A method and system for assessing acetabular morphology in a continuous pelvic tilt posture

Abstract

The application discloses a kind of continuous pelvic tilt posture under acetabular form evaluation method and system, belong to clinical evaluation technical field.Method includes: constructing pelvic three-dimensional model and femur three-dimensional model;Establish pelvic front plane anatomical reference coordinate system;Obtain the double hip axis of refined estimation;Get left and right two optimal acetabular opening planes, take the normal vector of left and right two optimal acetabular opening planes as the initial axis of corresponding side pelvic acetabulum;Construct the rigid body motion model of pelvic acetabular initial axis around the continuous rotation of double hip axis, calculate the change of acetabular axis direction under different pelvic tilt postures and corresponding acetabular anteversion angle, abduction angle;Establish acetabular abduction angle / anteversion angle curve under pelvic tilt, complete acetabular form evaluation.The application realizes the automatic calculation of acetabular space direction and accurate acetabular form evaluation, and lays a foundation for finding the most suitable patient acetabular prosthesis installation angle.

Description

Technical Field

[0001] This invention relates to the field of clinical assessment technology, and in particular to a method and system for assessing acetabular morphology under continuous pelvic tilt posture. Background Technology

[0002] Total hip arthroplasty (THA) is a common surgical procedure for treating end-stage hip joint disease. The spatial orientation of the acetabular cup prosthesis during surgery significantly impacts postoperative joint stability, prosthesis wear, and the risk of dislocation. Therefore, accurately assessing the spatial orientation of the acetabular cup or acetabulum itself is a crucial step in preoperative planning and postoperative evaluation.

[0003] Traditional methods typically measure the anteversion and abduction angles of the acetabular cup based on two-dimensional X-ray images. However, because X-ray images are two-dimensional projections, patient positioning deviations and pelvic rotation during the imaging process can significantly affect the measurement results, leading to substantial measurement errors.

[0004] With the development of medical image processing technology, measurement methods based on CT three-dimensional reconstruction have gradually emerged in recent years. These methods typically construct a three-dimensional model of the pelvis and establish an anatomical reference coordinate system, then determine the axial direction based on the acetabulum or acetabular cup model to calculate the anteversion and abduction angles of the acetabulum. However, existing three-dimensional measurement methods still have the following problems:

[0005] 1. Determining the acetabular axis typically relies on manual selection of edge points or identification of local geometric features. Operators need to manually mark acetabular edge points in the 3D model or perform interactive adjustments. Significant differences exist between different operators, leading to insufficient stability and repeatability of measurement results, making automated batch analysis difficult.

[0006] 2. Existing methods can usually only obtain acetabular angle parameters under a single body position. In actual clinical practice, the pelvis will undergo varying degrees of anterior or posterior tilting in the sagittal plane, and changes in pelvic posture will significantly affect the spatial orientation of the acetabulum. Static angle parameters obtained under a single body position are difficult to reflect the true functional state of the acetabulum during continuous posture changes, making it impossible to find the most suitable acetabular prosthesis installation angle for the patient during surgery.

[0007] 3. Currently, there is a lack of a unified mathematical model that can describe the changes in the spatial orientation of the acetabulum during continuous pelvic tilt. Existing studies mostly involve discrete measurements under limited body position conditions and comparison of angle differences, but a continuous functional relationship between the pelvic tilt angle and the spatial orientation of the acetabulum has not yet been established. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a method and system for evaluating the acetabular morphology under continuous pelvic tilt posture. It can automatically and stably determine the acetabular axis based on three-dimensional image data and establish a mathematical model of the spatial orientation change of the acetabulum under continuous pelvic tilt posture, thereby realizing the automated calculation of the spatial orientation of the acetabulum and the functional posture assessment, which facilitates finding the most suitable acetabular prosthesis installation angle for the patient during surgery.

[0009] This invention is achieved through the following technical solution:

[0010] A method for assessing acetabular morphology under continuous pelvic tilt postures includes the following steps:

[0011] S1: Acquire CT image data of the patient's pelvis and perform three-dimensional reconstruction to obtain a three-dimensional model of the pelvis and a three-dimensional model of the femur.

[0012] S2: Perform spatial standardization on the point cloud data of the 3D model of the pelvis to establish an anterior pelvic anatomical reference coordinate system;

[0013] S3: Perform spherical model fitting independently on the point cloud data of the femoral 3D model to obtain the optimal spherical model of the left and right femoral heads. Perform least squares spherical fitting on the point set in the optimal spherical model of the left and right femoral heads to obtain the refined estimated position of the center of the left and right femoral heads. Connect the center of the left and right femoral heads to obtain the dual hip axis.

[0014] S4: In the anatomical reference coordinate system of the anterior pelvic plane, take the center of rotation of the left and right femoral heads as the center of rotation, and the cross-sections where the center of rotation of the left and right femoral heads are located as the initial rotation section planes. Rotate the initial rotation section planes around the X-axis at multiple angles, calculate the intersection line between the 3D model of the pelvis and the rotation section plane, identify the feature points of the outer edge of the acetabulum on both sides in the intersection line, perform least squares plane fitting based on the feature points of the outer edge of the acetabulum on both sides to obtain the optimal acetabular opening planes on both sides, and take the normal vector of the optimal acetabular opening planes on both sides as the initial axis of the acetabulum on the corresponding side.

