Techniques for computer-assisted planning of fastener placement in vertebrae to be stabilized by a pre-formed spinal rod

Abstract

A computer-aided technique for planning fastener placement in a vertebra to be stabilized by a pre-formed spinal rod is presented, wherein two or more fasteners attach the rod to the vertebra. At least one of a target shape of the spine and the shape of the pre-formed rod is defined in patient-specific shape data, the bone mineral density of at least one vertebra is defined in patient-specific bone mineral density data, and patient-specific anatomical data is provided. The method implementation of the technique presented herein includes calculating a force distribution along the length of the rod based on the shape data and anatomical data. The method also includes generating a planning result for fastener placement based on the bone mineral density data of a given vertebra and the calculated force distribution. The planning result may indicate at least one of the following fastener parameters: the fastener extension in the vertebra, the fastener attachment position along the length of the rod, and at least one fastener parameter of the fastener to be inserted into the vertebra.

Description

Technical Field

[0001] This disclosure generally relates to surgical planning. More specifically, it provides a computer-aided technique for placing fasteners in a vertebra to be stabilized by a pre-formed spinal rod, wherein two or more fasteners attach the rod to the vertebra. This technique can be implemented as a method, computer program product, or device. Background Technology

[0002] Spinal interventional procedures have become a widely used surgical treatment, and are currently performed manually by surgeons, automatically by surgical robots, or semi-automatically by surgeons using robots. Surgical planning is necessary to ensure appropriate surgical outcomes in spinal interventions.

[0003] like Figure 1 As shown, in some spinal interventions, a pre-formed rod 10 is implanted to stabilize two or more vertebrae 12 of the patient's spine 14. The rod 10 is pre-formed according to the planned shape of the spine 14 before implantation. After implantation, the rod 10 stabilizes the spine according to the planned shape.

[0004] Figure 1 The diagram illustrates a pre-formed rod 10 connected to a vertebra 12 using fasteners 16 (such as bone screws, e.g., pedicle screws), each fastener 16 having a first end 16A attached to the rod and an opposing second end 16B anchored in the vertebra 12 along a dedicated fastener extension. Prior to spinal intervention, the surgeon may have planned the fastener extension based on preoperative imaging data of the spine 14 (such as computed tomography (CT) data). During the spinal intervention, computer-aided navigation techniques can be used to guide fastener placement along a trajectory consistent with the planned fastener extension.

[0005] It has been found that the surgical outcome of spinal rod implantation is critically dependent on the bone mineral density of the vertebra 12 into which the fastener 16 is to be inserted. Clearly, if the fastener 16 is placed in an area of ​​low bone mineral density, the fastener 16 cannot be securely anchored in a given vertebra 12. Therefore, it has been recommended that bone mineral density data be considered when planning the fastener extension portion in the vertebra 12.

[0006] As an example, US2005 / 0101970A1 teaches an intraoperative surgical planning technique for selecting the most effective screw trajectory from potential screw trajectories based on bone mineral density data. The most effective screw trajectory is the one that results in optimized screw pull-out strength.

[0007] It has been found that optimizing screw pull-out strength based on bone mineral density (BMD) data can produce better surgical outcomes compared to cases where BMD is not considered. However, there are still anatomical factors that could further improve surgical outcomes. Summary of the Invention

[0008] There is a need for a computer-aided technique for planning the placement of fasteners in the vertebrae, which would lead to improvements in surgical outcomes.

[0009] According to a first aspect, a computer-aided method is provided for planning the placement of fasteners in a vertebra to be stabilized by a pre-formed spinal rod, wherein two or more fasteners connect the rod to the vertebra. At least one of a target shape of the spine and the shape of the pre-formed rod is defined in patient-specific shape data, the bone mineral density of at least one vertebra is defined in patient-specific bone mineral density data, and patient-specific anatomical data is provided. The method includes calculating a force distribution along the length of the rod based on the shape data and anatomical data, and generating a planned fastener placement result based on the bone mineral density data of a given vertebra and the calculated force distribution.

[0010] Preforming the spinal rod can involve deviations from a straight (i.e., linear) longitudinal extension. As an example, preforming can produce an S-shape or a portion of an S-shape. The preformed rod can have a length extending over two, three, or more vertebrae. In particular, the preformed rod can extend over four or more vertebrae.

[0011] The planning results can be configured for visualization (e.g., to enable visual preoperative surgical analysis or provide visual intraoperative surgical navigation assistance). In some variations, the planning results may indicate at least one of the following: the fastener extension in the vertebra, the fastener attachment location along the length of the rod, and at least one fastener parameter of the fastener to be inserted into the vertebra.

[0012] The planned fastener extension in the vertebra can be defined by one or more of the following: extension direction, extension length, extension endpoint, and extension origin. The planned fastener extension can be used for surgical navigation purposes to define a fastener trajectory toward the vertebra to which the fastener will be received.

[0013] In some implementations, generating planning results includes analyzing the bone mineral density of a given vertebra, as indicated in bone mineral density data. This analysis can be performed to determine at least one of the following: fastener extension, fastener attachment location, and fastener parameters, or another planning result for fastener placement. When forces, as indicated by force distribution, are applied to the fastener, the corresponding planning result can satisfy at least one predefined stability criterion. The at least one predefined stability criterion can be selected from one or more of the following: bone stability criteria (e.g., the ability to support forces applied by the fastener), sagittal balance requirements (e.g., torsion or gradient along the length of the rod), static physiological effects (e.g., when standing or sitting), and non-static physiological effects (e.g., when walking or ascending).

