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CN-115919517-B - Bone relative motion measuring method, joint rotation axis acquisition and positioning method

CN115919517BCN 115919517 BCN115919517 BCN 115919517BCN-115919517-B

Abstract

The invention discloses a bone relative motion measuring method, a joint rotation axis acquiring and positioning method, which can effectively improve the effect of knee joint replacement operation, the dissatisfaction rate of knee replacement patients can be effectively reduced by measuring a-MSA or i-MSA preoperatively to determine the position of the rotation axis and then mounting the rotation axis of the prosthesis to the position intraoperatively. The invention is easy to implement and suitable for large-scale popularization.

Inventors

  • ZHENG LIWEN

Assignees

  • 中南大学湘雅二医院

Dates

Publication Date
20260512
Application Date
20220910

Claims (7)

  1. 1. A method for obtaining the most stable rotation axis of an individual, comprising the steps of: step 1, based on a bone relative motion measuring method, obtaining a 6-degree-of-freedom relative motion value of a bone of an individual target joint under different bending angles, wherein the bone relative motion measuring method specifically comprises the following steps: Firstly, performing first imaging on bones before movement based on Magnetic Resonance Imaging (MRI), so as to obtain a first image; Secondly, performing second imaging on the moved bone based on MRI to obtain a second image, and then rotating the second image to enable the imaging direction of the bone in the second image to be the same as that of the bone in the first image, wherein the basis for judging whether the imaging direction is the same is whether a comparison characteristic region frame is consistent or not, the characteristic region frame is formed based on a plurality of characteristic regions in the bone, and the characteristic regions are subcortical blood vessels of the bone; Measuring the angle difference of the second image after rotation and before rotation and the displacement distance between the second image after rotation and the first image, and calculating the relative motion value of bones based on the angle difference and the displacement distance; Step 2, three-dimensional meshing is carried out on bones according to the preset mesh size, and any point is taken out of each mesh to form a candidate point set; Step 3, quantitatively evaluating the stability of each point in the candidate point set in the step 2 by taking the relative motion value obtained in the step 1 as a basis, and selecting the most stable preset number of points as the most stable point group; And 4, finding out a straight line closest to all points in the most stable point group by using a least square method or a gradient descent method, namely, obtaining the individual most stable rotation axis of the individual target joint.
  2. 2. The method of claim 1, wherein in the second step, the feature region frame includes at least two feature regions at different levels in the MRI image, and the interval between the feature regions is not less than a predetermined number of MRI layers, and the size of each feature region does not exceed a predetermined size limit.
  3. 3. The method for obtaining the most stable rotation axis of an individual according to claim 1, wherein in the step 3, the stability of the point is evaluated based on the following method: The method comprises the steps of taking a point with stability to be evaluated as a target point, obtaining position coordinates of the target point under each angle according to bone relative motion values of joints under different angles, calculating average coordinates of the position coordinates, measuring the distance from the average coordinates to each position coordinate, and calculating the mean square error or arithmetic mean value of the distance from the average coordinates to each position coordinate, wherein the larger the mean square error or the arithmetic mean value is, the worse the stability of the target point is, and otherwise, the better the stability is.
  4. 4. The method for obtaining the individual most stable rotation axis according to claim 1, wherein in the step 3, the preset number of points in the most stable point group is determined by: And (2) when the total grids spliced by all the grids in the step (2) are standard bodies, selecting the point with the best stability and preset proportion as the most stable point group, wherein the standard bodies are the smallest cubes which can accommodate all bones at the far ends of bones at the side, close to the head of a human body, of the joints, and when the volumes of the total grids are different from the standard bodies, the preset proportion of the point is selected according to the inverse proportion of the volumes of the total grids and the standard bodies.
