Apparatus and method for standardizing axial alignment and position of kinematic data for a patient's body joints - Patents.com
The standardization system optimizes coordinate system alignment using mathematical optimization to correct for axial misalignment, ensuring consistent and reliable comparison of kinematic data, enhancing the evaluation of joint characteristics and facilitating personalized medical interventions.
Patent Information
- Application Number
- JP2024566886
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-10-05
- Filing Date
- 2023-05-12
- Publication Date
- 2025-05-20
Smart Images
Figure 2025515863000001_ABST
Abstract
Description
[Technical field]
[0001] The present disclosure relates to a standardized kinematic evaluation system for acquiring, standardizing and evaluating biomechanical kinematic data of a (selected) joint of a patient. The system comprises at least one acquisition device adapted to detect (record) the biomechanical kinematic characteristics of the joint of the patient by means of a sensor and provide it in a computer readable form, and a visual display device, in particular an operating room monitor, for visually outputting it to a user. Furthermore, the present disclosure relates to a standardization method and a computer readable storage medium according to the preamble of the independent claim. [Background technology]
[0002] In the kinematic analysis of moving bodies or segments, the position / attitude, i.e. alignment and location, of the underlying reference frame of each segment involved, and especially the alignment itself, have a significant influence on the resulting (kinematic) curves, especially the magnitude and characteristics / nature of the waveforms, of the three measured rotations and translations measured in any three spatial directions corresponding to the specific joints connecting those segments. In the past, this was attributed to crosstalk effects.
[0003] Crosstalk results from incorrect alignment, or more preferably, incorrect positioning, of the axes of a coordinate system, so that a rotation in one plane is partially perceived as a rotation in another plane.
[0004] Methods for minimizing the effects of crosstalk generally seek to minimize the effects of crosstalk by minimizing one or more selected objective functions for a particular activity, measurement system, or biomechanical model. Such minimizations are described, for example, in Baker et al., "A new approach to determine the hip rotation profile from clinical gait analysis data" (1999), Rivest, "A correction for axis misalignment in the joint angle curves representing knee movement in gait analysis" (2005), and Baudet et al., "Cross-Talk Correction Method for Knee Kinematics in Gait Analysis Using Principal Component Analysis (PCA): A New Proposal" (2014).
[0005] These methods suffer from the significant drawback that for at least one of the data sources being compared, the alignment, and preferably the position, of the underlying reference frame relative to the segments they represent is unknown.
[0006] The same can be said for methods that attempt to compare the extent to which data from different sources (e.g., different biomechanical models, different laboratories, different marker sets, etc.) are affected by crosstalk. These approaches quantify crosstalk using at least one representative parameter (e.g., flexion / extension and abduction / adduction indices), and it has been reasoned that lower values of such parameters can be interpreted as less crosstalk-related (Kainz et al., "Joint kinematic calculation based on clinical direct kinematic versus inverse kinematic gait models" (2016)).
[0007] However, before such comparisons can be made, all data sets need to be made comparable and standardized to some degree, as comparisons of non-standardized data may not be valid as it is not clear whether the kinematic differences displayed truly reflect different movement patterns or are simply the result of different axis positions, especially alignment.
[0008] Much of the existing literature dealing with the use of crosstalk minimization methods in rotational kinematic analysis attempts to justify the appropriate choice of the parameters to be optimized (or minimized) by reference to previous studies on the so-called “physiological” properties of the movement.
[0009] Such reasoning and logic may be incorrect, since an experiment attempting to measure, for example, the "physiological" range of rotations in the transverse and anterior planes of the knee joint in flexion (to know to what values these rotations should be optimized in a crosstalk minimization algorithm) would require the definition of a specific reference frame for a particular alignment. The precise definition of such a frame (and in particular its orientation) will necessarily affect the magnitude of the rotations measured. Thus, the obtained "physiological" profile, which is often cited as evidence that the selected objective function or functions are valid, cannot reasonably be used as a valid confirmation in practice, since it is itself highly dependent on the definition of the frame.
[0010] When considering two or more data sets, differences in the orientation of joint axes may occur, especially due to different kinematic constraints, different underlying assumptions considered, and different modality algorithms for axis definition (e.g., landmark-based vs. feature-based). As a result, the exact alignment of the joint reference frame with respect to the connected rigid body segments may differ from test to test. For example, if we consider two different tests where the same subjects perform the same movements using the same optical motion detection system to collect data, and the axes are defined by manually locating bone reference points using a special pointer, it is quite possible that the sets of axes defined in each test are not perfectly consistent, considering that the positions of one of the required reference points may be located slightly differently (even by a few millimeters). Extending this scenario to comparing data from different studies, alignment differences may be due to a variety of these numerous factors. Without implementing a protocol to reconcile these alignment differences, conclusions regarding the presence or absence of significant differences between groups are highly questionable.
[0011] Methods exist for minimizing the effects of crosstalk, but these methods attempt to achieve that objective by minimizing one or more selected objective functions. As mentioned above, these methods have significant drawbacks if the researcher wants to compare the quality of the values obtained with a data set in which crosstalk has not been minimized or where crosstalk has been minimized in another way.
[0012] To analyze kinematic data of a patient's joints, especially the knee joint, obtained from various sources, standardized definitions and computational conventions must be used. Although accurate transformations of various mathematical definitions exist, normalization or standardization of coordinate systems and accurate alignment of coordinates remain difficult.
[0013] For example, when manual assessments such as the so-called anterior drawer test are used for analysis, these assessments are highly subjective. Alternatively, a joint laxity measuring device can be used to immobilize a reference joint segment and apply a force to another joint segment, inducing and measuring the resulting relative joint motion. However, both of these approaches have the disadvantage that they do not take into account the effects of differences in the local position and orientation of the segments, leading to inconsistent results and misinterpretation of the underlying joint motion and stability.
[0014] Furthermore, studies have already been conducted to identify patient phenotypes based on kinematic joint signals during movements in daily life (e.g., Zgolli et al., "Kinematic-data clustering for healthy knee gait characterization" (2018); Mezghani et al., "Healthy Knee Kinematic Phenotypes Identification Based on a Clustering Data Analysis" (2021); Petersen et al., "Petersen et al. 2021, Patients with osteoarthritis can be divided into subgroups based on tibiofemoral joint kinematics of gait: an exploratory and dynamic radiostereometric study" (2021)).
