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Research Papers

# Carpal Tunnel Expansion by Palmarly Directed Forces to the Transverse Carpal Ligament

[+] Author and Article Information
Zong-Ming Li1

Department of Orthopaedic Surgery, Department of Bioengineering, and Department of Occupational Therapy, Hand Research Laboratory, University of Pittsburgh, Pittsburgh, PA 15213zmli@pitt.edu

Jie Tang, Matthew Chakan, Rodrigo Kaz

Department of Orthopaedic Surgery, Department of Bioengineering, and Department of Occupational Therapy, Hand Research Laboratory, University of Pittsburgh, Pittsburgh, PA 15213

1

Corresponding author. Also at 210 Lothrop Street, E1641 BST, Pittsburgh, PA 15213.

J Biomech Eng 131(8), 081011 (Jul 09, 2009) (6 pages) doi:10.1115/1.3148469 History: Received September 12, 2008; Revised March 09, 2009; Published July 09, 2009

## Abstract

This study investigated the expansion of the carpal tunnel resulting from the application of palmarly directed forces to the transverse carpal ligament (TCL) from inside the carpal tunnel. Ten fresh-frozen cadaveric hands were dissected to evacuate the carpal tunnel, and thus to expose the TCL. A custom lever device was built to apply forces, ranging from 10 N to 200 N, to the TCL. Without force application, the carpal tunnel area was $148.4±36.8 mm2$. The force application caused the TCL to form arches with an increase in cross-sectional areas of $33.3±5.6 mm2$ at 10 N and $48.7±11.4 mm2$ at 200 N, representing respective increases of 22.4% and 32.8% relative to the initial carpal tunnel area. The TCL length remained constant under the applied forces. It was found that the TCL arch formation was due to the narrowing of the arch width, which resulted from the migration of the bony insertion sites of the TCL. A geometrical model of the carpal tunnel was then developed to elucidate the relationships among the arch width, TCL length, arch height, and arch area. The model illustrated the effectiveness of carpal tunnel expansion by TCL elongation or arch width narrowing.

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Copyright © 2009 by American Society of Mechanical Engineers
Topics: Force , Arches , Tunnels , Elongation
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## Figures

Figure 3

Digitization of the TCL surface while the TCL was loaded with the lever device

Figure 4

A schematic of the cross-sectional area of the carpal tunnel is composed of two parts: the baseline area formed by the carpal bones with an assumed flat TCL (A1) and the area formed by the TCL arch (A2)

Figure 1

Cadaveric preparation of the carpal tunnel and TCL viewed (a) palmarly and (b) proximally

Figure 2

The custom lever device used to apply forces to the TCL

Figure 6

A representative plot of TCL arch curves in the transverse plane. The curves move progressively upward with increasing forces. The circles denote edge points of the TCL.

Figure 5

Representative surface plots of a TCL without force application (the “flat” surface) and the TCL under a 200 N force (the arched surface)

Figure 7

Changes in (a) arch height, (b) arch area, (c) arch width, and (d) TCL length with increasing forces

Figure 8

Geometric representation of the cross section of the carpal tunnel. (a) Initial carpal tunnel without an arch. (b) Arch formation by the elongation of the TCL with a constant arch width. (c) Arch formation by the arch width narrowing assuming a constant TCL length. The enclosed area by the dashed curve and line in Fig. 8 represents the initial carpal tunnel.

Figure 9

(a) Arch height and (b) arch area due to TCL lengthening (Δl) or arch width narrowing (Δa)

Figure 10

The changes in (a) arch height, (b) arch area, and (c) total area with the change in arch width (Δa)

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