Distal Semitendinosus Tendon: Anatomy, Insertion, Relations, Function, Clinical Significance, MRI & CT Imaging

Topic

Distal semitendinosus tendon

The distal semitendinosus tendon is the long terminal portion of the semitendinosus muscle, one of the medial hamstrings. After descending along the posterior thigh, the muscle transitions into a long, cord-like tendon that crosses the posteromedial aspect of the knee. It curves anteromedially to insert on the proximal tibia as part of the pes anserinus along with the sartorius and gracilis tendons.

This tendon is clinically important because it is frequently harvested as an autograft in anterior cruciate ligament (ACL) reconstruction, and is also prone to overuse injuries, tendinopathy, or tears in athletes.

Synonyms

Semitendinosus tendon
Pes anserinus tendon (medial component)
Distal hamstring tendon

Origin and Insertion

Origin (muscular): From the ischial tuberosity via the semitendinosus muscle belly
Course (tendinous portion):
- Forms a long cord-like tendon in the distal thigh
- Passes posteromedial to the knee joint capsule
- Curves anteriorly to cross the medial tibia
Insertion: Proximal medial surface of the tibia, as part of the pes anserinus complex with sartorius and gracilis tendons

Relations

Anteriorly: Medial collateral ligament (MCL) of knee, tibia
Posteriorly: Semimembranosus tendon and posterior knee capsule
Medially: Gracilis tendon
Laterally: Tibial condyle, medial meniscus
Superficially: Sartorius tendon at pes anserinus

Nerve Supply

Supplied by the tibial division of the sciatic nerve (L5–S2) via the semitendinosus muscle

Arterial Supply

Perforating branches of the deep femoral artery
Genicular branches of the popliteal artery

Venous Drainage

Accompanies arterial supply, draining into the popliteal vein and deep femoral vein

Function

Assists in flexion of the knee joint
Provides medial stabilization of the knee, especially against valgus stress
Works with gracilis and sartorius tendons in the pes anserinus to stabilize medial knee
Acts as a donor tendon for ACL and PCL reconstruction grafts

MRI Appearance

T1-weighted images:

Tendon shows low signal intensity (dark band-like structure)
Surrounded by bright subcutaneous and intermuscular fat

T2-weighted images:

Normal tendon remains low signal
Pathology (tendinopathy, partial tear) appears as focal bright hyperintensity within or around tendon

STIR (Short Tau Inversion Recovery):

Normal tendon: dark hypointense band
Pathology: hyperintense signal in tendon substance or adjacent soft tissues

Proton Density Fat-Saturated (PD FS):

Normal tendon: uniformly dark
Tendon strain, tendinosis, or tear: bright signal intensity, sometimes feathery or linear

T1 Fat-Sat Post-Contrast:

Normal tendon: no significant enhancement
Pathological tendon: enhancement in areas of inflammation, granulation tissue, or post-surgical changes
Abscess/tenosynovitis: rim or sheath-like enhancement

CT Appearance

Non-Contrast CT:

Tendon appears as a thin soft-tissue density band along medial knee
Surrounded by fat planes that enhance its visibility
Chronic calcific tendinopathy may appear as focal calcifications

Post-Contrast CT:

Normal tendon: minimal to no enhancement
Inflamed or injured tendon: mild focal enhancement at enthesis or along tendon sheath
Infection/abscess: rim-enhancing collection adjacent to tendon

MRI images

MRI image

Topics