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Conjoint tendon of biceps femoris & semitendinosus

The conjoint tendon of the biceps femoris and semitendinosus is a common tendon of origin formed by the fusion of these two posteromedial hamstring muscles. It plays a crucial role in the stability and movement of the knee joint and forms part of the proximal hamstring complex.

The tendon originates at the ischial tuberosity of the pelvis and is clinically important because of its frequent involvement in hamstring injuries, especially in athletes. Proximal hamstring tears usually occur at this conjoint tendon due to high tensile stress during sprinting, kicking, or sudden deceleration.

Synonyms

  • Common hamstring tendon

  • Conjoint tendon of ischial origin

  • Proximal hamstring tendon

Origin and Insertion

  • Origin:

    • Both the long head of the biceps femoris and the semitendinosus muscle originate from the superomedial impression of the ischial tuberosity via a strong, shared tendon known as the conjoint tendon.

  • Course:

    • The conjoint tendon forms a thick, cord-like structure descending from the ischial tuberosity.

    • Distally, the tendon separates into the individual tendons of the biceps femoris and semitendinosus.

  • Insertion:

    • Biceps femoris: inserts on the head of the fibula (lateral side of knee).

    • Semitendinosus: inserts on the anteromedial surface of the proximal tibia as part of the pes anserinus.

Nerve Supply

  • Both muscles are innervated by the tibial division of the sciatic nerve (L5–S2).

Arterial Supply

  • Inferior gluteal artery (proximal supply)

  • Perforating branches of the deep femoral (profunda femoris) artery

  • Medial circumflex femoral artery (minor contribution)

Venous Drainage

  • Venous blood drains into the profunda femoris vein and ultimately into the femoral vein.

Function

  • Acts as a common origin for the long head of the biceps femoris and semitendinosus

  • Provides powerful hip extension and knee flexion

  • Plays an important role in posterior thigh stability and force transmission

  • Clinically important as a frequent site of proximal hamstring injuries (avulsions, tendinopathy, tears)

Clinical Significance

  • Common site of hamstring avulsion injuries, especially in athletes involved in sprinting, hurdling, or kicking sports

  • May cause posterior thigh pain, weakness, or gait abnormalities when injured

  • Target for surgical repair or reconstruction in complete proximal hamstring tears

  • MRI evaluation of this tendon is crucial in preoperative planning

MRI Appearance

T1-weighted images:

  • Conjoint tendon appears as a low-signal intensity band at the ischial tuberosity

  • Surrounded by bright ischial fat, which improves contrast

  • Chronic tendinopathy may show thickening and intermediate signal

T2-weighted images:

  • Normal tendon remains low signal

  • Partial or complete tears appear as areas of high signal intensity within or around the tendon

  • Peritendinous edema may appear as bright signal intensity

STIR (Short Tau Inversion Recovery):

  • Normal tendon is dark (low signal)

  • Acute injury, inflammation, or edema shows bright hyperintensity

Proton Density Fat-Saturated (PD FS):

  • Normal tendon: uniformly low signal

  • Pathology: bright hyperintense signal in partial/complete tears or tendinopathy

T1 Fat-Sat Post-Contrast:

  • Normal tendon shows minimal enhancement

  • Tendinopathy or post-injury changes show heterogeneous enhancement

  • Abscess or granulation tissue may show peripheral or nodular enhancement

CT Appearance

Non-Contrast CT:

  • Tendon not well visualized directly (isodense to soft tissue)

  • Bony attachment at the ischial tuberosity may show avulsion fragments in injury

  • Surrounding fat planes highlight the tendon’s location

Post-Contrast CT:

  • Normal tendon does not enhance significantly

  • Pathologic changes (infection, tumor, post-traumatic changes) may show enhancement of peritendinous tissues

  • Hematoma or scarring may appear as focal soft tissue density

MRI image

Conjoint tendon of biceps femoris & semitendinosus MRI axial anatomy image-img-00000-00000

MRI image

Conjoint tendon of biceps femoris & semitendinosus MRI axial anatomy image-img-00000-00000_00001

MRI image

Conjoint tendon of biceps femoris & semitendinosus MRI sag anatomy image-img-00000-00000

MRI image

Conjoint tendon of biceps femoris & semitendinosus MRI sag anatomy image-img-00000-00000_00001

CT image

Conjoint tendon of biceps femoris & semitendinosus ct axial image