Reappraisal of the Silfverskiöld test : ultrasonographic study of the architectural properties of the triceps surae muscles

Abstract

The success of surgical correction of equinus contracture in children with spastic hemiplegic cerebral palsy (SHCP) depends on accurate identification of the affected muscles in the triceps surae. The Silfverskiöld test has long been used to decide surgical treatment, with minor consideration of the structural–functional complexity of the triceps surae muscles. This study used ultrasonography to investigate the architecture of the triceps surae muscles during passive knee and ankle motion in children with SHCP.Ten children with SHCP and 10 age-matched normal children were recruited. Static near-sagittal ultrasound images of the lateral (LG) and medial (MG) gastrocnemii and soleus (SOL) muscles were acquired at various knee and ankle joint angles. On the basis of these images, changes in fascicle length, pennation angle, and muscle width of the triceps surae muscles, as well as displacement of the fascicle–deep aponeurosis junction were measured and compared among the paretic and nonparetic legs of patients and both legs of normal children. Subsequently, real-time elastography was performed to evaluate the elasticity of gastrocnemius muscles and the Achilles tendon. The mean intensity of colors red, blue, green were measured using semi-quantitative method. Analysis of histograms for each color of the sonoelastography images was performed for quantifying the elasticity of the Achilles tendon and gastrocnemius muscles.Compared with fascicle length in normal legs, fascicle length was similar for the MG, longer for the LG and shorter for the SOL in paretic legs. The pennation angles were smaller for MG and LG in paretic legs than in normal legs, but were similar for SOL. The muscle widths of all triceps surae muscles were smaller in paretic legs than in normal legs. In the paretic legs of children with SHCP, the effects of ankle and knee joint positions were

different and showed a complex pattern, unlike that in normal conditions. The median blue colors intensity were significantly higher in SHCP group suggesting that both Achilles tendon and gastrocnemius muscle in SHCP are stiffer than those of normal child.In the paretic legs of children with Silfverskiöld-negative SHCP, the architectures and the elasticity of the triceps surae muscles and Achilles tendon were changed, and the normal actions between these muscles were disrupted according to knee and ankle joint positions. These results support the reliability of the Silfverskiöld test.