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RESEARCH PRODUCT

Medial gastrocnemius muscle and tendon interaction during gait in typically developing children and children with cerebral palsy

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1. IntroductionEfficient gait is dependent on optimal interaction between musclesand tendons [1]. Pathological changes in the extensibility of the MGmuscle fascicles, whole muscle-belly and Achilles tendon have beenreported in children with spastic cerebral palsy (CP) [2]. Studying therelative length of these tissues during gait can improve our understandingof their dynamics and, inferably, the control strategies used inCP. In-vivo dynamic ultrasound imaging has been used to visualise theinteraction between the MG muscle and tendon during 3D gait analysis.However, most studies combined ultrasound imaging of one variable(either fascicles or muscle-belly and tendon) with some form ofmusculoskeletal modelling to extrapolate the other variables, resultingin incomplete and variable findings [3–5].2. Research questionHow do MG muscle fascicles, belly, and Achilles tendon interactduring gait in children with cerebral palsy (CP) and typically developing(TD) children?3. Methods3D gait analysis was carried out in six children with CP (11 ± 3years, GMFCS I, uni/bilateral: 4/2) and six TD children (12 ± 4 years) asthey walked at a comfortable walking speed (average CP: 0.5 m/s, TD:1.0 m/s) on a treadmill. An ultrasound probe (Telemed SmartUS,60 mm) was attached to the non-preferred (TD) or most-affected (CP)leg using a custom-made probe holder (Probefix Dynamic, USONO),whose position was tracked by motion analysis. Images were collectedduring walking first with the probe on the mid muscle-belly, imagingfascicles and secondly with the probe on the most distal muscle tendonjunction (MTJ) to estimate both muscle-belly and tendon lengthchanges.Muscle-tendon unit (MTU) length-change represented combinedmuscle and tendon behaviour. Fascicle, MTU, muscle-belly andtendon length patterns were averaged over time-normalised gait cycles,and expressed relative to their lengths at initial contact [4]. Due to thesmall and heterogeneous sample, results are presented in a descriptiveway.4. ResultsGait kinematic and kinetic data showed that the children with CPhad mild gait deviations (1C-F). Children with CP showed reducedlength-changes of all tissues compared to TD (Fig. 1A and B). In TDchildren, the tendon contributed more to MTU length-changes thanmuscle, as opposed to more equal contributions in CP. In TD children,the muscle-belly behaviour did not reflect the fascicle behaviourwhereas in CP, muscle-belly and fascicle length patterns were similar.5. DiscussionOur initial findings of pathological tendon and muscle dynamicsduring CP gait are in line with a previous study imaging the MTJ [3], butless so with studies relying on modelling to estimate tendon length [4,5].The similar length pattern between muscle-belly and fascicle in CP mayindicate a stiff extracellular matrix. We highlight the importance ofcollecting experimental data from all three tissues in order to understandthe pathology. This feasibility study needs to be confirmed oncelarger samples are collected.