Method and device for testing a joint prosthesis

Abstract

The disclosure relates to a method (100) and a device for testing a joint prosthesis (20) that is suitable for replacing a joint at least partially.

Description

[0001] The disclosure relates to a method and a device for testing a joint prosthesis that is suitable for replacing a joint at least partially.

[0002] A joint is, for example, a knee, hip, shoulder, or elbow joint, and a joint prosthesis is a corresponding joint exoprosthesis or joint endoprosthesis.

[0003] Standardized procedures using a joint simulator for testing implant wear are known from the prior art. Using the joint simulator, an implant is subjected to a load according to a defined load curve, and the wear, for example, abrasion, is then determined.

[0004] The known test methods only partially reflect a true physiological, realistic load on the implant. For example, the definition of the load for the joint simulator does not take into account the specific geometry of the implants. Particularly in the area of ​​knee endoprostheses, there are, for example, cruciate-retaining (CR) or posterior stabilizing (PS) prostheses, especially ultracongruent (UC) prostheses. For instance, a load defined for an ultracongruent implant cannot simply be transferred to a cruciate-retaining implant. With a cruciate-retaining implant, the load differs significantly from that of ultracongruent implants, especially with increasing flexion of the knee joint.Furthermore, the known test methods take physiological properties, such as a complex capsule-ligament apparatus, into account, if at all, only in a very rudimentary way in the form of a one-dimensional displacement and a one-dimensional rotation, for example via mechanical springs.

[0005] Furthermore, the inherent compliance of the joint simulators used in the known methods poses a problem, as this leads to a distortion of the kinematics of the joint partners of the joint simulator.

[0006] Based on the already known test methods, a method according to claim 1 is proposed.

[0007] The procedure for testing a joint prosthesis suitable for replacing at least part of a joint includes the following steps: - Providing a multibody simulation model of the joint, - Generating a prosthesis-specific simulation model by adapting the multibody simulation model to the joint prosthesis, - Performing a multibody simulation for at least one load case based on the prosthesis-specific simulation model to determine joint reaction forces acting on the joint prosthesis in the load case based on an input of motion data associated with the load case, wherein joint reaction forces include both contact forces acting between joint partners and ligament-induced forces, - Generating load case-related load data for loading the joint prosthesis using a test device based on the joint reaction forces, subtracting the ligament-induced forces, - Performing a load-related test of the joint prosthesis using the test device comprising the joint prosthesis and a joint simulator by controlling the joint simulator based on the load data, wherein the test device includes a virtual model of a capsuloligamentous apparatus of the joint, and the ligament-induced forces based on the virtual model of the capsuloligamentous apparatus are applied to the joint simulator.

[0008] The multibody simulation model (MBS) describes the kinematics and dynamics of the joint in question and, if applicable, the corresponding extremities. Bones, for example, can be described as rigid bodies connected by the joint in question, acting as a coupling element, and subject to discrete forces or moments. During model creation, bones are segmented and reconstructed, for example, from CT data. Muscles with their corresponding muscle geometry, ligament structures, and tendons can be implemented based on CT and MRI datasets as well as anatomical specimens. The MBS includes, for example, elements that describe native bone geometries, muscle geometries, ligament structures, and tendons, as well as force elements to represent forces such as muscle and ligament forces and contact forces. Force elements include and / or describe, for example, corresponding points of application, stiffness parameters, etc.

[0009] According to the procedure, the MKS is adapted to the joint prosthesis being tested, so that a prosthesis-specific simulation model is created.

[0010] Adapting the MKS (Multi-Kinetic System) includes, for example, virtual implantation of the joint prosthesis. This can be done automatically, particularly through a predefined or predefinable positioning of the joint prosthesis, especially based on predefined or predefinable saw marks on the joint, and / or according to the "best-fit" principle. Virtual implantation can also be performed manually by manually defining the position of the joint prosthesis in relation to the joint. Another possibility would be virtual implantation through force balancing of the ligamentous structures.

[0011] Based on the prosthesis-specific simulation model, a multibody simulation is performed for at least one load case to determine the joint reaction forces acting on the joint prosthesis under that load case. Each load case defines the associated movement sequences. For example, with regard to a knee joint, load cases such as "climbing stairs," "sitting down and / or standing up," and "squatting" are defined.

