At the fracture site, two opposite processes occur simultaneously: on the one hand, the death of destroyed tissues, and on the other, the proliferation of young cells and tissues. Dead tissues undergo sterile decay and are resorbed by phagocytosis. The decay products of necrotic tissues, especially the periosteum, stimulate the regeneration of bone tissue and are, to one degree or another, the material for building future bone tissue.

Already in the first days after the fracture, along with the resorption of the hematoma, a complex proliferative process begins with the gradual development of first connective tissue provisional callus, and subsequently, by the end of the 1st week, osteoid tissue. The latter, by metaplasia, turns either directly into bone tissue (primary healing of a bone wound), or first into cartilage, and then into bone (secondary healing of a bone wound). The development of primary callus occurs the faster and more perfectly, the more accurately the fragments are compared and the more firmly they are fixed.

Pathological anatomy of bone tissue regeneration. Regeneration of bone tissue occurs after a violation of the integrity of the bone in trauma, inflammatory processes, surgical interventions (resection, bone grafting). During regeneration, a callus of various sizes and shapes is formed, which depends on the location and nature of the damage. As a rule, the size of the callus exceeds the size of the lost part of the bone. The callus arises from the cambial osteogenic elements of the periosteum, bone marrow, and sometimes paraosseous tissues. With appropriate localization of damage, regeneration can take part and growth cartilage epiphysis.

The development of corn occurs according to the general patterns of regeneration (see). In case of damage to the diaphysis, the periosteum is mainly involved in regeneration, in case of violation of the integrity of the epiphyses and spongy bones - the endosteum. In the periosteum, an embryonic tissue rich in cells and vessels, resembling granulation tissue, is first formed. Then bone beams or islands of cartilage are differentiated in it, which are also later replaced. bone structures. In spongy bones, regeneration begins with the proliferation of endosteal elements with the formation of osteogenic cellular fibrous tissue, which displaces the bone marrow. Then bone beams differentiate in this tissue, bypassing the stage of cartilaginous tissue.

The complexes of bone beams that initially arise are located regardless of the conditions of the functional load on the bone. They are built from functionally defective coarse bone tissue (see). Only in the future, undergoing restructuring, this bone tissue is replaced by functionally complete lamellar bone tissue, and at the same time, the beams receive an arrangement corresponding to the functional and anatomical features of this area of ​​the bone. In the course of regeneration, the entire damaged bone, and sometimes other bones, are restructured to one degree or another, which is associated with changes in the functional load and neurohumoral regulation metabolism.

In addition to direct mechanical loss of part of the bone, the defect can also occur as a result of some dystrophic diseases (for example, such as spontaneous bone resorption). In such cases, bone restoration in such cases resembles the formation of a callus with the appearance of an initially defective bone, which later, in the process of restructuring, is replaced by mature bone tissue.

The course and course of bone reparative processes is influenced by many factors - alimentary, endocrine, neurogenic, as well as external conditions, properties of the affected bone, etc. Slowing down of callus formation was noted in patients with beriberi (scurvy, rickets, osteomalacia in pregnant women), with hyperfunction of the adrenal glands, pathological conditions head or spinal cord(tumors, hemorrhages with paralysis, syringomyelia, disseminated sclerosis, spinal cord injuries), severe concomitant injuries and multiple bone fractures, damage to peripheral nerves, etc. Corn formation slows down due to advanced age, general nutritional decline, metabolic disorders, tuberculosis, syphilis, and especially in radiation sickness, especially if it is caused by isotopes that can be deposited in bone tissue (Sr90, etc.). But most main reason delayed union of the fracture is an inferior immobilization of fragments.

Pronounced clinical union of fractures of various bones of the skeleton occurs in various terms: bones of the phalanges - 2.5 weeks; metacarpal, metatarsal bones, rib - 3 weeks; clavicle - 3.5-4 weeks; bones of the forearm, ankle - 7-8 weeks; shoulder diaphysis - 6-7 weeks; diaphysis tibia, shoulder neck - 8-9 weeks; both bones of the lower leg - 10 weeks; hip diaphysis - 10-12 weeks; femoral neck - 6 months; vertebrae - 16-18 weeks; pelvis - 10 weeks These terms should be considered conditional, since even after a clinically pronounced fracture union, significant changes (transformation) in volume, shape, structure, elasticity, and density occur in the callus. The former density and elasticity of the bone are restored after 1 year, and plasticity - after 2 years. By this time, with a good comparison of bone fragments and the normal course of the reparative process, the fracture site becomes almost invisible even when cutting the bone. In case of improper union of the fracture due to unrepaired displacement of fragments, thickening of the bone, curvature, shortening and significant deformation of it is observed (Fig. 9).

Rice. 9. Formed callus in case of improperly healed fracture of the femur.

Healing of open fractures proceeds in different ways. During aseptic healing of a soft tissue wound by primary intention, the bone grows together, as in closed fracture. With the development of a wound infection purulent process affects not only the soft tissues of the wound, but also the bones (see Osteomyelitis.). Fracture healing is often combined with sequestration of non-viable parts of the bone. The development of the callus is slow, uneven, unstable. In some cases, repeated fractures (refractory) can easily occur.

Diagnosis. In the diagnosis of bone injury, the anamnesis is of great importance. Information about the mechanism, the circumstances of the injury helps to suspect the likelihood of a fracture of one or another bone. To establish a clinical diagnosis, however, a number of visual and palpatory clinical signs Visual signs include a change in the position of the limb (for example, rotation of the limb outward with a fracture of the femoral neck), a violation of the shape and length of the limb, disorders of active movements. Palpatory signs include pathological mobility, tenderness, and bone crepitus. In some cases, auscultatory signs may also be important - a violation of sound conduction along the length of the bone.

Clinical diagnostic methods in each case should be combined with X-ray examination, which allows, first of all, to confirm the correctness of the clinical diagnosis, to clarify the nature, features and localization of the fracture, the direction and nature of the displacement of bone fragments, the presence of complicating factors, such as dislocations, subluxations, etc. Some types of fractures (cracks, fractures, fractures of small bones of the wrist, etc.) are generally recognized only radiographically. X-ray data are of great importance in the provision of first aid and fracture reposition when choosing one or another method of its treatment.

How does the process of fracture healing proceed in the X-ray image? As you know, the reparative process is carried out with the help of the so-called callus. This callus comes from the endosteum, the bone substance itself, and the periosteum (endosteal, intermediary, and periosteal callus). The main, sharply predominant role in healing, as taught in particular by X-ray observations, falls to the share of the periosteal callus.

