Elliptical Morphology of the Carpal Tunnel Cross Section

Abstract

Although the carpal tunnel is known for its anatomical constituents, its morphology is not well recognized. The aim of this study was to investigate the morphometric properties of the carpal tunnel and its surrounding structures. Magnetic resonance, cross-sectional images of the distal carpal tunnel were collected from eight cadaveric hands. Morphological analyses were performed for the cross sections of the carpal tunnel, interior carpus boundary, and exterior carpus boundary. The specimens had a carpal arch width and height of 23.9 ± 2.9 mm and 2.2 ± 0.9 mm, respectively. The carpal tunnel, interior carpus boundary, and exterior carpus boundary had perimeters of 54.8 ± 4.5 mm, 68.5 ± 7.0 mm, and 130.6 ± 11.8 mm, respectively, and areas of 183.5 ± 30.1 mm², 240.7 ± 40.2 mm², and 1002.3 ± 183.7 mm², respectively. The cross sections were characterized by elliptical fitting with aspect ratios of 1.96 ± 0.15, 1.96 ± 0.19, and 1.76 ± 0.19 for the carpal tunnel, interior carpus boundary, and exterior carpus boundary, respectively. The major axis of the boundaries increased in pronation angle, relative to the hamate-trapezium axis, for the exterior carpus (6.0 ± 3.0°), interior carpus (8.2 ± 3.2°), and carpal tunnel (15.9 ± 2.2°). This study advances our understanding of the structural anatomy of the carpal tunnel, and the morphological information is valuable in the identification of structural abnormality, assistance of surgical planning, and evaluation of treatment of effects.

Keywords: carpal tunnel; carpus; morphology.

Figure 1

A representative magnetic resonance (MR) image of the carpal tunnel at the level of the hook of the hamate and the ridge of the trapezium displaying the balloon (i.e. carpal tunnel) boundary (dotted line), interior carpus boundary (solid line), and exterior carpus boundary (dashed line).

Figure 2

Morphological parameters of the carpal tunnel. Shown are the morphological parameters for carpal arch width (CAW, solid line with endpoints), carpal arch height (CAH, dashed line), cross-sectional area (shaded region), and perimeter (outline of shaded region) with elliptical fit parameters such as major axis length (dashed dot line), minor axis length (dotted line), and pronation angle (θ) relative to the hamate-trapezium axis (dashed line with arrows).

Figure 3

Linear regression analysis of perimeter as a function of carpal arch width (CAW) for the carpal tunnel and interior carpus boundary.

Figure 4

The mean and standard deviation of major and minor axes length with statistical results for the carpal tunnel, interior carpus boundary, and exterior carpus boundary (* and ◆ denote p < 0.05; † and ‡ denote p < 0.001).

Figure 5

Linear regression analysis of major axis length as a function of carpal arch width (CAW) for the carpal tunnel and interior carpus boundary.