A proposal for a new classification of soleus muscle morphology

Abstract

IntroductionThe soleus muscle (SM) is located in the superficial posterior compartment of the leg, together with the gastrocnemius muscle (GM) and plantaris muscle. There is little information on the morphological variability (pennation) of the SM. The aim of the study is to characterize the variations in the morphology of the pennation of the SM and to create the first accurate classification. Material and methodsEighty lower limbs (40 left, and 40 right) fixed in 10% formalin solution were examined. The morphology of the central tendon, medial and lateral aponeuroses was evaluated, together with the pennation angle. ResultsIn all cases, the soleus muscle was present. Four types could be distinguished based on muscle fibre morphology. In order of frequency: Type 1 – bipennate (43.75%); Type 4 – non-pennate (36.25%); Type 2 – unipennate (15%); Type 3 – multipennate (5%). No significant difference in type distribution was observed with regard to body side (p=0.9018) or gender (p=0.0844). ConclusionThe soleus muscle is characterized by high morphological variability. Based on the pennation angle, four types (1–4) of soleus muscle are distinguishable.