378 



HUMAN ANATOMY. 



Fig. 396. 



sacro-iliac junction. It is obvious that no anterior dislocation can be below the bi- 

 acetabular line and no posterior dislocation can be above it. 



As the femur is about equal in length to the tibia and tarsus, if the head is in 

 the socket the foot will be on the acetabular level when the thigh is vertical and the 

 knee flexed. If the head is dislocated anteriorly, the foot will be on a higher 

 level ; if posteriorly, the foot will be lower, and may even touch the surface on 

 which the patient 'lies. There will be corresponding changes in 'the level of the 



knees (AUis). . , ,• 



The femoral vessels are not often injured in hip luxations, because they he 

 above the joint and luxations are always primarily downward ; and because, as the 

 head approaches them in the inward variety only, and as for the production of that 

 variety abduction is necessary, the muscles beneath them— the pectineus and ilio- 

 psoas— are put upon the stretch and the vessels are lifted out of harm's way. 



The relations of the sciatic nerve to these injuries are of great importance. The 

 nerve is in close relation to the hamstring muscles, especially to the biceps. These 



structures are made tensfe 

 and are stretched across 

 the neck of the femur pos- 

 teriorly by flexion of the 

 thigh on the pelvis, espe- 

 cially if the leg is also 

 extended on the thigh, so 

 that the origin and inser- 

 tion of the hamstring mus- 

 cles are separated. If, in 

 a dislocation, the head of 

 the femur originally lies on 

 the anterior plane of the 

 pelvis, and either by the 

 force producing the dis- 

 placement (as is commonly 

 the case), by the action of 

 muscles, or during efforts 

 at reduction is made to pass 

 to the posterior plane, it 

 must traverse the narrow 

 space between the sciatic 

 nerve and hamstrings and 

 the edge of the acetabu- 

 lum. The nerve is thus 

 very apt to be bruised and 

 stretched and separated 

 somewhat from the biceps 

 tendon. Later, if replace- 

 ment by "circumduction" is attempted, the head may pass beneath the nerve, 

 which will then be tightly stretched over the front of the neck, will prevent full 

 extension of the thigh, and will cause continued pain and disability. Other com- 

 plications associated with the nerve may occur, and have been fully demonstrated 

 by AUis, whose excellent experimental and clinical work forms the basis for the fore- 

 going summary of the anatomy of hip luxations. 



In reduction of posterior dislocations by the method of circumduction the 

 thigh, which is already flexed, adducted, and inverted by the agencies above 

 described, is still hirther Jlexed and adducted and lifted upward to relax the ilio-psoas 

 and to bring the head of the bone near the margin of the acetabulum ; it is then 

 abducted, tightening the inner band of the ligament, and everted, tightening the outer 

 band and converting the femoral attachment of the whole ligament ( t)ut chiefly of 

 its outer limb) into a fulcrum around which, as a centre, — the abduction and eversion 

 being continued into circumduction, — the head of the bone sweeps, skirting the 

 lower edge of the acetabulum, and hnally, by extension of the thigh, re-entering 



Relation of the head of the femur to the innominate bone in pubic 



luxation. 



