Research On Robotic-assisted Femoral Shaft Fracture Reduction System Based On Compliant Actuator

Fractures of the femoral shaft are common high-energy injuries of the lower extremity.Minimally invasive technique showed smaller incisions,less blood transfusion and more effective recovery for humeral fractures.Closed intramedullary(IM)nailing is a standard technique for treating diaphyseal fractures,where an IM nail is necessary to be inserted into the distal medullary cavity from the proximal cavity passing the fracture site and statically locked.However,experiencedependence anatomical reduction is difficult to be achieved in a closed manual manner even after repeated attempts,or cannot be maintained effectively during the subsequent IM nail implanting and fixation.In addition,the entire surgical procedure is performed under C-arm fluoroscopy monitoring,which involves high risk of radiation exposure,especially for the medical staff.This is particularly the case in long bone fracture reduction because of the tube-shaped anatomy and the counteracting muscle forces.To address the above-mentioned drawbacks of traditional reduction and IM nailing techniques,we designed a clinical and technical acceptance robot-assisted system to achieve and maintain anatomic or functional reduction of femoral shaft fractures.The main contents of the thesis are presented as follows:The femur is well protected with powerful muscles.However,it causes serious fracture displacement and makes reduction difficult due to the muscle contraction.Firstly,this research aims to quantify the forces required during the process of femoral shaft fracture reduction by developing a simulation environment.Then,a set of measurement system is developed to obtain the value of the forces.Forces of skeletal traction and alignment are measured by three individual sensors,and the corresponding results can be recorded instantaneously during the fracture reduction process.The system not only provides reliable functional fracture reduction,but accurately obtains the relative fracture reduction mechanical parameters,conforming to the clinical medical ethics with the freedom C-arm monitoring and without additional trauma.The measurement and analysis of the reduction mechanical parameters provides theoretical basis for the development of fracture reduction robot and clinical references.In general,a closed fracture of the femoral shaft may be complicated by misalignment,and the fracture fragments can be simplified as non-uniplanar lines.Six degrees of freedom(DOFs)comprising displacements and rotations in a defined coordinate systems are required to complete the anatomical or functional reduction of femoral shaft fractures.Based on the theory of human anatomy and kinematics characteristics of the lower extremity,the technical requirements about the applicability,security,clinical and technical acceptance of the robotic-assisted fracture reduction system are proposed.The overall structure of the typical femoral fractures reduction robot is introduced in detail,including traction actuators,rotary actuators and sleeve-type reduction unit.Finally,the motor and pneumatic soft actuator control system of the robot are introduced.The mechanism of the manipulator comprises a six-degree of freedom serial-link robot,referred to as a 3P3 R robot,with three prismatic joints and three rotational joints(including one for the knee).The coordinate system and forward kinematics model of the robot are established.The available workspace of the robot is analyzed by utilizing Monte Carlo method.The Jacobian matrix of the robot is derived with the vector product method.The manipulability of the system is analyzed,and its operability over the entire work space is verified.In addition,the existence of an inverse kinematic solution of the system is established.The kinematic analysis and investigation of the workspace confirmed the feasibility of the mechanism for the given design parameters.The simulation results prove the applicability of the consumption and inverse kinematics model.The problem of trajectory planning in robot end-effector movement is very important,which is an important factor to improve work efficiency and ensure operation requirements,and is also the foundation of robot motion control and structure optimization.In this research,the typical femoral shaft fracture assisted reduction robot system is driven by the combination of pneumatic soft actuator and motor drive,and movements required for reduction of the fracture fragments are driven by corresponding drive under minimally invasive environment.The pneumatic soft actuator is flexible,it has nonlinear properties,and human muscle tissue is nonlinear too,which is a “soft contact soft” problem.In this research,the path planning in the process of fracture reduction is discussed,and the characteristics of the pneumatic soft actuator are theoretically and experimentally studied.Finally,the trajectory tracking control of the rotating joint and the moving joint are respectively driven by the pneumatic soft actuator and motor.This research presents a novel robot-assisted manipulator for femoral shaft fracture reduction with indirect contact with the femur.In order to prove the reliability of this technique,two groups of experiments are performed,providing a deeper analysis on the operability,repetitiveness,and effectiveness,etc.of the proposed robot.Therefore,related experimental models for simulating human femur characteristics are required.In this research,an alternative clinical testing model is proposed for orthopedic surgeons to practice femoral fracture reduction.This model imitates the human musculoskeletal system in shape and functional performance.In the first group of experiments,to check the repeatability and operability of the manipulator,we perform fracture reduction five times under different initial states of the fracture in the same muscle contraction force.The second group of experiments are performed to investigate the effectiveness of the manipulator.Fracture reduction are completed under four different muscle contraction forces.Experiments conducted on the artificial lower limb model demonstrate high reduction accuracy,safety,sufficient working space,and low radiation exposure of the proposed robot-assisted system.Thus,the minimally invasive teleoperated manipulator would have greater development prospect.