This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
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.
To detect this accident Allis advises that while an assistant pushes upward on the knee in the direction of the long axis of the femur, the surgeon by flexing and extending the knee will find the nerve alternately made tense and relaxed in the popliteal space.
When luxated posteriorly the foot is inverted whether it is a low or high dorsal. The thigh is adducted, bringing the knee of the affected side in front of the sound one. The thigh is usually slightly flexed. There is shortening, and the higher the position of the head the greater the shortening and the farther up the trochanter is above the Roser-Nelaton line. Shortening is best seen with the thighs flexed to a right angle (Fig. 517).
When luxated anteriorly the foot is everted or almost straight. If it is a low thyroid there will be little or no eversion; if it is a pubic luxation eversion will be more marked. The thigh is abducted; this is more marked in the thyroid and less in the pubic. The thigh is flexed in the thyroid but may be straight in the pubic. There is no shortening but there may be a slight lengthening difficult to demonstrate (Fig. 518).
As in the shoulder there are two methods of reducing a dislocated hip, the direct and the indirect. The direct consists in placing the head in as favorable a position as possible and then directly pushing or pulling it towards the socket.
The indirect consists in using the thigh as a lever and rotating the head into place. These methods may be used in combination.
Patient flat on the floor on his back. Flex the knee on the thigh, and the thigh on the abdomen; this brings the head down from a high position to a low one below the acetabulum. Ad-duct the thigh slightly; this relaxes the Y ligament and prevents the head catching on the rim of the acetabulum.
Grasp the ankle with one hand, then place the other hand or arm beneath the bent knee and lift upward and inward thus raising the head over the rim of the acetabulum into the socket. If the head does not enter rotate the thigh gently, first out and then in, lifting at the same time. This rotation is to open the rent in the capsule to its widest extent. Too much rotation narrows the rent and obstructs the entrance of the head. An assistant may at the same time endeavor with his hands to push the head up towards the socket.
Another way of using the direct method (Stimson) is to place the patient face downward on a table with the thigh flexed at a right angle hanging over its end. The leg is then flexed at the knee and pressure made directly downward, gently moving or rotating the head from side to side. This is a safe and efficient method.