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Shaft of humerus

The shaft or body of the humerus forms the long cylindrical mid-portion of the upper arm bone, extending from the surgical neck proximally to the supracondylar ridges distally. It serves as the primary structural support of the upper limb, providing broad surfaces for muscle attachment and neurovascular passage.

The humeral shaft exhibits a mild anterior curvature, optimizing mechanical leverage for the upper limb muscles. It transitions proximally from a rounded cross-section to a flattened shape distally. Its posterior surface bears the radial (spiral) groove, which accommodates the radial nerve and deep brachial artery.

Synonyms

  • Corpus humeri

  • Diaphysis of the humerus

  • Humeral body

Location and Structure

  • Shape: Cylindrical in the upper half, flattened anteroposteriorly in the lower half.

  • Borders:

    • Anterior border: Extends from the greater tubercle to the lateral epicondyle.

    • Lateral border: Runs from the posterior surface of the greater tubercle to the lateral supracondylar ridge.

    • Medial border: Extends from the lesser tubercle to the medial supracondylar ridge.

  • Surfaces:

    • Anterolateral surface: Origin of the brachialis and insertion of deltoid.

    • Anteromedial surface: Origin of coracobrachialis and attachment for brachialis.

    • Posterior surface: Traversed obliquely by the radial groove, containing the radial nerve and deep brachial artery.

Relations

  • Anteriorly: Brachialis, biceps brachii, and coracobrachialis muscles.

  • Posteriorly: Triceps brachii (medial and lateral heads).

  • Laterally: Deltoid insertion and cephalic vein.

  • Medially: Brachial artery, median nerve, and ulnar nerve (lower third).

  • Neurovascular groove: Radial nerve and deep brachial artery course along posterior surface.

Attachments

  • Deltoid: Inserts on the deltoid tuberosity (anterolateral surface).

  • Coracobrachialis: Inserts on the medial midshaft.

  • Brachialis: Originates from the distal anterior surface.

  • Triceps brachii: Medial and lateral heads arise from posterior surface above and below radial groove.

  • Medial and lateral intermuscular septa: Attach to respective borders separating flexor and extensor compartments.

Nerve Supply

  • Periosteal sensory supply:

    • Radial nerve: Posterior and lateral surfaces

    • Musculocutaneous nerve: Anterior surface

    • Ulnar nerve: Medial surface (distal portion)

Function

  • Structural support: Main framework of the upper arm connecting shoulder and elbow joints.

  • Muscular leverage: Provides attachment sites for flexors and extensors of the arm and forearm.

  • Force transmission: Transfers loads from hand and forearm to shoulder girdle.

  • Protection: Encloses radial nerve and deep brachial artery within its posterior groove.

Clinical Significance

  • Fractures: Commonly result from direct trauma or twisting injuries; classified as proximal, midshaft, or distal third fractures.

  • Radial nerve palsy: Often occurs with midshaft (spiral groove) fractures, causing wrist drop.

  • Pathological fractures: May occur in metastases, primary tumors, or osteoporosis.

  • Nonunion: Can result from poor alignment or soft-tissue interposition.

  • Imaging relevance: MRI and CT provide key information about fracture extent, healing, marrow pathology, and soft-tissue involvement.

MRI Appearance

  • T1-weighted images:

    • Cortex: Low signal (dark).

    • Bone marrow: Bright, reflecting fatty marrow composition.

    • Muscles: Intermediate signal intensity.

    • Radial groove: Appears as a linear depression on posterior surface.

    • Fracture lines: Low-signal linear defects with surrounding bright marrow edema.

  • T2-weighted images:

    • Cortex: Low signal.

    • Marrow: Bright, slightly less intense than on T1.

    • Muscle: Intermediate-to-dark; slightly darker than T1.

    • Pathology: Fracture edema, infection, or tumor infiltration shows hyperintense marrow signal.

    • Joint fluid or soft-tissue swelling: Bright hyperintense around fracture sites.

  • STIR:

    • Normal marrow: Intermediate-to-dark signal.

    • Abnormal marrow (edema, contusion, infection): Bright hyperintense signal.

    • Excellent for early detection of stress fractures, marrow edema, or infiltrative lesions.

  • Proton Density Fat-Saturated (PD FS):

    • Normal marrow: Intermediate-to-dark signal.

    • Pathologic areas: Bright signal foci in bone marrow or periosteum indicating edema or contusion.

    • Useful for differentiating acute vs chronic bone injury and evaluating adjacent soft-tissue inflammation.

  • T1 Fat-Sat Post-Contrast:

    • Normal humeral marrow: Mild homogeneous enhancement.

    • Infection or tumor: Heterogeneous or nodular enhancement pattern.

    • Healing fracture: Peripheral rim enhancement with central low-signal hematoma or callus formation.

CT Appearance

Non-Contrast CT:

  • Cortex: High attenuation, sharply marginated.

  • Trabecular bone: Fine honeycomb pattern with visible medullary canal.

  • Radial groove: Clearly visible along posterior surface.

  • Pathology: Detects fractures, sclerosis, osteolysis, or periosteal reaction with high precision.

  • Useful for: Evaluating fracture alignment, healing, cortical irregularities, and lytic or sclerotic lesions.

Post-Contrast CT (standard):

  • Bone: Minimal enhancement.

  • Soft tissues: Enhanced in inflammation, abscess, or tumor.

  • Periosteum and marrow: Show enhancement in osteomyelitis or tumor infiltration.

  • Applications: Assessment of fracture healing, infection, neoplasm, and post-surgical complications.

CT VRT 3D image

Shaft of humerus ct vrt image

MRI image

Shaft of humerus sagittal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Shaft of humerus ct coronal image