MR scanning and measuring method for realizing two-dimensional and three-dimensional image fitting of distal femur

Abstract

This invention relates to the field of orthopedic qualitative simulation digital research methods, and in particular to an MR scanning and measurement method for fitting two-dimensional and three-dimensional images of the distal femur. The method includes the following steps: S1, scanning a transverse section of the lateral knee joint using a magnetic resonance imaging system, and drawing the clinical condylar axis, surgical condylar axis, and posterior condylar axis on the transverse image; S2, scanning the first set of sagittal and coronal planes based on the clinical condylar axis; S3, scanning the second set of sagittal and coronal planes based on the surgical condylar axis; S4, scanning the third set of sagittal and coronal planes based on the posterior condylar axis; S5, performing three-dimensional stereoscopic measurement of cartilage thickness at key sites in the two-dimensional images from steps S2, S3, and S4. This invention achieves stereoscopic measurement of cartilage thickness at important sites of interest in the distal femur on two-dimensional MR images by accurately locating the scanning direction; contributing a novel qualitative simulation digital research method for femoral prosthesis morphology improvement.

Description

Technical Field

[0001] This invention relates to the field of orthopedic qualitative simulation digital research methods, and in particular to an MR scanning and measurement method for fitting two-dimensional and three-dimensional images of the distal femur. Background Technology

[0002] Total knee arthroplasty (TKA) is an effective treatment for various end-stage knee osteoarthritis. However, despite continuous improvements in TKA prosthesis design, it remains difficult to completely reconstruct the anatomy and function of the natural knee joint. The mismatch between the femoral prosthesis and the distal femur's morphological characteristics (especially the aspect ratio) is a recurring problem encountered during TKA surgery. Orthopedic surgeons often need to make intraoperative compromises based on their experience and habits, altering the natural anatomy of the knee joint to accommodate different prosthesis systems; however, regardless of the compromise chosen, different mechanisms significantly affect postoperative clinical outcomes and patient satisfaction. Therefore, improving femoral prosthesis design to achieve better morphological matching has increasingly become a hot research topic in orthopedics. To improve prosthesis matching, scholars both domestically and internationally have conducted extensive research over the past 20 years, and major TKA prosthesis manufacturers have also launched a series of femoral prostheses with improved aspect ratios based on the aforementioned research results; however, the matching results have not been satisfactory. Currently, various mainstream femoral prosthesis systems (including the aforementioned modified prosthesis systems) can only achieve relatively ideal coronal plane morphological matching in 10%-63% of patients, while the incidence of femoral prosthesis transverse diameter overhang can reach up to 89%, and the incidence of incomplete transverse diameter coverage can reach up to 84%.

[0003] One of the root causes of the failure to improve the aforementioned prosthesis morphology lies in the methodological bottleneck of previous research: the lack of ideal technical means for studying knee joint morphology, resulting in the inability to obtain true anatomical data of the natural knee joint, and the inability to reflect the significant impact of various osteotomy errors that inevitably occur during TKA on the morphology of the distal femoral osteotomy surface. Knee joint morphology research can be achieved through physical or imaging measurements. While physical measurements are more intuitive, the osteotomy surface morphology of both cadaveric specimens and living patients is significantly affected by the surgeon's operating habits, osteotomy errors, and the prosthesis system used; the limited availability of specimens and high costs further reduce the practicality of cadaveric studies. Among imaging methods, traditional two-dimensional imaging techniques (X-rays, 2D CT, or MR) cannot accurately reflect the complex three-dimensional images of the knee joint. Three-dimensional CT can reconstruct the three-dimensional structure of the knee joint and, combined with virtual osteotomy technology, simulate different surgical parameters to comprehensively analyze the morphological characteristics of the osteotomy surface; however, because it cannot display articular cartilage, it can only estimate the virtual osteotomy thickness, and it is difficult to accurately measure the original morphology of the natural knee joint. While 3D MRI theoretically combines the advantages of both MRI cartilage imaging and 3D CT, its low spatial resolution is its main drawback, limiting its clinical application advantages. Therefore, despite its relative ideality, 3D CT is currently not universally recognized as the best method for morphological research. Summary of the Invention

