Axial Skeleton and Head & Neck Landmarks

Axial Skeleton: Overview of the Thorax

  • The thorax is composed of a bony cage formed by:
    • Sternum
    • Costal cartilage
    • Ribs
    • Thoracic vertebrae

Functions of the Thorax

  • Protects the organs within the thoracic cavity.
  • Provides structural support for:
    • The pectoral girdle.
    • Upper extremities.

Sternum Anatomy

  • The sternum consists of three main parts:
    • Manubrium: Superior portion of the sternum.
    • Contains the Suprasternal notch (SSN).
    • Body: The largest portion, articulates with the 12 ribs.
    • Xiphoid process: Inferior portion of the sternum.
    • Joins with the body at the xiphisternal joint.

Types of Ribs

  • Ribs are classified into categories based on their anatomical connections:
    • True Ribs (1-7):
    • Seven pairs of ribs that articulate anteriorly with the sternum directly.
    • False Ribs (8-12):
    • Three pairs of ribs that contact the cartilage anteriorly but not the sternum.
    • Floating Ribs (11, 12):
    • Two pairs of ribs that articulate only with the vertebrae posteriorly.

Axial Skeleton Imaging

  • The axial skeleton can be easily visualized through most imaging techniques, making it useful for diagnosis and study.

Landmarks of the Head and Neck

Anatomic Landmarks

  • Glabella:
    • A slight elevation directly between the two orbits; located just superior to the base of the nose.
  • Nasion:
    • The central depression at the base of the nose where the frontal and nasal bones meet.
  • Superior Orbital Margin (SOM):
    • Located inferior to the eyebrow, forming the roof of the orbit.

Bony Landmarks of the Skull

Mastoid Process
  • Extends from the mastoid portion of the temporal bone at the level of the earlobe.
    • Used in clinical practice to delineate the posterior point of the inferior whole brain border.
    • An imaginary line from the SOM to the mastoid tip typically passes through the tragus of the ear.
External Occipital Protuberance (EOP)
  • A prominent feature on the posterolateral aspect of the occipital bone of the skull.

Landmarks Around the Eye

  • Lateral Orbital Margin (LOM):
    • Forms the lateral border of the bony orbit.
  • Medial Orbital Margin:
    • Difficult to palpate; limited clinical utility but useful radiographically.
  • Inner Canthus (IC):
    • Located at the medial aspect of the eye at the junction of the upper and lower eyelids.
  • Outer Canthus (OC):
    • The soft tissue landmark at the lateral aspect of the eye, formed at the junction of the upper and lower eyelids.