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Popliteus muscle

The popliteus is a small, triangular muscle located in the posterior compartment of the leg, forming the floor of the popliteal fossa. Despite its small size, it plays a crucial role in unlocking the knee joint during the initiation of flexion by laterally rotating the femur on the tibia when the foot is fixed. It also contributes to posterior knee stability and is intimately related to the posterior capsule and menisci.

Because of its deep location and close relation to neurovascular structures of the popliteal fossa, it is clinically significant in posterior knee injuries, posterolateral corner instability, and intra-articular pathology.

Synonyms

  • Posterior knee unlocker muscle

  • Floor muscle of popliteal fossa

Origin and Insertion

  • Origin:

    • Lateral condyle of femur (within the capsule of the knee joint)

    • Lateral meniscus (via popliteomeniscal fascicles)

    • Fibrous capsule of the knee joint

  • Course:

    • Muscle fibers run obliquely downward and medially across the back of the knee

    • Tendinous portion lies intra-articular, passing deep to the fibular collateral ligament

  • Insertion:

    • Posterior surface of tibia above the soleal line

Nerve Supply

  • Tibial nerve (branch of sciatic nerve, roots L4–S1)

Arterial Supply

  • Popliteal artery (muscular branches)

  • Posterior tibial recurrent artery

  • Genicular branches of the popliteal artery

Venous Drainage

  • Popliteal vein

  • Posterior tibial vein

Function

  • Unlocks the knee joint by laterally rotating femur on fixed tibia (or medially rotating tibia when foot is free)

  • Initiates knee flexion

  • Provides posterolateral stability of the knee joint

  • Protects posterior horn of the lateral meniscus by retracting it during flexion

  • Assists in resisting anterior translation of femur on tibia when standing

Clinical Significance

  • Popliteus tendon injuries may cause posterolateral knee pain and instability

  • Involved in posterolateral corner injuries of the knee

  • Popliteus tendinopathy may mimic meniscal tears clinically

  • Can be affected in knee dislocations or trauma

  • Pathology may be subtle and best evaluated with MRI

MRI Appearance

T1-weighted images:

  • Muscle shows low-to-intermediate signal intensity

  • Surrounding fat planes appear bright for contrast

T2-weighted images:

  • Muscle shows low-to-intermediate baseline signal

  • Strain, edema, or tear appears as bright signal intensity within muscle or tendon

STIR (Short Tau Inversion Recovery):

  • Normal popliteus shows show low-to-intermediate signal

  • Pathology (inflammation, strain, tear) appears as bright hyperintensity

Proton Density Fat-Saturated (PD FS):

  • Muscle and tendon show low-to-intermediate signal

  • Injury, tendinopathy, or edema appears as bright signal

T1 Fat-Sat Post-Contrast:

  • Normal muscle enhances mildly and uniformly

  • Pathologic changes (tendinopathy, inflammation, tumor, abscess) show heterogeneous or rim enhancement

CT Appearance

Non-Contrast CT:

  • Muscle appears as homogeneous soft tissue density in the floor of the popliteal fossa

  • Difficult to distinguish unless pathology is present

  • Hematomas may appear hyperdense acutely

Post-Contrast CT:

  • Normal muscle shows mild uniform enhancement

  • Inflammatory or neoplastic lesions show heterogeneous enhancement

  • Abscess or necrotic lesion appears as low-density area with rim enhancement

MRI image

popliteus muscle anatomy mri image

MRI image

popliteus muscle anatomy

CT image

Popliteus muscle ct axial image

CT image

Popliteus muscle ct sagittal image