[0014] Stability criteria can be defined based on force distribution. Bone stability criteria can be defined based on force distribution (such as by at least one of the direction and absolute value of the force vector indicated in the force distribution). The bone stability criteria defined based on the force distribution can then be evaluated based on bone mineral density data. In this regard, bone stability criteria can be evaluated with respect to the average or aggregate bone mineral density of the region of a possible (e.g., repeatedly varying) fastener extension and / or the region adjacent to that possible fastener extension. If the bone stability criteria are found to be met, the possible fastener extension can be incorporated into the planned outcome.

[0015] The patient-specific anatomical data upon which force distribution is calculated can include one or more geometry-related anatomical parameters and one or more weight-related anatomical parameters. These two types of anatomical parameters can be jointly evaluated to derive the patient's mass distribution. The force distribution can be calculated based on the patient's mass distribution, shape data, one or more optional other parameters (e.g., body mass index, sex, age), and one or more optional stability constraints.

[0016] Patient-specific shape data defines at least one of the target (i.e., planned) shape of the spine and the shape of the pre-formed rod. In some variations, the rod is pre-formed to achieve the target shape of the spine after implantation. The target shape of the spine can be defined first and then translated into the shape of the pre-formed rod. The pre-formation of the rod can be performed manually by the surgeon (e.g., preoperatively or intraoperatively). Alternatively, the pre-formation of the rod can be performed at the manufacturing site (e.g., based on patient-specific shape data). In this case, additive manufacturing techniques (such as 3D printing) can be used.

[0017] This method may include generating navigation instructions based on planning results. Navigation instructions may then be generated, for example, based on at least one of a fastener extension in the vertebra and a fastener attachment location along the rod. The generation of planning results may involve user input (e.g., confirmation or modification of automatically proposed fastener extensions or fastener attachment locations). One of the planning results and navigation instructions may be output to the user (e.g., visually on a display screen) or to the surgical robot (e.g., as a dataset for controlling the movement of the robotic arm). Planning results may be generated and / or output preoperatively. Navigation instructions may be generated and / or output intraoperatively.

[0018] Navigation commands can be configured to guide surgical instruments manipulated by a surgeon or surgical robot. At least one of the position and orientation of the surgical instrument can be tracked and used to generate navigation commands.

[0019] The planning results can be output as a dataset or as a set of display instructions. Therefore, the planning result output may include at least one fastener parameter and an indication of a given vertebra to which a fastener having said at least one fastener parameter is to be received. The at least one fastener parameter may indicate at least one of fastener length, fastener diameter, fastener thread (e.g., pitch), and fastener type. At least one of the fasteners intended to attach the rod to the vertebra may include bone screws (e.g., pedicle screws), bone screws, and K-wires.

[0020] The force distribution calculated based on shape and anatomical data can indicate at least one force vector component that extends non-coaxially (e.g., obliquely) relative to at least one of the fastener extension portion in the vertebra and the length of the fastener when the fastener is attached to the rod. The force distribution can indicate multiple force vectors at two or more different locations along the length of the rod. Each force vector can indicate the force exerted on the vertebra by the fastener attached at a given location along the length of the rod. The force distribution can be an estimate based on shape and anatomical data.

[0021] Force distribution can be further calculated based on generalized rod data. Generalized rod data can indicate at least one of rod length, rod diameter, and rod material parameters (e.g., material stiffness). In some variations, particularly for short rods that cover only two or three vertebrae, the rod can have a generalized shape along its longitudinal extension.

[0022] Patient-specific anatomical data can indicate one or more of the following: pelvic tilt, sagittal vertical axis translation, pelvic injury-lumbar lordosis mismatch, relationship between the C7 plumb line and the center of pelvic tilt, waist-to-height ratio, waist-to-hip ratio, mass distribution along the spinal axis, body mass index, weight, degree of pelvic injury, and thoracic kyphosis. Anatomical data can be measured or estimated. Anatomical data can be derived, at least in part, from image data of the patient for whom the plan is being performed.

[0023] A computer program product is also provided, comprising a program code portion that, when executed by a processor, causes the processor to perform the methods presented herein. The processor may be included in a local computing system located in an operating room, a central server, or a cloud computing resource. The computer program product may be stored on a CD-ROM, a semiconductor memory, or may be provided as a data signal (e.g., when downloaded from an internet server).

[0024] On the other hand, an apparatus is provided for planning the placement of fasteners in a vertebra to be stabilized by a pre-formed spinal rod, wherein two or more fasteners connect the rod to the vertebra. At least one of a target shape of the spine and the shape of the pre-formed rod is defined in patient-specific shape data, the bone mineral density of at least one vertebra is defined in patient-specific bone mineral density data, and patient-specific anatomical data is provided. The apparatus is configured to calculate a force distribution along the length of the rod based on the shape data and anatomical data. The apparatus is further configured to generate a planned fastener placement result based on the bone mineral density data of a given vertebra and the calculated force distribution.

[0025] As explained above, the planning results for fastener placement can indicate at least one of the following: the fastener extension in the vertebra, the fastener attachment position along the length of the rod, and at least one fastener parameter of the fastener to be inserted into the vertebra.

