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Surgical neck of humerus

The surgical neck of the humerus is the narrow constricted region distal to the tubercles and proximal to the humeral shaft. It represents a common site of fracture due to its relative structural weakness and frequent mechanical stress during falls or direct trauma.
It forms an important landmark separating the proximal metaphysis of the humerus from the diaphysis and serves as a transition zone between cancellous bone proximally and compact cortical bone distally.

Clinically, the surgical neck is significant because fractures in this region can endanger the axillary nerve and the posterior circumflex humeral artery, which wind around its posterior aspect.

Location and Structure

  • Lies immediately distal to the anatomical neck, below the greater and lesser tubercles.

  • Marks the junction of the humeral head and shaft.

  • Shape: Constricted circumference of bone forming a weak zone between the tubercles and shaft.

  • Composition: Transition from cancellous bone of the humeral head to dense cortical bone of the shaft.

  • Medullary canal: Expands slightly at this level to accommodate red and fatty marrow.

Relations

  • Anteriorly: Tendon of long head of biceps brachii passes medially within the bicipital groove.

  • Posteriorly: Axillary nerve and posterior circumflex humeral artery traverse the quadrangular space close to the neck.

  • Laterally: Deltoid muscle fibers covering the proximal humerus.

  • Medially: Insertion of pectoralis major (upper shaft) and proximity to the neurovascular bundle of the arm.

Attachments

  • No direct muscular origin or insertion at the surgical neck itself, but it serves as the transition zone between:

    • Proximal attachments: Supraspinatus, infraspinatus, subscapularis (via tubercles).

    • Distal attachments: Deltoid, pectoralis major, teres major, and latissimus dorsi on the shaft.

  • The capsular attachment of the shoulder joint extends slightly distal to the anatomical neck, partially overlying the surgical neck anteriorly and medially.

Nerve Supply

  • The axillary nerve (C5–C6) courses posterior to the surgical neck within the quadrangular space, supplying the deltoid and teres minor.

  • Musculocutaneous nerve lies anteriorly but further medial.

Function

  • Structural junction: Connects the humeral head and tubercles to the diaphysis.

  • Load transmission: Transfers mechanical forces from upper limb movements to the shaft.

  • Clinical importance: Key site of fractures affecting shoulder function and nerve integrity.

  • Surgical relevance: Landmark for proximal humerus fixation and exposure of the axillary nerve.

Clinical Significance

  • Fractures: Most frequent site of proximal humeral fractures; common in elderly osteoporotic individuals and in falls on the outstretched hand.

  • Nerve injury: Axillary nerve injury results in deltoid paralysis and loss of shoulder contour.

  • Vascular injury: Posterior circumflex humeral artery damage may lead to avascular necrosis of the humeral head.

  • Displacement: Fractures may result in impaction, angulation, or separation of fragments depending on muscle pull (deltoid, pectoralis major, latissimus dorsi).

  • Imaging relevance: MRI and CT are critical for assessing fracture lines, bone marrow edema, and neurovascular integrity.

MRI Appearance

  • T1-weighted images:

    • Cortex: Low signal (dark).

    • Marrow: Bright, reflecting fatty marrow in adults.

    • Fractures: Linear low-signal lines crossing cortex or trabeculae.

    • Edema or hemorrhage: Intermediate-to-bright signal replacing fatty marrow.

    • Muscles: Intermediate signal intensity surrounding the neck.

  • T2-weighted images:

    • Cortex: Low signal.

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

    • Pathology: Edema, contusions, or stress injuries appear hyperintense.

    • Joint fluid: Bright signal in glenohumeral recess if associated hemarthrosis.

  • STIR:

    • Normal marrow: Intermediate-to-dark signal.

    • Pathologic marrow: Bright hyperintensity in fractures, contusions, or infection.

    • Highlights bone marrow edema and periosteal reaction clearly.

  • Proton Density Fat-Saturated (PD FS):

    • Normal marrow: Intermediate-to-dark homogeneous signal.

    • Fractures or marrow edema: Bright hyperintense signal with cortical disruption.

    • Excellent for identifying subtle stress fractures and soft-tissue swelling.

  • T1 Fat-Sat Post-Contrast:

    • Normal marrow: Mild homogeneous enhancement.

    • Post-traumatic inflammation or infection: Patchy or irregular enhancement.

    • Tumor or metastasis: Intense heterogeneous enhancement with cortical erosion.

CT Appearance

Non-Contrast CT:

  • Cortex: High attenuation with sharp margins.

  • Trabecular bone: Honeycomb pattern transitioning to denser diaphyseal cortex.

  • Fractures: Visualized as lucent lines, displacement, or cortical step-off.

  • Sclerosis or callus: Seen in healing fractures or chronic stress changes.

  • Bone geometry: Clearly demonstrates tubercles, metaphysis, and shaft alignment.

Post-Contrast CT (standard):

  • Bone: No intrinsic enhancement.

  • Periosteum and soft tissues: Enhance in inflammation or post-surgical changes.

  • Usefulness: Evaluating fracture healing, osteomyelitis, or periosteal reaction.

  • 3D reconstruction: Excellent for preoperative planning and prosthetic alignment assessment.

CT VRT 3D image

Surgical neck of humerus ct vrt image

MRI image

Surgical neck of humerus sag cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Surgical neck of humerus ct coronal image