A method for detecting range of motion in hip replacement surgery

Abstract

The present invention provides a range of motion detection method for hip replacement surgery, comprising the following steps: obtaining the STL data of the femoral stem and acetabular cup after alignment from the preoperative plan as the object to be detected; obtaining the rotation center of the femoral head from the preoperative plan as the center, segmenting the STL data of the femoral stem and acetabular cup that may collide, and removing the remaining parts; detecting the range of motion of the femur: constructing a coordinate system with flexion and extension as the x-axis and abduction and adduction as the y-axis, with the coordinate origin being the current position of the object to be detected; then, based on the concept of breadth traversal, starting from the coordinate origin, traversing all coordinate points and detecting whether they collide, thereby obtaining the specific range of motion of the patient's femur; and sorting the boundary queue and drawing it. This detection method improves the strategy for detecting the range of motion of the femur, reducing the time required to update the femoral range of motion boundary after data replacement; and drawing the collision area when the current femoral range of motion collides.

Description

Technical Field

[0001] The present invention relates to the technical field of rigid object collision detection, and in particular to a method for detecting range of motion in hip replacement surgery. Background Art

[0002] Before the operation, the patient's hip joint and femur model are reconstructed based on the CT images. According to the given planning plan, a specific model of acetabular cup is placed in the patient's acetabulum, and the femoral stem is placed inside the femur, and they are adjusted to the angle given in the planning plan.

[0003] Then, the position of the acetabular cup is fixed, and various combination angles of the femoral stem within the range of 150 degrees of flexion, 50 degrees of extension, 40 degrees of adduction, and 50 degrees of abduction are simulated to detect whether the current femoral stem and acetabular cup collide with each other. The non-collision area between the femoral stem and the acetabular cup, that is, the movable range of the patient's femur, is drawn on the flexion, extension, adduction and abduction range chart.

[0004] A commonly used collision detection method currently uses a hierarchical bounding box (OBB) based on oriented bounding boxes. The basic idea is to replace the complex, difficult-to-detect geometric objects with a relatively simple geometric model containing the objects to be detected. After a rough collision check of their bounding boxes, if their bounding boxes intersect, a collision is likely between the original objects. Further bounding boxes are constructed and tested. If the bounding boxes do not intersect, there is no collision between the objects to be detected. This method, based on a hierarchical bounding box (OBB), has a time complexity for collision detection that depends on the number of triangles in the objects to be detected. Therefore, a single collision check on a detailed femoral stem and acetabular cup model takes too long.

[0005] Another collision detection method uses points as detection elements, individually checking all points within one of the objects to be detected. This method involves shooting two rays from random directions at that point and determining the number of triangles the rays intersect with the other object. If each ray intersects with exactly one triangle, the point is inside the object being detected, indicating a collision between the two objects. This method, based on point detection elements, cannot quickly determine that a collision has not occurred when the two objects are far apart. Furthermore, when only determining whether a collision has occurred is required, its time complexity is significantly higher than that of methods based on directional bounding boxes.

[0006] In addition, collision detection is performed after applying all possible combinations of flexion, extension, adduction and abduction within the medical range. The number of collision detections required is too many and the corresponding detection time is too long. Therefore, it takes too long to draw the range of motion of a patient's femur. In the surgical plan preview, each replacement of the acetabular cup or femoral stem requires redrawing the range of motion, so this method needs to be improved. Summary of the Invention

[0007] The purpose of the present invention is to provide a range of motion detection method for hip replacement surgery, which improves the strategy for femoral range of motion detection and reduces the time required to update the femoral range of motion boundary after data replacement; when a collision occurs in the current femur, the collision area is drawn.

[0008] The present invention discloses a method for detecting range of motion in hip replacement surgery, comprising the following steps:

[0009] S100, data preparation for the object to be detected: obtaining the STL data of the femoral stem and acetabular cup after the orthodontic treatment from the preoperative plan as the object to be detected; obtaining the rotation center of the femoral head from the preoperative plan as the center, segmenting the STL data of the femoral stem and acetabular cup that may collide, and removing the remaining parts; performing facet thinning on the selected STL data to reduce the number of triangular facets of the object to be detected;

[0010] S200, Femoral Range of Motion Testing: First, a coordinate system is constructed with flexion and extension as the x-axis and adduction and abduction as the y-axis. The maximum possible range of flexion and extension, adduction and abduction in medicine is used as the boundaries of the coordinate axes. Each coordinate point in this coordinate system represents a possible position of the femoral stem. The coordinate origin is the current position of the object to be tested without any rotation applied, and it can be confirmed that it is in a non-collision state.

[0011] Then, based on the breadth traversal idea, starting from the coordinate origin, traversing all coordinate points and checking whether they collide, the specific range of motion of the patient's femur can be obtained. An access bit is set for each coordinate point. Before exploration, its access bit is judged. If it is true, it means that it has been explored and the point is directly discarded; if not, the point is explored. When the exploration reaches a boundary point, it is directly added to the boundary queue as the boundary point of the range of motion.

