bone growth stops.
In long tubular bones, individual ossification centres appear in each epiphysis. Fusion of the epiphyses with the diaphysis usually occurs after birth. For example, in the tibia, the lower epiphysis merges with the diaphysis by the age of about 22 years, and the upper epiphysis – by 24 years. Short tubular bones normally have the ossification centre only in one epiphysis, the other epiphysis is ossified from the diaphysis. Some tubular bones have several ossification centres in their epiphysis at the same time. For example, in the upper epiphysis of the humerus, three centers appear; in the lower epiphysis of the humerus – there are four centers.
Volumetric bones are ossified like the epiphyses of long tubular bones i.e. enchondral ossification precedes periostal ossification. In flat bones, this process occurs vice versa, i.e. periostal ossification precedes ehchondral ossification.
It should be noted that, besides the main ossification centres, additional ossification centres may exist. They appear much later than the main centres. With the coming puberty, metaepiphysial cartilages become thinner and are replaced with osseous tissue. In the skeleton, synostoses start to develop. The distal epiphysis of the humerus and the epiphyses of the metacarpals are the first to fuse with their diaphyses. Formation of the synostoses comes to an end by about 24–25 years. Bone growth terminates when all the main and additional centers merge into one solid mass, i.e. when the cartilaginous layers separating the bone parts from each other disappear.
Significant individual differences in ossification rates are observed. The process of skeleton ossification in a child may be accelerated or decelerated; it depends on the genetic, hormonal and environmental factors. The term «osteal age» is used to assess the process of skeleton development in children. It is determined according to the number of ossification centres in bones and according to the time of their fusion. To evaluate ossification, roentgenography of the hand is made, because the age dynamics of ossification centre appearance and formation of synostosis are very clearly manifested in this part of the body. Ossification centres in carpal bones appear in the following periods:
– at birth, carpal bones are cartilaginous;
– ossification points emerge in the capitate and hamate bones during the first year of life;
– in the triquetral bone – during the third year of life;
– in the lunate bone – during the fourth year of life;
– in the scaphoid bone – during the fifth year of life;
– in the trapezium and trapezoid bones – during the sixth-seventh years of life;
– in the pisiform bone – in the tenth-fourteenth years of life.
Ossifcation of free parts of limbs is given in fig. 1.5.
V.S. Speransky distinguishes the following characteristic features in the ossification process:
1) ossification starts earlier in the connective tissue than in the cartilage;
2) ossification of the skeleton occurs in the cranial-caudal direction;
3) skull ossification spreads from the viscerocranium to the neurocranium;
4) in the free parts of extremities, ossification occurs from the proximal regions to the distal areas.
Fig. 1.5. Periods of ossification of free parts of limbs in male (Alexina L.A., 1985, 1998)
Osteal age does not always coincide with the passport age. In some children, the ossification process terminates 1–2 years earlier than it happens normally, in others – 1–2 years later. Starting from the age of 9 years, sexual differences of ossification can be distinguished clearly – in girls this process occurs more rapidly.
Body growth in girls terminates mainly at the age of about 16–17 years, in boys – at about 17–18 years. After this age, body growth in length is no more than 2 %.
In old age, bone rarefication termed osteoporosis occurs in different parts of the skeleton. In tubular bones, osseous tissue dissolves inside the diaphysis, as a result, the medullary cavity becomes wider.
At the same time, calcium salts are accumulated, and osseous tissue is developed on the outer surface of the bone, under the periosteum. Quite often, in places of attachment of ligaments and tendons, bony outgrowths called osteophytes develop. They also emerge along the edges of articular surfaces. In elderly persons, bone durability considerably decreases, and even minor injuries may cause fractures.
Skeleton ageing is characterized by individual changeability. In some persons, ageing symptoms appear as early as at the age of 35–40 years, in other persons – only after 70. Skeleton ageing symptoms are more manifested in women than in men. But this process significantly depends on the complex of factors: genetic, climatic, hormonal, alimentary (nutritive), functional, ecological etc.
1.9. Anomalies of Bone Development
1. Osteomalacia – disorder of calcification of newly formed osseous tissue which is caused by deficiency in calcium or vitamin D.
2. Osteoporosis – disorder of formation of the bony matrix during the skeleton formation (insufficient compensation of resorbed bone tissue). It occurs in elderly and old age and is caused by exessive resorption of osseous tissue.
3. Ectopic osteogenesis – ossification of soft tissues in abnormal places (in walls of arteries, kidneys etc.)
TEST QUESTIONS
1. What function does the skeleton carry out?
2. Name the types and functions of the bone marrow.
3. List the principles of the bone classification.
4. Give the characteristic of the primary and secondary bones.
5. What organic and inorganic substances are included into the composition of the bone (in what ratio)?
6. What connective tissue structure covers the bone from outside? What is its function?
7. What is the structural unit of osseous tissue? Name the types of osteocytes.
CLINICOANATOMICAL PROBLEM
During the surgical operation in a 10-year-old patient the metaepiphysial cartilage which separates the head of humerus from the body of humerus, was radically removed. What is the prognosis?
2. SKELETON OF TRUNK
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,
