Summary: Principles of the Surgical Correction of Posttraumatic Deformities of the Lower Extremities

Abstract

Normal function of the extremities depends as much on proper joint anatomy as on the presence of normal functional loads. Every surgical correction of posttraumatic deformities must be aimed at normalizing both of these factors in order to avoid local cartilage damage leading to painful restriction of motion. The lower extremity is unique in that its major points are positioned eccentrically with respect to the axis of weight bearing (in the stance phase of gait, this axis extends downward and outward at an angle of about 3° from the partial center of gravity S5). As a result, the level of the joint load depends basically on the body weight and the distance of the joint center from the weight-bearing axis. Because the distance of the weight-bearing axis from the joint center decreases from the hip to the ankle, the body must generate different intrinsic countermoments in the various joints in order to distribute the pressure loads more evenly. The “mechanical axis” of the lower extremity should not be confused with the weight-bearing axis. The mechanical axis is a straight line connecting the centers of the hip and ankle joints and is simply a graphic means of representing the loads on the knee. Deviation of the mechanical axis from the center of the knee can indicate no more than a qualitative alteration of loading; it cannot be used as a quantitative measure of joint loads.