Patent Grant
9972406
The present application relates to a computer-implemented method for modeling an orthopedic cast. More particularly, the present application relates to a method for rapidly modeling a custom-made and 3D-printed orthopedic cast.
Bone fractures occur in the general population due to trauma or bone diseases. Plaster or fiberglass casts have been employed for the treatment of most bone fracture patients. Traditional orthopedic casts or orthoses are produced by a body-based contacting model. The bottom mold for the cast is generated from surface shapes of injury limbs and filled up with plasters. Thermoplastic material, PE (Polyethylene) or CPP (copolymer polypropylene), is pasted on the mold and removed after it is cooled down. Bone fracture patients wear plaster splints after the surgery followed by orthoses for further recovery. Those casts may cause several skin diseases and a potential bone and joint injury due to their heavy structure and poor ventilation. Moreover, patients suffer mechanical pressures during the mold manufacture, and multi-reproduction of physical molds is unfeasible.
3D printing technology is a rapid growing manufacture technique for producing complex physical model using 3D digital model. Recently, the 3D printing technology has been extensively applied to surgical practices and medical training. The rapid manufacture of the physical model from medical images provides a technical means that results in minimal invasion in medical planning and treatment. Custom made rehabilitation tools produced using 3D printing technique has been deployed in the new development of orthoses.
Some novel concepts have been proposed as potential substitutes for plaster cast manufactured by the 3D printing technology. The mesh-like structure forms an artistic surface pattern of the model by changing its webby density, providing more solid fracture region with less material in healthy areas.
Another development is a model similar to Cortex but embedded with an ultrasound device for promoting the therapeutic process. Those new designs are fabricated using the 3D printing technique and environment friendly material. The cast geometries are generated from 3D scan models that are patient specific and are capable of offering wearing comfort and fashionable appearance. The mesh-like structure of the model presents excellent ventilation and significantly light weight. However, the mesh-like structure has less strength in supporting the injured limbs. Low intensity mechanical impact may break the webby beam. In addition, the webby shape is most likely to cause crack and fatigue due to the slender connecting bar.
A hybrid model for custom-fit wrist orthoses combines the webby frame with the shell cover to enhance the structural strength of the cast and to keep the ventilation of the cast. The design process mainly includes a process of modeling an inner frame and an outer cover via a CAD system. This approach may increase the stiffness of the model and prevent the model structure from breakage. However, an experienced CAD engineer is required for creating appropriate engineering structure.
Despite the technical advance and economic potential, 3D printing technologies have not become a primary means in fabrication of the orthopedic cast. Significant technical expertise is required for designing the cast, which is costly and timeconsuming. In order to perform a CAD process, the scanned data of subject limbs must be converted into a specific CAD file with geometric modifications. An experienced CAD engineer is required for creating the model and converting the model CAD file to an STL (Standard Template Library) file for 3D printing.
Clinical demands for developing a cast with good ventilation, light weight, and automatic design process and less requirements of expertise, have gotten more and more attention. The medical applications of the 3D printing are increasing due to its manufacture speed and cost effectiveness. The growing 3D printing technologies make it possible to fabricate a complex geometric model in orthopedic casts and significantly reduce the manufacturing time and cost.
One of the objectives of the application is to develop a rapid modeling technique for custom made orthopedic cast and to overcome the weakness of traditional alternatives, such as weight and ventilation. The proposed modeling method would require less expertise and more automatic than the conventional approaches do.
In an aspect of the application, a computer implemented method for modeling an orthopedic cast is proposed. The method may comprise: scanning an injured limb to extract raw body data; determining, from the extracted raw body data, target portion data of the injured limb, wherein the determined data may represent a fine cast surface for the orthopedic cast; patterning the fine cast surface to form flare edges, a ventilation structure and a blank area thereon; forming an opening gap on the blank area for assembling and disassembling the orthopedic cast; and offsetting the cast surface in parallel to thicken the orthopedic cast.
According to an embodiment of the present application, the method may include stretching points on surface areas near opening ends of the fine cast surface to create flare edges at the opening ends.
