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Trochanteric fossa

The trochanteric fossa is a deep depression located on the medial aspect of the greater trochanter of the femur. It serves as a major bony landmark on the proximal femur and is the primary insertion site of the obturator externus tendon, with contributions from the superior fibers of the obturator internus and occasionally the gemelli muscles.

It lies posterior and medial to the greater trochanter's lateral surface and plays a functional role in stabilizing the femoral head within the acetabulum by anchoring the short external rotator tendons. Its depth and orientation provide mechanical advantage for rotational control of the hip.

Synonyms

  • Digital fossa of the femur

  • Obturator fossa (less common)

Location and Structure

  • Position: Medial surface of the greater trochanter, just superior to the intertrochanteric crest

  • Shape: Deep, narrow, and vertically oriented depression

  • Surfaces:

    • Bordered laterally by the posterior greater trochanter

    • Opens medially toward the quadratus femoris plane

    • Forms a bony recess for tendon insertion

  • Bone composition: Thick cortical shell with cancellous bone medially

Relations

  • Anteriorly: Femoral neck

  • Posteriorly: External rotators (obturator externus, obturator internus, gemelli, quadratus femoris)

  • Superiorly: Superior aspect of greater trochanter

  • Inferiorly: Upper intertrochanteric crest

  • Laterally: Lateral surface of the greater trochanter

  • Medially: Posterior hip joint capsule

Attachments

  • Obturator externus muscle: Primary tendon insertion

  • Obturator internus (occasionally): Superior fibers may attach partly

  • Gemelli muscles (rare variants): Accessory slips may insert within the fossa

  • Capsular fibers: Posterior hip capsule blends near the medial border

Function

  • Serves as a stable anchoring point for external rotator tendons

  • Contributes to hip external rotation, especially during gait

  • Provides dynamic posterior support to the femoral head

  • Assists in fine rotational control and stabilization during standing and pivoting

Clinical Significance

  • Tendon injuries: Obturator externus tears or avulsions may localize to the fossa

  • Fractures: Intertrochanteric or greater trochanter fractures may extend into the fossa

  • Surgical relevance: Landmark for hip arthroscopy, posterior approaches, and hardware placement

  • Deep gluteal pain: Can be associated with tendinopathy or impingement of external rotators

MRI Appearance

T1-weighted images:

  • Cortical bone of the fossa: low signal (dark)

  • Cancellous bone: bright fatty marrow signal

  • Obturator externus tendon insertion: dark linear band entering the fossa

  • Surrounding muscles (external rotators): intermediate signal

T2-weighted images:

  • Cortex: low signal

  • Marrow: bright, though slightly less intense than T1

  • Tendon insertion: low-signal band

  • Fossa outline sharply defined against adjacent bright soft tissues

  • No intrinsic bright signal unless joint fluid encroaches

STIR:

  • Bone marrow: intermediate-to-dark

  • Tendons: dark

  • Soft tissues: bright fat-suppressed contrast makes fossa margins clear

  • Adjacent muscular tissue appears intermediate

T1 Fat-Sat Post-Contrast:

  • Bone marrow: mild homogeneous enhancement

  • Obturator externus tendon insertion: minimal enhancement

  • Hip capsule and soft tissue planes: smooth uniform enhancement

  • Clearly delineates tendon–bone interfaces

CT Appearance

Non-Contrast CT:

  • Cortical margins: high attenuation, sharply defined

  • Fossa appears as a deep, well-circumscribed depression in medial greater trochanter

  • Cancellous bone: lower attenuation

  • Tendon insertion not directly visible but impression noted by bony contour

  • Excellent for showing subtle cortical detail

MRI images

Trochanteric fossa MRI axial image-img-00000-00000

X Ray image

x ray Trochanteric fossa

CT image

Trochanteric fossa ct anatomy Location and Imaging Appearance -img-00000-00000