The skeleton of the trunk: main elements and functions

The trunk skeleton is part of the axial skeleton and includes the vertebral column and rib cage. These structures form the central support of the body, supporting the shoulder girdle, upper limbs, pelvis, and lower limbs, as well as the attachment of major muscle groups. [1]

The main idea of the axial skeleton is that it must be both strong and flexible enough. Strength is needed to support body weight and protect the nervous system, while flexibility is needed for movement, shock absorption during walking, and the ability to change body position without damaging the spinal cord. [2]

The spinal column acts as a "support mast" and a protective canal: individual vertebrae fold into the spinal canal, where the spinal cord passes and nerve roots branch off. Therefore, even relatively small changes in the shape of a vertebra or disc can affect not only posture and pain, but also neurological symptoms. [3]

The thoracic cage is formed by the ribs, sternum, thoracic vertebrae, and cartilaginous joints. Its function is twofold: to protect the heart and lungs and to participate in respiration, since changes in the volume of the thoracic cavity are directly related to the movements of the ribs and chest wall. [4]

Table 1. The skeleton of the trunk and its elements

Element	What does it consist of?	Key function
Spinal column	33 vertebrae, intervertebral discs, joints and ligaments	Support, spinal cord protection, mobility
Rib cage	Ribs, sternum, thoracic vertebrae, costal cartilages	Protection of organs, participation in respiration
Connections and ligaments	Joints between the vertebrae and ribs, ligamentous apparatus	Stability during movements and loads

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The spinal column: sections, discs and curves

The human spinal column is typically described as a system of 33 vertebrae, organized into five sections: seven cervical, twelve thoracic, five lumbar, five sacral, and approximately four coccygeal. In adults, the sacral and coccygeal vertebrae typically fuse to form a more rigid lower section of the axial frame. [6]

Each vertebra has a general structural plan: the vertebral body bears the primary compressive load, the arch forms the walls of the spinal canal, and the articular processes form paired intervertebral joints. This combination provides a compromise between strength and mobility and also creates "windows" for the exit of nerve roots through the intervertebral foramina. [7]

Intervertebral discs act as shock absorbers and cushions between the vertebral bodies. They help distribute pressure during standing and walking and allow for flexion and extension without direct bone-on-bone friction, while maintaining overall stability of the spinal column. [8]

Of particular importance are the physiological curves of the spine, which improve balance and spring function. Clinically, excessive or insufficient curves are most often discussed as a factor in muscle and ligament overload, as well as a condition that increases the risk of chronic pain and functional limitations. [9]

Table 2. Sections of the spine and typical features

Department	Number of vertebrae	The main role
Cervical	7	High mobility, head support
Chest	12	Connection with the ribs, protection of the chest organs
Lumbar	5	Basic axle load and damping
Sacral	5, fused	Transfer of load to the pelvis, stability
Coccygeal	about 4, often fused	Support in a sitting position, attachment of ligaments

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Chest: ribs, sternum and joints

The ribs form the bony framework of the thoracic cavity. There are typically 12 pairs of ribs, which articulate with the thoracic vertebrae at the back and are connected to the sternum in varying degrees at the front through the costal cartilages. This structure makes the rib cage both strong and elastic. [11]

For practical purposes, ribs are divided into true, false, and fluctuating ribs. True ribs, typically the 1st to 7th pairs, are directly connected to the sternum via cartilage. False ribs, typically the 8th to 10th pairs, are connected to the sternum indirectly via the cartilage of the rib above. Fluctuating ribs, typically the 11th to 12th pairs, are not connected to the sternum anteriorly. [12]

The sternum is the central bone of the anterior chest wall and consists of the manubrium, body, and xiphoid process. Through the costal cartilages, the sternum "sews" the right and left halves of the thorax together and contributes to the formation of a stable yet mobile anterior framework. [13]

