On closer examination, the structure of the hand, like any other department of our musculoskeletal system, is quite complex. It is made up of three main structures: bones, muscles, and ligaments that hold the bones together. There are three sections in the hand, namely, the wrist, fingers and metacarpus.
In this article we will take a closer look at the hand: structure, muscles, joints of the hand. Let's start with a description of the bones in its various departments.
Wrist bones
Since the hands must perform fairly precise and intricate movements, the structure of the bones of the hand is also extremely complex. In the wrist - 8 small bones of irregular shape, arranged in two rows. In the figure below you can see the structure of the right hand.
The proximal row forms an articular surface convex to the radius. It includes bones, if you count from the fifth to the thumb: pisiform, trihedral, lunate and scaphoid. The next row is the distal one. It connects to an irregularly shaped proximal joint. The distal row consists of four bones: trapezoid, polygonal, capitate and hamate.
Bonesmetacarpus
This section, consisting of 5 tubular metacarpal bones, also demonstrates the intricate structure of the hand. The skeleton of these tubular bones is complex. Each of them has a body, base and head. The metacarpal bone of the 1st finger is shorter than the others and is massive. The second metacarpal is the longest. The rest decrease in length as they move away from the first and approach the ulnar edge. The bases of the aforementioned metacarpus bones articulate with the bones that form the wrist. The first and fifth metacarpals have bases with saddle-shaped articular surfaces, the others are flat. The heads of the metacarpal bones, which have an articular surface (hemispherical), articulate with the proximal digital phalanges.
Finger bones
Each finger, with the exception of the first, which consists of only two phalanges and does not have a middle one, has 3 phalanges: distal, proximal and middle (intermediate). The shortest - distal; proximal - the longest. There is a phalanx head at the distal end, and its base at the proximal end.
Sesamoid bones of the hand
In the thickness of the tendons, in addition to these bones, there are sesamoid, located between the proximal phalanx of the thumb and its metacarpal bone. There are also unstable sesamoid bones. They are located between the proximal phalanges of the fifth and second fingers and their metacarpals. Usually sesamoid bones are located on the palmar surface. But sometimes they can be found on the back. The pisiform bone also refers tothe above type. Sesamoid bones and their processes increase the leverage of the muscles attached to them.
We examined the structure of the hand and the bones of the hand, now let's move on to the ligamentous apparatus.
Wrist joint
It is made up of the radius and the bones of the proximal row of the wrist: trihedral, lunate and navicular. The ulna is complemented by the articular disc and does not reach the wrist joint. The main role in the formation of the elbow joint is played by the ulna. Whereas the wrist - radial. The wrist joint is elliptical in shape. It allows abduction, adduction of the hand, flexion and extension. A small passive rotational movement (by 10-12 degrees) is also possible in this joint, but is carried out due to the elasticity of the articular cartilage. Through soft tissues, it is easy to detect the gap of the wrist joint, which is palpable from the ulnar and radial sides. With the ulna, you can feel the depression between the triquetral bone and the head of the ulna. On the radial side - a gap between the navicular bone and the lateral styloid process.
Movement of the wrist joint is closely related to the work of the mid-carpal joint, located between the distal and proximal rows. Its surface is complex, irregular in shape. With flexion and extension, the range of mobility reaches 85 degrees. Adduction of the hand in the above-mentioned joint reaches 40 degrees, abduction - 20. The wrist joint can perform circumduction, i.e. roundabout.
This joint is reinforcednumerous links. They are located between individual bones, as well as on the lateral, medial, dorsal and palmar surfaces of the wrist. The collateral ligaments (radius and ulna) play the most important role. On the ulnar and radial sides, between the bone elevations, there is a flexor retinaculum - a special ligament. In fact, it does not apply to the joints of the hand, being a thickening of the fascia. The flexor retinaculum turns the carpal groove into a canal through which the median nerve and flexor tendons of the fingers pass. Let's continue to describe the anatomical structure of the hand.
Carpometacarpal joints
They are flat, inactive. The exception is the joint of the thumb. The range of motion of the carpal-metacarpal joints is no more than 5-10 degrees. They have limited mobility, because the ligaments are well developed. Located on the palmar surface, they form a stable palmar ligamentous apparatus that connects the bones of the wrist and metacarpals. There are arcuate ligaments on the hand, as well as transverse and radial ligaments. The capitate bone is central in the ligamentous apparatus, a large number of ligaments are attached to it. Palmar developed much better than the back. The dorsal ligaments connect the bones of the wrist. They form thickenings of capsules that cover the joints between these bones. Interosseous are located in the second row of carpal bones.
