Orthopedists refer to the metacarpals as the five radiating tubular bones of the metacarpus. Thanks to their anatomy, they are highly flexible, which is what allows the hand to grasp in the first place. Any one of the metacarpal bones can be affected by open and closed fractures, but for which the prognosis is favorable.
What is the metacarpal bone?
The metacarpal bones are the bony base of the metacarpus. As such, it is the section between the carpus and the fingers. This area of the hand consists of five tubular bones arranged nearly parallel. Due to this multi-limb structure, the metacarpus has enormous elasticity. Its five bony limbs are numbered in ascending order starting from the thumb bone. Thus, the metacarpal consists of the Os metacarpale primum, secundum, tertium, quartum and quintum. The individual tubular bones of the metacarpal each consist of a base, a body or shaft, and a head. The heads of the bones are each located in the direction of the phalanges. The metacarpal bones converge in a radiating shape. This anatomical shape gives the metacarpus maximum flexibility. Although most animal species also have metacarpal bones, the structure of the human metacarpal differs significantly from the metacarpal of most other species. Birds, for example, possess only a single metacarpal bone instead of five bones. Horses also have only a single main bone in the metacarpus with a thin bone on the side.
Anatomy and structure
The first metacarpal bone is the shortest. The second and third are the longest. At its broad base, the metacarpal has a cubic shape. Between the individual bones of the human metacarpal lie the so-called musculi interossei. These skeletal muscles flex and extend the finger joints. The cartilaginous surfaces of the metacarpals are connected to the carpal bone and run out into so-called carpometacarpal joints. The first of these joints is the thumb saddle joint, which has the highest mobility compared to the rest of the finger joints. The third metacarpal bone has a stylar process that is connected to the extensor carpi radialis brevis muscle. The shaft of the metacarpal is triangular in cross-section. In the null position, the tip of the triangle points forward. At the head of the metacarpals, convex cartilaginous surfaces sit on top of the bones that act as articular heads in the metacarpophalangeal joints. To the sides of the heads are small bumps, which form the starting point for the five finger rays. The entire metacarpus is stabilized by tight ligaments. Muscles also connect the metacarpal bones to the sesamoid bones of the hand.
Function and tasks
The functions and tasks of the metacarpals are enormously varied. In addition to motor and stabilizing functions, the metacarpals even have communicative tasks. On the motor side, the grasping movement should be mentioned in particular, as it is almost irreplaceable for everyday life. The radiate structure of the metacarpal bones gives the metacarpals sufficient mobility to support the hand during grasping. The metacarpus also plays an important role in holding objects. Together with the palm, it forms a stable abutment during grasping and holding movements. However, the metacarpal bones do not exclusively perform motor tasks. The entire hand is traversed by highly sensitive nerves, tendons and vessels. For these nerves and tendons of the hand, the metacarpals form a stable bridge. The vessels of the hand also find ample room for accommodation in the metacarpals. The metacarpal bones can also be seen as the basis of many hand muscles, which are important not only for motor function, but also for stabilizing the finger joints. As parts of the metacarpals, the five phalanges, together with their nerves and muscles, perform both fine motor tasks and gross motor functions. For example, they allow the hand to feel, sense and recognize. However, they also serve as a communication instrument and even enable humans to communicate in a nonverbal way through their pointing functions.
Diseases
Fractures are the most common complaint of the metacarpals. Any of the five metacarpal bones can be affected by fractures. A fracture can occur at the head, the shaft, or even at the base of the metacarpal bones. Either the fracture is open or closed.In open fractures of the metacarpal, a skin wound is present in addition to the fracture. As a rule, falls or sports and work injuries are the cause of the fractures. Diagnosis is usually made with the aid of X-ray imaging of the hand. Often, several metacarpal bones are affected by a fracture at the same time, especially in fall-related fractures. Sometimes the bones at the fracture sites shift out of their physiological position. In such a case, corrective surgery is usually the treatment of choice. Since many joints are located in the metacarpals, this section of the hand is also often affected by osteoarthritis, especially in the thumb and its saddle joint. Pain in the metacarpus, however, does not have to correspond to bone or joint pain. Because numerous tendons run through the metacarpus, this section of the hand is equally susceptible to tendonitis. Musicians, masseurs and typists are particularly affected by such inflammations because they regularly overuse the metacarpus. Overstretching is also relatively common in this section of the hand. Most complaints of the metacarpus have a predominantly good prognosis.
