# Biomechanical characterization of cadaveric brachial plexus microstructure

Anne C Perruisseau-Carrier, Yann Marco, Vadim Fleury, David M Brogan,
Alexandra Forli, Nadia Bahlouli

► To cite this version:

Anne C Perruisseau-Carrier, Yann Marco, Vadim Fleury, David M Brogan, Alexandra Forli, et al. Biomechanical characterization of cadaveric brachial plexus microstructure. Hand Surgery and Rehabilitation, 2024, 43 (4), pp.101745. 10.1016/j.hansur.2024.101745. hal-05340814

HAL Id: hal-05340814

https://hal.univ-brest.fr/hal-05340814v1

Submitted on 31 Oct 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# Biomechanical characterization of cadaveric brachial plexus microstructure.

**Running head title:** Brachial plexus microstructure biomechanics.

Anne C. Perruisseau-Carrier<fnref n="1" />,<fnref n="2" />, Yann Marco<fnref n="3" />, Vadim Fleury<fnref n="3" />, David M Brogan<fnref n="4" />, Alexandra Forli<fnref n="2" />, Nadia Bahlouli<fnref n="1" />

**Corresponding author:** Anne C. Perruisseau-Carrier, aperruisseau@gmail.com

Orcid: 0000-0002-9474-1656

<footnote n="1">¹ ICube, Université de Strasbourg, CNRS 2-4 Rue Boussingault, 67000 Strasbourg, France</footnote>

<footnote n="2">² Hand Surgery, Plastic & Reconstructive Surgery, Grenoble University Hospital, 38000 Grenoble, France</footnote>

<footnote n="3">³ IRDL (Institut de Recherche Dupuy de Lôme), UMR CNRS 6027, ENSTA Bretagne, Brest, France</footnote>

<footnote n="4">⁴ Department of Orthopedic Surgery, Washington University in St. Louis, St. Louis, MO, United States</footnote>
1 ABSTRACT

2 INTRODUCTION

3 Peripheral nerves consist of axons and connective tissue. The amount of connective tissue in
4 peripheral nerves such as the brachial plexus varies proximally to distally. The proximal regions of the
5 brachial plexus are more susceptible to stretch injuries than the distal regions. A description of the
6 mechanical behavior of the peripheral nerve components is necessary to better understand the
7 deformation mechanisms during stretch injuries.

8
9
10
The purpose of this study was to model the biomechanical behavior of each component of the
peripheral nerves (fascicles, connective tissue) in a cadaveric model and report differences in elastic
modulus, maximum stress and maximum strain.

11 METHODS

12
13
14
Forty-six specimens of fascicles and epi-perineurium were subjected to cyclical uniaxial tensile tests
to obtain the stress and strain histories of each specimen, using a BOSE® Electroforce® 3330 and
INSTRON® 5969 materials testing machines.

15
16
Maximum stress, maximum strain and elastic modulus were extracted from the load-displacement
and stress-strain curves, and analyzed using Mann-Whitney tests.

17 RESULTS

18
19
20
Mean elastic modulus was 6.34MPa for fascicles, and 32.1MPa for connective tissue. The differences
in elastic modulus and maximum stress between fascicles and connective tissue were statistically
significant (p<0.001).

21 CONCLUSIONS

22
23
Peripheral nerve connective tissue showed significantly higher elastic modulus and maximum stress
than fascicles. These data confirm the greater fragility of axons compared to connective tissue,
suggesting that the greater susceptibility to stretch injury in proximal regions of the brachial plexus
might be related to the smaller amount of connective tissue.

Keywords: brachial plexus, biomechanics, peripheral nerves, tensile test, stretch injury.

## Introduction

The brachial plexus is a complex network of nerves, beginning with the cervical roots and terminating in peripheral nerves. An understanding of the biomechanical properties of each zone of the brachial plexus is essential to understand its behavior during stretch injury. The cervical root level is the most susceptible to permanent damage due to stretch lesions, such as nerve root avulsion [1-3]. Despite the growing interest in brachial plexus injury management in the last 30 years, little is known about the biomechanical reasons for the predominance of stretch injuries in the proximal brachial plexus.

The mechanical response of peripheral nerves to stretch injury is dictated in part by their histologic architecture.

