CLAVICLE: osteology, myology, ossification, clinical anatomy.

Bone: clavicle.

Features:

• It is also called collar bone.
• It is a long bone that connects upper limb to the shaft.
• Parts:it has a shaft and two ends.
•  The medial end articulates with the sternum called sternal end and the lateral end which articulates with the acromion process is called acromial end.
• Location:anterosuperior aspect of thorax.
• The bone placed horizontally in the body thus it prevent shoulder from falling forward.

Side determination:

• The medial side of the shaft is round and lateral part is flattened.
•  Medial end of the clavicle is round and the lateral end is oval in shape.
•  Medial part of the shaft is convex forward and lateral part is concave forward.
• The inferior aspect of the shaft has a shallow groove and rough area on the medial end.

 Osteology:

• The clavicle consist of a shaft and two ends .
• The medial end of the clavicle is round in shape and articulates with the manubrium of the clavicle (sternoclavicular joint).
• The lateral end of the clavicle is oval in shape and articulates with the acromion process of the scapula (acromioclavicular joint).
• The shaft is divided into two medial 2/3rd and lateral 1/3rd.
• The medial 2/3rd of the clavicle is cylindrical in shape and is convex forward.
• It has four surfaces anterior, posterior, superior and inferior.
• The middle of the inferior surface present longitudinal groove called subclavian groove.
• The lateral 1/3rd is flat .
• It has two surfaces superior and inferior.
• The inferior surface shows a prominent thickening near posterior border called conoid tubercle.
• Lateral to the tubercle is a rough ridge that runs obliquely uptown the lateral end of the bone called trapezoid line.
• It has two borders anterior and posterior border.
• The anterior border is concave and shows a small thickened area called deltoid tubercle.

Myology:

• Medial 2/3rd of the shaft:
• Pectoralis major muscle arise from the anterior surface of medial happy of the shaft.
• The clavicular head of the sternocleidomastoid muscle arises from the medial part of the upper surface of the medial 2/3rd of the shaft.
• Lateral 1/3rd of the shaft:
• Trapezius is inserted into the posterior border of the lateral 1/3rd of the shaft.
• The lateral part of the sternohyoid arises from the lower part of posterior surface.
• Deltoid arise from the anterior border of the lateral 1/3rd of the shaft.
• Subclavius is inserted into the groove  on the inferior surface of the shaft.

Special features of the clavicle.

1. It is the first bone to ossify and last bone to complete ossification.
2. It is the only long bone which lies horizontally.
3. It doesn't possess a medullary cavity.
4. It is the only long bone that ossified in membrane .
5. It is the only bone that has two primary centres.

Ossification

• Clavicle is the first bone to start ossification.
• Most of the part of the clavicle formed by intramembraneous ossification.
• The sternal and acromial ends are performed in cartilage.
• During 5th-6th week of foetal life two primary centres appear in the shaft later they fuse.
• The sternal end ossified from the secondary centres that appears tween 15 and 20 years of age and fuses with the shaft at the age of 25.

Clinical anatomy

• Fracture of the clavicle:
• Caused by indirect violence.
• Affects the weakest point of the bone (between middle 1/3rd and lateral 1/3rd).
• The thin slender clavicle of the neonate can be fractured during birth  it is called greenstick fracture.

• Failure of fusion of ossification center:
• The medial and lateral part of the bone remain separate.
• It is a congenital deformity.

Special features of clavicle

• The right clavicle is usually shorter than the left clavicle.
• In animals whose upper limb are used for the weight bearing purpose eg:tiger , clavicle is absent or rudimentary.
• Clavicle helps in the transmittionof shock to the trunk from the upper limb.