[0015] S5: Construct a rigid body motion model of the pelvis and acetabulum rotating continuously around the two hip axes. Based on the rigid body motion model, calculate the changes in the direction of the acetabular axis and the corresponding acetabular anteversion angle and acetabular abduction angle under different pelvic tilt postures.

[0016] S6: Establish the acetabular abduction / anteversion curve under pelvic tilt based on the functional relationship between the acetabular anteversion angle, acetabular abduction angle, and pelvic tilt angle, complete the acetabular morphology assessment, and then find the most suitable acetabular prosthesis installation angle for the patient based on the acetabular morphology assessment results.

[0017] The optimized method for performing three-dimensional reconstruction of the patient's pelvic CT image data in step S1 is as follows: export the patient's pelvic CT image data in DICOM format, import it into Mimics software for bone segmentation and reconstruction, and save the pelvic data after bone segmentation and reconstruction as a PELVIS.stl file, and save the bilateral pelvic data after bone segmentation and reconstruction as a FEMUR.stl file.

[0018] Furthermore, in step S2, the point cloud data of the pelvic 3D model is spatially standardized to establish the pelvic anterior plane anatomical reference coordinate system as follows:

[0019] S211: Read the PELVIS.stl file to obtain the point cloud data and topological relationships that constitute the pelvis;

[0020] S212: Translate the point cloud that constitutes the pelvis to its geometric centroid, perform principal component analysis based on the point cloud covariance matrix, and determine the principal axis direction so that the main geometric directions of the pelvis are initially aligned under a unified coordinate framework.

[0021] S213: The iterative tangent plane method is used to automatically identify key anatomical landmarks of the pelvis and to construct an anterior pelvic anatomical reference coordinate system based on these landmarks.

[0022] The optimized method for performing spherical model fitting independently on the point cloud data of the femoral 3D model in step S3 to obtain the optimal spherical models of the left and right femoral heads is as follows: Read the FEMUR.stl file, introduce the random sampling consensus algorithm into the point cloud data of the femoral 3D model, randomly select the minimum point set to estimate the parameters of the spherical models of the left and right femoral heads, and comprehensively evaluate the fitting residuals and the number of inliers during the iteration process to obtain the optimal spherical models of the left and right femoral heads.

[0023] Furthermore, in step 5, the change in the acetabular axis direction under different pelvic tilt postures is calculated according to equation (1), the acetabular anteversion angle is calculated according to equation (2), and the acetabular abduction angle is calculated according to equation (3):

[0024] (1);

[0025] (2);

[0026] (3);

[0027] in: This indicates the change in the direction of the acetabular axis under different pelvic tilt postures. This represents the initial axis direction vector of the pelvis and acetabulum. Indicates the pelvic tilt angle. Represents the direction vector of the two hip axes. Indicates the acetabular anteversion angle. This indicates the change in the direction of the acetabular axis under different pelvic tilt positions. Components in the axial direction, This indicates the change in the direction of the acetabular axis under different pelvic tilt positions. Components in the axial direction, Indicates the acetabular abduction angle. This represents the component of the change in the acetabular axis direction in the y-axis direction under different pelvic tilt postures.

[0028] Furthermore, the method for finding the most suitable acetabular prosthesis installation angle for the patient based on the acetabular morphology assessment results in step S6 is as follows:

[0029] After pelvic fixation is completed during the actual surgery, the intraoperative pelvic tilt angle is measured. The acetabular abduction / anteversion angle curve under pelvic tilt is used to find the acetabular anteversion angle corresponding to the intraoperative pelvic tilt angle. The acetabular prosthesis is implanted with the acetabular anteversion angle corresponding to the intraoperative pelvic tilt angle as the most suitable acetabular prosthesis installation angle for the patient.

[0030] The optimized approach involves using a posterolateral approach with the patient positioned in the lateral decubitus position and pelvic fixation during actual surgery.

[0031] Optimized, the intraoperative pelvic tilt angle is measured using a navigation system or position measurement device.

[0032] A system for evaluating acetabular morphology under continuous pelvic tilt postures, used to perform a method for evaluating acetabular morphology under continuous pelvic tilt postures as described in any of the above, comprising a pelvic 3D model and femur 3D model construction module, a pelvic anterior plane anatomical reference coordinate system establishment module, a dual hip axis acquisition module, a pelvic acetabular initial axis determination module, an acetabular anteversion angle and acetabular abduction angle determination module, and an acetabular morphology evaluation module.

[0033] The pelvic 3D model and femur 3D model construction module is used to acquire the patient's pelvic CT image data and perform 3D reconstruction to obtain the pelvic 3D model and femur 3D model.

[0034] The pelvic anterior plane anatomical reference coordinate system establishment module is used to perform spatial standardization processing on the point cloud data of the pelvic three-dimensional model and establish the pelvic anterior plane anatomical reference coordinate system.

