What are metacarpal bones? What functions do they perform? You will find answers to these and other questions in the article. The hand is the distal part of the hand, the skeleton of which consists of the metacarpal bones, fingers (phalanx) and the wrist.
Structure
What are metacarpal bones? We will answer this question further, and now we will find out the structure of the wrist. It consists of eight spongy short bones placed in two lines, four in each:
- upper: trihedral, scaphoid, lunate, pea-shaped;
- lower: capitate, trapezoid, hook-shaped, trapezoid bone.
The lower ends of the radius and ulna adhere to the carpal bones, forming a wrist complex joint, in which it is possible to make revolutions along all three axes. The bones of the lower line are attached at the top to the bones of the upper, at the bottom - to the knuckles of the metacarpus, as well as to each other, forming low-moving joints.
The metacarpal bones form the next line of bones. There are only five, according to the number of fingers. Their base is connected to the bones of the wrist. Like the metacarpals, the phalanges of the fingers are tubular short bones. Each finger has three phalanges: proximal (base), middle and distal or terminal (nail). Only the thumb is an exception, as it is formed by two phalanges - the nail and the main. Movable joints are formed between the phalanges of each finger and metacarpal bone.
Metacarpal bones
How many bones are in the metacarpus? It consists of five metacarpal tubular bones. The second oblong metacarpal is the most oblong, and the metacarpal bone of the thumb (first) is the shortest, which is distinguished by its massiveness.
The remaining knuckles towards the ulnar border of the hand decrease in length. Each metacarpal bone has a head, base, and body. Their bases are articulated with carpal bones. The articular surfaces of the bases of the fifth and first metacarpal bones have saddle outlines. The rest have a flat articular surface. The metacarpals have heads that differ in a hemispherical articular surface and connect to the proximal bones of the fingers.
Details
So, we continue to study the metacarpus. How many bones does she have? We already know that the five metacarpal bones form the metacarpus. By type, they belong to tubular short bones with a single real epiphysis (monoepiphyseal bones). They are called in order - I, II, III and so on, starting from the first finger.
At the proximal extremities of the bases of the II-V bones there are articular flat facets that serve as a connection with the bones of the second line of the wrist, and those that are placed on the sides, for communication between themselves. The basis of the metacarpal knuckle I is articular saddle-shaped and attached to the carpal trapezoid bone, but there are no lateral facets here.
The base of the II metacarpal bone forms a notch in the shape of an angle, covering the carpal bone. On the basis of the V metacarpal knuckle, on its ulnar side, there is a tubercle. On the heads of the metacarpal bones there are articular convex surfaces necessary for articulation with the proximal bones of the fingers. Rough grooves are visible on the sides of the heads - the places where the ligaments are attached.
Tubular bones
It is known that tubular small bones include metacarpal bones and phalanges of the fingers, as well as metatarsal bones. The tubular long bones include the femur, fibula, and tibia, as well as the ulnar, humerus, and radius. The oblong bones of the legs are approximately half human height.
What are tubular bones? These are bones of a trihedral or cylindrical shape, the width of which is less than the length. They have epiphyses on the extremities covered with hyaline articular cartilage and grow mainly due to an increase in body length (diaphysis). Between the diaphysis and epiphyses metaphyses are located, which contain epiphyseal cartilaginous plates in childhood and puberty.
Structure
So, you already know how many human bones (metacarpals) are involved in the movement of the fingers. And what is the structure of the tubular bone? Outside, it is covered with a periosteum - a layer of connective tissue. Bone pineal gland is represented mainly by bone spongy substance containing bone red brain, diaphysis - bone compact substance. In the center of the diaphysis there is a bone marrow canal, which in adults is filled with yellow marrow. This substance contains fat cells.
Brush
The metacarpal bones and phalanges of the fingers belong to the skeleton of the hand. What are the bones of the fingers? These are small bones placed one after another with a single real pineal gland (multi-pineal bones). They are called phalanges. Each finger has three phalanges: middle, distal and proximal. The thumb is an exception, as it has only two phalanges - distal and proximal. In all animals, it is poorly developed and reaches maximum growth only in humans.
The proximal bone base carries a single articular fossa, which is needed to connect to the spherical head. The bases of the distal and middle phalanges have two flat grooves, fenced off by a scallop. They are linked to the heads of the middle and proximal phalanges, which grow in the form of a block with a recess in the center.
The end of the phalanx is flattened and roughened. In the area of the interphalangeal and metacarpophalangeal joints of the hand, where the tendons are attached, there are sesamoid bones. They are constant on the first finger and mutable on others.
Spherical joints of the brush
The hand has metacarpophalangeal joints, which are formed by the bases of the proximal phalanx of the fingers and the heads of the metacarpal bones. All these joints have three mutually perpendicular axes of rotation, around which there is a distance and adduction, circumduction (circular motion), straightening and bending, and they also have a spherical shape. Extension and bending are possible at 9-100 °, reduction and abduction - at 45-50 °.
Collateral ligaments strengthen the metacarpophalangeal joints and are located on the sides of them. On the palm side, the capsules of these joints have extra ligaments called the palmar. Their fibers are intertwined with the fibers of the transverse deep metacarpal ligament, which inhibits the divergence of the heads of the knuckles of the metacarpus to the sides.
Flat joints
Everyone should know how many bones are in the metacarpus. And what are the carpal-metacarpal joints of the hand? These are joints of the distal line of the carpal bones with the bases of the metacarpals. These joints are inactive and have a flat shape, minus the wrist-metacarpal joint of the first finger. The magnitude of the movements in them does not exceed 5-10 °. Lability in these joints, as well as between the carpal bones, is localized by superbly developed ligaments.
Ligaments placed on the surface of the palm make up a strong ligamentous palm apparatus. He attaches the carpal bones to each other, as well as to the metacarpal bones. The capitate bone in the ligamentous apparatus is central. It is to her that most of the ligaments are attached.
The back ligaments of the hand are developed much weaker than the palmar. They combine the wrists together and are part of thick capsules that cover the joints placed between these bones. To the second line of the carpal bones, in addition to the palmar and dorsal, interosseous ligaments are also attached.
The bones of the distal line of the wrist and the four (II-V) metacarpals are manoeuvrable in relation to each other and are tightly connected to the whole device that makes up the main bone nucleus of the bone. In this regard, they are marked as a solid base brush.
The polygonal bone and the base of the first metacarpal bone forms the carpal-metacarpal joint of the first finger of the hand. The surfaces of the joints have a saddle shape. In the joint, such movements are possible: abduction and adduction, reverse movement (reposition) and opposition (opposition), as well as circumduction (circular motion).
The thumb is opposed to all other fingers, so the volume of grasping movements of the hand is significantly increased. The mobility parameters in the wrist-metacarpal joint of the first finger are 45-60 ° for adduction and abduction and 35-40 ° for reverse movement and contrast.