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

– S

), consists of five sacral vertebrae, vertebrae sacrales, which fuse to form a single bone in adults. Two parts and two surfaces are distinguished in the sacrum: the upper wide part, which is the base of the sacrum, basis ossis sacri; the lower part, which is the apex of the sacrum, apex ossis sacri; the anterior (concave) surface, which is the pelvic surface, facies pelviсa; the posterior surface (convex, rough), which is the dorsal surface, facies dorsalis (fig. 2.6).

Fig. 2.6. Sacrum and coccyx:

a – anterior aspect: 1 – anterior sacral foramina (foramina sacralia anteriora); 2 – transverse lines (lineae transversae)

b – posterior aspect: 3 – coccygeal horn (cornu coccygeum); 4 – sacral horn (cornu sacrale); 5 – median sacral crest (crista sacralis mediana); 6 – auricular surface (facies auricularis); 7 – lateral sacral crest (crista sacralis lateralis); 8 – sacral tuberosity (tuberositas ossis sacri); 9 – posterior sacral foramina (foramina sacralia posteriora); 10 – intermediate sacral crest (crista sacralis intermedia); 11 – sacral hiatus (hiatus sacralis)

Fig. 2.7.Sagittal section of sacrum:

1 – sacral canal (canalis sacralis), 2 – base of sacrum (basis ossis sacri); 3 – sacral horn (cornu sacrale)

Fig. 2.8. Horizontal section of sacrum:

1 – posterior sacral foramen (foramen sacrale posterius); 2 – sacral canal (canalis sacralis); 3 – median sacral crest (crista sacralis mediana); 4 – intervertebral foramen (foramen intervertebrale)

The superior articular processes, processus articulares superiores, project from the base of the sacrum; they articulate with the inferior articular processes of the V lumbar vertebra. The place of the junction of the sacrum with the body of the V lumbar vertebra bulges forwards, and is known as the sacral promontory, promontorium.

Four transverse lines, lineae transversae, running horizontally, are visible on the pelvic surface of the sacrum. They are the traces of the fusion of the sacral vertebral bodies. The anterior sacral foramina, foramina sacralia anteriora, open on the right and left ends of these lines.

There are five longitudinal crests on the dorsal surface of the sacrum. The unpaired median sacral crest, crista sacralis mediana, is formed by the fusion of the spinous processes. There is the paired intermediate sacral crest, crista sacralis intermedia, on each side of it. The intermediate sacral crest represents fused articular processes of the sacral vertebrae. There are the posterior intermediate foramina, foramina sacralia posteriora, near the intermediate crests. The paired lateral sacral crest, crista sacralis lateralis, lies laterally to these foramina. It is the trace of the fusion of the transverse processes and rudimental ribs. The paired lateral parts, partes laterales, with the auricular surfaces, facies auriculares, are located outside the posterior sacral foramina. They articulate with the auricular surfaces of the pelvic bone. There is the sacral tuberosity, tuberositas ossis sacri, behind the auricular surfaces. It is connected by ligaments with the tuberosity of the pelvic bone. In the process of the fusion of the sacral vertebrae into a single bone, the vertebral foramina form the sacral canal, canalis caralis (fig. 2.7). It terminates with the sacral hiatus, hiatus sacralis. The sacral horns, cornua sacralia, are on both sides of the hiatus. They are rudiments of the inferior articular processes. The anterior and posterior sacral foramina are connected with the sacral canal by the intervertebral foramina, foramina intervertebralia (fig. 2.8).

2.6. Coccyx

The coccyx, os coccygis (Co

– Co

), consists of 3–5 rudimental vertebrae in adults. Only the I vertebra has rudiments of superior articular processes named coccygeal horns, cornua coccygea, besides the body. The coccygeal horns are connected with the sacral horns by ligaments. The I vertebra also has lateral projections which are rudiments of transverse processes. The other vertebrae are round-shaped and small, they have no arch and no processes.

2.7. Anomalies and Developmental Defects of Vertebrae

Anomalies and developmental defects may be classified according to the following criteria:

I. Vertebral size anomalies:

1. Microspondylia – reduction in size of one or more vertebrae.

2. Brachyspondylia – reduction in width of one or more vertebrae.

3. Platyspondylia – flattening of some vertebrae which get a truncated cone shape.

4. Macrospondylia – increase in size of some vertebrae.

II. Slit-like Defects of Vertebrae:

1. Splitting of vertebral bodies (anterior splitspine, spina bifida anterior) – a slit-like defect of the vertebral body located more often in the sagittal plane.

2. Splitting of the vertebral arch (posterior split spine, spina bifida posterior) – a slit-like defect of the vertebral arch (near a spinous process or on its place).

3. Spondylolysis – in this case, the vertebral body is not fused with the pedicles of the vertebral arch: this anomaly may be observed either on one or on both sides, it happens most often in the V lumbar vertebra or in the I sacral vertebra; in case of bilateral spondylolysis, the posterior part of the arch with the inferior articular processes are separated from the pedicles of the arch with the superior articular processes.

4. Spondylolisthesis – displacement of the body of the upper vertebra frontwards (very seldom – backwards relative to the lower vertebra. Most often it occurs after compressive fracture of a vertebral body when the vertebra becomes wedge-shaped.

5. Rachischisis – in this case the vertebral body is not fused with the pedicles of the vertebral arch, and the vertebral arch is splitted.

III. Development anomalies of individual vertebrae:

1. Assimilation of the atlas:

– atlanto-occipital assimilation (occipitalization) – partial or complete fusion of the I cervical vertebra with the occipital bone: two-sided (symmetric) or one-sided (asymmetric);

– atlantoaxial assimilation – partial or complete fusion of the I and II vertebrae.

2. Manifestation of the atlas (formation of the occipital vertebra – proatlas) –inclusion of the atlas particles into the occipital bone which is manifested in the presence of anomalous bony prominences in the circle of the great (occipital) foramen.

3. Kimmerle`s anomaly – transformation of the vertebral artery groove on the atlas into the canal as a result of formation of a bony outgrowth above this groove.

4. Development anomalies of the II cervical vertebra:

– agenesia (absence) of the dens;

– the dens and the body of the II cervical vertebra are not fused together.

5. Thoracolisation of the cervical vertebrae – formation of cervical ribs (most often from the VII cervical vertebra).

6. Sacralisation – fusion of the V lumbar vertebra with the I sacral vertebra: there are 4 vertebrae in the lumbar part of the vertebral column; the sacrum consists of 6 vertebrae.

7. Lumbarisation – the I sacral vertebra and the II sacral vertebra are not fused together: there are 6 vertebrae in the lumbar part of the vertebral column; the sacrum consists of 4 vertebrae.