THE HIP- JOINT 431 



attitude of the limb are characteristic, and serve to distinguish 

 this dislocation from other injuries. 



More rarely, the neck of the femur becomes caught beneath 

 the obturator internus. The attitude of the limb resembles 

 that found in the variety just described, but the flexion and 

 rotation are more exaggerated. The head may injure the 

 sciatic nerve, which is stretched across it in the interval between 

 the inferior gemellus and the quadratus femoris. 



The lateral limb of the ilio-femoral ligament is the important 

 agent in maintaining medial rotation, and when it is torn the 

 limb adopts an everted position (Bigelow). 



3. Anterior Dislocation. From the subacetabular stage, the 

 head may pass forwards and medially in front of the obturator 

 externus. The greater trochanter is directed backwards and 

 laterally, and the limb is kept abducted, extended, and laterally 

 rotated, the eversion being produced and maintained by the ilio- 

 femoral ligament. This variety is sometimes referred to as 

 the " thyroid dislocation." 



The head may pass still further in an upward direction, 

 injuring the pectineus and adductor muscles, and it subsequently 

 comes to rest somewhere between the anterior inferior iliac spine 

 and the pubic tubercle, constituting the pubic, subspinous, and 

 pectineal varieties. 



(b) Irregular Dislocations are usually caused by extreme 

 violence and the position taken up by the head is very inconstant, 

 but it often tends to pass downwards and backwards towards 

 the lesser sciatic foramen ; the limb is usually everted (Bigelow). 

 When the ilio-femoral ligament is ruptured, the femoral head 

 may pass backwards below the obturator externus tendon, which 

 is consequently stretched across the upper aspect of the neck. 

 The head then assumes a position in the neighbourhood of the 

 ischial tuberosity. 



In the Reduction of a Dislocation of the Hip the head of 

 the bone is made to retrace its course through the tear in the 

 capsule. 



i. In the posterior group the limb is kept flexed and adducted 

 by the tension of the ilio-femoral ligament, which must first be 

 relaxed by flexing and adducting the thigh still further. As the 

 thigh is carried upwards and medially, the head of the femur 

 passes downwards and laterally and approaches the level of the 

 tear in the capsule, but it is still posterior to the acetabulum. 

 The thigh is next circumducted and laterally rotated. This 