[0015] Each of these uses complex methods to detect statistically significant differences between patient populations / groups. Unfortunately, further analysis shows that these patient populations are also inconsistent, for example when considering that the alignment of the local frames of the segments may differ. Another drawback of these methods is that complex statistical analyses must be performed on three or six time series (three translations, or three rotations, or both (i.e. both three translations and three rotations)) to identify statistically significant differences (e.g. by statistical parameter mapping). Thus, currently, there is no reliable and consistent assessment. Summary of the Invention
[0016] The problem and object of the present disclosure is therefore to avoid the drawbacks of the prior art, in particular to provide a standardization system or normalization system and method for standardization or normalization of biomechanical motion data. A sub-objective is to derive a result regarding the outcome of a medical intervention, in particular a result regarding the relationship between the parameters of a medical implant and a patient, based on the standardized biomechanical motion data. In particular, one object of the present invention is to provide an apparatus and method for standardizing or normalizing the axial alignment of biomechanical kinematic data, in particular rotational kinematic data and / or translational kinematic data, with respect to a patient's body joints. Thus, the kinematic data includes translational kinematic data and / or rotational kinematic data between two moving bodies or segments.
[0017] The problem is solved for the universal standardization system according to the invention by the features of claim 1, for the universal standardization method according to the invention by the features of claim 11 and for the computer-readable storage medium according to the invention by the features of claim 14.
[0018] One basic idea is to provide a normalization system and method for comparing kinematic patterns, which allows to align and / or position two frames for comparison by optimizing the values of selected criteria, without requiring prior knowledge of the position / pose, i.e. orientation and position, especially the orientation / alignment, of the original underlying reference frames. In other words, the present disclosure includes a normalization or normalization method or specially adapted control unit (similar to an algorithm) that allows to compare kinematic data from two or more sources (different tests, different subjects, different motion capture techniques, different laboratories, etc.) by processing the underlying kinematic data such that at least one selected parameter is optimized. By processing at least two data sets (by performing certain optimizations), differences due to axial misalignment or axial misalignment in the at least two data sets are or can be equally corrected, so that the resulting rotational and translational data can be properly compared.
[0019] In other words, the present disclosure proposes optimizing the alignment and / or positioning, i.e., in particular the position, of the coordinate systems in order to standardize the kinematic data. The proposed standardization system and method is based on the fundamental understanding that a method for minimizing crosstalk requires decisions on how to define the "correct" orientation and / or the "correct" position of the reference frames. These decisions are also considered as underlying assumptions and are reflected in the selection of the objective function to be optimized (or minimized).
[0020] In this example, an approach is proposed to solve this problem by providing a method or adapted control unit in which one or more specific (optimization) parameters or objective functions are selected and each data set of (kinematic data) is processed accordingly to obtain the resulting rotation and / or translation of the optimization. In particular, this process uses a (mathematical) optimization algorithm to identify the orientation and / or position of the segment reference frame that optimizes a pre-specified objective function. The resulting angle curves (course of standardized kinematic angles) and / or translation curves (course of standardized kinematic translations) may be recorded to be used for the comparison thereafter. The validity of the resulting comparison does not depend on the choice of the parameters and objective functions to be optimized. For example, a set of parameters and objective functions that results in waveforms that are easier to interpret clinically may be preferred, but this does not prevent the validity of the comparison.
[0021] In particular, an apparatus is proposed as a standardization system for standardizing the axial alignment of rotational kinematic data and / or the axial position, in particular the axial position / posture, of translational kinematic data with respect to the patient's body joints, comprising a number of sensors for detecting and / or recording kinematic data sets and a computer to which the sensors are connected or connectable for data transmission, the computer being adapted and designed to standardize the orientation from the rotational data obtained from the recorded kinematic data sets and / or the position of the tibial and femoral coordinate systems from the translational data obtained using mathematical optimization methods.
[0022] In particular, a method is proposed for standardizing the axial alignment and / or axial position of kinematic data, in particular rotational and / or translational kinematic data, for a patient's body joint using a device, preferably a standardization system according to the present disclosure, which comprises obtaining a kinematic data set for the patient's body joint by means of multiple sensors, transmitting it to a computer, providing rotational and / or translational data derived from the kinematic data set, and standardizing the orientation and / or position of the tibial and femoral coordinate systems relative to the provided rotational data using a mathematical optimization method.
[0023] In other words, the present disclosure relates to an apparatus and method that can identify / reduce the influence and effect of axial alignment on kinematic data (of a patient's joints, particularly the knee joint), where a normalization or standardization approach is provided.
[0024] Stated in yet another quite different way, the present disclosure relates to a standard kinematic assessment system for recording, standardizing and evaluating biomechanical kinematic data of a (selected) joint of a patient, the system comprising at least one detection device adapted to detect by means of sensors the biomechanical kinematic characteristics (in particular kinematic rotation and kinematic translation) of the patient's joint, record them and provide them in a computer readable form, and a visual display device, in particular an operating room monitor, for visually outputting to a user. Furthermore, the standard kinematic evaluation system comprises a control unit which processes the recorded kinematic characteristics of the patient and determines therefrom a sequence of the (observed) joint, in particular three kinematic angles (as a rotation angle graph) and / or three translations for a first joint element with a first joint coordinate system and a second joint element with a second joint coordinate system, determines a rotation vector or a rotation matrix for adjusting the orientation of the first joint coordinate system by a predefined objective optimization and / or determines a translation vector for adjusting the position of the first joint coordinate system by a predefined objective optimization using a standardization unit adapted and designed for this purpose to perform a standardization, determines a rotation vector or a rotation matrix for adjusting the orientation of the second joint coordinate system and / or determines a translation vector for adjusting the position of the second joint coordinate system, outputs via an evaluation unit adapted to perform an evaluation of the joint with respect to at least one predefined evaluation parameter based on the standardized kinematic angles and / or the standardized kinematic translations as motion data and outputs the evaluation by a display device.
