Semitendinosus Muscle: Anatomy, Origin, Insertion, Nerve and Blood Supply, Function, MRI & CT Imaging

Topic

Semitendinosus muscle

The semitendinosus is one of the three hamstring muscles located in the posterior compartment of the thigh. It lies medial to the biceps femoris and superficial to the semimembranosus. Its long, cord-like tendon is a key component of the pes anserinus, where it inserts along with sartorius and gracilis. The semitendinosus plays a major role in hip extension, knee flexion, and stabilization of the pelvis, making it critical for locomotion, posture, and athletic performance.

Synonyms

Hamstring medial tendon muscle
Pes anserinus hamstring
Posterior thigh flexor (semitendinosus)

Origin and Insertion

Origin: Ischial tuberosity (with a common tendon shared with long head of biceps femoris)
Course: Muscle belly descends in the posterior thigh, becoming a long tendon in the distal thigh
Insertion: Proximal medial tibia, specifically the medial surface just below the tibial condyle (via the pes anserinus)

Nerve Supply

Tibial division of the sciatic nerve (L5–S2)

Arterial Supply

Perforating branches of profunda femoris artery
Inferior gluteal artery
Popliteal artery branches

Venous Drainage

Companion veins of profunda femoris, inferior gluteal, and popliteal veins draining into femoral vein

Function

Extends the thigh at the hip joint
Flexes the leg at the knee joint
Medially rotates the tibia when the knee is flexed
Stabilizes pelvis during standing and walking

Clinical Significance

Commonly involved in hamstring strains and athletic injuries
Important in anterior cruciate ligament (ACL) reconstruction as a tendon graft source
May be affected in proximal hamstring avulsions
Site of pain syndromes in runners and athletes

MRI Appearance

T1-weighted images:

Normal muscle: low-to-intermediate signal intensity
Surrounding fat: bright, delineating muscle clearly
Chronic fatty infiltration: focal bright areas within muscle

T2-weighted images:

Normal muscle: low-to-intermediate signal intensity
Acute strain, edema, or hematoma: bright hyperintense areas within or around muscle fibers

STIR (Short Tau Inversion Recovery):

Normal muscle: Intermediate signal
Pathology (strain, myositis, inflammation, hematoma): bright hyperintensity

T1 Fat-Sat Post-Contrast:

Normal muscle: mild uniform enhancement
Inflammation, neoplasm, or infection: heterogeneous enhancement
Abscess: rim enhancement with non-enhancing center
Partial tear: enhancing margins with central low signal defect

CT Appearance

Non-Contrast CT:

Muscle: soft tissue density
Acute hematoma: hyperdense collection within or around muscle
Chronic atrophy or fatty infiltration: low-density areas compared to normal muscle

Post-Contrast CT:

Normal muscle: mild homogeneous enhancement
Pathological muscle: heterogeneous or irregular enhancement (tumor, inflammation, infection)
Abscess: peripheral rim enhancement with central low attenuation

MRI image