[0035] The dual hip axis acquisition module is used to independently perform spherical model fitting on the point cloud data of the femoral 3D model to obtain the optimal spherical model of the left and right femoral heads. The least squares spherical fitting is performed on the point set in the optimal spherical model of the left and right femoral heads to obtain the refined estimated position of the center of the left femoral head and the center of the right femoral head. The dual hip axis is obtained by connecting the center of the left femoral head and the center of the right femoral head.

[0036] The pelvic acetabular initial axis determination module is used to determine the initial axis of the pelvis and acetabulum in the anatomical reference coordinate system of the anterior pelvic plane, with the center of rotation of the left and right femoral heads as the rotation centers, and the cross-sections containing the center of rotation of the left and right femoral heads as the initial rotation cross-section planes. The initial rotation cross-section planes are rotated around the X-axis at multiple angles, and the intersection line between the 3D model of the pelvis and the rotation cross-section plane is calculated. The feature points of the outer edge of the acetabulum on the left and right sides are identified in the intersection line. Based on the feature points of the outer edge of the acetabulum on the left and right sides, least squares plane fitting is performed to obtain the optimal acetabular opening planes on the left and right sides. The normal vector of the optimal acetabular opening planes on the left and right sides is taken as the initial axis of the pelvis and acetabulum on the corresponding side.

[0037] The module for determining the acetabular anteversion angle and acetabular abduction angle is used to construct a rigid body motion model of the initial axis of the pelvis and acetabulum rotating continuously around the two hip axes. Based on the rigid body motion model, the module calculates the changes in the direction of the acetabular axis and the corresponding acetabular anteversion angle and acetabular abduction angle under different tilt postures of the pelvis.

[0038] The acetabular morphology assessment is used to establish a curve of acetabular abduction / anteversion angle under pelvic tilt based on the functional relationship between acetabular anteversion angle, acetabular abduction angle and pelvic tilt angle, and to complete the acetabular morphology assessment. Based on the acetabular morphology assessment results, the most suitable acetabular prosthesis installation angle for the patient is found for implantation.

[0039] Beneficial effects of the invention:

[0040] 1. This invention automatically extracts feature points on the outer edge of the acetabulum using a rotational simulation tomography method and calculates the acetabular opening direction using plane fitting, thereby automatically determining the acetabular axis. Compared with methods that rely on manual selection of edge points, this method can effectively reduce errors caused by human operation and improve the stability and repeatability of measurement results.

[0041] 2. This invention constructs a rigid body motion model of the pelvis rotating continuously around two hip axes, enabling the calculation of the acetabular spatial orientation under continuous pelvic tilt postures. Compared to traditional methods that only perform static measurements in a single position, this method can more systematically describe the overall change law of the acetabular spatial orientation during pelvic posture changes.

[0042] 3. This invention establishes a continuous functional relationship between individualized pelvic tilt angle and acetabular anteversion and abduction angles, and generates individualized acetabular abduction / anteversion curves under pelvic tilt. This realizes the transformation from discrete position measurement to continuous posture modeling, providing a new quantitative description method for acetabular spatial orientation analysis. It enables functional assessment of acetabular spatial orientation under different pelvic postures and can be applied to preoperative planning, functional posture assessment, and functional safety zone analysis for total hip arthroplasty, providing a reliable technical basis for individualized acetabular prosthesis placement. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the process of this invention.

[0044] Figure 2 This is a schematic diagram of principal component analysis (PCA) of pelvic data according to the present invention.

[0045] Figure 3 This is a schematic diagram of the anterior pelvic plane, the two hip axes, and the pelvic tilt angle of the present invention.

[0046] Figure 4 This is a schematic diagram illustrating the geometric definitions of the acetabular anteversion angle AA and acetabular abduction angle AI of the present invention.

[0047] Figure 5 This is a schematic diagram of the acetabular abduction angle / anteversion angle curve under pelvic tilt according to the present invention. Detailed Implementation

[0048] A method for assessing acetabular morphology under continuous pelvic tilt postures, the flowchart of which is shown below. Figure 1 As shown, it includes the following steps:

[0049] S1: Acquire CT image data of the patient's pelvis and perform three-dimensional reconstruction to obtain a three-dimensional model of the pelvis and a three-dimensional model of the femur.

[0050] Specifically, the method for three-dimensional reconstruction of the patient's pelvic CT image data is as follows: export the patient's pelvic CT image data in DICOM format, import it into Mimics software for bone segmentation and reconstruction, and save the segmented and reconstructed pelvic data as a PELVIS.stl file, and save the segmented and reconstructed bilateral pelvic data as a FEMUR.stl file.

[0051] S2: Perform spatial standardization on the point cloud data of the 3D model of the pelvis to establish an anterior pelvic anatomical reference coordinate system;

[0052] Specifically, the method for spatially standardizing the point cloud data of the pelvic 3D model and establishing the anterior pelvic anatomical reference coordinate system is as follows:

[0053] S211: Read the PELVIS.stl file to obtain the point cloud data and topological relationships that constitute the pelvis;

[0054] S212: Translate the point cloud that constitutes the pelvis to its geometric centroid, perform principal component analysis (PCA) based on the point cloud covariance matrix, and determine the principal axis direction so that the main geometric directions of the pelvis are initially aligned under a unified coordinate framework.

