RibEdit

The rib is a curved, elongated bone that forms a major part of the thoracic cage. In humans, there are 24 ribs arranged in 12 pairs on the left and right sides of the body. Ribs serve a dual purpose: they protect vital thoracic organs such as the heart and lungs, and they provide leverage and attachment points for muscles involved in respiration and upper-body movement. The upper seven pairs connect directly to the sternum via costal cartilage (true ribs), the next three pairs connect indirectly (false ribs), and the last two pairs do not connect to the sternum at all (floating ribs). For the bones themselves and their connections, see the sternum and costal cartilage, and for the breathing apparatus those muscles are described in intercostal muscles.

The rib’s design reflects a balance between protection, flexibility, and mobility. Their curved shape and the presence of a costal groove along the inferior border accommodate nerves and vessels that run along the rib’s underside. The ends of the ribs articulate with the thoracic vertebrae at the costovertebral joints and, for most ribs, with the vertebrae of adjacent levels via articular facets and ligaments. The tubercle of each rib articulates with the transverse process of the corresponding vertebra, forming the costotransverse joint. The rib’s anatomy supports the respiration process, with the rib cage expanding and contracting in coordination with the diaphragm and intercostal muscles.

Anatomy and structure

General layout

Humans typically have 12 pairs of ribs. The first seven pairs are called true ribs because their costal cartilage attaches directly to the sternum. The next three pairs (8–10) are false ribs because their cartilage connects to the cartilage of the rib above, rather than directly to the sternum. The last two pairs (11–12) are floating ribs, which do not connect anteriorly to the sternum.
Each rib consists of a curved bony shaft and a sternal end that joins the costal cartilage. The inferior border of a rib carries a costal groove that shelters blood vessels and nerves.
The joints that stabilize the rib include the costovertebral joints with the vertebral column and the costotransverse joints with the transverse processes of the thoracic vertebrae. These joints permit controlled movement during respiration.

Structure and connections

The head of a typical rib articulates with the bodies of two adjacent vertebrae at the costovertebral joints. The tubercle articulates with the transverse process of the same-numbered vertebra, forming a costotransverse joint.
The sternum connects with the true ribs through hyaline cartilage, allowing the chest wall to expand during inhalation.
The rib shaft is composed of osseous tissue, supplied by blood vessels and nerves that run in the costal groove on the inferior border. The bone’s structure provides strength while remaining lightweight for efficient respiration.
The first rib is broader and shorter and has a distinct groove for the subclavian vessels; ribs 11 and 12 lack certain anterior connections, reflecting their floating status.

Development and variation

Embryology and ossification

Ribs form from mesenchymal condensations that give rise to hyaline cartilage models. These models ossify through endochondral ossification, gradually converting cartilage into bone as fetal development progresses and continuing through adolescence.
Costal cartilage completes its maturation after birth, contributing to the rib cage’s gradual rigidity and stability.

Anatomical variation

Most people have a standard rib count and arrangement, but variations exist. A small percentage of individuals may have cervical ribs or other supernumerary ribs, which can influence surrounding neurovascular structures and sometimes contribute to conditions such as thoracic outlet syndrome.
Variations in rib shape, curvature, and incidence of fused ribs or extra costal joints are noted in anatomical literature and can influence radiographic interpretation.

Clinical note

Variations may be detected incidentally on imaging studies or during assessment for thoracic symptoms. In certain cases, anomalous ribs can contribute to nerve compression or vascular issues and may require clinical attention.

Function

Protection: The rib cage shields vital organs in the thorax, including the heart and lungs, by forming a rigid yet compliant enclosure.
Respiration: Inhalation and exhalation involve forward and outward expansion of the chest. The intercostal muscles, along with the diaphragm, raise and widen the rib cage to increase thoracic volume during inspiration; during exhalation, the cage returns toward its resting position.
Attachment points: Ribs provide anchorage for muscles involved in respiration, posture, and upper-extremity movement, including the intercostal muscles, abdominal muscles, and muscles of the shoulder girdle.

Clinical aspects

Rib fractures are common results of blunt chest trauma, sports injuries, or falls. They cause significant pain and can impair breathing, potentially leading to complications such as pneumonia if ventilation is reduced. Fractures are evaluated by imaging and managed with rest, pain control, and respiratory therapy; more severe fractures may require surgical stabilization.
Pneumothorax, a condition in which air accumulates in the pleural space, can occur with rib injury and chest wall trauma. It may require observation, supplemental oxygen, or procedures to evacuate air and seal the leak.
Flail chest refers to a segment of the chest wall that moves independently due to multiple adjacent rib fractures, posing a risk to breathing efficiency and requiring careful management, sometimes with mechanical ventilation.
Age-related changes such as osteoporosis can increase fracture risk, especially in the elderly, and influence treatment choices for rib injuries.

Evolution and comparative anatomy

The rib cage is a conserved feature across tetrapods, but the number, shape, and articulation of ribs vary among mammals and other vertebrates. These differences reflect adaptations for locomotion, breathing mechanics, and protection of vital organs.
In humans, the rib arrangement supports a high degree of chest wall compliance and resilience, enabling efficient respiration while allowing a wide range of arm and shoulder movements.

History and culture

The rib has appeared in medical, artistic, and cultural contexts as a symbol of protection, vulnerability, and the interconnectedness of the upper body with vital life-sustaining processes. In literature and art, the rib has occasionally served as a symbol of origin stories and human anatomy.