Syndesmosis is a type of continuous connection of bones. Classification of bone connections. Continuous connection of bones. Video lesson: Classification of bone joints. Continuous connections. Half-joints

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There are two main types of bone joints: continuous And intermittent, or joints and intermediate, third type of connections – semi-joint.

Continuous connections are present in all lower vertebrates and in the embryonic stages of development in higher ones. When the latter form bone primordia, their original material (connective tissue, cartilage) is preserved between them. With the help of this material, bone fusion occurs, i.e. a continuous connection is formed.

Intermittent connections develop at later stages of ontogenesis in terrestrial vertebrates and are more advanced, since they provide more differentiated mobility of skeletal parts. They develop due to the appearance of a gap in the original material preserved between the bones. In the latter case, remnants of cartilage cover the articulating surfaces of the bones.

Intermediate connection type –semi-joint. The semi-joint is characterized by the fact that the bones in it are connected by a cartilaginous lining, which has a slit-like cavity inside. The joint capsule is absent. Thus, this type of connection represents a transitional form between synchondrosis and diarthrosis (between the pubic bones of the pelvis).

Continuous connections

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Continuous connection – synarthrosis, or fusion, occurs when the bones are connected to each other by connecting tissue. Movements are extremely limited or completely absent.

Based on the nature of the connective tissue, they are divided into:

• connective tissue adhesions, or syndesmoses(Fig. 1.5, A),
• cartilaginous adhesions, or synchondrosis(Fig. 1.5, B), And
• fusion with bone tissue - synostosis.

Rice. 1.5. Types of bone connections (diagram):

A– syndesmosis;
B– synchondrosis;
IN– joint;

1 – periosteum;
2 - bone;
3 – fibrous connective tissue;
4 – cartilage;
5 – synovial and
6 – fibrous layer of the joint capsule;
7 – articular cartilage;
8 – joint cavity

Syndesmoses there are three types:

1) interosseous membranes, for example, between the bones of the forearm or lower leg;

2) ligaments, connecting bones (but not connected to joints), for example, ligaments between the processes of the vertebrae or their arches;

3) seams between the bones of the skull.

Interosseous membranes and ligaments allow some displacement of the bones. At the sutures, the layer of connective tissue between the bones is very small and movement is impossible.

Synchondrosis is, for example, the connection of the first rib with the sternum through the costal cartilage, the elasticity of which allows some mobility of these bones.

Synostosis develop from syndesmoses and synchondroses with age, when the connective tissue or cartilage between the ends of some bones is replaced by bone tissue. An example is fusion of the sacral vertebrae and overgrown sutures of the skull. Naturally, there is no movement here.

Intermittent connections

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Intermittent connection – diarthrosis, articulation, or joint(Fig. 1.5, IN), characterized by a small space (gap) between the ends of the connecting bones.

There are joints

• simple, formed by only two bones (for example, the shoulder joint),
• complex - when the joint includes a larger number of bones (for example, the elbow joint), and
• combined, allowing movement only simultaneous with movement in other anatomically separate joints (for example, the proximal and distal radioulnar joints).

The joint includes:

• articular surfaces,
• joint capsule, or capsule, and
• articular cavity.

Articular surfaces

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The articular surfaces of the connecting bones more or less correspond to each other (congruent).

On one bone forming a joint, the articular surface is usually convex and is called heads. On the other bone a concavity corresponding to the head develops - depression, or hole

Both the head and the fossa can be formed by two or more bones.

The articular surfaces are covered with hyaline cartilage, which reduces friction and facilitates movement in the joint.

Bursa

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The articular capsule grows to the edges of the articular surfaces of the bones and forms a sealed articular cavity.

The joint capsule consists of two layers.

Superficial, fibrous layer, formed by fibrous connective tissue, merges with the periosteum of the articulating bones and has a protective function.

Inner or synovial layer rich in blood vessels. It forms outgrowths (villi) that secrete a viscous liquid - synovia, which lubricates the articulating surfaces and facilitates their sliding.

In normally functioning joints there is very little synovium, for example in the largest of them - the knee - no more than 3.5 cm 3.

In some joints (the knee), the synovial membrane forms folds in which fat is deposited, which has a protective function here. In other joints, for example, in the shoulder, the synovial membrane forms external protrusions, over which there is almost no fibrous layer. These protrusions in the form bursae are located in the area of ​​tendon attachment and reduce friction during movements.

Jointin cavity

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The articular cavity is a hermetically sealed, slit-like space bounded by the articulating surfaces of the bones and the articular capsule. It is filled with synovium.

