Figure 3b. Carpal tunnel syndrome in a 65-year-old woman with an aberrant flexor muscle of the index finger. Longitudinal (a, b) and transverse (c, d) 5-12-MHz US scans of the carpal tunnel show the effects of flexion (a, c) and extension (b, d) of the index finger. With the fingers flexed, an anomalous muscle belly (*) lies proximal to the entrance of the carpal tunnel. Progressive extension of the index finger pushes the muscle inside the tunnel, thus causing compression of the median nerve (MN). Flexion and extension of the other digits did not affect the position of this muscle. FT = flexor tendon, P = pisiform.