A rare variation of plantaris muscle

Abstract

During routine dissection for undergraduate medical students, we observed two separate heads of plantaris muscle on left lower limbs of a 80 years old donated embalmed male cadaver in the Department of Anatomy, K. J. Somaiya Medical College, Sion, Mumbai, INDIA. Both the heads of the plantaris muscle were composed of a thick muscle belly and a long thin tendon. One head of the plantaris muscle originated from the lower part of the lateral supracondylar line of the femur superior to the origin of the lateral head of gastrocnemius while the other head of the plantaris muscle originated from the oblique popliteal ligament. The tendons of both the heads of the plantaris muscle ran downwards inferomedially posterior to the knee joint. Both the tendons united to form common tendon and ran along the medial side of the tendo calcaneus. The common tendon of both the heads of the plantaris muscle got inserted separately into the medial side of the calcaneus bone. The photographs of the variations were taken for proper documentation and for ready reference.The variations of plantaris muscle are very rare and not found in literature. The plantaris muscle is vestigial in human beings and has much clinical importance. The plantaris muscle is absent in 7–10% of the human population. Injury of the plantaris muscle causes the painful calf. It may occur at the myotendinous junction with or without an associated hematoma and partial tear of the soleus or the medial head of the gastrocnemius muscle. Injuries of the plantaris muscle and tendon is called as ‘tennis leg’. The long, thin tendon of the plantaris is humorously called ‘the freshman's nerve’, as it is often mistaken for a nerve by first-year medical students. Knowledge of anatomical variations of the plantaris muscle is important for physiotherapists, plastic surgeons performing tendon transfer operations, clinicians diagnosing muscle tears and radiologists interpreting MRI scans.