[0004] The purpose of this invention is to provide an MR scanning and measurement method for fitting two-dimensional and three-dimensional images of the distal femur, overcoming the shortcomings of the aforementioned prior art. By accurately positioning the scanning direction, it enables three-dimensional measurement of the cartilage thickness at important sites of interest in the distal femur on a two-dimensional MR image, and accurately fits it into the subsequent three-dimensional CT digital virtual osteotomy and measurement program. This two-dimensional MR scanning and measurement method can also reflect the variation in cartilage thickness corresponding to various possible intraoperative osteotomy operation errors. This method can contribute a qualitative simulation digital research method for the improvement of TKA femoral prosthesis morphology.

[0005] The technical solution adopted by this invention to solve its technical problem is:

[0006] The MR scanning and measurement method for fitting two-dimensional and three-dimensional images of the distal femur includes the following steps:

[0007] S1. Use a magnetic resonance imaging system to scan the transverse section of the lateral knee joint and draw the clinical condylar axis, surgical condylar axis and posterior condylar axis on the transverse image;

[0008] S2. Based on the clinical condylar axis scanning, the first group of sagittal and coronal planes: The coronal plane scanning direction of this group is perpendicular to the transverse plane and parallel to the clinical condylar axis. The sagittal plane scanning direction of this group is both perpendicular to the transverse plane and perpendicular to the clinical condylar axis.

[0009] S3. Based on the surgical condylar axis scanning, the second group of sagittal and coronal planes: The coronal plane scanning direction of this group is perpendicular to the transverse section and parallel to the surgical condylar axis. The sagittal plane scanning direction of this group is perpendicular to both the transverse section and the surgical condylar axis.

[0010] S4. Based on the posterior condylar axis scanning, the third group of sagittal and coronal planes: The coronal plane scanning direction of this group is perpendicular to the transverse section and parallel to the posterior condylar axis, while the sagittal plane scanning direction of this group is perpendicular to both the transverse section and the posterior condylar axis.

[0011] S5. Achieve three-dimensional stereoscopic measurement of cartilage thickness at key sites in the two-dimensional images of steps S2, S3, and S4.

[0012] Furthermore, in step S1, during the cross-sectional image scanning, the scanning direction is perpendicular to the long axis of the tibia on the dual-plane positioning phase, and the scanning range is from the distal end of the femoral condyle to the intersection of the femoral trochlea and the femoral shaft.

[0013] Furthermore, in step S1, a cross-section is selected that can clearly display the three anatomical landmarks: the most prominent point of the lateral epicondyle of the femur, the most prominent point of the medial epicondyle of the femur, and the medial epicondyle fossa. The line connecting the most prominent point of the medial epicondyle and the most prominent point of the lateral epicondyle of the femur is called the clinical condylar axis, the line connecting the medial epicondyle fossa and the most prominent point of the lateral epicondyle of the femur is called the surgical condylar axis, and the line connecting the most prominent points of the medial and lateral posterior condyles is called the posterior condylar axis.

[0014] Furthermore, in step S5, the thickness of the anterior and posterior condylar cartilage at any flexion angle is measured using sagittal images from any group of steps S2, S3, and S4; and the thickness of the medial and lateral distal cartilage at any eversion angle is measured using coronal images from any group of steps S2, S3, and S4.

[0015] Furthermore, during the measurement in step S5, the cartilage thickness is defined as the distance between the upper boundary of the superficial signal band of the articular cartilage and the upper boundary of the subcartilaginous low signal band.

[0016] Furthermore, the scanning slice thickness in the cross-sectional, sagittal, and coronal planes is 0.8-1.2 mm; preferably 1 mm.

