Robot for advanced long bone fracture reduction

Abstract

The invention relates to medicine and can be used for treating severe polytrauma and complex fractures, for example, of the tibia long bone. A robotized system for the closed reduction of a fractured femur comprises a system of actuators based on a Stewart platform, a working member assembly, Schanz pins, a perineal post, and a controller with software. The Stewart platform is mounted on a floor plate via a vertical column. The linear actuators are arranged between a base plate and an end effector having a C-shaped ring. The two ends of the actuators are connected by hinges to the base plate and the end effector, respectively. The Schanz pins are secured to mounting blocks which are fastened by round-head screws and wingnuts. The perineal post is mounted on a base plate via a vertical column. The post is connected to two additional links. An O-shaped ring of the perineal post is connected to the C-shaped ring by a trapezoidal steel ring. A Schanz pin is mounted on a steel block such as to be capable of holding a proximal fragment in place during the reduction process. The invention results in precise traction forces and the optimal alignment of bone fragments.

Description

[0001] Robot for advanced reduction of long bone fractures.

[0002] A61B34 / 30 Surgical robots

[0003] The invention relates to medicine, namely to traumatology and orthopedics, as well as to robotics, and can be used to treat patients with severe polytrauma and complex fractures of the long femur and tibia.

[0004] A "Robot for Reducing Long Bone Fractures" (US9610101 B2, published 04 / 04 / 2017) is known, comprising a frame; a support slidably connected to the machine base and capable of moving up and down; a plurality of electrohydraulic drives; and a parallel robot with six degrees of freedom located on the support, wherein the movement of the robot with six degrees of freedom is hydraulically controlled by means of a plurality of electrohydraulic drives. The robot for reducing long bone fractures includes two frames for fixing long bones, one frame is connected to the support, and the other is connected to the parallel robot with six degrees of freedom. The two frames for fixing long bones are located side by side. Each of the two frames for fixing long bones is rigidly connected to a corresponding mounting and fixing plate.

[0005] The disadvantages are the complexity of the design, unreliable connection of the long bone fixation units, and the use of heavy hydraulic drives that respond slowly to input commands from the controller.

[0006] A "Robot for Repairing Long Bone Fractures" (EP2862527 B1, published June 3, 2020) is known. It consists of a motor base and multiple sets of electrohydraulic actuators. A support capable of up and down movement is slidably attached to the motor base, and a parallel robot with six degrees of freedom is positioned on the support. The parallel robot with six degrees of freedom contains multiple first hydraulic cylinders. The number of first hydraulic cylinders is the same as the number of electrohydraulic actuators, and there is a one-to-one correspondence between the plurality of first hydraulic cylinders and the plurality of electrohydraulic actuators, and they are in a moving relationship. The robot for repairing long bone fractures can plan the motion trajectory of the parallel robot with six degrees of freedom according to a preoperative computed tomography scan and precisely control the movement of the injured limb through six degrees of freedom.When using a robot to repair a long bone fracture, only one CT scan is required to perform the repair, reducing radiation exposure for both the surgeon and patient. Furthermore, movement of the injured limb is controlled by a parallel robot with six degrees of freedom, ensuring high placement accuracy and good surgical stability.

[0007] Another disadvantage is the complexity of the design, as well as the incorrect and slow operation of the hydraulic system.

[0008] A medical system for robotic surgery for installing bones with an internal rod for fixing bone marrow (CN1561923 A, published June 21, 2006) is known. It consists of a multifunctional automatic operating table, a robot, a bone installation controller on the robot, a bone fixation mechanism, a high-precision fully automatic X-ray machine with a C-shape, an arm, a navigation robot, a robot controller, a main manual control station, and a slave manual control station.

[0009] The disadvantages include the length of the X-ray process, the difficulty of installing the pin on the patient's femur, and the limited range of motion of the robot due to its vertical position on the ground.

