The complex architecture of the semitendinosus muscle belly: insights from adult and fetal anatomy with clinical implications.

Abstract

Background: The semitendinosus muscle, a common hamstring injury site, often sustains damage at its myotendinous junctions. Understanding these connections is crucial for comprehending injury mechanisms and guiding treatment. This study aimed to investigate the semitendinosus muscle's architecture in adults and fetuses.

Materials and methods: 50 semitendinosus muscles from adult cadavers and 20 from fetal specimens were analyzed using standard anatomical dissection methods. An ultrasound examination was conducted on 20 semitendinosus muscles in living individuals.

Results: The proximal origin of the semitendinosus muscle was consistently divided into two distinct parts: a common part shared with the long head of the biceps femoris, and a solitary part originating directly from the ischial tuberosity. The presence of a tendinous intersection within the muscle belly, dividing most muscle fibers, was confirmed and investigated. Five categories of muscle fibers were identified based on their anatomical course, either inserting into the tendinous intersection or bypassing it, extending directly between the muscle's origins and distal tendon. In fetal specimens, two distinct origin sites and the tendinous intersection dividing the muscle belly into two parts were also discernible. The proportions between muscle parts in fetuses and adults were notably similar.

Conclusions: A detailed understanding of the semitendinosus muscle's architecture is vital for improving our grasp of injuries and optimizing treatment strategies. This structural intricacy further points to more complex biomechanics, suggesting specialized functions for its individual segments. The presence of these divisions in fetal specimens confirms their early developmental determination, unaffected by postnatal influences.