Morphological variability of the gastrocnemius muscle's third head: cadaveric dissection findings

Aim: The gastrocnemius tertius (GT) represents the presence of a third head (TH) of the gastrocnemius muscle (GM), the most common morphological variant of the GM. This cadaveric dissection series aimed to determine the frequency, morphological characteristics, and anatomical relationship of the GT with the popliteal neurovascular structures (PNVS). Materials and methods: Forty formalin-embalmed cadaveric lower limbs from the Department of Anatomy and Surgical Anatomy, Aristotle University of Thessaloniki, were examined. All specimens were donated to the Department after obtaining informed consent prior to death, in accordance with institutional and national ethical regulations. Results: The GT was identified in six of forty specimens (15%). In four cases (10%), the third head originated from the posterior distal surface of the femur, medial to the lateral head (LH), and fused with it. The popliteal vessels were located medially to the TH. In one case (2.5%), the TH arose from the LH and fused with the medial head (MH), with the popliteal vessels coursing between the TH and MH. In another case (2.5%), the TH did not fuse with the LH but instead formed a distinct tendon inserting into the calcaneal tendon. Conclusion: The GT was observed in 15% of Greek cadavers, representing the highest prevalence reported to date. Specific morphological configurations may predispose to PNVS compression, potentially affecting one or more components of the neurovascular bundle. Awareness of such GM variants, supported by thorough clinical assessment and targeted imaging, is essential for accurate diagnosis and effective management of popliteal fossa pathologies.