A new understanding of internal fixation for long shaft fractures -- lever reconstruction theory / 中华骨科杂志

ABSTRACT

Through the study of the anatomy and biomechanical characteristics of the long bone after internal fixation of fracture, researches showed that a new level system is formed. The intersection of fracture line and internal fixation serves as the fulcrum. The distance from external force point to fulcrum is power arm, and the distance from the fulcrum to the tail of internal fixation contacting bone is the resistance arm, and the power arm and resistance arm should be as equal as possible. This is the lever reconstruction theory. Plate and intramedullary nail fixation are commonly used in the treatment of long shaft fractures. The intramedullary nail mainly depends on the contact between the main nail and the inner wall of the medullary cavity, and the firmness of distal locking nail and the bone. According to the lever reconstruction theory, after intramedullary nail fixation, the power arm is the distance from the point of external force to the fulcrum, and the resistance arm is the distance from the fulcrum to the contact point of nail tail and bone. The intramedullary nail should be fully reamed before inserting and the main nail with larger diameter should be used to make it closely fit with the inner wall, and contact should be increased through distal locking to prolong the effective working distance. Plate fixation depends on the holding force between the distal screw and bone, which can increase the reliability of fixation. The power arm is the distance from the point of external force to the fulcrum, and the resistance arm is the distance from the fulcrum to the end of the opposite side. The type of lever formed varies with the location of the fracture. For example, if the power arm is shorter than or equal to the resistance arm, it can form a laborious lever or balance lever with stable structure. When the power arm is longer than the resistance arm, absolute stability cannot be achieved and it is prone to complications such as nonunion and fixation failure. At this time, effective working distance of the resistance arm should be extended and scientific and effective rehabilitation guidance should be given according to different fracture types. This theory can well explain the causes of complications related to internal fixation after long shaft fractures and point out a new direction for future treatment.