[0025] In particular, methods are provided for standardizing reference frame orientation and / or reference frame translation using specific mathematical criteria in biomechanical kinematic analysis.
[0026] Very small changes in the alignment or position of the underlying (reference) coordinate system can lead to large differences in the (characteristics of) the kinematic data, and according to the present disclosure, this effect can be taken into account when calculating the differences between gait patterns, thereby eliminating the possibility that the discovered differences are due to misalignment of such axes.
[0027] Examples of standardization scenarios include post-processing of gait experimental data (for standardization purposes) or pre-processing for comparison of known kinematic gait patterns (for harmonization purposes).
[0028] According to a further, second, independently claimable aspect of the present disclosure, a standard kinematic evaluation system for detecting, standardizing and evaluating biomechanical kinematic data of a patient's joints and an associated method for evaluating (determining) the laxity and / or stability and / or function of a human joint, in particular the knee, by normalizing (i.e. standardizing). The system or method is based on a predetermined mathematical objective optimization (reference frame alignment method) that optimizes, i.e. normalizes, a reference frame according to the present disclosure with respect to position and / or orientation. In this way, consistent and comparable measurements can be made. In particular, the independently claimable system and method obtain kinematic data over a period of time or at multiple time points and store them accordingly, and the comparison unit may be adapted to detect changes over time. Particular attention is therefore given to the detection of kinematic changes over time.
[0029] The standard kinematic evaluation system according to the second aspect may in particular comprise optical and / or inertial sensors, which are attached or attachable to the (relevant) joint segments (i.e. the joint segments adjacent to the joint under observation), in particular detachably fixed or fixable by hook-and-loop fasteners, adhesives or bands, etc., and adapted to acquire spatial or inertial data suitable for characterizing the movement of the joint segment during a series of activity cycles, whether passive, in which the joint is moved by a medical professional, or active, such as walking or running. The (raw) data acquired by the sensors are sent to a control unit, which processes these data based on a biomechanical model to calculate kinematic signals of the joint (in particular corresponding to the joint segments that are part of the joint). In particular, a reference frame alignment method according to the present disclosure, based on a mathematical optimization of predetermined statistical parameters, can be used to characterize these kinematic signals and to realign / reorient / or reposition the respective local joint segment coordinate frames to satisfy a predetermined underlying objective function.
[0030] This allows for a consistent and reliable standardization of kinematic measurements for accurate data comparison, in particular for analysis with respect to a time point of interest, whether current, past or future. Accurate quantification of joint laxity and / or joint stability and / or joint function in this way is particularly advantageous for detecting joint changes, in particular joint deterioration, i.e. for determining the optimal or best time for surgical intervention or for evaluating the course of treatment, in particular the course of post-operative physiotherapy and / or rehabilitation. Thus, in this example, a technical application for quantifying joint laxity of a human joint, an animal joint or a mechanical joint is provided, which is preferably adapted to detect and based on the detection evaluate changes over time, in particular deterioration and / or progression, of human and / or animal joints such as knee, hip, shoulder, head, neck, elbow, etc., and associated (tissue) soft parts such as ligaments, muscles, cartilage, etc. In particular, the control unit may be adapted to calculate a so-called optimization residual and output it to the medical personnel. Evaluating the optimization residual provides a direct objective measure of whether the joint / axis estimate corresponds to a perfect joint / hinge. Any non-zero value directly quantifies intra-articular laxity and is used in the clinical examination, assessment, and monitoring of joint laxity / instability.
[0031] According to a further, third, independently claimable aspect of the present disclosure, a phenotyping method is provided for identifying the kinematic phenotype of a human joint based on motion data to simplify treatment selection, such as implant type, implant location, and / or implant alignment relative to an affected joint segment, prior to surgery (e.g., in the case of an artificial knee joint).
[0032] According to this phenotyping method, in a first step, the center of rotation of a first joint segment, in particular the thigh, may be defined as the origin of a new frame (in particular after normalization according to the present disclosure in a second step) relative to the original (anatomical) first joint segment, in particular the thigh. This new position of the first joint segment (e.g. femur) allows to characterize the joint kinematics (in particular of the knee joint) and to recommend a treatment tailored to the patient, for example by determining the most suitable specific implant design and / or position and / or orientation for a specific phenotype / patient, thus optimizing patient satisfaction and implant life / durability.
[0033] This third aspect facilitates consistent identification of a subject's phenotype based on the kinematic signal, in particular by facilitating the analysis of three or six complete time series (three translations, or three rotations, or three translations and rotations) during one exercise load cycle, resulting in a simple evaluation of a 3×1 vector representing the frame center of the relative first joint segment (in particular the femur) after standardization of the kinematic data set with the so-called REFRAME. This phenotyping method allows for a virtual femoral center of rotation to be determined using an appropriate kinematic definition (femoral translation and any rotation definition represented in the tibial frame) and an appropriate optimization criterion, in particular the minimization of the root mean square (RMS) error of all three translational components. This virtual femoral center of rotation is directly related to the characteristic movements of common implants such as medially stabilized (MS) implants with a center of rotation located on the medial side, laterally stabilized (LS) implants with a center of rotation located on the lateral side, or posterior stabilized (PS) implants with a center of rotation located more distally. In particular, the phenotyping method may further include determining a virtual femoral center of rotation, and selecting an implant type based on the femoral center of rotation, in particular determining the implant type from LS implant, MS implant, and PS implant. In particular, in one step according to the present disclosure, a new joint coordinate system may be identified, and it may be determined which of the MS coordinate system, the LS coordinate system, and the PS coordinate system the new joint coordinate system is most similar to. The most similar COS indicates the type of implant. For example, if the joint coordinate system is most similar to the LS-COS, it may be determined that the LS implant is suitable.
