20 - An Anomalous Muscle Attached to the Sciatic Nerve: A Case Report

Poster Board Number: 20
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Abstract Body : In humans, there have been several reports of anomalous muscles in the popliteal fossa including variations of the hamstring muscles, plantaris, soleus, and gastrocnemius. Here we describe an unusual variation of what most closely resembles an additional head of the gastrocnemius muscle known as gastrocnemius tertius. Gastrocnemius tertius is present in 1.9-5% of the population. It has been reported to attach proximally to the midline of the posterior aspect of the distal femur. Distally, it typically attaches to the medial aspect of the lateral gastrocnemius head. However, a distal attachment to the medial head of the gastrocnemius has also been reported. In this case-study, we discover a muscle head that is proximally attached directly to the sciatic nerve, blending distally with the lateral head (medial aspect) of the gastrocnemius muscle.

The atypical muscle was found in a cadaver of a 95-year-old female during a routine dissection for medical education at the Northeast Ohio Medical University. It was unilateral, found only within the left lower limb. There were no signs of previous trauma. The right lower extremity exhibited a typical anatomical presentation. The anomalous muscle head was innervated by the tibial nerve and received its blood supply from at least the lateral sural artery. Hematoxylin and Eosin (H&E) staining was also performed to further investigate the muscle’s composition. Preliminary histological analysis shows the presence of muscle, fat, fibrous connective tissue, and neurovascular. No neoplastic tissue appears to be present.

Although muscle variants in the popliteal region often attach to surrounding soft tissues structures, the presentation of a gastrocnemius tertius attaching directly to the sciatic nerve has not been, to our knowledge, previously described. These results indicate that it is possible for gastrocnemius tertius to attach to nervous tissue, and it may present only unilaterally. This work adds breadth and depth to our current knowledge about the human body.