FUNCTIONAL ANALYSIS OF THE SHOULDER JOINT OF ANIMALS

Abstract

According to the results of the study it was found that at the most bent position of the shoulder joint the posterior part of the articular head of the humerus is in contact only with the central most concave part of the articular cavity of the scapula, while its posterior half protrudes beyond the posterior edge of the humeral head and between the anterior parts. heads and depressions there is a rupture of contact with formation of a crack. Movements in the shoulder joint of ungulates are straightforward, which ensures the speed of translational movements and not fatigue of the animal, but reduces the freedom and variety of permissible movements. Lateral movements in the shoulder joint of these animals are only accompanying, namely the extension is accompanied by abduction, and flexion - reduction. Unlike terrestrial stop-, toes - and phalanx-walking animals, a completely different type of movement in the shoulder joint of mammals, whose limbs are the working organ. In diggers (mole, blind man) - it is monotonous flexion-extension movements, in floating (seal, whale), flying (bats), bipeds (jerboa) - these are large rotational movements, in primates and humans - these are movements around many axes of the joint. The shape of the shoulder joint for established walking animals is characterized by more movements of the thoracic extremities. Distinctive features of the shoulder joint of walking feet are the following: 1) the articular head of the humerus has a spherical shape 2) the articular cavity of the scapula is slightly concave and is half the size of the head of the humerus. 3) large and small humps of the humerus are located below the top of the articular head. 4) the lateral and medial muscular humps of the humerus are pushed back, and the scapular hump is located at the anterior edge of the articular cavity of the scapula. These features of the structure of the shoulder joint of the feet indicate different movements (washing, swimming, climbing). In large walking (badger, bear) the articular head of the humerus is compacted and divided (in the badger) into two sections: posterior, more convex and anterior flat, and in the bear the articular head of the humerus is flattened. In large feet walking, the articular cavity of the scapula is deep. The large and small humerus of these animals are higher, and the lateral and medial muscular humps go forward from the axis of rotation of the joint. Walking was the result of adaptation of animals to faster movement and prolonged loading of the limbs. Therefore, in the shoulder joint, the walking fingers are directed movements and are characterized by the following features:

1) the articular head of the humerus has an ellipsoidal shape and is divided into 2 sections: posterior convex and narrowed and anterior - much flat and expanded. 2) a large humerus protrudes above the top of the articular head and part of its inner surface is covered with cartilage. 3) lateral and medial muscular humps are located in front of the articular head of the humerus; the scapular tubercle is further from the anterior edge of the articular cavity of the scapula. 4) muscles that act on the shoulder joint contain more tendons.

In cats, the articular head of the humerus has a spherical shape with a slight flattening in the anterior part, in dogs the head of the humerus is very clearly divided into 2 sections: posterior convex and anterior flattened, acts as a support.

For ungulate limbs is characterized by a supporting type of structure. The limbs of ungulates, with a massive body and a small area of ​​support, feel the load, with the following devices in the shoulder joint:

1) the articular head of the humerus is strongly flattened. The articular cavity of the scapula increases in size and more fully covers the articular head of the humerus. 2) large and small humps of the humerus significantly protrude above the top of the articular head and act as a braking device and limit extension. 3) the lateral and medial muscular humps are displaced far forward, beyond the anterior edge of the articular head of the humerus, and the scapular tubercle is removed from the anterior edge of the articular cavity of the scapula. 4) muscles of the shoulder joint are statistical.

As a result of these adaptive changes, ungulates increase the direction of movement and strength of the shoulder joint, but decreases the freedom and variety of movements. Thus, the change in the type of support in the transition from the toes and phalanx to walking causes changes in the shoulder joint and surrounding muscles: 1) The articular head of the humerus goes from a convex spherical shape to a flatter shape. 2) The shape of the articular cavity of the scapula changes. The more convex articular head of the humerus of the foot of walking animals corresponds to the flat articular cavity of the scapula, while in the phalanx of the walking flat articular head of the humerus corresponds to the deeper articular cavity of the scapula. 3) Large and small humps of the humerus with the transition from foot to toe - and the phalanx of walking move forward, develop more strongly and protrude beyond the most convex part of the articular head, acquiring the value of bone brakes and extensors (bull, horse). 4) Lateral and medial muscular humps of the humerus move forward, and the scapular tubercle is removed from the anterior edge of the articular cavity of the scapula, so that the muscles are able to show great strength at low tension. 5) The muscles surrounding the shoulder joint with the transition from the foot to the toe - and the phalanx of walking, become more static, giving greater strength to the joint and ensuring the direction of their permissible movements.

