Motion mapping and positioning of lumbrical muscles in the carpal tunnel-a cadaveric study

Dynamic incursion of lumbrical muscle proximal to the distal edge of transverse carpal ligament (TCL) has been long debated for its role in causing median nerve compression in the carpal tunnel. This study aims to evaluate the pattern of lumbrical incursion into the carpal tunnel in various finger positions and determine their extent of presence and relationship with respect to the TCL and to each other in the carpal tunnel.

Dissection of 30 fresh frozen cadaveric hands was done to map the lumbrical muscles. The distance from each lumbrical muscle's proximal origin to the TCL's distal edge was measured using a Vernier caliper in three finger positions namely full extension, lumbrical, and full flexion position. Statistical tests like paired t-test, ANOVA and Chi-Square test were used to evaluate the mean changes in lumbrical incursion, percentage of incursion, relative positions and the proportion of hands showing lumbrical origins proximal to the TCL.

The second lumbrical exhibited the highest mean incursion in all finger positions, followed by the third. Significant increases in incursion were observed from full extension to lumbrical position and from lumbrical position to full flexion in all lumbricals. The number of hands with lumbrical origins proximal to the TCL increased significantly from complete extension to complete flexion.

Lumbrical incursion significantly increases the content within the carpal tunnel with various finger positions. In full flexion, there is significant pressure of lumbricals within the tunnel. Hence, along with the tendons and median nerve, the lumbricals should be considered a dynamic content of the carpal tunnel. These muscles could ¹significantly contribute to idiopathic Carpal tunnel syndrome in the backdrop of alteration in tunnel size or content. The second lumbrical, due to its proximal-most origin, is pivotal in this process.

Level V.