[0055] This step completes the preprocessing of the point cloud data that constitutes the pelvis, aligning the main geometric directions of the pelvis within a unified coordinate framework. This ensures the consistency of spatial orientation of pelvic models from different individuals and can eliminate the influence of differences in the scanning positions of different subjects and the posture of the initial model on spatial analysis.

[0056] Specifically, a schematic diagram of principal component analysis (PCA) on pelvic data is shown below. Figure 2 As shown, the first principal axis direction (PC1) can be determined as the initial positive X-axis direction, the second principal axis direction (PC2) as the initial positive Y-axis direction, and the third principal axis direction (PC3) as the initial positive Z-axis direction.

[0057] S213: The iterative tangent plane method is used to automatically identify key anatomical landmarks of the pelvis and to construct an anterior pelvic anatomical reference coordinate system based on these landmarks.

[0058] Specifically, the schematic diagrams of the anterior pelvic plane (APP plane), hip axes, and pelvic tilt angle (PT) used in this invention are as follows: Figure 3 As shown: The pubic symphysis (PS) can be used as the origin of the coordinate system, the APP plane as the coronal plane, and the positive X-axis defined by the direction from the left anterior superior iliac spine (ASIS) to the right anterior superior iliac spine. An orthogonal, right-handed pelvic anterior plane anatomical reference coordinate system is established using the right-hand rule. After the pelvis tilts around the bihip axes at a certain angle, the angle between the APP plane and the coronal plane of the coordinate system (with a normal vector of (0,1,0)) is defined as the pelvic tilt angle (PT). Subsequent calculations of acetabular direction parameters and automatic positioning of the femoral head center are all completed within this pelvic anterior plane anatomical reference coordinate system framework.

[0059] S3: Perform spherical model fitting independently on the point cloud data of the femoral 3D model to obtain the optimal spherical model of the left and right femoral heads. Perform least squares spherical fitting on the point set in the optimal spherical model of the left and right femoral heads to obtain the refined estimated position of the center of the left and right femoral heads. Connect the center of the left and right femoral heads to obtain the dual hip axis.

[0060] Specifically, the method for independently performing spherical model fitting on the point cloud data of the femoral 3D model to obtain the optimal spherical model of the left and right femoral heads is as follows: read the FEMUR.stl file, introduce the random sampling consensus algorithm into the point cloud data of the femoral 3D model, randomly select the minimum point set to estimate the parameters of the spherical model of the left and right femoral heads, and comprehensively evaluate the fitting residuals and the number of inliers during the iteration process to obtain the optimal spherical model of the left and right femoral heads.

[0061] A random sampling consensus algorithm is introduced into the point cloud data of the 3D femoral head model. A minimum set of randomly selected points is used to estimate the parameters of the left and right femoral head spherical models. This removes potentially irregular regions and noise points from the 3D reconstructed model, thus obtaining the optimal spherical models of the left and right femoral heads. Based on this, least-squares spherical fitting can be further performed using the interior point set determined by RANSAC to refine the estimation of the spherical center position, thereby improving the accuracy and numerical stability of femoral head center localization. The final coordinates of the left and right femoral head spherical centers are used to determine the spatial position and orientation of the two hip axes, serving as key geometric input parameters in the theoretical modeling of pelvic rotational motion and subsequent numerical analysis. Furthermore, the approximate radius of the femoral head can also be obtained.

[0062] S4: In the anatomical reference coordinate system of the anterior pelvic plane, take the center of rotation of the left and right femoral heads as the center of rotation, and the cross-sections where the center of rotation of the left and right femoral heads are located as the initial rotation section planes. Rotate the initial rotation section planes around the X-axis at multiple angles, calculate the intersection line between the 3D model of the pelvis and the rotation section plane, identify the feature points of the outer edge of the acetabulum on both sides in the intersection line, perform least squares plane fitting based on the feature points of the outer edge of the acetabulum on both sides to obtain the optimal acetabular opening planes on both sides, and take the normal vector of the optimal acetabular opening planes on both sides as the initial axis of the acetabulum on the corresponding side.

[0063] The method for determining the initial axis of the pelvis and acetabulum in this invention is a simulated rotational tomography method. Specifically, taking any cross-section of the left acetabulum as an example, the steps for geometric analysis of the point set of this cross-section are as follows:

[0064] First, the filtering range is set with the rotation center as the center and an approximate radius of 1.2 times the femoral head as the radius. Points within the range are considered as the acetabular region point set.

[0065] Then, the set of points in the acetabular region is divided into upper and lower parts. The most prominent point in the lower part, i.e. the point with the smallest x-coordinate value, can be considered as the edge point of the acetabulum on that cross section.

[0066] For the left acetabulum, the cross-sectional point set can be axially symmetric along the left and right axes of symmetry, or the search for the point with the smallest x-coordinate value can be changed to the point with the largest x-coordinate value.

