A bilateral third head of the gastrocnemius which is morphologically similar to the plantaris

Bilateral Gastrocnemius Tertius Muscles: Cadaveric Findings of a Rare Variant

The posterior compartment of the leg typically contains three muscles in the superficial flexor group: the gastrocnemius, plantaris, and soleus. The gastrocnemius has medial and lateral heads (MH and LH) that originate from the medial and lateral condyles of the femur, respectively. However, a third head (TH) of the gastrocnemius, is a rare accessory muscle bundle of the gastrocnemius muscle that covers the surface of the popliteal fossa. Bilateral THs of gastrocnemius were identified in a 67-year-old male during a routine educational cadaveric dissection. Both gastrocnemius TH muscles consisted of a superficial belly with distinct neurovasculature heads and originated from the lateral condyle of the femur and inserted into the Achilles tendon. To our knowledge, the co-existence of bilateral gastrocnemius TH muscles has only been reported once. The male donor was found to exhibit an anatomical anomaly and could be clinically underdiagnosed due to its clinically silent nature and the lack of reports. Insight into the potential implications of bilateral and unilateral gastrocnemius TH and identification during clinical evaluation offers a path for future research to better identify and manage cases of gastrocnemius TH and its effects.

A novel categorization of the muscular branches of the tibial nerve within the popliteal fossa

BACKGROUND

The muscular branches of the tibial nerve within the popliteal fossa innervate the gastrocnemius, soleus, plantaris, and popliteus muscles. Various branching patterns have been described in textbooks; however, the underlying fundamental rules explaining the patterns remain unclear. Understanding the fundamental rule explaining the branching pattern of the innervating nerves is essential for understanding the ontogeny of skeletal muscles. Therefore, this study aimed at establishing a theory to explain the branching pattern of the muscular branches of the tibial nerve within the popliteal fossa.

METHODS

The branching patterns of the muscular branches of the tibial nerve within the popliteal fossa were examined macroscopically in 62 lower limbs derived from 31 adult cadavers (22 males and 9 females, aged 49-95 years).

RESULTS

The branch to the medial head of the gastrocnemius muscle invariably arose from the posteromedial side of the tibial nerve. The branches to the soleus muscle and lateral head of the gastrocnemius muscle had a common trunk in all the lower limbs and invariably arose from the posterolateral side. The branches to the plantaris and popliteus muscles arose anteriorly from the tibial nerve in this order (plantaris branch first, followed by the popliteus branch). These branches invariably arose more distally than the branch to both the heads of the gastrocnemius and soleus muscles.

CONCLUSIONS

Based on these fundamental branching patterns, we suggest a novel branching categorization. The branches could be categorized into a posterior group and an anterior group, which has independent branches to the plantaris and popliteus muscles. This fundamental branching pattern and novel categorization contribute to the understanding of the ontogeny of the skeletal muscles around the flexor compartment of the leg.