The development of the callus passes through three stages - connective tissue, osteoid and bone. The blood poured out from the broken vessels forms a large hematoma in the area of ​​the fracture between the fragments and fragments. The blood coagulates very quickly, and in fibrinous blood clot from the bone marrow and especially the periosteum, already in the first hours after the injury, a huge number of young connective tissue elements rush, the number of fibroblasts increases. In 7-10 days everything sprouts in this first stage by proliferating connective tissue. Then, under normal conditions of healing in the second stage, a metaplastic transformation of this more primitive connective tissue into osteoid occurs, which also requires the same week or a week and a half. Previously, osteoid callus without sufficient reason, mainly because of its "cartilaginous density" when palpated, was unconditionally taken for cartilaginous. In fact, cartilage tissue is formed only when the ends of the fragments rub against each other, that is, when there is no complete immobilization. Then already, in the third stage, the osteoid tissue is impregnated with apatites and turns into bone. The callus is initially large and has a loose structure, but later on, at a much slower pace, the reverse development of this callus begins, its restructuring, reduction and structural reconstruction with a very gradual slow recovery of more or less normal bone architectonics.

Connective tissue and osteoid corns, of course, are not determined radiologically at all. The first signs of corn appear in the picture only when it is calcified. The time of appearance of callus varies widely and depends on a number of conditions: on age, on the fracture site in different bones and in different parts of the same bone, on the type of degree of displacement of fragments, on the degree of detachment of the periosteum, on the amount of involvement in the process muscles surrounding the bone, on the method of treatment, on complications of the course of the regenerative process, for example, an infection or some general disease, etc. It should be assumed that an important role is played by nervous influences. Based on convincing experimental data, R. M. Minina considers the relationship between the phenomena of bone tissue regeneration and the nervous system to be firmly established, and she considers dystrophic lesions of the nervous system as the predominant factor in this respect. Open fractures heal much more slowly than closed ones. It is practically important that since signs of calcification of the callus have already appeared on the radiographs, the conservative reposition of the fragments is late.

With subperiosteal children's fractures, the corn is very small; it surrounds the fracture site in the form of a regular spindle-shaped clutch. The first deposits of lime are shown on good picture baby bone by the end of the first week. They have the appearance of single, tender, spotty, structureless shadows surrounding the bone and located parallel to the cortical layer. Between the outer layer of the cortical substance and the shadow of the calcified periosteal callus, at first there is a free strip corresponding to the cambial layer of the periosteum with osteoblasts.

In adults, the first tender cloud-like foci of calcification appear on the radiograph, on average, not earlier than 3-4 weeks (on the 16-22nd day) after the fracture. At the same time, or a few days earlier, the ends of the fragments become somewhat dull and the contours of the cortical layer of the fragments become somewhat uneven and blurred in the area of ​​the callus, losing their sharp limitation. Further side surfaces, the ends and corners of the bones in the area of ​​the fracture are even more smoothed out, the shadow of the callus becomes more intense and takes on a focal granular character. Then the individual sections merge and, with complete calcification, the callus acquires the character of a circular homogeneous mass. Gradually, the shadow thickens and the so-called bone consolidation occurs on the 3rd-4th-6th-8th month of the fracture. Thus, bone consolidation fluctuates over a very wide range. During the first year, the callus continues to be modeled; in terms of structure, it does not yet have a layered structure; a clear longitudinal striation appears only after 1 1/2 -2 years. The fracture line disappears late, between the 4th and 8th month; in the future, according to the development of the osteosclerosis belt in the bone substance, it thickens on the x-ray. This darker fracture line, the so-called bone suture, can be seen even when the callus has already completed its reverse development, that is, it has completely resolved.

This shows that the integrity of the bone under normal conditions is restored much more slowly than is commonly believed in the clinic. X-ray symptoms the course of the fracture healing process is very late compared to the clinical symptoms. This should be emphasized in order to warn the clinician against being too conservative; using radiological guidance alone, the clinician runs the risk of becoming too reticent in providing bone with functional loading. Already a connective tissue callus with barely noticeable clouds of calcification can be quite complete from a functional and clinical point of view, and preventing the limb from functioning in such a case means delaying the pace of further normal evolution and involution of the entire recovery process.

Bone callus in relatively rare cases acquires a narrow diagnostic value. The callus provides the radiologist with the opportunity to retrospectively recognize a violation of the integrity of the bone, which in acute period remained clinically or radiographically examined after injury. This happens mainly with subperiosteal fractures in childhood, but also with cracks and fractures of small tubular bones(phalanges, metacarpal and metatarsal bones) in adults. It is important that even the fracture line, at first doubtful or completely invisible, sometimes clearly appears on the pictures only a few weeks or months after: the injury. With such a late diagnosis of a fracture based on the appearance of only one callus, it is necessary to be careful not to mix it with traumatic periostitis - the callus at the fracture site surrounds the entire bone in the form of a clutch, while the periosteal outgrowth rises above the bone only in one direction. Distinctive recognition is also required by all the complex phenomena of restructuring, which are discussed in detail in a separate chapter (book 2, p. 103).

Rice. 27. Reactive osteosclerotic case around a metal pin in the medullary canal femur developed after a year and a half of his stay.

Some features represent healing processes in new methods of treating intramedullary fractures. osteosynthesis, i.e., intraosseous fixation of fragments with a metal pin, made of stainless steel. The idea of ​​“pinching” fragments with a metal needle was first expressed in 1912 by I.K. Spizharny. These methods are used not only for fresh closed non-infected fractures of large tubular bones (femur, shoulder, lower leg bones and especially forearm), but also for open infected fractures, delayed consolidation, false joints, reconstructive osteotomies, etc. Thanks to the metal rod, the best comparison of fragments is achieved and, more importantly, their secure hold. The whole healing process is qualitatively improved and somewhat accelerated. The pin acts as an aseptic foreign body as: a stimulator of recovery phenomena.

The X-ray picture of reparative processes with the use of metal pins was studied by N. N. Devyatov and N. S. Denisov under our supervision. The initial signs of endosteal callus emanating from the bone marrow canals of the fragments appear primarily at the ends of the bone fragments, moreover, on the distal fragment earlier than on the proximal one. Periosteal callus appears on radiographs 6-7 days after endosteal callus. This periosteal callus develops first on the lateral surfaces of the fragments, and only subsequently forms a circular sleeve. With comminuted fractures, the callus here also acquires bizarre shapes, is often excessive, with a cloud-like structure. Callus calcification in diaphyseal fractures of the femur, shoulder and forearm bones most often appears within the 2nd month, and by the end of the 3rd month, bone consolidation occurs. The bone suture lasts for a long time, it disappears after 6-8 months and later, and the complete reverse development of the callus ends, like without a pin, only after 1 1/2-2 years. If at the ends of the bone fragments, instead of the formation of an endosteal callus, an end bone plate appears, then this is a sure early symptom of the onset of the formation of pseudarthrosis.