[0012] Multibody simulation is performed based on input motion data associated with the load case. The resulting joint reaction forces that induce the movement are then calculated. Load case-associated motion data includes, for example, data on joint loading, data from motion analyses, and data on the morphology of the extremity or joint. Optionally, the input can also include further data such as patient-related data, for example, height, weight, age, etc. The input data may already be available and then provided for the multibody simulation; alternatively, the input data can be collected in vivo for the respective load case.

[0013] The joint reaction forces determined by the multibody simulation include both contact forces acting between joint partners and ligament-induced forces.

[0014] Based on the joint reaction forces, load case-related load data are generated, which specify a load on the joint prosthesis using the test device.

[0015] The load data includes the forces and moments acting on a respective joint partner during a load case over the duration of the load case, for example in the form of load curves or discrete values.

[0016] The ligament-induced forces are subtracted from the joint reaction forces, so that the load data only include the contact forces adjusted for the ligament-induced forces.

[0017] The joint prosthesis is now tested using the test device. The test device comprises a joint simulator, including the articulating surfaces of the joint, which can be moved by one or more suitable actuators. The joint prosthesis to be tested is positioned on the joint simulator according to its intended purpose, for example, by embedding it using templates or by measuring it.

[0018] The joint simulator is controlled by a suitable control unit that activates the actuator(s) for each load case according to the load data. This causes the joint components of the joint simulator to move according to the load case, thus simulating a real load.

[0019] Furthermore, the test device is designed to include a virtual model of the joint's capsuloligamentous apparatus. This virtual model describes the ligament-induced forces.

[0020] According to the invention, the ligament-induced forces are taken into account via the virtual model of the capsular-ligamentous apparatus. This also leads to an increase in the contact forces acting between the joint partners. For this reason, when generating the load case-specific load data, the ligament-induced forces are subtracted from the joint reaction forces.

[0021] The present invention allows load cases to be defined in a design-specific manner, i.e., adapted to the joint prosthesis, and the joint prosthesis to be loaded during testing depending on its geometry. This enables a realistic investigation of wear behavior. This is particularly advantageous with the ongoing development of implants, for example, posteriorly or medially stabilized designs, since the joint dynamics and wear behavior can be analyzed in accordance with the respective geometry of the implant.

[0022] According to one embodiment, the joint simulator is controlled in six degrees of freedom based on the load data and / or the virtual model of the capsuloligamentous apparatus. The control can also be achieved by superimposing the load data and the virtual model of the capsuloligamentous apparatus. The corresponding load data comprises six parameters that describe the six degrees of freedom, namely three forces along three linearly independent, in particular orthogonal, axes and the respective moments about the axes. Control in six degrees of freedom enables the following movements of the respective joint partner: translational movements along the three axes and rotational movements about the three axes. In a knee joint, for example, the axes are defined as the mediolateral axis, the anteroposterior axis, and the superoinferior axis. The rotational movements are accordingly defined as flexion, abduction, and internal rotation with the associated angles.Defined in moments.

[0023] According to one embodiment, each degree of freedom of the joint simulator can be controlled either based on displacement and / or angle, or based on force and / or moment. This means that each degree of freedom can be controlled by both force and position. Force control can be advantageous, for example, when contact is expected, and position control can be advantageous during unrestricted movement.

[0024] According to one embodiment, the joint partners of the joint simulator can be kinematically and / or dynamically recorded, particularly in real time. Real-time recording of the kinematics of all joint partners enables the accurate acquisition of the relative kinematics, i.e., precise sensory acquisition of the position and orientation of all articulating joint partners, without external influences. Particularly in conjunction with ensuring sufficient system stiffness of the joint simulator, this prevents the virtually considered forces of the capsuloligamentous apparatus from being distorted during the test. The recording is carried out, for example, via an optical, particularly 3D, measuring system. For dynamic recording, the test device includes, for example, a measuring device for recording the forces acting in the six degrees of freedom, such as a load cell.