[0067] Subsequently, the cross section is rotated around the X-axis by a series of angles, and the cross section of the pelvis and the plane generated after rotation is calculated and analyzed. Since the geometry of the acetabulum is approximately that of a spherical shell, the images before and after rotation have similar geometry. The same geometric feature algorithm can stably obtain a series of landmark points on the outer edge of the acetabulum.

[0068] Specifically, a step size of 10° can be used. To rotate within the range of rotation, for each acetabular region, the resulting outer edge points of the acetabulum are set together, and the Singular Value Decomposition (SVD) method is used to fit the optimal plane in the least squares sense. This plane can be regarded as an approximate geometric expression of the acetabular opening, and its normal vector is defined as the acetabular axis of the corresponding side of the pelvis.

[0069] This invention automatically extracts feature points on the outer edge of the acetabulum using a simulated rotational tomography method and calculates the acetabular opening direction using plane fitting, thereby automatically determining the acetabular axis. Compared to methods relying on manual selection of edge points, this method effectively reduces errors caused by human operation and improves the stability and repeatability of measurement results. Furthermore, this invention establishes a continuous functional relationship between the pelvic tilt angle and the acetabular anteversion and abduction angles, realizing the transformation from discrete position measurement to continuous posture modeling, and providing a new quantitative description method for acetabular spatial orientation analysis.

[0070] S5: Construct a rigid body motion model of the pelvis and acetabulum rotating continuously around the two hip axes. Based on the rigid body motion model, calculate the changes in the direction of the acetabular axis and the corresponding acetabular anteversion angle and acetabular abduction angle under different pelvic tilt postures.

[0071] Specifically, the change in the acetabular axis direction under different pelvic tilt postures can be calculated according to equation (1), the acetabular anteversion angle can be calculated according to equation (2), and the acetabular abduction angle can be calculated according to equation (3):

[0072] (1);

[0073] (2);

[0074] (3);

[0075] in: This indicates the change in the direction of the acetabular axis under different pelvic tilt postures. This represents the initial axis direction vector of the pelvis and acetabulum. Indicates the pelvic tilt angle. Represents the direction vector of the two hip axes. Indicates the acetabular anteversion angle. This indicates the change in the direction of the acetabular axis under different pelvic tilt positions. Components in the axial direction, This indicates the change in the direction of the acetabular axis under different pelvic tilt positions. Components in the axial direction, Indicates the acetabular abduction angle. This represents the component of the change in the acetabular axis direction in the y-axis direction under different pelvic tilt postures.

[0076] Specifically, the geometric definitions of the acetabular anteversion angle AA and acetabular abduction angle AI are shown in the diagram below. Figure 4 As shown.

[0077] This invention constructs a rigid body motion model of the pelvis rotating continuously around two hip axes, enabling the calculation of the acetabular spatial orientation under continuous pelvic tilt postures. Compared to traditional methods that only perform static measurements in a single body position, this invention can systematically describe the overall change law of the acetabular spatial orientation during pelvic posture changes.

[0078] S6: Establish the acetabular abduction / anteversion curve under pelvic tilt based on the functional relationship between the acetabular anteversion angle, acetabular abduction angle, and pelvic tilt angle, complete the acetabular morphology assessment, and then find the most suitable acetabular prosthesis installation angle for the patient based on the acetabular morphology assessment results.

[0079] Specifically, a schematic diagram of the acetabular abduction angle / anteversion angle curve under pelvic tilt is shown below. Figure 5 As shown. Figure 5 Showing posterior pelvic tilt To lean forward The diagram illustrates the changes of AI and AA with PT during the process. The red curve represents the change of AI with PT, and the blue curve represents the change of AA with PT. Points A and B are the start and end points of the AI ​​curve, M is the start point of the linear interval of AI, points C and D are the start and end points of the AA curve, and point N is the end point of the linear growth interval of AA. The dashed lines represent the straight lines fitted to AI and AA during linear growth, and their slopes are denoted as... , , deg represents degree.

[0080] Specifically, the method for finding the most suitable acetabular prosthesis installation angle for the patient based on the acetabular morphology assessment results is as follows:

[0081] After pelvic fixation is completed during the actual surgery, the intraoperative pelvic tilt angle is measured. The acetabular abduction / anteversion angle curve under pelvic tilt is used to find the acetabular anteversion angle corresponding to the intraoperative pelvic tilt angle. The acetabular prosthesis is implanted with the acetabular anteversion angle corresponding to the intraoperative pelvic tilt angle as the most suitable acetabular prosthesis installation angle for the patient.

[0082] In an optimized approach, the patient can be placed in a lateral decubitus position via a posterolateral approach during surgery, and the pelvis can be fixed. The intraoperative pelvic tilt angle can be measured using a navigation system or a position measurement device.

[0083] Previous studies based on imaging and functional posture analysis have shown that pelvic tilt angle (PT) in different body positions is mainly distributed within a limited range and roughly corresponds to different functional states. This study selected PT as the main research range, in which... This refers to the tilt range for everyday functional postures. This represents the theoretically extreme attitude range, used only to observe the nonlinear behavior of the model.