Around the metal rod inside the medullary canal naturally develops a dense cylindrical bone case, or sheath (Fig. 27), which only very slowly, over many months, undergoes reverse development after the removal of the metal rod. Sometimes, over the head of a nail protruding outside the bone (for example, above and inside the region of the greater trochanter), reactive calcification and even ossification of soft tissues, most likely displaced bone marrow, occurs in the form of a fungus.

The bone after a fracture is restored through the formation of a bone callus - Callus. The main source of bone regeneration is osteogenic elements in the cambial layer of the periosteum, bone marrow, Haversian canals, and along the circumference of the intraosseous vessels. Due to the multiplication of these cellular elements, osteoid tissue is formed, which subsequently turns into young bone tissue. Bone cells do not have the ability to reproduce, so they do not take any part in bone regeneration. Bone healing in a closed fracture goes through the following phases.

The first phase is preparatory. It is characterized by the coagulation of lymph and blood that has flowed into the tissues, the development of bio-physical, colloidal-chemical changes and an inflammatory reaction resulting from trauma and circulatory disorders in the area of ​​the fracture. The resulting blood clot envelops the ends of the fragments in the form of a muff, and the serum released from the clot, as well as the serous inflammatory exudate, diffuse into the soft tissues. Emigration of vasogenic cells occurs, reproduction of fibroblasts, osteoblasts, cells of the reticuloendothelial system and the formation of new vascular capillaries.

Almost simultaneously with cell proliferation, phagocytosis and cytolysis of destroyed erythrocytes, leukocytes, and local tissue cells by cells of the reticuloendothelial system are observed. If we trace all the changes that occur in the area of ​​the fracture during the first 4 days, we can notice their great similarity with the processes of regeneration and resorption during the healing of soft tissue wounds.

The second phase is the formation of primary connective tissue callus. As inflammation subsides, dead blood cells and local tissue dissolve, osteogenic cells of the cambial layer of the periosteum, bone marrow and endosteum penetrate into the blood clot. Gradually multiplying, the cells germinate the entire blood clot containing a dense network of newly formed capillaries.

A huge number of osteogenic cells such as fibroblasts, vascular capillaries and connective tissue fibers represent a kind of granulation tissue, which, in contrast to soft tissue granulations, does not tend to scar. Its cellular elements are transformed by differentiation into osteoblasts and bone bodies, and the interstitial substance and collagen fibers into the main substance.

Osteoblasts, together with new capillaries and connective tissue, constitute the osteoblastic granulation tissue, which forms the primary connective tissue provisional callus. This callus contains neither salts of lime nor newly formed bone tissue. However, it has a dense texture and acts as a provisional bandage that prevents free displacement of the bone at the fracture site. The ends of the fragments give a picture of aseptic inflammatory osteoporosis, since due to local acidosis, resorption of lime salts occurs - decalcification. Thus, from a biochemical point of view, the second phase is characterized by hypocalcemia.

The duration of the formation of connective tissue callus is different. A large amount of inflammatory exudate, the presence of soft tissue between the ends of the fragments, infection, reduced ability of osteogenic cells to reproduce prolong the development of osteogenic tissue and, consequently, the duration of the second phase; vice versa, good blood supply, contact of fragments, biological activity of cellular elements and the absence of infection contribute to the growth of osteogenic tissue and reduce the time of the second phase of fracture healing.

Along with the multiplication of osteogenic cells, islands of chondroid tissue are formed in the connective tissue callus. They arise as a result of metaplasia of young connective tissue cells. The development of chondroid tissue is inversely proportional to the strength of the immobilization of the fracture. Proper placement of the ends of the fragments and good immobilization make it difficult for the formation and reproduction of cartilage cells in the connective tissue callus. High mobility and friction of fragments with poor fixation of the fracture contribute to the excessive development of cartilaginous tissue.

Thus, it should be recognized that the formation of chondroid tissue with the subsequent development of cartilage cells is a sign of a perverted fracture healing process. It is known that the formation of osteocytes, which completes the healing of any fracture, occurs from an undifferentiated mesenchymal cell through the phase of osteoblast development (primary pathway) or the phase of development of chondrocytes or fibroblasts. This secondary path of callus formation is the least perfect, as it takes more time and leads to the formation of less durable bone tissue.

Rice. 106. Scheme of the formation of connective tissue callus.

The third phase is ossification. It starts from the 12-21st day. Some of the osteoblasts are grouped into beams, some of them go to the formation of the bone marrow. In place of the developed connective tissue callus, lime salts are deposited, coming from the autolyzed dead areas of the damaged bone, partially decalcified, the ends of the fragments, and also from the blood.

Experiments on dogs found that 2 weeks after the fracture, the level of calcium in the blood serum begins to rise and lasts three to four weeks.

This hypercalcemia is due to increased function of the parathyroid glands and coincides with the moment of lime deposition at the fracture site. In the future, once again there is a short-term decrease in the amount of calcium and again its increase.

Osteoblasts are also of great importance in the process of callus ossification. These cells produce the enzyme phosphatase, which promotes the deposition of calcium salts and their binding to osteoid tissue albuminoids. In addition, osteoblasts produce carbonic acid, under the influence of which a double salt, calcium carbonate-phosphate, is released from the blood.

From the moment of deposition of lime salts, consolidation begins, i.e., compaction of soft callus. Such a callus is not yet able to withstand a static or dynamic load and therefore can be easily damaged if there is no reliable immobilization of the fracture. The deposition of lime salts leads to hardening of the soft callus until it becomes hard bone. On the small fragments present at the fracture, bone beams also develop and lime salts are deposited. In this phase of fracture union, both load and muscle tension accelerate the process of bone formation.

Bone trabeculae appear initially at some distance from the ends of the fragments, both from the side of the cambial layer of the periosteum and in the medullary canal. They are very short, arranged haphazardly and everywhere are interconnected. Bone cells and the intermediate basic substance, which is part of the bone beams, do not have the proper correct relationship. Over time, bone beams, developing along the continuation, occupy more and more areas of the mesenchymal tissue of the callus. Finally, in places where the bone fragments have the greatest contact, the bone beams merge with each other. Then they acquire more or less regular layering, and elongated bone marrow spaces form between them, and, finally, new osteons appear.

The newly formed bone tissue does not have a complete structure and is functionally defective.

The fourth phase is the final restructuring of the callus. It represents, in essence, the transformation of the bone according to the laws of statics and dynamics. The location of the bone beams at the fracture site occurs strictly according to the law of pressure. Bone beams that do not function in the static and dynamic load of the bone dissolve, and everything that must withstand pressure remains in place and strengthens. 2 months after the fracture, the newly formed bone can freely bear the load - the weight of the body.

