Osteology of the Anterolateral Thoracic Wall

Osteology of the Anterolateral Thoracic Wall

  • The ribcage provides rigidity and flexibility, protecting internal organs from forces.
  • Fractures can occur with enough force due to design imperfections.

Introduction to Anterolateral Thoracoabdominal Wall

  • The study includes the thoracic and abdominal cavities and their contents.
  • The anterolateral thoracic and abdominal walls are discussed together due to common features.
  • The initial focus is on the osteology of the thoracic cage.

Session Objectives

  • Discuss the osteology of the thoracic cage.
  • Discuss palpable landmarks and anatomical lines of reference.
  • Components of the thoracic cage and identification in medical imaging.
  • Medical implications of rib fractures.

Thorax Definition

  • The thorax is a barrel-shaped cavity forming the upper torso.
  • Superiorly continuous with the neck at the level of the first ribs (thoracic inlet).
  • Inferiorly, the diaphragm forms a clear boundary separating the thoracic and abdominal cavity (thoracic outlet).
  • Thoracic Inlet and Outlet: Anatomical terms.
  • Thoracic Outlet Syndrome: Medical condition involving compression of vessels at the thoracic inlet.

Thoracic Wall Components

  • Posteriorly: Vertebral column and rib associations, previously discussed.
  • Bilaterally: Ribs separated by intercostal spaces with muscular sheaths and neurovascular bundles.
  • Anteriorly: Rib bone continuous with costal cartilages, fusing with the sternum.

Surface Anatomy

  • Anatomical lines serve as reference points for medical procedures.
    • Anterior Median (Midsternal) Line: Intersection of the midsagittal plane with the sternum.
    • Midclavicular Line: Vertical line through the midpoint of the clavicle.
    • Anterior Axillary Line: Vertical line through the anterior axillary fold (pectoralis major border).
    • Midaxillary Line: Deepest point of the axillary fossa.
    • Posterior Axillary Line: Posterior axillary fold (latissimus dorsi muscle).
    • Scapular Lines: Align with inferior angles of the scapula.
    • Posterior Median (Midvertebral) Line: Intersection of the midsagittal plane with vertebral spinous processes.

Bony Framework of the Thorax

  • Thoracic vertebrae (posteriorly).
  • Sternum (anteriorly).
  • Ribcage (interconnecting element).
  • 12 pairs of ribs span from posterior to anterior.

Rib Classification

  • Based on cartilaginous attachments to the sternum.
    • True Ribs (1-7): Direct costal cartilage attachment to the sternum.
    • False Ribs (8-10): Indirect attachment; costal cartilages fuse.
    • Floating Ribs (11-12): No attachment to the sternum; suspended in muscular sheaths.
  • Note: Some sources classify floating ribs as a type of false rib.
  • Ribs are numbered sequentially from top to bottom.

Typical Ribs (3-9)

  • Broad and flat.
  • Long axis runs superoinferiorly.
  • Head: Articulates with vertebrae at the intervertebral disc.
    • Superior Articulating Facet: Articulates with the inferior articulating demi facet on the superior vertebrae.
    • Inferior Articulating Facet: Articulates with the superior demi facet on the inferior vertebrae.
  • Neck: Connects head to the body
  • Tubercle: Muscular attachment and articulation with the transverse process of the inferior vertebrae.
  • Body: Arches laterally with greatest curvature at the costal angle.
  • Costal Angle: Area of structural weakness; common site for rib fractures.
  • Point tenderness along the costal angle suggests rib fractures after blunt force trauma.
  • Central core: Cancellous or spongy bone with bone marrow。

Costal Groove

  • Notch on the deep inferior surface of each rib.
  • Accommodates the intercostal neurovascular bundle.
  • Intercostal neurovascular bundle: Intercostal vein, artery, and nerve (from superior to inferior).
  • The inferior shelf protects neurovascular structures from mechanical trauma.

Chest Tube Placement Considerations

  • Incision in the inferior portion of the intercostal space near the superior margin of the inferior rib.
  • Avoids damage to the neurovascular bundle along the inferior margin of the superior rib.

Atypical Ribs

  • First Rib:
    • Short and broad.
    • Oriented in a transverse plane.
    • Tubercles for anterior and middle scalene muscle attachment.
    • Grooves for subclavian artery and vein.
    • Single facet for articulation with the first thoracic vertebra.
  • Second Rib:
    • Similar curvature but larger than the first rib.
    • Long axis oriented more obliquely.
    • Tubercle for posterior scalene insertion.
  • Ribs 10-12:
    • Single facet on their heads.
    • Articulate with a complementary facet on a single vertebra.

Costal Cartilages

  • Ribs 1-10 communicate with the sternum via costal cartilages.
  • Projections of hyaline cartilage that fuse with the rib laterally and insert into the sternum.
  • Cartilages of ribs 7-10 fuse together, forming the costal margin.
  • Cartilages of ribs 11 and 12 are short with a free medial margin.
  • Flexibility and elasticity to the rib cage, providing resiliency during blunt force trauma.
  • Ossification increases rigidity with age, potentially contributing to rib fractures during CPR in the elderly.

Rib Fractures

  • Common after blunt force chest trauma.
  • Young individuals: High impact forces (e.g., motor vehicle accidents, contact sports).
  • Elderly: Falls are the primary cause due to decreased bone strength.
  • Diagnosis: Difficult to view on plain film radiographs; Chest CTs and MRIs provide more accurate diagnosis.
  • Fracture Types:
    • Anterior-directed forces: Outward fractures along the costal angle and lateral wall; easier to diagnose.
    • Side impact forces: Inward fracture pattern at the point of contact; harder to diagnose and more serious due to potential puncture of the thoracic cavity, resulting in hemo or pneumothorax.
  • Treatment: Rest and pain medication to promote normal breathing, minimizing alveolar collapse and pneumonia risk.

Sternum

  • Composed of three bones, resembling a sword.
    • Manubrium: The