Ultrasound of the tibialis anterior with foot inversion

These are axial images of the tibialis anterior with the foot in neutral position (left, A) and with the foot inverted (right, B). Note that the interosseus membrane (arrows) bulges out with foot inversion due to thickening of the tibialis posterior muscle that lies just deep to it. Needle electromyography or therapeutic botulinum toxin injections can be guided by ultrasound through the anterior tibialis to locate this muscle.