External, or periosteal, callus (Callus externus) is formed due to the multiplication of cells of the cambial layer of the periosteum, which is why it is called periosteal. Osteoid tissue develops at the ends of fragments in the form of protrusions that grow towards each other and give rise to bone trabeculae. External callus grows rapidly and reaches largest sizes. It covers the ends of bone fragments in the form of a clutch, forming a spindle-shaped thickening.

Internal, or endosteal, callus (Callus interims) develops from the side of the bone marrow from the cells of the endosteum of both ends of the fragments and from the bone marrow. The processes of regeneration of osteoblasts and osteoid tissue, as well as the resorption of dead tissue elements and fat, are somewhat slower due to worse blood supply conditions due to the destruction of the branches of the intraosseous arterial highway (a. nutritiae).

The internal callus initially fills the entire medullary cavity of the tubular bone in the area of ​​the fracture, and then, as it is finally restructured, forms a kind of internal sleeve that fastens the ends of the fragments and bone fragments together.

Intermediate callus (Callus intermedius). The source of its formation is the cells of the Haversian canals of the cortical layer of the bone, the cells of the endosteum covering the bone beams, as well as the outer and inner calluses, which penetrate between the ends of the fragments.

Intermediate callus is located between the surfaces of both fragments. The size of this callus is directly proportional to the distance of the ends of the fragments. The better they are in contact with each other, the less developed the intermediate callus. She has highest value in the healing of epiphyseal fractures of tubular bones.

Periosteal callus (Callus paraossalis). In its formation is involved, by direct metaplasia, intermuscular connective tissue and muscles adjacent directly to the damaged bone.

Initially, the callus appears at some distance from the fragments in the form of bone processes that are sent to the muscle tissue and intermuscular loose tissue. Significant bruises and ruptures of soft tissues during a fracture, hemorrhages and displacement of fragments contribute to the development of an extensive near-osseous callus.

The volume of the callus is always much larger than the bone at the fracture site. The more damaged the bone and surrounding tissues, the thicker the bone and the more displaced fragments, the larger the size of the callus. In case of fractures with displacement at an angle, a powerful compact bone develops on the concave side, as a result of which the resistance of the bone to static and dynamic loads increases. Such a functional adaptation is explained by squeezing the tissues on the concave side and more favorable conditions for their blood supply.

Fissures, subperiosteal fractures, epiphyseal and intra-articular fractures, fractures of bones with poor development of the periosteum (for example, coffin and navicular bones, flat bones of the carpal and hock joints) are usually accompanied by the formation of sparse callus and its slow development.

Bone fractures at sites of attachment of muscles rich in sharpei fibers heal faster than fractures of bones free of muscle

The callus, having reached a certain size, begins to decrease in volume due to tissue compaction, resorption of areas old bone and small fragments at the site of the former fracture, as well as excess parts of the callus.

Rice. 108. Subtrochanteric and fracture of the femur in a horse. Purulent osteomyelitis; paraosseous callus formation ( Surgical clinic MBA).

Its internal structure gradually takes on the normal structure of the bone. The bone substance gradually acquires a lamellar thin-layered structure. In the tubular bones, the medullary canal is restored, and thus, at the site of the former fracture, the bone acquires its original structure.

Excess tissue is resorbed by giant cells called osteoclasts.

Rational functional load accelerates the restructuring of the callus. Restoration of the medullary canal and resorption of excess callus serve to reliable signs completion of its restructuring.

An overgrown callus (Callus luxuriens) is characterized by the presence of bony protrusions, ridges and spines and an irregularly fusiform shape. Such excessive callus develops in places of attachment of muscles and tendons rich in Sharpei fibers in comminuted, comminuted fractures, accompanied by significant interstitial hemorrhage, in open infected fractures. Callus luxuriens causes pain and creates mechanical obstructions that limit mobility in a nearby joint. Treatment is useless.

Healing of open fractures is often accompanied by delayed callus formation. The most important reasons that lengthen the healing time of open fractures:

1) insufficient formation of blood clots, which are stimulants for the development of primary callus, a nutrient medium and a source of formation of non-cellular living matter, the primary stimulus for cell proliferation (O. B. Lepeshinskaya);

2) acute infections arising from the soil inflammatory processes and destructive changes that delay the appearance of bone-forming cellular elements;

3) necrosis of bone fragments with their subsequent rejection;

4) the presence of sequesters and infected bone fragments that support suppuration;

5) perversion of the periosteal reaction with a tendency to diffuse or focal calcification and the formation of exostoses;

6) a tendency to develop fibrocartilage in the connective tissue callus;

7) destructive changes in the resulting callus.

Conditions that slow down and accelerate the formation of callus. The duration of callus consolidation depends on the time of assistance, its quality, the nature and location of the fracture, the age of the animal, tissue response, and many other reasons. On average, it takes 3 to 4 weeks for small animals and 4 to 6 weeks for large animals to develop a callus when a tubular bone is fractured. There are cases when the consolidation of the callus slows down or stops, and complete fusion of bone fragments does not occur.

Most common causes delayed union of fractures are: bone defects at the fracture site or destruction of the periosteum and bone marrow; the introduction of soft tissues between bone fragments; insufficient reposition of fragments or poor immobilization; the presence of a fracture line passing through the nutrient hole of the bone, as a result of which the blood supply to the bone is disturbed; penetration of synovial fluid into the gap between fragments (with intra-articular fractures); trophic disorders caused by damage to the nerve branches at the fracture site; vasospasm due to irritation of the nerves at the fracture site; lack or deficiency of vitamins A, B, C, D in the feed; mineral metabolism disorders (rickets, osteomalacia), wound infection, foreign bodies, pregnancy, endocrine disorders caused by hypofunction of the goiter and parathyroid glands; prolapse of the function of the gonads (castration); infectious diseases and exhaustion also delay normal development callus.

Rice. 109. Callus luxuriens.

With delayed consolidation of the callus, it is necessary to eliminate the causes that inhibit the union of the fracture and increase tissue reactivity. To accelerate the formation of callus, apply: Bogomolets antireticular cytotoxic serum, bone meal, powder eggshell, vitamins C, D, phosphorus with fish oil.

Of the physical methods of treatment, the following are shown: irradiation with a solux lamp for slowly resolving infiltrates, heliotherapy, vibration massage, repercussion ultraviolet irradiation, Ca-P iontophoresis (2% Ca and 5% NaIiP04), tapping with a wooden hammer in the fracture area (Turner method) and combined method such as diathermo-calcium iontophoresis, ultraviolet irradiation and calcium iontophoresis.

