chap, xix.] DISLOCATIONS OF THE HIP. 413 



Bigelow states that there is no evidence to show 

 that the head of the femur has ever been actually 

 displaced into the sciatic notch. 



In these backward dislocations the ilio-psoas 

 muscle is greatly stretched. The quadratus femoris, 

 the obturators, the gemelli, and the pyriformis are more 

 or less lacerated. The pectineus is often torn, and 

 the glutei muscles 

 even may be ruptured 

 in part. The great 

 sciatic nerve may be 

 compressed between 

 the femoral neck and 

 the rotator muscles, 

 or between the head 

 of the bone and the 

 tuber ischii. In both 

 of the backward lux- 

 ations there is shor- 

 tening, due to the 

 circumstance that the 

 line between the an- 

 terior superior spine 

 and the femoral 

 condyles is lessened 



by the displacement Fig> 4 i._ O bturator or Thyroid Disloca- 



back wards of the tion (Bigelow). 



bone, with the addi- 

 tional shortening in the dorsal dislocation brought 

 about by the passing of the femoral head above the 

 level of the acetabulum. The adduction and in- 

 version in the main depend upon the position of 

 the head and cervix, which must follow the plane 

 of the bone upon which they lie. This position 

 is maintained by the tense Y ligament. The 

 damage done to the chief external rotators places 

 them also hors de combat. The flexion is due to 



