Ultrasound imaging of thoracolumbar fascia. A: Illustration of layers composing the thoracolumbar fascia corresponding to aponeuroses of back and abdominal wall muscles. Arrows indicate directions of pull for individual muscles. B-C: ultrasound image of thoracolumbar fascia in longitudinal (B) and transverse (C) planes showing echogenic (dense connective tissue) and echolucent (loose connective tissue) layers within the thoracolumbar fascia. A distinct echolucent plane (red line) is visible within the thoracolumbar fascia in the longitudinal image corresponding to the loose connective tissue layer located between the aponeurosis of the erector spinae muscles and the combined aponeuroses of the abdominal wall muscles, serratus posterior and latissimus dorsi.