The study of morphological regularities of the development of the sacral
and coccygeal parts of the spine is necessary in order to understand correctly the
nature of the complicated processes, occuring during antenatal life.
Injury of the sacral and coccygeal parts of the spine is one of the most
complicated problems of modern orthopedics and traumatology. The duration and
complicacy of the treatment, disability, high level of disability result in significant
economic expenses, that determines the medical and social significance of the
problem.
Complex of morphological research methods was used, namely:
macroscopy, microscopy of series of the consecutive histological and
topographic-anatomical sections, ordinary and thin preparation, graphic and
plastic reconstruction, vascular injections followed by radiography, morphometry
(digital computer histometry), statistical processing of digital data. All digital
indices obtained were processed by methods of variation statistics, that confirms
the reliability of the data concerning specific features of the qualitative
characteristics of the sacral and coccygeal vertebrae bone tissue in the dynamics
of prenatal ontogenesis and has important significance for prenatal diagnostics,
forensic practice, especially for monitoring fetal development in health and early
screening of malformations. The use of such methods made it possible to trace
and objectively assess the topographic and anatomical features of the spine during
the prenatal period of human ontogenesis.
The chronological sequence of the development and formation of
topography of the structures of the sacral and coccygeal parts of the spine in the
early period of human ontogenesis has been established. The topographic and
anatomical features of the relationships of the structures of the sacral and
coccygeal parts of the spine from the moment of their anlage till birth, the
dynamics of their formation and growth, taking into account the morphogenesis
of the adjacent structures have been defined. Investigation of morphogenesis and
spatial-hours relationships of the sacral and coccygeal parts of the human spine,
their joining during intrauterine period of the development and in newborns from
the point of view of topographic and anatomical approach to embryogenesis
problems has been fulfilled by means of adequate morphological methods.
Features of the blood supply and venous outflow of the spine have been clarified.
Critical periods, morphological preconditions and time of possible origin of some
congenital defects of the spine have been established. On the base of the results
obtained, the task of the prenatal diagnostics of congenital malformations of the
sacral and coccygeal parts of the spine was solved.
The source of cartilage and bone formation is the mesenchyme. In the
early stages of development, the entire skeleton of the embryo consists of
mesenchymal rudiments, which only in shape remotely resemble the outlines of
future bones. Henceforth, this mesenchyme is either directly transformed into
bone tissue, or pre-replaced by hyaline cartilage, in place of which the bone
develops. By the end of the embryonic period, in 13,0 mm embryos PCL sacral and
coccygeal vertebrae are on the connective tissue stage, the bodies of the sacral
and coccygeal vertebrae are differentiated by rudiments of intervertebral discs
and along them passes to the coccygeal part of chord, which is the supporting
base for sacral and coccygeal vertebrae. In 15,0 mm preterm infants PCL the
number of sacral and coccygeal vertebrae may exceed compared to the definitive
condition. In 15.0 mm preterm infants PCL body of the sacral vertebrae are of
quadrangular form with rounded edges 34±0.8 μm in size. In the preterm of 16,0 mm PCL the body of 1 sacral vertebra, from which the legs and vertebral arches move away, surrounding the rudiment of the spinal
cord, was formed. The sacroiliac joint is in a continuous joining. In preterm
infants 17.0 mm PCL sacral and coccygeal part of the spine is bent relative to the
lumbar and thoracic part at an obtuse angle of 130º. Behind there is the spinal
cord which runs till the last coccygeal vertebrae.
On the sagittal section of the prefetus 20,0 mm PCL (7th week) all parts
of the spine are determined, which have in this period 38 vertebral rudiments,
compared with the embryonic period, where anlage of 43-44 pairs of somites was
marked. As a result of absorption of 5-6 somites at the beginning of the prefetal
period, 38 vertebral rudiments were observed. In the cervical region 7 vertebrae
are formed, in the thoracic - 13, 5 lumbar and 13 sacrococcygeal.
In the prefetus 25,0 mm PCL sacral vertebrae, active processes of the
sacrococcygeal plexus formation take place. In preterm infants, the connective
tissue stage of the sacral and coccygeal vertebrae formation is completed by the
end of 8 weeks. The chord at this stage is quite well developed and passes through
the vertebral bodies till the coccygeal spine.