In the articular cavity between the articular surfaces there is negative pressure (below atmospheric pressure). The atmospheric pressure experienced by the capsule helps strengthen the joint. Therefore, in some diseases, the sensitivity of the joints to fluctuations in atmospheric pressure increases, and such patients can “predict” weather changes.

The tight pressing of the articular surfaces to each other in a number of joints is due to tone, or active muscle tension.

In addition to the obligatory ones, auxiliary formations may be found in the joint. These include articular ligaments and lips, intra-articular discs, menisci and sesamoids (from Arabic, sesamo– grain) bones.

Articular ligaments

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Articular ligaments are bundles of dense fibrous tissue. They are located in the thickness or on top of the articular capsule. These are local thickenings of its fibrous layer.

The bones in the human body are not located isolated from each other, but are interconnected into one single whole. Moreover, the nature of their connection is determined by functional conditions: in some parts of the skeleton, movements between bones are more pronounced, in others - less. Also P.F. Lesgaft wrote that “in no other department of anatomy is it possible to so “harmoniously” and consistently identify the connection between form and function” (function). By the shape of the connecting bones, you can determine the nature of the movement, and by the nature of the movements, you can imagine the shape of the joints.

The main point when connecting bones is that they “are connected to each other in such a way that, with the smallest volume of the junction, there is the greatest variety and magnitude of movements with the greatest possible strength in the most advantageous counteraction to the influence of shocks and shocks” (P.F. Lesgaft) .

The whole variety of bone connections can be presented in the form of three main types: continuous connections - synarthrosis, discontinuous - diarthrosis and semi-continuous - hemiarthrosis (half-joints)

Continuous bone connections– these are connections in which there is no break between the bones; they are connected by a continuous layer of tissue (Fig. 5).

Rice. 5. Connective tissue connections

Intermittent connections- these are connections when there is a gap between the connecting bones - a cavity.

Semi-continuous connections- connections that are characterized by the fact that in the tissue that is located between the connecting bones there is a small cavity - a gap (2-3 mm) filled with liquid. However, this cavity does not completely separate the bones, and the essential elements of a discontinuous connection are missing. An example of this type of joint is the joint between the pubic bones.

Depending on the nature of the tissue located between the connecting bones, there are continuous connections (Fig. 6):

a) with the help of connective tissue itself - syndesmoses,

b) cartilaginous – synchondrosis;

c) bone – synostosis.

Rice. 6. Connective tissue connections – 2 (staple suture, cartilaginous connections)

Syndesmoses. If collagen fibers predominate in the connective tissue located between the bones, such connections are called fibrous, if elastic - elastic. Fibrous compounds, depending on the size of the layer, can be in the form of ligaments (between the processes of the vertebrae), in the form of membranes 3-4 cm wide (between the bones of the pelvis, forearm, lower leg) or in the form of sutures (between the bones of the skull), where the layer of connective tissue is only 2-3 mm. An example of continuous connections of the elastic type are the yellow ligaments of the spine, located between the vertebral arches.

Synchondroses. Depending on the structure of the cartilage, these connections are divided into connections using fibrous cartilage (between the vertebral bodies) and connections using hyaline cartilage (costal arch, between the diaphysis and the epiphysis, between individual parts of the skull bones, etc.).

Cartilaginous connections can be temporary (connections of the sacrum with the coccyx, parts of the pelvic bone, etc.), which then turn into synostoses, and permanent, existing throughout life (synchondrosis between the temporal bone and the occipital bone).

Hyaline compounds are more elastic, but fragile compared to fibrous ones.

Synostosis . These are connections of bones with bone tissue - ossification of epiphyseal cartilages, ossification of sutures between the bones of the skull.

Continuous bone connections (except synostoses) are mobile. The degree of mobility depends on the size of the tissue layer and its density. The connective tissue joints themselves are more mobile, the cartilaginous ones are less mobile. Continuous connections also have a pronounced property of shock absorption and shock absorption.

Discontinuous bone connections – these are connections that are also called synovial connections, cavitary connections or joints (Fig. 7, 8). The joint has its own specific design, location in the body and performs certain functions.

Rice. 7. Joints

Rice. 8. Joints

In each joint, basic elements and accessory formations are distinguished. The main elements of the joint include: the articular surfaces of the connecting bones, the articular capsule (capsule) and the articular cavity.

The articular surfaces of connecting bones must correspond to each other in shape to a certain extent. If the surface of one bone is convex, then the surface of the other is somewhat concave. The articular surfaces are usually covered with hyaline cartilage, which reduces friction, facilitates the sliding of bones during movements, acts as a shock absorber and prevents fusion of bones. The thickness of the cartilage is 0.2-4 mm. In joints with limited mobility, the articular surfaces are covered with fibrocartilage (sacroiliac joint).