[0017] The beneficial effects of this invention are as follows: Compared with the prior art, the MR scanning and measurement method of this invention for achieving two-dimensional and three-dimensional image fitting of the distal femur has the following advantages:

[0018] (1) By accurately positioning the scanning direction, the function of three-dimensional measurement of cartilage thickness at important sites of interest in the distal femur can be realized on a two-dimensional MR image;

[0019] (2) It can achieve accurate fitting between two-dimensional MR and three-dimensional CT;

[0020] (3) It can reflect the variation in cartilage thickness corresponding to the corresponding diameter when there are various possible errors in intraoperative osteotomy.

[0021] (4) This program can break through the methodological bottleneck of previous related studies and contribute a brand-new qualitative simulation digital research method for the improvement of femoral prosthesis morphology. Attached Figure Description

[0022] Figure 1 A schematic diagram of the sagittal and coronal localization phases for determining the MR transverse scanning direction in this invention;

[0023] Figure 2 A schematic diagram of the selected cross-sectional MR image for this invention;

[0024] Figure 3 This is a schematic diagram of the first group of sagittal and coronal planes based on clinical TEA scanning according to the present invention. In the figure, the solid line below the two parallel lines represents the clinical TEA, the dashed line above the line represents the coronal plane scanning direction, and the dashed line perpendicular to the two parallel lines represents the sagittal plane scanning direction.

[0025] Figure 4 This invention is based on surgical TEA scanning of the second group of sagittal and coronal planes. In the figure, among the two parallel lines, the solid line at the bottom represents the surgical TEA, the dashed line at the top represents the coronal plane scanning direction, and the dashed line perpendicular to the two parallel lines represents the sagittal plane scanning direction.

[0026] Figure 5 This invention is based on scanning the third group of sagittal and coronal planes along the posterior condylar axis. In the figure, among the two parallel lines, the solid line below represents the posterior condylar axis, the dashed line above represents the coronal plane scanning direction, and the dashed line perpendicular to the two parallel lines represents the sagittal plane scanning direction.

[0027] Figure 6 To simulate the standard osteotomy procedure of this invention, the thickness of the posteromedial condyle cartilage is measured in a sagittal image based on surgical TEA. The solid lines extending vertically in the large image represent the anatomical axis of the distal femur, and the dashed lines extending horizontally in the large image are perpendicular to the solid lines extending vertically, simulating a 0° flexion osteotomy in the sagittal plane.

[0028] Figure 7 To simulate the standard osteotomy procedure of this invention, the thickness of the distal medial condyle cartilage is measured in a coronal image based on surgical TEA. The solid line extending in the vertical direction in the large image is the anatomical axis of the distal femur. The angle between the dashed line extending in the vertical direction and the solid line extending in the vertical direction in the large image is equal to the eversion angle measured in the CT image, simulating osteotomy perpendicular to the mechanical axis of the femur in the coronal plane. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0030] Example 1: An MR scanning method for fitting two-dimensional and three-dimensional images of the distal femur.

[0031] like Figure 1-5 In the illustrated embodiment, an MR scanning method for fitting two-dimensional and three-dimensional images of the distal femur includes the following steps:

[0032] S1: Cross-sectional image scanning method

[0033] like Figure 1 As shown, a transverse section of the knee joint was scanned using a magnetic resonance imaging (MRI) system. In the dual-plane positioning phase, the scanning direction was perpendicular to the long axis of the tibia; the scanning range extended from the distal femoral condyle to the intersection of the femoral trochlea and femoral shaft. The transverse section was used as a reference to determine the scanning directions in the sagittal and coronal planes. First, a transverse section was selected that clearly displayed the three anatomical landmarks simultaneously: the most prominent point of the lateral epicondyle, the most prominent point of the medial epicondyle, and the medial epicondyle fossa. (See figure...) Figure 2 As shown, the line connecting the most prominent points of the medial epicondyle and the lateral epicondyle of the femur is called the clinical transcondylar axis (Clinical TEA), while the line connecting the fossa of the medial epicondyle and the most prominent point of the lateral epicondyle is called the surgical transcondylar axis (Surgical TEA). The line connecting the most prominent points of the medial and lateral posterior condyles is the posterior condylar axis.