For hemarthroses and interstitial hemorrhages, ultrashort-wave therapy (UHF) is recommended. With cicatricial contractures - diathermy, iodine-ionogalvanization, paraffin treatment and tissue therapy.

Healing occurs by the formation of a bone callus, that is, a newly formed bone tissue connecting the ends of both fragments. This new bone tissue, having completed the cycle of its development, then undergoes a process of reverse development until the complete disappearance of all, so to speak, surpluses.

It is interesting to note that in the vast majority of cases amount of bone tissue, forming a callus, is much larger than required for fastening bone fragments. It seems that until the fused fracture is practically tested for strength, the callus remains redundant.
This amazing natural phenomenon still remains unexplained from the point of view of the regularities that regulate and control the processes of bone tissue regeneration.

In general, it should be noted that number of studies, devoted to the study of the processes of healing of a broken bone in humans, is very small. At the same time, the number of experimental studies is enormous. Therefore, the proposed patterns in the evolution of callus development are based mainly on the study of animals in which artificially, mainly by surgery, either a bone defect is created throughout (this occurs most often), or the bone is subjected to a simple osteotomy.

But not to mention that none animal cannot be fully equated with a person, the conditions under which a fracture occurs in a person has nothing to do with the so-called experimental fracture. This must be kept in mind when using experimental data for clinical purposes. An example is the judgments of some experimenters about the role of a hematoma in the formation of callus: during the surgical creation of an experimental fracture, hemostasis is performed, the wound is repeatedly dried with gauze napkins, and the hemorrhage that remains between the fracture planes, around them and away from them has nothing to do with a hematoma in the resulting the human fracture does not have an injury.

So, talking about the healing of a fracture in a person, it seems necessary to compare the morphological data with the clinical manifestations of the evolution of the development of fracture union. This is all the more important because not always X-ray morphologically pronounced callus marks an fusion: often on the radiograph you can see distinct, newly appeared bone growths from both fragments, and clinically not only there is no fusion, but almost the same is determined at the fracture site. mobility of fragments, as in the beginning of treatment.

Conversely, especially in the area epimetaphyses, radiographically there are no signs of callus formation yet, and clinically one can state sufficient immobility and stability of fragments even for the appointment of functional therapy. By the way, the same phenomena are observed, though much less frequently, in diaphyseal fractures.

These undeniable facts put before clinician very heavy and complex issue- is it really important and necessary to accurately match the fragments during reposition. Is it really important and necessary to ensure complete immobility at the fracture site?

After all daily clinical observations show that quite often unmatched fragments grow together perfectly, and ideally repositioned and firmly held in some cases, for some reason, they show a tendency to slow union, and sometimes they do not grow together at all, forming a false joint.

Also good known that neither the intake of calcium supplements, nor vitamin foods have a noticeable effect on the course of fracture healing, just as the state of the central and peripheral nervous system does not have any pronounced effect on this process: everyone knows that bone fractures in patients who have undergone childhood cerebral paralysis, grow together in the same time frame and as well as in perfectly healthy people; the wars that have taken place in our century have undoubtedly shown that fractures heal no worse when peripheral nerves are damaged than without them.

All this testifies that the leading role in determining fracture union remains with the clinic, which should have both laboratory and radiological capabilities at its disposal, so that decisions can be made based on a combination of all the data necessary for each specific case.

In essence, the process callus formation occurs as a result of tissue irritation caused by trauma. Therefore, we are talking about traumatic inflammation in the fracture area, which is characterized by hyperemia, which means the emigration of mobile cells (leukocytes) and the subsequent formation of immobile, that is, tissue cells.

It is important to note that all this difficult process initially develops in the area of ​​​​the hematoma, from which a blood clot is formed. V. O. Markov writes about this in his monograph: “That part of the extravasators is organized, which is located directly in the plane of the fracture and close to it.” And further: "The proliferative response of inflamed tissues, of which the organization of blood extravasators is a part, represents the beginning of the regenerative process of bone damage."

Bone tissue, like any other tissue derived from connective tissue, is formed from middle embryonic layer. However, it is important to note that even the first rudiments of newly emerging germinal tissue bear clear signs of specificity. From this we can conclude that the formation of callus is the inevitable result of phylogenetic functional predetermination, or, as they say now, programming. Consequently, it is unlikely that any measures will be able, ceteris paribus, to accelerate the passage of the natural path of bone formation during fracture healing.

This very important factual circumstance should underlie our judgments about the possibility of applying the methods stimulation of bone tissue regeneration with the aim of accelerating it: we need to think not about accelerating regeneration (which is hardly possible!), but about combating slow consolidation and the formation false joints, that is, about creating the most favorable conditions for the development of callus in the usual time.

All researchers agree that callus formation both periosteum and endosteum are involved. However, we must clearly imagine that the occurrence of a fracture with its numerous tiny bone fragments that penetrate into the surrounding soft tissues and into the bone marrow canal, with bleeding that does not stop immediately after the violation of the integrity of the bone and other pathological phenomena, radically changes the quality of the cellular elements of both the periosteum and the endosteum: the poorly differentiated cambial cells of both are activated.

And if these cells in the periosteum are located only in the immediate vicinity from the cortical bone, then the concept of endosteum should be significantly expanded, because cambial cells are located inside the compact bone, surrounding the vessels of the Haversian canals, and in the supporting substance of the bone marrow, and along the newly formed blood vessels germinating blood clot. Therefore, it seems that there are no sufficient grounds to talk about the predominant role of the periosteum in the formation of callus. It is more correct to represent this entire complex process as a complex of biological, strictly directed reactions from all tissues of the damaged area, against the background of certain biochemical and enzymatic changes that ensure the gradual and cyclical formation of callus, that is, the process of fracture healing.

It is in this aspect that it is necessary to touch upon the issue of the influence of the function of the injured limb on the structure of the resulting callus.
Given the above, it is necessary to recognize the functional load on the fracture site as unnecessary and even harmful before the organization of provisional callus, that is, before the onset of ossification.

The point is that the presence major organic matter and the histological structures that make up the osteoid tissue are not enough to call it a formed callus. It is necessary that the osteoid tissue perceive mineral salts, mainly phosphate and carbonate salts of calcium, and that they eventually turned out to be associated with each other. This stage of development will mark the formation of a true regenerate, that is, such a bone tissue that is able to respond to the functional load with an adequate response.

All of the above is directly reflection in clinical course . First period, period acute inflammation, clinically accompanied by an increase in local, sometimes general temperature and phenomena of swelling in the area of ​​the fracture and near it. Approximately by the end of the first week, and with epimetaphyseal fractures a little later, this swelling is significantly reduced, and sometimes completely disappears. As the swelling decreases, the intensity of pain, both independent and on palpation, decreases. By the end of the second week, if the area of ​​the fracture is available for examination, a significant reduction in the mobility of the fragments can usually be noted.

