assess the effective mechanical advantage of the plantarflexors in children who ITW and TD children. Children who ITW were shown to have a greater plantarflexor effective mechanical advantage than TD children during propulsion, which consequently reduces the estimated muscle force requirements for children who ITW.