Purpose of study: To compare the medial gastrocnemius (MG) muscle belly length and volume in children with spastic diplegic cerebral palsy (SDCP) with that of normally developing (ND) children, and to assess the effect of gastrocnemius recession (GR) on MG muscle belly length and volume in the SDCP group.

Method: The MG muscle belly length and volume at the resting ankle angle were assessed with 3D ultrasound in 10 ND children, mean age 9.4 years, and in 7 children (9 limbs) with SDCP (mean age 8.1 years) who had fixed equinus deformities (mean 24 degrees). The children with SDCP were assessed just before, and at 7 weeks and 1 year after GR surgery. Muscle length was normalised to fibular length, and muscle volume was normalised to body mass.

Results: In both the ND and SDCP groups, muscle length was significantly related to fibular length (p=0.001) and muscle volume was significantly related to body mass (p< 0.001). The MG in the SDCP group had a mean reduction in normalised length of 19% and in normalised volume of 59% when compared to the ND group (p< 0.001). GR surgery lead to a further reduction in MG length (p=0.014) and a mean reduction of MG volume of 10% at 7 weeks (p=0.025). However, there was an increase in muscle volume of 39% (24% increase compared to the preoperative assessment) at 1 year following surgery (p< 0.001).

Conclusions: The MG belly is significantly shorter and thinner in children with SDCP compared to ND children. GR surgery reduces MG length but leads to an improvement in MG volume and thus in the ability of the MG to generate power.