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

• Published in: PeerJ (San Francisco, CA) Vol. 6; p. e4610
• Main Authors: Bolsterlee, Bart, Finni, Taija, D'Souza, Arkiev, Eguchi, Junya, Clarke, Elizabeth C, Herbert, Robert D
• Format: Journal Article
• Language: English
• Published: United States PeerJ. Ltd 18.04.2018; PeerJ, Inc; PeerJ Inc
• Subjects: Anatomy; Anatomy & physiology; Anatomy and Physiology; Ankle; Cadavers; Diffusion tensor imaging; Kinesiology; Magnetic resonance imaging; Methods; MRI; Muscle architecture; Muscle function; Musculoskeletal system; NMR; Nuclear magnetic resonance; Passive muscle properties; Physiology; Radiology and Medical Imaging; Skeletal muscle; Soleus; Soleus muscle; Studies; Tendons; Three dimensional models; Ultrasonic imaging; Ultrasound; Ultrasound imaging; Australia; New South Wales Australia; Passive muscle properties; Soleus; Muscle architecture; MRI; Diffusion tensor imaging
• ISSN: 2167-8359; 2167-8359
• DOI: 10.7717/peerj.4610

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 using diffusion tensor imaging (DTI) techniques. 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. The posterior compartments of the soleus comprised 80 ± 5% of the total muscle volume (356 ± 58 cm ). 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 (  < 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. 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.