[0034] S2: Based on clinical TEA scans of the first group of sagittal and coronal planes

[0035] like Figure 3 As shown, draw a line connecting the most prominent points of the medial and lateral epicondyles on the selected transverse section S1 (clinical TEA). The coronal scanning direction should be perpendicular to the transverse section and parallel to the clinical TEA; the sagittal scanning direction should be perpendicular to both the transverse section and the clinical TEA.

[0036] S3: Based on surgical TEA scans of the second group of sagittal and coronal planes

[0037] like Figure 4 As shown, draw a line from the most prominent point of the lateral epicondyle to the concave part of the medial epicondyle on the S1 transverse section (surgical TEA). The coronal scanning direction should be perpendicular to the transverse section and parallel to the surgical TEA; while the sagittal scanning direction should be perpendicular to both the transverse section and the surgical TEA.

[0038] S4: Based on the third group of sagittal and coronal planes scanned along the posterior condyle axis.

[0039] like Figure 5As shown, draw the line connecting the most prominent points of the medial and lateral posterior condyles of the femur (posterior condylar axis) on the S1 transverse section. The coronal scanning direction should be perpendicular to the transverse section and parallel to the posterior condylar axis; the sagittal scanning direction should be perpendicular to both the transverse section and the posterior condylar axis.

[0040] S4: Cartilage Stereometry (Achieving three-dimensional stereometry measurement of cartilage thickness at key sites within a two-dimensional image)

[0041] The three sets of coronal and sagittal images above represent two-dimensional cross-sections of three-dimensional stereoscopic images at three different femoral prosthesis external rotation angles. In any of the sagittal images, the thickness of the anterior and posterior condylar cartilages can be measured at any flexion angle (simulating any femoral prosthesis flexion angle). In any of the coronal images, the thickness of the medial and lateral distal cartilages can be measured at any valgus angle (simulating any femoral prosthesis valgus angle). During measurement, cartilage thickness is defined as the distance between the upper boundary of the most superficial signal band of the articular cartilage and the upper boundary of the subchondral low signal band at that location.

[0042] Example 2 illustrates the procedure for measuring the cartilage thickness of the posteromedial condyle and distal medial condyle using a simulated standard osteotomy procedure as an example.

[0043] The standard procedure requires coronal eversion osteotomy perpendicular to the femoral mechanical axis, sagittal osteotomy perpendicular to the distal femoral anatomical axis, and external rotation osteotomy parallel to the surgical TEA. Therefore, a set of coronal and sagittal images based on the surgical TEA were selected.

[0044] like Figure 6 As shown, a positioning line perpendicular to the distal femoral anatomical axis is drawn in a sagittal image that fully displays the distal femoral shaft (simulating a 0° sagittal flexion osteotomy). In consecutive sagittal images, the section where the posteromedial condyle is most prominent along this positioning line is selected. In this section, the cartilage thickness at the most prominent point of the posteromedial condyle is measured along the positioning line.

[0045] like Figure 7 As shown, in a coronal image that fully displays the distal femoral shaft, a positioning line is drawn with the distal femoral anatomical axis as the baseline to determine the corresponding valgus angle (based on the valgus angle measured in 3D CT). This positioning line is parallel to the femoral mechanical axis (simulating 0° valgus relative to the mechanical axis in the coronal plane). In consecutive coronal images, the section where the distal medial condyle is most prominent along this positioning line is selected. In this section, the cartilage thickness at the most prominent point of the distal medial condyle is measured along this positioning line.

[0046] In summary, this invention enables three-dimensional measurement of cartilage thickness at key sites of interest in the distal femur on a two-dimensional MR image by accurately locating the scanning direction. It allows for precise fitting of two-dimensional MR and three-dimensional CT scans and can reflect the variations in cartilage thickness corresponding to various possible intraoperative osteotomy errors. This program can contribute a qualitative simulation-based digital research method to the morphological improvement of TKA femoral prostheses.