By the end of the third week of pain palpation of the fracture site almost pass, and the mobility of the fragments decreases so much that only their springiness can be detected. Then the strength of the adhesion increases, and by about the fourth or fifth week, the mobility of the fragments disappears completely. Radiographically, by this time, a clearly visible "haze" of callus, unevenly impregnated with salts, is determined. The gap between the fragments is still preserved, and the ends of the fragments are clearly contoured, but appear to be osteoporotic. Over time, the callus thickens, decreasing in size. By this time, the patient is already freely moving the limb, without experiencing pain.

For epimetaphyseal fractures, X-ray detectable callus is significantly less than with fractures of the diaphysis. Clinical picture differs from the one just described in that the movements in the nearby joint are more limited at first.

It should be borne in mind that clinically and radiologically determined fracture union is not synonymous with recovery and rehabilitation. The latter is delayed until full functional adaptation to domestic and professional needs. Below is a comparison table of average consolidation times (according to Bruns) and average recovery times.

As noted in the introduction, the increase in injuries in last years, caused by industrial, domestic, motor transport and gunshot causes, takes on the character of an epidemic (state report of the Ministry of Health of the Russian Federation, 1999). There is a constant increase in the severity of the nature of injuries, developed complications and mortality. Thus, over the past decade, the number of limb injuries has increased by an average of 10-15% (Dyachkova, 1998; Shevtsov, Iryanov, 1998). Specific share fractures of tubular bones in persons who have undergone trauma, it ranges from 57 to 63.2%. The number of high-energy, complex, combined and multi-comminuted fractures that are difficult to treat is increasing. The majority of victims with this pathology (50-70%) are people of working age. For this reason, the organization right tactics treatment of fractures and prevention of complications is not only an important medical, but also social problem(Popova, 1993, 1994).

Often in the process of treating fractures, even with the correct observance of all conditions and the availability of qualified assistance, various complications develop, including pseudarthrosis, nonunion of the fracture, deformity and change in the length of the limb, slowing down the time of consolidation, infection, etc., which can lead to disability. It should be stated that, despite all the achievements of modern traumatology and orthopedics, the number of complications after fracture treatment by qualified specialists continues to remain at the level of 2-7% (Barabash, Solomin, 1995; Shevtsov et al., 1995; Shaposhnikov, 1997; Shved et al. ., 2000; Muller et al., 1990).

It became obvious that further progress in traumatology and orthopedics is impossible without the development of new approaches and principles for the treatment of injuries of the musculoskeletal system, based on fundamental knowledge about the biomechanics of fractures and the biology of reparative bone tissue regeneration processes. That is why we felt it would be useful to dwell briefly on some of the general issues associated with the characteristics and pathogenesis of fractures, with an emphasis on the biomechanics and biology of injury.

Characteristics of bone fractures

Due to the fact that the bone is a viscoelastic material, determined by its crystalline structure and the orientation of collagen, the nature of its damage depends on the speed, magnitude, area, which is affected by external and internal forces. The highest strength and stiffness of the bone is observed in the directions in which the physiological load is most often applied (Table 2.4).

If the impact occurs within a short period of time, then the bone accumulates a large number of internal energy, which, when released, leads to massive destruction of its structure and damage to soft tissues. At low speeds loading, energy can be dissipated due to shielding by bone beams or through the formation of single cracks. In this case, the bone and soft tissues will have relatively minor damage (Frankel and Burstein, 1970; Sammarco et al., 1971; Nordin and Frankel, 1991).

Bone fractures are the result of mechanical overload and occur within fractions of a millisecond, disrupting the structural integrity and stiffness of the bone. There are numerous classifications of fractures, which are well represented in a number of numerous monographs (Muller et al., 1996; Shaposhnikov, 1997; Pchikhadze, 1999).

It should be noted that among traumatologists, clearly little attention is paid to classifications based on the force of impact on the bone. In our opinion, this is not constructive, because The energy of a bone fracture ultimately determines the pathogenesis and nature of the fracture. Depending on the amount of energy released during the fracture, they are divided into three categories: low-energy, high-energy and very high-energy. An example of a low-energy fracture is a simple torsion fracture of the ankle. High-energy fractures occur in road traffic accidents, and very high-energy fractures occur in bullet wounds (Nordin and Frankel, 1991).

The energy of injury must always be considered in the context of the structural and functional features of bone tissue and the biomechanics of injury. So, if the acting force is small and applied to a small area, then it causes minor damage to bone and soft tissues. With a greater amount of force, which has a significant area of ​​application, for example, in an accident, a crushing fracture is observed with fragmentation of the bone and serious damage to the soft tissues. High force acting on a small area with high or extremely high energy, such as bullet wounds, leads to deep damage to soft tissues and necrosis of bone fragments caused by molecular shock.

Bone fractures under the influence of indirect force are caused by influences acting at some distance from the fracture site. In this case, each section of the long bone experiences both normal stress and shear stress. Under the action of a tensile force, transverse fractures occur, axial compression - oblique, torsion forces - spiral, bending forces - transverse, and a combination of axial compression with bending - transverse oblique (Chao, Aro, 1991).

Undoubtedly, many complications are the result of an incomplete assessment of the biomechanical characteristics associated with the type of fracture, the properties of the damaged bone, and the chosen method of treatment.

The process of occurrence of fractures of long bones, as a rule, occurs according to the following scheme. When bending, the convex side is in tension, and the inner side is in compression. Since bone is more sensitive to tension than compression, the stretched side breaks first. The tensile fracture then propagates through the bone, resulting in a transverse fracture. Destruction on the compression side often leads to the formation of a single fragment in the form of a "butterfly" or multiple fragments. In torsion damage, there is always a bending moment that limits the propagation of cracks throughout the bone. It is clinically well known that spiral and oblique fractures of long bones heal faster than some transverse types. This difference in internal healing rate is usually associated with differences in the degree of soft tissue damage, fracture energy, and fragment surface area (Kryukov, 1977; Heppenstall et al., 1975; Whiteside and Lesker, 1978).

In tension, external forces act in opposite directions. In this case, the bone structure lengthens and narrows, the rupture proceeds mainly at the level of the cement line of osteons. Clinically, these fractures are observed in bones with a greater proportion of cancellous substance. During compression caused, for example, by a fall from a height, equal but opposite loads act on the bones. Under the action of compression, the bone structure shortens and expands. Bone fragments can be pressed into each other. If a load is applied to a bone in such a way as to cause it to deform about an axis, then fractures occur due to bending. The geometry of the bone determines its biomechanical behavior in the event of fractures. It has been established that in tension and compression, the load to failure is proportional to the cross-sectional area of ​​the bone. The larger this area, the stronger and stiffer the bone (Müller et al., 1996; Moor et al., 1989; Aro and Chao, 1991; Nordin and Frankel, 1991).

