Development and age-related features of bone connections in ontogenesis

In lower vertebrates (living in water), parts of the skeleton are connected by continuous joints (by means of fibrous, cartilaginous or bone tissue). These connections are inactive or immobile. With access to land, movements become more complicated. Therefore, they provide greater mobility of the bone levers and enable the animals to make movements with a large scope and variety necessary for movement on land. Along with the joints, transitional forms of the joints (symphysis, or semi-joints) are also formed.

In man in embryogenesis, all the compounds are initially formed as continuous. Later, the mesenchymal layer between the bones is gradually replaced by a fibrous or cartilaginous tissue. Joints (synovial joints) are formed from 6-11 weeks of embryogenesis. Cracks are formed in mesenchymal interlayers. A joint capsule and ligaments form from the surrounding joint of the mesenchyme. The deep layer of the capsule is transformed into a synovial membrane. In the zones of the knee, temporomandibular and other complex joints, there are two joint cracks. The mesenchyme between the ends of the articulating bones becomes an intraarticular disc or menisci. The cartilaginous articular lip is formed from the intraarticular cartilage. The center of this cartilage dissolves, and the peripheral part grows to the edges of the articular surface of the bone. In the formation of symphisms from the mesenchymal layer between the articulating bones formed cartilage, and in its thickness - a narrow slit.

In newborns, all the anatomical elements of the joints are basically formed. However, their differentiation continues. Epiphyses of connecting bones at this age are represented by cartilage. At 6-10 years of age, the structure of the synovial membrane becomes more complicated, the number of villi, folds increases, vascular networks and nerve endings in the synovial membrane are formed. There is a collagenization of the joint capsule. At this time, the capsule and ligaments thicken, their strength increases. The formation of all the joint elements ends at the age of 13-16 years. With the optimal functional load for many years, joints do not experience obvious involutive changes. With prolonged excessive physical exertion, as well as with age, structural and functional changes in the joints are observed. This can be a thinning of the articular cartilage, sclerosis of the joint capsule, ligaments, the formation of osteophytes (bony outgrowths) on the edges of the articular surfaces. A common sign of these changes is a decrease in mobility in the joints.

Aging joints is associated with the type of build. In the brachymorph type of constitution, the aging rate of the hand, foot, large joints (humerus, elbow, etc.) is usually somewhat more intense than in humans of the dolichomorph type of build. The aging of the joint ends of most bones in women compared with men is also accelerated.

Involutive changes occur in some sequence. Most often, according to the timing and activity of the onset of such changes, the knee, hip joints and connections of the lumbar spine, sacroiliac joint are in first place. These joints have a significant load when standing, walking, which speeds up their "wear and tear". Further on the frequency of the onset is often followed by changes in the joints of the cervical spine, joints of the upper limb.

[1], [2], [3], [4], [5], [6]