Accessory soleus muscle
Painless diffuse bulge on the posterior medial aspect of distal right leg and ankle region; more after work. No trauma, skin changes or difficulty in walking.
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The diffuse bulge pointed by the patient is a muscle with normal echopattern; located between Achilles tendon and flexure hallucis longus tendon and replaces the pre-Achilles fat pad. It shows continuity with the soleus muscle cranially. There is an aponeurosis in posterior most part of the above-mentioned muscle which forms a very short tendon which is inserted into the upper border of the calcaneum, medial to the Achilles tendon insertion.
The Achilles tendon is normal. Flexure hallucis longus tendon is normal. Adjacent neurovascular bundle is normal.
Comparison with the asymptomatic side does not show accessory muscle.
A young male presented with a diffuse painless bulge on the posterior medial aspect of right distal third leg and ankle region. Ultrasound was done to localize and evaluate the bulge. Ultrasound shows a muscle with normal echopattern between Achilles tendon and flexure hallucis longus tendon; which inserts through a short tendon at the upper surface of the calcaneum. There is no such muscle in the asymptomatic left leg-ankle region. Findings favor an accessory soleus muscle which is unilateral.