Bursa- This is a connective tissue membrane that hermetically surrounds the articular surfaces of the bones. It has two layers: the outer - fibrous (very dense, strong) and the inner - synovial (on the side of the joint cavity it is covered with a layer of endothelial cells that produce synovial fluid).

Articular cavity- a small gap between the connecting bones, filled with synovial fluid, which, by wetting the surfaces of the connecting bones, reduces friction, the force of adhesion of molecules to the surfaces of the bones strengthens the joints, and also softens shocks.

Additional formations are formed as a result of functional requirements, as a reaction to an increase and specificity of the load. Additional formations include intra-articular cartilage: discs, menisci, articular lips, ligaments, outgrowths of the synovial membrane in the form of folds, villi. They are shock absorbers, improve the congruence of the surfaces of connecting bones, increase mobility and variety of movements, and contribute to a more even distribution of pressure from one bone to another. Discs are solid cartilaginous formations located inside the joint (in the temporomandibular joint); menisci have the shape of crescents (in the knee joint); lips in the form of a cartilaginous rim surround the articular surface (near the glenoid cavity of the scapula); ligaments are bundles of connective tissue that go from one bone to another; they not only inhibit movements, but also direct them, and also strengthen the joint capsule; outgrowths of the synovial membrane are folds protruding into the joint cavity, villi filled with fat.

The joint capsule, ligaments, muscles surrounding the joint, atmospheric pressure (negative pressure inside the joint) and the adhesion force of synovial fluid molecules are all factors that strengthen joints.

Joints perform mainly three functions: they help maintain the position of the body and its individual parts, they participate in the movement of parts of the body in relation to each other, and, finally, they participate in locomotion - the movement of the entire body in space. These functions are determined by the action of active forces - muscles. Depending on the nature of muscle activity in the process of evolution, compounds of various shapes and having different functions were formed.

There are three types of bone joints.

1. Continuous joints in which there is a layer of connective tissue or cartilage between the bones. There is no gap or cavity between the connecting bones.
2. Discontinuous joints, or joints (synovial joints), are characterized by the presence of a cavity between the bones and a synovial membrane lining the inside of the joint capsule.
3. Symphyses, or semi-joints, have a small gap in the cartilaginous or connective tissue layer between the connecting bones (a transitional form from continuous to discontinuous joints).

Continuous connections

have greater elasticity, strength and, as a rule, limited mobility. Depending on the type of tissue connecting the bones, there are three types of continuous connections:

1) fibrous joints, 2) synchondrosis (cartilaginous joints) and

3) bone connections.

Fibrous connections

articulationes fibrosae are strong joints between bones using dense fibrous connective tissue. Three types of fibrous joints have been identified: syndesmoses, sutures and impactions.

Syndesmosis, syndesmosis, is formed by connective tissue, the collagen fibers of which fuse with the periosteum of the connecting bones and pass into it without a clear boundary. Syndesmoses include ligaments and interosseous membranes.

Ligaments, ligamenta, are thick bundles or plates formed by dense fibrous connective tissue.

Interosseous membranes, membranae interosseae, are stretched between the diaphyses of long tubular bones. Often, interosseous membranes and ligaments serve as the origin of muscles.

A suture, sutura, is a type of fibrous joint in which there is a narrow connective tissue layer between the edges of the connecting bones. The connection of bones by sutures occurs only in the skull. Depending on the configuration of the edges of the connecting bones, a serrated suture, sutura serrata, is distinguished; scaly suture, sutura squamosa, and flat suture, sutura plana.

A special type of fibrous joint is impaction, gomphosis (for example, dentoalveolar joint, articulatio dentoalveolaris). This term refers to the connection of the tooth with the bone tissue of the dental alveolus. Between the tooth and the bone there is a thin layer of connective tissue - periodontium, periodontum.

Synchondroses, synchondroses, are connections between bones using cartilage tissue. Such connections are characterized by strength, low mobility, and elasticity due to the elastic properties of cartilage. The degree of bone mobility and the amplitude of springing movements in such a joint depend on the thickness and structure of the cartilaginous layer between the bones. If the cartilage between the connecting bones exists throughout life, then such synchondrosis is permanent.

In cases where the cartilaginous layer between the bones persists until a certain age (for example, sphenoid-occipital synchondrosis), this is a temporary connection, the cartilage of which is replaced by bone tissue. Such a connection replaced by bone tissue is called a bone connection - synostosis, synostosis (BNA).