[0010] A system for anatomical bone fracture reduction (EP 2753253 A1, published July 16, 2014) is known in which first and second manipulators, and optionally a third manipulator, are attached to the fracture fragments to be reduced via percutaneous attachment using devices such as Schanz pins. A basic processing system determines, based on one or more medical images of the fracture, manipulations such as rotations and translations of bone fragments necessary for the proper repositioning and alignment of the fragments for optimal fracture healing. The processing system outputs motion reference signals (position, velocity, acceleration, and force) to a controller, which in turn directs the first, second, and third manipulators to perform the calculated manipulations.

[0011] A disadvantage is the complexity of the design of manipulators for proper attachment of bone fragments. Three Stewart platform mechanisms are used for bone extension and alignment, making the entire mechanical system and its control quite complex. A "Bone Fusion System" (EP 1542602B 1, published November 17, 2010) is known, including devices and kits for fusing two or more bones using a bone plate. The bone plate may include a body portion configured to receive a recess in one or more bones and one or more elements that facilitate improved positioning and / or attachment of the body portion to the bones, including a protrusion, cap, hole, rough surface facing the bone, and / or a thickened perimeter.

[0012] The disadvantage is that all fusion operations are performed manually and do not ensure precise resection of the fused bones. In other words, the system does not include a robotic mechanism. Furthermore, this patent expired on June 22, 2023.

[0013] A device for osteosynthesis of fractures of the end of the femur is known (FR2519857A1, published 23.03.1984) comprising a plate in which holes are provided for the passage of screws intended for insertion into the bone to fix the fracture of the bone parts and a plate, the outer plate is intended for application to one of the extremities of the femur and has an extension to allow the insertion of three holes located in an isosceles triangle.

[0014] A drawback of this design is the inaccuracy of plate placement when inserted into the femur for fracture fixation. This device is used manually and does not require a robotic mechanism.

[0015] The objective of the invention is to develop an autonomous robotic system designed to perform closed reduction of fractured femurs, capable of applying precise traction forces and ensuring optimal alignment of bone fragments.

[0016] The technical result is achieved in that the proposed autonomous robotic system designed to perform closed repositioning of fractured femurs includes a drive system based on the Stewart platform, an end effector unit, Shantz pins, a perineal post, optimization software and a controller for improved repositioning of long tubular bone fractures, the Stewart platform is mounted on a ground plate using a vertical column, six linear actuators are located between the base plate and the end effector with a C-shaped ring, universal joints connect both ends of the actuators to the base plate and the end effector, the end effector unit of the robotic system based on the Stewart platform is two C-shaped rings connected by steel screws and medium-strength flange locknuts, with the ability to interact with a sealing ring that is connected by a steel link, Shantz pins are fixed on mounting blocks,secured with stainless steel round head screws and plastic wing nuts to ensure precise fixation of the distal fragment, the perineal post is mounted on the base plate through a vertical column, the post is connected to two additional links connected through pivot joints to position the distal femoral fragment into the O-ring, the O-ring of the perineal post is connected to the C-ring through a trapezoidal steel ring, a Schanz pin is mounted on a steel block to securely hold the proximal fragment in place during the reduction process. (R. ALFRED).

[0017] By intelligently managing the fracture reduction process, the system minimizes stress on surrounding soft tissues, such as muscles, tendons, and ligaments, thereby reducing the risk of further injury. This advanced approach not only improves the accuracy of bone alignment but also enhances patient recovery by optimizing the procedure to minimize tissue destruction.

[0018] Interestingly, there is currently no robotic or autonomous system available on the market for femur fracture reduction. The equipment currently used for femur fracture reduction consists of a manual traction table. We view this opportunity as a "blue ocean market," representing untapped and undeniable market space. We aim to create new demand and render existing competition irrelevant.