[0084] Clinically, to reduce the risk of acetabular prosthesis dislocation, preoperative planning is usually based on the combined anteversion theory. The combined anteversion satisfies the following relationship:

[0085] Combined anteversion angle = femoral anteversion angle + acetabular anteversion angle;

[0086] Clinical studies generally suggest that maintaining the combined anteversion angle at approximately 40° improves joint stability. The femoral prosthesis abduction angle is typically fixed, and preoperative planning primarily focuses on the femoral anteversion angle. However, due to the anatomical limitations of the femoral medullary canal, the adjustment space for the anteversion angle after femoral prosthesis implantation is limited, and it tends to be relatively fixed. In contrast, the acetabular prosthesis, with its hemispherical structure, offers greater freedom of angle adjustment on the acetabular bed; therefore, the acetabular side becomes the primary target for individualized preoperative control.

[0087] Taking the lateral approach to total hip arthroplasty as an example, after completing the measurement of the patient's femoral anteversion angle and the planning of the femoral prosthesis, if the measured femoral anteversion angle is 25°, and with a combined anteversion angle of 40° as the target, the target acetabular anteversion angle of the patient in the functional position can be calculated in reverse to be approximately 15°.

[0088] Subsequently, by examining the acetabular abduction / anteversion curve under pelvic tilt, it was found that when the acetabular anteversion angle was 15°, the corresponding pelvic tilt angle was approximately 2°, which is consistent with the pelvic posture of a patient without severe pelvic deformity in a standing position (it is generally believed that the pelvic tilt range in a standing position is -10° to 10°). Therefore, 15° can be determined as the target acetabular prosthesis anteversion angle for this patient.

[0089] In actual surgery, after pelvic fixation using a posterolateral approach in the lateral decubitus position, the patient's intraoperative pelvic tilt angle can be measured using a navigation system or position measurement device. If the intraoperative pelvic tilt angle is approximately 50°, it is necessary to convert the change in anteversion angle caused by the difference in pelvic tilt between the intraoperative and functional positions by referring to the acetabular abduction / anteversion angle curve under pelvic tilt. According to the curve conversion results, in order to achieve the target acetabular anteversion angle of 15° in the functional position postoperatively, the acetabular prosthesis should be implanted intraoperatively at an anteversion angle of approximately 36°.

[0090] Therefore, the method provided by this invention realizes the reverse mapping from "functional position target angle" to "actual implantation angle during surgery", which can provide quantitative basis for individualized precise implantation of acetabular prostheses and help reduce the risk of postoperative dislocation.

[0091] A system for evaluating acetabular morphology under continuous pelvic tilt postures, used to perform a method for evaluating acetabular morphology under continuous pelvic tilt postures as described in any of the above, comprising a pelvic 3D model and femur 3D model construction module, a pelvic anterior plane anatomical reference coordinate system establishment module, a dual hip axis acquisition module, a pelvic acetabular initial axis determination module, an acetabular anteversion angle and acetabular abduction angle determination module, and an acetabular morphology evaluation module.

[0092] The pelvic 3D model and femur 3D model construction module is used to acquire the patient's pelvic CT image data and perform 3D reconstruction to obtain the pelvic 3D model and femur 3D model.

[0093] The pelvic anterior plane anatomical reference coordinate system establishment module is used to perform spatial standardization processing on the point cloud data of the pelvic three-dimensional model and establish the pelvic anterior plane anatomical reference coordinate system.

[0094] The dual hip axis acquisition module is used to independently perform spherical model fitting on the point cloud data of the femoral 3D model to obtain the optimal spherical model of the left and right femoral heads. The least squares spherical fitting is performed on the point set in the optimal spherical model of the left and right femoral heads to obtain the refined estimated position of the center of the left femoral head and the center of the right femoral head. The dual hip axis is obtained by connecting the center of the left femoral head and the center of the right femoral head.

[0095] The pelvic acetabular initial axis determination module is used to determine the initial axis of the pelvis and acetabulum in the anatomical reference coordinate system of the anterior pelvic plane, with the center of rotation of the left and right femoral heads as the rotation centers, and the cross-sections containing the center of rotation of the left and right femoral heads as the initial rotation cross-section planes. The initial rotation cross-section planes are rotated around the X-axis at multiple angles, and the intersection line between the 3D model of the pelvis and the rotation cross-section plane is calculated. The feature points of the outer edge of the acetabulum on the left and right sides are identified in the intersection line. Based on the feature points of the outer edge of the acetabulum on the left and right sides, least squares plane fitting is performed to obtain the optimal acetabular opening planes on the left and right sides. The normal vector of the optimal acetabular opening planes on the left and right sides is taken as the initial axis of the pelvis and acetabulum on the corresponding side.

[0096] The module for determining the acetabular anteversion angle and acetabular abduction angle is used to construct a rigid body motion model of the initial axis of the pelvis and acetabulum rotating continuously around the two hip axes. Based on the rigid body motion model, the module calculates the changes in the direction of the acetabular axis and the corresponding acetabular anteversion angle and acetabular abduction angle under different tilt postures of the pelvis.

[0097] The acetabular morphology assessment is used to establish a acetabular abduction / anteversion curve under pelvic tilt based on the functional relationship between the acetabular anteversion angle, acetabular abduction angle, and pelvic tilt angle. Based on the acetabular abduction / anteversion curve under pelvic tilt, the acetabular morphology is assessed, and the most suitable acetabular prosthesis installation angle for the patient is found according to the assessment results.

