This invention relates to a surgical system.
For example, in U.S. Pat. Publication 2018344371 a system for HTO was disclosed including a removable shim, a wedge prosthesis and a support plate.
According to one example embodiment there is provided a removable wedge for high tibial osteotomy surgery according to independent claim 1, a method of designing a wedge for high tibial osteotomy surgery according to independent claim 9, a process for manufacturing a wedge for high tibial osteotomy surgery according to independent claim 10, a method for pre-operative planning of a high tibial osteotomy surgery according to independent claim 11 or 28, a reusable wedge according to independent claim 23 or a prosthetic implant according to independent claim 26.
It is acknowledged that the terms “comprise”, “comprises” and “comprising” may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, these terms are intended to have an inclusive meaning – i.e., they will be taken to mean an inclusion of the listed components which the use directly references, and possibly also of other non-specified components or elements.
Reference to any document in this specification does not constitute an admission that it is prior art, validly combinable with other documents or that it forms part of the common general knowledge.
The accompanying drawings which are incorporated in and constitute part of the specification, illustrate embodiments of the invention and, together with the general description of the invention given above, and the detailed description of embodiments given below, serve to explain the principles of the invention, in which:
In general terms, one or more embodiments may relate to a custom wedge for HTO, and/or an implementation of pre-operative planning software for HTO surgery, where the wedge parameters are optimised for each patient from functional / task simulations and/or using a deformable model for soft tissues.
The wedge may have the advantage that it can be inserted to precisely define the corrected position while a support plate is attached (no need for pinning but could be), then removed, which may allow fixing of the support plate to be more accurate than with a removable shim or wedge prosthesis that is not locked in place in a patient specific location. The wedge may also form part of the support plate itself.
The pre-operative planning software may have the advantage that it is numerically stable and/or able to provide an effective and efficient decision-making tool for deciding the sagittal wedge angle and the coronal wedge angle based on loading data, heatmaps, pressures graphs, and/or visual constructs of corrections with weightbearing line, mechanical axis. The software may display pressure maps along-side 3D models of the leg virtually corrected by a wedge of a user selected angle. This may allow the user to visualize the correction to be done. The software may also automate parts of or the whole process from image processing to simulations.
Referring to
Referring to
A second cut 28 (bi-planar osteotomy) can also be included, of width 30, to preserve the attachment of the patella tendon, using a narrow saw blade to avoid overcutting. Alternatively, the osteotomy may be performed below the level of the tibial tubercle.
The exact position, size and orientation of the gap 26 will determine the final orientation of the top of the tibial plateau 12, and hence the load distribution in the tibia and femur and the final orientation of the tibia relative to the femur.
Referring to
In order to model the contact pressures by various offloading angles, a 3D model of the knee is required, plus:
The model may also include the Femur and distal femur cartilage and the tibia and proximal tibia cartilage. Depending on the requirements of the application the model may also include the meniscus, the anterior cruciate ligament, the posterior cruciate ligament, the medial collateral ligament, the lateral collateral ligament, the patella and patella cartilage, and/or one or more muscles or other soft tissues.
The 3D Model may include the surface geometry of the entire tibia and fibula, which may be represented by a triangulated mesh (but other representations may be used according to the application requirements, e.g. b-splines, non-uniform rational basis spline (NURBS)). The 3D model of the bones and cartilage are created from the MRI. This can be through manual segmentation or automatic segmentation. Automatic segmentation can be via a series of image filters like thresholding, region-growing, and edge detection. It can also be through a model-based method such as an active shape model, active appearance model, or a convolutional neural network.
The models produced above are typically of portions of bones since the field-of-view of each scan only covers a joint. For example, a knee MRI scan may produce 3D models of the distal femur and the proximal tibia, but not of the whole femur or whole tibia. The whole-bone geometries are required to simulation the kinematics of the whole limb.
To obtain models of the whole bones, statistical shape models (SSM) are used to reconstruct whole-bone models from the partial bone models, magnetic resonance imaging (MRI) scans of the hip, knee, and ankle are obtained a low, high, and low resolutions, respectively. Partial 3D models of the femur, tibia, and fibula are segmented from the scans. For the femur, a mean femur model is morphed to fit to the partial femur 3D models through optimisation of the model’s position, orientation, and shape as parameterised by the SSM. After this morph, a finer-scale morph is performed at the proximal and distal femur regions using a local morphing method. A similar process is performed for the tibia and fibula. FE model generation using morphing and region mapping methods may allow the process to be unsupervised and / or automated. If medium or higher resolution scans are obtained for the hip and ankle, femur and tibia models can be constructed from the segmentations directly without using a shape model. The models would consist of segmented proximal and distal ends, with interpolated triangles spanning the space in between (the diaphysis of the bones). We do not need highly accurate diaphysis geometry because the subsequent finite element modelling is not concerned with the diaphysial region. Low res scans: >=10 mm slice spacing, medium res scans: ~3 mm slice spacing, and high res scans : ~1 mm slice spacing.