[0025] Generating the prosthesis-specific simulation model involves, for example, adjusting the simulation model parameters based on one or more of the following: a) the geometry of the joint prosthesis, b) the material of the joint prosthesis, c) the intended position and / or orientation of the joint prosthesis, particularly in relation to the joint or extremities, d) soft tissue parameters, especially parameters of the capsuloligamentous apparatus, e) patient data. The geometry of the joint prosthesis can, for example, be discretely described using a surface mesh and thus imported into the multibody simulation system (MBS). The material and material properties of the joint prosthesis can also be considered in the model.By adjusting the parameters to one or more of the aforementioned sizes, the influence of one or more of the following factors on joint dynamics and wear behavior of the joint prosthesis can be investigated: intraoperative influencing factors, such as positioning of the joint prosthesis, soft tissue situation, malpositions, especially of extremities, design parameters, such as geometry and material.

[0026] According to one embodiment, the virtual model of the joint's capsuloligamentous apparatus can be individually adapted. This individual adaptation allows, for example, the virtual capsuloligamentous apparatus, and thus the testing of the joint prosthesis, to be tailored to the capsuloligamentous apparatus of an individual patient. For instance, patient-specific ligamentous conditions such as instabilities, total loss, limitations, etc., can be modeled and taken into account.

[0027] According to one embodiment, the multibody simulation may include an inverse kinematic analysis and / or an inverse dynamic analysis and / or a forward dynamic analysis, in particular a coupled inverse and forward dynamic analysis. The inverse kinematic analysis is performed once for each load case, for example, with the position of the joint partners being specified. In the coupled inverse and forward dynamic analysis, the motion data is used as input data for calculating muscle forces in the inverse dynamic analysis. In the forward dynamic analysis, the calculated muscle forces are used as input data, and the resulting motion, i.e., joint kinematics and contact kinetics, is determined accordingly.

[0028] Further embodiments relate to a test device for testing a joint prosthesis comprising a joint simulator with two joint partners, at least one actuator for moving the joint simulator or the joint partners, a control device for controlling the actuator according to predefinable load data, and a computing unit, in particular comprising a virtual model of a capsuloligamentous apparatus, wherein the computing unit of the test device is programmed or programmable such that, when the program is executed, a load-case-related test of the joint prosthesis is performed, wherein the control of the joint simulator or the actuator is based on load-case-related load data generated according to a method according to claim 1, and wherein, based on the virtual model of the capsuloligamentous apparatus, ligament-induced forces can be applied to the joint simulator.

[0029] According to one embodiment, the joint simulator can be controlled in six degrees of freedom based on the load data and / or the virtual model of the capsule-ligament apparatus, and each degree of freedom of the joint simulator can be controlled in a displacement- and / or angle-based or force- and / or moment-based manner.

[0030] According to one embodiment, the test device may include sensors for kinematic and / or dynamic detection of the joint partners.

[0031] Further advantageous embodiments will become apparent from the following description of exemplary embodiments of the invention, using the example of a knee joint and the example of a knee joint endoprosthesis, and from the drawing. The drawing shows Fig. 1 a schematic representation of a joint simulator; Fig. 2 another schematic representation of the joint simulator Fig. 1; Fig. 3 another schematic representation of the joint simulator Fig. 1; Fig. 4 steps of a procedure for testing a joint prosthesis, Fig. 5 a diagram showing the forces acting on different joint prostheses during a movement cycle.

[0032] The following describes a test device and test procedure for testing a joint prosthesis using a knee joint endoprosthesis as an example, based on the figures.

[0033] The test device includes a joint simulator 10, which in this example represents a knee joint. The joint simulator 10 is shown in the following example. Fig. 1, Fig. 2 to Fig. Figure 3 shows the joint simulator 10, which comprises two joint partners 12 and 14, in this example a femoral joint partner 12 and a tibial joint partner 14. In this example, the two joint partners 12 and 14 are equipped with a femoral prosthesis component 16 and a tibial prosthesis component 18. The femoral prosthesis component 16 and the tibial prosthesis component 18 form the joint prosthesis 20 to be tested.

[0034] The two joint partners 12, 14 are movable by a respective actuator 22, 24, in the example a femoral actuator 22 and a tibial actuator 24, in order to simulate a movement of a knee joint.

[0035] The joint simulator is controlled via a suitable control unit (not shown) which controls the actuators 22, 24. This causes the joint partners 12, 14 of the joint simulator 10 to move, thus simulating a real load on the joint prosthesis 20.