The human skeleton is a collection of bones connected to each other and is the passive part of the musculoskeletal system. It functions as a support for soft tissues, a point of application of muscles and a container for internal organs. The skeleton of a newborn child includes 270 bones. As you grow older, some of them fuse (mainly the bones of the pelvis, skull and spine), so in a mature person this figure reaches 205-207. Different bones connect to each other in different ways. An ordinary person, when asked: “What types of bone joints do you know?” remembers only the joints, but that’s not all. The branch of anatomy that studies this topic is called osteoarthrosisyndesmology. Today we will briefly get acquainted with this science and the main types of bone connections.

Classification

Depending on the function of the bones, they can connect to each other in different ways. There are two main types of bone connections: continuous (synarthrosis) and discontinuous (diarthrosis). At the same time, they are further divided into subspecies.

Continuous connections can be:

1. Fibrous. This includes: ligaments, membranes, fontanelles, sutures, impactions.
2. Cartilaginous. They can be temporary (using hyaline cartilage) or permanent (using fibrocartilage).
3. Bone.

As for discontinuous joints, which can simply be called joints, they are classified according to two criteria: according to the axes of rotation and the shape of the articular surface; as well as by the number of articular surfaces.

According to the first sign, joints are:

1. Uniaxial (cylindrical and block-shaped).
2. Biaxial (ellipsoidal, saddle-shaped and condylar).
3. Multiaxial (spherical, flat).

And for the second:

1. Simple.
2. Complex.

There is also a type of block joint - the cochlear (helical) joint. It has a beveled groove and ridge that allows the articulated bones to move in a spiral manner. An example of such a joint is the humeroulnar joint, which also operates along the frontal axis.

Biaxial joints are called connections that operate around two axes of rotation out of the three existing ones. So, if the movement is carried out along the frontal and sagittal axes, then these connections can realize 5 types of movement: circular, abduction and adduction, flexion and extension. From the point of view of the shape of the articular surface, these are saddle-shaped (for example, the carpometacarpal joint of the thumb) or ellipsoidal (for example, the wrist joint) joints.

When movement is carried out along the vertical and frontal axes, the joint can realize three types of movements: rotation, flexion and extension. In shape, such joints are classified as condylar (for example, the temporomandibular and knee).

Multiaxial joints and are called connections in which movement occurs along three axes. They are capable of a maximum number of types of movement - 6 types. In terms of their shape, such joints are classified as spherical (for example, the shoulder joint). Varieties of the spherical type are: nut-shaped and cup-shaped. Such joints are characterized by a deep, durable capsule, a deep articular fossa and a relatively small range of motion.

When the surface of a ball is endowed with a large radius of curvature, it approaches an almost flat state. These types of bone joints are briefly called planar joints. They are characterized by: strong ligaments, a small difference between the areas of the articulated surfaces, and the absence of active movement. Therefore, flat joints are often called amphiarthrosis or sedentary.

Number of articular surfaces

This is the second sign for classifying open types of joints of skeletal bones. It divides simple and complex joints.

Simple joints have only two articular surfaces. Each of them can be formed by one or several bones. For example, the joint of the phalanges of the fingers is formed by only two bones, and in the wrist joint there are three bones on only one surface.

Complex joints may have several articular surfaces in one capsule at once. In other words, they are made up of a series of simple joints that can work together or separately. A prime example is the ulnar synovial joint, which has six distinct surfaces that form three joints: the humeroulnar, brachioradialis, and proximal joints. The knee joint is often classified as a complex joint, based on the fact that it has patellas and menisci. Thus, adherents of this opinion distinguish three simple joints in the knee synovial joint: meniscal-tibial, femoral-meniscal and femoral-patellar. In fact, this is not entirely correct, since the menisci and patellas still belong to the auxiliary elements.

Combined joints

Considering the types of joints of the body bones, it is also worth noting a special type of joints - combined. This term refers to those synovial joints that are located in different capsules (that is, anatomically separated) but work only together. These include, for example, the temporomandibular joint. It is worth noting here that in true combined synovial joints, movement cannot occur in only one of them. When combining joints with different surface shapes, movement begins at the joint that has fewer axes of rotation.

Conclusion

Types of bones, connection of bones, joint structure - all this and much more is studied by such a science as osteoarthrosisyndesmology. Today we got to know her superficially. This will be quite enough to feel confident when you hear the question: “What types of bone joints do you know?”

Summarizing the above, we note that bones can be connected by continuous and discontinuous connections, each of which performs its own special functions and has a number of subtypes. Scientists view bone as an organ, and the types of bone connections as a serious topic of research.