The whole-bone 3D models are then aligned to the patient’s weight bearing (WB) X-ray to represent their neutral (standing) pose and reconstruct their knee mechanical and anatomical axes. One way of performing the alignment is to
The registered 3D models are then articulated according to knee joint angles calculated from motion capture. The joint angles may simulate walking, Sit to stand, Squat to stand, stair climb and descending, Jogging/running, side-step and/or other sport-specific motions or tasks. Motion capture (such as optical mo-cap) may identify the knee joint angles, or they can be simulated by performing these activities using a database or statistical model of body motion. Simulation
After alignment, the 3D models are used to generate a finite element (FE) model of the knee. In a rigid-body model of the knee, the 3D models are used as is (surface models). In a deformable model of the knee, the 3D models are converted into volumetric meshes with either tetrahedral or hexahedral elements. Boundary conditions and constraints are then mapped onto points or regions of the meshes to simulate mechanical loads (e.g. body weight, muscle forces, and ground reaction force), contact (between bones, cartilage layers, the meniscus), and mechanical constraints (e.g. ligaments, meniscus). In general, the tibia and fibular are fixed in position and orientation while the femur is free to move while a force (e.g. half body-weight while standing) is applied at the femoral head. The geometric configuration of the FE model is modified for each wedge angle by altering the direction of load at the femoral head to efficiently simulate the change in mechanical axis resulting from the insertion of a wedge. Alternatively, we can fix the femur and leave the tibia and fibula free to move, depending on the surgeon’s preference. Also, the forces can be applied at the bone centre of mass as a rigid-body force to further simplify the simulation.
The morphed mesh has the same mesh topology for every patient. Therefore, the anatomical points and regions can be defined once on the mean mesh in terms of their vertex and face indices and know where they are on any morphed patient mesh. This allows boundary conditions to be automatically assigned, loads to be automatically assigned, and other constraints on the relevant points and regions of the mesh to be automatically assigned. If a shape model was not used in the 3D Modelling step, the points and regions can still be defined manually.
Further details of the process of morphing and region mapping are provided in copending New Zealand patent application number 763679, entitled “Orthopaedic Pre-Operative Planning Software”, filed by the same Applicant as the present application on 20 Apr. 2020, the contents of which are incorporated herein by reference.
The locations of the osteotomy entry and hinge points are defined on the FE model with input from the surgeon. In the planning software, the user can click these points through the user interface, or the software can define them automatically based on heuristics about their standard positions.
The FE simulation is run for a range of wedge size and angles to generate pressure maps from which an optimal set of wedge properties can be determined automatically or by a surgeon.
A maj or challenge of FE modelling of musculoskeletal system is the numerical stability of the model, and its computational performance. Both tend to decrease as the fidelity of the model increases, especially in a deformable FE model. Significant improvements in stability and performance can be made by using a rigid-body model that allows the simulation to be run automatically in minutes rather than with manual adjustments over hours or days.
An implementation of an appropriate rigid-body model uses tension-compression contact modelling to estimate relative pressure between the medial and lateral compartments of the knee. The rigid-body model may have far fewer degrees of freedom than a fully deformable model and so may solves faster or be better conditioned numerically. It may require no manual tuning for the simulation to solve, whereas a deformable model may require days of tuning. Note that the goal of the simulation is to determine how the wedge angle changes the relative loading of the compartments. Therefore, the absolute pressure is not important.
The criteria for the suggested correction could be:
On the left hand top area of the screen 800 is a chart 802 of the peak, mean, or total pressure (force) in the medial 804 and lateral 806 tibial compartment versus coronal wedge angle. The user can also alternatively select the pressure chart for sagittal wedge angles at a given coronal angle
On the right hand side, a 3D model 808 is shown of a fixed front-on view of the leg showing the native and post-op mechanical axis. This also shows the planned wedge, femur, tibial, and cartilage on each bone, plus the other soft tissue structures if available, focused on the knee. As the user selects different wedge angles, the wedge model changes along with the knee geometry. The tibia below the wedge is fixed while the tibia above the wedge and the femur (plus soft tissue) pivots according to the wedge.
Below the chart 802 is a series of 3D pressure maps 810 for a range of different coronal angles for the selected sagittal angle. This panel 810 can be expanded upwards to show a grid of all pressure maps for all coronal and sagittal angles. In the expanded view, the user can zoom in and out from the full grid to a particular pressure map. Selecting a pressure map will update the selected angles and the models in the 3D scene.
Sending the final model for designing wedge to a 3D printer may be done as described below.
The 3D HTO wedge angle is designed as above, then FE model wedge shape and the parts (wedge, plate, screws, ...) are determined in order to achieve the desired wedge angle in terms of a practical surgical plan. Solidworks may be used to design the wedge, based on the FE model results. Lastly the wedge and support plate may be 3D printed using Dental SG resin. The 3D printer may be provided offsite or at the surgery.