[0034] Thus, according to the third aspect, a method and system are provided for evaluating knee kinematic characteristics before surgery to identify the type of implant that best fits the needs, gait pattern and kinematic profile of a particular patient, in order to improve the treatment outcome and the useful life of the medical device. In particular, the disclosure according to the third aspect may be part of a medical device for measuring joint characteristics in a clinical environment during preparation for a knee prosthesis surgery, and in particular may be part of a standard kinematic evaluation system according to the present disclosure. In particular, the (same) method may be used to identify the actual hip joint rotation axis from gait data including an anatomical reference in the pelvis. In particular, it is important that the orientation of the axis is also indicated so that a consistent interpretation of the joint kinematics without crosstalk between the axes is possible. This allows (correctly) comparing new kinematic data with previous kinematic data. In particular, in one step, the joint center may be identified in order to evaluate the knee adduction moment. Moreover, it should be noted that this approach does not only apply to joints and medical applications, but also to other fields of application in which kinematic patterns from different sources and moving bodies are (to be) collected. In particular, this method may also greatly simplify the comparison of kinematic patterns, since less effort is required to correctly position the coordinate frames. In particular, in one step, a (first) alignment is roughly performed, and in a subsequent step the results are calculated using REFRAME, in particular according to the standard kinematic evaluation method according to the present disclosure.
[0035] Advantageous embodiments are defined in the dependent claims and are specifically described below.
[0036] According to one embodiment, the at least one acquisition device may comprise as sensors at least one acceleration sensor and / or one gyro sensor, in particular an inertial measurement unit (IMU), and the acquisition device may be adapted to be attached to a joint area of the patient, such as one of the patient's limbs, in particular to the first joint element and / or the second joint element.
[0037] According to a further preferred embodiment, the at least one acquisition device may comprise as sensor system at least one optical acquisition unit, in particular a 3D acquisition unit, preferably a stereo camera, which acquires the biomechanical movement characteristics of the patient's joint preferably by means of optical markers, in particular passive infrared markers attached to the patient's joint area, preferably attached to at least the first joint element and / or the second joint element.
[0038] Preferably, the minimization of the variance, standard deviation, squared error and / or regression statistical error of one or more kinematic parameters, in particular one or more kinematic angles and / or one or more kinematic translations, may be specified as the predetermined objective optimization. Thus, of the three kinematic angles, particularly preferably two kinematic angles may be specified, in which the minimization of the variance or squared error is sought as the objective function, in particular in exactly one cycle of the joint movement, in particular in one step cycle, and the change in orientation of the first joint coordinate system and the change in orientation of the second joint coordinate system are defined as the object to be specified and the result, respectively. Thus, the control unit calculates the distortion / reorientation of the first local joint coordinate system around the origin and the distortion / reorientation of the second local joint coordinate system around the origin, in which one, two or three of the three kinematic angles are taken into account, for example the surface of the graph of the corresponding kinematic angles is approximately minimized around its zero line. In other words, the variance, standard deviation, squared error, or statistical error of regression of one or more kinematic angles may be the selected parameters. A model that uses the variance, standard deviation, root mean square error, root mean square error, or statistical error of regression of one or more kinematic angles as a criterion for minimizing crosstalk.
[0039] In particular, the standard kinematic evaluation system may be adapted to capture the knee joint in a tibial coordinate system (tibia COS) as a first joint coordinate system and in a femoral coordinate system (femoral COS) as a second joint coordinate system and to determine (by gait analysis) in particular the sequence of the three kinematic angles of flexion, adduction and internal rotation and / or the sequence of the three kinematic translations for just one step cycle, and the control unit may be adapted in particular to output the gait type and / or the size of the artificial knee joint (knee implant) and / or the orientation of the artificial knee joint as evaluation parameters.
[0040] Preferably, the predetermined objective optimization may be defined as minimizing the root mean square error (RMSE) of the adduction kinematic angle (graph) and / or the root mean square error (RMSE) of the internal rotation kinematic angle (graph). Minimizing the root mean square error (RMSE) is a particularly preferred objective optimization since individual deflections are not weighted too strongly, minimizing possible errors.
[0041] In particular, the RMSE (Root Mean Square Error) may be chosen as a measure of the deviation of the varus / valgus and internal / external rotation curves, which can be reduced from 0.79±0.30° to 0.29±0.30° by rotating the coordinate system by 3.32±1.24° around the corresponding screw axis.
[0042] Preferably, the predefined objective optimization may be defined as minimizing the variance (of the graph) of the adduction kinematic angle and / or minimizing the variance (of the graph) of the internal rotation kinematic angle. When minimizing the variance, the corresponding kinematic angle graph may be offset relative to the zero line, but the graph should be as smooth as possible, i.e. flat relative to the "new offset zero line".
[0043] According to one embodiment, the control unit may comprise a storage unit containing a database in which standardized kinematic angles and / or standardized kinematic translations are linked to evaluation parameters, in particular in which standardized kinematic angles are linked to the size and alignment of the knee prosthesis, so that depending on the selected evaluation parameters (columns selected by the evaluation side), an optimal match between the evaluation parameters and the corresponding standardized kinematic angles can be found.
[0044] According to a further embodiment, the control unit may be trained as an artificial intelligence system with a data set comprising standardized kinematic angles and / or kinematic translations as input and with the artificial joint of the patient's joint as output, whereby the control unit is adapted to output, by means of the artificial intelligence, an assessment of the artificial joint, in particular of the size and alignment, when new biomechanical kinematic characteristics of the patient are detected using the standardized kinematic angles and / or standardized kinematic translations. Once standardized kinematic data in the form of standardized kinematic angles of a general patient are available according to the present disclosure, the assessment can be carried out using the artificial intelligence and the trained system. This is different from the prior art, where possible small errors lead to disproportionately large deviations, making the assessment impossible.
[0045] In particular, the control unit may be adapted to determine the kinematic angles using the recorded biomechanical properties of the patient when using an inertial measurement unit (IMU) as a sensor to calculate the three kinematic angles based on the acceleration and angular velocity. Typically, the IMU comprises an acceleration sensor for acquiring the acceleration in three directions and a gyroscope for determining the angular velocity.
[0046] In particular, a kinematic dataset of level gait on an (established) knee joint simulator (VIVO, AMTI, Watertown, Massachusetts) may be used or input into a standard kinematic evaluation system and may be recorded simultaneously with multiple sensors, preferably acceleration sensors and / or optical sensors, in particular at least one inertial measurement unit.
[0047] In particular, the sensor of the detection device may preferably be located in / on the knee cuff, i.e. for example temporarily attached to the knee in the manner of a bandage.