Peripheral nerves consist of a collection of axons, organized in fascicles and surrounded by connective tissue. This connective tissue is organized in layers consisting of the endoneurium, perineurium and epineurium (Fig. 1) [4]. The endoneurium encloses each axon, the perineurium each fascicle and the epineurium the entire nerve. According to Sunderland, the perineurium is the primary contributor to peripheral nerve resistance to failure in tension [4,5].

Nerve roots are also a collection of axons, but with important distinctions. The axons of the nerve root are, as a group, enveloped within the meningeal layers (pia mater, arachnoid mater, dura mater) that enclose the entire root, and are not organized in fascicles. The dura mater of the nerve root is continuous with the epineurium of the nerve and constitutes the primary contributor to nerve root tensile support [4,6], whereas the pia matter is continuous with the perineurium of the nerve root [7].
Previous histological studies suggested that the different regions of the brachial plexus differ in the amount of connective tissue, proximal regions (roots, trunks) containing less connective tissue than distal regions (cords, terminal branches) [8]. Considering the greater fragility of nerve roots and proximal structures of the brachial plexus in both animal and human studies [3,9,10], the amount of connective tissue present in each region could play a role in the mechanical resistance of the brachial plexus and peripheral nerves to stretch injuries. However, no studies have focused on differences in biomechanical behavior between connective tissue and axons in their interpretation of the mechanical properties of the brachial plexus.

Standardized data characterizing the differences of the biomechanical properties of the brachial plexus microstructure would allow further characterization of the mechanical behavior of the overall brachial plexus and its terminal nerve branches.

The purpose of this study was to determine the biomechanical behavior of the connective tissue and axon constituents of brachial plexus peripheral nerves in cadavers, in terms of elastic modulus, maximum stress and maximum strain.

## 62 Material and Methods

### 63 Tissue harvesting

Four whole cadaveric brachial plexi (2 left and 2 right) from 4, divided into a total of 46 segments, were used for this experiment. The plexi were harvested from fresh frozen cadaveric specimens thawed at room temperature for 48 hours before dissection. The cadaveric specimen was placed in supine position, and an anterior approach to the brachial plexus was used. The plexus was exposed after the clavicle was removed and an anterior scalenectomy was performed. Plexi were then harvested en-bloc, and each specimen was individually submerged in 0.9% sodium chloride (normal saline), frozen and stored until use. Contralateral plexi were harvested for macroscopic
71 biomechanical characterization according to region [11]. Prior to mechanical testing, each specimen
72 was thawed at room temperature for 3 hours in normal saline until testing, which was performed
73 within 4 hours of thawing.

74 Mechanical experimental set-up

75 Each brachial plexus was dissected under magnification in order to isolate epi-perineurium (EP,
76 hereafter referred to as “connective tissue”) and fascicle samples (Fig. 2). The connective tissue and
77 fascicle samples were stored in normal saline until testing, which was performed within 4 hours of
78 thawing.

79 BOSE® Electroforce® 3330 (electromagnetic motor, 3.2kN cell) (BOSE®ElectroForce®3330 Series II,
80 Minnetonka, MN) and an INSTRON® 5969 (electromechanical, 2kN cell) (INSTRON®, Norwood, MA)
81 material testing machines were used to apply axial stretch to the samples (Fig. 3). Experimental data
82 were acquired and digitized on a personal computer at a sampling rate of 4Hz.

83 To mimic tensile loading, each sample was anchored to the testing set-up by mechanical grips and
84 protected by a polyimide sheet with a slit at the center to prevent specimen dehydration during the
85 tests (Fig. 4). Initial length between grips and the width and thickness of each sample were measured
86 with a caliper (WILMART®006122). Cross-sectional area was calculated from width and thickness
87 values.

88 Cyclical uniaxial tensile test trials were performed to obtain the stress and strain histories of the
89 brachial plexus specimens. Cyclic tests using a sawtooth waveform were performed at a strain rate of
90 0.2mm/sec and a strain range that increased by 10% of the specimen's initial length (L0) with each
91 trial until rupture. For each deformation level, 3 cycles were completed.

92 Data analysis

93 Load readings were converted to nominal stresses using the following formula:
94

$$\sigma_i(t) = \frac{F(t)}{S_0}$$

95

96

where $\sigma_i(t)$ is the nominal stress at time t, $F(t)$ the load at time t, and $S_0$ the initial cross-sectional area of the sample.

