Clavicle

CLAVICLE (COLLAR BONE)
  Latin: clavicula ("little key")
       : Because the bone rotates along its axis like a key when the shoulder is abducted.

         
Some of the peculiarities of clavicle are:
1.  The clavicle is a long bone, in fact modified long bone since unlike other long bones, it doesn't have medullary cavity.
2. It is subcutaneous throughout. It is palpable. And in person with less fat , it is clearly visible as it bulge in the skin.
3. It ossifies from two primary centres.
4. It ossifies in membrane.
5. It is the only long bone that lies horizontally.
           Clavicle is the first bone to start ossifying.
Clavicle is the most commonly broken bone.

Clavicle serves as a strut between the shoulder blade and the sternum or breastbone.

SHAPE:
  Its shaft is Doubly curved i.e. concavo-convex.

DETERMINATION OF SIDE:
- Lateral one-third of its shaft is concave forwards while the medial two-third of its shaft is convex forwards.
- Lateral end is flattened while the medial end is quadrilateral.
- Inferior surface has a longitudinal groove called subclavian groove in middle one-third.

WORK:
It receives weight of upper limb via lateral one-third through coracoclavicular ligament and transmits weight of upper limb to axial skeleton via medial two-third part.

Articulations:
     Medial end articulates with clavicular notch of the manubrium of sternum to form sternoclavicular joint.
     Lateral end articulates with acromian process of scapula to form acromioclavicular joint.

FEATURES:
A. Lateral 1/3rd of shaft:
      - flattened from above downwards. so has 2 borders: anterior and posterior. Anterior is concave forwards and posterior border is concave forwards. And 2 surfaces: superior and inferior.  Superior is subcutaneous and inferior presents an elevation called conoid tubercle and a ridge called trapezoid ridge.

B. medial 2/3rd of shaft:
     -It is rounded. So has 4 surfaces: anterior, posterior, superior and inferior. Anterior surface is convex forwards, posterior surface is smooth, superior surface is rough in its medial part, and inferior surface has rough oval impression(for costoclavicular ligament) at the medial end and also a subclavian groove (nutirent foramen lies at the lateral end of subclavian groove).


ATTACHMENTS:
A. Ends:
- lateral end: margin of articular surface for acromioclavicular joint gives attachment to joint capsule.

- medial end: margin of articular surface for sternoclavicular joint gives attachment to:
                                                                                          1. firbous capsule all around
                                                                                          2. Articular disc posterosuperiorly.                                                                                                          3.Interclavicular ligament.

B. Shaft:
- Lateral one-third:
    a. Anterior border gives origin to deltoid muscle.
    b. Posterior border provides insertion to trapezius.
    c. Conoid tubercle and trapezoid ridge (on inferior surface) provides attachment to the conoid and the trapezoid parts of the coracoclavicular ligament.

- Medial two-third os haft:
   a. Anterior surface gives origin to pectoralis major.
   b. Superior surface (half part) gives origin to sternocleidomastoid.
   c. Oval impression on inferior surface provides attachment to costoclavicular ligament.
   d. Subclavian groove provides insertion to subclavius muscle and the margin of groove provides attachment to clavipectoral fascia.
   e. Posterior surface gives origin to sternohyoid muscle.



Note: Nutrient artery for clavicle is a branch of suprascapular artery.




OSSIFICATION:
- 1st bone to ossify.
-ossifies in membrane except for its medial end.
- ossifies from two primary centres and one secondary centre.
     The two primary centres appear in the shaft between the 5th and 6th weeks of intrauterine life and fuse about the 45th day. The secondary centre centre for medial

end appears during 15-17 years and fuses with the shaft during 21-22 years. Occasionaly there may be a secondary centre for acromial end.





Clinical Aspect:
- Clavicle is fractured by falling on the outstretched hand. Common site of fracture is junction between two curvature. Lateral fragment will be displaced downwards.
- Cleidocranial dysostosis: Clavicle is congenitally absent in these patient or imperfectly developed. The shoulders droop.