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Obturator externus tendon

The obturator externus tendon is the strong terminal portion of the obturator externus muscle that inserts onto the trochanteric fossa of the femur. It plays a crucial role as part of the short external rotators of the hip, contributing to dynamic stability of the femoral head within the acetabulum. The tendon passes beneath the femoral neck, posterior to the hip joint capsule, making it an important structure in both surgical anatomy and imaging of the hip.

Synonyms

  • Tendon of the external obturator

  • Obturator tendon (externus component)

  • External obturator insertion tendon

Location and Attachments

  • Proximal attachment (origin): Formed by converging fibers of the obturator externus muscle, which arises from the external obturator membrane and adjacent bony margins of the pubis and ischium

  • Course: The tendon passes posterolaterally beneath the acetabulum and hip capsule, winding around the posterior aspect of the femoral neck

  • Distal attachment (insertion): Inserts into the trochanteric fossa of the femur via a short, thick tendon

Relations

  • Anteriorly: Hip joint capsule and femoral neck

  • Posteriorly: Quadratus femoris muscle

  • Superiorly: Acetabulum and obturator foramen

  • Inferiorly: Adductor magnus upper fibers and obturator foramen

Function

  • Provides external rotation of the thigh at the hip joint

  • Contributes to adduction in certain positions of the hip

  • Functions as a dynamic stabilizer of the femoral head in the acetabulum, particularly during locomotion and pivoting movements

  • Helps maintain posterior hip joint stability with other short external rotators

Clinical Significance

  • May be injured in groin or hip strains involving external rotators

  • Involved in posterior hip impingement and labral pathology due to its proximity to the capsule

  • Can be visualized in hip arthroscopy and MRI, important in differentiating muscle/tendon tears from capsular lesions

  • Pathology includes tendinitis, partial tear, avulsion, or enthesopathy at its femoral insertion

MRI Appearance

T1-weighted images:

  • Normal tendon shows very low signal (dark band-like structure)

  • Surrounding fat appears bright, outlining the tendon

  • Chronic degeneration may show focal high signal within tendon substance

T2-weighted images:

  • Normal tendon remains very low signal

  • Partial tear, tendinitis, or edema appears with focal bright signal at tendon or insertion site

STIR (Short Tau Inversion Recovery):

  • Normal tendon is dark

  • Pathology (tendinitis, tear, inflammation) shows bright hyperintense signal

  • Fat is suppressed, improving visualization of tendon abnormalities

T1 Fat-Sat Post-Contrast:

  • Normal tendon does not enhance

  • Pathological tendon shows enhancement in tendinitis or at enthesis (insertion site)

  • Abscess or infective involvement shows rim or diffuse enhancement

CT Appearance

Non-Contrast CT:

  • Tendon appears as a soft tissue density structure inserting into the trochanteric fossa

  • Calcific enthesopathy may appear as focal calcifications at insertion

  • Adjacent fat planes help define tendon margins

Post-Contrast CT:

  • Normal tendon does not enhance significantly

  • Inflammatory or neoplastic involvement of tendon or enthesis may appear as soft tissue thickening with enhancement

  • Abscess or infection shows low attenuation with rim enhancement around tendon

MRI images

Obturator externus tendon MRI axial anatomy image-img-00000-00000

MRI images

Obturator externus tendon MRI axial anatomy image-img-00000-00000_00001

CT image

Obturator externus tendon CT axial anatomy image-img-00000-00000