Unilateral Absence of Plantaris Muscle - Case Report

Background - Unilateral absence of plantaris muscle.

Case report - During a routine dissection of lower limb on a female cadaver (age 89 yrs), it was observed that the plantaris muscle of the left lower limb was absent. Although the soleus and gastrocnemius muscle were normal, no attachment of plantaris muscle was identified at its origin or insertion. However, the plantaris muscle was observed on the right side, normal in origin, insertion, position and shape.

Discussion - Plantaris muscle originates from the lower part of lateral supracondylar line and the oblique popliteal ligament and gets inserted on to the calcaneus just medial to Achille's tendon via a long slender tendon. Variation in this muscle is very common; it may be sometimes absent (approx. 10% cases) or it may be double.

Conclusion - Despite its vestigial nature, documentation of anatomical variation of plantaris muscle is clinically important. Anatomical variations and injuries of the plantaris muscle can contribute to understanding of etiology of cases of knee pain (Patellofemoral pain syndrome) or leg pain (tennis leg), complicate surgery while resembling a nerve, and may serve as useful tendon grafts despite debates regarding its potential role in proprioception and knee stability. Imaging is important to diagnose isolated injuries and exclude serious conditions like DVT