In very young cerebral palsy (CP) children, peroneus longus (PL) overactivity by spastic co-contraction is a major contributor to dynamic equinovalgus during swing phase (SW) and at initial contact (IC). This study assessed the effects of abobotulinum toxin A injections into PL.

Eleven male children with hemiparesis (7 right; age 3.1±0.6 yo) were injected once in PL, without GastroSoleusComplex (GSC) injection. GSC was assessed for functional length (X_V1) and spasticity (X_V3). Gait analysis videos were evaluated using the Edinburgh visual gait score (EVGS-validated in CP): pre- vs. post-injection values were compared using paired t-tests. EMG monitored tibialis anterior (TA), gastrocnemius medialis (GM) and PL during gait. Swing phase was divided into three periods (SW1, SW2, SW3) to measured, using EMG: GM and PL co-contractions and TA recruitment during SW (SW, SW1, SW2, SW3), during standing on tiptoes (EMGmaxPL, EMGmaxGM), standing on heels (EMGmaxTA). For each measured EMG variable, efficacy indices was assessed using the ratio (EMG_{VARIABLE-X_POST}−EMG_{VARIABLE-X_PRE})/(EMG_{VARIABLE-X_POST}+EMG_{VARIABLE-X_PRE}) and compared with an inefficacy theoretical index of 0.

Comparison involved 1937 pre-toxin strides (mean per child 176±114) vs. 1231 post-toxin strides (mean 112±79). There were no difference in X_V1-GSC (X_V1-GSC-pre103°[6]; X_V1-GSC-post103°[6] or in X_V3-GSC (X_V3-GSC-pre89°[8]; X_V3-GSC-post96°[4.5]). EVGS-global-score was improved (P=0.007) with better clearance in SW (P=0.07), increased knee re-extension in terminal SW (P=0.04) and decreased hindfoot valgus at IC (P=0.02). The normalised-EMGmax was unchanged for PL (−0.06 [0.16]) but increased for GM (0.18 [0.20], P=0.007) and TA (0.28 [0.19], P<0.001). There were reductions of co-contraction in PL (P<0.0001; SW, −0.26 [0.14]; SW1, −0.22 [0.14]; SW2, −0.27 [0.14]; SW3, −0.26 [0.18]) and in GM (SW, −0.26 [0.14]), P=0.06; SW1,−0.21(0.18), P<0.001; SW2, −0.25 [0.20], P<0.01; SW3, −0.21 [0.25], P=0.06). TA recruitment was decreased: SW, −0.08 (0.18), P=0.06; SW1, −0.11 (0.20), P<0.001; SW2, −0.07 (0.17) NS; SW3, −0.07 (0.24), NS.

In this retrospective study, PL injections in very young CP children improved foot clearance and decreased hindfoot valgus, which was associated with reductions of PL and GM co-contractions and of TA recruitment. This constitutes an argument supporting that increased TA recruitment in children with hemiparesis may be an attempt by the nervous system to compensate for plantar flexor co-contraction rather than the opposite (increased co-contraction due to increased TA recruitment). We can discuss a central action of abobotulinum toxin A.