A Minimally Invasive Surgical Instruments For Fracture Reduction In Vertebral Confined Space

Type B thoracolumbar burst fracture is a burst fracture upper well back wall of vertebra caused by vertical external force.Upon impulse force,broken bone may intrude vertebral canal,oppress spinal nerve and limit limb movement.Open surgical treatment for this fracture is not widely applied due to that it may make patients bleed excessively and even damage their nervous system.Minimally invasive open operation has several advantages for patients,including small cut,less bleeding and quick recovery.However,traditional minimally invasive instruments can not flexiblely clip broken bones in the narrow internal space of the vertebra.Thus,a new surgical instrument is desperately necessary for this open operation.In this work,a novel minimally invasive instrument has been designed suitable for reduction of fracture in the vertebral confined space.As a multi-degree automatic minimally invasive internal reposition forcep,it can get into narrow pedicle channel and complete spinal decompression and posterior wall reconstruction.The specific researches are as follows:This fracture-reduction minimally invasive surgical instrument has a four-DOF manipulator based on screw drive.The four DOFs contains operating rod rotation,wrist deflection and two bionic compound pliers.Wire drive system is able to avoid the movement coupling among joints and meet the requirements of equipment assembly and wire rope pretightening.The overall control scheme of minimally invasive surgery system was confirmed by selecting suitable stepping motor,drive,controller and other important components.After calibrating link parameters,the coordinate system for the surgical instrument was established based on D-H method,and the forward kinematics analysis was carried out.Besides,kinematics modeling of surgical instruments was established,and the rationality of the forward kinematics analysis was verified.Algebraic analytic method was used for inverse kinematic analysis to obtain analytic expression of each joint variable.Finally,working space of the surgical instrument was analyzed and terminal trace of the actuator was drawn,which demonstrated that this surgical instrument can be flexiblely used in the narrow internal space of the vertebra.According to the above the design,the control system for the fracture-reduction minimally invasive surgical instrument has been constructed.PS2 wireless pad was used for verification of the DOF functionality and movement coupling.The experimental platform was set up to mearsure friction and slip coefficient between gripper teeth and bones,and verify the reliability of bionic reposition tongs.In vitro simulation experiment for minimally invasive surgery was conducted using this surgical instrument installed on three-coordinate linear guide line marking machine.It was proved that the instrument can flexiblely clip broken bones in the narrow internal space of the vertebra.This new instrument having multiple DOFs can reduce surgical risk caused by hand shaking of surgeons,and avoid harm from radiation for surgeons.