[0026] The device is configured to perform any of the methods and method steps presented herein. Attached Figure Description

[0027] Other details, advantages, and aspects of this disclosure will become apparent from the following embodiments, taken in conjunction with the accompanying drawings, in which:

[0028] Figure 1A spinal rod used to stabilize multiple vertebrae is schematically shown;

[0029] Figure 2A and Figure 2B A surgical planning system with optional imaging capabilities is illustrated schematically;

[0030] Figure 3 The process of obtaining a pre-formed spinal rod is illustrated schematically;

[0031] Figures 4A-4D This illustrates the process of obtaining bone mineral density data from CT data;

[0032] Figures 5A-10 This shows how exemplary anatomical parameters can be obtained;

[0033] Figure 11 A flowchart illustrating an embodiment of the method of this disclosure is shown;

[0034] Figure 12 The force distribution acting along the length of the spinal column is schematically shown;

[0035] Figure 13A and Figure 13B The processing of bone mineral density data is illustrated schematically;

[0036] Figure 14 The illustration schematically depicts a surgical navigation scenario based on a tracking surgical tool; and

[0037] Figure 15 schematically shown Figure 14 The navigation view in the surgical navigation scenario. Detailed Implementation

[0038] In the following description of exemplary implementations of this disclosure, the same reference numerals are used to denote the same or similar parts.

[0039] The implementation described below involves computer-aided techniques for planning the placement of fastener 16 in vertebral column 12, which is to be stabilized by pre-formed spinal column 10 (see below). Figure 1 While these implementations will be described primarily in the context of generating surgical planning information to assist surgeons in guiding surgical instruments during spinal interventions, it should be understood that planning information can alternatively or additionally be used to control surgical robots operating in a fully or semi-automatic manner. As understood herein, semi-automatic operation includes situations where the surgical robot constrains the surgeon's manipulation of surgical instruments.

[0040] Figure 2AAn exemplary surgical planning system 100 is schematically illustrated, which is also configured to obtain at least a portion of the input data required to generate planning results for a spinal intervention. In other variations, the input data may be obtained from one or more other systems.

[0041] Figure 2A The surgical planning system 100 includes a planning device 20 configured to generate surgical planning results and an output device 22 configured to output the planning results (e.g., for preoperative information, verification, modification, or confirmation purposes, or for intraoperative navigation purposes). The generation of planning results by device 20 may include user interaction (e.g., verification, modification, or confirmation of automatically generated planning result proposals). In this case, a user input device (such as a keyboard or mouse) may be provided. Figure 2A (Not shown in the image).

[0042] exist Figure 2A In this design, device 20 is implemented as a locally deployed computer system. Alternatively, device 20 may be implemented as a remote server or as a cloud computing resource.

[0043] exist Figure 2A In this scenario, output device 22 is a display device configured to visually output the planning results. In other variations, output device 22 may be configured (e.g., additionally or alternatively) to output one or more of sound and tactile information. Output device 22 may be configured to include or comprise a computer monitor, an augmented reality device (e.g., a head-mounted display, HMD), a speaker, an actuator configured to generate tactilely detectable information, or a combination thereof.

[0044] The planning device 10 is configured to generate planning results from input data. Therefore, in the initial stages of the computer-aided planning technique described herein, the input data must be obtained by the planning system 100. In the implementation described herein, the input data includes at least patient-specific shape data defining the shape of the pre-formed rod 10 or the target shape of the patient's spine 14, patient-specific bone mineral density data defining the bone mineral density of at least one of the vertebrae 12, and patient-specific anatomical data.

[0045] In one implementation, surgical imaging techniques are used to obtain at least some of the input data. For this reason, Figure 2AThe surgical planning system 100 includes an imaging device 24 configured (e.g., preoperatively or intraoperatively) to acquire image data of at least some vertebrae 12 of the patient's spine 14. In some variations, this image data will be used to generate one or more of patient-specific shape data, patient-specific bone mineral density data, and patient-specific anatomy data. In these or other variations, one or more of the patient-specific shape data, patient-specific bone mineral density data, and patient-specific anatomy data are generated "offline" or externally (and, for example, obtained by the planning system 100 in the form of one or more datasets generated at a location remote from the surgical planning system 100).

[0046] exist Figure 2A In the exemplary scenario shown, the imaging device 24 of the surgical planning system is a C-arm with cone-beam computed tomography (CBCT) imaging capability. In other cases, the imaging device 24 is a conventional CT scanner, EOS scanner, or X-ray device that generates slice images. In a further scenario, the imaging device 24 utilizes magnetic resonance (MR)-based or ultrasound-based imaging techniques.

[0047] Figure 2A An exemplary CBCT-based imaging device 24 includes a radiation source 28 configured to generate a cone-shaped radiation beam. Furthermore, the imaging device 24 has a flat panel detector 30 configured to detect the radiation beam projected by the radiation source 28 through one or more vertebrae 12. The detector 30 is configured to generate image data representing two-dimensional projected images of the vertebrae 12. Figure 2B The projected image shown, containing the imaging volume 32 of vertebra 12, is captured at more than two angular orientations of the C-arm relative to the imaginary longitudinal axis A of vertebra 12. In some variations, three-dimensional image data of vertebra 12 is derived from the obtained two-dimensional projected image using reconstruction (e.g., back projection) techniques. Reconstruction can be performed by imaging device 24 or by planning device 20.

[0048] Once raw data has been obtained using one or more of the imaging techniques or other data acquisition techniques discussed above, the raw data is processed to generate one or more of the following: patient-specific shape data, patient-specific bone density data, and patient-specific anatomy data required to produce the planned results.

[0049] Patient-specific anatomical data is combined with patient-specific shape data to calculate the force distribution at one or more locations along the length of rod 10.

