The Hip Joint. 323 



and partly to the tension of the psoas and iliacus muscles, 

 while the flexion is due to the over-stretching of these 

 muscles. 



4. Dislocation on to the Pubes results from falls 

 on the feet or knees, when the limb is extended or thrown 

 backward behind the centre of gravity. In it, the head 

 of the bone rests in front of the body of the pubes, gener- 

 ally outside of the femoral vessels and under the psoas 

 and iliacus muscles, and, therefore, stretching the anterior 

 crural nerves ; the posterior surface of the neck is in con- 

 tact with the rim of the acetabulum, while the trochanter 

 major sinks into the acetabulum. The shaft of the bone 

 is abducted, slightly flexed and rotated outwards from 

 much the same causes as in the other variety of forward 

 dislocation, i.e., dislocation into the thyroid foramen, and 

 the surrounding soft parts are disturbed to nearly the 

 same degree as in the other form. The rent in the cap- 

 sule. Hamilton, Gunn and Barwell state that it is the 

 posterior portion of the capsule that is torn. Treves, 

 Tillaux and Morris, on the other hand, believe that, in 

 nearly every case of dislocation, the head of the bone 

 leaves the acetabulum through a rent in the lower and an- 

 terior part of the capsule, and that the condition of rota- 

 tion of the limb, at the time of the receipt of the injury, 

 influences the position the limb will assume, i.e., the form 

 of dislocation. Thus, if the limb be flexed and rotated in- 

 wards, or if the pelvis be rotated outwards, the head of 

 the bone will sweep around an axis formed by the untorn 

 part of the capsule, so as to occupy the neighborhood of the 

 sciatic notch, but if the flexion and rotation be more mark- 

 ed, then the head will be carried back on to the dors.um ilii. 

 Should, however, the limb be rotated outwards at the time 

 of the receipt of injury, or should the position of the pel- 

 vis be correspondingly altered, then a forward dislocation 