Stages of healing of bone fractures

The healing of a bone fracture can be considered as one of the manifestations of consistently developing general biological processes. Can be distinguished three main phases - bone damage, repair and remodeling(Shaposhnikov, 1997; Grues and Dumont, 1975). After an injury, the development of acute circulatory disorders, ischemia and tissue necrosis, inflammation is observed. In this case, the structural-functional and biomechanical properties of the bone are disorganized.

In this phase, circulatory disorders play an extremely important role. At the same time, improper osteosynthesis associated with vascular damage can worsen the course of fracture consolidation. So, with intramedullary osteosynthesis, bone nutrition from the internal blood supply pool is difficult, and plate osteosynthesis can lead to damage to the vessels coming from the periosteum and soft tissues. Such damage can occur with the development of complete or incomplete compensation of impaired blood flow, as well as its decompensation.

In the latter case, there is a complete disruption of microcirculatory connections between adjacent blood supply pools and destruction of vascular connections between the bone and surrounding soft tissues. If blood flow decompensation is observed, then unfavorable conditions are created for the development of reparative reactions and its spread to the ends of the fragments. The process of vascularization of necrosis zones slows down by 1-2 weeks. In addition, the resulting extensive layer of fibrous tissue, which inhibits or even completely stops the reparative processes (Omelyanchenko et al., 1997) of damage to the bone and soft tissues as a result of injury in initial stage healing, causing avascularity and necroticity of the cortical ends of fragments at the fracture site, yet allows them to be used as mechanical support elements for any fixing device (Schek, 1986).

The next stage - the stage of restoration or regeneration of the bone, proceeds due to intramembrane and (or) endochondral ossification. The previously widely held belief that bone regeneration necessarily goes through a stage bone resorption turned out not to be entirely true. In some cases, with stable osteosynthesis, avascular and necrotic areas of the fracture ends can be replaced with new tissue by Haversian remodeling without resorption of necrotic bone. According to the theory of biochemical induction, Haversian bone remodeling or contact healing requires the implementation of a number of principles, among which an important role belongs to the exact matching (axial alignment) of fragments, the implementation of stable fixation and revascularization of necrotic fragments. If, for example, fracture fragments are deprived of a full blood supply, then the process of bone tissue restoration slows down. All this is accompanied by complex metabolic changes in bone tissue, the fundamental basis of which remains unclear. It is assumed that the resulting products induce osteogenesis processes, limited in strictly defined time parameters, determined by the rate of their utilization (Schek, 1986).

The induction and expansion of undifferentiated osteogenic tissue in the periosteal callus is one of the first key moments in the healing of fractures by the external callus. In experiments on rabbits, it was shown that during the first week after injury, active cell proliferation begins in the deep layer of the periosteum, the fracture zone. The mass of new cells formed in this case, which are formed in the surface zone, exceeds that observed from the side of the endosteum. As a result this mechanism a periosteal callus is formed in the form of a cuff. It should be emphasized that the process of cell differentiation towards osteogenesis is closely related to angiogenesis. In those areas where the partial pressure of oxygen is sufficient, the formation of osteoblasts and osteocytes is observed, where the oxygen content is low, cartilage tissue is formed (Ham, Cormack, 1983).

It is rather difficult to determine at this moment what tactics of osteosynthesis is best to use, since the use of excessively rigid immobilization or, on the contrary, elastic, which creates high mobility of bone fragments, slows down the process of fracture consolidation. If the callus of the fracture, which is formed as a result of deformation or micromovements of the regenerate, is unstable, then the processes of proliferation of connective tissue elements are stimulated. If the stresses in the regenerate exceed the allowable limits, then instead of the formation of a bone callus, a reverse process can be observed associated with osteolysis and stimulation of the formation of stromal tissue (Chao and Aro, 1991).

The next phase begins with the formation of bone bridges between fragments. During this period, the restructuring of the callus occurs. At the same time, bone trabeculae, which are formed in the immediate vicinity of the original fragments in the form of a kind of spongy network, are firmly fastened together. Between these trabeculae there are cavities with dead bone matrix, which is processed by osteoclasts and then replaced by new bone with the help of osteoblasts. For this period, the callus is presented in the form of a spindle-shaped mass of spongy bone around the bone fragments, the necrotic areas of which have already been disposed of in a larger mass. Gradually, the callus transforms into spongy bone. During the processes of callus ossification, the total amount of calcium per unit volume increases approximately four times, and the tensile strength of the callus increases three times. The callus covers the fracture fragments and acts both as a stabilizing structural framework and as a biological scaffold that provides cellular material for fusion and remodeling.

It is assumed that the biomechanical properties of callus depend on the amount of new bone tissue connecting fracture fragments and the amount of mineral rather than on the total amount of connective tissue in it (Aro et al., 1993; Black et al., 1984).

It is believed that during this period of time the entire system of immobilization of bone fragments should be as immobile as possible. It turned out that osteosynthesis using systems with low axial bending and torsional rigidity was ineffective in this case. A number of authors have shown that there are rather narrow limits of permissible micromovements of bone fragments, the violation of which leads to a slowdown in the processes of consolidation. Competitive relationships between fibrous and bone tissues can serve as one of the mechanisms. This must be taken into account when developing tactics for the treatment of bone fractures. So, in the presence of an excess gap in combination with system instability, hypertrophic nonunion can be observed due to the degeneration of bone cells into connective tissue elements (Ilizarov, 1971, 1983; Muller et al., 1996; Shevtsov, 2000).

Even after an “ideal” comparison of fragments, for example, with a transverse fracture of the diaphysis of long bones, gaps always remain at the fracture site, which alternate with areas of direct bone contacts. At the same time, the growth of secondary osteons from one fragment to another does not require mandatory close contact between them. As a result of this process, a lamellar or spongy bone is formed, filling the gap between the fragments. The resulting new bone has a porous structure, which should be taken into account when performing x-ray examination and determining the timing of removal of systems for osteosynthesis (Aro et al., 1993).

