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Do you know how the collarbone works like a key? What is its mysterious turning principle?
The clavicle, often called the clavicle or keybone, is a slender S-shaped bone about 6 inches (15 centimeters) long that plays a supporting role connecting the shoulder blades to the sternum. Everyone has a clavicle on each side of the body. It is the only long bone lying horizontally in the human body. Together with the scapula, it forms the shoulder girdle. In some people with less fat, the position of the clavicle is so obvious that it is named "clavicula" in Latin, "little key" because of its rotational movement when the shoulder is abducted, as if it were a key.
Structure of the clavicle
The clavicle is a thin, double-curved long bone located just above the first rib. It serves as a support, keeping the shoulder blade in place and allowing the arm to hang freely. The medial rounded end of the clavicle (sternal end) is connected to the sternostylous joint of the sternum, while the lateral flat end (acromial end) is connected to the acromial joint of the scapula.
The interior of the clavicle is composed of a layer of cancellous bone and a layer of dense bone shell. The formation of this layer of dense bone is related to the layer of fascia that wraps around the bone, stimulating the ossification of adjacent tissues.
Function and Importance
The main functions of the clavicle include:
- Provides solid support to the shoulder blades and free limbs, allowing the arms to move freely.
- Acts as a flexible support bar allowing free movement of the shoulder blades on the chest wall.
- Protect the neurovascular bundles supplying the upper limbs.
- Transmits physical impacts from the upper limbs to the axial skeleton.
The clavicle is the first bone to begin bone formation during growth, but it is the last bone to complete. It is completed between the ages of 21 and 25.
Clinical significance and fracture
Fractures of the clavicle are usually caused by external impacts or falls, especially when the arm is extended. The most common fracture site is the junction of the two curves. In most cases, the damaged muscle raises the medial bone end and may sometimes puncture the skin.
Clavicles of other animals
In primitive bony fishes, clavicle bones were present and connected to the fins, but are missing in most modern fish. Over evolution, the collarbones of many mammals also shrank or disappeared, allowing the shoulder blades greater freedom of movement, which is important for fast-running animals.
Conclusion
The shape and structure of the clavicle varies between species, and the characteristic clavicle in humans may have begun to form as early as 3 to 4 million years ago. Because of this, the clavicle of different animals and humans also reveals their movement patterns and survival needs during their evolution, which makes people think deeply: How deeply is the evolution of the clavicle related to our daily life?