97

Displacement data were used to calculate the tensile strain $e_i$ imposed during the tensile test:

98

$$e_i(t) = \frac{\Delta L}{L_0}$$

99

100

101

where $\Delta L$ is the displacement and $L_0$ the initial length. Nominal strain was then converted to true strain $\epsilon_i$ which represents a better metric for large displacement measurement [12].

102

$$\epsilon_i(t) = \ln\left(1 + \frac{\Delta L}{L_0}\right)$$

103

104

105

106

107

108

109

110

Statistical analysis

111

112

113

Normality was assessed on Shapiro-Wilk test, and Mann-Whitney tests were performed between specimens for maximum strain, maximum stress and elastic modulus. Analyses were used R software (R-4.3.1, astatsa.com).

114
115 **Results**

116 Mechanical properties in the brachial plexus microstructure specimens are shown in Tables 1 & 2 and
117 Figures 5 & 6.

118 Twenty-eight of the 46 tested specimens testing, 18 being excluded for loss of fixation or rupture at
119 clamp level. Twelve fascicles and 16 connective tissue samples were included in the descriptive
120 analysis. Initial length and cross-sectional area values are presented in Table 1.

121 Representative samples of individual stress-strain curves for connective tissue and fascicle samples
122 are shown in Figure 6, and show strong non-linear behavior typical of hyperelasticity, and features of
123 viscoelasticity such as cyclic accommodation (progressive loss of stiffness over cycles), and increasing
124 permanent strain at zero force.

125 The mean elasticity modulus was 6.34 MPa for fascicles and 32.1MPa for connective tissue, and
126 statistically significant (p<0.001).

127 The mean maximum stress was 0.87MPa for fascicles and 3.21MPa for connective tissue, and
128 statistically significant (p<0.001).

129

130 **Discussion**

131 Then present study found significant mechanical differences between fascicles and epi-perineurium
132 and provided further data on human brachial plexus biomechanical characteristics.

133 The majority of mechanical studies on brachial plexus and peripheral nerves used uniaxial tensile
134 loading until failure, without preconditioning cycles [13-18], except for two [11,19]. *In vivo*, nerves
135 cross joints and are therefore subject to physiological variations in tension that have to be
136 reproduced on tensile testing, using either preconditioning cycles or cyclic tensile loading. This study
137

allowed us to stay as close as possible to physiological conditions, and the results showed that nerves exhibited a strong non-linear behavior, combining hyperelasticity and viscoelasticity.

138

139

Microstructurally, the results for connective tissue were similar to those reported in the literature. Both Lynch et al. [20] and Graham et al. [21] reported similar elasticity modulus values for, respectively, tendons (34.0 MPa) and collagen fibrils (32.0MPa).

140

141

142

The biomechanical characteristics of fascicles, isolated from their epi-perineurium, have not been reported in the literature to date. The biological tissue closest to fascicles studied in the literature is myelinated axons from the white matter of the spinal cord. The elasticity modulus reported in the literature for white matter in mammals ranges from 0.061MPa to 1.19MPa [22-25]. The present elastic modulus values for fascicles are therefore greater than those reported for isolated myelinated axons. This difference can be explained by the histological difference between white matter and fascicles: the presence of endoneurium, and therefore collagen, in fascicles alters their biomechanical behavior and suggests a role of endoneurium in peripheral nerve resistance to traction.

143

144

145

146

147

148

149

150

151

152

Only a few studies describe the actual histology of the brachial plexus. The most thorough and accurate one is the histological study by Bonnel [8], who described the microscopic structure of the brachial plexus through histological cross-sections of 21 brachial plexi, and found that percentage connective tissue and number of fascicles increased proximally to distally as percentage fascicular area decreased. At the root level, percentage connective tissue was just 29% while, at the terminal branches, it ranged from 73% to 86%. Stodieck reported 4.5-field lower collagen content in nerves roots than in peripheral nerves [26].

153

154

155

156

157

158

159

Biomechanically, various authors reported lower elastic moduli and lower maximum stress in the proximal than in the distal portions of the brachial plexus, in both animal models [13, 17] and human cadaveric models [11]. This fits the observed clinical pathology of these injuries, as two-thirds of

160

161
162 brachial plexus stretch injuries involve the supraclavicular plexus, and especially roots and trunks
163 [1,27].