In the thumb, the carpometacarpal joint is formed by the base of the first metacarpal and polygonal bone. The articular surfaces are saddle-shaped. This joint can perform the following actions: abduction,adduction, reposition (reverse movement), opposition (opposition) and circumduction (circular movement). The volume of grasping movements, due to the fact that the thumb is opposed to all the others, increases significantly. 45-60 degrees is the mobility of the carpometacarpal joint of this finger during adduction and abduction, and 35-40 during reverse movement and opposition.
The structure of the hand: metacarpophalangeal joints
The named joints of the hand are formed by the heads of the metacarpal bones with the participation of the bases of the proximal phalanges of the fingers. They are spherical in shape, have 3 axes of rotation perpendicular to each other, around which extension and flexion, abduction and adduction, as well as circular movements (circumduction) are carried out. Adduction and abduction is possible at 45-50 degrees, and flexion and extension - at 90-100. These joints have collateral ligaments located on the sides that strengthen them. The palmar, or accessory, are located on the palmar side of the capsule. Their fibers are intertwined with the fibers of the deep transverse ligament, which prevents the heads of the metacarpal bones from moving apart.
Interphalangeal joints of the hand
They are block-shaped, and the axes of their rotation are transverse. Extension and flexion is possible around these axes. Proximal interphalangeal joints have a flexion and extension volume of 110-120 degrees, distal - 80-90. The interphalangeal joints are very well reinforced thanks to the collateral ligaments.
Synovial as well as fibrous sheathsfinger tendons
The extensor retinaculum, like the flexor retinaculum, plays a huge role in strengthening the position of the tendons of the muscles passing under them. This is especially true when the hand is working: when it is extended and flexed. Nature conceived a very competent structure of the hand. The tendons find support in the aforementioned ligaments from their inner surface. The separation of the tendons from the bones prevents ligaments. This allows for intense work and strong muscle contraction to withstand great pressure.
Reducing friction and slipping of the tendons going to the hand from the forearm is facilitated by special tendon sheaths, which are bone-fibrous or fibrous canals. They have synovial sheaths. Their largest number (6-7) is located under the extensor retinaculum. The radius and ulna have grooves that correspond to the location of the tendons of the muscles. As well as the so-called fibrous bridges that separate the channels from each other and pass to the bones from the extensor retinaculum.
The palmar synovial sheaths refer to the flexor tendons of the fingers and hands. The common synovial sheath extends to the center of the palm and reaches the distal phalanx of the fifth finger. Here are the tendons of the superficial and deep flexors of the fingers. The thumb has a long flexor tendon, located separately in the synovial sheath and passing to the finger along with the tendon. Synovial sheaths in the palm area are devoid of muscle tendons that go tofourth, second and third fingers. Only the tendon of the fifth finger has a synovial sheath, which is a continuation of the general.
Muscles of the hand
In the figure below you can see the muscles of the arm. The structure of the hand is shown here in more detail.
Muscles in the hand are only on the palmar side. They are divided into three groups: middle, thumb and small fingers.
Because the movements of the fingers require great precision, there are a significant number of short muscles in the hand, complicating the structure of the hand. The muscles of the hand of each of the groups will be considered below.
Medium muscle group
It is formed by worm-like muscles, starting from the tendons of the deep flexor of the fingers and attached to the proximal phalanges, or rather their bases, from the second to the fifth finger, if we consider the structure of the hand. These muscles of the hand also come from the dorsal and palmar interosseous, located in the spaces between the bones of the metacarpus, attached to the base of the proximal phalanges. The function of this group is that these muscles are involved in the flexion of the proximal phalanges of these fingers. Thanks to the palmar interosseous muscles, it is possible to bring the fingers to the middle finger of the hand. With the help of the dorsal interosseous, they are diluted to the sides.
Thumb muscles
This group forms the elevation of the thumb. These muscles begin near the nearby bones of the metacarpus and wrist. As for the thumb, its short flexor is attached near the sesamoid bone,which is located near the base of the proximal phalanx. The opposing thumb goes to the first metacarpal bone, and the adductor thumb is located on the side of the internal sesamoid bone.
Muscles of the thumb
This group of muscles forms an elevation on the inside of the palm. These include: abductor little finger, opposing little finger, short palmar, and flexor brevis.
They originate from nearby bones in the wrist. These muscles are attached to the base of the fifth finger, more precisely its proximal phalanx, and to the fifth metacarpal bone. Their function is reflected in the title.
In the article we tried to most accurately represent the structure of the hand. Anatomy is a fundamental science, requiring, of course, a more thorough study. Therefore, some questions remained unanswered. The structure of the hand and wrist is a topic that is of interest not only to physicians. Knowledge of it is also necessary for athletes, fitness instructors, students and other categories of people. The structure of the hand, as you noticed, is quite complex, and you can study it for quite some time, relying on various sources.