[0048] Furthermore, the sensors are preferably connected to a control unit (such as a specially adapted computer system) or coupled to the control unit for data transmission. The obtained kinematic angle / rotation data is normalized or standardized by optimizing (mathematical optimization methods) the orientation of the tibial and femoral coordinate systems.
[0049] In particular, with regard to a standard kinematic assessment method for detecting, standardizing and evaluating biomechanical kinematic data of a patient's (selected) joints in the standard kinematic assessment system according to the present disclosure, the object of the present disclosure is solved in that the method comprises the following steps: acquiring biomechanical motion characteristics of the patient by a sensor of the detection device; determining by a control unit based on the provided motion characteristics of the patient a sequence of kinematic angles and / or kinematic translations of the joint for a first joint element having a first joint coordinate system and a second joint element having a second joint coordinate system; determining by a standardization unit of the control unit using a predetermined objective optimization a rotation vector or a rotation matrix for adjusting an orientation of the first joint coordinate system and / or a rotation vector or a rotation matrix for adjusting an orientation of the second joint coordinate system and / or a translation vector for adjusting a position of the first joint coordinate system and / or a translation vector for adjusting a position of the second joint coordinate system; standardizing the sequence of kinematic angles by adjusting the first and second joint coordinate systems with the corresponding identified rotation vector or rotation matrix and / or standardizing the sequence of kinematic translations by adjusting the first and second joint coordinate systems with the corresponding identified translation vector; evaluating the joint with respect to a predetermined evaluation parameter based on the standardized kinematic angles and / or the standardized kinematic translations; and outputting the evaluation by a display device.
[0050] In particular, the standard kinematic evaluation method and the control unit of the standard kinematic evaluation system may be adapted to use the crosstalk minimization method as the objective optimization.
[0051] Preferably, the control unit of the standard kinematic evaluation method and system may be adapted to optimize the orientation of the reference frame for the knee kinematic characteristics.
[0052] Preferably, the control unit of the standard kinematic evaluation method and system may be adapted to provide normalization (or standardization) of kinematic measurement systems, in particular including optical marker-based systems and inertial measurement unit (IMU)-based systems.
[0053] In particular, a standard kinematic assessment method may capture, standardize and assess the patient's knee joint as a joint, with minimization of the (graphed) root mean square error (RMSE) of the adduction kinematic angle and / or the (graphed) root mean square error (RMSE) of the internal rotation kinematic angle defined as a predetermined objective optimization.
[0054] According to a further embodiment of the standard kinematic assessment method, the patient's knee joint may be recorded, standardized and assessed as a joint, and minimization of the variance of the kinematic angle of adduction and / or the kinematic angle of internal rotation is defined as the predetermined objective optimization.
[0055] With regard to a computer readable storage medium, the object is achieved in that the medium comprises instructions which, when executed by a computer, cause the computer to carry out the steps of the standardized evaluation method according to any of the present claims.
[0056] Hereinafter, the present invention will be described in more detail based on preferred embodiments with reference to the drawings. [Brief description of the drawings]
[0057] [Figure 1] FIG. 1 is a perspective view of a knee joint with a femoral coordinate system, illustrating the errors in analysis and evaluation of the prior art that can occur when the orientation is misaligned. [Diagram 2] FIG. 1 illustrates a schematic diagram of a standard kinematic assessment system according to a first preferred embodiment of the present disclosure. [Diagram 3] FIG. 1 shows a schematic diagram illustrating the three kinematic angles of a patient's knee joint and the corresponding standardization. [Figure 4] FIG. 1 shows a schematic diagram illustrating the three kinematic angles of a patient's knee joint and the corresponding standardization. [Diagram 5] 1 illustrates a sequence of a standard kinematic evaluation method according to a first preferred embodiment of the present disclosure. [Figure 6] A comparison is shown where the input to a standard kinematic assessment system or method comes from different sources. [Figure 6a] A schematic diagram is shown to illustrate the standardization of the patient's kinematic data by comparison with a kinematic simulation in which both the amplitude and the characteristics of curves a-d are radically changed by reorienting the reference system, the joint coordinate system. [Figure 6b] A schematic diagram is shown to illustrate the standardization of the patient's kinematic data by comparison with a kinematic simulation in which both the amplitude and the characteristics of curves a-d are radically changed by reorienting the reference system, the joint coordinate system. [Figure 6c] A schematic diagram is shown to illustrate the standardization of the patient's kinematic data by comparison with a kinematic simulation in which both the amplitude and the characteristics of curves a-d are radically changed by reorienting the reference system, the joint coordinate system. [Figure 7] 13A-13C show an overview of various acquisitions of standardized patient kinematic data according to the standard kinematic evaluation system or method of the present disclosure with respect to reorientation of the joint coordinate system. [Figure 8] 1 shows a flow chart of a standard kinematic assessment method according to a preferred embodiment. [Figure 9] Schematic showing exemplary frame positions in the knee joint and typical centers of rotation for common implants. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0058] The drawings are schematic in nature and are intended merely to aid in the understanding of the invention. Identical elements are provided with identical reference numbers. Features of the various embodiments are interchangeable.
[0059] FIG. 1 shows an example of a deviation caused by a 3° rotation of the so-called flexion axis of the knee joint. For a femur with a distance between the medial and lateral epicondyles of 10 cm, an AP or PD error of 5 mm (total) in detecting the bony landmarks leads to a 3° rotation of the reference system, i.e. the femoral coordinate system (FCS), around the Z axis. The maximum width of the corridor of adduction and internal rotation for a ±3° rotation Ry and Rz of the orientation of the tibial and femoral coordinate systems is already 14.5°. As explained at the beginning of this disclosure, misalignment of the axes of the joint coordinate systems leads to crosstalk and crosstalk effects, e.g. where a rotation in one plane is partially perceived as a rotation in the other plane. Thus, a rotation of the femoral coordinate system around one axis not only changes one kinematic angle, but also affects the other two kinematic angles.
[0060] 2 shows a schematic diagram of a standard kinematic evaluation system 1 according to a first preferred embodiment of the present disclosure. The standard kinematic evaluation system 1 is used to acquire, standardize, and evaluate (in a standardized and comparable manner) biomechanical kinematic data of a knee joint G of a patient (P), as described below.