164
165 Our results bring a microstructural perspective to these historical histological and biomechanical
166 findings and current clinical observations. Nerves containing more connective tissue can be expected
167 to exhibit higher elastic modulus and maximum stress. Proximal regions of the brachial plexus,
168 composed mainly of axons, thus tend to be more fragile and to rupture before distal regions when
169 exposed to traction injury.

170 These differences, along with the histologic differences described by Bonnel [8], suggest a
171 histological and structural explanation for roots' greater vulnerability to rupture, which accounts for
172 up to 70% of the brachial plexus traction injuries [1].

173
174 This study is not without limitations. We used only a small number of specimens for tensile loading;
175 but even so, we were able to demonstrate significant differences in elastic modulus and maximal
176 stress. We only used one strain rate and were therefore not able to study fascicle and connective
177 tissue viscoelasticity and rate-dependent behavior. Additionally, our strain rate was relatively low
178 and not representative of the high-energy injury mechanisms encountered in brachial plexus injury,
179 especially in road accidents. While the study investigated mechanical failure of the nerve tissue itself,
180 it did not analyze nerve function at different strain rates. Whereas maximum strains were as high as
181 0.57 and 0.74 in our study, nerve conduction loss occurs from 12% elongation [28]. Biomechanically,
182 cadaveric and live patients' peripheral nerve biomechanics may differ, and the present results can be
183 extrapolated to clinical practice only with caution.

184 Subsequent studies are therefore needed to assess brachial plexus microstructure biomechanical
185 behavior at different strain rates and under different mechanisms before extrapolating to patient
186 care. Moreover, we did not study differences in connective tissue biomechanical characteristics
187 between proximal and distal regions of the brachial plexus or between upper and lower roots, which
188 could, along with histological differences, explain the greater fragility of proximal regions of the
189 brachial plexus [11].

190

191 **Conclusion**

192 The present study confirmed the greater fragility of isolated fascicles compared to connective tissue,
193 making them liable to rupture under stretch injury. Along with previous histological and
194 biomechanical studies of the brachial plexus, these differences suggest a microstructural explanation
195 for the greater vulnerability of roots. These results provide a foundation description of brachial
196 plexus and peripheral nerve biomechanical properties, which further studies can expand.

197 Additional studies on histological differences between proximal and distal regions of the brachial
198 plexus could provide further explanations of peripheral nerve biomechanics and of the vulnerability
199 of roots and trunks and open the way for digital modeling of peripheral nerves and brachial plexus
200 biomechanical behavior, to better understand and prevent injury.

201 **Disclosure of interest:** The authors do not have any conflicts of interest to disclose.

202 **Acknowledgments:** The authors gratefully acknowledge Pr Romuald Seizeur and the Department of
203 Anatomy, Faculty of Medicine, University of Western Brittany, Brest, France, for allowing them to
204 conduct this research, and the persons who donated their bodies to the Department of Anatomy;
205 and Dr Cedric Bain, Dr Guilhem Bles of the Dupuy de Lôme Research Intitute and Dr Hamdi Jmal of
206 the ICube Laboratory for their help with the mechanical trials. The authors also thank Pr Philippe
207 Liverneaux for his advice.

208 **Declaration on generative AI and AI-assisted technologies:** No generative AI and AI-assisted
209 technologies were used in the writing process for this manuscript.
210 **References**

211 1. Chuang DC. Adult brachial plexus reconstruction with the level of injury: review and personal experience. Plast Reconstr Surg. 2009;124:e359-e369.

213 2. Narakas AO. Lesions found when operating traction injuries of the brachial plexus. Clin Neurol Neurosurg. 1993;95:S56-64.

215 3. Soldado F, Ghizoni MF, Bertelli J. Injury mechanisms in supraclavicular stretch injuries of the brachial plexus. Hand Surg Rehabil. 2016;35:51-4.

217 4. Sunderland S. The anatomy and physiology of nerve injury. Muscle Nerve. 1990;13:771-84.

218 5. Rydevik BL, Kwan MK, Myers RR, Brown RA, Triggs KJ, Woo SL, et al. An in vitro mechanical and histological study of acute stretching on rabbit tibial nerve. J Orthop Res. 1990;8:694-701.

