Muscle and tendon lengthening behaviour of the medial gastrocnemius during ankle joint rotation in children with cerebral palsy

Abstract

Children with cerebral palsy (CP) commonly present with reduced ankle range of motion (ROM) attributable, in part, to changes in mechanical properties of the muscle-tendon unit (MTU). Detailed information about how muscle and tendon interact to contribute to joint rotation is currently lacking but might provide essential information to explain the limited effectiveness of stretching interventions in children with CP. The purpose of this study was to quantify which structures contribute to MTU lengthening and thus receive the stretch during passive ankle joint rotation. Fifteen children with CP (age, in mean ± SD, 11.4 ± 3 years) and 16 typically developing (TD) children (age, in mean ± SD, 10.2 ± 3 years) participated. Ultrasound was combined with motion tracking, joint torque and EMG to record fascicle, muscle and tendon lengthening of the medial gastrocnemius during passive ankle joint rotations over the full ROM and a common ROM. In children with CP, relative to MTU lengthening, muscle and fascicles lengthened less (CP, 50.4% of MTU lengthening; TD, 63% of MTU lengthening; P < 0.04) and tendon lengthened more (CP, 49.6% of MTU lengthening; TD, 37% of MTU lengthening; P < 0.01) regardless of the ROM studied. Differences between groups in the amount of lengthening of the underlying structures during a similar amount of joint rotation and MTU displacement indicate possible differences in tissue mechanical properties attributable to CP, which are not evident by assessment at the level of a joint. These factors should be considered when assessing and treating muscle function in children with CP, for example during stretching exercises, because the muscle might not receive much of the applied lengthening stimulus.

Medial gastrocnemius muscle stiffness cannot explain the increased ankle joint range of motion following passive stretching in children with cerebral palsy

“…Nonetheless, for any remodelling of the muscle to take place, the fascicles must experience sufficient stretching stimulus. In a previous study, we have shown that when rotating the ankle joint, this stretching stimulus to the muscle fascicles is smaller in children with CP than their typically developing peers (Kalkman et al., ). Likewise, it has been shown that when stretching over the full ROM, muscle and tendon lengthen less than in typically developing children (Hösl, Böhm, Arampatzis, & Döderlein, ).…”

“…Altered muscle–tendon properties in CP might lead to a reduced ROM, but these alterations might also mediate the response to stretching interventions, as seen in typically developing individuals. For example, previous studies show that in CP, muscles are shorter (Fry, Gough, & Shortland, ; Malaiya et al., ; Oberhofer, Stott, Mithraratne, & Anderson, ), tendon slack length is longer (Barber, Barrett, & Lichtwark, ; Gao, Zhao, Gaebler‐Spira, & Zhang, ) and relative muscle‐to‐tendon stiffness is increased (Kalkman et al., ). It is unknown how these altered properties mediate the acute response of a muscle to stretching in individuals with CP.…”

Stretching Interventions in Children With Cerebral Palsy: Why Are They Ineffective in Improving Muscle Function and How Can We Better Their Outcome?

“…This is accompanied by a greater length of the Achilles tendon in children with CP (Wren et al, 2010;Barber et al, 2012). Furthermore, some studies have reported reduced muscle fascicle lengths at rest in children with CP than in TD children (Mohagheghi et al, 2008;Matthiasdottir et al, 2014;Kalkman et al, 2018b; D' Souza et al, 2019;Frisk et al, 2019), but others have not detected differences (Shortland et al, 2002;Malaiya et al, 2007).…”

“…It has been shown that, when the ankle joint is passively dorsiflexed n children with CP, the belly of medial gastrocnemius muscle elongates less compared to TD children (Matthiasdottir et al, 2014). Additionally, some studies have reported lengthening of the muscle fascicles to be unaltered during passive joint rotation (Matthiasdottir et al, 2014), while others show a reduction in fascicle lengthening in CP when compared to TD children (Barber et al, 2011;Kalkman et al, 2018b). These inconsistent findings could potentially be accounted for by different ways of comparing groups.…”

“…Additionally, due to differences in Achilles tendon moment arm length (Kalkman et al, 2017) and joint stiffness (Alhusaini et al, 2010) between TD and CP participants, comparisons in terms of joint angles should be interpreted with caution. To circumvent this problem, fascicle lengthening during passive joint rotations has been additionally studied over a common torque range and a common MTU lengthening, where it was found that irrespective of the method used the stiffness of the muscle fascicles relative to their in-series tendon was higher in children with CP (Kalkman et al, 2018b).…”