[0019] Long-term experience by orthopedic surgeons shows that the accuracy of manual fracture reduction consistently decreases, and incomplete reduction ultimately leads to changes in patient gait. Furthermore, both the patient and the surgical team are exposed to high levels of X-ray radiation, which surgeons can at least avoid. Manual fracture reduction procedures are also labor-intensive and time-consuming due to the elongated anatomy of the femur and strong opposing forces from the surrounding muscles. Surgeons must apply significant traction to realign the fractured segments of the long bone, which can lead to soft tissue deformation. With our proposed R.ALFRED system, the reduction process can be autonomous, the required forces can be delivered precisely, and the overall fracture reduction time can be reduced. Surgeons can avoid radiation exposure by monitoring the procedure remotely.

[0020] The proposed invention is a new medical robotic device designed for the autonomous repositioning (fixation) of fractured femurs. A conceptual diagram of the complete system is shown in Fig. 1, and Fig. 2 illustrates a physical prototype of the system, hereinafter referred to as R. ALFRED.

[0021] Specification:

[0022] 1- Base plate cover, 2- Universal drive, 3- Base plate, 4- Upright column, 5- Ground plate, 6- Side screws, 7- Center screws, 8- Medium strength flange locknuts, 9- High strength flange locknuts, 10- End effector C-ring, 11- Steel screw for 2" г0 C-shaped end effector, 12- sealing ring, 13- steel connection between the sealing ring and the second с-shaped ring, 14 - 2nd C-shaped end effector, 15- plastic wing nut, 16- stainless steel hex head screws, short, 17- pan head screw with hex slot, 18- Schanz pin mounting block, 19-Schanz pin, 20- stainless steel hex head screws, long, 21- vertical column, 22- figure bracket 1, 23-figure bracket 2, 24- ground plate, 25- C-ring, 26- connection of O-ring and C-ring, 27-O-Ring, 28- Schanz pin mounting block, 29- Schanz pin, 30- plastic wing nut 6-6 plastic on ring O, 31- Hexagon socket head cap screw, 32- 6-6 nylon plastic wing nut on C-ring, 33- Linear motors (actuators).

[0023] Stewart Platform-Based Robotic System: This mechanism, equipped with six linear actuators, performs the traction and rotational maneuvers necessary to align and fixate the femoral fragments.

[0024] Perineal post: A device designed to stabilize the proximal femur fragment, allowing the robot to manipulate the distal fragment for alignment. A detailed sketch of the Stewart platform-based robotic system, along with its specific components, is shown in Fig. 3. Additionally, Fig. 4 provides an annotated sketch of the perineal post with all parts labeled.

[0025] Although the X-ray machine is depicted in Fig. 1, it is not an integral part of the current robotic system. However, it highlights our future vision of incorporating X-ray imaging control into the system to improve accuracy and safety.

[0026] Reduction of a fractured femur requires significant traction to align the proximal and distal bone fragments. The robotic system developed here autonomously applies the required traction to achieve precise alignment of the bone fragments, ensuring correct anatomical positioning. The system sequentially performs traction and rotation. First, the robot applies the required traction to align the distal (closer to the knee) and proximal (closer to the hip) femur fragments. Then, holding the proximal fragment stationary, the system rotates the distal fragment to perfectly align the transverse irregularities of both fragments, ensuring reliable and anatomically precise reduction.

[0027] The Stewart platform is mounted on ground plate 5 via vertical column 4. Six linear actuators 33 are located between base plate 3 and the C-shaped ring of end effector 10. Universal joints 2 connect both ends of the actuators to the base plate and end effector. The actuators operate simultaneously to apply the required traction and torque.

[0028] The working element unit of the robotic system based on the Stewart platform includes two C-shaped rings 10, 14, connected by steel screws 11 and medium-strength flange locknuts 8. These rings interact with a sealing ring 12, which is connected by a steel link 13. Shantz pins 19 are mounted on Shantz pin mounting blocks 18, secured with round-head screws made of stainless steel 20 and plastic wing nuts 15, which ensures precise fixation of the distal fragment.

