Generality
The carpus is, in the human being, the set of 8 bones which, in each hand, takes place between the lower extremities of the radius and ulna and the initial extremities of the 5 metacarpals.
The carpus inserts numerous ligaments, including: the transverse carpal ligament, the wrist ligaments, the ligaments of the intercarpal joints, and the ligaments of the carpometacarpal joints.
The carpus is essential for the correct functionality of the wrist joint.
The main problems that can affect the carpus are fractures of the scaphoid, lunate, triquetroum, trapezius or hook.
What is the carpus?
The carpus is, in the human being, the group of 8 bones which, in each hand, resides between the distal ends of the radius and ulna and the proximal ends of the 5 metacarpals.
Better known as carpal bones, the bones that make up the carpus of the human hand are: the scaphoid, the lunate, the triquetroum, the pisiform, the trapezius, the trapezoid, the capitate and the hook.
BRIEF REVIEW OF WHAT THE RADIO, ULNA AND METACARPI ARE
Belonging to the category of long bones, the radius and the ulna are the two bony elements that make up the skeleton of the arm; the arm is the anatomical section of the upper limb that begins just below the elbow and ends at the wrist.
At the level of their distal extremities (ie the extremities furthest from the trunk of the body), the radius and ulna have, respectively, two articular surfaces and a bony prominence (styloid process), fundamental in constituting the wrist joint.
Moving on to the 5 metacarpals of the hand, these are the long bones that take place between the carpus of the hand and the phalanges of the hand; in all 14, the phalanges of the hand are the bones of the fingers of the hand.
Each metacarpus corresponds to a finger of the hand: the first metacarpus corresponds to the thumb, the second metacarpus corresponds to the second finger of the hand (index), the third metacarpus corresponds to the third finger (middle) and so on.
Three regions can be recognized in the metacarpals: a central region, called the body; a proximal region, called the base; finally, a distal region, identified with the term head.
The base of the metacarpals is the border point with the carpal bones, while the head is the border point with the phalanges.
THE CARPUS IS THE EQUIVALENT OF THE FOOT TARSUS
The carpus is equivalent, at the level of the foot, to the tarsus. In the tarsus, there are 7 bones and they border on the tibia and fibula, on the proximal side, and with the 5 metatarsals, on the distal side. Tibia and fibula are the bones of the leg and correspond, respectively, to the radius and ulna; the metatarsals are the equivalent of the metacarpals.
Anatomy
The carpus is a group of bones, which inserts various ligaments and tendons and which takes part in fundamental joints of the human body.
CARPUS BONES: PROXIMAL AND DISTAL ROW
Irregularly shaped, the 8 bones of the carpus form the anatomical region of the wrist (not to be confused with the joint of the same name), arranged in two rows: a proximal row, close to the bones of the radius arm and ulna, and a distal row, bordering with the base of the metacarpal bones.
The bones of the proximal row are: scaphoid, lunate, triquetroum and pisiform.
The bones of the distal row, on the other hand, are: trapezius, trapezoid, capitate and hooked.
PROXIMAL CARPAL BONES
The bones of the proximal row play a fundamental role in the constitution of the wrist joint.
While the scaphoid and semilunar articulate with the two articular surfaces of the radius, the triquetroum and pisiform inserts an important ligament that comes from the styloid process of the ulna.
DISTAL CARPAL BONES
The carpal bones of the distal row have the important task of articulating the carpus to the metacarpals.
While the trapezius, trapezoid and capitate articulate with the base of one metacarpal bone only, the hook joins two adjacent metacarpal bones.
To be precise, the trapezius borders on the metacarpus which will then give rise to the thumb; the trapezoid makes contact with the metacarpus of the index; the capitate is at the base of the metacarpus of the middle finger; finally, the hook is articulated with the metacarpals of the ring and little fingers.
ARTICULATIONS
The joints in which the carpal bones take part are:
- The wrist joint or radiocarpal joint. It is the most important joint in the hand. It is a joint element of the synovial type.
- The intercarpal joints. They are the joints that are located between the various carpal bones and that give the latter a certain degree of mobility. Furthermore, they contribute to the stability of the wrist.
- The carpometacarpal joints. They are the joints that join the carpal bones of the distal row and the corresponding metacarpals. They are not particularly mobile; they are essential to provide stability to the wrist.
LIGAMENTS
A ligament is a band of fibrous connective tissue, which connects two bones or two parts of the same bone together.