The cast surface may be offset by a specific distance to form two parallel cast surfaces without connection on the opening ends. The two parallel cast surfaces maybe linked at the opening ends by connecting edge nodes on one cast surface of the two surfaces with corresponding edge nodes on the other cast surface of the two surfaces.
In one embodiment of the application, the centerline maybe bounded on, for example, the Voronoi diagram of the orthopedic cast and may be composed of points centered the maximal inscribed sphere. The centerline maybe a spline line and may comprise tangent vectors varied along the spline line. The clipping plane maybe defined by a normal vector, which averages a couple of successive tangent vectors from an endpoint of the centerline.
In one embodiment of the application, the method may further comprise applying different extending coefficients on the closest distance between the centerline and the points on the surface areas near the opening ends to stretch the opening ends to create flare edges at the opening ends.
In one embodiment of the application, the cast surface may have a polyline tube shape. The step of patterning the fine cast surface as mentioned in the above may comprise cutting the cast surface along the longitudinal direction of the surface to form a plurality of polyline loops; determining a reference vector for each of the polyline loops to create a bundle of vector lines for locating centers of the ventilation holes along a circumferential direction; determining the blank area in accordance with angles between the reference vector and a start vector line and a symmetric end vector line of the created vector lines; and forming an opening gap on the determined blank area of the cast surface.
As an example, the method may further comprise determining the centers of the ventilation holes in an area other than the blank area of the cast surface; and forming the ventilation holes on the cast surface based on the centers. To this end, the method may further comprise determining a centerline of the cast surface along a longitudinal direction thereof, wherein the centerline may be geometrically defined as a shortest path to connect two endpoints of the orthopedic cast; and removing end portions of the surface, which may be outside of clipping planes, wherein the clipping planes may be normal to the centerline.
In one embodiment of the application, the method may further comprise averaging the tangent vectors along the centerline, wherein the average of the tangent vectors may be employed as a normal line of the cutting planes; integrating all micro segments composing of the centerline to obtain a total length of the centerline; subtracting two marginal lengths from the total length to define an effective length of the centerline; and cutting, within effective length, the cast surface along the longitudinal direction of the surface to form a plurality of surface segments with polyline loops. The cut surface segments may have the same extension length in the longitudinal direction.
According to an embodiment of the application, the centers of the ventilation holes may be located on the polyline loop with the closest distance to the bundle of vector lines. The ventilation holes may be formed by modeling a plurality of spheres with same diameter based on the centers, and removing portions of the cast surface intersecting with the spheres to form the ventilation holes. The opening gap may be formed by creating a path of the opening gap along the reference points and two end points on the flare edges; modeling a tube along the path, wherein the tube may be centered with the path; and removing portions of the cast surface intersecting with the tube to form the opening gap.
In another aspect of the present application, a system for modeling an orthopedic cast from raw body data of an injured limb is proposed. The system may comprise: a memory that may store executable instructions; a processor electrically coupled to the memory that may execute the executable instructions to perform operations of the system. The executable instructions may be configured to: digitize the raw body data and transfer the same as specific type of file; determine, from the extracted raw body data, target portion data of the injured limb, wherein the determined data may represent a fine cast surface for the orthopedic cast; pattern the fine cast surface to form flare edges, a ventilation structure and a blank area thereon; form an opening gap on the blank area for assembling and disassembling the orthopedic cast; and offset the cast surface in parallel to thicken the orthopedic cast.
In a further aspect of the present application, an orthopedic cast modeled from raw body data of an injured limb is proposed. The orthopedic cast may include a cast surface with a tube like shape; flare edges at opening ends of the cast surface; and a surface pattern formed on the cast surface and including a ventilation area and a blank area. A plurality of ventilation holes may be formed on the ventilation area and an opening gap may be formed on the blank area.
According to an embodiment of the application, the ventilation area may comprise a plurality of ventilation holes. In addition, the blank area may comprise an opening gap for assembling and disassembling the cast.
With the modeling method of the present disclosure, less expertise will be required and more automatic will be achieved.
Exemplary non-limiting embodiments of the present application are described below with reference to the attached drawings. The drawings are illustrative and generally not made according to an exact scale. The same or similar elements on different figures are referenced with the same reference numbers.
Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. When appropriate, the same reference numbers are used throughout the drawings to refer to the same or like parts.
The scanned data of an injured limb may be obtained by, for example, a photometric scanner, Artec Eva and Artec Space Spider (Luxembourg). Patients should be placed in an appropriate position for obtaining the adequate data for reconstructing an image of the injured limb. For example, the surface geometry of limb may be digitized and transferred as a polygonal STL (Standard Template Library) file with over a plurality of points and triangle elements (for example, 200,000 points and 400,000 triangle elements). The number of the points and the elements may vary widely from one anatomic site to another. The initial cast surface model may be generated from clipping the raw body data as shown in
At step S102, the target portion data for a fine cast surface is determined by clipping the raw body data. The determined data represents a fine cast surface for the orthopedic cast. The cast surface has tube like flare openings at the opening ends, which are formed by stretching points on surface areas near opening ends of the fine cast surface. In this step, a computation of centerline L is proposed to create a fine cast model with a visually perpendicular end plane. After the centerline L is determined, the end portions of the cast surface, which are outside of clipping planes normal to the centerline, will be removed. The clipping location may be determined by orthopedic technicians in accordance with the injury site. It should be noticed that the clipping plane 102 may not be visually perpendicular to the cast surface 101.
Computing centerline L of the raw cast surface 101 is used not only for creating desired edges of the fine cast model 103, but also for subsequent modeling steps. The centerline computation and fine edge clipping process may be implemented as follows.
At step S103, flare openings are generated by stretching points on surface areas near opening ends of the fine cast surface.
The flare opening for tube-like cast geometry may create a funnel-shaped end. Flare edges are required by orthopedists and are modeled in both end sides of the fine cast model to ensure the wearing comfort and safety. The funnel-shaped geometry with round corners may produce a smooth touching surface and thus may prevent injuries from the usual movement of part (such as the wrist) of the injury limbs. Points on the surface areas near the opening edges may be stretched by extending vectors. Referring to
{right arrow over (A)}i′−{right arrow over (C)}i=bi({right arrow over (A)}i−{right arrow over (C)}i) (1)
Where Ci (i=0, 1, . . . , n) are central points on the centerline. Ci is the point with the closest distance to the original surface vertex point Ai. {right arrow over (A)}i′ is the new vertex point stretched from Ai·bi is the extending coefficient with respect to points same layer as Ai. Values of coefficient bi may lineally vary along the centerline.
The maximal extending coefficients may be applied on the opening ends of the tube-like cast. Not all surface points are applied with the extending factor. In this embodiment, surface points with a certain distance (for example, 3˜5 mm) to the clipping plane are applied with the extending coefficient. There is no exact standard to determine the values of the coefficients depending on the original geometry. For example, the maximal coefficient used in this embodiment may be 1.15, but the present application is not limited thereto. The funnel-shaped opening ends are more or less intuitive and different values of the maximal coefficient with orthopedic feasibility are acceptable. Flare shapes 104 and 105 may be generated in both sides of the cast 103 in this step.
The process now turns to step S104, in which the fine cast surface is patterned to form a ventilation area and a blank area.
The process begins with step S201. In this step, the cast surface is cut along the longitudinal direction of the surface to form a plurality of polyline loops. An algorithm may be developed to perform this step automatically. For example, the algorithm may firstly average the tangent vectors along the centerline, which is a spline line. It then uses the average of the tangents as the normal vector of the cutting planes. For example, the total length of the centerline may be computed by integration of all micro segments that compose of the centerline. The effective length of the centerline may be defined by subtracting two marginal lengths from the total length as illustrated in
Then the process 2000 turns into step S202, in which a reference vector for each of the polyline loops is determined to create a bundle of vector lines for locating centers of the ventilation holes along a circumferential direction. In this step, a user specified point on the cast surface and a mapping point of the user specified point on the centerline is selected.
Each reference vector Lv may be used to create a bundle of vector lines Li for further locating the centers of holes. In terms of technical needs, the number of holes for each slice may be pre-defined. As shown in
Where β is the angle between two adjacent vectors and m is the number of holes for each slice. The centers of holes are located at the polyline loop 301 with the closest distance to the vector lines Li. Each vector line Li determines one hole center.
