Clavicle

Original Editor

Top Contributors - Sehriban Ozmen, Natalie Patterson, Kim Jackson, Chelsea Mclene, Admin, Feride Orman and Lucinda hampton

Description

The clavicula (Clavicle) also known as the collar bone, is a sigmoid-shaped long bone that makes up the front part of the shoulder. It sits between the shoulder blade and the sternum. There are 2 clavicles in a person, one on the right and the other one on the left side. It is the only long bone in the body that lies horizontally.

Articulations

Due to the clavicle’s structure, there are only two planar diarthrosis articulations that can be found. This type of articulation is also known as a ‘double plane joint’ – where two joint cavities are separated by a layer of articular cartilage.

The Sternoclavicular joint: The articulation between the clavicle and the Manubrium

The Acromioclavicular joint: The articulation between the clavicle and the Scapula<section>

Acromioclavicular joint

Acromioclavicular joint (Articulatio acromioclavicularis)

The first is the acromioclavicular joint, which is formed by the acromial end of the clavicle and the acromion of the scapula respectively. It enables slight gliding movement about the shoulder region. The synovial joint is surrounded by a capsule of articular cartilage filled with intra-articular synovium.

From infancy, the articular cartilage starts off as hyaline cartilage, but soon develops into fibrocartilage (at the scapula acromion and the clavicle acromial end at ages 17 and 24, respectively).The acromioclavicular ligament forms a strong connection between the clavicle and the scapula acromion, which restricts movement about the clavicle at its acromial end. </section><section>

Sternoclavicular joint

Sternoclavicular joint (Articulatio sternoclavicularis)

The other is the sternoclavicular joint, which is formed by the sternal end of the clavicle and the manubrium of the sternum. This synovial joint is important as it anchors the clavicle and scapula to the axial skeleton. However the joint enables a variety of limited movements of the arm, including:

• protraction and retraction
• depression and elevation
• slight rotation

Like the acromioclavicular joint, the sternoclavicular joint is surrounded by an articular cartilage capsule, but with a fibrocartilage articular disk inside that creates a clavicular and a sternal synovial cavity. Sternoclavicular joint ligaments stabilise the joint on its anterior and posterior surfaces. The joint is also reinforced by two accessory ligaments:

• The anterior interclavicular ligament, which covers the superior surface of the joint. This ligament is responsible for preventing dislocation of the clavicle upon shoulder depression.
• The posterior costoclavicular ligament, which runs from the clavicle costal tuberosity to the superior and medial surface of the first rib. In contrast, this ligament prevents clavicle dislocation upon shoulder elevation.

</section>

Muscle attachments

A total of five muscles are attached to the clavicle, found distributed at either the lateral third or medial two thirds of the bone.

Two muscles are attached to the lateral third of the clavicle:

• The trapezius muscle, which is attached along the posterior surface of the lateral third of the clavicle.
• The deltoid muscle, where the anterior portion of the muscle is attached to the periosteum at the anterior surface of the bone.

Three muscles are attached to the medial third of the clavicle:

• The sternocleidomastoid muscle, clavicular head of the muscle attaches to the medial third of the clavicle.
• The pectoralis major muscle, which is attached to the anterior surface of the bone.
• The subclavius muscle, which is attached to a groove found in the middle of the bone’s inferior surface. From there, the muscle extends into both lateral and medial areas of the clavicle. It's action is to draw the clavicle downwards and forward

Clinical relevance

The Clavicle plays an essential role in functional movement, serving as the connection between the axial skeleton and the pectoral girdle. This allows the clavicle to act as a brace for the shoulder, allowing weight to be transferred from the upper limbs to the axial skeleton.

Injuries and Treatment

Fractured or broken collar bone, most commonly caused by a fall or blow to the shoulder. It is usually managed with conservative management of wearing a sling and rest. If the fracture results in the bone piercing the skin surgery will be considered to fit a plate with screws.