FEACTUEES OF THE CLAVICLE. 83 



FRACTURES OF THE UPPER EXTREMITY. 



Fractures of the Clavicle. The collar bone is one of the 

 commonest bones to be broken. There should, therefore, be 

 certain anatomical reasons for its liability to fracture. 



The bone is set between the sternum and the scapula. It thus 

 has to bear the brunt of all falls upon the shoulder, and to a great 

 extent those upon the outstretched hand. Thus fracture by 

 indirect violence is easily produced. The bone is long and slender, 

 and has a thick layer of brittle compact tissue, derived from 

 ossification in membrane, enclosing cancellous tissue, without 

 a medullary cavity. Therefore it readily gives way under direct 

 violence. Lastly it is ossified at quite an early intra-uterine age, 

 and is consequently less capable of withstanding injury in infant 

 life than are some other bones which are still partly composed of 

 cartilage. Fractures of the clavicle in young life are often 

 incomplete, " greenstick," owing to the thick periosteal covering. 

 When the clavicle is broken by a fall on the extended and 

 abducted arm or upon the greater tuberosity of the humerus, 

 force is applied to it through the glenoid fossa of the scapula and 

 the coraco-clavicular ligament, and causes a species of torsion of 

 the clavicle at the junction of the outer with the middle third. It 

 is at this point, therefore, that an oblique fracture usually occurs. 



Immediately there is a triple displacement of the outer frag- 

 ment. The weight of the arm, aided perhaps by the traction of the 

 pectoralis minor, the lower fibres of the pectoralis major, and the 

 latissimus dorsi, induces a downward displacement. Moreover, the 

 trapezius is as it were thrown out of gear, and can no longer support 

 the weight of the upper limb. Inward displacement is caused by 

 the pull of the pectorals, the trapezius, the levator anguli 

 scapulae, the rhomboids and the latissimus dorsi. In addition, 

 the outer fragment is rotated so that its inner end looks backwards, 

 the point of the shoulder turning forwards. This change of 

 position is brought about chiefly by the action of the pectorals. 



The inner fragment is but slightly if at all altered in its 

 position. This is due to the antagonistic action of the clavicular 



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