11 - A Preliminary Report on Varying Morphological Patterns and Characteristics of the Soleus Muscle

Poster Board Number: 11
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Abstract Body : Intro: The soleus muscle is one of the most powerful plantar flexors of the foot. Its unique architecture is built upon several different muscle fascicular compartments held together by multiple tendinous structures. Due to the great amount of force generated during contraction of the soleus, the myotendinous junctions (MTJ) are susceptible to strain or injury. The MTJ serves as an interface between muscle tissue and a tendon and may differ in morphology between individuals. This study aims at identifying variations in the soleus muscle’s tendinous structures including the central tendon, calcaneal tendon, and intramuscular aponeuroses as a starting point to understanding the distribution of connective tissue and its relationship to injury susceptibility and morphological classification of the soleus.
Methods: We used forty (n=40) soleus muscles, representing both left and right sides, from twenty (n=20) formalin-embalmed cadavers (average age 78 years old; 10 males, 10 females) who donated their bodies for medical education to Kansas City University. Soleus muscles were dissected in-situ, then removed for precise measurements of connective tissues. Four tendons (calcaneal, central, medial origin, and lateral origin) were measured on the anterior and posterior surface of the soleus. Variations of these structures seen on the anterior surface of the muscle were subsequently visualized and reconstructed in three-dimensions using an Artec Space Spider. Each muscle was then cut in cross-section at three locations: proximal, middle, and distal to simulate views observed in a clinical setting on MRI. Each myotendinous junction (central tendon, lateral aponeurosis, and medial aponeurosis) was followed through the course of the muscle by measuring and comparing its appearance at the three locations to better understand variations in the soleus architecture.
Results: We found that the soleus muscle is not anatomically homogeneous. In fact, approximately half of the donor specimens had a variation between their own two soleus muscles. Within a single muscle, the proximal location displayed a similar length of intramuscular lateral and medial aponeuroses (intramuscular continuation of the medial and lateral origin tendon), despite the size of origin tendon on the anterior surface. In most specimens, the central tendon was not internally visualized until the middle portion of the muscle despite visualization on the anterior surface.
Discussion: The muscular compartments making up the soleus muscle intertwine to form a complex architecture creating unique arrangements of tendinous structures. These structures, however, have been shown to vary not only between people, but even within the same person. With a better understanding on how these myotendinous structures differ in relationship to the morphological pattern of the soleus’ muscular arrangement, we can better anatomically classify the soleus.
Significance: This data can contribute to the creation of a soleus-specific classification system that accurately reflects the variability in anatomy which can further be applied to diagnosing and treating soleus muscle injuries. Future directions include recognizing the reoccurring patterns within a particular sub-classification of the soleus on various study specimens such as MRI and ultrasound images.
Funding: This research was supported by Kansas City University office of research.