CHAPTEE VIII. 

 DISLOCATIONS. 



A DISLOCATION is the partial or complete separation of bony 

 surfaces normally in contact at an articulation. 



From this definition it will be apparent that the anatomical 

 relationships of a joint are of importance in determining the 

 frequency, the extent and the treatment of a dislocation. For 

 instance, the imperfect co-aptation of the head of the humerus 

 and the glenoid cavity of the scapula explains to some extent the 

 frequency with which dislocation occurs at the shoulder. On the 

 other hand the great strength of the crucial ligaments of the 

 knee is a reason for the fact that a dislocation at this joint is 

 rarely other than a partial one. And again, the intimate relation- 

 ship of the bones of the elbow means less likelihood of dislocation 

 and more difficulty in reduction. 



In most dislocations there is more or less laceration of the 

 capsule and ligaments of the joint, with but little tearing of 

 the surrounding muscles. Thus the amount of blood extravasated 

 is not as a rule so great as it is in a fracture occurring in the same 

 region. Blood-stained synovial fluid, however, is often secreted 

 so abundantly as to cause considerable swelling of the part. 



SPECIAL DISLOCATIONS. 



Upper Extremity. 



Dislocations at the Sterno-clavicular Joint. This articulation 

 is one of great strength, even in spite of the want of close 

 co-aptation of the articular surfaces, and is the only one 

 connecting the upper extremity with the trunk. The posterior 

 sterno-clavicular ligament is stronger than the anterior. The 

 costo-clavicular ligament holds the clavicle very firmly down to 



C.A.A. 8 



