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. 2011 Dec;29(12):1951-6.
doi: 10.1002/jor.21468. Epub 2011 May 23.

Area and shape changes of the carpal tunnel in response to tunnel pressure

Zong-Ming Li  1 , Tamara L Masters, Tracy A Mondello
Affiliations

Area and shape changes of the carpal tunnel in response to tunnel pressure

Zong-Ming Li et al. J Orthop Res. 2011 Dec.

Abstract

Carpal tunnel mechanics is relevant to our understanding of median nerve compression in the tunnel. The compliant characteristics of the tunnel strongly influence its mechanical environment. We investigated the distensibility of the carpal tunnel in response to tunnel pressure. A custom balloon device was designed to apply controlled pressure. Tunnel cross sections were obtained using magnetic resonance imaging to derive the relationship between carpal tunnel pressure and morphological parameters at the hook of hamate. The results showed that the cross-sectional area (CSA) at the level of the hook of hamate increased, on average, by 9.2% and 14.8% at 100 and 200 mmHg, respectively. The increased CSA was attained by a shape change of the cross section, displaying increased circularity. The increase in CSA was mainly attributable to the increase of area in the carpal arch region formed by the transverse carpal ligament. The narrowing of the carpal arch width was associated with an increase in the carpal arch. We concluded that the carpal tunnel is compliant to accommodate physiological variations of the carpal tunnel pressure, and that the increase in tunnel CSA is achieved by increasing the circularity of the cross section.

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Figures

Figure 1
Figure 1
A custom balloon device to apply controlled pressure to the carpal tunnel.
Figure 2
Figure 2
(a) A sample MRI at the hook of hamate with contrasted carpal tunnel cross section, and (b) a schematic drawing of the carpal tunnel cross section partitioned into A1 and A2.
Figure 3
Figure 3
Carpal tunnel areas (mm2) at various pressure levels (mmHg). (a) Total area, A, (b) bony portion area, A1, (c) carpal arch area, A2
Figure 4
Figure 4
Carpal arch width (mm) at various pressure levels (mmHg)
Figure 5
Figure 5
Carpal tunnel areas (mm2) at various arch widths (mm). (a) Total area, A, (b) bony portion area, A1, (c) carpal arch area, A2
Figure 6
Figure 6
Carpal tunnel circularity (a) and aspect ratio (b) at various pressure levels (mmHg)
See this image and copyright information in PMC

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