Repetitive use of wrist and finger is well known cause of damage of the median nerve and the soft tissue around it and contributes to development of the carpal tunnel syndrome. The aim of this study is to unveil the stiffness variation of the structures in the carpal tunnel according to the hand and the wrist motions.

This study was designed as a prospective, cross-sectional study and 26 healthy volunteers were enrolled (Fig. 1). Target structures for stiffness measurement in the carpal tunnel were median nerve (MN), transverse carpal ligament (TCL), and tendon of flexor digitorum superficialis (FDS) and profundus (FDP). Stiffness measurement were done transversely at the carpal tunnel inlet (pisiform bone to scaphoid tubercle) of non-dominant hand in combination of the 2 wrist joint motions; wrist neutral and wrist 30 degrees extension, and the 3 finger motions; finger neutral, full finger grasp, and full finger extension.

Stiffness (m/s) of mean and range of the target structures in wrist neutral-finger neutral position were 2.3(1.6–3.4), 3.4(2.7–3.9), 2.9(2.7–3.4), and 3.2(2.8–3.8) each. Those in wrist extension-finger full extension position were 3.0(2.3–4.0), 4.0(3.3–5.1), 3.5(2.8–5.1), and 3.9(2.9–5.0) (Table 1). Stiffness was significantly higher compared to wrist neutral-finger neutral position in other all five wrist-finger motions (Fig. 2).

Generalized estimating equation (GEE) analysis among the all six wrist-finger joint motions shows that wrist and finger joint movement increases stiffness of the structures in carpal tunnel compared to the wrist neutral-finger neutral position. Further study with large sample size and with carpal tunnel syndrome patients should be required to clarify these tendencies.