The effect of wrist position on the relative motion of tendon, nerve, and subsynovial connective tissue within the carpal tunnel in a human cadaver model

Abstract

The purpose of this study was to measure the effect of wrist position on the relative motion of the middle finger flexor digitorum superficialis (FDS) tendon, subsynovial connective tissue (SSCT), median nerve, and flexor retinaculum during simulated active finger motion. The relative motion of each tissue was measured by fluoroscopy in 10 human cadavers. Measurements were obtained for wrist positions of neutral (0 degree extension), 30 and 60 degrees of flexion, and 30 and 60 degrees of extension. The shear strain index (SSI) was defined as the difference in motion between two tissues (tendon, SSCT, or nerve) divided by tendon excursion, expressed as a percentage. The motion of the tendon, SSCT, and nerve in the 60 degree flexed position was significantly less than the motion in all other wrist positions (p < 0.001). The SSI at 60 degrees of flexion for tendon–SSCT and tendon–nerve were significantly increased compared with all other positions (p < 0.001). Because the SSCT and tendon are physically connected, a decrease in SSCT motion relative to the tendon would increase the shear strain on the SSCT with tendon motion. Thus, this result suggests that the SSCT may be predisposed to shear injury from activity done in 60 degrees of wrist flexion.

Finite element model of subsynovial connective tissue deformation due to tendon excursion in the human carpal tunnel

“…The methods for collecting this data are described in detail in the previously published studies (Yoshii et al, 2008; Yoshii et al, 2009). A summary of these methods is warranted and follows.…”

“…Instead of reporting the relative motion of the tendon, SSCT and nerve, Yoshii et al compared these motions by using their shear strain index (SSI) (Yoshii et al, 2008). …”

Tensile properties of the transverse carpal ligament and carpal tunnel complex

“…In addition, the tendons and median nerve together with the TCL form a pulley system (Brooks et al, 2003;Fuss and Wagner, 1996;Stecco et al, 2010). During finger and hand movements the median nerve and tendons move in longitudinal, transverse, and volar/dorsal directions (Lopes et al, 2011;Ugbolue et al, 2005;Yoshii et al, 2008). The median nerve becomes compressed as the carpal tunnel contents move within the carpal tunnel (Armstrong and Chaffin, 1979;Ugbolue et al, 2005).…”

D6-2 The Effect of Keyboard Typing on the Median Nerve at the Proximal Carpal Tunnel

“…Additionally, repetitive finger movements could result in a higher shear strain between the median nerve and the sub synovial connective tissue (Kursa et al, 2006;Yoshii et al, 2008). However, the association between computer work and CTS remains inconclusive, and the pathophysiological relationship between keyboard typing activity and CTS remains questionable.…”