Plastic Surgery of the Hip

Abstract

PLASTIC substances can be molded easily, as they lend themselves to adaptation by external forces. But animate plastic tissues have an innate power of self-adaptation to changing conditions. Certain tissues of the body can be molded and reshaped by the surgeon's hand. They can be transplanted to other parts of the body, where they may serve a new purpose in the repair of bodily defects, but they also have an inherent capacity to adapt themselves to their new surroundings, to take on new functions, and, by growth, to meet greater demands placed upon them. We have been accustomed to think that the soft tissues of the body are more plastic or changeable than the bones. Plastic surgery, for the most part, has meant the repair of defects of the face and skin grafting, to correct contractures and replace lost tissue. But we have learned that bones are also fit matter for the surgeon's plastic art, and, indeed, present even more remarkable and striking illustrations of that innate plasticity which is a characteristic of living structures. According to Wolff's law, the external form and the internal architecture of bone are determined by the mechanical forces which operate upon it, and are altered when the direction of stress and strain is altered. They adapt themselves to changed function and to altered mechanical forces. It is well known that the lamellæ of the head and neck of the femur are designed with exact mathematical precision in this peculiarly shaped bone to bear a given weight with the use of the least amount of material. This bone is as precisely adapted to the demands placed upon it as is a reinforced concrete building or a bridge. If the angle of the neck with the shaft becomes altered by accident or disease so that there arises a coxa vara, Nature proceeds to absorb all the lamellæ. Simultaneously they are replaced with new ones in different lines of direction which are as mechanically correct as were the old ones, and which hear the body weight with the same paucity of material but the same coefficient of safety. In cases of bony ankylosis of the hip, we frequently observe that Nature has laid down lamellæ which arise in the bones of the pelvis and sweep downward in curved, unbroken lines through the head and neck of the femur. The direction and curve of these lines may be entirely different from those of the normal femur, because the line of weight-bearing is different. A change of function has brought about a complete change of architecture. Here is an exhibition of plastic power which soft tissues cannot surpass. But there is another natural law, even more profound and mysterious than that enunciated by Julius Wolff.