Thoracic Wall: Comprehensive Study Notes
Thoracic Wall: Bones, Joints, Spaces, Muscles, and Neurovasculature
Overview of the Thoracic Wall and Cavity
Thoracic Cavity: The space enclosed by the thoracic cage, intercostal muscles, and diaphragm.
Superior thoracic aperture: Located superiorly.
Inferior thoracic aperture: Located inferiorly.
Thoracic Wall:
Characteristics: Rigid yet flexible, constantly in motion.
Formed by:
Skin
Subcutaneous tissue
Thoracic cage (ribs and costal cartilage, sternum, thoracic vertebrae and intervertebral discs)
Muscles (e.g., intercostals, pectorals)
Fascia
Functions:
Protection of thoracic and abdominal organs.
Respiration.
Muscle attachment.
Viscera of the Thorax (Anterior View References)
Key structures visible anteriorly include:
Heart (with apex and coronary vein)
Left lung (with apex and cardiac notch)
Right lung
Subclavian artery and vein
Common carotid arteries
Internal jugular vein
Diaphragm (inferior boundary)
Rib landmarks: 1^{st}, 4^{th}, 6^{th}, 10^{th} ribs
Sternum parts: Manubrium, xiphoid process, costal cartilage.
Thoracic Apertures
Superior Thoracic Aperture (Thoracic Inlet):
Slope: Antero-inferiorly.
Communication: Connects the thoracic cavity with the neck and upper limb.
Boundaries:
Posterior: Body of the T_1 vertebra.
Lateral: 1^{st} rib and its cartilage.
Anterior: Superior border of the manubrium.
Inferior Thoracic Aperture (Thoracic Outlet):
Slope: Posterior aspect is more inferior than the anterior.
Size: Larger than the superior aperture.
Enclosure: Enclosed by the diaphragm.
Function: Serves as a passageway to and from the abdominal cavity; structures pass either posterior to or through the diaphragm.
Boundaries:
Posterior: Body of the T_{12} vertebra.
Lateral: 12^{th} rib and the distal end of the 11^{th} rib.
Anterior: Costal cartilage of ribs 7-10 and the xiphisternal joint.
Infrasternal Angle (Subcostal Angle): Formed by the costal margin and the xiphisternal joint.
Ribs
General Characteristics:
Flat bones.
Contain active hematopoietic tissue (red bone marrow).
Classification by Sternum Attachment:
True Ribs (Vertebrosternal Ribs): Ribs 1-7; attach directly to the sternum via their own costal cartilages.
False Ribs (Vertebrochondral Ribs): Ribs 8-10; attach indirectly to the sternum, usually by joining the cartilage of the rib above.
False, Floating Ribs (Free Ribs): Ribs 11, 12; do not attach to the sternum at all.
Typical vs. Atypical Ribs: This classification is distinct from true/false/floating.
Typical Ribs: Ribs 3-9; share common features.
Head: Possesses two facets for articulation with two adjacent vertebral bodies and the intervertebral disc between them.
Neck: The constricted portion between the head and the tubercle.
Tubercle: Has an articular part (articulates with the transverse process (TP) of the corresponding vertebra) and a non-articular part (attachment site for the lateral costotransverse ligament).
Body (Shaft): Features a costal angle (point of sharpest curvature) and a costal groove (for the intercostal neurovascular bundle).
Articulation: The inferior facet articulates with the numerically corresponding vertebra.
Atypical Ribs: Ribs 1, 2, 10-12; possess unique characteristics.
1^{st} Rib:
Morphology: Widest, nearly horizontal, shortest, and most sharply curved rib.
Head: Single facet for articulation with only one vertebral body (specifically, T_1).
Features: Grooves for the subclavian vessels (artery and vein), and a scalene tubercle (for scalenus anterior attachment).
Orientation: When correctly oriented, its head touches a flat surface, and its undersurface is smoother.
Attachments: Features insertion sites for anterior and middle scalene muscles, origin of subclavius, and 1^{st} digitation of serratus anterior. Associated with sympathetic trunk, supreme intercostal vein, superior intercostal artery, T_1 nerve root, suprapleural membrane, costoclavicular ligament.
2^{nd} Rib:
Length: Almost twice the length of the 1^{st} rib.
Features: Noticeable tuberosity for the serratus anterior (specifically, its 2^{nd} digitation) and scalene posterior.
Attachments: Insertion of posterior scalene muscle.
Ribs 10-12:
Head: Ribs 10-12 have a single facet on the head, articulating with only one vertebral body (their numerically corresponding vertebra).
Ribs 11 and 12: Are short and lack both a neck and a tubercle, meaning they do not articulate with the transverse processes of their corresponding vertebrae.
Costal Cartilages and Intercostal Spaces
Costal Cartilages:
Function: Provide flexibility to the thoracic cage.
Attachment to Sternum:
Directly: Ribs 1-7 (vertebrosternal ribs).
Indirectly: Ribs 8-10; their cartilages join the cartilage above to form the costal margin.
