Prevalence and morphology of the gastrocnemius tertius: anatomical study and literature review.

Background: The gastrocnemius muscle (GM) third head or gastrocnemius tertius (GT) is a well-described GM variant. The purpose of the current study was to investigate the GT prevalence and morphology (including the proximal and distal attachments, and relationship with the neurovascular structures) in a cadaveric Central European population.

Methods: A total of seventy-three lower limbs were dissected and investigated for GT presence; when the variant was identified, morphometric measurements were obtained.

Results: The GM third head was observed in 10.96% (8/73 cases) under the form of two different morphological variants. The commonest variant type (6 cases) with proximal attachment from the femur posterior surface and fused with the GM lateral head. The second variant type (2 cases) proximal attachment was from the femur posterior surface and fused with the GM medial head. To understand this variation, we performed a brief literature review with meta-analysis. The GT variant has been identified with a pooled prevalence of 4.34%, under great morphological variability.

Conclusion: Clinicians, especially orthopaedics, should be aware of this variant, as it has been proven to cause popliteal neurovascular compression.