An example wedge 900 is shown in
The anterior flange 904 is included to determine the wedge position within the first cut, and to allow effective insertion and withdrawal. A posterior face 910 of the flange 904 is designed to conform to the geometry of the anterior tibia 912. In particular, the posterior face 910 should mould over the tibial tuberosity. The flange 904 includes 2 tabs 914, and each tab includes a hole 916. As described later, the holes 916 may be used for insertion and/or removal during surgery.
The wedge may be 3D printed on a Formlabs 3D printer using Dental SG resin. This allows it to be sterilised in an autoclave. Alternatively, it may be printed or milled from plastic, nylon, metal, bone, or any combination thereof.
The anterior flange shape is generated from the Boolean subtraction of the tibia geometry from a solid extrusion of the wedge 20-30 mm inferiorly into the tibia.
A reusable wedge may also be employed that is adjustable to desired angles in the coronal and sagittal planes.
As shown in
The wedge could also be adjusted automatically and wirelessly. In this case, the wedge could contain an internal wireless communication module (e.g. Bluetooth), power supply (e.g. wireless rechargeable battery), actuators that adjust the wedge angles, sensors to measure the wedge’s current angles and a controller to drive the actuators to a predetermined coronal and/or sagittal correction. In this case, the wedge can be configured directly from the planning software running on a computer with a compatible wireless communication module (e.g. Bluetooth). The wedge would communication its current angles back to the planning software to confirm that it has been correctly configured.
The wedge could also contain load-cells to measure the force being exerted on its superior and inferior faces. This is useful to prevent breaking the bone by using imposing wedge angles that are too large. A possible use case is when the wedge is inserted into the bone cut in its lowest angles configuration then adjusted up to the desired angles. As the angle is incrementally increased, the wedge can transmit the force it is experiencing to the software which displays the value to the user. If the force exceeds a threshold, a graphical and/or audio warning is emitted by the software and/or the wedge.
The wedge could also be made of a bio-absorbable or integrable material, e.g. bone allograft. In this case, the wedge would be a permanent implant left in the patient’s body. Such a wedge would incorporate with the bone.
Using such a wedge would avoid having to use a plate to fix the bone and act as mechanical support. As shown in
As mentioned above Virtual reality (VR) allows the HTO operation to be practiced using the previous models. Similarly, during the operation, using the patient’s real-time image processing (registration of the 3D models on lower limb of the patient during the operation) the location of the implants can be matched against the surgical plan.
Once the cuts are made, several holes are drilled in the cortex/lateral hinge, to reduce the likelihood of a fracture. Additionally, the depth 32 of the first cut 24 may be adjusted, to reduce the likelihood of a fracture in the cortex/lateral hinge. The depth 32 of the first cut 24 may finish 1 cm from the cortex. It may be controlled by the slow introduction of stacked osteotomes.
The wedge is inserted anteromedially, reflecting the medial collateral ligament posteriorly with a retractor. The support plate is inserted attached using sequential screws (locking and non-locking). The support plate may be a Tomofix® support plate marketed by DePuySythes. The Tomofix® may be surgically inserted according to the technique annexed hereto.
The 2 holes are used as a point of attachment for a tool to hold and pull or push wedge during insertion and retraction.
Referring to
The system 1000 includes a data store for the X-Ray data 1002, the MRI data 1004, and the gait data 1006. The X-Ray data 1002 and the MRI data 1004 is used to construct the shape model and segmentation data 1008. The shape model and segmentation data 1008 and gait data 1006 is used to construct the opensim model 1010, which calculates the kinematics, muscle forces and joint reaction force to generate an elastic foundation model 1012. The elastic foundation model 1012 may then be used to simulate the 3D contact pressure graphs.
Using a UI, the user may initially create a case, then upload the MRI and X-Ray data together with patient details such as patient height. The MRI data may have a minimum of 5-mm spacing and 5-mm thickness in the hip and ankle, 0.5 mm spacing and thickness in the knee and with a 150-mm range centre on the knee joint.
Image segmentation may occur automatically or may involve user intervention.
Templating occurs through the generation and running of FE models of the knee at a range of wedge angles to generate pressure maps of the knee at each wedge angle. This may occur automatically or may involve user intervention.
Once the 3D model is complete the system is then free to generate reports. For example the UI described earlier in relation to
While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of the Applicant’s general inventive concept.
Number | Date | Country | Kind |
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763680 | Apr 2020 | NZ | national |
763731 | Apr 2020 | NZ | national |
This application is a bypass continuation of International PCT Patent Application No. PCT/NZ2021/050062 filed on Apr. 12, 2021, which claims priority New Zealand Patent Application No. 763680 filed on Apr. 20, 2020, and New Zealand Patent Application No. 763731 filed on Apr. 21, 2020, which are incorporated by reference herein in their entirety.
Number | Date | Country | |
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Parent | PCT/NZ2021/050062 | Apr 2021 | WO |
Child | 17967701 | US |