Articulation of the Manubrium and Body of the Sternum

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Anatomy > Gray's Anatomy of the Human Body > III. Syndesmology > 5g. Articulation of the Manubrium and Body of the Sternum

Henry Gray (1821–1865). Anatomy of the Human Body. 1918.

Articulation of the Manubrium and Body of the Sternum

The manubrium is united to the body of the sternum by either of two types of joints:

• An amphiarthrodial joint, where a piece of fibrocartilage connects the segments
• A diarthrodial joint, with each surface covered by a thin layer of articular cartilage

In the diarthrodial type, the cartilage covering the body may continue directly into the cartilage of the second costal facets.

Anatomical studies by Rivington observed the diarthrodial type in about one-third of cases; Maisonneuve reported a higher frequency. This form is uncommon in childhood and may evolve from an amphiarthrosis via resorption of the intervening fibrocartilage. Diarthrodial joints here rarely ossify, while the amphiarthrodial type often ossifies by the mid-30s.

The manubrium and body are also joined by:

• The anterior intersternal ligament
• The posterior intersternal ligament

These consist of longitudinal collagenous fibers that reinforce the articulation.

Mechanics of the Thorax

The thoracic cage expands and contracts during respiration. Each rib functions as a movable lever, with its motion centered near the costotransverse joint. The elevation of a rib produces forward and upward displacement of its anterior end, increasing thoracic volume.

Movements of the ribs are grouped based on their articulation:

• Vertebrosternal ribs (true ribs)
• Vertebrochondral ribs (false ribs)
• Vertebral ribs (floating ribs)

General Mechanics

Each rib forms a segment of a greater arc than the rib above. Elevating a rib:

• Increases the transverse diameter of the thorax
• Elevates the sternum via rib coupling
• Opens the costochondral angle

The anterior ends of the ribs sit lower than the posterior; thus, elevation also moves them anteriorly, expanding the thorax in both anteroposterior and transverse directions.

File:Gray316.png

FIG. 316 – Movements of the sternum and ribs during expiration (a), quiet inspiration (b), and deep inspiration (c).

File:Gray317.png

FIG. 317 – Axis of movement (AB and CD) of a vertebrosternal rib. Dashed lines show inspiratory position.

File:Gray318.png

FIG. 318 – Axis of movement (AB) of a vertebrochondral rib. Dashed lines show inspiratory position.

Vertebrosternal Ribs

These include ribs 1–7. The **first rib** has a rigid attachment to the manubrium, but due to the absence of an interarticular ligament, its head is relatively mobile. The **first and second ribs**, with the manubrium sterni, move as a unit.

In quiet breathing:

• Movement of the first and second ribs is minimal.
• The third to sixth ribs elevate during inspiration, pushing the sternum upward and forward.
• This movement increases both the anteroposterior diameter and transverse diameter of the thorax.

Elevation of the middle shaft of each rib causes eversion of the inferior border and widening of the thoracic cavity, especially near the costal angles.

Vertebrochondral Ribs

These include ribs 8–10 (and sometimes rib 7), which articulate indirectly with the sternum via shared costal cartilages.

Movements of these ribs:

• Help enlarge the upper abdominal space, accommodating displaced abdominal viscera during diaphragm contraction
• Involve a sequence where the lower ribs push up the ones above, ultimately pushing the sternum forward and upward

Due to limited posterior rib rotation:

• Anterior elevation is limited
• The shaft swings outward and backward
• The subcostal angle widens
• Thoracic diameter increases laterally

In deep inspiration, this group helps expand the lower thoracic cavity and upper abdominal volume.

Vertebral (Floating) Ribs

Ribs 11 and 12:

• Lack anterior articulation
• Are only attached posteriorly via costocentral joints
• Have no interarticular ligament

Movements:

• Limited but multidirectional
• During inspiration, these ribs are depressed to anchor the diaphragm and prevent superior displacement of abdominal organs

Clinical Relevance

• Fusion (ossification) of the manubriosternal joint may affect thoracic mobility in aging
• Rib mechanics play a vital role in conditions such as asthma, emphysema, and flail chest
• Understanding rib dynamics is crucial for interpreting respiratory pathologies on imaging

See Also

• Sternum
• Thoracic skeleton
• Costovertebral joint
• Respiration
• Diaphragm
• Synovial joint
• Fibrocartilage

Gray's Anatomy

• Gray's Anatomy Contents
• Gray's Anatomy Subject Index
• About Classic Gray's Anatomy
• Glossary of anatomy terms

Anatomy atlases (external)

[1] - Anatomy Atlases

Adapted from the Classic Grays Anatomy of the Human Body 1918 edition (public domain)