[0098] In summary, the present invention provides a method and system for assessing acetabular morphology under continuous pelvic tilt posture. First, CT data of the patient's pelvis is acquired and three-dimensionally reconstructed to establish an anterior pelvic anatomical reference coordinate system. The center points of both femoral heads are automatically identified, and dual hip axes are constructed. Under the anterior pelvic anatomical reference coordinate system, multi-angle cross-sectional analysis of the acetabular region is performed using simulated rotational tomography. Feature point sets of the acetabular outer edge are extracted and planar fitted to obtain the acetabular opening direction vector as the initial acetabular axis. Furthermore, the pelvis is treated as a rigid structure, and a motion model of continuous pelvic rotation around the dual hip axes is constructed. The corresponding acetabular anteversion and abduction angles are calculated based on the direction of the rotated acetabular axis. Based on the functional relationship between the angle parameters and the pelvic tilt angle, an individualized acetabular abduction / anteversion angle curve under pelvic tilt is established, enabling dynamic assessment of acetabular spatial orientation under continuous pelvic posture changes. Thus, based on the dynamic assessment results of the acetabular morphology, the most suitable acetabular prosthesis installation angle for the patient is found for implantation. This invention features a high degree of automation and good stability, enabling continuous dynamic analysis of acetabular spatial orientation and providing quantitative basis for individualized prosthesis placement in total hip arthroplasty.

[0099] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for evaluating acetabular morphology under continuous pelvic tilt postures, characterized in that: Includes the following steps: S1: Acquire CT image data of the patient's pelvis and perform three-dimensional reconstruction to obtain a three-dimensional model of the pelvis and a three-dimensional model of the femur. S2: Perform spatial standardization on the point cloud data of the 3D model of the pelvis to establish an anterior pelvic anatomical reference coordinate system; S3: Perform spherical model fitting independently on the point cloud data of the femoral 3D model to obtain the optimal spherical model of the left and right femoral heads. Perform least squares spherical fitting on the point set in the optimal spherical model of the left and right femoral heads to obtain the refined estimated position of the center of the left and right femoral heads. Connect the center of the left and right femoral heads to obtain the dual hip axis. S4: In the anatomical reference coordinate system of the anterior pelvic plane, take the center of rotation of the left and right femoral heads as the center of rotation, and the cross-sections where the center of rotation of the left and right femoral heads are located as the initial rotation section planes. Rotate the initial rotation section planes around the X-axis at multiple angles, calculate the intersection line between the 3D model of the pelvis and the rotation section plane, identify the feature points of the outer edge of the acetabulum on both sides in the intersection line, perform least squares plane fitting based on the feature points of the outer edge of the acetabulum on both sides to obtain the optimal acetabular opening planes on both sides, and take the normal vector of the optimal acetabular opening planes on both sides as the initial axis of the acetabulum on the corresponding side. S5: Construct a rigid body motion model of the pelvis and acetabulum rotating continuously around the two hip axes. Based on the rigid body motion model, calculate the changes in the direction of the acetabular axis and the corresponding acetabular anteversion angle and acetabular abduction angle under different pelvic tilt postures. S6: Establish the acetabular abduction / anteversion curve under pelvic tilt based on the functional relationship between acetabular anteversion angle, acetabular abduction angle and pelvic tilt angle, complete the acetabular morphology assessment, and find the most suitable acetabular prosthesis installation angle for the patient based on the acetabular morphology assessment results.

2. The method for evaluating acetabular morphology under continuous pelvic tilt posture according to claim 1, characterized in that: The method for performing three-dimensional reconstruction of the patient's pelvic CT image data in step S1 is as follows: export the patient's pelvic CT image data in DICOM format, import it into Mimics software for bone segmentation and reconstruction, and save the pelvic data after bone segmentation and reconstruction as a PELVIS.stl file, and save the bilateral pelvic data after bone segmentation and reconstruction as a FEMUR.stl file.

3. The method for evaluating acetabular morphology under continuous pelvic tilt posture according to claim 2, characterized in that: In step S2, the point cloud data of the pelvic 3D model is spatially standardized to establish the pelvic anterior plane anatomical reference coordinate system, as follows: S211: Read the PELVIS.stl file to obtain the point cloud data and topological relationships that constitute the pelvis; S212: Translate the point cloud that constitutes the pelvis to its geometric centroid, perform principal component analysis based on the point cloud covariance matrix, and determine the principal axis direction so that the main geometric directions of the pelvis are initially aligned under a unified coordinate framework. S213: The iterative tangent plane method is used to automatically identify key anatomical landmarks of the pelvis and to construct an anterior pelvic anatomical reference coordinate system based on these landmarks.

4. The method for evaluating acetabular morphology under continuous pelvic tilt posture according to claim 3, characterized in that: In step S3, the method for independently performing spherical model fitting on the point cloud data of the femoral 3D model to obtain the optimal spherical model of the left and right femoral heads is as follows: read the FEMUR.stl file, introduce the random sampling consensus algorithm into the point cloud data of the femoral 3D model, randomly select the minimum point set to estimate the parameters of the spherical model of the left and right femoral heads, and comprehensively evaluate the fitting residuals and the number of inliers during the iteration process to obtain the optimal spherical model of the left and right femoral heads.

