DISLOCATIONS OF THE PELVIS AND COCCYX.—Dislocation of the pubic and sacro-iliac symphyses occurs in connec tion with fracture of the pelvis, the symp Backward Dislocations. — The dorsal form is by far the most common of the dislocations of the hip. The thigh is adducted, rotated inward, and more or less flexed; so that tbe knee rests upon the front of the opposite thigh when the patient is recumbent, and there is appar ent shortening (Fig. 13). The upper and outer part of the thigh is broadened, and the trochantcr is above Nelaton's line (a line drawn from the antero-superior spine of the ilium to the tuberosity of the ischium). The head of the femur may be obscurely felt in the buttock.
The actual shortening cannot easily be determined on account of the difficulty of placing the two limbs in symmetrical positions. Voluntary movement and fric tion are lost; passive flexion and adduc tion alone are possible.
The characteristic position and limita tion of motion readily distinguishes the dislocation from a fracture of the neck of the femur.
Etiology.—The dislocation is usually produced by violence transmitted along the shaft of the femur while the thigh is flexed, adducted, and rotated inward; or the head of the bone may be thrown out of place by exaggerated adduction, in ward rotation, and slight flexion; or, again, the dislocation may result second arily from an obturator dislocation by the same three motions.
Pathology.—The head of the bone usu ally tears through the capsule low down behind, passes below and then upward behind the obturator, and rests finally on that muscle close behind the acetabu lum, or, more rarely, it leaves its socket higher up, pushes the obturator ahead of it outward or -upward, and lies on the edge of the acetabulum itself. The cap sule is irregularly torn behind, the liga mentum teres is ruptured, the quadratus femoris and gemelli are usually torn, the two obturators and pyriforms less fre quently. Rarely the head of the bone rests on the great sciatic notch or the dorsum ilia. The edge of the acetabulum may be shattered and the head of the bone split.
Treatment. — The surgeon must en deavor to relax the Y-ligament and other untorn portions of the capsule, to bring the head of the bone opposite the rent in the capsule (if necessary) and then to lift or pry it into place. To do this the
patient is laid flat on his back and the pelvis steadied by an assistant or by the surgeon's foot. The patient's knee is then flexed at a right angle, the thigh rotated inward and flexed to or a little beyond a right angle, and then lifted bodily upward, rotated a little outward, and extended in abduction. The lifting and outward rotation should replace the bone with a distinct jump.
Or the patient may be laid on his face on a table, whose edge comes just above the groin, so as to leave the lower ex tremities dangling. The sound limb is now held horizontally by an assistant, and the dislocated one allowed to hang vertically downward. The surgeon grasps the ankle of the dislocated limb, flexes the knee to a right angle, and, while diverting the patient's attention, swings the limb gently from side to side. Under the influence of gravity the mus cles soon relax and the bone may slip into place of itself or aided by a sharp quick pressure downward on the calf.
If these methods fail, ether should be administered and reduction attempted several times by the first method. Fail ing again, try traction in slight flexion and adduction, aided by direct pressure on the great trochanter.
If the limb is too strongly flexed or too soon rotated outward the dorsal dis location may be tranformed into a thy roid one. If this occurs, the dislocation must be restored to its original form by reversing the movements: flexion in ab duction and outward rotation, followed by adduction and rotation inward.
Everted Dorsal Dislocations. — If the outer branch of the Y-ligament is rupt ured, the limitation to abduction and outward rotation is, in great part, re moved, and the head of the bone is free to rise higher than before. Hence, when this rupture occurs, if the head remains behind the acetabulum only slight flexion and adduction persist, while, if it has moved upward and forward near to or above the antero-inferior spine of the ilium (in which position it can be felt). there will be extension, abduction, and slight outward rotation: the so-called everted dorsal. Reduction is effected by converting the dislocation into the com mon dorsal form and treating it as such.