Bilateral Partial Fusion of the Plantaris Muscle With the Lateral Head of the Gastrocnemius Muscle and a Right-Sided Nerve Variation: A Case Report

The plantaris muscle (PM) is a part of the superficial muscles of the posterior compartment of the calf.It has a short belly and a long tendon and has been described as a vestigial muscle, although its status remains debatable.The morphology, including the origin and insertion of this muscle, varies significantly.These variations may result in neurovascular compression and disturbed biomechanics of the leg.During routine dissection of the back of the leg for MBBS first-year students, the author observed an unusual fusion of the PM with the lateral head of the gastrocnemius bilaterally in a female cadaver of 56 years.In addition, on the right side, the nerve to the lateral head of the gastrocnemius arising from the tibial nerve traveled superficial to the PM and ended in the gastrocnemius muscle 7 cm below the popliteal fossa.The fusion of the PM to the lateral head of the gastrocnemius is reported, but bilateral occurrence of such variation is rare.Also, a variant course of the nerve to the lateral head of the gastrocnemius is rarely reported.This aberrant fusion of the PM may be the cause of posterior calf pain syndromes and may be misinterpreted as partial tears and soft tissue lesions on radiographs.The comprehension of these variations is essential for surgeries in the back of the leg, such as selective neurotomy and botulinum toxin injection, and for management of disturbed gait, along with avoiding misinterpretation of radiographs.