[0050] Computer simulation tools (e.g., software tools using the so-called Finite Element Method (FEM)) can be used to calculate force distribution. Examples of such FEM simulation tools include software programs "SimScale", "COMSOL", and "ANSYS". A model of rod 10 can first be loaded into the FEM software tool. This model can be defined by shape data (e.g., rod length, rod diameter, etc.). The forces acting on the rod at predetermined locations can be used as input conditions or constraints for the FEM simulation. The forces acting on the rod at predetermined locations can correspond to the forces acting on the rod via fasteners attached to the rod at those predetermined locations. The force distribution along the length of rod 10 can then be calculated based on the model and the input conditions of the FEM simulation tool (such as SimScale, COMSOL, or ANSYS). The model of rod 10 can be defined by shape data, while the input conditions used for the FEM simulation (specifically, the forces exerted on the rod by each fastener) can be determined based on anatomical data. For example, a larger pelvic tilt will result in a larger force acting on rod 10. This also applies to larger sagittal imbalances and other deviations of the patient's spine from anatomically correct posture. Anatomical data can be used, for example, based on trigonometric calculations to determine the forces acting on fasteners attached to the corresponding vertebrae, as referenced below. Figures 5A to 10 As described, any force acting on the fastener can be "converted" into a force acting on rod 10 at a predefined fastener location (action force = reaction force). This can generate input conditions for the FEM simulation tool to simulate the force distribution along the length of rod 10.

[0051] In some implementations, patient-specific shape data defines at least one of the planned (or target) spinal shape and the actual or planned rod shape. For example, patient-specific shape data may define the planned shape of the spine 14 after the rod 10 is implanted and may be used to manufacture the pre-formed rod 10.

[0052] The preformed rod 10 can be manufactured in a multi-step process, such as... Figure 3 As exemplarily shown in the figure. It begins with two-dimensional or three-dimensional image data 40 acquired by imaging device 24 or otherwise obtained (as illustrated in...). Figure 3 (Schematally shown on the left side of the diagram), in the first step, the user generates a planned (or target) shape model 42 of at least a portion of the spine 14 (i.e., indicating the spinal shape that should be produced by the implantation of the rod 10). In some variations, the planned (or target) shape model 42 is defined by the user via the planning device 20 or another computer system. For this purpose, image data 40 (e.g., on the output device 22) is visualized, and the user is given the opportunity to define the planned shape model 42 (e.g., relative to the visualized image data 40).

[0053] In the second step (shown in) Figure 3 In the middle section, the planned (or target) shape model 42, thus defined, is converted into a dataset 44 indicating patient-specific shape data. In this example, dataset 44 indicates the planned rod shape in its longitudinal extension (which will deviate from the straight or linear extension). The rod shape will typically include one or more bends (e.g., in the form of an "S" or a portion of an "S"). Dataset 44 may describe a pre-formed computer-aided design (CAD) model of the rod 10. In the first embodiment, the user-indicated portion of the planned (or target) shape model 42 (e.g., between two user-indicated vertebrae 12 (such as conventional symbols L1 and L5)) is converted into dataset 44. In a more refined second embodiment, the user can (e.g., additionally) define further shape constraints (such as rod diameter) that will be input into dataset 44. In the third embodiment, these shape constraints are predefined. In a typical implementation, the rod 10 will extend over three, four, or more vertebrae and needs to be attached to these three, four, or more vertebrae.

[0054] In the third step (shown in) Figure 3 (on the right side), using, for example, additive manufacturing, rod bending machines or any other manufacturing / forming technology, to manufacture the actual rod 10 based on dataset 44.

[0055] In an alternative variant, the shape of the rod 10 is manually defined by a user (such as a surgeon) according to the patient's needs by bending a straight or roughly pre-bent rod using a bending tool. The actual shape of the rod 10 is then converted into a dataset indicating patient-specific shape data by scanning the user-bent rod 10 using a laser scanner or otherwise.

[0056] Patient-specific bone mineral density data can also be derived from image data obtained using one or more of the imaging techniques or other data acquisition techniques discussed above. In some variations, patient-specific bone mineral density data is derived from 3D CT image data, such as... Figures 4A to 4D As shown.

[0057] Figure 4A A view of a specific vertebra 12 taken along the sagittal plane is shown, and the locations of the vertebrae are indicated respectively. Figure 4B , 4C And the positions of the three lateral planes B, C, and D shown in 4D. Figure 4B , 4C and 4D Figure 4AThe internal structure of vertebral 12 was visualized and further processed to derive volumetric (i.e., three-dimensional) bone mineral density data of vertebral 12. This processing can be based on Hounsfield units (HU) as treated as or converted into actual bone mineral density data. Figure 4B , 4C In 4D, the average HU of a specific cross-sectional area is shown.

[0058] In some implementations, a dedicated bone density dataset is generated for each vertebra of interest 12. In this implementation, vertebral segmentation techniques are applied to the image data.

[0059] At least some of the patient-specific anatomical data can be obtained from image data acquired using one or more of the imaging techniques discussed above (particularly using an EOS scanner). Of course, other data acquisition techniques can also be used.

[0060] Now refer to Figures 5A to 10 Exemplary patient-specific anatomical parameters may be included in describing anatomical data.

[0061] Figure 5A and Figure 5B Different patient-specific pelvic tilt angles (PT) of 13° and 45° are shown. As is known in the art, a larger pelvic tilt angle requires a larger force to stabilize the lumbar spine. This is because, for a given weight f, the torque required for stabilization increases with... Figure 5A and Figure 5B The distance d between the two lines shown in each of the diagrams increases with the increase of the pelvic tilt. In other words, as the pelvic tilt increases, a greater force will act on the rod 10, or in other words, the force transmitted by the fasteners 16 on the vertebrae 12 (attached to the rod 10) will be greater.

[0062] refer to Figure 6 Pelvic injury-lumbar lordosis (PI-LL) mismatch is a patient-specific anatomical parameter that can be used to calculate a force vector along the length of the pre-formed rod 10 within the lumbar region, which also depends on the pelvic tilt. Figure 6 In the middle, SS indicates the sacral slope.