[0061] The standard kinematic evaluation system 1 comprises at least one acquisition device 2 for detecting biomechanical movement characteristics of the knee joint G of a patient P, which acquisition device 2 detects by means of an optical sensor system 4 and makes them available in a computer-readable form to a control unit 8. Furthermore, the standard kinematic evaluation system 1 comprises a display device, for example in the form of an operating room monitor, for displaying data concerning the surgical intervention performed on the patient P and for outputting the evaluation results.
[0062] According to the present disclosure, the control unit 8 is particularly adapted to process the detected kinematic characteristics of the patient P provided by the acquisition device 2 and determine, based on the kinematic data, a sequence of three kinematic angles 14, 16, 18 (and / or three kinematic translations) of the knee joint G relative to a first joint element G1 having a first joint coordinate system 20 and a second joint element G2 having a second joint coordinate system 22 as a rotation angle graph. In other words, for just one step cycle of the patient, the three kinematic angles 14, 16, 18 (and / or three kinematic translations) of the model joint are extracted from the abundant kinematic data.
[0063] Thus, the standard kinematic evaluation system 1 is particularly adapted to obtain the knee joint G using the tibia coordinate system (tibia COS) as the first joint coordinate system 20 and the femur coordinate system (femur COS) as the second joint coordinate system 22 and to determine the sequence of three kinematic angles 14, 16, 18, namely flexion 14, adduction 16 and internal rotation 18, in just one step cycle.
[0064] In order to be able to compare kinematic analyses (and different simulations) of different patients as well as possible, or, if possible, to allow a standardized analysis and associated evaluation of data acquired with different acquisition methods for one patient (e.g., time-shifted, using different acquisition methods such as optical and ancillary sensors), it is necessary to standardize the kinematic angle data according to certain criteria in order to provide a uniform and standardized data acquisition system and a standardized data base.
[0065] For this purpose, the standardization is performed by a predefined objective optimization using a standardization unit 10. The standardization unit 10 is adapted and designed to identify a rotation vector 24 for adjusting the orientation of the first joint coordinate system 20 and a rotation vector 26 for adjusting the orientation of the second joint coordinate system.
[0066] The standard kinematic evaluation system 1 comprises an evaluation unit 12 adapted to perform an evaluation for the joint G with respect to at least one predefined evaluation parameter based on the standardized kinematic angles 14', 16', 18' as kinematic data. In the present embodiment, the size of the knee prosthesis for the surgical intervention and the orientation of the knee prosthesis are output as evaluation parameters. The evaluation is output visually by the display device 6, in particular by displaying preoperative CT data of the patient P, in which the simulated knee prosthesis is displayed with the corresponding size and position.
[0067] The standard kinematic evaluation system1 minimizes errors and therefore allows for a robust and reliable evaluation. Patient safety is also further improved, as surgeons receive better support when preparing for the surgical intervention and implanting the knee prosthesis.
[0068] In order to acquire the patient's movement characteristics, at least one acquisition device 2 is equipped with a plurality of inertial measurement units 28 (hereinafter referred to as IMU) as sensors, and the inertial measurement units 28 are attached to two (detachable) knee cuffs 36 positioned on the thigh and lower leg of the patient P.
[0069] In addition to the IMU, the standard kinematic evaluation system 1 comprises another acquisition device 2, which comprises an optical recording unit 30 in the form of a stereo camera 32, which is arranged obliquely upward with respect to the floor surface in order to externally acquire the biomechanical kinematic characteristics of the joint G of the patient P. For this purpose, in the knee cuff 36, as well as the IMU 28, an infrared marker is also arranged.
[0070] 3 and 4 are schematic visualizations of the three kinematic angles 14, 16, 18 and the joint coordinate systems 20, 22 of the standard kinematic evaluation system 1. The optimization objective in this embodiment is to minimize the root mean square error (RMSE) while varying the orientation of the joint coordinate systems 20, 22. That is, the objective is to find the first rotation vector 24 and the second rotation vector 26 such that both the root mean square error (RMSE) of the adduction kinematic angle 16 and the root mean square error (RMSE) of the internal rotation kinematic angle 18 are minimized. In this example, the first femoral rotation vector 24 (Rx, Ry, Rz) is (-0.055; 2.106; 2.44) and the second tibial rotation vector 26 (Rx, Ry, Rz) is (0.051; 2.157; -0.295). The rotations are gimbal mounted. That is, first rotate around the X axis, then rotate around the Y axis, and finally rotate around the Z axis (same origin).
[0071] FIG. 5 shows the process of determining the orientation / alignment of the tibial and femoral coordinate systems (reference frames) by minimizing the root mean square error (RMSE) of adduction and internal rotation for standardization. In particular, adduction / internal rotation may be assumed to be zero throughout the cycle. First, the patient's kinematic characteristic data is obtained, including the kinematic characteristic data of the patient's joint of interest. Then, from the abundant kinematic characteristic data, three kinematic angles 14, 16, 18 during one step cycle are extracted. At this point, these kinematic angles 14, 16, 18 are still subject to error, and a slight misalignment of the tibial coordinate system 20 or femoral coordinate system 22 will have a significant impact on the kinematic angle sequence.
[0072] The next step is an objective optimization with respect to minimizing the root mean square error (RMSE) of the adduction and internal rotation angles, i.e., two of the three kinematic angles, and a rotation vector is calculated and applied to the coordinate system, and the newly oriented coordinate system forms the reference system for the femur and tibia, resulting in the standardized kinematic angles 14', 16', 18' and their sequence, which have changed according to the reorientation of the coordinate systems 20, 22.
[0073] FIG. 6 shows the standardization of the orientation of the reference frame when measuring the kinematic characteristics of the knee with a comparative data set of kinematic characteristics of another patient, specifically six patients. This standardization makes it possible to compare data obtained from different data sets, different acquisition methods, etc. with each other. Only by standardization is it recognized that, for example, alignment errors alone are the cause of incomparable kinematic characteristic data, and this error is corrected by standardization. The standard kinematic evaluation system 1 is used to standardize the orientation of the reference frame obtained from measurements of different data sources and make them comparable.