The ligaments that have relations with the carpal bones are: the transverse carpal ligament, the ligaments of the wrist, the ligaments of the intercarpal joints and the ligaments of the carpometacarpal joints.
The table below is a complete list of every single ligament that interacts with the carpus; for the transverse carpal ligament and wrist ligaments, there is also a small description of the course of each.
It is a ligament so large that anatomists recognize a radial side and an ulnar side in it.
The radial side is inserted at the level of the scaphoid and the trapezius, while the ulnar side engages at the level of the pisiform and the hook.
The transverse carpal ligament is one of the structures that make up the so-called carpal tunnel. The anomalies that concern him are among the main causes of the known carpal tunnel syndrome.
Wrist ligaments
Palmar radiocarpal ligament
It resides on the part of the palm of the hand; starts from the radius and touches both the carpal bones of the proximal row and the carpal bones of the distal row.
Dorsal radiocarpal ligament
It resides on the back of the hand; starts from the radius and touches both the carpal bones of the proximal row and the carpal bones of the distal row.
Ulnar collateral ligament
It runs from the styloid process of the ulna to the triquetroum and pisiform.
Radial collateral ligament
It runs from the styloid process of the radius to the scaphoid and trapezius.
Dorsal ulnocarpal ligament
It originates at the level of the ulnar styloid process and ends, with more fibers, at the level of the triquetroal, capitate and semilunar carpal bones.
Ligaments of the intercarpal joints
Radiated carpal ligament
They are the ligaments that connect the carpal bones together.
Dorsal intercarpal ligament
Palmar intercarpal ligament
Interosseous intercarpal ligament
Piso-uncinate ligament
Ligaments of the carpometacarpal joints
Piso-metacarpal ligament
They are the ligaments that join the carpal bones to the base of the metacarpals.
Dorsal carpometacarpal ligament
Volar carpometacarpal ligament
Development
The process of ossification of the carpal bones begins only after birth.
The first carpal bones to ossify are the capitate and the uncinate: their ossification occurs within the first year of life (after 2 and a half months, the capitate, and after 4-6 months, the uncinate).
Then, in succession, they ossify the triquetroum (after 2 years), the lunate (after 5 years), the trapezius (after 6 years), the trapezoid (after 6 years), the scaphoid (after 6 years) and the pisiform (after 12 years).
Function
The carpus is a fundamental element of the wrist joint, therefore it contributes significantly to the functions of the latter, which are the movements of:
- Flexion. It is the movement that allows you to bring your palm closer to your arm. Imagining that you are looking at an upper limb fully extended forward, the flexion of the wrist is the movement that bends the hand downwards.
- Extension. It is the movement that allows the back of the hand to be brought closer to the arm. Imagining that you are looking at an upper limb fully extended forward, the extension of the wrist is the movement that bends the hand upwards.
- Radial deviation. It is the movement that allows you to bring the side of the hand with the thumb towards the radius.
- Ulnar deviation. It is the movement that allows you to bring the side of the hand with the little finger to the ulna.
- Circumstance. It is the rotational movement of the hand.
Associated pathologies
Among the carpal bones, those that most commonly fracture are: the scaphoid, the triquetroum, the lunate, the hook and the trapezius; the trapezoid, the capitate and the pisiform are rarely subject to fractures.
FRACTURE OF THE SCAFOID
The scaphoid is the tarsal bone most prone to fractures.
The main causes of scaphoid fractures include falls with the hands extended forward.
If the bone fracture alters the blood supply to the scaphoid itself, the latter no longer receives the correct blood supply and undergoes osteonecrosis.
Inadequate treatment of scaphoid fractures promotes wrist arthritis.
FRACTURE OF THE TRIQUETER
Typically, triqueter fractures are a consequence of direct blows to the back of the hand or falls with the wrist in extreme flexion.
FRACTURE OF THE SEMILUNAR
Typical causes of lunate fracture include direct blows to the wrist and chronic trauma.
When the lunate fractures are due to chronic trauma, it is possible that osteonecrosis phenomena also take place. The phenomena of osteonecrosis favor the onset of wrist arthritis.
Lunar fractures represent the second most common type of tarsal fracture.
FRACTURE OF THE UNCINATO
Usually, hook fractures are a consequence of falling with an outstretched hand or an abnormal grip of objects, such as golf clubs or tennis rackets.
KEYSTONE FRACTURE
Typical causes of trapezius fractures include violent blows to the back of the hand and falls with a hand closed in a fist and with radial deviation.
Trapezius fractures represent the third most common type of tarsal fracture.
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