[0063] refer to Figure 7 The sagittal vertical axis (SVA) translation is another patient-specific anatomical parameter that can be used in some implementations of this disclosure to calculate the force distribution on the rod 10. The SVA allows for estimation of the force vector (in terms of force intensity and direction) acting on the pre-formed rod 10 in the lumbar region. Similarly, as... Figure 8The relationship between the C7 plumb line and the pelvic tilt center point (PTCP) shown for the three cases A, B and C has a significant impact on determining the strength and direction of the force acting on the preformed rod 10 along the longitudinal extension of the rod 10.

[0064] refer to Figure 9 This shows the force F generated by the global equilibrium analysis. GB F GB It is calculated based on the physiological shape of the patient's anatomical structure, especially the spine (i.e., geometry-related anatomical parameters), the patient's mass distribution (i.e., weight-related anatomical parameters), and other optional parameters (such as sex, age, and body mass index).

[0065] Now for reference Figure 10 Pelvic injury degree (PI) and sacral slope are also patient-specific anatomical parameters that affect global balance and therefore the forces acting on the preformed rod 10 along its extension, albeit on the second order of magnitude. Similarly, thoracic kyphosis can be considered a patient-specific anatomical parameter for calculating the forces acting on the preformed rod 10.

[0066] Other patient-specific anatomical data include parameters such as waist-to-height ratio, waist-to-hip ratio, mass distribution along the spinal axis, body mass index, and weight. Clearly, one, two, or more of the above patient-specific anatomical parameters, along with other patient-specific anatomical parameters, can be used to define the patient-specific anatomical data as input to the planning device 20.

[0067] Having already discussed how to obtain exemplary patient-specific anatomical data, patient-specific shape data, and patient-specific bone mineral density data, we will now refer to... Figure 11 Flowchart 1100 is used to explain the processing of those input data in the context of surgical planning. Flowchart 1100 illustrates an embodiment of the method of this disclosure for planning the placement of fasteners in a plurality of vertebrae 12, to be stabilized by pre-formed rods 10, as performed by planning device 20. Figure 1 As shown in the image.

[0068] In step 1102, the planning device 20 calculates the force distribution at one or more points along the length of the rod 10 based on one or more of patient-specific shape data and patient-specific anatomical parameters (i.e., anatomical data), such as Figure 12As illustrated schematically. To calculate force distribution, considering shape data defining at least one of the target shape of the spine 14 and the shape of the pre-formed rod 10, one or more geometry-related anatomical parameters (such as PT, SVA translation, PI-LL mismatch, and PI, or one or more) and one or more weight-related anatomical parameters (such as mass distribution along the spinal axis, body mass index, and body weight, or one or more) are jointly evaluated (see also above). Figure 9 (Discussion). In some variations, force distribution is also calculated based on universal rod data. Universal rod data indicates at least one of rod length, rod diameter, and rod material parameters. Universal rod data may be at least partially included in patient-specific shape data, as the rod length or rod diameter may have been selected in a patient-specific manner (as referenced above). Figure 3 (As described).

[0069] It can be used for a series of two or more locations along the length of rod 10 and as possible. Figure 9 The information shown is used to calculate the force distribution. At each location considered, a force vector can be calculated, defined jointly by the force value or force intensity and the force direction. Thus, in some variations, the force distribution indicates the force vector at different locations along the length of the rod 10. Each force vector can indicate the force that will be transmitted by the fastener 16 on the associated vertebra 12 (when it is assumed that the fastener 16 is attached to the rod 10 at a given location along the length of the rod 10).

[0070] like Figure 12 As very schematically illustrated, from the perspective of possible fastener attachment positions at rod 10, force vectors F1, F2, F3, etc., are generally not "pull-out force vectors" that are away from the plane of the vertebra 12 into which the particular fastener 16 will be inserted. Instead, the force may include, or at least include, a compressive force pointing toward the particular vertebra 12. Other force vector components may be obliquely (i.e., may extend non-coaxially) pointing toward at least one of the fastener extension in the particular vertebra 12 and the length of the fastener 16 when the fastener 16 is attached to rod 10.

[0071] exist Figure 11 In step 1104, the planning device 20 is based on the bone mineral density data of the given vertebra 12 (see Figure 4) and the calculated force distribution (see Figure 5). Figure 12 The calculated planning results are generated. These results can be output from device 22 (see...). Figure 2A This information is presented to the user for purposes of information, verification, confirmation, or modification. Furthermore, as will be discussed in more detail below, the planning results can also form the basis for surgical navigation instructions used to guide surgeons or surgical robots.

[0072] In some embodiments, the planning results indicate a fastener extension in a specific vertebra 12. The planned fastener extension may be defined by one or more of the following: extension direction, extension length, extension endpoint in the vertebra 12, and extension starting point on the surface of the vertebra 12. The planned fastener extension in the vertebra 12 can be used for surgical navigation purposes to define a fastener trajectory toward that vertebra 12. The fastener trajectory toward the vertebra 12 is typically defined by a line collinear with the fastener extension in the vertebra 12.

[0073] It is generally desirable to select the fastener extension in the vertebra 12 such that the fastener 16 is securely anchored therein. Therefore, the fastener 16 should extend in and / or near a region of high bone density. However, selecting the fastener extension solely based on bone density data to optimize, for example, the pull-out force ignores the finding that the force transmitted by the rod 10 (which connects multiple such fasteners 16) on a given fastener 16 will have a force vector component that extends obliquely relative to the extension of the given fastener 16 in the vertebra 12, or even in a direction opposite to the pull-out direction, such as... Figure 12 As shown. Therefore, it is proposed that in step 1104, the fastener extension portion in a given vertebra 12 be selected not only based on the bone mineral density data of the vertebra 12, but also based on the force distribution calculated in step 1102, as will now be referred to. Figure 13A and Figure 13B The explanation given.

