The volar antebrachial fascia represents a thickening of the volar forearm fascia as it approaches the carpal tunnel. Proximally, it is continuous with the forearm fascia, and distally it blends with the proximal TCL complex. I define the carpal tunnel inlet as the region beneath the antebrachial fascia and proximal TCL complex. This area is often overlooked as a clinically important site of MN compression in CTS.
Careful evaluation of the carpal tunnel inlet is important when assessing CTS sonographically. Beginning the examination in the distal forearm region and systematically scanning through the antebrachial fascia and proximal TCL complex frequently reveals important findings of MN compression that may be overlooked if imaging begins more distally within the tunnel. Both short and long-axis transducer orientations provide complementary information regarding nerve size, echotexture, and focal compression, allowing for a more complete assessment of CTS pathology.