Cha;>. XXIV.J THE SPINE. 547 



extension, although the circumstances under which 

 such a procedure is advisable are neither frequent 

 nor very distinctly marked. 



Since, in severe injuries, dislocation and fracture 

 are so usually associated, it is common to deal with 

 these lesions under the title of "fracture-dislocation." 



Fracture-dislocation may be due to (1) indirect, 

 or (2) direct violence 1. The injuries from indirect 

 violence are by far the more common. They are due 

 to a violent bending of the head, or of the spine above 

 the seat of lesion, forwards and downwards. Thus, 

 the cervical spine has been more than once broken by a 

 "header" into shallow water; while the dorsal vertebrae 

 have been fractured and displaced by the acute bending 

 of the column, produced by a heavy sack falling upon 

 the back of the neck. 



This form of injury is most commonly met with in 

 the cervical and upper dorsal regions. These parts of 

 the column possess great mobility, the bodies that 

 compose th'em are not large, and are influenced by 

 violence applied to the head. In a well- marked case 

 there is some crushing of the vertebrae involved, and 

 the usual deformity depends upon a sliding of the 

 centrum above downwards and forwards upon the 

 centrum below. Complete displacement of any two 

 vertebrae from one another is prevented by a locking 

 of the posterior processes. In some cases the luxation 

 is complete, a condition that is least frequently met 

 with in the lumbar spine. 



In the cervical and dorsal regions, the parts, after 

 the dislocation, may often be returned to their normal 

 position ; but in the loins this replacement is usually 

 impossible, owing to the locking of the large and 

 powerful articular processes. In the neck the laminae 

 and spines may be fractured, while the articulating 

 processes, being broad and nearly horizontal, usually 

 escape, even when there is much displacement of the 