[0074] Figure 13A A vertebra 12 with its volumetric bone mineral density information already obtained is shown, as explained above with reference to Figure 4. Using this volumetric bone mineral density information, bone mineral density and changes in bone mineral density can be evaluated along any selected fastener extension of the vertebra 12. For this purpose, the fastener extension can be defined by a cylindrical volume within the bone mineral density volume derived for the vertebra 12. In some embodiments, the cylindrical volume may further depend on one or more fastener parameters, such as the fastener diameter. Figure 13B As shown, for any fastener extension, the aggregate bone mineral density (HU) along the fastener extension can be calculated. tot The mean bone mineral density (HU / mm) per unit length is also considered. In addition to, or as an alternative to, bone mineral density and its variation along the selected fastener extension, bone mineral density in the region adjacent to the fastener extension can be evaluated. Such an adjacent region may be necessary to support a significant force vector component extending non-coaxially relative to the fastener extension.

[0075] Therefore, bone mineral density data can be evaluated to determine whether predetermined bone stability criteria are met. Bone stability criteria can be defined based on force distribution.

[0076] For example, suppose for along rod 10 ( Figure 13A For a given (e.g., user-selected, iteratively varied, or automatically planned) fastener attachment location (not shown), the force distribution indicates that the force vector acting on the fastener 16 at that location is substantially coaxially oriented along the length of the fastener 16 away from the associated vertebra 12, see [reference]. Figure 13A The force vector F1 in the middle. In this case, the fastener extension in the vertebra 12 is typically planned by the device 20 such that the aggregate bone density along the fastener extension in the vertebra 12 (see Figure 13B Maximizing or at least exceeding the selected threshold may be sufficient. This threshold can constitute a bone stability criterion and can be selected based on the absolute value or intensity of the force vector, or the absolute value or intensity of the "pull-out" vector component of the force vector.

[0077] To generate an appropriate fastener extension in a given vertebra 12 for a given force vector F1, the planning device 20 can thus begin by evaluating a predetermined fastener extension (e.g., a fastener extension extending perpendicularly from a pre-formed rod 10 and optionally within the plane of the pre-formed rod 10). The fastener extension can then be modified (e.g., iteratively, regarding the angle of the fastener extension relative to the rod 10) to maximize the aggregate bone density along the fastener extension, or until the aggregated fastener extension is above a selected threshold.

[0078] On the other hand, assuming that for a given (e.g., user-selected, iteratively varied, or automatically planned) fastener attachment location along the length of rod 10, the force distribution indicates that the force vector acting on fastener 16 at that location has a vector component that is significantly inclined to the length of fastener 16 (see...). Figure 13A If the force vectors F2 and F3 are present, then it is important that there is sufficiently high bone density in the region where the force will be primarily supported by bone. This situation is caused by... Figure 13BRegions R1 for force vector F2 and R3 for force vector F3 are shown in the diagram, both located near the fastener extension in vertebra 12. Compared to the case of force vector F1, there may be a lower force vector component in the fastener pull-out direction, which means that planning the fastener extension to optimize aggregate bone density may still result in bone fragmentation in local vertebral regions that need to support large forces (such as region R1 for force vector F2 and region R2 for force vector F3). One or both of the location and size of the regions (such as region R1 or R2) can be defined as a bone stability criterion based on force distribution (e.g., based on force vector direction). In some variations, the (e.g., average or aggregate) bone density in this region may be affected by a threshold decision, similar to the scenario discussed above with reference to force vector F1.

[0079] To generate a suitable fastener extension in a given vertebra 12 for a given force vector F2 or F3, the planning device 20 can thus begin by evaluating a predetermined fastener extension (e.g., a fastener extension extending perpendicularly from the rod 10 and optionally located in the plane of a pre-formed rod 10). The fastener extension can then be modified (e.g., iteratively, regarding the angle of the fastener extension relative to the rod 10, and / or regarding the fastener attachment location along the length of the rod 10) until the fastener extension is found to be adjacent to a region of high bone density at the desired location.

[0080] In some implementations, the planning results (not only of the fastener extension, or only of the fastener extension) indicate the fastener attachment location along the length of rod 10. For example, from... Figure 12 It will be understood that the attachment position of the fastener 16 along the length of the rod 10 has an impact on the force transmitted by the fastener 16 to the given vertebra 12, as well as on the extension of the fastener 16 within the vertebra 12. Therefore, within a certain range, the planning device 20 can also plan the fastener attachment position along the length of the rod 10 for a given vertebra 12, taking into account bone density data and force distribution, so as to meet specific surgical requirements.

[0081] exist Figure 13A In the example, and for force vectors F2 or F3, the fastener attachment positions on the rod can be selected such that the starting point of the fastener extension on the surface of vertebra 12 will be adjacent to the high bone density region R1 or R2 on the desired side of the fastener 16, respectively. Clearly, the fastener extension (e.g., in terms of the extension direction as viewed from rod 10) and the fastener attachment positions along the length of the rod can be planned (e.g., optimized) simultaneously under the same conditions to achieve optimal surgical results.

