HUMAN ANATOMY – VOLUME 1

The subtalar joint (art. subtaláris) is formed by the posterior talar articular surface of the calcaneus and the posterior calcaneal articular surface of talus. The articular surfaces are congruent. The joint performs movements about the sagittal axis.

The talocalcaneonavicular joint (art. talocalcaneonavicularis) is formed by articular surface of the head of talus, the navicular bone in the front and the calcaneus underneath. The articular capsule attaches along the edges of articular surfaces and is strengthened by several ligaments. The t a l o c a l c a n e a l i n t e r o s s e o u s l i g a m e n t (l i g . t a l o c a l - c á n e u m i n t e r ó s s e u m) is very strong and is situated in the tarsal sinus between sulci of the calcaneus and talus. The p l a n t a r c a l c a - n e o n a v i c u l a r l i g a m e n t (l i g . c a l c a n e o n a v i c u l á r e p l a n t á r e) connects the inferior medial part of the sustentaculum tali and inferior surface of the navicular bone. The t a l o n a v i c u l a r l i g a - m e n t (l i g . t a l o n a v i c u l á r e) connects the dorsal surfaces of the neck of the talus and the navicular bone.

The movements in this joint, together with subtalar joint, are made about the sagittal axis. During abduction and adduction (eversion and inversion) the talus is fixated. Movement of the navicular and calcaneal bones causes displacement of the whole foot. During adduction of the foot its medial margin rises, while the back of the foot turns somewhat laterally. During abduction the lateral margin rises, and the back of the foot shifts medially. The total volume of movements about the sagittal axis does not exceed 55°.

The calcaneocuboid joint (art. calcaneocuboídea) is formed by adjacent articular surfaces of the calcaneus and the cuboid bones. This is a saddle joint with congruent articular surfaces and a limited degree of movement. The articular capsule is strengthened by the l o n g p l a n t a r l i g - a m e n t (l i g . p l a n t á r e l ó n g u m). This ligament begins on the inferior surface of the calcaneus, spreads out to the front like a fan and attaches to the bases of II–V metatarsal bones. Next to it is a short durable c a l c a n e o c u b o i d l i g a m e n t (l i g . c a l c a n e o c u b o í d e u m).

For practical reasons the calcaneocuboid and the talonavicular joints (which are part of the talocalcaneonavicular joint) are considered as the transverse tarsal joint (art. tarsi transversa), or Chopart’s joint. Apart from the ligaments strengthening each of the two articulations, Chopart’s joint has a common b i f u r c a t e l i g a m e n t (l i g . b i f u r c á t u m), which consists of two parts. The bifurcated ligament begins on the upper lateral margin of the calcaneus. One of its parts attaches to the posterior lateral margin of the navicular bone, and the other — to the back of the cuboid bone. When the bifurcated ligament is dissected, the structure of

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the foot looses its stability. This ligament is therefore called the key of the Chopart’s joint.

The cuneonavicular joint (art. cuneonaviculáris) is formed between plane articular surfaces of the navicular bone and three cuneiform bones. The articular capsule attaches along the edges of articular surfaces. The joint is strengthened by numerous ligaments, including the plantar and d o r s a l c u n e i f o r m l i g a m e n t s, i n t e r o s s e o u s i n t e r c u n e i - f o r m l i g a m e n t s, the p l a n t a r and d o r s a l i n t e r c u n e i f o r m l i g a m e n t s. Movement in this joint is very slight.

The tarsometatarsal joints (art. tarso-metatarsáles), or Lisfranc’s joints, are formed between the plane articular surfaces of the navicular and cuneiform bones and the metatarsal bones. These articulations include three independent, isolated joints: the junction of the medial cuneiform and I metatarsal bone; junction of II and III metatarsal bones with the intermediate and the lateral cuneiform bones; and articulation between the cuboid bone with the IV and V metatarsal bones. The articular cavities do not communicate among themselves. The capsules are attached along the edges of articular surfaces. They are strengthened by the d o r s a l a n d p l a n t a r t a r s o m e t a t a r s a l l i g a m e n t s (l i g g . t a r s o m e t a t a r - s á l i a d o r s á l i a e t p l a n t á r i a). The i n t r a-a r t i c u l a r i n - t e r o s s e o u s c u n e o m e t a t a r s a l l i g a m e n t s are also considered important. The m e d i a l i n t e r o s s e o u s c u n e o m e t a t a r s a l l i g - a m e n t, which connects the medial cuneiform bone and the base of the II metatarsal bone, is called the key of the Lisfranc’s joint. There is only slight movement possible in these joints.

The intermetatarsal joints (artt. intrmetatarsáles) are formed between adjacent bases of metatarsal bones. The articular surfaces are strengthened by t r a n s v e r s e d o r s a l and p l a n t a r m e t a t a r s a l l i g a m e n t s (l i g g . m e t a t a r s á l i a d o r s á l i a e t p l a n t á r i a). Between the articular surfaces, in the articular cavities there are m e t a t a r - s a l i n t e r o s s e o u s l i g a m e n t s (l i g g . m e t a t a r s á l i a i n t e r o s - s e a). Movement in the intermetatarsal joints is very limited.

