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Clavicle | Collar Bone

Outline:
Clavicle:

  • It is a modified long bone having two curves.
  • Medial 2/3 is convex and lateral 1/3 is concave as seen from front.
  • It has two borders and two surfaces.

Muscles and ligaments attached to clavicle:
Lateral 1/3:

  • Trapezius muscle,
  • Deltoid Muscle,
  • Coracoclavicular ligament.

Medial 1/3:

  • Sternocleidomastoid muscle,
  • Pectoralis major muscle,
  • Subclavius muscle,
  • Costoclavicular ligament.

Functions of Clavicle:
Acts as a strut to hold the upper limb laterally away from the body.
Clavicle Fractures:

  • Most commonly fractured bone of human body,
  • Weakest point is junction of medial 2/3 and lateral 1/3.
  • Fracture may involve compression of brachial plexus and subclavian vessels

Ossification of clavicle:
Clavicle is the first bone of the body to start the process of ossification. It shows both intramembranous and endochondral types of ossification. It has 2 primary centers and one secondary center of ossification.

Clavicle | Collar bone:

Clavicle is a modified long bone having two curves. The medial 2/3 of the bone has a convex curve and the lateral 1/3 has a concave curve as seen from front. It is the only long bone of human body that lies horizontally in its natural position. Like all long bones, it has two ends. The lateral end articulates with the acromion process of scapula and the medial end articulates with the sternum and first costal cartilage. Towards the medial side, the shaft of the bone is rounded while towards the lateral side, it is flattened and forms a superior and inferior surface. The clavicle is subcutaneous throughout its length and can easily be seen in all subjects. Clavicle has two borders and two surfaces. The borders are anterior and posterior and the surfaces are superior and inferior.

Muscles and Ligaments attached to clavicle:

Lateral 1/3 of clavicle: Lateral 1/3 of clavicle gives attachment to following important muscles and ligaments;

  • Trapezius muscle: It is inserted into the posterior border of the lateral 1/3 of clavicle.
  • Deltoid muscle: It originates from anterior border of the lateral 1/3 of clavicle.
  • Coracoclavicular Ligament: As the name indicates (Coraco = coracoids process, clavicular = clavicle) it is a ligament attached to the coracoids process of scapula and the clavicle. It has two points of attachment on clavicle. The conoid part is attached to the conoid tubercle and the trapezoid part is attached to the trapezoid ridge. The conoid tubercle and trapezoid ridge lie at the inferior surface of lateral 1/3 of clavicle.
    Function of coracoclavicular ligament: It is a strong ligament and is responsible for bearing most of the weight of the hanging upper limb. The upper limb can hang from the clavicle because of this strong ligament.

Medial 2/3 of clavicle: Lateral 1/3 of clavicle gives attachment to following important muscles and ligaments;

  • Sternocleidomastoid muscle: it originates from the superior surface of medial 2/3 of clavicle.
  • Pectoralis major muscle: It originates from the antero-superior part of the medial 2/3 of clavicle.
  • Subclavius muscle: It is inserted into the middle of the posterior surface of clavicle. It extends in both later and medial parts of clavicle.
  • Costoclavicular ligament: As the name indicates (Costo= Rib and clavicular = clavicle), costoclavicular ligament is attached to the clavicle and first costal cartilage. The attachment on the clavicle lies at the posterior surface near the medial end of the bone.

Joint capsules:
The lateral end of clavicle forms a sliding synovial joint with acromion process of scapula. It provides attachment to the joint capsule of this joint. The medial end of clavicle forms a double plane synovial joint with manubrium sterni and provides attachment to the joint capsule of this joint.

Functions of clavicle:

Clavicle acts as a strut to hold the upper limb laterally away from the body. It also bears a part of the weight of upper limb (the remaining is borne by the scapula). By being laterally away from the body, the functional efficiency of upper limb increases greatly.

Clavicle Fractures:

Because the clavicle transmits forces from the upper limb to the trunk, it may itself be damages by these forces. In fact clavicle is the most commonly fractured bone in the human body. The most common reason of fracture is a fall on the shoulder or outstretched hand. The weakest point of the clavicle where it gets fractured most easily is the junction of the convex medial 2/3 and concave lateral 1/3. After the fracture occurs at this point, the lateral fragment of the bone is displaced downward by the weight of upper limb while the medial fragment is pulled upward by the force of sternocleidomastoid muscle.
The clavicle fracture may result in compression of brachial plexus, subclavian artery and subclavian vein causing immense pain over the side of the neck.

Ossification of clavicle

Clavicle is the first bone of human body to start the process of ossification. It shows both intramembranous and intracartilaginous types of ossification. Clavicle has a total of three centers of ossification. Two of them are primary and one is secondary. The two primary centers of ossification appear during the fifth to sixth week of intrauterine life. They are for the body and acromial end of clavicle. The secondary center of ossification appears at the sternal end of clavicle at 18th to 20th year. It unites with the rest of the bone at about 25th year of life; the point at which the process of ossification is complete.