Ultrasound Imaging of Torn Soleus Muscle

Abstract

Figure 1. In comparison with the normal side, the left calf appeared markedly swollen, without noticeable ecchymosis. A 51-year-old man was referred for ultrasound (US) examination because of persistent left calf swelling for 3 months. The swelling developed abruptly after he had stumbled against a stone, sustaining an inversion injury to his ankle. He described calf pain and swelling but no ecchymosis. Three months after injury, active and passive range of motion of the ankle and toes were not limited, including ankle plantar flexion and toe flexion. Skin color and sensation also appeared normal over the swollen area (Figure 1). US imaging revealed a hyperechoic, homogeneous mass originating beneath the mid-portion of the Achilles tendon and ending at the posterior proximal tibia, with an intact distal musculotendinous junction of the medial gastrocnemius muscle (Supplemental Video and Figure 2A). The mass was observed to occupy the space between both heads of the gastrocnemius and deep plantar flexors (tibialis posterior, flexor digitorum profoundus and flexor hallucis longus), with overlying anechoic fluid (Supplemental Video and Figure 2B). The patient was eventually diagnosed with tear of the soleus muscle and an organized hematoma. The soleus muscle, originating from the fibula and medial border of the tibia, merges with the gastrocnemius muscle, forming the Achilles tendon and attaching on the calcaneus. Tear of the medial head of the gastrocnemius muscle at the musculotendinous junction (ie, “tennis leg”) is the more common calf muscle tear, and is typically caused by abrupt extension of the knee and simultaneous forced dorsiflexion of the ankle [1,2]. In this patient, there had been a severe ankle sprain with simultaneous knee buckling. As such, although his gastrocnemius muscle had been protected from overload, the soleus muscle had become vulnerable to the twisting force. In addition, we conclude that the lack of ecchymosis could be attributed to the intact