Anatomy of bone system. The manual for medical students / Анатомия костной системы. Учебное пособие для медицинских вузов

The skeleton of trunk consists of the vertebral column, or backbone, columna vertebralis, and the thorax, cavea thoracis (thorax).

The vertebral column in an adult person consists of 24 individual vertebrae, sacrum and coccyx. There are the cervical vertebrae (7), thoracic (12) and lumbar ones (5) distinguished in the vertebral column. The sacrum consists of five fused sacral vertebrae. The coccyx consists of 3–5 fused coccygeal vertebrae. The thorax consists of 12 pairs of ribs with corresponding thoracic vertebrae and the sternum.

2.1. General Vertebral Features

The vertebra, vertebra, is comprised of the vertebral body, corpus vertebrae, anteriorly, the vertebral arch, arcus vertebrae, posteriorly and vertebral processes, processus vertebrae. The vertebral body is anterior and supporting part of the vertebra. The arch is located behind the vertebral body. The vertebral arch is attached to the body with the help of two pedicles of vertebral arch, pediculi arcus vertebrae, thus bounding the vertebral foramen, foramen vertebrale (fig. 2.1).

The foramina of all vertebrae form the vertebral canal, canalis vertebralis, enclosing the spinal cord. Openings for blood vessels named nutrient foramina, foramina nutricia, are visible on the surface of the vertebral body.

Seven processes project from the vertebral arch. An unpaired spinous process, processus spinosus, projects dorsally along the median line. The paired transverse processes, processus transversus, project on the right and on the left in the frontal plane. The paired superior and inferior articular processes, processus articularis superior et processus articularis inferior, project up and down from the arch. The bases of the articular processes bound the superior and inferior vertebral notches, incisura vertebralis superior et incisura vertebralis inferior. The inferior notches are deeper than the superior ones. When the vertebrae are articulated with each other, the inferior and superior notches form an intervertebral foramen, foramen intervertebrale, on the right and on the left. The intervertebral foramina transmit spinal nerves and blood vessels.

Fig. 2.1. Thoracic vertebra:

a – lateral aspect: 1 – vertebral body (corpus vertebrae); 2 – superior costal demi-facet (fovea costalis superior); 3 – superior vertebral notch (incisura vertebralis superior); 4 – superior articular process (processus articularis superior); 5 – transverse process (processus transversus); 6 – transverse costal facet (fovea costalis processus transversi); 7 – spinous process (processus spinosus); 8 – inferior articular process (processus articularis inferior); 9 – inferior vertebral notch (incisura vertebralis inferior); 10 – inferior costal demi-facet (fovea costalis inferior)

b – superior aspect: 1 – spinous process (processus spinosus); 2 – vertebral arch (arcus vertebrae); 3 – pedicles of vertebral arch (pediculi arcus vertebrae); 4 – superior costal demi-facet (fovea costalis superior); 5 – superior articular process (processus articularis superior); 6 – transverse costal facet (fovea costalis processus transversi); 7 – transverse process (processus transversus)

2.2. Cervical Vertebrae

The cervical vertebrae, vertebrae cervicales (C

– C

), form the upper (cervical) part of the vertebral column. Two upper cervical vertebrae of seven significantly differ from other ones, therefore, they are termed atypical vertebrae. We will study them later. The other five vertebrae are structured according to the general principle: their bodies are relatively small, have an ellipsoid form, the vertebral foramen is large and triangular.

The distinctive feature of all cervical vertebrae is the presence of transverse foramina, foramen transversarium, in the transverse processes. They are formed as a result of the fusion of the transverse processes and the rudiments of the cervical ribs. The vertebral artery and vein pass through these foramina.

The groove for spinal nerve, sulcus nervi spinalis, passes along the superior surface of the transverse prosesses of the III–VII cervical vertebrae. These processes end with two tubercles – anterior and posterior, tuberculum anterius et tuberculum posterius. The anterior tubercle of the VI vertebra is more developed than the anterior tubercles of other cervical vertebrae. It is termed carotid tubercle, tuberculum caroticum, because the carotid artery can be compressed to it during hemorrhage.

The spinous processes are short and directed downwards, and their ends are bifurcated. The spinous process of the VII cervical vertebra is the longest, and its end is thickened. This vertebra is called prominent, vertebra prominens, because the apex of its spinous process is clearly palpated in a living person.

The articular processes of the cervical vertebrae are short and located obliquely between the frontal and horizontal planes. Meanwhile, the superior articular processes are directed backwards and slightly upwards, the inferior articular processes are directed forwards and slightly downwards (fig. 2.2).

Fig. 2.2. Typical cervical vertebra (superior aspect):

1 – vertebral body (corpus vertebrae); 2 – transverse process (processus transversus); 3 – superior articular process (processus articularis superior); 4 – spinous process (processus spinosus); 5 – transverse foramen (foramen transversarium)

The shape of the first two cervical vertebrae is influenced by their close location to the skull. They are involved in head turning. Therefore, they are termed «rotational vertebrae».

The I cervical vertebra is called the atlas, atlas (C

). It differs from the general structure of individual vertebrae: it has no body no notches and no spinous or articular processes (fig. 2.3).

The atlas has an anterior arch, arcus anterior atlantis, instead of the body. Its anterior surface has an anterior tubercle, tuberculum anterius; on its posterior surface there is a small articular facet, fovea dentis, with which the II cervical vertebra is joined.

The lateral masses of atlas, massae laterales atlantis, are located on the both sides. Each of them bears an ellipsoid, concave superior articular surface, facies articularis superioris, joining with the corresponding occipital condyle. The inferior articular surfaces, facies articulares inferiores, form round, slightly concave articulate areas connected with the II cervical vertebra.

