Quantitative 3D ultrasound of muscle in children with unilateral cerebral palsy

Abstract

Background and Objective(s): Altered muscle size and composition may contribute to muscle weakness and stiffness that impact on physical function in children with spastic Cerebral Palsy (CP). Ultrasound has been used extensively to quantify muscle composition in children with neuromuscular disorders (e.g. Duchenne's Muscular Dystrophy) by analysing the echo intensity and pattern of the images, but has had limited application to CP muscle research. This study used freehand threedimensional ultrasound (3DUS) to evaluate muscle volume and muscle composition, based on ultrasound echo intensity and pattern, of the medial gastrocnemius muscle in both limbs (more- and less-involved) in children with unilateral spastic CP compared to typically developing (TD) children. Study Design: Cross-sectional study. Study Participants & Setting: Twenty-six ambulant children with unilateral spastic CP [mean age 6.0 years (SD 2.4), mean body weight 19.3 kg (SD 4.4), mean height 117.3 cm (SD 16.1), 19 males, GMFCS I=17, II=9, limb distribution moreinvolved: left=12] and ten TD children with no known neurological conditions [mean age 4.6 years (SD 2.0), mean body weight 22.9 kg (SD 8.7), mean height 108.0 cm (SD 13.3), 5 males] participated in the study. Materials/Methods: Ultrasound images were acquired using a 9.0 MHz linear transducer. Four reflective markers attached to the transducer were tracked using a four camera optical motion system to determine the 3D position and orientation of the transducer. Ultrasound images were transformed into the global coordinate system to create a reconstructed 3D volume. 3DUS images of both limbs in children with CP and the right limb in TD children were obtained at rest and were analysed using quantitative methods to determine muscle volume, echo intensity parameters using histogram statistics (mean, median, kurtosis, skewness, entropy) and echo pattern parameters using Haralick features (blob area, contrast, correlation, energy and homogeneity). Image processing was performed on all ultrasound images (∼200 per muscle) and averaged to represent a global measure of muscle echo intensity and echo pattern. Results: Normalised MG volume of the more-involved limb was significantly smaller [CP more-involved mean=1.2 cm3/ kg/m (SD 0.5)] than the less-involved limb [CP less-involved mean=1.6 cm3/kg/m (0.5), p=0.15] and the TD group [TD mean=2.5 cm3/kg/m (SD 0.6), p<0.0001], the latter of which was significantly larger than CP less-involved (p=0.0001). Significant differences in all echo parameters were found between TD and CP children (Table 1). The more-involved limb was smaller and had a higher echo intensity and more heterogenous echo pattern compared the TD group. Compared to the more-involved limb, the less-involved limb was larger but had a similar echo appearance. Conclusions/Significance: The MG muscle of both limbs in children with unilateral spastic CP is smaller and, on the basis of quantitative 3DUS structurally different to TD children. Both limbs in children with unilateral CP had ultrasound findings consistent with disruption of normal muscle architecture. The similarity of size and echo appearance of the MG between the less- and more-involved limbs of the CP group, and the contrast between the less-involved limb and the TD group, may be indicative of bilateral muscle impairment in children with unilateral CP. On the basis of these findings it may incorrect to assume that muscles of the contralateral lower limb in children with unilateral CP are typically developed, and inappropriate to use of the less-involved limb as a control group in CP muscle research.L6184697432017-09-29 <br />