5. The method for evaluating acetabular morphology under continuous pelvic tilt posture according to claim 1, characterized in that: In step 5, the change in the acetabular axis direction under different pelvic tilt postures is calculated according to equation (1), the acetabular anteversion angle is calculated according to equation (2), and the acetabular abduction angle is calculated according to equation (3). （1）； （2）； （3）； in: This indicates the change in the direction of the acetabular axis under different pelvic tilt postures. This represents the initial axis direction vector of the pelvis and acetabulum. Indicates the pelvic tilt angle. Represents the direction vector of the two hip axes. Indicates the acetabular anteversion angle. This indicates the change in the direction of the acetabular axis under different pelvic tilt positions. Components in the axial direction, This indicates the change in the direction of the acetabular axis under different pelvic tilt positions. Components in the axial direction, Indicates the acetabular abduction angle. This represents the component of the change in the acetabular axis direction in the y-axis direction under different pelvic tilt postures.

6. The method for evaluating acetabular morphology under continuous pelvic tilt posture according to claim 1, characterized in that: The method for finding the most suitable acetabular prosthesis installation angle for the patient based on the acetabular morphology assessment results in step S6 is as follows: After pelvic fixation is completed during the actual surgery, the intraoperative pelvic tilt angle is measured. The acetabular abduction / anteversion angle curve under pelvic tilt is used to find the acetabular anteversion angle corresponding to the intraoperative pelvic tilt angle. The acetabular prosthesis is installed at the acetabular anteversion angle corresponding to the intraoperative pelvic tilt angle as the most suitable acetabular prosthesis installation angle for the patient.

7. The method for evaluating acetabular morphology under continuous pelvic tilt posture according to claim 6, characterized in that: In actual surgery, a posterolateral approach is used to position the patient in the lateral decubitus position and fix the pelvis.

8. The method for evaluating acetabular morphology under continuous pelvic tilt posture according to claim 6, characterized in that: The intraoperative pelvic tilt angle is measured using a navigation system or a body position measurement device.

9. A system for assessing acetabular morphology under continuous pelvic tilt postures, used to perform a method for assessing acetabular morphology under continuous pelvic tilt postures as described in any one of claims 1 to 8, characterized in that: It includes modules for constructing 3D models of the pelvis and femur, establishing an anatomical reference coordinate system for the anterior plane of the pelvis, acquiring dual hip axes, determining the initial axis of the pelvis and acetabulum, determining the acetabular anteversion angle and acetabular abduction angle, and assessing the acetabular morphology. The pelvic 3D model and femur 3D model construction module is used to acquire the patient's pelvic CT image data and perform 3D reconstruction to obtain the pelvic 3D model and femur 3D model. The pelvic anterior plane anatomical reference coordinate system establishment module is used to perform spatial standardization processing on the point cloud data of the pelvic three-dimensional model and establish the pelvic anterior plane anatomical reference coordinate system. The dual hip axis acquisition module is used to independently perform spherical model fitting on the point cloud data of the femoral 3D model to obtain the optimal spherical model of the left and right femoral heads. The least squares spherical fitting is performed on the point set in the optimal spherical model of the left and right femoral heads to obtain the refined estimated position of the center of the left femoral head and the center of the right femoral head. The dual hip axis is obtained by connecting the center of the left femoral head and the center of the right femoral head. The pelvic acetabular initial axis determination module is used to determine the initial axis of the pelvis and acetabulum in the anatomical reference coordinate system of the anterior pelvic plane, with the center of rotation of the left and right femoral heads as the rotation centers, and the cross-sections containing the center of rotation of the left and right femoral heads as the initial rotation cross-section planes. The initial rotation cross-section planes are rotated around the X-axis at multiple angles, and the intersection line between the 3D model of the pelvis and the rotation cross-section plane is calculated. The feature points of the outer edge of the acetabulum on the left and right sides are identified in the intersection line. Based on the feature points of the outer edge of the acetabulum on the left and right sides, least squares plane fitting is performed to obtain the optimal acetabular opening planes on the left and right sides. The normal vector of the optimal acetabular opening planes on the left and right sides is taken as the initial axis of the pelvis and acetabulum on the corresponding side. The module for determining the acetabular anteversion angle and acetabular abduction angle is used to construct a rigid body motion model of the initial axis of the pelvis and acetabulum rotating continuously around the two hip axes. Based on the rigid body motion model, the module calculates the changes in the direction of the acetabular axis and the corresponding acetabular anteversion angle and acetabular abduction angle under different tilt postures of the pelvis. The acetabular morphology assessment is used to establish a curve of acetabular abduction / anteversion angle under pelvic tilt based on the functional relationship between acetabular anteversion angle, acetabular abduction angle and pelvic tilt angle, thereby completing the acetabular morphology assessment and finding the most suitable acetabular prosthesis installation angle for the patient based on the acetabular morphology assessment.

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