Fig. 2.3. I cervical vertebra (atlas) (superior aspect):

1 – anterior arch of atlas (arcus anterior atlantis); 2 – lateral mass (massa lateralis); 3 – transverse foramen (foramen transversarium); 4 – transverse process (processus transversus); 5 – groove for vertebral artery (sulcus arteriae vertebralis); 6 – posterior arch of atlas (arcus posterior atlantis); 7 – posterior tubercle (tuberculum posterius); 8 – superior articular surface (facies articulars superior); 9 – anterior tubercle (tuberculum anterius); 10 – facet for dens (fovea dentis)

The posterior arch of the atlas, arcus posterior atlantis, corresponds to the arch of a typical vertebra. There is a reduced spinous process in the form of a small posterior tubercle, tuberculum posterius, on the back surface of the posterior arch. The groove for vertebral artery, sulcus arteriae vertebralis, passes on the superior surface of the posterior arch behind the lateral mass.

The vertebral foramen, foramen vertebrale, is bounded with arches and lateral masses. It is much larger than the vertebral foramina of other vertebrae, and only its posterior part corresponds to them. In its anterior part narrowed on the sides with the lateral masses, the dens of the II cervical vertebra is located. The transverse process, рrocessus transversus, is perforated by the transverse foramen, foramen transversarium, for the passage of blood vessels like transverse processes of the other cervical vertebrae. The ends of the transverse processes are slightly thickened. They have no anterior and posterior tubercles and no the groove for spinal nerve.

Fig. 2.4. II cervical vertebra (axis) (posterior aspect):

1 – dens (dens); 2 – superior articular facet (facies articularis superioris); 3 – spinous process (processus spinosus); 4 – transverse process (processus transversus); 5 – transverse foramen (foramen transversarium)

The II cervical vertebra is termed the axis, axis (C

). Its distinctive feature is the presence of a dental process or dens, dens axis, projecting vertically from the superior surface of its body. The dens is the body of the atlas relocated during the development (fig. 2.4).

The dens plays the role of a pivot, around which the atlas together with the skull rotates to the right and to the left.

The dens of the II cervical vertebra is cylindrical, it has an apex, apex dentis, and articular facets on its anterior and posterior sides. The anterior articular facet, facies articularis anterior, articulates with fovea dentis of the anterior arch of the atlas; the posterior articular facet, facies articularis posterior, joins with the transverse ligament of the atlas. The axis has no superior articular processes. Instead of them there are slightly convex superior articular facets, facies articulares superiores, are on the sides of the dens. These facets articulate with the inferior articular surfaces on the lateral masses of the atlas. The ends of the transverse processes of the axis are slightly thickened like the ends of the I vertebra; there is the foramen transversarium at the base of each transverse process. The groove for spinal nerve is absent.

2.3. Thoracic Vertebrae

The thoracic vertebrae, vertebrae thoracicae (Th

– Th

), are much bigger than the cervical vertebrae (fig. 2.1). The height and transverse size of the thoracic vertebrae bodies gradually increase from the I to XII vertebra. The distinctive feature of the thoracic vertebrae is the presence of the articular facets or demi-facets for articulation with ribs. These facets are located on the lateral sides of the bodies and on the transverse processes.

Most vertebrae have two demi-facets. They are directly in front of the pedicle of the vertebral arch: one – at superior edge, the other – at inferior edge. They are called the superior costal facet and inferior costal facet, respectively, fovea costalis superior et fovea costalis inferior. Each such facet (demi-facet to be more precise) of one vertebra, together with the nearest demi-facet of the adjacent vertebra, form an articular area for articulation with the head of the rib. An exception is the I vertebra: it has a complete facet to articulate with the I rib, and a demi-facet to articulate with the II rib. The X vertebra has only the superior demi-facet for articulation with the X rib. The XI and XII vertebrae have one complete facet for articulation with the corresponding ribs.

The articular processes of the thoracic vertebrae are located in the frontal plane. The articular surfaces of superior articular processes are directed backwards, the articular surfaces of the inferior articular processes are directed forwards. The transverse processes are directed laterally and backwards; their length increases from the I to the IX vertebra but then they become shorter. The ends of the transverse processes are thickened. They have a transverse costal facet, fovea costalis processus transversi, for articulation with the tubercle of the rib. The XI and XII vertebrae do not have such facet.

The spinous processes of the thoracic vertebrae are longer than the spinous processes of the cervical vertebrae; they are tilted downwards and lie on each other like tiles.

2.4. Lumbar Vertebrae

The distinctive feature of the lumbar vertebra, vertebrae lumbales (L

– L

), is a beanshaped massive body. The transverse size of the body is wider than the anteroposterior size. The height and width of the body gradually increases from the I to the V vertebrae. The vertebral foramen is large and triangular with rounded angles. The articular processes are well developed, their articular surfaces are located in the sagittal plane: the articular surfaces of the superior processes are directed medially, the articular surfaces of the inferior processes are directed laterally (fig. 2.5).

The superior articular process may have a rudimental tubercle named mammillary process, processus mamillaris. The lumbar vertebra`s transverse processes are formed by fusion of rudimental ribs with the transverse processes of the vertebra. They are located in the frontal plane, their ends are tilted backwards. Often the accessory process, processus accessorius, may be present at the base of the transverse process. The spinous processes are short and flat, their ends are thickened; they are located almost at the same level with the vertebral body and directed backwards.

Fig. 2.5. Lumbar vertebra (lateral aspect):

1 – vertebral body (corpus vertebrae); 2 – superior articular process (processus articularis superior); 3 – spinous process (processus spinosus); 4 – inferior articular process (processus articularis inferior); 5 – transverse process (processus transversus)

2.5. Sacrum

The sacrum, os sacrum (S