The metatarsophalangeal joints (artt. metatarsophalageae) are formed between heads of the metatarsal bones and bases of the proximal phalanges. The articular surfaces of the phalanges are almost spherical, while the articular fossae of the metatarsal bones are oval in shape. The thin articular capsule is strengthened at the sides by c o l l a t e r a l l i g a - m e n t s and at the bottom by the p l a n t a r l i g a m e n t s. The heads of the metatarsal bones are connected by the d e e p t r a n s v e r s e m e t a - t a r s a l l i g a m e n t (l i g . m e t a t a r s á l e t r a n s v e r s u m p r o f u n - d u m), which accretes the capsules of all metatarsophalangeal joints. Move-

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Fig. 83. Structure of arches of foot.

A — longitudinal arch; 1 — calcaneus; 2 — talus; 3 — navicular; 4 — intermediate cuneiform; 5 — II metatarsal bone; 6 — phalanges of 2nd digit.

B — transverse arch: I — V — transversal cut of metatarsal bones.

ments in these joints are flexion and extension about the frontal axis, with the total volume of 90°. Abduction and the adduction about the sagittal axis are possible only within a limited volume (table 7).

The interphalangeal joints of foot (artt. interphalangeae pedis) are hinge joints. They are formed between bases and heads of neighboring phalanges of the foot. They have loose articular capsules, attached along the edges of articular surfaces. The capsules are strengthened by the p l a n t a r and the c o l l a t e r a l l i g a m e n t s. The interphalangeal joints carry out flexion and extension about the frontal axis with the total volume of these movements no more than 90°.

Characteristics of the joints of the lower extremities are demonstrated in the table 7.

The foot as a whole

The foot is adapted for creating support. This is determined by the presence of tight joints and durable ligaments. The joined bones of the foot form several l o n g i t u d i n a l and t r a n s v e r s e a r c h e s (Fig. 83).

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Five longitudinal arches begin at the calcaneus and spread in fan-like fashion forward to the heads of metatarsal bones. At the level of the highest points of the longitudinal arches is the transverse arch. Due to the structure of these arches the foot rests on three main points of support instead of its whole surface. These points are the calcaneal tuber in the back, and heads of the I and V metatarsal bones in front.

The arches of the foot are supported by the shape and arrangement of the bones and by ligaments (these are so-called passive supports), and by muscle tendons (active supports). The strongest support of the longitudinal arches are the long plantar, the plantar calcaneonavicular and some other ligaments. The transverse arch of the foot is strengthened by the deep transverse metatarsal ligament and other ligaments stretched in the transverse direction.

Muscles and their tendons, that are oriented in the longitudinal direction, actively strengthen corresponding arches, while muscles and tendons oriented transversally strengthen the transverse arch. If the active and passive supports become relaxed, the arches of the foot will lower resulting in a «flat foot», or «fallen arch».

Questions for revision and examination

1.Why is the sacrum considered the «key» of the pelvic ring? What type of articulations is formed between the sacrum and the hipbones?

2.Name the sizes of the greater and lesser pelves. What practical importance to they

have?

3.What differences (in structure) are there between the coxal and the shoulder joints?

4.What ligaments support the knee joint? Where are these ligaments situated and how do they influence movement in this joint?

5.Where is the subtalar joint located and what is its structure?

6.Which joint is called the transverse joint of the foot? What ligament acts as the «key» of this joint?

7.Name the arches of the foot. What formations serve as active and passive supports of these arches?

THE MUSCULAR SYSTEM

Skeletal muscles are attached to bones and, by contracting, cause them to move (Fig. 84). Muscles participate in formation of body cavities and have influence upon organs of sight, hearing and equilibrium. They help to retain the body in balance, provide support and movement, accomplish respiration and swallowing and perform facial gestures. Muscles compose approximately 20–22 percent of total body weight in a newborn, up to 40 percent in an adult and 25–30 percent in senile age. The human body contains about 400 muscles, which contract voluntarily, when a person wills them to.

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Fig. 84. Beginning and attachment of a muscle.

1 — muscular bundles; 2 — tendon.

STRUCTURE OF THE SKELETAL MUSCLES

The principle elements of the skeletal muscles are striated muscle fibers. These fibers are surrounded by loose connective tissue called e n - d o m y s i u m. Bundles, or fascicles, of fibers are separated from one another by connective tissue layers called perimysium, and the whole muscle is surrounded by the e p i m y s i u m (o u t e r p e r i m y s i u m). Loose connective tissue found in muscles performs functions of support and demarcation between functional elements. It also holds the blood vessels, which nourish muscle fibers, and nerves.

The length of muscle fibers varies from several millimeters to 12.5 cm (in the sartorius muscle), and its thickness—from 9 to 100 mm. In short muscles the length of fibers may be equal to the length of the muscle, while in long muscles it is much shorter.

