Analysis of reproducibility of 2D Ultrasound imaging with transient ShearWave Elastography on spastic gastrocnemius medialis muscle in children with spastic hemiplegic cerebral palsy

Abstract

The aim of the study was to assess the intra- and inter-operator reliability of pennation angle (PA) and muscle thickness (MT) 2D measurements and of shear elastic measurement, using ultrasound imaging (US). Those measurements were realised on spastic gastrocnemius medialis muscle at rest and at maximal passive stretching, in children with spastic hemiplegic cerebral palsy. The paretic side measurements were compared to the non-paretic side. Eight patients took part in 2 inter-session reliability experiments, realised at a 7 days interval by two different operators. The Aixplorer ® Supersonic US scanner with the transient ShearWave Elastography (SWE) software was used. The stretching experiments were made manually and controlled by a goniometer. The intra-operator reliability of the 2D measurements was good. Both operators found a coefficient of variation (CV) ≤ 7% and 6.04% for MT at rest and at maximal passive stretching respectively, ≤ 9.77% for PA at rest. The reliability of the shear elastic modulus measurement in the sagittal plane was only good at rest for both operators with a CV ≤ 9.82%, versus 25.29% at stretching. The inter-operator reliability of 2D measurements was good for MT exclusively (CV ≤ 9.69% for the two sessions and two operators). At rest, MT was weaker in the paretic side (10.17 ± 1.52 mm) versus non-paretic side (12.43 ± 2,85 mm) ( P < 0.0001), and the shear elastic modulus was stronger in the paretic side versus non-paretic side (29.45 ± 5.7 Kpa vs 23.77 ± 3.93 Kpa) ( P < 0.0001). This is the first description of muscle spastic structure in children with cerebral palsy using SWE with Supersonic Shear Imaging. 2D US associated with SWE contribute to assess muscular atrophy and muscle elasticity. These structural properties reflect some of the functional abilities regardless of motor control. It should enable further research on therapies which impact muscle tissue quality, such as botulinum neurotoxin injections, in children with cerebral palsy.