Spastic co-contraction of gastrocnemius medialis and peroneus longus during swing phase of gait in hemiplegic children

Abstract

Spastic cocontraction [1] 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 [3] , comparing the paretic and non-paretic side. 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) [4], 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. GM and PL CCIs during SW were higher on the paretic than on the non-paretic side (Wilcoxon:CCI GM , P < 0.01;CCI PL , P < 0.01). When subdividing the SW, there was a CCI increase on the paretic side during mid and late SW for GM (Wilcoxon: CCI GMT2 , P < 0.01;CCI GMT3 , P < 0.001), and during early, mid and late SW for PL (Wilcoxon: CCI PLT1 , P = 0.03;CCI PLT2 , P = 0.014 and CCI PLT3 , P < 0.001). 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.