HUMAN ANATOMY – VOLUME 1

They can be fibrous, cartilaginous and bony. Fibrous joints (junctúra fibrosa) include sutures, gomphoses and syndesmoses. Sutures (suturae) are joints between bones of the skull, made up of thin layers of connective tissue. There are three kinds of sutures, depending on the shape of the bone edges involved. P l a n e (h a r m o n i c) s u t u r e s are found in the facial skull, where edges of bones are straight. S e r r a t e s u t u r e s are formed between bones with jagged edges. They are found in the cranial portion of the skull. An example of a s q u a m o u s s u t u r e is the junction between the squamae of the temporal and parietal bones. Sutures provide amortization of impacts and concussions during walking, jumping, etc. Sutures also serve as zones of bone growth. After age 40–50 many sutures become fused (synosteotic). Premature fusion of sutures can result in deformation of the skull. Asynchrony of suture fusion, particularly of paired sutures, is the main reason for asymmetry of the skull. A g o m p h o s i s is a connective fiber joint between the root of a tooth and walls of a dental alveolus.

Syndesmoses are connections created by ligaments and interosseous membranes. Neighboring bones are connected by ligaments in the form of thick bundles of compact connective tissue. These ligaments strengthen the joints, directing and restricting their movement. The majority of ligaments is formed by collagen fibers. Ligamenta flava, which join the arches of adjacent vertebrae, are composed of elastic fibers. Ligaments collagen fibers have little tensility and high strength. Interosseous membranes are found between diaphyses of tubular bones. They provide mobility of the connected boned relative to each other, and can serve as places of the beginning of muscles.

Articulations formed by cartilage tissue are called cartilaginous joints, or synchondroses (junctúra cartiláginea, s. synchondrósis). These joints have considerable strength and elasticity due to high elastic properties of cartilage. They are subdivided into constant synchondroses, which exist throughout life (e.g. intervertebral diskc), and temporary synchondroses, which become replaced at a certain age by bone tissue (e.g. epiphyseal cartilage of tubular bones).

Bony adhesions (synostoses) are formed as a result of substitution of synchondroses by bone tissue. An example of synostosis is the substitution of cartilage between pubic, iliac and ischial bones by bony tissue and formation of the hipbone.

Cartilaginous joints also include symphyses (semi-joints), which consist of a layer of cartilage between bones with a narrow slit-like cavity inside. Thus, symphyses occupy an intermediate position between continuous and discontinuous joints. An example of this kind of articulation is the pubic symphysis.

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Synovial joints (articulatio, s. articulationis synovialis) are discontinuous joints (Fig. 66). They are typically formed by cartilage-covered articular surfaces, an articular capsule, and a joint cavity, filled with synovial fluid. In addition some joints may have formations such as an articular disk, a meniscus, or an articular labrum.

A r t i c u l a r s u r f a c e s can be complementary (congruent) to each other, or may have different shape and size (be incongruent). A r t i c u l a r c a r t i l a g e (cartilágo articuláris) is generally hyaline. Fibrous articular cartilage can be found only in the temporomandibular and sternoclavicular joints. The thickness of articular cartilage varies from 0.2 to 6 mm. Under mechanical loads it becomes flattened, and acts like a spring due to its resilience (Fig.67).

The a r t i c u l a r c a p s u l e (c á p s u l a a r t i c u l á r i s) is attached to the edges of the articular cartilage or at some distance from it. It accretes firmly with the periosteum, forming a closed a r t i c u l a r c a v i t y, the pressure inside which is maintained below atmospheric. The capsule is

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Fig. 68. Types of joints, which have additional formations.

A — knee joint, right; on a horisontal section articular capsule and cruciformial ligaments are clearly evident and also proximal epiphysis of tibia with meniscuses are distinquished: 1 — patellar ligament; 2 — subpatellar bursa; 3 — transverse ligament of knee; 4 — articular capsule; 5 — lateral meniscus; 6 — fibular collateral ligament; 7 — posterior cruciformial ligament; 8 — medial meniscus; 9 — fibular collateral ligament; 10 — anterior cruciate ligament.

