Topic Overview

Clavicle

General Features

• Long bone placed horizontally in the root of the neck.

• Connects axial skeleton (sternum) to appendicular skeleton (scapula).

• Acts as a strut to keep the upper limb away from the trunk → permits free mobility.

• Curved in an S-shape:

  • Medial two-thirds → convex forward.

  • Lateral one-third → concave forward.

• Subcutaneous throughout → easily palpable.

• Classified as a modified long bone:

  • No medullary cavity.

  • Ossifies in membrane.

Attachments & Relations (Summary)

• Medial end (sternal end): articulates with manubrium sterni (sternoclavicular joint).

• Lateral end (acromial end): articulates with acromion process of scapula (acromioclavicular joint).

• Superior surface: subcutaneous, no major attachments.

• Inferior surface:

  • Medial part → costoclavicular ligament (rhomboid fossa).

  • Lateral part → conoid tubercle (conoid ligament), trapezoid line (trapezoid ligament).

• Anterior border (lateral third) → deltoid.

• Posterior border (lateral third) → trapezius.

• Medial two-thirds → origin of sternocleidomastoid (superior surface), pectoralis major (anterior surface), sternohyoid (posterior surface).

Ossification of Clavicle

• First bone to ossify in the body.

• Begins: 5th–6th week intrauterine life.

• Mode: membranous ossification (shaft), with cartilaginous ossification at the ends.

• Primary centers: two, appear in shaft, fuse by 45 days of IUL.

• Secondary center: appears in sternal end at 15–17 years, fuses by 21–22 years.

• Unique because:

  • Both membranous and cartilaginous ossification occur.

  • First to ossify, last to complete ossification.

Clinical Anatomy

• Most commonly fractured bone in the body.

  • Fracture usually at the junction of medial two-thirds and lateral one-third.

  • Medial fragment displaced upward by sternocleidomastoid.

  • Lateral fragment displaced downward by weight of limb & pulled medially by pectoralis major.

• May be absent congenitally (cleidocranial dysostosis) → shoulders approximated in front of chest.

• Subcutaneous position → prone to injury in falls, traffic accidents.

• Important landmark for central venous catheterization (subclavian vein lies posterior to clavicle).

• Ossification pattern important in forensic age estimation.