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Medial border of humerus

The medial border of the humerus refers to the longitudinal medial margin of the humeral shaft extending between the proximal and distal ends of the bone. It serves as an important anatomical landmark for muscle attachment, neurovascular relations, and surface anatomy of the arm.

It is a key reference in orthopedic anatomy, trauma evaluation, surgical approaches to the arm, and imaging interpretation of the humeral shaft.

Synonyms

  • Medial margin of the humerus

  • Ulnar border of the humerus (classical anatomical term)

Location

  • Extends along the medial aspect of the humeral shaft

  • Runs from the medial lip of the bicipital groove proximally

  • Continues inferiorly to the medial supracondylar ridge distally

  • Forms the medial outline of the arm

  • Oriented toward the body midline in anatomical position

Anatomical components

  • Cortical bone forming the medial edge of the shaft

  • Muscle attachment areas:

    • Coracobrachialis (midshaft insertion nearby)

    • Medial head of triceps (origin along adjacent posterior surface)

    • Brachialis (adjacent anterior surface)

  • Transition zones:

    • Proximally merges with the surgical neck region

    • Distally continues as the medial supracondylar ridge

Relations

Anteriorly:

  • Brachialis muscle

Posteriorly:

  • Medial head of triceps muscle

Medially:

  • Neurovascular bundle of the arm (brachial artery, median nerve, ulnar nerve distally)

Laterally:

  • Humeral shaft body

Superiorly:

  • Surgical neck and proximal humerus

Inferiorly:

  • Medial supracondylar ridge and medial epicondyle

X-ray appearance

Plain radiographs (AP and lateral arm views):

  • Medial border: Seen as a smooth, linear cortical margin of the humeral shaft

  • Cortical density: Uniform and continuous

  • Alignment: Helps assess shaft straightness and rotation

  • Best seen on: AP view with arm in anatomical position

CT appearance

Non-contrast CT:

  • Medial border: Clearly defined cortical edge of the humerus

  • Cortical thickness: Uniform along the shaft

  • Trabecular bone: Normal cancellous pattern centrally

  • Spatial assessment: Accurate delineation of contour and cortical integrity

MRI appearance

T1-weighted images:

  • Cortical bone: Low signal intensity

  • Marrow cavity: High signal intensity in the shaft

  • Medial border: Sharp interface between cortex and surrounding soft tissues

T2-weighted images:

  • Cortex: Low signal

  • Surrounding muscles: Intermediate signal

  • Marrow: Intermediate-to-high signal depending on composition

STIR:

  • Fat suppression: Uniform suppression of marrow fat

  • Cortical outline: Well visualized against suppressed marrow

  • Adjacent soft tissues: Bright relative signal

Proton density fat-saturated (PD FS):

  • Marrow: Fat suppressed

  • Cortex: Persistently low signal

CT VRT 3D image

Medial border of humerus

CT image

Medial border of humerus ct