Continuous bone connections
Bones can connect to one another using a continuous connection when there is no gap between them. This connection is called synarthrosis. A discontinuous connection, in which there is a cavity between the articulating bones and a joint (articulatio) is formed, is called diarthrosis, or synovial joint (juncturae synovialis).

Continuous connections of bones - synarthrosis
Continuous bone connections, depending on the type of tissue connecting the bones, are divided into 3 groups: fibrous connections (juncturae fibrosae), cartilaginous connections (juncturae cartilagina) and connections through bone tissue - synostoses.
Fibrous joints include syndesmosis, interosseous membrane and suture.
Syndesmosis is a fibrous connection through ligaments.
Ligaments (ligamenta) serve to strengthen the joints of bones. They can be very short, for example, interspinous and intertransverse ligaments (ligg. interspinalia et intertransversaria), or, conversely, long, like the supraspinous and nuchal ligaments (ligg. supraspinale et nuchae). Ligaments are strong fibrous cords consisting of longitudinal, oblique and overlapping bundles of collagen and a small amount of elastic fibers. They can withstand high tensile loads. A special type of ligament includes the yellow ligament (ligg. flava), formed by elastic fibers. They have the strength and strength of fibrous syndesmoses, but at the same time they are characterized by great extensibility and flexibility. These ligaments are located between the vertebral arches.
A special type of syndesmosis includes dentoalveolar syndesmosis or inclusion (gomphosis) - the connection of the roots of the teeth with the dental alveoli of the jaws. It is carried out by fibrous bundles of periodontium, running in different directions depending on the direction of the load on a given tooth.
Interosseous membranes: radioulnar syndesmosis (syndesmosis radioulnaris) and tibiofibular (syndesmosis tibiofibularis). These are connections between adjacent bones through interosseous membranes - respectively, the interosseous membrane of the forearm (membrana interossea antebrachii) and the interosseous membrane of the lower leg (membrane interossea cruris). Syndesmoses also close openings in the bones: for example, the obturator foramen is closed by the obturator membrane (membrana obturatoria), there are atlantooccipital membranes - anterior and posterior (membrana atlantooccipitalis anterior et posterior). Interosseous membranes close the openings in the bones and increase the surface area for muscle attachment. The membranes are formed by bundles of collagen fibers, are inactive, and have openings for blood vessels and nerves.
A suture (sutura) is a joint in which the edges of the bones are firmly articulated by a small layer of connective tissue. Sutures occur only on the skull. Depending on the shape of the edges of the skull bones, the following sutures are distinguished:
- serrated (sut. serrata) - the edge of one bone has teeth that fit into the recesses between the teeth of another bone: for example, when connecting the frontal bone with the parietal;
- scaly (sut. squamosa) is formed by placing obliquely cut bones on top of each other: for example, when connecting the scales of the temporal bone with the parietal;
- flat (sut. plana) - the smooth edge of one bone is adjacent to the same edge of the other, characteristic of the bones of the facial skull;
- schindylosis (splitting; schindylesis) - the sharp edge of one bone fits between the split edges of another: for example, the connection of the vomer with the beak of the sphenoid bone.
In cartilaginous joints (juncturae cartilaginea), bones are held together by layers of cartilage. Such joints include synchondrosis and symphysis.
Synchondrosis is formed by continuous layers of cartilage. This is a strong and elastic connection with slight mobility, which depends on the thickness of the cartilage layer: the thicker the cartilage, the greater the mobility, and vice versa. Synchondroses are characterized by spring functions. An example of synchondrosis is a layer of hyaline cartilage at the border of the epiphyses and metaphyses in long tubular bones - the so-called epiphyseal cartilages, as well as costal cartilages connecting the ribs to the sternum. Synchondrosis can be temporary or permanent. The former exist until a certain age, for example epiphyseal cartilages. Permanent synchondrosis remains throughout a person’s life, for example, between the pyramid of the temporal bone and the neighboring bones - the sphenoid and occipital.
Symphyses differ from synchondroses in that there is a small cavity inside the cartilage connecting the bones. The bones are also fixed by ligaments. Symphyses were previously called semi-joints. There are the symphysis of the manubrium of the sternum, the intervertebral symphysis and the pubic symphysis.
If a temporary continuous connection (fibrous or cartilaginous) is replaced by bone tissue, it is called synostosis. An example of synostosis in an adult is the connections between the bodies of the occipital and sphenoid bones, between the sacral vertebrae, and the halves of the lower jaw.