122 CLINICAL APPLIED ANATOMY. 



Dislocations at the Interphalangeal Joints, The dislocation 

 most commonly seen is a backward displacement of the distal 

 phalanx of the little finger, and as a rule the anterior ligament is 

 fully torn. Keduction, however, by extension is fairly easy, and 

 a dorsal splint will prevent recurrence. 



Lower Extremity. 



Dislocations at the Hip- Joint. The conformation and strength 

 of the hip- joint, including the depth of the acetabular cavity and 

 the perfect way in which the head of the femur fits into it, the 

 thickness of the capsule and the strength of the muscles that 

 surround the joint, explain the comparative rarity of traumatic 

 dislocations at this articulation. On the other hand, it must be 

 remembered that the head of the femur is at the end of a long 

 lever even when violence is applied to the knee, and much more 

 so when it is applied to the foot, a factor which it might be 

 thought would predispose to displacement of the head from its 

 socket, but as a matter of fact fracture of the neck of the femur 

 is much more common than dislocation at the joint. The 

 probable explanation of these two lesions, both arising from the 

 same kind of violence, is to be found in the position of the limb 

 at the time when the force is applied. In order that fracture 

 of the neck may occur, the limb should be in the fully extended 

 position, without abduction or adduction ; in order that dis- 

 location should occur, the hip- joint must be flexed and the limb 

 abducted. 



The only dislocations at the hip-joint which are seen with any 

 comparative frequency are those which are termed " regular," 

 in which the ilio-femoral or ^-shaped ligament remains intact. 

 The lower portion of the acetabulum is shallowest and the margin 

 is notched, and it is at this position as a rule that the head of 

 the bone slips out of the socket. 



The most usual dislocation is a dorsal one, in a direction 

 upwards and backwards. The capsule is torn posteriorly, and as 

 a rule the ligamentum teres is ruptured. As soon as the head of 