[0047] The above-described specific embodiments are merely specific examples of the present invention. The patent protection scope of the present invention includes, but is not limited to, the product form and style of the above-described specific embodiments. Any appropriate changes or modifications made by a person skilled in the art that conform to the claims of the present invention should fall within the patent protection scope of the present invention.

Claims

1. A method for MR scanning and measurement for fitting two-dimensional and three-dimensional images of the distal femur, characterized in that: Includes the following steps: S1. Use a magnetic resonance imaging system to scan the transverse section of the lateral knee joint and draw the clinical condylar axis, surgical condylar axis and posterior condylar axis on the transverse image; S2. Based on the clinical condylar axis scanning, the first group of sagittal and coronal planes: The coronal plane scanning direction of this group is perpendicular to the transverse plane and parallel to the clinical condylar axis. The sagittal plane scanning direction of this group is both perpendicular to the transverse plane and perpendicular to the clinical condylar axis. S3. Based on the surgical condylar axis scanning, the second group of sagittal and coronal planes: The coronal plane scanning direction of this group is perpendicular to the transverse section and parallel to the surgical condylar axis. The sagittal plane scanning direction of this group is perpendicular to both the transverse section and the surgical condylar axis. S4. Based on the posterior condylar axis scanning, the third group of sagittal and coronal planes: The coronal plane scanning direction of this group is perpendicular to the transverse section and parallel to the posterior condylar axis, while the sagittal plane scanning direction of this group is perpendicular to both the transverse section and the posterior condylar axis. S5. Achieve three-dimensional stereoscopic measurement of cartilage thickness at key sites in the two-dimensional images of steps S2, S3, and S4.

2. The MR scanning and measurement method for fitting two-dimensional and three-dimensional images of the distal femur according to claim 1, characterized in that: In step S1, during the cross-sectional image scanning, the scanning direction is perpendicular to the long axis of the tibia on the dual-plane positioning phase, and the scanning range is from the distal end of the femoral condyle to the intersection of the femoral trochlea and the femoral shaft.

3. The MR scanning and measurement method for achieving two-dimensional and three-dimensional image fitting of the distal femur according to claim 1, characterized in that: In step S1, a cross-section is selected that can clearly display the three anatomical landmarks: the most prominent point of the lateral epicondyle of the femur, the most prominent point of the medial epicondyle of the femur, and the medial epicondyle fossa. The line connecting the most prominent point of the medial epicondyle and the most prominent point of the lateral epicondyle of the femur is called the clinical condylar axis, the line connecting the medial epicondyle fossa and the most prominent point of the lateral epicondyle of the femur is called the surgical condylar axis, and the line connecting the most prominent points of the medial and lateral posterior condyles is called the posterior condylar axis.

4. The MR scanning and measurement method for achieving two-dimensional and three-dimensional image fitting of the distal femur according to claim 1, characterized in that: In step S5, the thickness of the anterior and posterior condylar cartilage at any flexion angle is measured using sagittal images from any group of steps S2, S3, and S4; and the thickness of the medial and lateral distal cartilage at any eversion angle is measured using coronal images from any group of steps S2, S3, and S4.

5. The MR scanning and measurement method for achieving two-dimensional and three-dimensional image fitting of the distal femur according to claim 4, characterized in that: In step S5, the cartilage thickness is defined as the distance between the upper boundary of the superficial signal band of the cartilage at the key site and the upper boundary of the subchondral low signal band.

6. The MR scanning and measurement method for achieving two-dimensional and three-dimensional image fitting of the distal femur according to claim 1, characterized in that: The scanning slice thickness in the transverse, sagittal, and coronal planes is 0.8-1.2 mm.

7. The MR scanning and measurement method for achieving two-dimensional and three-dimensional image fitting of the distal femur according to claim 1, characterized in that: The scanning slice thickness in the transverse, sagittal, and coronal planes is 1 mm.

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