[0036] According to the illustrated embodiment, the joint simulator 10 is controlled in six degrees of freedom, or, when testing the joint prosthesis 20, is controlled in six degrees of freedom. The six degrees of freedom are exemplified by the following: Fig. Figure 2 illustrates this. Accordingly, the six degrees of freedom encompass the following movements of each joint partner: translational movements along three axes and rotational movements about these three axes. In this example, the three axes are defined as the mediolateral axis A_ml, the anteroposterior axis A_ap, and the superoinferior axis A_si. The rotational movements are defined accordingly as flexion R_ml, abduction R_ap, and internal rotation R_si with their associated angles and moments. Each degree of freedom of the joint simulator can be controlled based on displacement and / or angle, or force and / or moment. The joint partners 12 and 14 of the joint simulator 10 are kinematically and dynamically recorded during testing of the joint prosthesis 20, particularly in real time. For this purpose, the test device includes suitable sensors (not shown).For example, the test device includes a measuring device for detecting the forces acting in the six degrees of freedom, such as a load cell, as well as an optical, three-dimensional measuring device.

[0037] The joint simulator 10 is controlled based on load data according to a prosthesis-specific simulation model. This will be further explained with reference to Fig. 4 explained. Additionally, the test device is designed to include a virtual model of a capsuloligamentous apparatus 26 of the joint. The virtual model of the capsuloligamentous apparatus of the joint describes the ligament-induced forces K_L_virt. An illustration of the virtual model of the capsuloligamentous apparatus 26 is shown in Fig. 3 shown.

[0038] Finally, with reference to Fig. 4 a procedure for testing the joint prosthesis 20 on the joint simulator 10 is described.

[0039] Procedure 100 includes step 110 for providing a multibody simulation model (MBS) of the knee joint. The multibody simulation model (MBS) describes the morphology and biomechanics of the knee joint and, if applicable, the lower extremity.

[0040] According to the procedure, the MKS is adapted to the joint prosthesis 20, so that a prosthesis-specific simulation model MKS_PI is generated, see step 120.

[0041] Adapting the multibody simulation model (MBS) includes, for example, a virtual implantation of the joint prosthesis 20, so that the joint prosthesis is imported into the MBS.

[0042] The generation of the prosthesis-specific simulation model MKS_PI includes, for example, adjusting parameters of the multibody simulation model MKS or the prosthesis-specific simulation model MKS_PI depending on one or more of the following parameters: a) a geometry of the joint prosthesis, b) material of the joint prosthesis, c) intended position and / or orientation of the joint prosthesis, in particular in relation to the joint or extremities, d) soft tissue parameters, in particular parameters of the capsuloligamentous apparatus, e) patient data, cf. input E_1, E_2.

[0043] Based on the prosthesis-specific simulation model MKS_PI, a multibody simulation is performed for at least one load case (see step 130) to determine the joint reaction forces GRK acting on joint prosthesis 20 in load case 20. Each load case defines the associated movement sequences. For example, with regard to the knee joint, load cases such as "climbing stairs," "sitting down and / or standing up," and "squatting" are defined.

[0044] The multibody simulation is performed based on an input E_3 of motion data associated with the load case. The resulting joint reaction forces GRK, which induce the movement, are then calculated.

[0045] The joint reaction forces GRK determined by the multibody simulation include both contact forces K_K acting between joint partners and ligament-induced forces K_L.

[0046] Based on the joint reaction forces GRK, load case-related load data D_L are generated, which specify a load on the joint prosthesis 20 using the test device, see step 140.

[0047] The load data D_L include the forces and moments acting on a respective joint partner 12, 14 during a load case over the duration of the load case, for example in the form of load curves or a multitude of discrete values.

[0048] The ligament-induced forces K_L are subtracted from the joint reaction forces GRK, so that the load data D_L only include the contact forces K_K adjusted for the ligament-induced forces K_L.

[0049] The joint prosthesis is now tested using the test device, see step 150.

[0050] The joint simulator 10 is controlled via the control unit, which activates the actuators 22 and 24 for each load case according to the load data D_L. This causes the joint partners 12 and 14 of the joint simulator 10 to move according to the load case, thus simulating a real load.