According to the theory of fracture stresses, it is believed that the balance between local fracture stresses and the mechanical characteristics of the callus is a determining factor in the course of both primary and spontaneous healing of a bone fracture. So, in an experiment on animals, it was found that when creating a compression of 100 kgf, in all cases, a rapid and then a slow decrease in the compression force is observed in all cases. 2 months after osteosynthesis, this value decreased by 50% and remained at this level until the fracture was consolidated. These experiments confirmed the fact that with unstable fixation, the union of the fracture is accompanied by bone resorption along the fracture line, while this does not occur with stable fixation. Unstable fixation and mobility of bone fragments leads to the formation of a large callus, while stable rigid fixation leads to the formation of a small callus of a homogeneous structure (Perren, 1979). Interfracture stress is inversely proportional to the size of the gap. Three-dimensional analysis showed that the interface between the ends of the fracture fragments and the gap tissue represents a critical zone of high perturbations, containing the maximum values ​​of the main stresses and significant stress gradients from the endosteal to the periosteal side. If the stress value exceeds a critical level, for example, with a small gap between bone fragments, then the processes of tissue differentiation become impossible. In order to circumvent this situation, one can, for example, use small sections of the bone near the fracture gap, stimulating resorption processes and reducing the overall stress in the bone. Obviously, it is necessary to develop new pathogenetic approaches that affect the processes of remodeling and mineralization of bone tissue. This biological response is often observed when rigid external fixation is used during the treatment of long bone fractures (DiGlota et al., 1987; Aro et al., 1989, 1990).

Types of union of bone fractures

Exists different types union of bone fractures. V general case the terms primary and secondary bone healing are used. During primary healing, in contrast to the secondary one, the formation of callus is not observed.

Clinical observations allow us to distinguish the following types of fusion:

1. Bone fusion due to the processes of internal remodeling or contact healing in areas of tight contact with the load;
2. Internal remodeling or "contact healing" of the bone in contact zones without load;
3. Resorption along the surface of the fracture and indirect fusion with the formation of callus;
4. slow consolidation. The gap along the fracture line is filled by indirect bone formation.

In 1949, Danis encountered the phenomenon of primary healing of bone fractures that were rigidly stabilized to prevent any movement between the fragments, with little or no callus formation. This type of remodeling is called contact or Haversian and is realized mainly through contact points and fracture gaps. Contact healing is observed with a narrow fracture gap, stabilized, for example, by means of interfragmentary compression. It is known that the fracture surface is always microscopically incongruent. Upon compression, the protruding parts break to form one large contact zone, in which direct new bone formation occurs, as a rule, without the formation of periosteal callus (Rahn, 1987).

Contact healing of the bone begins with direct internal remodeling in the contact areas without callus formation. In this case, the internal rearrangement of the Haversian systems, connecting the ends of the fragments, as a rule, leads to the formation of a strong union. It is important to note that direct fusion does not accelerate the rate and speed of bone tissue recovery. It has been established that the area of ​​direct contact within the fracture is directly dependent on the magnitude of the applied force created by the external fixation system (Ashhurst, 1986).

Indirect fusion of the bone is accompanied by the formation granulation tissue around and between bone fragments, which is then replaced by bone, due to the processes of internal remodeling of the Haversian systems. If the stresses in the regenerate exceed the allowable limits, then instead of the formation of callus, the reverse process can be observed, associated with osteolysis and stimulation of the formation of stromal tissue. Radiologically, this process is characterized by the formation of periosteal callus, expansion of the fracture zone, followed by filling of the defect with new bone (Ham, Cormack, 1983; Aro et al., 1989, 1990).

Currently, there are no clear criteria for the conscious use of biomechanical approaches to fracture healing that optimize the processes of reparative regeneration and reduce the development of complications. This is true for both bone and transosseous osteosynthesis. We are only at the beginning of the path of understanding these complex mechanisms, which require deeper study (Shevtsov et al., 1999; Chao, 1983; Woo et al., 1984).

In this context, it is important to emphasize that the rate of bone tissue regeneration in normal and pathological conditions is to some extent a constant value. In this regard, traumatologists and orthopedists still do not have a common opinion about the advantages of certain fixation methods, since practice shows that with correct intramedullary, extracortical or external osteosynthesis, the union of fractures occurs approximately at the same time (Ankin, Shaposhnikov, 1987) . Until now, even with the use of all known growth factors and other approaches, no one in the world has been able to speed up this process. Instability of bone fragments, impaired oxygenation, development of inflammation and other unfavorable factors only slow down the processes of proliferation and differentiation of osteogenic cells (Fridenshtey, Lalykina, 1973; Fridenshtein et al., 1999; Ilizarov, 1983, 1986; Shevtsov, 2000; Alberts et al., 1994; Chao and Aro 1991).

Since the level of our knowledge does not allow changing the rate of bone recovery, it is necessary to use a pragmatic approach in the treatment of fractures to create favorable biomechanical and biological conditions for realizing the existing potential of the preserved bone tissue and supporting cells to optimize their functioning processes.

The final phase of bone healing follows Wolf's law, in which the bone is remodeled to its original shape and strength, allowing it to carry its usual load. The cellular and molecular mechanisms underlying this regularity still remain undeciphered. For practice, it should be remembered that Wolf's law applies more to cancellous bone. Adaptation of the cortical layer is slow, and therefore this law is of little importance (Müller et al., 1996; Roux, 1885, 1889; Wolf, 1870, 1892).

Bone remodeling takes a certain amount of time to the extent that the bone has weak mechanical properties. Thus, rigid plates cannot be safely removed from the diaphysis until 12-18 months after fixation. Often, after the removal of rigid implants, repeated bone fractures are observed due to the absence of callus formation. However, primary bone healing, provided either by rigid plating or rigid external fixation, requires that the regenerating fracture site be supported and protected until the bone reaches sufficient strength to prevent re-fracturing or bending when it is accidentally subjected to functional stresses. On the one hand, rigid fixation prevents the development of callus, on the other hand, it leads to long-term use systems for osteosynthesis before adequate bone remodeling occurs and it becomes possible to remove the implant. This disadvantage was inherent in early external fixation devices, in which attempts were made to reproduce stability by increasing the rigidity of the frames in multiplanar configurations. Often, additional interfragmentary rods are used to increase the stability of the structure. Although these rigid structures sometimes gave anatomical restoration of the bone, in some cases they were accompanied by a delay - up to the complete prevention - of fracture healing. External fixation depends, of course, on the correct fixation of screws, rods or pins to the bone. At the same time, at the moment of applying the external fixator, a “competition” begins between the healing of the fracture and the decrease in the strength of the structure due to the loosening of the rods and other implanted parts of the fixator. From a theoretical standpoint, methods that rely on structures that are too rigid and therefore require longer times for nail fixation and frame retention will often fail because the fracture cannot be adequately remodeled by the time the nail is loosened and the fixator is removed.

A.V. Karpov, V.P. Shakhov
External fixation systems and regulatory mechanisms of optimal biomechanics