B — sternoclavicular joint (the right one is opened); 1 — articular disc; 2 — articular capsule; 3 — interclavicular ligament; 4 — anterior sternoclavicular ligament; 5 — costo clavicular ligament; 6 — sternal end of clavicule; 7 — first rib; 8 — sternum.

C — acromioclavicular joint; scapular ligaments: 1 — coracoacromial ligament; 2 — trapezoid ligament; 3 — conoid ligament; 4 — acromial end of clavicle; 5 — coracoid process; 6 — superior transverse scapular ligament; 7 — scapula; 8 — articular lip; 9 — glenoid cavity; 10 — acromion; 11 — acromioclavicular joint and ligament.

made up of two layers: a fibrous membrane on the outside and a synovial membrane inside. The fibrous m e m b r a n e (membrána fibrósa) is thick and very durable. It is formed by fibrous connective tissue. In some places the fibrous membrane is thickened by ligaments, which strengthen the capsule. These l i g a m e n t s are called c a p s u l a r if they are situated within the capsule wall, and e x t r a c a p s u l a r when they are situated outside the capsule. Some joint have i n t r a c a p s u l a r l i g a m e n t s inside the joint cavity, which are covered by the synovial membrane (e.g. the cruciate ligaments of the knee joint). The thin s y n o v i a l m e m b r a n e (membrána synoviális) lines the fibrous membrane from the inside, forming microprotrusions called synovial v i l l i, which greatly increase its surface area. Often the synovial membrane forms f o l d s (e.g. in the knee joint), in the base of which there are accumulations of fatty tissue.

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T h e a r t i c u l a r c a v i t y (c á v u m a r t i c u l á r e) is a closed fis- sure-like space confined by the articular surfaces and capsule. It is filled with synovial fluid, a mucoid lubricant, which moistens the articular surfaces, allowing them to glide freely against each other. S y n o v i a l f l u i d also provides nutrients to the articular cartilage.

A r t i c u l a r d i s c s and m e n i s c i (dísci et menísci articuláres) are intraarticular cartilaginous plates of different shapes, which reduce or eliminate incongruity between articular surfaces. Disks, which divide the joint cavity completely into two sections, are found in the sternoclavicular, temporomandibular and some other joints. Menisci form a partial division in the knee joint (Fig.68). Discs and menisci can be shifted during movement, thus acting as shock absorbers.

Some joints (shoulder and hip joints) have an articular labrum, which is attached along the border of the articular surface, increasing the depth of the articular fossa.

CLASSIFICATION OF JOINTS (CONTINUATION)

Joints can be classified based on their anatomy or on their biomechanic properties. According to the anatomic classification, joints are subdivided into simple and compound (composite), depending on the number of bones involved, and into complex and combination joints. S i m p l e j o i n t s are formed by two articular surfaces (e.g. the shoulder joint, the hip joint

C o m p l e x j o i n t s have an articular disc or meniscus (the sternoclavicular, temporomandibular and knee joints). Combination joints are groups of articulations, which are isolated anatomically, but function simultaneously. An example of this is the temporomandibular joints.

According to the biomechanic classification, joints are subdivided into u n i a x i a l, b i a x i a l and m u l t i a x i a l, depending on the number of rotation axes they have. Uniaxial joints have one rotation axis, around which they can perform flexion and extension or abduction and adduction movements, or rotation to the outside (supination) and inside (pronation). Uniaxial articulations include h i n g e (elbow joint) and p i v o t j o i n t s (proximal and distal radioulnar articulations) (Fig.69). Biaxial joints have two axes of rotations, for example, flexion-extension and abduction-adduction. Such joints are the radiocarpal articulation (e l l i p s o i d), the carpometacarpal joint of the thumb and the atlanto-occipital joint (c o n d y l a r).

Multiaxial (triaxial) joints (shoulder and hip joints) are formed by spherical articular surfaces. They can perform all types of movement: flexion-extension, abduction-adduction and supination-pronation (rotation).

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Fig. 69. Articular facets.

A — pivot joint; B — ellipsoid joint; C — saddle joint; D — spheroidal (ball and socket) joint.

Multiaxial joints also include articulations with flat articular surfaces, which resemble spherical surfaces of a large diameter. The articular surfaces of these joints can make only slight gliding movements against each other.

