In vivo operating lengths of the gastrocnemius muscle during gait in children who idiopathically toe‐walk

Abstract

Children who idiopathically toe-walk (ITW) habitually operate at greater plantarflexion angles than typically developing (TD) children, which might result in shorter, sub-optimal gastrocnemius fascicle lengths. However, currently no experimental evidence exists to substantiate this notion. Five children who ITW and 14 TD children completed a gait analysis, whilst gastrocnemius fascicle behaviour was simultaneously quantified using ultrasound. The moment-angle (hip, knee and ankle) and moment-length (gastrocnemius) relationships were determined from isometric maximum voluntary contractions (MVC) on an isokinetic dynamometer combined with ultrasound. During gait, children who ITW operated at more plantarflexed angles (Δ = 20 • ; P = 0.013) and longer muscle fascicle lengths (Δ = 12 mm; P = 0.008) than TD children. During MVC, no differences in the peak moment of any joint were found. However, peak plantarflexor moment occurred at significantly more plantarflexed angles (−16 vs. 1 • ; P = 0.010) and at longer muscle fascicle lengths (44 vs. 37 mm; P = 0.001) in children who ITW than TD children. Observed alterations in the moment-angle and moment-length relationships of children who ITW coincided with the ranges used during gait. Therefore, the gastrocnemius muscle in children who ITW operates close to the peak of the force-length relationship, similarly to TD children. Thus, this study indicates that idiopathic toe-walking is truly an ankle joint pathology, and children who ITW present with substantial alterations in the gastrocnemius muscle functional properties, which appear well adapted to the characteristic demands of equinus gait. These findings should be considered when prescribing clinical treatments to restore typical gait. K E Y W O R D S equinus, idiopathic toe-walking, muscle, ultrasoundThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Children who idiopathically toe-walk have greater plantarflexor effective mechanical advantage compared to typically developing children

“…The EMA was also negatively associated with toe-walking severity for children who ITW. However, children who ITW are not weaker than TD children, and indeed operate close to their optimal joint angle during gait (Harkness-Armstrong et al 2021 ). Therefore, it is unlikely that equinus is a strategy to reduce the muscle force requirements of gait for children who ITW, and rather, it appears more likely to be an additional consequence of the altered gait kinematics.…”

“…It is currently unknown what effect this will have on the required plantarflexor muscle force for gait, but data from this study indicate that if the gait kinematics matches those of TD children, the required muscle force could increase by up to 42% in children who ITW. Furthermore, clinical interventions may also, in the short-term, shift children who ITW away from their optimal joint angle (Harkness-Armstrong et al 2021 ). Consequently, if recovery and post-intervention rehabilitation time is not sufficient to allow plastic changes in the muscle properties, or if a child does not have adequate muscle strength or endurance to meet the compound effects of reduced EMA and impaired utilisation of the force–length properties post-intervention, this may be a reason why current clinical interventions have poor medium to long term outcomes and high rates of recurrence (Dietz and Khunsree 2012 ; van Kuijk et al 2014 ).…”

“…It is likely that these treatments negatively alter the plantarflexor EMA and thus, increase the plantarflexor muscle force required for gait. Moreover, we have recently shown that children who ITW present with substantial alterations in the gastrocnemius muscle functional properties, with the optimum joint angle in more plantarflexed positions than typical, but well aligned with the active range of motion during gait (Harkness-Armstrong et al 2021). Consequently, treatments may, in the short-term, shift children who ITW away from their optimum joint angle.…”

“…Therefore, equinus gait has been suggested to be, in part, a compensatory mechanism for plantarflexor weakness (Hampton et al 2003 ). However, children who ITW do not present with plantarflexor weakness and indeed, were shown to operate close to optimal joint angle during gait (Harkness-Armstrong et al 2021 ).…”

Reply to Veerkamp et al.: Comments on Harkness‐Armstrong et al. (2021)

“…

We would like to thank Veerkamp and colleagues for both their interest and their further exploration of the experimental data we reported in our recent publication in Experimental Physiology (Harkness-Armstrong et al, 2021). Idiopathic toe-walking (ITW) is an interesting, under-

…”