Spastic co-contraction of gastrocnemius medialis and peroneus longus during swing phase of gait in hemiplegic children
Dr Maria VINTIa, Prof Jean-Michel GRACIESa, Dr Andrea MERLOb, Dr Nicolas BAYLEa, Prof Elke VIEHWEGERc, Mr Guillaume AUTHIERc, Prof Brigitte CHABROLd, Dr Christophe BOULAYc
a AP-HP, Service de Rééducation Neurolocomotrice, Hôpitaux Universitaires Henri Mondor, Créteil, b Movement Analysis Laboratory, Rehabilitation Department, Reggio Emilia Local Health Unit Correggio, Italy, c Laboratoire d'Analyse de la Marche, service de chirurgie orthopédique pédiatrique, CHU Timone Enfants, Marseille, d Service de neurologie pédiatrique, CHU Timone Enfants, Marseille
Introduction: Spastic cocontraction  is a form of muscle overactivity [1,2] that may alter gait in infant hemiparesis. We quantified EMG activity in Gastrocnemius Medialis (GM) and Peroneus Longus (PL) during the swing phase (SW) of gait in very young hemiparetic children with an equino-valgus pattern , comparing the paretic and non-paretic side.
Materials and Methods: Ten hemiparetic children (age 3±1, mean±SD) were monitored for GM and PL EMG during gait. The SW was divided into three thirds (initial-T1, middle-T2 and end-T3). In each period, a Cocontraction Index (CCI) , ratio of the Root Mean Square (RMS) EMG from each muscle during that period to the peak 500-ms RMS obtained from voluntary plantar flexion during a selected submaximal state (standing on tiptoes) was measured.
Results: GM and PL CCIs during SW were higher on the paretic than on the non-paretic side (Wilcoxon:CCIGM, p<0.01;CCIPL,p<0.01). When subdividing the SW, there was a CCI increase on the paretic side during mid and late SW for GM (Wilcoxon: CCIGMT2,p<0.01;CCIGMT3,p<0.001), and during early, mid and late SW for PL (Wilcoxon:CCIPLT1,p=0.03;CCIPLT2,p=0.014 and CCIPLT3,p<0.001).
Discussion and conclusion: GM and PL cocontraction increases may contribute to the equinus on the paretic side. Specifically, PL cocontraction increase might cause the hind-foot valgus at late swing, moving the first metatarsal downwards and pronating the forefoot. Quantification of cocontraction could provide a better understanding of the adverse muscle actions and contribute to better target the therapeutic actions, especially botulinum toxin injection in PL, to improve gait in very young hemiparetic children before orthopaedic deformation.
 Gracies JM. Pathophysiology of spastic paresis. II: Emergence of muscle overactivity. Muscle Nerve 2005;31:552-71.
 Vinti M, Couillandre A, Hausselle J, et al. Influence of effort intensity and gastrocnemius stretch on co-contraction and torque production in the healthy and paretic ankle. Clin Neurophysiol 2013;124:528-35
 Boulay C, Pomero V, Viehweger E, et al. Dynamic equinus with hindfoot valgus in children with hemiplegia. Gait Posture 2012;36:108-12
Keywords : cerebral palsy; spastic co-contraction; equinus; gastrocnemius medialis; peroneus longus; EMG