Narrowing carpal arch width to increase cross-sectional area of carpal tunnel — a cadaveric study

Abstract

Background Carpal tunnel morphology plays an essential role in the etiology and treatment of carpal tunnel syndrome. The purpose of this study was to observe the morphological changes of the carpal tunnel as a result of carpal arch width narrowing. It was hypothesized carpal arch width narrowing would result in increased height and area of the carpal arch. Methods The carpal arch width of eight cadaveric hands was narrowed by a custom apparatus and cross-sectional ultrasound images were acquired. The carpal arch height and area were quantified as the carpal arch width was narrowed. Correlation and regression analyses were performed for the carpal arch height and area with respect to the carpal arch width. Findings The carpal tunnel became more convex as the carpal arch width was narrowed. The initial carpal arch width, height, and area were 25.7 (SD 1.9) mm, 4.1 (SD 0.6) mm, and 68.5 (SD 14.0) mm2, respectively. The carpal arch height and area negatively correlated with the carpal arch width, with correlation coefficients of −0.974 (SD 0.018) and −0.925 (SD 0.034), respectively. Linear regression analyses showed a 1 mm narrowing of the carpal arch width resulted in proportional increases of 0.40 (SD 0.14) mm in the carpal arch height and 4.0 (SD 2.2) mm2 in the carpal arch area. Interpretation This study demonstrates that carpal arch width narrowing leads to increased carpal arch height and area, a potential mechanism to reduce the mechanical insult to the median nerve and relieve symptoms associated with carpal tunnel syndrome.

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

“…These structural changes are likely related to the soft tissue components of the carpal tunnel boundary which provides the carpal tunnel with some degree of compliance [8, 12–15]. Recent studies support that the cross-sectional area of the carpal tunnel can be increased by narrowing the carpal arch width (CAW), i.e., distance between the trapezium and hook of hamate [13, 14, 16, 17]. Geometric modeling [16] and in vitro [13, 16] studies have shown that CAW narrowing is associated with palmar bowing of the TCL which increases the height and cross-sectional area of the carpal arch.…”

“…Recent studies support that the cross-sectional area of the carpal tunnel can be increased by narrowing the carpal arch width (CAW), i.e., distance between the trapezium and hook of hamate [13, 14, 16, 17]. Geometric modeling [16] and in vitro [13, 16] studies have shown that CAW narrowing is associated with palmar bowing of the TCL which increases the height and cross-sectional area of the carpal arch. These changes may provide additional space within the carpal tunnel for its contents; however, such previous studies have not investigated the impact of CAW narrowing on the tunnel contents.…”

“…These changes may provide additional space within the carpal tunnel for its contents; however, such previous studies have not investigated the impact of CAW narrowing on the tunnel contents. Additionally, the in vitro strategy of force application to achieve CAW narrowing involved directly applying invasive force to the carpal bones or transverse carpal ligament [13, 15]. Non-invasive, in vivo narrowing of the CAW by applying external transverse force across the wrist has not been explored.…”

Three-dimensional stiffness of the carpal arch

“…Prior to experimentation, each specimen was preconditioned by displacing the ridge of the trapezium by 2 mm in a set of the 14 directions; the order of the 14 directions was randomized within a set, and the preconditioning was repeated for 10 sets. A preconditioning magnitude of 2 mm was chosen because it is the largest displacement magnitude used for testing and the carpal arch remains relatively elastic within this amount of displacement (Gabra et al, 2012; Li et al, 2013; Xiu et al, 2010). …”

“…Experimental studies have investigated the uniaxial stiffness characteristics of the wrist in the medial-lateral (Fuss and Wagner, 1996; Xiu et al, 2010) and dorsal-palmar directions (Garcia-Elias et al, 1989a). The two-dimensional mechanics of the wrist have also been investigated with respect to the compliance of the carpal tunnel (Tung et al, 2010), force transmission across wrist (Garcia-Elias et al, 1989b; Schuind et al, 1995), and manipulation of the carpal tunnel's cross-sectional area (Li et al, 2013; Li et al, 2011; Li et al, 2009). Three-dimensional studies of the wrist structure have been mainly studied with computational modeling with a particular focus on force transmission across the carpus (Fischli et al, 2009; Guo et al, 2009; Majima et al, 2008; Majors and Wayne, 2011; Marquez-Florez et al, 2015; Matsuki et al, 2009).…”