Thenar and hypothenar muscle origins on the transverse carpal ligament

The thenar and hypothenar muscles of the hand have origins on the transverse carpal ligament (TCL). Understanding the morphological distribution of this muscle-ligament interaction has clinical and biomechanical benefits. Robot-assisted ultrasonography was used to reconstruct the three-dimensional TCL volar surface and TCL-muscle interface in ten cadaveric specimens. The interface areas and radial-ulnar length at discretized proximal-distal tunnel levels were calculated. The total area of the TCL volar surface was 457.4 ± 62.2 mm². The TCL-thenar and TCL-hypothenar interface areas were 142.3 ± 38.0 mm² (30.8 ± 6.6%) and 32.3 ± 22.4 mm² (7.0 ± 4.7%), respectively. The TCL area not interfaced by the thenar or hypothenar muscles was 282.72 ± 40.8 mm² (62.1 ± 7.4%). The relative radial-ulnar TCL-muscle interface length was significantly dependent upon muscle group (p < 0.001) and proximal-distal carpal tunnel level (p < 0.001). The maximum percentage of the radial-ulnar length of the TCL volar surface occupied by the TCL-thenar and TCL-hypothenar interface was 57.0 ± 9.9% and 15.5 ± 9.6%, respectively. Quantification of the three-dimensional muscle coverage distribution on the TCL can help to advance anatomical understanding, inform biomechanical mechanisms for utilizing the muscle-ligament interaction, and minimize potential functional disruption of carpal tunnel release.