  5. 5. A method for obtaining the average most stable rotation axis of a population suitable for knee joints and elbow joints, comprising the steps of: Step 1), acquiring the intercondylar axes, namely TEA, of a tested joint of a plurality of targets; step 2) obtaining individual most stable rotation axes of all the joints tested in step 1) based on an individual most stable rotation axis obtaining method according to any one of claims 1 to 4; Step 3), determining a three-dimensional space coordinate system of the joint, namely, taking a straight line of the TEA as an X axis, drawing an inscribed circle of a femoral/humeral diaphyseal cavity at the near side of the TEA by using a horizontal height of a standard length, and taking a vertical line from a circle center to the X axis as a Z axis, wherein the Y axis direction is vertical to the X axis and the Z axis; Step 4), determining an inner-outer sagittal plane coordinate system, namely, taking a plane which is perpendicular to an X axis and passes through the femur/humerus inner condyle as an inner sagittal plane, taking a plane which is perpendicular to the X axis and passes through the femur/humerus outer condyle as an outer sagittal plane, establishing a two-dimensional coordinate system which is called an inner sagittal plane coordinate system by taking the femur/humerus inner condyle as an origin and taking a Y axis and a Z axis as coordinate axis directions, and establishing a two-dimensional coordinate system which is called an outer sagittal plane coordinate system by taking the femur/humerus outer condyle as an origin and taking the Y axis and the Z axis as coordinate axis directions on the outer sagittal plane; Step 5), an intersection point is formed between the individual most stable rotation axis of each joint to be tested and the inner sagittal plane, a front-back position, namely Y-axis coordinate, of the intersection point in the inner sagittal plane coordinate system is represented by a parameter inner side-front-back M-AP, a near-far position, namely Z-axis coordinate, is represented by a parameter inner side-near-far M-PD, a front-back position, namely Y-axis position, of the intersection point between the individual most stable rotation axis and the outer sagittal plane is represented by a parameter outer side-front-back L-AP, a near-far position, namely Z-axis position, is represented by a parameter outer side-near-far L-PD, and crowd average values of the four parameters are obtained, namely crowd average relative position relation between the individual most stable rotation axis and TEA, so that crowd average most stable rotation axis is obtained.
  6. 6. The method for obtaining the average most stable rotation axis of population according to claim 5, wherein in the step 3), the standard length is TEA medial-lateral condyle distance x a, wherein a is a coefficient, and the value is 0.44-1.0.
  7. 7. A method of positioning a knee joint rotation axis in the real world, comprising the steps of: Step ①, for a target knee joint to be tested, firstly shooting knee joint CT or MRI, acquiring an individual most stable rotation axis based on the individual most stable rotation axis acquisition method according to any one of claims 1 to 4 as a target rotation axis or acquiring a crowd average most stable rotation axis based on the crowd average most stable rotation axis acquisition method according to any one of claims 5 to 6 as a target rotation axis, and then positioning the projection of the target rotation axis in this direction on a horizontal/coronal plane; Step ②, finding a Posterior Condylar Axis (PCA) on the imaging image, and then measuring the distance between the PCA and two intersection points of the horizontal plane projection of the target rotation axis and the inner side and the outer side of the cortical bone to be respectively used as an inner side anterior-posterior distance and an outer side anterior-posterior distance; Step ③, finding a common tangent line of a bone distal boundary on the inner side and the outer side of the femur on the imaging image as a hypocondylar axis, and then measuring the distances between the hypocondylar axis and two intersection points of the coronal plane projection of the target rotation axis and the inner side and the outer side of the cortical bone as an inner side near-far distance and an outer side near-far distance respectively; Step ④, finding out PCA of a real knee joint, finding out parallel lines corresponding to the front inner side front-rear distance of the PCA based on the inner side front-rear distance obtained in step ②, and making a near-far direction straight line as an inner near-far running straight line through the intersection point of the parallel lines and the inner side skeleton surface of the knee joint; the method comprises the steps of obtaining a lateral anterior-posterior distance of a PCA (principal component analysis) in a step ②, finding a parallel line corresponding to the lateral anterior-posterior distance of the PCA on the basis of the lateral anterior-posterior distance obtained in the step ②, making a line in a near-far direction as a lateral near-far running line through an intersection point of the parallel line and the lateral bone surface of the knee joint, finding a hypocondylar axis of a real knee joint, finding parallel lines corresponding to the medial near-far distance and the lateral near-far distance above the hypocondylar axis according to the medial near-far distance and the lateral near-far distance obtained in the step ③, respectively, and making two straight lines in the anterior-posterior direction as medial and lateral anterior-posterior running lines through intersection points of the two parallel lines and the lateral bone surface of the knee joint respectively, wherein the intersection point of the far-near running line and the anterior-posterior running line on the medial side of the knee joint is the point where a target rotation axis penetrates out of the medial bone cortex of the knee joint, and the far-near running line and the lateral running line on the lateral side of the knee joint is the point where the target rotation axis penetrates out of the lateral bone cortex of the knee joint, and the intersection point of the knee joint prosthesis is the installation position of the rotation axis.

