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Topic

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Neck of femur

The neck of the femur is the flattened, pyramidal segment of bone that connects the head of the femur to the shaft at the intertrochanteric line and crest. It lies at an angle of approximately 125–135° to the shaft (angle of inclination) and is directed superomedially, slightly forward, and upward to articulate with the acetabulum of the pelvis.

Structurally, the femoral neck is composed of cortical and cancellous bone. The superior surface of the neck is convex and covered by capsule; the inferior surface is flattened and gives passage to retinacular vessels. The anterior surface joins the intertrochanteric line, while the posterior surface blends with the intertrochanteric crest.

The femoral neck plays a vital role in transmitting body weight from the pelvis to the femoral shaft. Its relatively narrow structure makes it biomechanically vulnerable to fractures, especially in the elderly with osteoporosis.

Attachments

  • Capsular fibers of the hip joint capsule attach around the base of the femoral neck.

  • Retinacular fibers of the capsule enclose vessels supplying the neck and head.

Synonyms

  • Femoral neck

  • Collum femoris

Function

  • Connects the femoral head to the shaft and aligns the hip joint with the femoral axis.

  • Distributes weight transmission from pelvis to femur during standing and locomotion.

  • Provides surface for capsular and vascular attachment.

Nerve Supply (related structures)

  • No direct motor innervation; pain fibers to capsule/neck region from femoral nerve, obturator nerve, and sciatic nerve articular branches.

Arterial Supply

  • Medial and lateral circumflex femoral arteries (branches of profunda femoris artery) → retinacular branches (chief supply).

  • Artery of ligamentum teres (from obturator artery) → minor supply to femoral head.

  • Nutrient arteries from periosteal vessels of shaft contribute minimally.

Venous Drainage

  • Venous plexus accompanies arterial branches → profunda femoris vein → femoral vein.

MRI Appearance

T1-weighted images:

  • Bone cortex: hypointense

  • Bone marrow: intermediate signal (fatty marrow bright in adults, hypointense if infiltrated or edematous)

  • Useful for detecting fractures, avascular necrosis, marrow infiltration

T2-weighted images:

  • Cortex: hypointense

  • Marrow: variable (normal marrow intermediate; edema hyperintense)

  • Detects stress fractures, marrow edema, cystic changes

PD Fat-Saturated (Proton Density with Fat Suppression):

  • Cortex: dark hypointense outline

  • Marrow edema or occult fracture lines: hyperintense

  • Very sensitive for stress fractures and bone marrow pathology

STIR:

  • Suppresses fat, showing bright marrow edema, fractures, osteonecrosis, or infection

  • Useful in early detection of occult femoral neck fractures

T1 Fat-Saturated Post-Contrast:

  • Bone cortex: unchanged, hypointense

  • Marrow and capsule: enhancement in osteomyelitis, tumors, inflammatory arthritis

  • Helps differentiate viable vs. necrotic bone in avascular necrosis

3D T2-weighted Imaging:

  • Cortex: sharply hypointense, marrow intermediate

  • Allows multiplanar reconstructions for fracture morphology, head-neck junction abnormalities, and pre-surgical planning

CT Appearance

Non-contrast CT:

  • Cortex: hyperdense, sharply outlined

  • Cancellous bone marrow: relatively hypodense compared to cortex

  • Gold standard for detecting cortical fractures, callus formation, and bone remodeling

CT Post-Contrast:

  • Bone cortex: unchanged

  • Surrounding soft tissues: enhancement of hematomas, infections, or tumors

  • 3D CT reconstructions used in orthopedic trauma evaluation and surgical navigation

Clinical Significance

  • Femoral neck fractures: common in elderly (intracapsular vs extracapsular); risk of avascular necrosis due to disrupted blood supply.

  • Stress fractures: in athletes and military recruits, often occult on X-ray, best detected on MRI.

  • Avascular necrosis (AVN): ischemic damage to femoral head/neck, seen as serpiginous low T1/high T2 signal with collapse.

  • Developmental dysplasia of the hip (DDH): abnormal femoral neck angle or orientation.

  • Arthritis and impingement syndromes: altered femoral head-neck offset contributing to femoroacetabular impingement (FAI).

CT VRT 3D image

neck of femur 3D CT VRT anatomy image

CT image

neck of femur ct axial

MRI image

neck of femur MRI axial anatomy image-img-00000-00000