Muscle Shortening and Spastic Cocontraction in Gastrocnemius Medialis and Peroneus Longus in Very Young Hemiparetic Children.

OBJECTIVES: Muscle shortening and spastic cocontraction in ankle plantar flexors may alter gait since early childhood in cerebral palsy (CP). We evaluated gastrosoleus complex (GSC) length, and gastrocnemius medialis (GM) and peroneus longus (PL) activity during swing phase, in very young hemiparetic children with equinovalgus. METHODS: This was an observational, retrospective, and monocentric outpatient study in a pediatric hospital. Ten very young hemiparetic children (age 3 ± 1 yrs) were enrolled. These CP children were assessed for muscle extensibility (Tardieu scale XV1) in GSC (angle of arrest during slow-speed passive ankle dorsiflexion with the knee extended) and monitored for GM and PL electromyography (EMG) during the swing phase of gait. The swing phase was divided into three periods (T1, T2, and T3), in which we measured a cocontraction index (CCI), ratio of the Root Mean Square EMG (RMS-EMG) from each muscle during that period to the peak 500 ms RMS-EMG obtained from voluntary plantar flexion during standing on tiptoes (from several 5-second series, the highest RMS value was computed over 500 ms around the peak). RESULTS: On the paretic side: (i) the mean XV1-GSC was 100° (8°) (median (SD)) versus 106° (3°) on the nonparetic side (p = 0.032, Mann-Whitney); (ii) XV1-GSC diminished with age between ages of 2 and 5 (Spearman, ρ = 0.019); (iii) CCIGM and CCIPL during swing phase were higher than on the nonparetic side (CCIGM, 0.32 (0.20) versus 0.15 (0.09), p < 0.01; CCIPL, 0.52 (0.30) versus 0.24 (0.17), p < 0.01), with an early difference significant for PL from T1 (p = 0.03). CONCLUSIONS: In very young hemiparetic children, the paretic GSC may rapidly shorten in the first years of life. GM and PL cocontraction during swing phase are excessive, which contributes to dynamic equinovalgus. Muscle extensibility (XV1) may have to be monitored and preserved in the first years of life in children with CP. Additional measurements of cocontraction may further help target treatments with botulinum toxin, especially in peroneus longus.

Planovalgus foot deformity in cerebral palsy corrected by botulinum toxin injection in the peroneus longus: Clinical and radiological evaluations in young children.

BACKGROUND: In children with cerebral palsy (CP), overactivity of the peroneus longus (PL) muscle is a major contributor to pes planovalgus. This retrospective study assessed whether abobotulinumtoxinA injections into a PL showing premature activity on electromyography (EMG) clinically improved foot morphology in children with CP. METHODS: Study participants were <6 years old, had a diagnosis of CP, good functional abilities (Gross Motor Function Classification System level 1 or 2), equinovalgus (initial contact with the hallux or head of the first metatarsal) and overactive PL on EMG. The fore-, mid- and hindfoot were evaluated clinically and radiologically before and after injection of abobotulinumtoxinA (6-7 U/kg) into the PL. Radiological data were compared with reference values for children without pes planovalgus. RESULTS: In total, 16 children (8 males; 10 hemiplegia, 6 diplegia; mean age: 3.2±1.5 years) received treatment. Mean pre-and post-treatment angles in clinical assessment of dorsiflexion of the talocrural articulation did not differ with both knees flexed (24.4±7.5 vs. 22.2±8.0 degrees; P=0.19) or extended (17.2±8.0 vs. 16.6±6.8 degrees; P=0.36). Radiographic data pre-treatment versus reference data revealed forefoot pronation (metatarsal stacking angle 2.1±8.3 vs. 8.0±2.9 degrees; P=0.002), midfoot planus (lateral talo-first metatarsal 28.5±15.0 vs. 13.0±7.5 degrees; P<0.001; talocalcaneal angle 54.6±8.6 vs. 49.0±6.9 degrees; P=0.004) and significantly decreased calcaneus dorsiflexion, without hindfoot equinus (calcaneal pitch angle 7.9±6.0 vs. 17.0±6.0 degrees; P<0.001). After treatment, the metatarsal stacking angle did not differ from reference values (P=0.15). As compared with before treatment, treatment improved mean angles for metatarsal stacking (2.1±8.3 vs. 7.1±3.9 degrees, respectively, P=0.002), lateral talo-first metatarsal and talocalcaneal (both P<0.001), with no change in the hindfoot. CONCLUSION: PL may be an early target for abobotulinumtoxinA treatment in pes planovalgus associated with premature PL activity in children with CP.

Dynamic EMG of peroneus longus in hemiplegic children with equinovarus.

OBJECTIVE: In hemiplegic children the appearance of equinovarus is correlated with premature electromyography (EMG) activity of the gastrocnemius medialis (GM) prior to initial contact. The goal was to analyze the onset of EMG activation in the GM and, more particularly, the peroneus longus (PL) in cases of equinovarus: is PL activity likewise premature? MATERIAL AND METHODS: As 15 hemiplegic children (age 5 years±1.5) with equinovarus walked, their PL and GM EMG activity was being recorded. The latter was normalized in terms of gait cycle percentage (0-100%) and detected through semi-automatic selection with activation threshold set at 20µV. A paired t-test compared activation onset of the PL versus the GM muscles. RESULTS: As regards the healthy limb, activity onset of the GM (+14.55%) and the PL (+19.2%) muscles occurred only during the ST. In cases of equinovarus, activation of the GM (-5.2%) and the PL (-6.1%) occurred during the SW and was premature. For each muscle, comparison between the healthy and the hemiplegic side was highly significant (P<0.001). CONCLUSION: Premature PL and GM EMG activity preceding initial contact corresponds not to a disorder secondary to imbalance but rather, more probably, to motor command dysfunction. While the PL consequently contributes to equinus deformity, its possible role in varus genesis is less evident. EMG study needs to be completed by comparing PL and tibialis posterior strength while taking foot bone morphology into full account.