Adaptive changes of joints in narrowly specialized forms are established. Thus, the shoulder joint of digging mammals (mole, blindfold) was formed as a result of uniform movements. In this regard, the head of the humerus acquires a narrow elongated shape and connects with the same elongated cavity of the scapula, the width of which is almost equal to such a head, eliminates the possibility of lateral movements. In addition, in digging forms, the articular head of the humerus is displaced so polar that its long axis is almost parallel to the length of the axis of the humerus, so that the reference value of the humeral joint is minimized.  The basis of the shape of the shoulder joint of floating animals (seal, dolphin) is a segment of a regular ball, due to the presence of large rotational movements in the shoulder joint (steering value of fins and fins). The shoulder joint of flying forms of movement - rotation is also peculiarly specialized. Unlike other mammals, the extension in the humeral joint of the wing arms is replaced by an inward rotation, and the flexion is replaced by an outward rotation, due to which the articular head of the humerus has acquired the shape of a transverse roller.  The shoulder joint of monkeys, has a similar structure to that of the foot and toes of walking animals, the head of the humerus has a front flattened section. The shoulder joint of monkeys, the thoracic limbs of which have a supporting function, in connection with the vertical position of the body, as well as the shoulder joint of man, whose thoracic limbs are transformed into tools, the closest to a spherical shape.  The cartilage of a shoulder joint - is thinner on periphery, and on concave, on the contrary, - is thinner in the center and thicker on periphery is investigated. We studied the thickness of articular cartilage on 45 preparations of the shoulder joint of 17 species of animals and compared with the anatomy of the human shoulder joint. The data of this study give grounds to establish: 1. In typical walking animals, with a greater working function of the thoracic limbs (marmot, beaver, nutria) on the head of the humerus, the articular cartilage reaches a greater thickness in its posterior part. This distribution of articular cartilage indicates that in walking the greatest load falls on the back of their limbs, which are in a bent position during support. 2. In the finger - and the phalanx of walking animals (domestic cat, lion, dog, pig, camel, bull, elk, sheep, horse) cartilage on the articular cavity of the scapula is thick in the center and thinner on the periphery. At the same time the big thickness of a head of a joint of a humerus, experiences big pressure at the maximum extension in a joint. The same distribution of cartilage of the joint in large walking (badger, bear), with a large body weight. 3. In monkeys, resting on the movement of all four limbs, in the distribution of articular cartilage, there is an articular head of the humerus, which acts as a support plane at high load on the limbs. 4. In monkeys and humans, whose shoulder joint is closest to the ball and whose limbs have little support function or are completely devoid of such (in humans), the articular cartilage in the scapula is thinned in the center and thickened in the center and thinned on the periphery).  Thus, the results show that the thickness of the articular cartilage depends on the distribution of the load experienced by the joint during movement, and the shape of the articular surfaces. The cartilage is most delicate in those areas where the joint is under great pressure. Therefore, the generally accepted position of greater thickness of articular cartilage in the center of convex articular surfaces and smaller - on the periphery is correct only for the most spherical shoulder joints of those mammals whose thoracic limbs have little support function (monkeys), as well as for the human shoulder joint.  The connecting apparatus of the shoulder joint - the capsule of the shoulder joint of walking animals (marmot, beaver, nutria, otter) is a thin bag with a bundle of fibrous fibers and fixed directly on the edges of the articular surfaces. Inside the joint there is an internal ligament separated from the capsule which originates on the hump of the scapula, passes along the head of the humerus and  to the posterior edge of the small mound, this ligament restricts movement in the joint.  The capsule of the shoulder joint of the walking foot (badger, bear), as well as the walking fingers (cat, lion, dog) is thicker, with almost evenly developed fibrous layer in all areas and reinforced by three ligaments, which are local thickenings of the capsule wall, and internal - is an independent entity. The capsule of the shoulder joint of the walking phalanx (camel, bull, horse) is even thicker than in the walking finger and is reinforced by two ligaments which, with the thick wall of the capsule. In all fingers - and the phalanx of the walking wall of the capsule at the level of the tendons of the muscles forms a large number of folds - a margin for stretching during movements. This is evidenced by the presence in these places of fat between the tendons and the capsule, which protect it from pressure from the tendon strands at the time of their tension. The capsule of the shoulder joint of digging (mole, blindfold), floating (seal, dolphin) and jumping (jerboa) animals is strengthened only by the internal ligament.  All these connections have an inhibitory effect, mainly on the lateral movements in the shoulder joint and the relationship of the articular surfaces. The shoulder joint of walking animals has a great variety and mobility. Combat movements reach almost the same scale as flexion-extension. Large scope is provided by: large sphericity of the constituent surfaces and insignificant area of ​​contact between them, the lack of bone brakes focus, greater muscle dynamics around the shoulder joint, and other features of the structure of the limb as a whole and its function. Due to these features, the shoulder joint of walking animals provides, along with the locomotor function of the extremities, also one working function.