Date Published: May 22, 2019
Publisher: Public Library of Science
Author(s): Kishor Lakshminarayanan, Rakshit Shah, Zong-Ming Li, Gabriel Costa Serrão de Araújo.
The purpose of this study was to investigate the sex-based differences in the carpal arch morphology. Carpal arch morphology was quantified using palmar bowing and area of the arch formed by the transverse carpal ligament. The carpal arch was imaged at the distal and proximal tunnel levels using ultrasonography in 20 healthy young adults (10 women and 10 men). It was found that females had a smaller carpal arch height compared to men at both distal and proximal levels (p<0.05) and smaller carpal arch width only at the proximal level (p<0.05) but not distally. Palmar bowing index, the carpal arch height to width ratio, was significantly smaller in females at the distal level (p<0.05) but not at the proximal level. Carpal arch cross-sectional area normalized to the wrist cross-sectional area was found to be significantly smaller in females at both tunnel levels compared to men (p<0.05). This study demonstrates that females have a smaller carpal arch compared to men with a reduced palmar bowing distally and a smaller arch area at both tunnel levels. The findings help explain the higher incidence of carpal tunnel syndrome in women as a smaller carpal arch makes the median nerve more vulnerable to compression neuropathy.
The carpal tunnel is formed by the transverse carpal ligament (TCL) at its volar boundary and the carpal bones at its medial, lateral, and dorsal boundaries. The tunnel serves as a passageway for the median nerve and digit flexor tendons. The median nerve is situated beneath the TCL and provides motor and sensory function to the hand. The delicate positioning of the median nerve within the tunnel makes it susceptible to compression from area reduction or shape alteration of the TCL-formed carpal arch. Prolonged compression of the median nerve could lead to compression neuropathy known as carpal tunnel syndrome (CTS).
There were no significant sex differences in age (p = 0.12) and BMI (p = 0.61), but the males had greater body weight (p<0.01), body height (p<0.01), wrist width (p<0.01), and wrist thickness (p<0.05) than females. Sample ultrasound images at the distal and proximal tunnels are shown in Fig 2. In general, females had a smaller carpal arch than men, specifically a reduced palmar bowing and smaller arch area. In this study, we used an imaging processing algorithm to automatically identify the targeted cross sections of the distal and proximal carpal arch. The algorithm eliminated operator dependency to find the arch cross sections that contained the anatomical configuration for manual tracing of the TCL volar boundary. The imaging protocol and automated algorithm demonstrate using ultrasonography as a low-cost alternative to high-resolution MRI for the examination of the TCL-formed carpal arch. The ultrasonographic method can be applied to clinical studies to understand morphological changes of carpal arch in pathological condition (e.g. CTS). Source: http://doi.org/10.1371/journal.pone.0217425