[0082] In some implementations, the planning result (e.g., in addition to either the fastener extension or the fastener attachment location) indicates at least one fastener parameter of the fastener 16 to be inserted into a given vertebra 12. This at least one fastener parameter may indicate at least one of fastener length, fastener diameter, fastener thread (e.g., thread type, pitch, thread length), and fastener type. The type of fastener 16 intended to attach the rod to the vertebra may include bone screws (e.g., pedicle screws, see...). Figure 1 , 13A At least one of (13B) bone screws and Kirschner wires. If, for example, the planning device 20 finds that the bone density of a given vertebra 12 is low in a situation where a large force will be borne in the vertebra 12, the planning results may indicate one or both of a larger fastener diameter and a longer fastener length compared to a scenario with higher bone density or lower force.

[0083] In addition to the at least one fastener parameter, the planning outcome may also include an indication of the given vertebra to which the fastener having the at least one fastener parameter will be received. The vertebra may be indicated visually (e.g., in the context of visualization of CT data) or using conventional symbols (such as L1, L2, etc.) or proprietary symbols.

[0084] As will become apparent from the above, the generated plan results may include analyzing the bone mineral density of a given vertebra 12 (as indicated in the bone mineral density data) to determine at least one of the following: fastener extension, fastener attachment location, and fastener parameters, such that at least one predefined stability criterion is met when a force, as indicated by the force distribution, is applied to the fastener 16. As explained above, this at least one predefined stability criterion may be a bone stability criterion. In other cases, the predefined stability criterion may be at least one of sagittal balance requirements, static physiological effects, and non-static physiological effects.

[0085] In some variations, bone mineral density (BMD) data are correlated with the calculated force distribution. High (e.g., maximum) BMD is required at bone locations where large forces will act. High BMD is not required at bone locations where small forces will act. Threshold decisions can be applied to assess forces as large / small and bone mineral density as high / low (of course, this disclosure is not limited to such a binary decision but can be implemented at a higher granularity). The resulting force distribution or force tolerance requirement can be derived from one or more stability criteria. As an example, sagittal balance requirements affect the resulting force distribution, thus necessitating (re)establishing the sagittal balance of the spine.

[0086] In optional step 1106, navigation instructions are generated based on the planning results and output to the surgeon or surgical robot. In some cases, the generation of navigation instructions will require tracking surgical tools operated by the surgeon or surgical robot. Therefore, as... Figure 14 As shown, the surgical system 100 may include an optical surgical tracking component, which includes one or more optical trackers 1412, a camera 1414, an (optional) electromagnetic radiation source 1416, and a tracking controller 1418. Of course, in other cases, the tracking component may be selected for electromagnetic tracking or inertial tracking.

[0087] Electromagnetic radiation source 1416 is configured to emit at least one of infrared and visible light. Specifically, electromagnetic radiation source 1416 may be configured to fill the entire surgical site with electromagnetic radiation. Each of one or more trackers 1412 includes three or more reflectors (e.g., spherical bodies) that reflect the electromagnetic radiation emitted by electromagnetic radiation source 1416. Thus, one or more trackers 1412 are configured as so-called passive trackers. In other variations, at least one of one or more trackers 1412 may be implemented as an active device configured to emit electromagnetic radiation. As an example, each active tracker 1412 may include three or more light-emitting diodes (LEDs) emitting electromagnetic radiation of the infrared or visible spectrum. If all trackers 1412 are configured as active devices, electromagnetic radiation source 1416 may be omitted in some variations.

[0088] Camera 1414 has at least one image sensor, such as a charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) sensor. The image sensor is configured to detect electromagnetic radiation reflected (or emitted) by one or more trackers 1412. In some variations, camera 1414 may have multiple image sensors. In particular, camera 1414 may be a stereo camera with at least two image sensors.

[0089] The tracking controller 1418 is configured to process image data generated by the camera 1414 and calculate the position and orientation of one or more trackers 1412 in a tracking coordinate system. This calculation is typically performed with 5 or 6 degrees of freedom (DOF). The tracking coordinate system may have a rigid relationship relative to the camera 1414 and may specifically be centered on the center of the camera 1414.

[0090] exist Figure 14In the exemplary scenario shown, a dedicated tracker 1412 is provided for the surgical tool 1436 (such as a surgical screwdriver configured to screw the fastener 16 into the vertebra 12). In other variations, the surgical tool 1436 is a surgical drill configured to drill a hole in the vertebra 12 to receive the fastener 16.

[0091] like Figure 14 As shown, the planning device 20 can be communicatively coupled to the tracking controller 1418. In some variations, the planning device 20 jointly processes planning results and at least one of position and orientation information received from the tracking controller 18 for generating navigation instructions intraoperatively. Since planning results can be generated preoperatively, in other variations, the planning results can be transmitted to the tracking controller 1418 or another device coupled to the tracking controller 1418 (e.g., via a data carrier or communication network) for generating navigation instructions.

[0092] Figure 15 An exemplary navigation view 1500 displayed by output device 22 is shown. The navigation view visualizes image data of vertebra 12 (e.g., captured by imaging device 24) acquired preoperatively or intraoperatively. This image data has been registered relative to a tracking coordinate system such that the position and orientation of at least one of the tracked surgical instruments 1436 or other tracked entities are known relative to the image data.

[0093] The navigation instructions in navigation view 1500 indicate the current tip position 1502 of the tracked surgical tool 1436 (or the fastener attached to the surgical tool 1436) relative to the planned fastener trajectory 1504 derived from the planned fastener extension in the vertebra 12 to be surgically treated. In other scenarios, the tool trajectory, rather than the tool tip, can be visualized.

[0094] As explained above, the planned fastener trajectory 1504 can be derived by extending the planned fastener extension beyond the specific vertebra 12 that will receive the fastener 12. Navigation instructions, when output to the surgeon, will instruct the surgeon to attempt to align the actual tool tip or trajectory with the planned fastener trajectory. Figure 15 In the scenario shown, the surgeon would therefore need to move the tool tip to the left to reach the planned tool trajectory. If the surgeon is replaced by or assisted by a surgical robot, the navigation instructions are output as a dataset to the surgical robot for control or verification purposes.

