Ultrasound of the Musculoskeletal System – Chapter #10: Wrist

The most useful bony landmarks to identify the proximal carpal tunnel are the pisiform at its ulnar side and the scaphoid at its radial side. At ultrasound examination, these bones appear as round hyperechoic structures with posterior acoustic shadowing. Once these landmarks are demonstrated in a single image, the orientation of the probe should be adjusted to optimize the depiction of the soft tissues contained within the tunnel (Fig. 26). Tilting the probe back and forth may be helpful to distinguish the hypoechoic median nerve by the adjacent anisotropic tendons. Relative to the flexor carpi radialis, the flexor pollicis longus tendon runs in a deeper location, slightly closer to the midline. Oblique longitudinal ultrasound images can depict these tendons in the same plane. The proximal carpal tunnel is larger in size compared with the distal tunnel. In a comparative ultrasound-cadaveric study, ultrasound has proved to be accurate in evaluating the different diameters, the outline and the cross-sectional area of the carpal tunnel and the median nerve (Kamolz et al. 2001). The transverse carpal ligament appears as a thin slightly convex band of 1−1.5 mm thickness (Fig. 26). Its attachments to the pisiform and the scaphoid are readily detected with US.