I recently performed a diagnostic ultrasound of the carpal tunnel and was reminded of a useful scanning technique for better visualization of the thenar motor branch (TMB). During a short-axis (anatomic transverse) scan of the carpal tunnel, I routinely assess the median nerve (MN), palmar cutaneous branch of the MN, and the TMB. However, the TMB can sometimes be challenging to visualize. In my experience, rotating the ulnar end of the transducer distally aligns the transducer more parallel to the TMB, significantly improving visualization.
This short video begins with an illustration demonstrating the relationship between the US transducer and the TMB in both the short-axis and oblique positions. The cine clip shows the TMB first scanned in the short-axis position, followed by imaging the TMB in the oblique orientation. For a deep dive into carpal tunnel imaging, check out the Anatomy and Live Scan Lesson in the Wrist Module for a more comprehensive review of imaging the carpal tunnel.