Neck of Radius: Anatomy, Relations, Function, Clinical Imaging

Topic

Neck of radius

The neck of the radius is the narrowed portion of the proximal radius, situated immediately below the radial head and above the radial tuberosity. It serves as a transition between the articular head and the shaft of the bone, allowing rotational movement of the radius during pronation and supination of the forearm.

This region is of great structural and clinical importance — it accommodates the annular ligament that encircles the radial head and neck, permitting smooth rotation within the radial notch of the ulna. The neck’s cortical contour and angulation are crucial for proper elbow biomechanics and forearm motion.

Fractures of the radial neck are common, especially in children (as Salter-Harris type II injuries) and in adults from fall on outstretched hand (FOOSH) injuries, which may disrupt elbow function and radial head alignment.

Synonyms

Proximal radial neck
Radial head-neck junction
Subcapital region of radius

Location and Structure

Position: Between the radial head and the radial tuberosity, just distal to the articular surface of the head.
Shape: Cylindrical, slightly constricted, with smooth cortical margins.
Orientation: The neck is inclined slightly medially to align the radial head with the capitulum of the humerus.
Surface:
- Anterior: Smooth, related to the supinator muscle.
- Posterior: Covered by fibers of the supinator.
- Medial: Encircled by the annular ligament and adjacent to the radial notch of the ulna.
- Lateral: Subcutaneous and palpable distal to the radial head.

Relations

Superiorly: Radial head articulating with the capitulum of the humerus.
Inferiorly: Radial tuberosity, providing attachment for the biceps brachii tendon.
Medially: Annular ligament and radial notch of ulna.
Laterally: Supinator muscle and deep fascia of the forearm.
Anteriorly: Oblique cord and origin fibers of flexor muscles.
Posteriorly: Supinator muscle and posterior interosseous vessels.

Function

Rotational axis: Serves as a pivot for pronation and supination of the forearm.
Force transmission: Transfers load from the radial head to the shaft during axial compression.
Joint stability: Maintains alignment of the proximal radioulnar and humeroradial joints.
Muscle attachment surface: Provides anchorage for supinator and oblique cord fibers.

Clinical Significance

Fractures: Radial neck fractures are common in children (greenstick or physeal) and adults (non-displaced or angulated).
Dislocations: Associated with Monteggia fractures or annular ligament injuries.
Osteochondral lesions: Occur with repetitive stress or trauma.
Deformity: Malunion may restrict forearm rotation or cause valgus deformity of the elbow.
Post-surgical evaluation: Radiologists assess healing, alignment, and avascular necrosis post fixation or radial head replacement.

MRI Appearance

T1-weighted images:
- Cortex: Low signal (dark) with smooth contour.
- Bone marrow: Bright (fatty marrow signal).
- Surrounding muscle: Intermediate signal intensity.
- Annular ligament: Thin low-signal band encircling the neck.
- Fractures: Linear low-signal cortical disruption with surrounding bright marrow edema.
T2-weighted images:
- Cortex: Dark, sharply defined.
- Marrow: Bright, slightly less than T1 but higher than muscle.
- Joint fluid: Hyperintense; outlines annular ligament and radial head recess.
- Pathology: Bone contusions and fractures appear as bright hyperintense areas within marrow or along cortex.
STIR:
- Normal marrow: Intermediate-to-dark signal.
- Pathologic changes: Bright hyperintense regions indicate marrow edema, stress injury, or inflammation.
- Sensitive for early detection of occult fractures and post-traumatic edema.
Proton Density Fat-Saturated (PD FS):
- Normal neck: Intermediate-to-dark signal with uniform marrow texture.
- Abnormal: Bright hyperintense foci in fractures, bone bruise, or periosteal reaction.
- Provides clear visualization of surrounding soft-tissue changes and annular ligament thickening.
T1 Fat-Sat Post-Contrast:
- Normal bone: Mild homogeneous enhancement.
- Inflammation or fracture: Patchy enhancement in marrow and periosteum.
- Osteomyelitis: Intense irregular enhancement with cortical disruption.
- Postoperative changes: Linear enhancement along surgical hardware or scar tissue.

CT Appearance

Non-Contrast CT:

Cortex: High attenuation, sharply defined.
Trabecular bone: Fine, homogeneous density.
Neck contour: Narrowed transition between head and shaft, best appreciated on coronal and sagittal planes.
Pathology: Excellent for detecting subtle fractures, comminution, angulation, or joint incongruity.
Post-trauma: Demonstrates displacement, impaction, or callus formation in healing fractures.

Post-Contrast CT (standard):

Normal bone: Uniform enhancement of marrow cavity.
Inflammation or infection: Focal enhancement along cortex and periosteum.
Post-surgical evaluation: Detects cortical irregularity, fixation integrity, and bone healing response.

CT VRT 3D image

MRI image

CT image

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