Like other dislocations, those of the hip may be complicated by laceration of muscles, blood vessels, or nerves, or by fracture of one or other of the bones in the vicinity.
Dislocation on to the Dorsum Ilii.—This, the commonest form of dislocation of the hip, is usually the result of the patient falling from a height, or receiving a heavy weight on the back while stooping forward with the thigh flexed, slightly adducted, and rotated medially. It is also said to have occurred from muscular action. The shaft of the femur acts as the long limb of a lever of which the neck is the short limb, the femoral attachment of the [inverted Y]-ligament forming the fulcrum. The head, thus brought to bear upon the lower and back part of the capsule, tears it and leaves the socket, passing upwards and coming to rest on the dorsum of the ilium, above and anterior to the tendon of the obturator internus ([Fig. 73]). The articular surface is directed backward, while the trochanter looks forward.
Fig. 72.—Dislocation of Right Femur on to Dorsum Ilii.
Clinical Features.—The affected limb is flexed, adducted, and inverted, so that the knee crosses the lower third of the opposite thigh, and the ball of the great toe lies on the dorsum of the sound foot. There is shortening to the extent of from 11/2 to 2 inches, the trochanter being displaced above Nélaton's line, and lying nearer to the anterior superior iliac spine than on the normal side. The patient is unable to move the limb or to bear weight upon it; abduction and lateral rotation are specially painful; and traction fails to restore the limb to its proper length. On making these attempts a characteristic elastic resistance is felt.
The head of the femur in its new position may sometimes be felt through the fibres of the gluteus maximus, but swelling of the soft parts often obscures this sign. The normal depression behind the great trochanter is lost, the gluteal fold is raised, and there is often a degree of lordosis which compensates for the flexion. The fingers can be pressed more deeply into Scarpa's triangle on the dislocated than on the normal side—a point in which this injury differs from fracture of the base of the neck of the femur.
In a certain number of cases the lateral limb of the [inverted Y]-ligament is ruptured and the limb is everted—dorsal dislocation with eversion.
