Three-dimensional architecture of the whole human soleus muscle in vivo

Bart Bolsterlee; Taija Finni; Arkiev D'Souza; Junya Eguchi; Elizabeth C Clarke; Robert D Herbert

doi:10.7717/peerj.4610

Three-dimensional architecture of the whole human soleus muscle in vivo

PeerJ. 2018 Apr 18:6:e4610. doi: 10.7717/peerj.4610. eCollection 2018.

Authors

Bart Bolsterlee^{1

2}, Taija Finni³, Arkiev D'Souza^{1

2}, Junya Eguchi^{1

2}, Elizabeth C Clarke⁴, Robert D Herbert^{1

2}

Affiliations

¹ Neuroscience Research Australia (NeuRA), Sydney, New South Wales, Australia.
² University of New South Wales, Sydney, New South Wales, Australia.
³ Faculty of Sport and Health Sciences, University of Jyväskylä, Jyväskylä, Finland.
⁴ Murray Maxwell Biomechanics Laboratory, Institute for Bone and Joint Research, Kolling Institute of Medical Research, Sydney Medical School, University of Sydney, Sydney, New South Wales, Australia.

Abstract

Background: Most data on the architecture of the human soleus muscle have been obtained from cadaveric dissection or two-dimensional ultrasound imaging. We present the first comprehensive, quantitative study on the three-dimensional anatomy of the human soleus muscle in vivo using diffusion tensor imaging (DTI) techniques.

Methods: We report three-dimensional fascicle lengths, pennation angles, fascicle curvatures, physiological cross-sectional areas and volumes in four compartments of the soleus at ankle joint angles of 69 ± 12° (plantarflexion, short muscle length; average ± SD across subjects) and 108 ± 7° (dorsiflexion, long muscle length) of six healthy young adults. Microdissection and three-dimensional digitisation on two cadaveric muscles corroborated the compartmentalised structure of the soleus, and confirmed the validity of DTI-based muscle fascicle reconstructions.

Results: The posterior compartments of the soleus comprised 80 ± 5% of the total muscle volume (356 ± 58 cm³). At the short muscle length, the average fascicle length, pennation angle and curvature was 37 ± 8 mm, 31 ± 3° and 17 ± 4 /m, respectively. We did not find differences in fascicle lengths between compartments. However, pennation angles were on average 12° larger (p < 0.01) in the posterior compartments than in the anterior compartments. For every centimetre that the muscle-tendon unit lengthened, fascicle lengths increased by 3.7 ± 0.8 mm, pennation angles decreased by -3.2 ± 0.9° and curvatures decreased by -2.7 ± 0.8 /m. Fascicles in the posterior compartments rotated almost twice as much as in the anterior compartments during passive lengthening.

Discussion: The homogeneity in fascicle lengths and inhomogeneity in pennation angles of the soleus may indicate a functionally different role for the anterior and posterior compartments. The data and techniques presented here demonstrate how DTI can be used to obtain detailed, quantitative measurements of the anatomy of complex skeletal muscles in living humans.

Keywords: Diffusion tensor imaging; MRI; Muscle architecture; Passive muscle properties; Soleus.

Grants and funding

The study was supported by the Australian National Health and Medical Research Council (NHMRC; Program Grant APP1055084). R Herbert is supported by a research fellowship from the Australian NHMRC. A D’Souza is supported by a scholarship from the Royal Freemasons Benevolent Institute. E Clarke is supported by a Sydney Medical School Foundation Fellowship. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.