Morphological and positional changes of the carpal arch and median nerve during wrist compression

Abstract

Background The carpal tunnel is a fibro-osseous structure containing the median nerve and flexor tendons. Its cross-sectional area has been shown to increase during compressive force application to the carpal bones in modeling and in vitro studies. The purpose of this study was to investigate the morphological and positional changes of the carpal arch and median nerve while in vivo compressive force was applied in the radioulnar direction across the wrist. Methods Ultrasound images of the carpal tunnel and its contents were captured for 11 healthy, female volunteers at the distal tunnel level prior to force application and during force application of 10 and 20 N. Findings With applied force, the carpal arch width significantly decreased, while the carpal arch height and area significantly increased (P < 0.001). The median nerve shape became more rounded as the compressive force magnitude increased, reflected by decreases in the nerve’s flattening ratio and increases in its circularity (P < 0.001). The applied force also resulted in nerve displacement in the radial-volar direction. Interpretation This study demonstrates that noninvasively applying radioulnar compressive force across the wrist may potentially provide relief of median nerve compression to patients suffering from carpal tunnel syndrome.

Subject-specific finite element analysis of the carpal tunnel cross-sectional to examine tunnel area changes in response to carpal arch loading

“…The increases in volar area and total CSA with force directed at radial-volar direction was 14.7 and 11.4 mm 2 , respectively. These results are consistent with a previous in-vivo study which showed that 10 N of transverse compressive force results in a volar area increase of 5.65 mm 2 (Marquardt et al, 2015). Similarly, another in vivo study evaluating the pinching of the index finger against thumb reported a decrease of 0.8 mm in CAW and an increase of 5.1 mm 2 in volar area (Shen and Li, 2013).…”

“…CAW values during widening always remained lower than the length of the TCL itself, indicating the TCL did not assume a tensioned state. Narrowing of CAW has been shown to increase the volar area of the carpal tunnel in previous biomechanical studies (Li et al, 2013; Marquardt et al, 2016; Marquardt et al, 2015). The reduction in CAW was maximized in radial volar direction (at 138° from 25.1 to 24.4 mm).…”

“…This CAW change is attributable to the mobility of carpal bones which is guided by bone/cartilage configuration and inter-carpal ligaments (Gabra et al, 2012; Xiu et al, 2010). Attempts to widen (Sucher et al, 2005) or narrow (Li et al, 2013; Marquardt et al, 2016; Marquardt et al, 2015) the CAW have been made to alter the carpal tunnel morphological structure as a means to increase the carpal tunnel cross-sectional area (CSA) for median nerve decompression. Widening the CAW can be limited due to the mechanical constraint imposed by the thick band of the transverse carpal ligament.…”

“…Widening the CAW can be limited due to the mechanical constraint imposed by the thick band of the transverse carpal ligament. Narrowing of the CAW has been examined by applying forces to the carpal bones in cadaveric hands (Gabra and Li, 2016) and to the radio-ulnar aspects of the wrist in human subjects (Marquardt et al, 2016; Marquardt et al, 2015). Decreasing the CAW at the distal row was demonstrated to increase the volar arch area of the carpal tunnel (Fig.…”

“…Decreasing the CAW at the distal row was demonstrated to increase the volar arch area of the carpal tunnel (Fig. 1), i.e., the area formed by the TCL divided by a reference line from the ridge of the trapezium and hook of the hamate (Li et al, 2013; Li et al, 2011; Li et al, 2009; Marquardt et al, 2016; Marquardt et al, 2015). However, previous studies were limited to the examination of effects of CAW on volar area without the inclusion of the dorsal arch area formed by carpal bones.…”