Thorax and Chest Wall

Thorax and Chest Wall Components

• The thorax includes the rib cage, attached fascia and muscles, and visceral organs inside.
• The rib cage consists of the thoracic vertebrae, ribs, cartilages, and the sternum.

Thorax and Chest Wall Functions

• Provides a foundation for muscle attachments for the upper extremities, head, spine, and pelvis.
• Protects the heart, lungs, and other viscera.
• Increases the stability of the thoracic spine during movements.
• Plays a major role in ventilation.

Components of the Thorax

• The thorax consists of the sternum, 12 pairs of ribs, costal cartilages, and thoracic vertebrae.

Structure of the Rib Cage

• The rib cage forms a closed chain involving several joints and muscles.
• The anterior border is the sternum.
• The lateral border consists of the ribs.
• The posterior border is the thoracic vertebrae.
• The superior border is the manubrium along with the superior borders of the 1st costal cartilages, 1st ribs, and T1 vertebra.
• The inferior border includes the xiphoid process, shared costal cartilages of ribs 7-10, inferior portions of the 11th and 12th ribs, and the T12 vertebra.

Sternum

• The sternum protects the heart.
• The manubrium, the body of the sternum, and the xiphoid process make up its components.
• The manubrium and the body of the sternum form a posteriorly concave angle of approximately 160°.
• The xiphoid process typically angles posteriorly from the distal end of the sternal body.

Thoracic Costal Facets

• The thoracic vertebrae possess 6 costal articular surfaces.
• Four are on the vertebral body(demifacets).
• Two are are on the transverse processes(costotransverse facets).
• Demifacets of vertebral bodies are referred to as the superior and inferior costovertebral facets.

Ribs

• The ribs gradually increase in length from rib 1 to 7, then decrease in length from rib 8 to 12.
• The posteriorly located rib head articulates with the corresponding thoracic vertebra.
• Ribs 1–10's costal tubercles articulate with the transverse processes of the thoracic vertebrae.
• Ribs are joined either directly or indirectly to the sternum via costal cartilages.

Rib Types

• True ribs (vertebrosternal ribs) are ribs 1–7, and attach directly to the sternum via costochondral and chondrosternal joints.
• False ribs (vertebrochondral ribs) are ribs 8–10 and indirectly articulate with the sternum via rib 7.
• Floating ribs are ribs 11–12, and possess no sternal attachment.

Typical vs Atypical Ribs

• Ribs 3-9 are classified as typical ribs.
• Typical ribs have a rib head with 2 articular facets, a tubercle, neck, shaft, and costal groove that contains the intercostal neurovascular bundle.

Typical Rib Head Articulation Details

• The superior facet articulates with the demifacet of the vertebra above its level.
• The inferior facet articulates with the demifacet of the vertebra at the same level.
• Atypical ribs do not have all the features characteristic of typical ribs and include the 1st, 2nd, 10th–12th ribs.
• Atypical ribs articulate with their own vertebra through one full facet.

Manubriosternal Joint

• The manubriosternal joint (sternal angle) is a horizontal ridge at the level of the 2nd rib anterior attachments.
• It is a synchondrosis joint with a fibrocartilaginous disc.
• It typically ossifies around age 60 years.

Xiphisternal Joint

• The xiphisternal joint is a synchondrosis joint, ossifying around age 40-45 years.

Costochondral Joints

• Costochondral joints articulate between ribs 1-10 and costal cartilages, are synchondroses and have no ligamentous support,.
• They begin to fuse by the age of 35.

Chondrosternal Joints

• Chondrosternal joints articulate with the costal cartilages of ribs 1-7 with the sternum.
• Ligaments & jt capsules provide support.
• They also ossify with age.

Interchondral joints

• Interchondral joints occur as the costal cartilages of ribs 7-10 each articulate with the superiorly adjacent cartilage.
• Interchondral joints create an indirect connection to the sternum for ribs 8-10.
• These joints tend to fuse with age.

Costovertebral Joints

• Costovertebral joints are synovial joints with a fibrous capsule, formed by the rib head, 2 adjacent vertebral bodies, and the intervertebral disc (IVD).
• The interosseous (intra-articular) ligament attaches the rib head to the Annulus fibrosus (AF) of IVD.
• The radiate ligament is located within the capsule, attaching to the anterolateral portion; it reinforces the joint.

Costotransverse Joints

• Costotransverse joints are synovial joints and are formed by the costal tubercle of the rib with the costal facet on the transverse process of the corresponding vertebra.
• There are 10 pairs of costotransverse joints (T1–T10).