Muscle fibers form the fleshy part of the muscle called the v e n t e r, which continues into the muscle t e n d o n. The muscle fascicles or the tendon attach to bones. Tendons consist of dense connective tissue, which are rich in collagen fibers and are formed as a continuation of muscle connective tissue elements into the periosteum. Tendons of different muscles vary in structure. Muscles of extremities have long tendons, muscles of abdominal walls have broad flat tendons called a p o n e u r o s i s. Some muscles have an intermediate tendon, which divides the muscle into two venters. Muscle fibers are some muscles (the straight muscle of abdomen) are interrupted by tendon partitions (short tendons). Tendons are considerably thinner than muscles, but possess very high durability.

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CLASSIFICATION OF MUSCLES

There are several ways of classification of skeletal muscles. Muscles can be classified according to topography, shape, orientation of fibers, function and position relative to joints. They are divided into superficial and deep, lateral and medial, and internal and external.

Muscles can be of many possible shapes (Fig. 85). Walls of the abdomen are formed by broad strap muscles. Fusiform muscles are typical for the extremities. They attach to bones and move them like levers. Fascicles in a fusiform muscle are oriented parallel to its longitudinal axis. Muscles in which fiber fascicles are situated only on one side of the tendon are called unipennate. If they are situated on two sides, the muscle is called bipennate. And if fascicles extend from several sides of the tendon, the muscle is called multipennate.

Some muscles have two or more heads of origin, which connect with each other into a common venter that continues into one insertion tendon. These are named according to the number of their heads, for example, biceps, triceps, etc. There are also muscles, which have a common venter and several points of attachment (e.g. the extensor muscle of fingers). Some muscles have a circular fiber arrangement. These usually surround natural

Fig. 85. Forms of muscles.

A — fusiform muscle; B — unipennate muscle; C — bipennate muscle; D — two-headed muscle; E — strap (band-shaped) muscle; F — two-bellied muscle; G — sphincter.

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openings and are called sphincters. There are also muscles with radial fiber arrangement found around openings (dilator muscles).

Many muscles of the body are named according to their shape. Thus, there is a rhomboid muscle, the orbicular muscles, etc. Some muscles were named based on the orientation of their fibers (transverse muscle of the abdomen) or according to their function (levator scapulae muscle, pronator teres, pronator quadratus, etc).

Muscles can be divided into groups according to their association with joints. They can bear influence upon only one joint (monoarticular) or two or more joints (biarticular and multiarticular). Some muscles have a point of origin on a bone, and insert into the skin without passing over any joints (muscles of facial expression, ets.)

Finally, muscles are divided according to function into synergists and antagonists. Synergists are muscles, which cause movement in the same direction, while antagonists cause movement in opposite directions.

THE AUXILIARY APPARATUS OF MUSCLES

The work of muscles is directed by specialized anatomic formations that compose the auxiliary apparatus of muscles. These include fasciae, fibrous canals, tendon sheaths, synovial bursae and trochleae of muscles.

Fasciae are connective tissue encasements of muscles. They separate muscles from each other, support them during contraction, and for some muscles they serve as a point of origin. In pathological processes fasciae can restrict the spreading of pus or blood (during hemorrhage). Fasciae are divided into superficial and deep. Superficial fasciae are situated beneath the skin separating muscles from subcutaneous fat. Deep fasciae are situated between adjacent muscle layers. There are, 0sually, intermuscular partitions between groups of muscles with different functions. These begin on a superficial or deep fascia and attach to the periosteum. In places, where fasciae are connected to each other, and which undergo considerable pressure, there are often thickenings of the fascia called f a s c i a l n o d e s. These nodes usually contain blood vessels and nerves. Another example of fascial thickenings are tendon arcs, which pass over neurovascular bundles or tendons. Fasciae can have thickening in regions of joints, forming retinacula of tendons. Retinacula are usually attached to bone protrusions and serve to fix tendons in a certain position, preventing their displacement during muscle contraction.

Between retinacula of muscles and underlying bones there are osteofibrous or fibrous canals, divided into sectors with connective tissue partitions. These canals contain s y n o v i a l t e n d o n s h e a t h s (Fig.

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86, 87). The visceral part of a s y n o v i a l s h e a t h directly lines the tendon, while the parietal part fuses with the wall of the canal. The visceral and parietal layers continue into each other at the end of the sheath and along the length of the sheath, forming a mesotendinium. The mesotendinium contains vessels and nerves, which nutrify the tendon. During muscle contraction, the visceral part of the sheath moves with the tendon. The two parts slide easily

region of a joint. These serve to

increase the angle between the tendon and the bone. The largest sesamoid bone found in the body is the patella. Sometimes there is a synovial bursa situated between the bone and the muscle, tendon or skin, which decreases friction and eases the sliding of the muscle. On the outside the wall of the

Fig. 87. Synovial sheath of tendon.

A — transverse section; B — longitudinal section. 1 — fibrous sheath; 2 — synovial sheath; 3 — tendon; 4 — synovial cavity; 5 — mesotendon.

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