[0012] S300, sorting and drawing the boundary queue: rearranging the boundary queues that were previously queued in disorder according to the angles between them and the coordinate origin, and finally obtaining the boundary curve of the femoral range of motion by fitting the ordered points through B-spline;

[0013] S400, draw the collision area of ​​the current collision: calculate the flexion, extension, adduction and abduction set by the current surgeon and apply them to the femur, and update the corresponding directional bounding box for it. Then, use the hierarchical bounding box based on the directional bounding box OBB to obtain all the collision points between the objects to be detected, and obtain the indicator line of the area surrounding the collision through B-spline fitting.

[0014] Preferably, the traversal method in step S200 comprises the following steps: based on the current coordinate P, the exploration direction is divided into four directions: up, down, left, and right. The exploration step is a given n, which is represented in the coordinate system as the positive y-axis direction, the negative y-axis direction, the positive x-axis direction, and the negative x-axis direction, obtaining P1, P2, P3, and P4. The four points are explored sequentially: assuming the current detection point is PX, a collision check is performed on it. If there is no collision, PX is added to the queue to be expanded. If there is a collision, P and PX are used as the left and right starting points of the dichotomy. If two adjacent coordinate points are found with different collision conditions, the non-collision point is considered as an active range boundary and stored in the boundary queue. PX is discarded. After all four points have been explored, P is removed from the exploration queue. When the exploration queue is empty, the traversal ends.

[0015] The innovation of the present invention is:

[0016] 1. Adjust the bounding box hierarchy based on the oriented bounding box (OBB). When the pose matrix of the object to be detected is new, avoid regenerating the OBB. Instead, apply the pose matrix to the OBB synchronously, which reduces the time required for a collision detection when the objects to be detected are the same but have different poses.

[0017] 2. A new method for detecting the range of motion of the femur is proposed. First, a two-dimensional coordinate system is established for the angle corresponding to the range of motion of the femur. Based on the idea of ​​breadth traversal, a four-field search is performed starting from the coordinate origin, and finally the boundary from the non-collision state to the collision state is obtained, which is the boundary of the range of motion of the femur. This method greatly reduces the number of collision detections required to draw the range of motion of the femur, and reduces the specific time required to less than 1s. When the surgeon replaces the acetabular cup or femoral stem, the object to be detected changes, and the update of the femoral range of motion responds more quickly, which optimizes the user experience of the surgeon.

[0018] The beneficial effect of the hip registration method for hip replacement surgery disclosed in the present invention is: a new method for detecting the range of motion of the femur is proposed. First, a two-dimensional coordinate system is established for the angle corresponding to the range of motion of the femur. Based on the idea of ​​breadth traversal, a four-field search is performed starting from the coordinate origin, and finally the boundary from the non-collision state to the collision state is obtained, which is the boundary of the range of motion of the femur. This method greatly reduces the number of collision detections required to draw the range of motion of the femur, and reduces the specific time required to less than 1s. When the surgeon replaces the acetabular cup or femoral stem, the object to be detected changes, and the update of the femoral range of motion responds more quickly, which optimizes the user experience of the surgeon. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a flow chart of drawing the femoral activity boundary of the present invention. DETAILED DESCRIPTION

[0020] The present invention will be further described and explained below in conjunction with specific embodiments and accompanying drawings:

[0021] Please refer to Figure 1 In order to explain the technical details included in the steps in more detail, the present invention will be further explained with reference to the accompanying drawings.

[0022] A method for detecting range of motion in hip replacement surgery comprises the following steps:

[0023] S100, data preparation for the object to be detected: obtaining the STL data of the femoral stem and acetabular cup after the orthodontic treatment from the preoperative plan as the object to be detected; obtaining the rotation center of the femoral head from the preoperative plan as the center, segmenting the STL data of the femoral stem and acetabular cup that may collide, and removing the remaining parts; performing facet thinning on the selected STL data to reduce the number of triangular facets of the object to be detected;

[0024] S200, Femoral Range of Motion Testing: First, a coordinate system is constructed with flexion and extension as the x-axis and adduction and abduction as the y-axis. The maximum possible range of flexion and extension, adduction and abduction in medicine is used as the boundaries of the coordinate axes. Each coordinate point in this coordinate system represents a possible position of the femoral stem. The coordinate origin is the current position of the object to be tested without any rotation applied, and it can be confirmed that it is in a non-collision state.

[0025] Then, based on the breadth traversal idea, starting from the coordinate origin, traversing all coordinate points and checking whether they collide, the specific range of motion of the patient's femur can be obtained. An access bit is set for each coordinate point. Before exploration, its access bit is judged. If it is true, it means that it has been explored and the point is directly discarded; if not, the point is explored. When the exploration reaches a boundary point, it is directly added to the boundary queue as the boundary point of the range of motion.

[0026] S300, sorting and drawing the boundary queue: rearranging the boundary queues that were previously queued in disorder according to the angles between them and the coordinate origin, and finally obtaining the boundary curve of the femoral range of motion by fitting the ordered points through B-spline;

[0027] S400, draw the collision area of ​​the current collision: calculate the anteversion and abduction angle set by the current surgeon and apply it to the femur, and update the corresponding directional bounding box for it. Then, use the hierarchical bounding box based on the directional bounding box OBB to obtain all the collision points between the objects to be detected, and obtain the indicator line of the area surrounding the collision through B-spline fitting.