[0051] The ligament-induced forces K_L_virt are taken into account in the joint simulator 10 via the virtual model of the capsuloligamentous apparatus 26.

[0052] Finally, it shows Fig. 5 a diagram showing for three different exemplary designs of joint prostheses 20, for a movement cycle which is assigned, for example, to a load case, the joint reaction force acting in the anteroposterior direction, i.e., along the axis A_ap.

Claims

[1] Method (100) for testing a joint prosthesis (20) suitable for replacing a joint at least partially, the method comprising (100) the following steps: - Providing (110) a multibody simulation (MBS) model of the joint, - Generating (120) a prosthesis-specific simulation model (MKS_PI) by adapting the multibody simulation model (MKS) to the joint prosthesis (20), - Performing (130) a multibody simulation for at least one load case based on the prosthesis-specific simulation model (MKS_PI) to determine joint reaction forces (JRC) acting on the joint prosthesis (20) in the load case based on an input (E_1) of motion data associated with the load case, wherein joint reaction forces (JRC) include both contact forces (K_K) acting between joint partners (12, 14) and ligament-induced forces (K_L), - Generating (140) load case-related load data (D_L) for loading the joint prosthesis (20) using a test device based on the joint reaction forces (GRK), subtracting the ligament-induced forces (K_L), - Performing (150) a load case related test of the joint prosthesis (20) using the test device comprising the joint prosthesis (20) and a joint simulator (10) by controlling the joint simulator (20) based on the load data (D_L), wherein the test device comprises a virtual model of a capsuloligamentous apparatus (26) of the joint, and the ligament-induced forces (K_L_virt) based on the virtual model of the capsuloligamentous apparatus (26) are applied to the joint simulator (10). [2] Method (100) according to claim 1, wherein the joint simulator (10) is controlled based on the load data (D_L) and / or the virtual model of the capsuloligamentous apparatus (26) in up to six, in particular six, degrees of freedom. [3] Method (100) according to claim 2, wherein a respective degree of freedom of the joint simulator (10) is controlled in a displacement- and / or angle-based or force- and / or moment-based manner. [4] Method (100) according to one of the preceding claims, wherein the joint partners (12, 14) of the joint simulator (10) are kinematically and / or dynamically detected, in particular in real time. [5] Method (100) according to one of the preceding claims, wherein the generation (120) of the prosthesis-specific simulation model (MKS_PI) comprises adjusting parameters of the simulation model depending on one or more of the following: a) a geometry of the joint prosthesis (20), b) material of the joint prosthesis (20), c) an intended position and / or orientation of the joint prosthesis (20), in particular with respect to the joint or extremities, d) soft tissue parameters, in particular parameters of a capsuloligamentous apparatus, e) patient data. [6] Method (100) according to one of the preceding claims, wherein the virtual model of the capsuloligamentous apparatus (26) of the joint is individually adaptable. [7] Test device for testing a joint prosthesis (20) comprising a joint simulator (10) with two joint partners (12, 14), at least one actuator (22, 24) for moving the joint simulator (10) or the joint partners (12, 14), a control unit for controlling the actuator (22, 24) according to predefinable load data (D_L) and a computing unit, in particular comprising a virtual model of a capsuloligamentous apparatus (26), wherein the computing unit of the test device is programmed or programmable such that, when the program is executed, a load-case-related test of the joint prosthesis (20) is performed, wherein the control of the joint simulator (10) or the actuator (22, 24) is based on load-case-related load data generated according to a method (100) according to one of claims 1 to 6, and wherein, based on the virtual model of the capsuloligamentous apparatus (26) Ligament-induced forces (K_L_virt) can be applied to the joint simulator (10). [8] Test device according to claim 7, wherein the joint simulator (10) can be controlled in up to six, in particular six, degrees of freedom based on the load data (D_L) and / or the virtual model of the capsuloligamentous apparatus (26), and wherein each degree of freedom of the joint simulator (10) can be controlled in a displacement- and / or angle-based or force- and / or moment-based manner. [9] Test device according to one of claims 7 or 8, wherein the test device comprises sensors for kinematic and / or dynamic detection of the joint partners (12, 14).

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