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The amplitude of movement in a joint is defined by the shape, size and congruence of articular surfaces. Its mobility also depends on the tension of the articular capsule and its ligaments, as well as on individual, age and sexual characteristics.

Anatomic movement of the joints is defined by the difference in angles of articular surfaces. Thus, if an articular fossa has an angle of 140°, and the articular head — 210°, the possible amplitude of movement will be 70°. The greater is the difference of curvatures of the articular surfaces, the larger is the amplitude of movement in the joint.

AGE CHARACTERISTICS OF JOINTS

In embryogenesis all articulations are at first formed as continuous joints. Later, as bones are gradually drawn closer together, the mesenchyme layer between them becomes thinner and is replaced by fibrous or cartilage tissue. Synovial joints start forming during weeks 6–11 of embryogenesis. A slit appears in the mesenchyme layer between bones and the surrounding mesenchyme forms the articular capsule and ligaments. The deep layer of the capsule transforms into the synovial membrane. In complex articulations such as the knee and temporomandibular joints two articular slits are formed, and the mesenchyme between them transforms into an articular disk or meniscus. The cartilaginous glenoid labrum is formed from articular cartilage, when its central part resolves and becomes thin, while the peripheral part accretes to the borders of the articular surface. Symphyses are formed by transformation of mesenchyme between bones into cartilage, and generation of a narrow slit in its thickness.

In newborns all anatomic parts of joints are formed, however, their differentiation is still taking place. At this age the epiphyses of articulating bones are made up of cartilage. During ages 6–10 the structure of the synovial membrane becomes more complex: the number of synovial villi and folds increases and a vascular network and nerve endings are formed. The capsule goes through collagenation. During this period the capsule and its ligaments become significantly thicker and more durable. The formation of all joint elements becomes completed at age 13–16. With optimal functional loading joints do not undergo any involutional changes for many years. In circumstances of excessive long-term physical loading, as well as during aging, structural and functional changes do take place. These changes include thinning of articular cartilage, sclerosis of the capsule and ligaments, osteophyte formation at the borders of articular surfaces. A typical manifestation of these changes is a decrease of movement in the joint.

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Aging of bones and joints can be correlated with constitutional types. In persons with the brachymorphic constitutional type aging in hands, feet and large joints (shoulder joint, elbow joint, etc.) is usually faster compared to people with dolichomorphic constitution. Articular ends of most bones undergo age changes faster in women than in men. Involutional changes of different joints come about in a certain sequence. In terms of timing and intensity of changes, the knee and hip joints, joints of the lumbar section of the vertebral column and the sacroiliac articulation are usually the first to be afflicted. These joints bear significant pressure during standing and walking, which accelerates their deterioration. The next to undergo involution are usually articulations of the cervical section of the spine and upper extremity joints.

Questions for revision and examination

1.What are the different types of joints? Give the description of each type.

2.What are synovial joints?

3.Give the anatomical and biomechanic classifications of joints.

4.What is a syndesmosis? Describe its structure and give an example.

5.What is a synovial bursa? What is its function, and where is it situated?

6.What determines the amplitude of movement in a joint?

ARTICULATIONS OF THE BONES OF THE TRUNK

Joints of the vertebral column

Bodies of adjacent vertebrae are connected by intervertebral disks (dísci intervertebráales) or intervertebral symphyses (sýmphyses intervertebráles). Vertebral arches and processes are connected by means of joints and ligaments. Each vertebral disc is composed of a central part called the n u c l e u s p u l p o s u s, and a peripheral part called the a n u - l u s f i b r o s u s. The nucleus pulposus, which is a residue of the notochord (chorda) acts as a shock absorber between bodies of two adjacent vertebrae. Sometimes it contains a narrow horizontal slit, thus making a symphysis (semijoint). The peripheral part of the intervertebral disc (fibrous ring) is formed by fibrous cartilage (Fig. 70, 71).

The thickness of an intervertebral disc depends on its level in the vertebral column and the mobility of the corresponding section of the spine. In the thoracic portion, which is the least mobile, the disks are 3–4 mm thick; in the cervical portion, which has a high degree of movement, disks are 5–6 mm thick, and in the lumbar portion — 10–12 mm.

