US Case 1: Anatomical variations in Dorsal Compartment 1 (DC1) of the Wrist
The tendon of abductor pollicis longus (APL) and extensor pollicis brevis (EPB) lie side by side within the first dorsal compartment of the wrist lateral to the radial styloid. APL is in the more volar position with EPB laying more dorsally.
A possible anatomical variant often seen with US examination of the wrist is a central vertical septum separating the APL and EPB tendons as demonstrated below. This central septum maybe seen to form a vertical hypoechoic band. The volar part of the tunnel contains the larger APL and the dorsal part the smaller EPB.
The other possible variant would be when APL splits into multiple slips with in DC1 giving the appearance of 4 or 5 tendons within the tunnel. Anyone have a good image of this?