221 6. McCabe JS, Low FN. The subarachnoid angle: an area of transition in peripheral nerve. Anat Rec. 1969;164:15-33.

223 7. Kucenas S, Takada N, Park HC, Woodruff E, Broadie K, Appel B. CNS-derived glia ensheath peripheral nerves and mediate motor root development. Nat Neurosci. 2008;11:143-51.

225 8. Bonnel F. Microscopic anatomy of the adult human brachial plexus: an anatomical and histological basis for microsurgery. Microsurgery. 1984;5:107-18.

227 9. Steer JM. Some observations on the fine structure of rat dorsal spinal nerve roots. J Anat. 1971;109:467-85.

229 10. Zapałowicz K, Radek A. Experimental investigations of traction injury of the brachial plexus. Model and results. Ann Acad Med Stetin. 2005;51:11-4.

231 11. Perruisseau-Carrier A, Marco Y, Fleury V, Jmal H, Brogan DM, Forli A et al. Biomechanical characterization of cadaveric brachial plexus regions using uniaxial tensile tests. Hand Surg Rehabil. Article In Press.

234 12. Schwab R, Harter A. Extracting true stresses and strains from nominal stresses and strains in tensile testing. Strain. 2021;57:e12396.
236

237

238

239

240

241

242

243

244

245

246

247

248

249

250

251

252

253

254

255

256

257

258

259

260

261

13. Beel JA, Stodieck LS, Luttges MW. Structural properties of spinal nerve roots: biomechanics. Exp Neurol. 1986;91:30-40.

14. Kawai H, Ohta I, Masatomi T, Kawabata H, Masada K, Ono K. Stretching of the brachial plexus in rabbits. Acta Orthop Scand. 1989;60:635-8.

15. Nishida N, Kanchiku T, Ohgi J, Ichihara K, Chen X, Taguchi T. Mechanical properties of nerve roots and rami radiculares isolated from fresh pig spinal cords. Neural Regen Res. 2015;10:1869-73.

16. Singh A, Lu Y, Chen C, Cavanaugh JM. Mechanical properties of spinal nerve roots subjected to tension at different strain rates. J Biomech. 2006;39:1669-76.

17. Singh A, Shaji S, Delivoria-Papadopoulos M, Balasubramanian S. Biomechanical Responses of Neonatal Brachial Plexus to Mechanical Stretch. J Brachial Plex Peripher Nerve Inj. 2018;13:e8-e14.

18. Zapałowicz K, Radek M. The distribution of brachial plexus lesions after experimental traction: a cadaveric study. J Neurosurg Spine. 2018;29:704-710.

19. Kerns J, Piponov H, Helder C, Amirouche F, Solitro G, Gonzalez M. Mechanical Properties of the Human Tibial and Peroneal Nerves Following Stretch With Histological Correlations. Anat Rec (Hoboken). 2019;302:2030-2039.

20. Lynch HA, Johannessen W, Wu JP, Jawa A, Elliott DM. Effect of fiber orientation and strain rate on the nonlinear uniaxial tensile material properties of tendon. J Biomech Eng. 2003;125:726-731.

21. Graham JS, Vomund AN, Phillips CL, Grandbois M. Structural changes in human type I collagen fibrils investigated by force spectroscopy. Experimental cell research.2004;299:335-342.

22. Ichihara K, Taguchi T, Shimada Y, Sakuramoto I, Kawano S, Kawai S. Gray matter of the bovine cervical spinal cord is mechanically more rigid and fragile than the white matter. Journal of neurotrauma. 2001;18:361-7.
262

23. Mazuchowski EL, Thibault LE. Biomechanical properties of the human spinal cord and pia mater. Summer Bioengineering Conference. 2003:1205-1206.

263

264

24. Oakland R, Hall R, Wilcox R, Barton D. The biomechanical response of spinal cord tissue to uniaxial loading. Proceedings of the Institution of Mechanical Engineers, Part H : Journal of Engineering in Medicine. 2006;220:489-92.

265

266

267

25. Ramo NL, Troyer KL, Puttlitz CM. Viscoelasticity of spinal cord and meningeal tissues. Acta biomaterialia. 2018;75:253-62.