[0029] The perineal post serves to immobilize the proximal femur fragment, facilitating manipulation of the distal fragment using the Stewart platform. Mounted on the base plate 24 via the vertical column 21, the post is connected to two additional links (the shaped bracket 22 and the shaped bracket 23) connected via pivot joints to position the distal femur fragment in the "O" ring 27. The "O" ring 27 of the perineal post is connected to the C-ring 25 via a trapezoidal steel link 26. The Schanz pin 29 is mounted on the steel Schanz pin mounting block 28 to securely hold the proximal fragment in place during the reduction process.

[0030] The system works as follows.

[0031] After a femur fracture, the fragments are typically displaced and disoriented. To reduce the fracture and realign the fragments, surgeons apply traction to realign the fragments and then rotate the distal fragment to conform to the fragments' cross-sectional irregularities. Our R. ALFRED robotic system consists of two units: one unit, called the perineal post (Fig. 4), firmly holds the proximal fragment in place during the reduction process, and the other unit, called the Stewart-based robot (Fig. 3), applies the necessary traction and orientation to the distal femoral fragment.

[0032] Initially, the subject's femur, containing the proximal femur fragment, is secured in an "O" ring 27, which is fixed to the end of a perineal pin. The femur fragment is held in the "O" ring using Schanz pins 29, which are drilled into the femur using a minimally invasive procedure.

[0033] The subject's femur, containing the distal femur fragment, is then secured in another "O" ring (12 mm) using a pair of 19 mm Schanz pins drilled into the femur using a minimally invasive process. This "O" ring is attached to the end of the robot on the Stewart platform. The required force is transmitted to the distal bone segment through these Schanz pins, which can be pulled and rotated by the robot's actuators, causing the same bone movement. The goal here is to immobilize the proximal segment and manipulate the distal fragment of the fractured femur.

[0034] The robot controller consists of three modules: a robot trajectory generation module, a coupled dynamic model of the robot and human leg, and an impedance-based control module.

[0035] The robot must be given a predetermined trajectory to precisely maneuver its end effectors 10 and 14 to apply the required traction force and position the distal fragment so that it aligns perfectly with the proximal femoral fragment. There are an infinite number of possible trajectories for realigning the fragments, and our goal is to find the shortest of these trajectories while avoiding any collision between the bone fragments. The robot's trajectory generation module uses a genetic algorithm to find the shortest repositioning trajectory that also avoids any collision between the bone fragments.

[0036] To understand the dynamics of the interaction between a human leg and a robot based on the Stewart mechanism for fracture reduction, it is necessary to combine the dynamic model of the human leg based on link segments with the dynamic model of the robot.

[0037] For a robotic system linked to a human leg for femur fracture reduction, an impedance-based controller must be developed. The controller must develop dynamic force-motion models to regulate the interaction between the robot and the human leg. This approach enables adaptive responses based on forces measured at the points of interaction (i.e., between the robot and the fractured bone).

[0038] The main objectives of the system are traction control, in which the robot must apply the appropriate force to pull the distal part of the femur flush with the proximal part, alignment control - the controller must direct the rotation of the distal fragment, aligning it with the proximal fragment and minimizing the external forces acting on the muscles, and interaction force minimization, in which the controller must ensure minimal impact of external forces on the surrounding soft tissues (muscles, tendons) during the repositioning process.

[0039] The objective is also to create a robot path that minimizes the distance between corresponding points on the cross-sections of the proximal and distal fragments (these points are determined by analyzing 3D reconstructions of X-ray images and are marked using the surgeon's expert knowledge) and avoids any collisions between bone fragments. The goal is to find the shortest path that connects these points while adhering to the constraints of the robotic system (e.g., response limits and the requirement to avoid collisions). The following steps are performed to create the required optimal robot trajectory: a) The objective function is determined using the formula:

[0040] Minimize where Pi are the coordinates of the points on the proximal fragment, P are the coordinates of the points on the distal fragment. b) The constraints are determined

[0041] Geometrical constraints: Robot movements must be within the allowable actuation range of the linear motors.

