What are metacarpus 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 metacarpal bones, fingers (phalanges) and wrist.
Building
What are metacarpus 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, navicular, lunate, pisiform;
- lower: capitate, trapezium, hamate, trapezius.
The lower ends of the radius and ulna interlock with the carpal bones, forming a complex wrist joint, in which rotations can be made in all three axes. The bones of the lower line are attached above to the bones of the upper, below - to the knuckles of the metacarpus, as well as to each other, forming slow-moving joints.
The next line of bones is formed by the bones of the metacarpus. There are only five of them, according to the number of fingers. Their base is connected to the bones of the wrist. Just like the metacarpal bones,the phalanges of the fingers are tubular short bones. Each finger has three phalanges: proximal (basic), 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 the metacarpal bone.
Metacarpus bones
How many bones are in the metacarpus? It consists of five metacarpal tubular bones. The most oblong is the second metacarpal bone, and the shortest is the metacarpal bone of the thumb (first), which is distinguished by its massiveness.
The rest of the knuckles decrease in length towards the ulnar border of the hand. Each metacarpal has a head, base, and body. Their bases articulate with the carpal bones. The articular surfaces of the bases of the fifth and first metacarpal bones have a saddle shape. The rest have a flat articular surface. The metacarpal bones have heads that are distinguished by a hemispherical articular surface and are connected 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 five metacarpal bones form the metacarpus. By type, they belong to tubular short bones with a single true epiphysis (monoepiphyseal bones). They are called in order - I, II, III, and so on, starting from the first finger.
On the proximal extremities of the bases of the II-V bones there are articular flat facets that serve as a connection withbones of the second line of the wrist, and those that are located on the sides - for communication with each other. The basis of the I knuckle of the metacarpus has an articular saddle shape and is articulated with the carpal trapezoid bone, while there are no lateral facets here.
The base of the II bone of the metacarpus forms a cut in the form of an angle, covering the carpal bone. On the base of the fifth metacarpal knuckle, on its ulnar side, there is a tubercle. The heads of the metacarpal bones have convex articular surfaces necessary for articulation with the proximal bones of the fingers. Rough notches are visible on the sides of the heads - the places where the ligaments are attached.
Tubular bones
It is known that the bones of the metacarpus and phalanxes of the fingers, as well as the metatarsal bones, belong to the tubular small bones. The tubular long bones include the femur, fibula, and tibia, as well as the ulna, humerus, and radius. The oblong bones of the legs are about half the size of a human being.
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 at their extremities, covered with hyaline articular cartilage, and grow mainly due to an increase in body length (diaphysis). Metaphyses are located between the diaphysis and the epiphyses, containing epiphyseal cartilaginous plates in childhood and puberty.
Structure
So, you already know how many human bones (metacarpus) are involved in the movement of the fingers. What is the structure of a tubular bone? Outside, it is covered with a periosteum - a layerconnective tissue. The bone epiphysis is represented mainly by bone spongy substance containing bone red marrow, the diaphysis is represented by compact bone substance. In the center of the diaphysis there is a medullary canal, which in adults is filled with yellow bone marrow. This substance contains fat cells.
Brush
The bones of the metacarpus and phalanges of the fingers belong to the skeleton of the hand. What are finger bones? These are small, placed one after another bones with a single real epiphysis (mnoepiphyseal 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 its maximum growth only in humans.
The basis of the proximal bone carries a single articular fossa, which is needed to connect with the spherical head. The bases of the distal and middle phalanges have two flat notches separated by a comb. They are linked to the heads of the middle and proximal phalanges, which grow in the form of a block with a depression in the center.
The end of the phalanx is flattened and rough. In the region 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 changeable on the others.
Ball joints of the hand
The hand has metacarpophalangeal joints, which are formed by the bases of the proximal phalanges of the fingers and the heads of the metacarpalbones. All these joints have three mutually perpendicular axes of rotation, around which there is a distance and adduction, circumduction (circular movement), extension and flexion, and they also have a spherical shape. Extension and flexion are possible at 9-100°, adduction and abduction - at 45-50°.
Collateral ligaments reinforce the metacarpophalangeal joints and are placed on the sides of them. From the side of the palm, the capsules of these joints have additional ligaments, which are called 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 carpometacarpal joints of the hand? These are the articulations 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 carpometacarpal joint of the first finger. The magnitude of 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 located on the surface of the palm make up a strong ligamentous palmar apparatus. It attaches the carpal bones to each other as well as to the metacarpal bones. The capitate bone of the ligamentous apparatus is central. It is to her that most of the ligaments are attached.
The dorsal ligaments of the hand are much less developed than the palmar ligaments. They unite the wrists and are part of thick capsules,which cover the joints located between these bones. In addition to the palmar and dorsal bones, the interosseous ligaments are also attached to the second line of the carpal bones.
The bones of the distal line of the wrist and the four (II-V) bones of the metacarpus are hardly maneuverable in relation to each other and are tightly connected into an integral device that makes up the main bone nucleus of the bone. In this regard, they are marked as a hard base of the brush.
The polygonal bone and the base of the first bone of the metacarpus forms the carpometacarpal joint of the first finger. The surfaces of the joints have a saddle shape. The following movements are possible in the joint: abduction and adduction, reverse movement (reposition) and opposition (opposition), as well as circumduction (circular movement).
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 carpometacarpal joint of the first finger are 45-60° in adduction and abduction and 35-40° in reverse movement and opposition.
