Elsevier

Clinical Biomechanics

Volume 59, November 2018, Pages 56-61
Clinical Biomechanics

Dimensional changes of the carpal tunnel and median nerve during manual mobilization of the carpal bones — Anatomical study

https://doi.org/10.1016/j.clinbiomech.2018.09.001Get rights and content

Highlights

  • Cross-sectional area of the carpal tunnel increased during the manual mobilization of the carpal bones in cadaver.

  • The mobilization increased the anterior-posterior diameter of the carpal tunnel.

  • Both the carpal tunnel and the median nerve became rounder during the technique.

Abstract

Study design

Cross-sectional study.

Background

The carpal tunnel is a clinically important fibro-osseous conduit for the median nerve and associated tendons. It is mechanically dynamic and therapeutic manual techniques that appear to move and change tunnel shape is part of clinical practice.

Objectives

To measure changes in dimensions of the carpal tunnel and median nerve with manual mobilization of the carpal bones in cadavers.

Methods

A total of 20 cryopreserved upper extremities from cadaveric specimens were used in the study. The wrist was cut using an anatomical saw at the level of the pisiform. Measurements of the cross-sectional area (CSA), anteroposterior diameter (APD), transverse diameter (TD), perimeter, flattening ratio and circularity of the carpal tunnel and of the median nerve, were taken, both in the anatomical position of the wrist and during the mobilization technique of the carpal bones.

Results

During the mobilization technique, the tunnel CSA (p < 0.011), APD (p < 0.001) and circularity (p < 0.001) significantly increased, while TD (p < 0.001), perimeter (p < 0.004) and flattening ratio (p < 0.001), decreased. The median nerve showed similar behavioral tendencies to the tunnel but only the CSA (p < 0.005), APD (p < 0.005) and flattening ratio (p < 0.004) of the nerve showed significant differences.

Conclusion

Application of external manually applied compressive force across the wrist can increase the CSA of the carpal tunnel and the median nerve in cadavers. These results are consistent with other studies in which similar results were found non-invasively using ultrasound.

Introduction

The carpal tunnel is a fibro-osseous entity bound by the scaphoid and trapezium bones on the radial side, the pisiform and hamate hook on the ulnar side and enclosed by the flexor retinaculum on the ventral side (Drake et al., 2009). The median nerve runs along tendons of the m. flexor digitorum superficialis and profundus and tendon of the m. pollicis longus through this tunnel. In this narrow passage, the median nerve is vulnerable to compression. Involvement of the median nerve at this level is known as carpal tunnel syndrome (CTS) and is the most common neuropathy of the upper limbs (Ibrahim et al., 2012; Keith et al., 2009). Its prevalence ranges between 3% and 6% of the general adult population and affects women more than men (Atroshi et al., 1999).

The space available for the median nerve in the carpal tunnel is influenced by the cross-sectional area (CSA) formed by the carpal bones and the transverse carpal ligament. The tunnel area can vary with flexion and extension of the wrist, during daily living activities (Garcia-Elias et al., 1992) and after surgical release of the carpal tunnel (Lee et al., 2005; Richman et al., 1989). These changes can be important because they may relate to the increase or decrease in CTS symptoms.

From cadaveric studies (Li et al., 2009; Li et al., 2011; Li et al., 2013), it has been observed that the dimensions of the carpal tunnel can increase when outwardly-directed forces are applied with a custom balloon device from inside the tunnel to apply controlled pressure to the carpal tunnel. This effect occurs when the carpal arch width narrows as the distance between the trapezoid and the hook of the hamate decreases, increasing the anteroposterior diameter (APD) and the circularity of the tunnel. Recently it has been shown using ultrasound in asymptomatic subjects that similar changes can also occur in vivo when applying a compressive force transverse to the carpal tunnel both with a pneumatic actuator (Marquardt et al., 2015) and manually (Bueno-Gracia et al., 2018). From these studies, it was hypothesized that these changes may assist transiently in relieving pressure around the median nerve in patients with CTS.

What is of value in contextualizing and establishing the extent to which non-invasive measurement approaches resemble the events that would occur anatomically is to perform such maneuvers in cadavers also. To our knowledge there are no studies on the effect of applying external compressive transverse forces to the carpal bones on carpal tunnel and median nerve dimensions in cadavers. Hence, the hypothesis of this study is that manual mobilization of the carpal bones can produce changes in the cross-sectional dimensions and area of the carpal tunnel and median nerve in cadavers.

Section snippets

Study design

This was a cross-sectional study designed to document and analyze the effect of manual mobilization of carpal bones on the dimensions of the carpal tunnel and median nerve at the wrist in cadaver specimens. Donations were made to the dissection laboratory of the Universitat Internacional de Catalunya. The local Ethical Committee approved the present study (reference number CBAS-2018-03). The sample size calculation was made with reference to data from a previous in vivo study (Bueno-Gracia et

Results

Reliability of tunnel and nerve with the ImageJ software was excellent. The ICC ranged from 0.98 to 0.99 for all measurements (Table 1).

The initial area of the tunnel was 186.33mm2 ± 47.44. The APD was 10.04 mm ± 2.00 and the TD 23.19 mm ± 3.12 (Table 2). The flattening ratio and circularity were 2.36 ± 0.34 and 0.72 ± 0.05, respectively. All the carpal tunnel shape descriptors were significantly modified by the mobilization of the carpal bones. The CSA increased by 5.93mm2 (p < 0.011) and the

Discussion

This study investigated the morphological changes of the carpal tunnel and median nerve during the application of manual and external forces at the wrist in cadavers. Initial values for the tunnel and median nerve were similar to other studies (Bueno-Gracia et al., 2017; Bueno-Gracia et al., 2018; Cobb et al., 1993; Hobson-Webb et al., 2008; Lange, 2013; Li et al., 2009; Pacek et al., 2010; Yazdchi et al., 2012). The results confirmed the hypotheses that pressure application to the tunnel

Conclusion

This study demonstrated that the application of a manually applied external compressive force across the wrist can increase the cross-sectional area (CSA) of the carpal tunnel and the median nerve in fresh-frozen cadavers. The carpal tunnel and median nerve became rounder, due to a reduction in the transverse diameter (TD) and an increase in the anterior-posterior diameter. This manual intervention is hypothesized to produce transient reductions in tunnel pressure which may be offered for pain

Conflict of interest

The authors certify that there are no conflicts of interest (or funding sources are explicitly declared in the paper, especially those that might pose a conflict of interest).

Financial disclosure and conflict of interest

Authors of the manuscript affirm that they have no financial affiliation (including research funding) or involvement with any commercial organization that has a direct financial interest in any matter included in this manuscript, except as disclosed in an attachment and cited in the manuscript. Any other conflict of interest (i.e., personal associations or involvement as a director, officer, or expert witness) is also disclosed in an attachment.

Acknowledgements

We express our sincere gratitude for the opportunity to make use of the materials and resources of the Body Donation from UIC-Barcelona. Body donors are fundamental for the evolution of science, both in terms of teaching and research. Thanks to these donations, the present study has been possible. We also thank Judith Pascual for their help and assistance in the laboratory.

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