Once the centers of the ventilation holes are determined, a plurality of spheres with same diameter will be modeled based on the centers. At step S203, the ventilation holes are formed by removing portions of the cast surface intersecting with the spheres.
After the centers of holes are selected, a plurality of micro spheres 601 with those centers may be modeled as shown in
At step S204, the blank area is determined in accordance with angles between the reference vector and a start vector line and a symmetric end vector line of the created vector lines. Generally, the angles are same as each other. After the blank area is determined, a path of the opening gap is created along the reference points and two end points on the flare edges.
Once the ventilation area and the blank area are determined, an opening gap will be formed on the blank area for assembling and disassembling the orthopedic cast.
The previous steps have created a marker specified to a user on the cast surface. Based on the marker point Cr, the array of alpha points Cri may be selected in previous steps as illustrated in
Creating a smoothing curve as the path for opening gap 805 is developed in this embodiment. More points located at geodesics will be added into the control point set. The control point set multiplies the points for modeling an accurate and rational path line. A spline line passing through all points in the control point set is built and run through the cast surface 103. The spline line may be defined as the path of the opening gap 805.
At step S205, a tube 806 will be modeled for creating the opening gap 805. The opening gap is formed by removing portions of the cast surface intersecting with the tube. In this step, a circle may be created at one end point of the spline line and sweep along the path to generate the tube 806. The spline line is then served as the centerline of the tube 806. A small size of the tube will develop a small gap which would better enclose the injury limbs. The smaller size of the tube 806, the better cast structure will be modeled. For the consideration of the manufacturing feasibility, e.g. accuracy of 3D printing, the diameter may be set as around, for example, 2 mm. But the diameter of the tube is not limited thereto. A parametric tube may be created for adjustments of the gap space. Once the tube 806 is built, the opening gap 805 will be developed by performing Boolean subtraction between the tube and cast surface as displayed in
At step S105, the cast surface is offset in parallel so as to thicken the orthopedic cast.
{right arrow over (p)}′={right arrow over (p)}+t·{right arrow over (n)}pi (3)
Where {right arrow over (p)} is an original vertex of an element; {right arrow over (p)}′ is the offset vertex. {right arrow over (n)}pi is the normalized direction vector of the element and t is the thickness. Due to the curve shape of the cast surface with concave shape in some regions, a relatively great thickness may result in wrapping element shapes on the cross section, where sides of two or more elements intersect. A small thickness (e.g. 1 mm) is suggested in each step of offsetting to avoid geometric error. Offsetting elements with a small thickness is able to technically smooth the surface and further reduce the occurrence of wrapping elements. The accumulation of thicknesses can generate the resulting thickness as required by users.
The above steps and related algorithms may be developed by, for example, Visualization Toolkit (VTK, Kitware) and integrated into an intelligent designing system. The cast geometry is built from scanned data making an orthosis custom made.
As will be appreciated by one skilled in the art, the present application may be embodied as a system, a method or a computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment and hardware aspects that may all generally be referred to herein as a “unit”, “circuit,” “module” or “system.” Much of the inventive functionality and many of the inventive principles when implemented, are best supported with or integrated circuits (ICs), such as a digital signal processor and software therefore or application specific ICs. It is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating ICs with minimal experimentation. Therefore, in the interest of brevity and minimization of any risk of obscuring the principles and concepts according to the present application, further discussion of such software and ICs, if any, will be limited to the essentials with respect to the principles and concepts used by the preferred embodiments.
In addition, the present application may take the form of an entirely software embodiment (including firmware, resident software, microcode, etc.) or an embodiment combining software. For example, the system may comprise a memory that stores executable components and a processor, electrically coupled to the memory to execute the executable components to perform operations of the system, as discussed in reference to
Although the preferred examples of the present application have been described, those skilled in the art can make variations or modifications to these examples upon knowing the basic inventive concept. The appended claims are intended to be considered as comprising the preferred examples and all the variations or modifications fell into the scope of the present application.
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