Book : Human Anatomy
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Posted by: CHELSEA
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Writer CHELSEA

Clavicle

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In human anatomy, the clavicle or collarbone is a long bone that serves as a strut between the shoulder blade and the sternum or breastbone. There are two clavicles, one on the left and one on the right. The clavicle is the only long bone in the body that lies horizontally. Together with the shoulder blade it makes up the shoulder girdle. It is a palpable bone and in people who have less fat in this region, the location of the bone is clearly visible, as it creates a bulge in the skin. Clavicle fractures are fairly common and occur in people of all ages. Most fractures occur in the middle portion, or shaft, of the bone. Occasionally, the bone will break where it attaches at the ribcage or shoulder blade.

Structure:

The collarbone is a large doubly curved long bone that connects the arm to the trunk of the body. Located directly above the first rib it acts as a strut to keep the scapula in place so that the arm can hang freely. Medially, it articulates with the manubrium of the sternum (breastbone) at the sternoclavicular joint. At its lateral end it articulates with the acromion, a process of the scapula (shoulder blade) at the acromioclavicular joint. It has a rounded medial end and a flattened lateral end.

From the roughly pyramidal sternal end, each collarbone curves laterally and anteriorly for roughly half its length. It then forms an even large posterior curve to articulate with the acromion of the scapula. The flat acromial end of the collarbone is broader than the sternal end. The acromial end has a rough inferior surface that bears a ridge, the trapezoid line, and a slight rounded projection, the conoid tubercle. These surface features are attachment sites for muscles and ligaments of the shoulder.

It can be divided into three parts: medial end, lateral end and shaft.

Medial end:

The medial end is quadrangular and articulates with the clavicular notch of the manubrium of the sternum to form the sternoclavicular joint. The articular surface extends to the inferior aspect for attachment with the first costal cartilage.

It gives attachments to:

  • fibrous capsule joint all around
  • articular disc superoposteriorly
  • interclavicular ligament superiorly

Lateral end:

The lateral end is flat from above downward. It bears a facet for attachment to the acromion process of the scapula, forming the acromioclavicular joint. The area surrounding the joint gives an attachment to the joint capsule. The anterior border is concave forward and posterior border is convex backward.

Shaft:

The shaft is divided into the medial two-thirds and the lateral one third. The medial part is thicker than the lateral.

Medial two-thirds of the shaft:

The medial two-thirds of the shaft has four surfaces and no borders.

The anterior surface is convex forward and gives origin to the pectoralis major. The posterior surface is smooth and gives origin to the sternohyoid muscle at its medial end. The superior surface is rough at its medial part and gives origin to the sternocleidomastoid muscle. The inferior surface has an oval impression at its medial end for the costoclavicular ligament. At the lateral side of inferior surface, there is a subclavian groove for insertion of the subclavius muscle. At the lateral side of the subclavian groove, the nutrient foramen lies. The medial part is quadrangular in shape where it makes a joint with the manubrium of the sternum at the sternoclavicular joint. The margins of the subclavian groove give attachment to the clavipectoral fascia.

Lateral third of the shaft:

The lateral third of the shaft has two borders and two surfaces.

The anterior border is concave forward and gives origin to the deltoid muscle. The posterior border is convex backward and gives attachment to the trapezius muscle. The superior surface is subcutaneous. The inferior surface has a ridge called the trapezoid line and a tubercle; the conoid tubercle for attachment with the trapezoid and the conoid ligament, part of the coracoclavicular ligament that serves to connect the collarbone with the coracoid process of the scapula.

Signs and symptoms:

Clinical signs and symptoms of clavicle fracture include the following:

  • The patient may cradle the injured extremity with the uninjured arm.
  • The shoulder may appear shortened relative to the opposite side and may droop.
  • Swelling, ecchymosis, and tenderness may be noted over the clavicle.
  • Abrasion over the clavicle may be noted, suggesting that the fracture was from a direct mechanism.
  • Crepitus from the fracture ends rubbing against each other may be noted with gentle manipulation.
  • Difficulty breathing or diminished breath sounds on the affected side may indicate a pulmonary injury, such as a pneumothorax.
  • Palpation of the scapula and ribs may reveal a concomitant injury.
  • Tenting and blanching of the skin at the fracture site may indicate an impending open fracture, which most often requires surgical stabilization (see the image below).
  • Nonuse of the arm on the affected side is a neonatal presentation.
  • Associated distal nerve dysfunction indicates a brachial plexus injury.
  • Decreased pulses may indicate a subclavian artery injury.



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