REGION OF THE HIP. 



Luxation by Adduction. If the thigh is flexed and adducted the angle of the 

 neck and shaft prevents any bony fulcrum from forming. If now the shaft is strongly 

 rotated inward the iliofemoral or Y ligament becomes tense. It is wound around 

 the neck of the bone and acts as a ligamentous fulcrum. The shaft revolves on its 

 long axis, and as it turns inward the head turns outward and presses against the 

 lower posterior part of the capsule, which ruptures, and a dorsal luxation is produced. 

 A backward thrust in the long axis of the femur also favors the production of the 

 luxation (Fig. 515). 



By outward rotation of the shaft the head can be conducted around the edge of 

 the acetabulum until it lies in the thyroid foramen on the anterior plane, thus changing 

 a primary dorsal into a secondary thyroid luxation. 



The Rent in the Capsule. The capsule ruptures at its lower anterior or pos- 

 terior portion according to whether it is primarily an anterior or a posterior luxation. 

 If, however, the limb is rotated while the 

 head is out of its socket, as in the produc- 

 tion of a secondary position, then the cap- 

 sule is torn still further, but the Y ligament 

 is practically never torn either when the 

 original luxation occurs or the secondary. 



The rent in the capsule through which 

 the head emerges has been proven both by 

 Robert Morris and Dr. Allis to be always 

 equal in size to the head of the femur 

 and never a slit. Therefore in every case 

 there exists a rent in the capsule large 

 enough to allow of returning the head, 

 provided it is not closed or obstructed by 

 a rotation or malposition of the limb, or by some foreign substance such as torn 

 muscle or infolding of the capsule. 



Injuries to the Muscles. When the thigh is abducted the adductor muscles 

 are made tense, and if it is hyperabducted they are torn ; these overstretched 

 muscles, some of which may be ruptured, are the three adductors, the pectineus, 

 and the gracilis. If the luxation is an anterior one the obturator externus will be 

 torn because it arises from the outer surface of the thyroid membrane. If a posterior 



FIG. 516. Showing the sciatic nerve caught 

 around the neck of the femur. (After an illustration 

 by Dr. Allis in his prize essay on the hip.) 



FIG. 517- Posterior or dorsal luxation of the left hip (From an original sketch by the author). The shortening is 

 seen by comparing the position of the knees, the thigh is adducted and rotated inward. 



one the internal obturator may be injured. Allis has pointed out that when the 

 head passes from one plane to another it may tear the obturator externus, quadratus 

 femoris, and upper fibres of the adductor magnus. The tearing of these muscles 

 usually exerts but little influence on the reduction of the luxation. 



Injuries to the Nerves. Rarely the anterior crural nerve may be injured by 

 being stretched over the head of the femur. The sciatic nerve has been injured, 

 and Allis has shown how, when a dorsal is rotated into a thyroid luxation, the sciatic 

 nerve is likely to be caught around the neck of the femur (Fig. 516). This is favored 

 by making a large circle while circumducting the knee, and also by extending the 

 leg on the thigh, thus making the nerve tense and causing it to lie closer to the socket. 