Description

Bone relative motion measuring method, joint rotation axis acquisition and positioning method Technical Field The invention relates to the fields of biomechanics and surgery, in particular to a bone relative motion measuring method, a joint rotation axis acquiring and positioning method. Background Total knee arthroplasty (Total knee arthroplast, TKA) is currently performed in a very large number of orthopedic procedures, primarily for the treatment of patients with end-stage knee osteoarthritis (Osteoarthritis, OA). However, according to investigation, 8-25% of patients are currently unsatisfactory for the operation. In order to improve the surgical effect, researchers have conducted many researches for over twenty years, and the knee joint rotation axis is considered as an important factor affecting the surgical effect, and the design and the intraoperative installation of the TKA artificial joint are based on the correct positioning of the knee joint rotation axis. To locate this axis, a well-defined rotation axis of the knee joint needs to be made first. However, if the conventional definition of the rotation axis is directly applied to the application scene of the knee joint, there arises a problem that the definition of the rotation axis is clear for a strict pivot motion because there is an absolute stable rotation axis for the strict pivot motion, but the knee joint motion is mainly pivot motion (flexion-extension motion) and combines various motions of varus-valgus and valgus-varus simultaneously, and the motions also have individual differences. In other words, the movement of the knee joint is complex, there is no absolute stable axis of rotation, so the traditional axis of rotation definition cannot be directly applied to the knee joint. There are many papers currently targeting knee joint rotation axis, but no researchers clearly describe the precise definition of knee joint rotation axis, which results in the problem that the design and installation of artificial joints cannot be accurately adapted to individuals during surgery. Disclosure of Invention The invention provides a bone relative motion measuring method, a joint rotating shaft acquiring and positioning method, and aims to solve the technical problem that the existing joint rotating shaft cannot be positioned accurately, so that the joint replacement operation effect is poor. In order to achieve the technical purpose, the technical scheme of the invention is that, A method for measuring relative motion of bones, comprising the steps of: Firstly, performing first imaging on bones before movement based on Magnetic Resonance Imaging (MRI), so as to obtain a first image; secondly, performing second imaging on the moved bones based on MRI to obtain a second image, and then rotating the second image to enable the imaging direction of the bones in the second image to be the same as that of the bones in the first image, wherein the basis for judging whether the directions are the same is whether a contrast characteristic area frame is consistent or not, the characteristic area frame is formed based on a plurality of characteristic areas in the bones, and the characteristic areas are subcortical vessels of the bones; and thirdly, measuring the angle difference of the second image after rotation and before rotation and the displacement distance between the second image after rotation and the first image, and calculating the relative motion value of the bone based on the angle difference and the displacement distance. In the second step, the characteristic region is a region which is clung to the lower part of the cortical bone and is where a blood vessel intersecting with the cortical bone is located. In the second step, the characteristic region frame comprises at least two characteristic regions positioned at different layers in an MRI image, the interval between the characteristic regions is not smaller than the preset MRI layer number, and the size of each characteristic region is not more than the preset size limit. A method for obtaining an individual most stable rotation axis, comprising the steps of: Step1, based on the method or a traditional measuring method for measuring joint movement based on an imaging technology, obtaining 6-degree-of-freedom relative movement values of bones of individual target joints under different bending angles; Step 2, three-dimensional meshing is carried out on bones according to the preset mesh size, and any point is taken out of each mesh to form a candidate point set; Step 3, quantitatively evaluating the stability of each point in the candidate point set in the step 2 by taking the relative motion value obtained in the step 1 as a basis, and selecting the most stable preset number of points as the most stable point group; And 4, finding out a straight line closest to all points in the most stable point group by using a least square method or a gradient descent method, namely, obtaining the individual