[0095] Once all the required bone fasteners 16 have been implanted in the vertebrae 12 according to the corresponding associated planning results (e.g., fastener extensions), the pre-formed rod 10 is then attached to the fastener head 16A, as shown. Figure 1As shown in the diagram. In some variations, the tracker 1412 is temporarily attached to the rod 10 so that the rod can also be guided to position according to the planned rod location (e.g., in the navigation view displayed by the output device 22).

[0096] If vertebrae 12 are also tracked (individually or jointly), any movement of one or more tracked vertebrae 12 will be detected by the tracking controller 1418 (at 5 or 6 DOF). Then, when generating navigation instructions, movement involving one or both of rotation and translation can be considered in real time by, for example, updating the visual representation of the vertebrae 12 in the navigation view 1500.

[0097] As has been apparent from the above description of exemplary implementations of this disclosure, the techniques presented herein improve surgical planning for fastener placement by relying not only on bone mineral density data but also taking into account the estimated force distribution in the bone. It will be apparent that the exemplary implementations discussed above can be modified in many ways.

Claims

1. A computer-aided method for planning the placement of fasteners in a vertebra to be stabilized by a pre-formed spinal rod, wherein two or more fasteners connect the rod to the vertebra, wherein at least one of a target shape of the spine and a shape of the pre-formed rod is defined in patient-specific shape data, the bone mineral density of at least one vertebra is defined in patient-specific bone mineral density data, and wherein patient-specific anatomical data is provided, the method comprising: The force distribution along the length of the rod is calculated based on the shape data and the anatomical data; and The plan for fastener placement is generated based on the bone mineral density data of the given vertebra and the calculated force distribution.

2. The method according to claim 1, wherein The planning results indicate at least one of the following: the fastener extension in the vertebra, the fastener attachment position along the length of the rod, and at least one fastener parameter of the fastener to be inserted into the vertebra.

3. The method according to claim 1, wherein Generating the planning results includes analyzing the bone mineral density of the given vertebra as indicated in the bone mineral density data, wherein the planning results satisfy at least one predefined stability criterion when forces as indicated by the force distribution are applied to the fastener.

4. The method according to claim 3, wherein The at least one predefined stability criterion is selected from one or more of bone stability criteria, sagittal balance requirements, static physiological effects, and non-static physiological effects.

5. The method according to claim 1, wherein The calculation of the force distribution is based on patient-specific anatomical data including one or more geometry-related anatomical parameters and one or more weight-related anatomical parameters.

6. The method according to claim 5, wherein Two types of anatomical parameters were jointly assessed to derive the patient's mass distribution.

7. The method of claim 6, wherein The force distribution is calculated based on the patient's mass distribution and shape data.

8. The method according to claim 1, comprising: Navigation instructions are generated based on the plan results.

9. The method according to claim 8, wherein The navigation instructions are configured to guide surgical tools operated by a surgeon or surgical robot.

10. The method of claim 2, comprising: The planning results are output, including at least one fastener parameter and an indication of a given vertebra to receive a fastener having the at least one fastener parameter.

11. The method according to claim 2, wherein The at least one fastener parameter indicates at least one of fastener length, fastener diameter, fastener thread, and fastener type.

12. The method according to claim 1, wherein At least one of the fasteners includes a bone screw, a bone nail, and a Kirschner wire.

13. The method according to claim 1, wherein, The force distribution indicates at least one force vector component that extends non-coaxially relative to at least one of the fastener extension portion in the vertebra and the length of the fastener when the fastener is attached to the rod.

14. The method of claim 1, wherein The force distribution indicates the force vector at different locations along the length of the rod.

15. The method of claim 1, wherein The force distribution is further calculated based on general rod data.

16. The method of claim 15, wherein The general rod data indicates at least one of the rod length, rod diameter, and rod material parameters.

17. The method of claim 16, wherein The rod has a general shape along its longitudinal extension.

18. The method of claim 1, wherein The anatomical data indicate one or more of the following: pelvic tilt, sagittal vertical axis translation, pelvic injury-lumbar lordosis mismatch, relationship between the C7 plumb line and the center point of pelvic tilt, waist-to-height ratio, waist-to-hip ratio, mass distribution along the spinal axis, body mass index, weight, degree of pelvic injury, and thoracic kyphosis.

19. A computer program product for planning the placement of fasteners in a vertebra to be stabilized by a pre-formed spinal rod, wherein two or more fasteners connect the rod to the vertebra, wherein at least one of a target shape of the spine and a shape of the rod is defined in patient-specific shape data, a bone density of at least one vertebra is defined in patient-specific bone density data, and wherein patient-specific anatomical data is provided, the computer program product including a program code portion that, when the computer program product is executed, causes a processor to: The force distribution along the length of the rod is calculated based on the shape data and the anatomical data; and The plan for fastener placement is generated based on the bone mineral density data of the given vertebra and the calculated force distribution.

20. A device for placing fasteners in a vertebra to be stabilized by a pre-formed spinal rod, wherein two or more fasteners connect the rod to the vertebra, wherein at least one of a target shape of the spine and a shape of the rod is defined in patient-specific shape data, and a bone mineral density of at least one vertebra is defined in patient-specific bone mineral density data, and wherein, The device is configured to provide patient-specific anatomical data and is designed to: The force distribution along the length of the rod is calculated based on the shape data and the anatomical data; and The plan for fastener placement is generated based on the bone mineral density data of the given vertebra and the calculated force distribution.

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