Topics

Topic

design image
Third trochanter

The third trochanter is an anatomical variant located on the posterolateral proximal femoral shaft, typically forming a prominent bony tubercle along the gluteal tuberosity. Although not present in all individuals, when present it forms a distinct lateral projection that resembles an accessory trochanter.

It serves primarily as an attachment site for the gluteus maximus muscle, contributing to hip extension and external rotation force. Its prominence varies widely, and large third trochanters may be incidental findings on imaging.

Synonyms

  • Accessory trochanter

  • Tuberositas glutea prominence

  • Variant gluteal ridge tubercle

Location and Structure

  • Found on the proximal third of the femoral shaft, lateral to the gluteal tuberosity

  • Appears as a rounded or triangular bony protuberance

  • Represents an enlarged or accentuated portion of the gluteal ridge

  • More commonly seen in robust or physically active individuals

Relations

  • Anteriorly: Lateral femoral surface and vastus lateralis muscle

  • Posteriorly: Gluteal tuberosity and gluteus maximus tendon

  • Superiorly: Proximal femoral diaphysis

  • Inferiorly: Upper lateral femoral shaft

  • Laterally: Tensor fasciae latae and iliotibial band region

Attachments

  • Primary attachment:

    • Gluteus maximus muscle, inserting onto the gluteal tuberosity and contributing to external rotation and hip extension

  • Secondary association:

    • Connective fibers of the iliotibial band may lie adjacent

    • Occasionally blends with deep fascia of the lateral thigh

Function

  • Serves as an additional tether point for gluteus maximus, enhancing mechanical leverage

  • Contributes to hip extension, external rotation, and posterior thigh stabilization

  • Supports lateral hip stability during weight-bearing and gait

Clinical Significance

  • May mimic a bone spur, healed avulsion, or osteochondroma in imaging when prominent

  • Can be mistaken for a pathologic lesion if its variant nature is not recognized

  • Rarely symptomatic, but large projections may cause soft-tissue irritation

  • Helpful landmark during hip and femoral surgeries

MRI Appearance

T1-weighted images:

  • Cortical bone: low signal

  • Marrow inside the proximal femoral shaft near the region appears bright

  • Third trochanter: visible as a low-signal bony projection along the gluteal tuberosity

  • Surrounding gluteus maximus tendon: intermediate signal

T2-weighted images:

  • Cortical bone: dark

  • Marrow: bright relative to muscle

  • Third trochanter margin: sharply low signal

  • Adjacent muscles and connective tissue: intermediate-to-bright depending on fat content

STIR:

  • Bone cortex: dark

  • Bone marrow: intermediate-to-dark

  • Adjacent fat: bright due to fat suppression

  • Muscle tissues: intermediate signal, providing contrast with cortical margin

CT Appearance

Non-Contrast CT:

  • Third trochanter appears as a well-defined, high-density cortical projection

  • Internal cancellous bone pattern continuous with rest of femur

  • Excellent visualization of contour, size, and cortical thickness

  • Adjacent soft tissues appear as typical soft-tissue attenuation

MRI images

Third trochanter MRI axial image-img-00000-00000