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of the vertebral canal, be-

ginning at the axial vertebra and down to the level of the first coccygeal vertebra. At the level of the middle atlanto-occipital articulation this ligament connects with the cruciate ligament of atlas, and to the bottom it accretes with the intervertebral discs.

Arches of neighboring adjacent vertebrae are connected by l i g a m e n t a f l a v a (l i g g . f l á v a e), which are formed by yellowish elastic connective tissue. These ligaments are very durable and resilient.

Between the articular processes there are zygapophyseal (intervertebral) joints (art. zygapophysiáles s. intervertebráles). The articular capsules of these joints are strengthened by fibers, which are attached to the borders of the articular surfaces. These articulations pertain to flat multiaxial immovable joints.

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tween the apex of the sacrum and the first coccygeal vertebra. Its vertebral disc often contains a fissure. Several ligaments strengthen this joint. One of them is the paired l a t e r a l s a c r o c o c c y g e a l l i g a m e n t (l i g . s a c r o c o c c ý g e u m l a t e r á l e), which runs from the lower edge of the lateral sacral crest and is analogous to intertrasversal ligaments. The v e n - t r a l s a c r o c o c c y g e a l l i g a m e n t (l i g . s a c r o c o c c ý g e u m v e n t r á l e) is a continuation of the anterior longitudinal ligament. The s u p e r f i c i a l d o r s a l s a c r o c o c c y g e a l l i g a m e n t (l i g . s a c r o c o c c ý g e u m d o r s á l e s u p e r f i c i á l e) runs between the edge of the sacral hiatus and the posterior surface of the coccyx. The d e e p d o r s a l s a c r o c o c c y g e a l l i g a m e n t (lig. sacrococcýgeum dorsále profúndum) is a continuation of the posterior longitudinal ligament and is situated on the posterior surface of the bodies of the Cx 1 and sacral vertebrae. The sacral and coccygeal horns are joint by connective tissue (syndesmoses). In women the sacrococcygeal joint is more mobile than in men. During labor the coccyx can shift somewhat backwards, which enlarges the maternal pathways.

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Articulations between the vertebral column and skull

The occipital bone of the skull articulates with the C1 and C2 vertebrae. These articulations can be described as highly durable, mobile and complex in structure (table 3).

The atlantooccipital joint (art. atlantooccipitális) is a combination condylar joint. It is formed by the two condyles of the occipital bone and the corresponding superior articular facets of the atlas. Each of these joints has its own articular capsule. They are strengthened by two atlantooccipital membranes. The a n t e r i o r a t l a n t o - o c c i p i t a l m e m b r a n e (membrána atlantooccipitáalis antérior) is stretched between the base of the occipital bone and the anterior arch of the atlas. The p o s t e r i o r a t - l a n t o - o c c i p i t a l m e m b r a n e (membrána atlantooccipitális postérior) is thicker and wider than the anterior membrane. It is attached to the posterior edge of the foramen magnum and the posterior arch of the atlas. The right and left atlantooccipital joints can move simultaneously. They can perform tilting movements (flexion-extention) forward, up to 20°, and backward, up to 30°, about the frontal axis. Movement can also be produced in these joints about the sagittal axis, tilting the head from the median line up to 20°.

The middle atlantoaxial joint (art. atlantoaxiális mediána) is formed by the anterior and posterior articular facets of the dens (Fig. 72). In the front it articulates with the facet for dens on the anterior arch of the

Fig. 72. Atlanto-axial joints.

A — horizontal cut, superior aspect. 1 — posterior articular facet; 2 — superior articular facet; 3 — dens (saw cut); 4 — fovea dentis; 5 — anterior articular facet; 6 — transverse ligament of atlas.

B — ligaments of a median atlantoaxial joint; posterior aspect. Frontal section at a level of posterior arch of atlas. 1 — alar ligament; 2 — longitudinal bands; 3 — occipital bone; 4 — apical ligament of dens; 5 — capsule of atlanto-occipital joint; 6 — axis; 7 — transverse ligament of atlas; 8 — lateral mass.

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