[0028] The traversal method in step S200 specifically follows the following steps: Based on the current coordinate P, the exploration direction is divided into four directions: up, down, left, and right. The exploration step is a given n, which in the coordinate system represents the positive y-axis, negative y-axis, positive x-axis, and negative x-axis directions, resulting in P1, P2, P3, and P4. These four points are explored sequentially: assuming the current detection point is PX, a collision check is performed on it. If there is no collision, PX is added to the queue to be expanded. If there is a collision, P and PX are used as the left and right starting points for the dichotomy. If two adjacent coordinate points are found with different collision conditions, the non-collision point is considered as an active range boundary and stored in the boundary queue. PX is discarded. After all four points have been explored, P is removed from the exploration queue. When the exploration queue is empty, the traversal ends.

[0029] The innovative features of the present invention's range of motion detection method for hip replacement surgery are:

[0030] 1. Adjust the bounding box hierarchy based on the oriented bounding box (OBB). When the pose matrix of the object to be detected is new, avoid regenerating the OBB. Instead, apply the pose matrix to the OBB synchronously, which reduces the time required for a collision detection when the objects to be detected are the same but have different poses.

[0031] 2. A new method for detecting the range of motion of the femur is proposed. First, a two-dimensional coordinate system is established for the angle corresponding to the range of motion of the femur. Based on the idea of ​​breadth traversal, a four-field search is performed starting from the coordinate origin, and finally the boundary from the non-collision state to the collision state is obtained, which is the boundary of the range of motion of the femur. This method greatly reduces the number of collision detections required to draw the range of motion of the femur, and reduces the specific time required to less than 1s. When the surgeon replaces the acetabular cup or femoral stem, the object to be detected changes, and the update of the femoral range of motion responds more quickly, which optimizes the user experience of the surgeon.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for detecting the range of motion of the femur in hip replacement surgery, characterized in that: The following steps are involved: S100, data preparation of the object to be detected: obtaining the stl data of the femoral stem and acetabular cup after correction from the preoperative plan as the object to be detected; The rotation center of the femoral head is obtained from the preoperative planning as the center, and the STL data of the femoral stem and acetabular cup that may collide are segmented, and the remaining parts are removed; the selected STL data is sparsely sliced ​​to reduce the number of triangular facets of the object to be detected; S200, Femoral range of motion detection: First, a coordinate system is constructed with flexion-extension range of motion as the x-axis and abduction-adduction range of motion as the y-axis. The maximum possible ranges of flexion-extension and abduction-adduction range of motion in medicine are used as the boundaries of the coordinate axes. Each coordinate point in this coordinate system represents a possible position of the femoral stem. The coordinate origin is the current position of the object to be detected without any rotation applied, and it can be confirmed that it is in a non-collision state. Then, based on the breadth traversal idea, starting from the coordinate origin, traversing all coordinate points and checking whether they collide, the specific range of motion of the patient's femur can be obtained. An access bit is set for each coordinate point. Before exploration, its access bit is judged. If it is true, it means that it has been explored and the point is directly discarded; if not, the point is explored. When the exploration reaches a boundary point, it is directly added to the boundary queue as the boundary point of the range of motion. S300, sorting and drawing the boundary queue: rearranging the boundary queues that were previously queued in disorder according to the angles between them and the coordinate origin, and finally obtaining the boundary curve of the femoral range of motion by fitting the ordered points through B-spline; S400, draw the collision area of ​​the current collision: calculate the flexion, extension, abduction and adduction range of motion set by the current surgeon and apply it to the femur, and update the corresponding directional bounding box for it, then use the hierarchical bounding box based on the directional bounding box OBB to obtain all the collision points between the objects to be detected, and obtain the indicator line of the area surrounding the collision through B-spline fitting; when adjusting the hierarchical bounding box based on the directional bounding box, when the new posture matrix of the object to be detected is used, the posture matrix is ​​synchronously applied to the hierarchical bounding box based on the directional bounding box.

2. A method for detecting the range of motion of the femur in hip replacement surgery according to claim 1, characterized in that: The specific steps of the traversal method in step S200 are as follows: based on the current coordinate P, the exploration direction is divided into four directions: up, down, left and right, and the exploration step size is a given n, which is expressed in the coordinate system as the positive direction of the y-axis, the negative direction of the y-axis, the positive direction of the x-axis, and the negative direction of the x-axis, obtaining P1, P2, P3, and P4; exploring the four points in turn: assuming that the current detection point is PX, a collision check is performed on it. If there is no collision, PX is added to the queue to be expanded; if there is a collision, P and PX are used as the left and right starting points of the dichotomy. When two coordinate points are adjacent and the collision situations are different, the non-collision point is used as an activity range boundary and stored in the boundary queue. At the same time, PX is discarded. After all four points are explored, point P is removed from the exploration queue; when the exploration queue is empty, the traversal ends.

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