Introduction The relationship of tibialis anterior (TA) muscle architecture including muscle thickness (MT), cross-sectional area (CSA), pennation angle (PA) and fascicle length (FL) to strength and ankle function was examined in ambulatory individuals with CP and unilateral foot drop. Methods Twenty individuals with CP participated in muscle ultrasound imaging, unilateral strength testing, and 3D gait analysis. Results Muscle size (MT and CSA) were positively related to strength, fast gait velocity, and ankle kinematics during walking. Higher PA was related to a more dorsiflexed ankle position at initial contact and inversely with fast gait velocity. FL was related to strength, fast velocity, and step length at self-selected speed. Discussion Muscle architecture partially explains the degree of impairment in strength and ankle function in CP. Treatments to increase TA size and strength may produce some gait improvement, but other factors that may contribute to ankle performance deficits must be considered.

We have developed a vector Doppler ultrasound imaging method to directly quantify the magnitude and direction of muscle and tendon velocities during movement. The goal of this study was to evaluate the feasibility of using vector Tissue Doppler Imaging (vTDI) for estimating the tibialis anterior tendon velocities during dorsiflexion in children with cerebral palsy who have foot drop. Our preliminary results from this study show that tendon velocities estimated using vTDI have a strong linear correlation with the joint angular velocity estimated using a conventional 3D motion capture system. We observed a peak tendon velocity of 5.66±1.45 cm/s during dorsiflexion and a peak velocity of 8.83±2.13 cm/s during the passive relaxation phase of movement. We also obtained repeatable results from the same subject 3 weeks apart. Direct measurements of muscle and tendon velocities may be used as clinical outcome measures and for studying efficiency of movement control.

We have developed a vector tissue Doppler imaging (vTDI) method to quantify the magnitude and direction of tissue motion. The goal of this study was to quantify the repeatability of vTDI in measuring the contraction velocity of the tibialis anterior (TA) tendon in patients with cerebral palsy and foot drop (impaired dorsiflexion). vTDI was implemented on Ultrasonix Sonix Touch ultrasound system with a 5–14-MHz linear array transducer. The array was electronically split into two transmit and two receive apertures to estimate velocity vectors. Transmit and receive beams were steered by ±15 deg. We conducted 42 trials on 7 subjects. Our preliminary results show that TA tendon velocities measured using vTDI have a strong linear correlation with the joint angular velocity estimated using a conventional 3-D motion capture system. We observed a peak velocity of 5.20±1.58 cm/s during dorsiflexion and 8.45±2.06 cm/s during the gravity-aided passive relaxation phase. The R2 values for all 42 trials were 0.77±0.10. A second velocity measurement was made on three subjects after an interval of 4 weeks. We obtained repeatable velocity estimates with the standard deviation of the radius of action less than 0.13 cm. This demonstrates that vTDI is a feasible and reproducible method for measuring tendon velocities.