Robotic long bone fracture reduction : methods, tools and algorithms

Abstract

Long bone fracture reduction is a term used to describe the process of moving fractured long bones, such as the femur, back into anatomical alignment. The current reduction process has a number of shortcomings including unacceptable errors in alignment and accumulative exposure to radiation. Few advancements are being made to address these problems. This research aimed to understand the force required to reduce fractures and design a robot and control system for the reduction process. The aims are achieved by developing solutions through modeling and results are shown in both simulation and in a real-world phantom study. Significant contributions of this work include a model of the lower extremity that can be fractured, computing the force at a specified displacement [ 1, 2, 3, 4], a control system that reduces the risk and discomfort for a patient [5] and discussions on overall system design [ 6, 7). The model uses correct anatomical geometry, Hill type muscle models, and derived equations of motion to represent salient features of a fractured femur. Simulation results are compared with published data from patients with femurs under traction as well as limited data during reduction. The fracture model results showed the maximum force for reducing bones to be approximately 400 N. Current best practice for fracture reduction is to translate the bone into postilion followed by rotation. This research showed a better outcome can be achieved with simultaneous motion in 6 axes. Finally, the angle of the proximal segment of the femur in the hip is shown to have significant influence on the reduction force. A parallel robot is developed for its inherent safety and compact size in an operating room.