[0074] 6a-6c are schematic diagrams of multiple recordings of the kinematic angles of flexion 14, adduction 16 and internal rotation 18 by two different acquisition devices, an optical device and an IMU. It can be easily seen that standardization aligns the different kinematic angles 14, 16, 18 to obtain standardized kinematic angles 14', 16', 18' that can be used for evaluation by the standard kinematic evaluation system 1. This is a reasonable result, since the patient P has a single step cycle, which needs to be simulated identically by the different acquisition methods.
[0075] Figure 7 is a schematic diagram of a series of different recorded kinematic characteristics with and without standardization by the standard kinematic evaluation system 1. Again, it can be seen that after standardization the curves are more closely aligned with each other.
[0076] 8 shows a flow chart of a standard kinematic assessment method according to a preferred embodiment of the present disclosure. The standard kinematic assessment method for acquiring, standardizing and evaluating biomechanical kinematic data of the knee joint G of a patient P includes the following steps:
[0077] In a first step S1, biomechanical movement characteristics of a patient P are acquired by sensors 4 of an acquisition device 2. In particular, they may be acquired using a stereo camera and optical markers or sensors attached to the patient.
[0078] In the next step S2, the control unit 8 determines a sequence of three kinematic angles 14, 16, 18 of the knee joint G relative to a first joint element G1 (femur) having a first joint coordinate system 20 and a second joint element G2 (tibia) having a second joint coordinate system 22 based on the provided movement characteristics of the patient P.
[0079] In the subsequent step S3, the standardization unit 10 of the control unit 8 uses a predetermined objective optimization to determine a rotation vector 24 for adjusting the orientation of the first joint coordinate system 20 and a rotation vector 26 for adjusting the orientation of the second joint coordinate system 22.
[0080] After the two rotation vectors 24, 26 are determined, in step S4, the sequence of kinematic angles 14', 16', 18' is standardized by adjusting the first and second joint coordinate systems 20, 22, respectively, by the determined rotation vectors 24, 26. That is, the coordinate systems are rotated according to the rotation vectors to adjust their orientation (and / or the translation vectors are moved to adjust their positions). The sequence of original kinematic angles 14, 16, 18 (and / or kinematic translations) is similarly adapted to become the sequence of standardized kinematic angles 14', 16', 18' (and / or kinematic translations).
[0081] In the final step S5, the knee joint is evaluated with respect to a predetermined evaluation parameter based on the standardized kinematic angles. Specifically, a gait classification is selected as the evaluation parameter, and output by the display device 4 in the final step S6.
[0082] Figure 9 shows examples of different frame positions, or coordinate systems, in the knee joint. Typical centers of rotation for common implants are shown in the figure: MS implant center of rotation, LS implant center of rotation, and PS implant center of rotation.
[0083] In particular, a standard kinematic evaluation method for acquiring, standardizing, and evaluating biomechanical kinematic data of the joint G of the patient P may be performed in the standard kinematic evaluation system 1 according to the present disclosure to obtain a translation vector and define a virtual position of a new joint coordinate system, which is a frame. Then, as a further step, a phenotyping method according to the third aspect of the present disclosure may be performed. For example, if it is determined that the new joint coordinate system is most similar to the MS coordinate system (COS) for a joint, it may be determined that an MS implant is suitable. On the other hand, if it is determined that the new joint coordinate system is most similar to the LS COS, it may be determined that an LS implant is suitable. And if it is determined that the new joint coordinate system is most similar to the PS COS, it may be determined that a PS implant is suitable. [Explanation of symbols]
[0084] 1: Standard kinematic evaluation system 2: Acquisition device 4: Sensor system 6:Display device 8: Control unit 10: Standardized Unit 12: Evaluation unit 14: Flexion kinematic angle 14': Standardized flexion kinematic angle 16: Adduction kinematic angle 16': Standardized adduction kinematic angle 18: Internal rotation kinematic angle 18': Standardized internal rotation kinematic angle 20: First joint coordinate system 22: Second joint coordinate system 24: First rotation vector 26: Second rotation vector 28: Inertial Measurement Unit (IMU) 30: Optical recording unit 32: Stereo camera 34: Storage Unit 36: Knee cuff G: Joints G1: First joint element G2: Second joint element P:Patient S1: A step of acquiring biomechanical motion characteristics using an acquisition device. S2: Step to identify the sequence of kinematic angles S3: Step to find the direction to adjust S4: Step to standardize the sequence of kinematic angles S5: Step to evaluate the joint S6: Step to output the evaluation
Claims
1. A standard kinematic evaluation system (1) for acquiring, standardizing and evaluating biomechanical kinematic data of a joint (G) of a patient (P), comprising: at least one acquisition device (2) adapted to acquire biomechanical motion characteristics of said joint (G) of a patient (P) by means of a sensor system (4) and to provide said biomechanical motion characteristics in a computer readable format; a visual display device (6), in particular an operating room monitor, for visual output to a user; Equipped with a control unit (8) processes the provided and acquired kinematic characteristics of the patient and calculates at least one sequence of at least one, in particular three, kinematic angles (14, 16, 18) and / or at least one, in particular three, kinematic translations of the joint (G) for a first joint element (G1) having a first joint coordinate system (20) and a second joint element (G2) having a second joint coordinate system (22), determining, by means of a predetermined objective optimization, a rotation vector (24) or a rotation matrix for adjusting the orientation of the first joint coordinate system (20) and / or determining a rotation vector (26) or a rotation matrix for adjusting the orientation of the second joint coordinate system (22) using a standardization unit (10) adapted and designed for this purpose in order to perform the standardization, and determining, by means of a predetermined objective optimization, a translation vector for adjusting the position of the first joint coordinate system (20) and / or determining a translation vector for adjusting the position of the second joint coordinate system (22) in order to perform the standardization, 1. A standard kinematic evaluation system (1), characterized in that it is adapted to perform an evaluation of the joint (G) with respect to at least one predefined evaluation parameter based on the standardized kinematic angles (14', 16', 18') and / or standardized kinematic translations as kinematic data by means of an evaluation unit (12) adapted for this purpose and to output said evaluation via a display device (6).
