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 posterior 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 production of a secondary position, then the capsule 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 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.

Fig. 5i6.   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. 5i6. - 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.

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.