Semimembranosus Tendon (Proximal): Anatomy, Origin, Course, Function, Clinical Significance, MRI & CT Imaging

Topic

Semimembranosus tendon (proximal)

The semimembranosus tendon forms the proximal attachment of the semimembranosus muscle, one of the hamstring muscles of the posterior thigh. It arises from the ischial tuberosity as a thick flattened tendon before transitioning into the muscular belly. This tendon is located medial to the conjoined tendons of the semitendinosus and long head of the biceps femoris.

It plays a critical role in hip extension and knee flexion, while also contributing to dynamic stabilization of the pelvis. Clinically, the proximal semimembranosus tendon is a common site of hamstring origin injuries, particularly in athletes, and may be affected by chronic tendinopathy or avulsion injuries.

Synonyms

Proximal semimembranosus origin
Medial hamstring tendon (proximal)
Ischial tuberosity attachment of semimembranosus

Origin and Insertion

Origin: Proximal semimembranosus tendon arises from the superolateral impression of the ischial tuberosity, shared with other hamstring tendons
Course:
- Begins as a broad flattened tendon from the ischial tuberosity
- Transitions into a fusiform muscular belly descending along the posteromedial thigh
Insertion (distal, for reference): Into the posteromedial aspect of the medial tibial condyle, also sending expansions to the oblique popliteal ligament and fascia over the popliteus

Nerve Supply

Tibial division of the sciatic nerve (L5, S1, S2)

Arterial Supply

Perforating branches of profunda femoris artery
Inferior gluteal artery
Genicular branches of the popliteal artery

Venous Drainage

Accompanying veins draining into profunda femoris and popliteal veins

Function

Extension of the thigh at the hip joint
Flexion of the leg at the knee joint
Medial rotation of the leg when the knee is flexed
Stabilization of pelvis during ambulation
Contributes to posterior knee stability via expansions into oblique popliteal ligament

Clinical Significance

Hamstring origin injuries: Proximal tendon is prone to acute tears or avulsion in athletes (sprinting, kicking, hurdling)
Tendinopathy: Chronic overuse may cause proximal hamstring tendinopathy, often presenting with deep gluteal pain
Avulsion fractures: Particularly in younger athletes, tendon may avulse with a fragment of the ischial tuberosity
Imaging relevance: MRI is gold standard for diagnosis; CT useful for detecting avulsion fractures

MRI Appearance

T1-weighted images:

Normal tendon: uniform low signal intensity
Surrounded by bright peritendinous fat enhancing visibility
Chronic tendinopathy may show thickening or intermediate signal

T2-weighted images:

Normal tendon: low signal intensity
Tendinopathy or partial tear: focal bright signal areas within or around tendon
Complete tear: discontinuity with fluid/bruising appearing hyperintense

STIR (Short Tau Inversion Recovery):

Normal tendon: dark, low signal
Pathology: bright hyperintense changes in partial tear, edema, or peritendinous inflammation

Proton Density Fat-Saturated (PD FS):

Normal tendon: low signal
Abnormal tendon: focal or diffuse hyperintensity in tendinosis, microtears, or avulsion injuries

T1 Fat-Sat Post-Contrast:

Normal tendon: no significant enhancement
Pathological tendon: enhancement along torn or inflamed regions; abscess or severe tendinopathy shows focal contrast uptake