2. At least one of the acquisition devices (2) comprises as sensors at least one acceleration sensor and / or one gyro sensor, in particular an inertial measurement unit (28), 2. The standard kinematic evaluation system (1) according to claim 1, characterized in that the acquisition device (2) is adapted to be attached to the area of the joint (G) of the patient (P), in particular to the first joint element (G1) and / or the second joint element (G2).
3. said at least one acquisition device (2) comprises as a sensor system at least one optical recording unit (30), in particular a 3D recording unit, preferably a stereo camera (32); 3. The standard kinematic assessment system (1) according to claim 1 or 2, characterized in that the optical recording unit (30) acquires the biomechanical kinematic characteristics of the joint (G) of the patient (P) preferably using optical markers, in particular passive infrared markers, attached in the area of the joint (G) of the patient (P), preferably on the first joint element (G1) and / or the second joint element (G2).
4. The standard kinematic evaluation system (1) according to any one of claims 1 to 3, characterized in that the predetermined optimization objective is the minimization of the variance, the standard deviation, the squared error and / or the statistical error of the regression of one or more kinematic angles (14, 16, 18).
5. said standard kinematic evaluation system (1) being adapted to acquire a knee joint (G) using a tibia coordinate system as a first joint coordinate system (20) and a femoral coordinate system as a second joint coordinate system (22) and to determine, in particular, in exactly one step cycle, a sequence of three kinematic angles (14, 16, 18) of flexion, adduction and internal rotation; 5. The standard kinematic evaluation system (1) according to any one of claims 1 to 4, characterized in that the control unit (8) is adapted in particular to output the gait type and / or the size of the knee prosthesis and / or the orientation of the knee prosthesis as evaluation parameters.
6. 6. The standard kinematic evaluation system (1) according to claim 5, characterized in that the minimization of the root mean square error (RMSE) of the kinematic angle of adduction (16) and / or the kinematic angle of internal rotation (18) is defined as the predetermined objective optimization.
7. 6. The standard kinematic evaluation system (1) according to claim 5, characterized in that the minimization of the variance of the kinematic angle of adduction (16) and / or the kinematic angle of internal rotation (18) is defined as the predetermined objective optimization.
8. 8. The standardized kinematic evaluation system (1) according to any one of claims 1 to 7, characterized in that the control unit (8) has a storage unit (34) containing a database in which the standardized kinematic angles (14', 16', 18') are linked to evaluation parameters, in particular in which the standardized kinematic angles (14', 16', 18') are linked to the size and alignment of the artificial knee joint.
9. 8. The standard kinematic evaluation system (1) according to claim 1, characterized in that the control unit (8) is trained as an artificial intelligence system with a training data set comprising standardized kinematic angles (14', 16', 18') and / or standardized kinematic translations as input and with the artificial joint of the joint (G) of the patient (P) as output, whereby the control unit (8) is adapted to output, by means of artificial intelligence, an assessment of the artificial joint, in particular an assessment of its size and alignment, once new biomechanical kinematic characteristics of the patient (P) are obtained using the standardized kinematic angles (14', 16', 18') and / or standardized kinematic translations.
10. 10. The standard kinematic evaluation system (1) according to claim 1, characterized in that the control unit (8) is adapted to determine the kinematic angles (14, 16, 18) and / or to calculate the kinematic translations based on the acquired biomechanical kinematic characteristics of the patient (P), in particular based on the accelerations and angular velocities of the three kinematic angles (14, 16, 18) when using an inertial measurement unit (28) as a sensor.
11. A standard kinematic evaluation method for acquiring, standardizing and evaluating biomechanical kinematic data of the joint (G) of a patient (P), in particular in a standard kinematic evaluation system (1) according to any one of claims 1 to 10, comprising: A step (S1) of acquiring biomechanical motion characteristics of a joint (G) of a patient (P) by a sensor system (4) of an acquisition device (2); determining (S2) by a control unit (8) a sequence of kinematic angles (14, 16, 18) and / or kinematic translations of said joint (G) relative to a first joint element (G1) having a first joint coordinate system (20) and a second joint element (G2) having a second joint coordinate system (22) based on the provided kinematic characteristics of said patient (P); determining (S3) by a standardization unit (10) of the control unit (8) using a predefined objective optimization a rotation vector (24) or a rotation matrix for adjusting the orientation of the first joint coordinate system (20) and / or a rotation vector (26) or a rotation matrix for adjusting the orientation of the second joint coordinate system (22) and / or determining using a predefined objective optimization a translation vector for adjusting the position of the first joint coordinate system (20) and / or a translation vector for adjusting the position of the second joint coordinate system (22); standardizing the sequence of kinematic angles (14', 16', 18') by adjusting the first and second joint coordinate systems (20, 22) by the identified rotation vectors (24, 26) or rotation matrices and / or standardizing the sequence of kinematic translations by adjusting the first and second joint coordinate systems (20, 22) by the identified translation vectors (S4); - performing (S5) an evaluation of said joint (G) with respect to predetermined evaluation parameters based on said standardized kinematic angles (14', 16', 18') and / or standardized kinematic translations; and outputting the evaluation by a display device (4).
12. The standard kinematic evaluation method includes acquiring, standardizing, and evaluating the knee joint of a patient (P) as a joint (G); 12. The method of claim 11, characterized in that in the step (S3) of identifying the orientation and / or position adjustments, the minimization of the root mean square error (RMSE) of the kinematic angle of adduction (16) and / or the kinematic angle of internal rotation (18) of the femur (P) is defined as the predetermined objective optimization.
13. The standard kinematic evaluation method includes acquiring, standardizing, and evaluating the knee joint of a patient (P) as a joint (G); 12. The method of claim 11, characterized in that in the step (S3) of identifying orientation and / or position adjustments, the minimization of the variance of the kinematic angles of adduction (16) and / or of the kinematic angles of internal rotation (18) is defined as the predetermined objective optimization.
14. A computer readable storage medium comprising instructions which, when executed by a computer, cause the computer to perform the method steps of the standard kinematic assessment method according to any one of claims 11 to 13.