[0042] • Orientation constraints: ensure that the distal fragment does not rotate beyond a specified limit to maintain bone alignment.

[0043] • Physical Limitations: The robot must not apply excessive force that could damage bones or surrounding tissue.

[0044] • Collision avoidance: ensuring that bone fragments do not collide during the repositioning process. c) Robot motion parameterization:

[0045] Representation of the position and orientation of the distal fragment using variable translations and rotations (roll, pitch and yaw). d) Optimization algorithm:

[0046] A genetic algorithm (GA) is implemented to find the shortest path for a robot, taking into account the given constraints.

[0047] B. Module of coupled dynamics of a robot and a human leg:

[0048] To simulate the dynamic interaction between a human leg and a Stewart platform used for fracture reduction, a dynamic model of the human leg was developed based on link segments and then coupled to a dynamic model of the robot. Here's a step-by-step breakdown of the process:

[0049] The human leg is modeled as a series of connected rigid segments, typically representing:

[0050] • Hip

[0051] • Shin (tibia + fibula)

[0052] • Foot Each segment is treated as a rigid body with a mass, center of mass, and moment of inertia. For simplicity, we used two main segments (the femur and the lower leg) connected by a rotational joint (the knee), with the hip and ankle providing additional degrees of freedom.

[0053] For each segment {the dynamic equation is expressed using Lagrangian dynamics: Where,

[0054] - mass matrix of leg segment i, these are Coriolis and centrifugal forces,

[0055] Gi(0[) represents the gravitational forces acting on segment i,

[0056] Tj is the applied torque at the joint on segment i,

[0057] 6i is the articulation angle for segment I.

[0058] This equation is derived from Lagrange's formula, which takes into account the potential energy due to gravity and the kinetic energy due to motion.

[0059] The Stewart platform can be modeled as a parallel manipulator with six degrees of freedom (DOF). The platform generates the necessary forces and moments to control the motion of the distal segment of the fractured femur.

[0060] Using the Newton-Euler approach, the platform dynamics can be described as follows: Where,

[0061] M R -3TO Stewart platform mass matrix,

[0062] WITH Д (X) - Coriolis force and centrifugal force of the robot,

[0063] G R - gravitational force acting on the platform,

[0064] F R - the force / torque vector applied by the robot drives,

[0065] X is the position vector of the robot's end effector (the distal femur). To achieve a fully coupled dynamic model, we couple the distal end of the human femur (tibia) to the end effector of the Stewart platform. Coupling is achieved through interaction forces and moments between the leg and the robot.

[0066] The forces and moments exerted by the Stewart platform on the femur must satisfy both the dynamics of the leg and the dynamics of the robot: Where:

[0067] • т interaction 11 ^interaction— moments and forces of interaction between the robot and the leg,

[0068] • The interaction forces are determined by the boundary condition where the distal femur (leg) is attached to the end effector of the Stewart platform.

[0069] By solving these coupled dynamic equations, a desired trajectory of the robot's end effector is generated that ensures alignment of the femur fragments while minimizing stress on the surrounding muscles.

[0070] The joint dynamics of the robot and the human limb can be written as: where,

[0071] M(Q) is the mass-inertia matrix of the combined system,

[0072] C(q, q) ~ Coriolis force and centrifugal force,

[0073] C(d) for gravity s

[0074] T robot~ the torque applied by the robot's drives,

[0075] T Human torque generated by muscle forces or passive leg dynamics. Impedance control creates the desired relationship between position and force, where the system's stiffness, damping, and inertia can be adjusted. The general form of an impedance controller is: Where

[0076] ( / -actual position of the leg (joint angles),

[0077] Qdesired — desired position (aligned position of femur fragments).

