Validation of a scanning technique with minimal compression for measuring muscle volume with freehand 3D ultrasound.

Freehand 3D ultrasound (3D-US) is a promising technique for measuring muscle volume but it requires gel pads or water tanks to limit probe compression on the skin which makes it hard to use in clinical applications. Our objectives were to measure the effect of different compressions on muscle volume in order to assess the clinical applicability of a minimal compression method for lower limb muscles. 4 muscles of the lower limb on 15 healthy volunteers were scanned with a new commercial freehand 3D-US setup accessible to clinical experimentators. Each muscle was scanned with 3 levels of compression: standard compression, minimal compression and gel pad (method validated against MRI). Volume was calculated using software segmentation tools. Acquisitions and segmentations were done by the same examiner. There was a significant impact of standard compression on volume measurements, but no difference between minimal compression and gel pad. Standard compression underestimated volume with a mean bias of 16 mL. For minimal compression, 75 % of measured differences were below the predefined clinically acceptable limits of 10 mL. Mean bias for this method was 1.1 mL. In conclusion, standard compression in freehand 3D-US induces a systematic bias in volume calculations. But, with a trained examiner and the necessary precautions to minimize compression, this bias could be abolished and become acceptable in clinical applications. When a high accuracy is required, gel pads could still be important to consider.

Pathological and physiological muscle co-activation during active elbow extension in children with unilateral cerebral palsy.

OBJECTIVE: To address the roles and mechanisms of co-activation in two flexor/extensor pairs during elbow extension in children with cerebral palsy (CP). METHODS: 13 Typically Developing (TD) and 13 children with unilateral spastic CP performed elbow extension/flexion at different speeds. Elbow angle and velocity were recorded using a 3D motion analysis system. The acceleration and deceleration phases of extension were analyzed. Co-activation of the brachioradialis/triceps and biceps/triceps pairs was computed for each phase from surface electromyographic signals. Statistical analysis involved linear mixed effects models and Spearman rank correlations. RESULTS: During the acceleration phase, there was strong co-activation in both muscle pairs in the children with CP, which increased with speed. Co-activation was weak in the TD children and it was not speed-dependent. During the deceleration phase, co-activation was strong and increased with speed in both groups; co-activation of brachioradialis/triceps was stronger in children with CP, and was negatively correlated with extension range and positively correlated with flexor spasticity. CONCLUSIONS: Abnormal patterns of co-activation in children with CP were found throughout the entire movement. Co-activation was specific to the movement phase and to each flexor muscle. SIGNIFICANCE: Co-activation in children with CP is both physiological and pathological.

Impact of muscle activation on ranges of motion during active elbow movement in children with spastic hemiplegic cerebral palsy.

BACKGROUND: Children with spastic hemiplegic cerebral palsy are restricted in their daily activities due to limited active ranges of motion of their involved upper limb, specifically at the elbow. Their impaired muscles are frequently targeted by anti-spastic treatments that reduce muscle tone. But these treatments do not necessarily improve the limb function. There is a lack of comprehensive knowledge of the quantitative relations between muscle activation and joint active ranges of motion. Consequently, the objective of this study is to quantify the impact of muscle activation on the elbow active ranges of motion. METHODS: During voluntary elbow pronation/supination and extension/flexion movements, kinematic and electromyographic measurements were collected from the involved upper limb of 15 children with spastic hemiplegic cerebral palsy (mean age=8.7 years, standard deviation=2.2) and the dominant upper limb of 15 age-matched children who are typically developing. Representative indicators of the muscle activation, such as the muscle co-activation, were extracted from the electromyographic measurements. FINDINGS: Muscle co-activation in the involved upper limb accounted for 78% and 59% of the explained variance of the supination and extension limited active ranges of motion respectively. The agonist and antagonist muscle activations were both longer in the involved upper limb. INTERPRETATIONS: This study succeeded in quantifying the impact of longer antagonist muscle activation on decreased elbow active ranges of motion in children with spastic hemiplegic cerebral palsy. Longer agonist muscle activation suggests that strengthening agonist muscles could increase the extension and supination ranges of motion, which constitutes a perspective of future clinical studies.