X-ray anatomy of the skeleton

The skeleton passes a complex path of development. It begins with the formation of a connective tissue skeleton. From the second month of intrauterine life, the latter is gradually transformed into a cartilaginous skeleton (only the cranial vault, the bones of the facial skull and the body of the clavicles do not pass the cartilaginous stage). Then a prolonged transition from the cartilaginous to the bone skeleton takes place, which ends on average to 25 years. The process of ossification of the skeleton is well documented with the aid of radiographs.

The newborn at the ends of most bones does not yet have ossification nuclei and they consist of cartilage, so the epiphyses are not visible on the radiographs and the radiographic joint slits appear unusually wide. In subsequent years, ossification points appear in all epiphyses and apophyses. The fusion of epiphyses with metaphyses and apophyses with diaphysis (the so-called synostosis) occurs in a certain chronological order and, as a rule, is relatively symmetrical on both sides.

Analysis of the formation of centers of ossification and the timing of synostosis is of great importance in radiodiagnosis. The process of osteogenesis for one reason or another may be disrupted, and then there are congenital or acquired anomalies in the development of the whole skeleton, separate anatomical regions or a single bone.

With the help of radial methods, various forms of ossification of the skeleton can be detected: the asymmetry of the appearance of the points of ossification.

Among the whole variety of bones (in humans there are more than 200), it is customary to select tubular (long: humerus, forearm bones, thighbone of the lower leg, short: clavicles, phalanges, bones of the pastern and metatarsus) spongy (long: ribs, sternum, short: vertebrae, wrist bones , metatarsus and metatarsus), flat (skull bones, pelvis, shoulder blades) and mixed (skull base) bones.

The position, shape and magnitude of all bones are clearly reflected in the radiographs. Since x-ray radiation is absorbed mainly by mineral salts, the images show predominantly dense parts of the bone, i. E. Bone beams and trabeculae. Soft tissue - the periosteum, endoste, bone marrow, vessels and nerves, cartilage, synovial fluid - under physiological conditions do not give a structural X-ray image, as well as the surrounding bone of fascia and muscle. In part, all these formations are distinguished on sonograms, computer and especially magnetic resonance tomograms.

Bony beams of a spongy substance consist of a large number of closely adhering bone plates that form a dense network resembling a sponge, which was the reason for the name of this type of bone structure - spongy. In the cortical layer the bone plates are very dense. Metaphyseal and epiphyses consist mainly of spongy substance. It gives on the roentgenogram a special bone pattern composed of interlaced bone beams. These bony beams and trabeculae are arranged in the form of curved plates connected by transverse bars, or they have the form of tubes forming a cellular structure. The ratio of bone beams and trabeculae with bone marrow spaces determines the bone structure. It, on the one hand, is due to genetic factors, and on the other - throughout the life of a person depends on the nature of the functional load and is largely determined by the conditions of life, work, sports loads. Radiographs of tubular bones differ in diaphysis, metaphysis, epiphyses and apophyses. Diaphysis is the body of the bone. In it, along the entire length, the medullary canal is allocated. It is surrounded by a compact bone substance, which causes an intense uniform shadow along the edges of the bone - its cortical layer, which gradually becomes thinner towards the metaphyses. The outer contour of the cortical layer is sharp and distinct, and it is uneven at the points of attachment of the ligaments and tendons of the muscles.

The apophysis is the projection of the bone near the epiphysis, which has an independent nucleus of ossification; it serves as a place for the beginning or attachment of muscles. The articular cartilage on the radiographs does not give a shadow. As a consequence, between epiphyses, i.e. Between the joint head of one bone and the joint cavity of another bone, a bright band called the x-ray joint gap is determined.

The x-ray image of flat bones differs significantly from the pattern of long and short tubular bones. In the cranial vault, the spongy substance (diploid layer) is well differentiated, bordered by thin and dense outer and inner plates. In the bones of the pelvis, the structure of the spongy substance, covered at the edges with a fairly pronounced cortical layer, is distinguished. Mixed bones in the X-ray image have a different shape, which can be properly evaluated by producing images in different projections.

A feature of CT is the image of bones and joints in the axial projection. In addition, computer tomograms reflect not only bones, but also soft tissues; one can judge the position, volume and density of muscles, tendons, ligaments, the presence of pus accumulation in the soft tissues, tumor growths, etc.

An extremely effective method of studying the muscles and ligament apparatus of the limbs is sonography. Torn tendons, lesions of their cuffs, effusion in the joint, proliferative changes in the synovial membrane and synovial cysts, abscesses and hematomas in soft tissues - this is far from a complete list of pathological conditions detected by ultrasound.

Especially it is necessary to stop on radionuclide visualization of the skeleton. It is performed by intravenous introduction of technetium-labeled phosphate compounds (99mTc-pyrophosphate, 99mTc-diphosphonate, etc.). The intensity and rate of inclusion of RFP in bone tissue depend on two main factors - the magnitude of blood flow and the intensity of metabolic processes in the bone. Both increase and decrease in blood circulation and metabolism inevitably affect the level of inclusion of RFP in bone tissue, and therefore find their reflection on scintigrams.

If a vascular component is to be examined, a three-step procedure is used. At the 1-st minute after intravenous injection of RFP in the computer memory register the phase of arterial blood circulation, from the 2nd to the 4th minute follows the dynamic series of the "blood pool". This is the phase of general vascularization. After 3 hours, a scintigram is produced, which is a "metabolic" image of the skeleton.

In a healthy person, the RFP is relatively evenly and symmetrically accumulated in the skeleton. Its concentration is higher in the areas of bone growth and the area of articular surfaces. In addition, the scintigram shows a shadow of the kidneys and bladder, since about 50% of the RFP is excreted at the same time through the urinary tract. Reduction in the concentration of RFP in the bones is observed in abnormalities of skeletal development and metabolic disorders. Separate areas of weak accumulation ("cold" foci) are found in the area of bone infarcts and aseptic necrosis of bone tissue.

Local increase in concentration of RFP in the bone ("hot" foci) is observed in a number of pathological processes - fractures, osteomyelitis, arthritis, tumors, but without the history and clinical picture of the disease, it is usually impossible to decipher the nature of the "hot" focus. Thus, the technique of osteoscintigraphy is characterized by high sensitivity, but low specificity.

In conclusion, it should be noted that in recent years, radiotherapy has been widely used as an integral part of intervention interventions. These include biopsy of bones and joints, including biopsy of intervertebral discs, iliac sac, peripheral bones, synovial membranes, and periarticular soft tissues, as well as injections of medications into joints, bone cysts, hemangiomas, aspiration of lime deposits from mucosal bags, vascular embolization with primary and metastatic bone tumors.