Costotransverse Ligaments

• The Lateral costotransverse ligament is a short band running between the lateral costal tubercle and the tip of transverse process.
• The Costotransverse ligament contains short fibers running within the costotransverse foramen, between the neck of the rib posteriorly and the corresponding transverse process.
• The Superior costotransverse ligament runs from the neck of the rib to the inferior border of the transverse process above.

Kinematics of the Ribs

• Movement of the rib cage relates to types/angles of articulations, movement of the manubriosternum, and elasticity of costal cartilages.
• Costovertebral & costotransverse joints are mechanically linked.
• The axis of motion for elevation & depression passes through both joints.
• The length, shape, and downward angle of each rib are unique.
• The axis of rotation for each rib is slightly different.

Rib Kinematics: Upper Ribs

• Upper ribs' axes of rotation most closely approximate a coronal axis.
• Motion occurs predominantly in the sagittal plane.

Rib Kinematics: Lower Ribs

• Lower ribs' axes of rotation most closely approximate an anteroposterior axis.
• Motion occurs closer to the frontal plane.

Rib Kinematics: Ribs 11 & 12

• The axes of rotation pass through the costovertebral joint only.
• Its movement approximates a coronal axis.

Rib Cage Movement

• Movement around costovertebral & costotransverse joints also creates movement at costochondral & chondrosternal joints, with the exception of floating ribs.

Ribcage Kinematics (Ribs 2-7)

• During inhalation the costocartilage rotates upward and becomes more horizontal.
• Rib movement pushes the sternum anteriorly & superiorly.
• The anterior-posterior (AP) diameter of the thorax increases.
• Movement predominantly occurs in the sagittal plane, otherwise known as pump-handle motion.

Ribcage Kinematics (Ribs 8-10)

• During inhalation, the ribs rotate upward and elevate.
• Rib elevation occurs around the more AP axis.
• Rib motion occurs in a more frontal plane.
• The transverse diameter of the lower thorax increases, or bucket-handle motion.
• Lower ribs have a more angled shape and indirect attachment to the sternum.
• More motion at the lateral aspect of the rib cage.

Rib Kinematics Overall

• Orientation of axes of rib motion gradually changes from rib 2 to 10.
• Intermediate ribs function as a transitional zone with qualities of both the pump-handle and bucket-handle motions.

Ventilatory Muscles

• Ventilatory muscles exhibit increased fatigue resistance & a greater oxidative capacity.
• They have life-sustaining actions.
• They contract rhythmically rather than episodically.
• They work primarily against elastic properties of lungs & airway resistance.
• Control is both voluntary & involuntary.

Muscles Recruitment for Ventilation

• Any muscle attaching to the chest wall can potentially contribute to ventilation.
• Muscle recruitment relies on the type of breathing taking place.
• At rest (normal tidal breathing), only primary inspiratory muscles are used, including the diaphragm, intercostal muscles, and scalenes.
• Active or forced breathing recruits accessory muscles of breathing and occurs with increased activity or in pulmonary pathologies.

Thoracoabdominal Expansion

• Normal thoracoabdominal expansion with diaphragmatic contraction occurs during inhalation.
• The diaphragm descends/flattens.
• With passive exhalation, elastic recoil of the relaxing diaphragm, thorax, & lungs leads to decreased thorax size.
• The abdominal viscera return to their resting position.

Intercostals and Scalenes

• External intercostals and parasternal fibers of internal intercostals elevate ribs and increase intrathoracic volume.
• They stabilize intercostal spaces to prevent inward collapse of the thoracic wall.
• Scalenes elevate the sternum and first 2 ribs in the pump-handle motion and also contribute to the stability of the rib cage.

Accessory Inspiratory Muscles

• The serratus posterior's superior portion elevates the upper ribs, increasing intrathoracic volume. Its inferior portion stabilizes lower ribs for the initial contraction of the diaphragm.
• Sternocleidomastoid elevates the sternum and upper ribs.
• The latissimus dorsi elevates the lower ribs when the arms are fixed.
• The pectoralis minor elevates the upper ribs, requiring contraction of the upper trapezius and levator scapulae to stabilize the scapula.
• The pectoralis major elevates the middle ribs and sternum, which requires the arms to be fixed in at least 90° flexion or ABD.
• Quadratus lumborum stabilizes the lower ribs for diaphragmatic contraction during early forced inspiration.
• Iliocostalis thoracic and cervicis increase intrathoracic volume by extending the trunk.

Accessory Expiratory Muscles

• Abdominals (rectus abdominis, external obliques, internal obliques, transversus abdominis) decrease intrathoracic volume by flexing the trunk and depressing the ribs. These muscles compress the abdominal wall, increasing intra-abdominal pressure and pushing the relaxed diaphragm upward, decreasing intrathoracic volume.
• Transversus thoracis decreases intrathoracic volume by depressing ribs and pulling them inward.
• The internal intercostals depress the ribs.