[0078] / ^-coefficient for the stiffness matrix

[0079] D is the coefficient for the attenuation matrix x,

[0080] Fd eS ired~ desired force to apply

[0081] In this case, the robot must balance applying sufficient force to reposition the bone while minimizing unnecessary forces that could strain muscles or tissues. The force applied by the robot will be dynamically adjusted based on real-time measurements of forces and moments at the point of interaction (the Schanz pins connecting the robot to the bone).

[0082] The system should include force sensors on the Shantz pins that measure the force applied by the robot and the force applied by the muscles. The measured force F measured can be compared with the desired force F deSired , and the controller adjusts the robot's actions accordingly: where K p ...

[0083] The human leg, modeled as a system of links and segments, can be represented as follows: This is a dynamic model for passive leg movement where т muscle п R еD represents the torques generated by the muscles. These torques must be minimized during robot interaction.

[0084] The interaction forces between the robot and the human leg are governed by the following coupled dynamic model:

[0085] This formula takes into account the relationship between the dynamics of the robot and the human leg, allowing the controller to provide smooth interaction without applying excessive force to the human limb.

[0086] Using impedance control, the robotic system can dynamically adjust its behavior to ensure proper femur alignment while minimizing interaction forces. This control method is suitable for coupling the dynamics of the human leg and the robot, ensuring a natural interaction that supports bone reduction without placing undue strain on the surrounding muscles.

[0087] The robotic system was developed in a laboratory with a full set of hardware and software. The R. ALFRED system was tested for its intended purpose, closed reconstruction of a fractured femur, using a phantom study. The bones used in the study were printed on a 3D printer from a real model of a human femur, previously fractured and based on accurate anatomical models of human bones and phantom muscles.

[0088] Experimental tests were conducted to confirm that the robot's end-effector trajectories during fracture reduction represent the shortest path among many viable paths. This is also supported by relevant documentation that the robot's path avoids any potential bone collisions.

[0089] The reliability of the robotic machining process has been verified through numerous tests, and it has been demonstrated that the objectives are always achieved without any failures. The robotic system design and the software for controlling the robot and generating its optimal trajectory are well documented with sketches and process drawings. A single document containing the necessary instructions for using the robotic system has also been created.

[0090] As a result of careful research, a system comprising a robot, optimization software and a controller for advanced long bone fracture reduction (R. ALFRED) was developed.

[0091] Below are the important characteristics of R. ALFRED:

[0092] The robot's mechanism is based on a parallel configuration of its drives, which provides it with greater rigidity and precision of movement compared to a sequential configuration.

[0093] The fracture reduction process using this robotic system is completely autonomous, and surgeons or orthopedists can control the operation from outside the high-radiation operating room.

[0094] Fracture reduction can be achieved by applying high traction forces using robotic actuators, which would otherwise be quite labor-intensive for surgeons to apply manually.

[0095] Fracture reduction is achieved by creating optimal robotic trajectories to minimize the forces acting on the soft tissues near the bone fragments. This helps prevent soft tissue overstretching and promotes rapid patient recovery.

Claims

Invention formula 1. A robotic system for improved reduction of long bone fractures, comprising a Stewart platform-based actuator system, an end effector assembly, Schanz pins, a perineal post, optimization software, and a controller for improved reduction of long bone fractures, the Stewart platform being mounted on a ground plate using a vertical column, six linear actuators being located between the base plate and an end effector with a C-shaped ring, universal joints connecting both ends of the actuators to the base plate and the end effector, the end effector assembly of the robotic system based on the Stewart platform, two C-shaped rings connected by steel screws and medium-strength flange locknuts, with the ability to interact with a sealing ring that is connected by a steel link, Schanz pins being secured to mounting blocks,secured with stainless steel round head screws and plastic wing nuts to ensure precise fixation of the distal fragment, the perineal post is mounted on the base plate through the vertical column, the post is connected to two additional links connected through pivot joints to position the distal femoral fragment into the O-ring, the O-ring of the perineal post is connected to the C-ring through a trapezoid steel ring, the Schanz pin is mounted on a steel block to securely hold the proximal fragment in place during the reduction process.

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