The volume of the lateral gastrocnemius appears reduced in some Idiopathic toe walkers

Plantarflexion contractures are often the focus for intervention in children who toe walk (TW). Caserta et.al1 found reduced plantarflexor strength in TW and greater proportions of type 1 fibres were identified in the plantarflexors2. Variable but mild differences in kinematics have been found between children with mild bilateral cerebral palsy (CP) and TW3,4. Children with CP have reduced muscle volumes compared to typically developing children5. Plantarflexor morphology in TW has not yet been described. Is ankle plantarflexor volume reduced in children who toe walk? Eight children (5male) aged 7-15 yr (mean=11.86 yrs) referred to our orthopaedic department for toe walking and plantarflexion contractures, with no underlying diagnosis, had a routine examination in the gait laboratory. They were matched for age and sex to children with CP (GMFCS I-II) who had also been examined. Assessment included gait analysis and 2D ultrasound imaging of the lateral gastrocnemius(LG). Muscle volumes were estimated by the Vanmechelen et.al6 method, normalised to mass. Selective motor control (SCALE) was assessed according to Fowler et.al7. Mobility was assessed using the Gillette Functional Assessment Questionnaire (GFAQ) 8. Data was compared to a large database of controls (unpaired t-test) and between groups (paired t-test). One limb per subject was randomly selected for analysis. All children had plantarflexor contractures: mean passive dorsiflexion range (knee extended) of -9.4° (SD10.9°) for TW and -6.5° (SD7.2°) for CP. TW had close to normal motor control (SCALE:Median=10, Range=8-10) whereas CP had a greater variability (SCALE:Median=9.5, Range=5-10). Walking function was within normal limits for TW (GFAQ Median=10 Range=8-10) but more variable for CP (GFAQ Median=8 Range=5-10). No difference in speed/cadence was found between groups (p=0.5/p=0.86) and these were within normal limits. All children were in ankle plantarflexion at initial contact (no difference between groups, p=0.48). Mean ankle dorsiflexion in stance and swing were not different between groups (p=0.94, p=0.84). For four TW children, normalised mean LG volume was significantly smaller than controls (1.07vs1.53 ml/kg) (p<0.01) but no different to CP (1.01 ml/kg) (p=0.64). The other TW had LG CSA which was too great for the US field of view. In the presence of an ankle plantarflexion contracture, TW children show less variability in selective motor control and functional mobility to a matched CP group. TW and CP show similar kinematics at the ankle, cadence and speed. A subgroup of TW children had reduced normalised LG compared to control data, comparable in size to the CP group. Other subjects’ muscles were larger and could not be measured. This suggests subgroups of TW with different muscle sizes, which has implications for aetiology and management. Further work is required to further elucidate the triceps surae muscle morphology in TW and relationship between morphology and toe walking.