Design of an External Fixator and Motion Application System for Use in an In Vivo Fracture Study

摘要

In the United States, there are approximately 1 million fractures annually [1]. These fractures can be treated successfully with the use of casts or internal fixation (i.e. screws, bone plates, or intramedullary rods). However, for approximately 1 out of 20 people with a fracture, these treatments are not successful and result in either a malunion or a non-union. A malunion or a non-union reduces the ability of the bone to withstand the loads it is intended to take. This can cause pain and suffering for the patient. Clinically, non-unions can be treated using mechanical stimulation via an external fixator. Current treatments and the literature suggest that the mechanical environment of a healing fracture callus can influence tissue differentiation, perhaps even stimulate healing [2,3,4,5,6,7]. This leads to the overarching question, what is the precise relationship between the local mechanical environment of a fracture and patterns of bone repair? In order to answer this question, one must be able to control and measure the amount of motion or force applied to the fracture so as to properly relate the healing patterns with a particular stimulus. The aforementioned studies have attempted to control motion using various means, but none have simultaneously measured and controlled the amount of motion and force. Nor have any reported in vivo values of fracture callus stiffness. The aim of this work was to develop and validate an external fixator and motion application system that could be used to apply controlled and measurable motion and force to a healing fracture callus in a mouse model. The data will be used to calculate the callus stiffness throughout the healing period during the in vivo studies and non-invasively assess healing.