Intercostal Spaces:
Numbering: Numbered according to the superior rib (e.g., the 1^{st} intercostal space lies between ribs 1 and 2).
Contents: Filled by intercostal muscles and membranes.
Count: There are 11 intercostal spaces.
Neurovasculature: Each space typically contains two sets of intercostal vessels (anterior and posterior) but only one intercostal nerve.
Subcostal Space: The space below the 12^{th} rib.
Dynamics: The dimensions of intercostal spaces change with respiration.
Thoracic Vertebrae and Sternum
Thoracic Vertebrae (12)
Features:
Costal Facets on Vertebral Bodies: Bilateral superior and inferior costal facets (or demifacets) on the posterolateral aspects of their bodies, crucial for rib head articulation.
Costal Facets on Transverse Processes (TPs): Costal facets on the TPs facilitate articulation with the rib tubercle.
Exceptions: Vertebrae T{11} and T{12} do not have costal facets on their transverse processes.
Sternum
Description: A flat bone forming the middle anterior part of the thoracic cage.
Function: Protects underlying viscera and serves as an attachment point for ribs.
Parts of the Sternum:
Manubrium: (Spans vertebral level T3-T4)
Jugular Notch (Suprasternal Notch): Palpable superior border (vertebral level T_2).
Clavicular notches (for sternoclavicular joints).
Synchondroses for the 1^{st} rib.
Manubriosternal Joint (Sternal Angle of Louis): (Located at vertebral level T4/T5)
An important anatomical landmark.
Marks the level of the 2^{nd} pair of costal cartilages.
Indicates the transverse thoracic plane, defining the superior border of the mediastinum.
Body (Gladiolus): (Spans vertebral level T5-T9)
Features costal notches for ribs 2-7 (specifically costal cartilages).
Often shows transverse ridges, representing the lines of fusion of four separate sternebrae.
Xiphoid Process: (Vertebral level T_{10})
Its appearance varies (bifid, perforated, pointed).
Xiphisternal Joint: (Located at vertebral level T_9 in a supine position)
Corresponds to the level of the central tendon of the diaphragm.
Marks the inferior limit of the heart and the superior limit of the liver.
Joints of the Thoracic Wall
Costovertebral Joints:
Type: Synovial plane joints, allowing gliding movements.
Articulations:
Heads of Ribs 2-9: Articulate with the superior costal facet of their numerically corresponding vertebra, the inferior costal facet of the vertebra above it, and the intervening intervertebral disc. These joints have two joint cavities separated by an intra-articular ligament. They are supported by radiate ligaments.
Heads of Ribs 1, 10-12: Articulate only with their single, numerically corresponding vertebral body.
Costotransverse Joints:
Type: Synovial plane joints, allowing gliding movements.
Articulations: Between the rib tubercle and the transverse process of the corresponding vertebra.
Support: Supported by costotransverse ligaments.
Variations: The shape of the articulating surfaces of the TPs differs between superior and inferior ribs.
Exceptions: Ribs 11 and 12 do not articulate with the transverse processes as they lack tubercles.
Costochondral Joints:
Type: Primary cartilaginous joints (synchondroses).
Articulations: Between the sternal end of the rib and its costal cartilage.
Movement: Normally, no movement occurs.
Interchondral Joints:
Type: Synovial plane joints.
Articulations: Between the costal cartilages of ribs 6-9. The articulation between 9^{th} and 10^{th} ribs is fibrous.
Support: Interchondral ligaments.
Sternocostal Joints:
Type:
1^{st} Rib: Primary cartilaginous joint (synchondrosis).
2^{nd}-7^{th} Ribs: Synovial plane joints.
Articulations: Between costal cartilages and the sternum.
Support: Strengthened by anterior and posterior radiate sternocostal ligaments.
2^{nd} Sternocostal Joint: Divided into two compartments by an articular disc.
Manubriosternal Joint:
Type: Secondary cartilaginous joint (symphysis).
Often fuses to become a synostosis in older individuals.
Xiphisternal Joint:
Type: Primary cartilaginous joint (synchondrosis).
Often fuses to become a synostosis in older individuals.
Sternoclavicular Joint:
Type: Saddle type of synovial joint (a joint of the upper extremity).
Articulations: Sternal end of the clavicle with the manubrium and 1^{st} costal cartilage.
Support: Anterior and posterior sternoclavicular ligaments; costoclavicular ligament.
Clinical Considerations: Rib Fractures and Flail Chest
Rib Fractures:
Cause: Usually a result of blunt trauma to the thorax.
Common Site: Ribs 4-9 are most commonly injured.
Complications: Can result in injury to underlying organs, such as pulmonary laceration, hemothorax (blood in pleural cavity), or pneumothorax (air in pleural cavity).
1^{st} Rib Fracture: Though not easy to fracture, its presence is an indicator of severe underlying injury due to the protected position of the 1^{st} rib.
Flail Chest:
Definition: A life-threatening condition characterized by the fracture of three or more adjacent ribs in two or more separate locations.
Mechanism: Creates a