The chest wall limits the thoracic cavity on all sides: the sternum and cartilage in front, the ribs and intercostal spaces on the sides, and the thoracic vertebrae and discs behind. This "frame" is necessary to protect the organs and facilitate breathing, as the muscles of the chest wall change its shape and the volume of the thoracic cavity. [14]

Table 3. Classification of ribs by connection with the sternum

Group	What pairs?	How do they connect at the front?
True	1-7	Direct connection with the sternum through cartilage
False	8-10	Indirect connection through the cartilage of the 7th rib
Oscillating	11-12	There is no anterior connection with the sternum

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How the trunk skeleton works in movement and breathing

In torso movements, the spine functions as a system of segments, where the total mobility is composed of small movements between adjacent vertebrae. This allows for bending, turning, and maintaining balance without overloading a single joint. Stability is ensured by ligaments, facet joints, and muscle control. [16]

The rib cage participates in breathing by changing the size of the chest cavity. The ribs rise and fall, and the costal cartilages provide elasticity that facilitates passive exhalation. Therefore, age-related changes in cartilage tissue and limited rib mobility can affect the "mechanics of inhalation," especially in chronic lung diseases. [17]

Classically, two characteristic types of rib movement are described: the upper ribs exhibit a predominant movement that increases the anteroposterior dimension of the thorax, while the lower ribs exhibit a pronounced component that increases the transverse dimension. Studies of rib kinematics confirm that the contribution of different types of movement depends on the level of the ribs and the range of respiratory volumes. [18]

Functionally, the core skeleton distributes loads between the spine, rib cage, and pelvis. When lifting heavy objects or sitting for long periods, the load can be redistributed in such a way that the discs and facet joints become overloaded, and weak core muscles increase the risk of fatigue and pain. [19]

Table 4. Functions of the trunk skeleton and “what happens if it is disrupted”

Function	What are the key structures?	Typical result in case of violation
Support and load transfer	Lumbar spine, discs, sacrum	Back pain, decreased exercise tolerance
Protection of the nervous system	Spinal canal and vertebral arches	Neurological symptoms with compression
Protection of the chest organs	Ribs, sternum, thoracic vertebrae	Risk of organ injury due to fractures and deformities
Respiratory mechanics	Ribs, cartilage, muscles of the chest wall	Shortness of breath with limited chest mobility

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Clinical significance: common problems and how to examine

Trunk pain is most often associated with muscle and ligament strain, degenerative changes in the discs and joints, as well as poor posture and movement habits. It is important to remember that the same pain location can have different sources, so assessment typically begins with a history, physical examination, neurological assessment, and identification of risk factors. [21]

Chest and spine injuries require special attention, as rib fractures can be associated with pleural and lung damage, and spinal trauma can be accompanied by spinal cord or nerve root damage. Even with a "simple" rib fracture, assessing breathing and monitoring for complications is important, and if spinal injury is suspected, ruling out instability and compression of neural structures becomes a priority. [22]

In cases of spinal and thoracic deformities, the key question is usually functional: is there limited breathing, severe pain, neurological symptoms, or rapid progression of the deformity? In such situations, the examination plan is tailored individually, but the logic remains the same: first, confirm the anatomical changes, then assess the impact on function and risks. [23]

Instrumental diagnostics depend on the objectives. Radiography is suitable for assessing bone structures and deformities, computed tomography helps clarify complex bone lesions, and magnetic resonance imaging is especially valuable for assessing soft tissues, discs, and nerve structures. The choice of method is determined by the symptoms and what needs to be ruled out first. [24]

Table 5. Methods of examination of the skeleton of the trunk and when they are needed

Method	What shows best	When do they usually choose?
X-ray	Position of vertebrae and ribs, fractures, deformations	Trauma, suspected deformity, posture control
Computed tomography	Details of bone injuries, complex fractures	Trauma requiring accurate bone assessment
Magnetic resonance imaging	Discs, ligaments, spinal cord, roots	Neurological symptoms, suspected compression
Laboratory tests	Indirect signs of inflammation and bone tissue metabolism	Suspected inflammatory or metabolic causes

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