Accessory head of the semitendinosus muscle: an unusual variation

Background: Various studies regarding the morphology of the muscles of the hamstring compartment have exhibited anatomical variations in terms of origin or insertion points. However, variation of the semitendinosus muscle is uncommon. In this case we report an accessory head of the semitendinosus muscle. Materials and methods: During routine dissection for medical teaching purposes, a unilateral morphological variant of the semitendinosus muscle was noted on the left side in an 82-year-old female. Results: The accessory head of the semitendinosus muscle originated lateral to the midpoint of the semitendinosus muscle. Fibres of the accessory head originated from the medial border of the long head of biceps femoris as well as the midpoint of the semitendinosus. The accessory head had a common insertion point with the semitendinosus muscle. Conclusions: This case report adds to the existing body of knowledge about the semitendinosus muscle, which is of anatomical and clinical value. Knowledge of the anatomical variants is essential for anatomists and clinicians and may avoid misinterpretation during diagnostic procedures.