268

269

26. Stodieck LS, Beel JA, Luttges MW. Structural properties of spinal nerve roots: Protein composition. Experimental neurology.1986;91:41-51.

270

271

27. Kim DH, Murovic JA, Tiel RL, Kline DG. Mechanisms of injury in operative brachial plexus lesions. Neurosurg Focus. 2004;16:E2.

272

273

28. Wall EJ, Massie JB, Kwan MK, Rydevik BL, Myers RR, Garfin SR. Experimental stretch neuropathy. Changes in nerve conduction under tension. J Bone Joint Surg Br. 1992;74:126-9.

274

275

## Figure legends

276

**Figure 1:** Histological view of a peripheral nerve (brachial plexus, middle trunk) stained following the Gomori technique. 1: Epineurium. 2: Fascicles. 3: Perineurium. 4: Endoneurium.

277

278

**Figure 2:** View of a brachial plexus sample during individualization of a fascicle (*) from the surrounding epi-perineurium (arrow), under x3.3 magnification.

279

280

**Figure 3:** Material testing machines: A, BOSE Electroforce® 3330 (electromagnetic motor, 3.2kN cell); and B, INSTRON 5969 (electromechanical, 2kN cell).

281

282

**Figure 4:** Mechanical test set-up. L0: initial length. e0: initial thickness. l0: initial width. The specimen (*) is anchored to the grips, and covered with a polyimide sheet.

283

284

**Figure 5:** Envelope curve and definition of the elastic modulus (E) defined from the linear part of the envelope curve (example from specimen n° 29). The star represents the point of failure of the

285
286 material. The red dotted line represents the maximum strain, the green dotted line the maximum
287 stress.

288 **Figure 6:** Examples of stress-strain data obtained for fascicles and epi-perineurium samples. A: fascicle. B: epi-perineurium (EP). Elastic modulus values (E, MPa) were calculated on the linear part of the envelope curve.

291
<figure><img src="image_2.png" /></figure>

1

2

3

4

1000 µm
<figure><img src="image_3.png" /></figure>

<figure><img src="image_4.png" /></figure>
<figure><img src="image_5.png" /><figcaption>A</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>B</figcaption></figure>
<figure><img src="image_7.png" /></figure>

*

e0

L0

L0
<figure><img src="image_8.png" /><figcaption>Figure 5: Envelope curve and definition of the elastic modulus (E) defined from the linear part of the envelope curve (example from specimen n° 29). The star represents the point of failure of the material. The red dotted line represents the maximum strain, the green dotted line the maximum stress.</figcaption></figure>
<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /><figcaption>**Figure 6:** Examples of stress-strain data obtained for fascicles and epi-perineurium samples. A: fascicle. B: epi-perineurium (EP). Elastic modulus values (E, MPa) were calculated on the linear part of the envelope curve.</figcaption></figure>
<table><caption>**Table 1**</caption><thead><tr><th>Variable</th><th>Fascicles<br>(Mean [range])</th><th>Epi-perineurium<br>(Mean [range])</th></tr></thead><tbody><tr><td>L<sub>0</sub> (mm)</td><td>9.39 [6.69 – 13.3]</td><td>8.25 [4.68 – 13.27]</td></tr><tr><td>S<sub>0</sub> (mm<sup>2</sup>)</td><td>5.46 [0.72 – 12.9]</td><td>3.49 [0.18 – 15.3]</td></tr></tbody></table>

Table 1: Initial length (L₀) and initial cross-sectional area (S₀) of the tested specimens.

<table><caption>**Table 2**</caption><thead><tr><th>Variable</th><th>Fascicles<br>(Mean ± SD)</th><th>Epiperineurium<br>(Mean ± SD)</th><th>p value</th></tr></thead><tbody><tr><td>E (MPa)</td><td>6.34 ± 3.79</td><td>32.1 ± 32.6</td><td>&lt;0.001*</td></tr><tr><td>Maximum<br>stress (MPa)</td><td>0.87 ± 0.41</td><td>3.21 ± 2.77</td><td>&lt;0.001*</td></tr><tr><td>Maximum<br>strain</td><td>0.57 ± 0.161</td><td>0.74 ± 0.320</td><td>0.12</td></tr></tbody></table>

Table 2: Elastic modulus (E), maximum stress and maximum strain for fascicles and epiperineurium specimens. *significant differences.