BG67358B1 - Method of designing patient-specific implants for surgical treatment of diseases in the cervical spine - Google Patents

Abstract

The invention relates to a method for designing patient-specific implants which will find application in the surgical treatment of diseases of the cervical spine. The method includes the following seven consecutive steps: scanning of the patient's anatomical structures; pre-preparation; creating a CAD model of the spine; virtual adaptation of the parameters of the implant (the cage); physical construction of the cage; validation of the cage geometry; implementation in the patient through surgery. The advantages of the proposed method for designing patient-specific implants, which will find application in surgical treatment of diseases of the cervical spine, are related to the ability to build a virtual and physical prototype of the spine and implant based on the collected medical images from the patient, as the parametric construction of the CAD model of the implant allows in real time the implant to be personalized in order to achieve the necessary correction of the spinal curvature and to be validated virtually and physically, and then to be materialized through high-speed prototyping technologies.

Description

Field of technology

The invention relates to a method for creating personalized implants by scanning with computed tomography or similar methods, reconstruction of the bone system in 3D, virtual 3D construction and rapid fabrication by 3D additive or conventional technologies of individualized for the needs of the patient patient implants. the intervertebral disc or vertebral body, which will find application in the surgical treatment of diseases of the cervical spine.

BACKGROUND OF THE INVENTION

The neck is anatomically the most complex and mobile segment of the spine. The spine consists of a series of bony vertebrae that are separated by intervertebral cartilaginous discs. Each vertebra consists of a body (in Latin corpus vertebrae), an arch (in Latin arcus vertebrae), lateral growths (in Latin processus laterales vertebrae), articular growths (in Latin processus articulares vertebrae) and a prickly growth (in Latin .processus spinosus vertebrae). The disc consists of an outer ring and an inner heart-shaped pulpos. The structure of the spine allows the body to turn and bend to adopt a wide range of postures. It is often affected by diseases associated with natural mechanical stress and wear (disc herniation, osteochondrosis, etc.), tumors or trauma. Thanks to the development of modern neurosurgical and microscopic techniques as well as the overall advancement in spinal surgery, most of these diseases can be treated or at least controlled. The most common goal of surgery is to remove the compression of the underlying nerve structures (decompression) and to restore the supporting function of the spine (stabilization). For this purpose, parts of the spine are removed - intervertebral discs, parts or whole vertebral bodies, after which bone substitutes, titanium alloys, polymers such as polyether-ether-ketone (PEEK) or other suitable materials are placed and fixed. Most cervical replacements do not perfectly resemble the intervertebral disc space or vertebral body, and the surgeon must adapt the patient's individual anatomy to the implant. For diseased or damaged discs, surgery can be used to insert a spinal implant - a replacement for the intervertebral disc or vertebral body - a cage (also called a spacer) to replace the damaged intervertebral disc and restore normal anatomical relationships in the affected segment.

The cage is a small thin-walled part, usually made of a special medical alloy of titanium, most often Ti6A14V / ISO 5832-3, ISO 5832-2. with perforated or structured walls. The purpose of using cages is to restore the lost height of the disc and reduce the pressure on the nerve roots. The height of the lost disc is restored when the cages are placed in the space between the two vertebrae. The goal is for the surrounding bone tissue to "grow" through the perforated walls of the cages and eventually form a bone bridge - ossification (or adhesion) that holds the vertebrae together and provides a stable structure.

BG 67358 Bl

In recent years, cages have undergone numerous modifications to improve their efficiency. Some of the developed structures are HAC ™. Ray TFC Contact, Contact Fusion Cage ™ and INTER FIX ™ and others, which shows a significant variety of constructions. This is also due to the fact that different systems have different applications (cervical, lumbar vertebrae, etc.).

• Cages have the following functions and specifications:

1) Maintaining the space between the vertebrae (if the space becomes too narrow, the nerve roots can be compressed);

2) Preservation of the normal arcuate curve of the cervical segment of the spine called lordosis. Wear of the vertebrae and intervertebral discs (osteochondrosis) leads to a change in the normal, anatomical configuration and straightening of the segment or even reverse distortion - kyphosis. Correction of these deformities can be achieved by placing cages of appropriate size and shape;

3) Support the formation of a bone bridge between two vertebrae - fusion (ossification).

o Cages come in a variety of shapes and sizes. Some have a cylindrical shape and others a parallelepiped. The cages are placed in a pre-cleaned and prepared disc space between two vertebrae of the spine. Usually, they are made of bone, metal, plastic or carbon fiber. Osteoconductive tissue (autograph - own bone, allograph, other bone substitutes or other substances that stimulate bone growth, such as demineralized bone matrix) can be placed inside the cages. The goal is, after the surgical intervention, the cage to create optimal conditions for fusion of the treated segment of the spine.

Ensuring a stable position of the cages in the intervertebral disc space is done by additional reinforcement with anterior cervical plate.

• The anterior cervical plaques are attached to the front of two or more vertebrae. They help to:

1) Increasing the stability of the operated segment of the cervical spine immediately after surgery;

2) Support the restoration of the normal curve of the spine - lordosis;

3) Provide optimal conditions for fusion at the operated level;

4) Reducing the time during which the patient must wear a collar after surgery.

The plates are fixed with screws screwed into the adjacent vertebrae. The front neck plates and screws are available in different designs and sizes. Most plates are made of metal (mainly titanium alloy). Some newer plate designs are made of composite materials that are resorbed over time.

With regard to operations to remove the compression of the underlying nerve structures (decompression) and to restore the supporting function of the spine (stabilization), the possible methods and surgical techniques can generally be reduced to the following 4 alternatives:

Alternative solution 1: Autotransplantation - use of own bone.

Autotransplantation - using one's own bone, is the oldest of the listed surgical techniques. It is based on taking the patient's own bone - most often the pelvic wing or lower leg. The taken piece of bone (bone span) is shaped with different tools so that it corresponds to the anatomy and the needs of the specific case. Then it is placed and fixed in the desired position. The advantages

BG 67358 Bl of the technique are primarily related to the fact that the bone itself creates the best conditions for fusion - it is not a foreign material and naturally integrates with the surrounding bone structures. The disadvantages of this technique are significant. Taking the bone span from another location involves, in practice, additional surgery with the resulting risks of infection and other complications. It has been shown that the site of bone marrow retrieval remains painful for a long period of time and this often causes significant discomfort to patients. The time of the intervention is significantly extended with the resulting increased risk of infections and slower recovery. Although with its own tissue, fusion is not completely guaranteed. Due to the above, this technique is used only exceptionally and in the absence of other alternatives.

All the listed disadvantages are overcome in the proposed method with individually designed titanium implants while maintaining the described advantages.

Alternative solution 2: Pre-prepared, standardized implant.

This is the most commonly used method, especially in the treatment of one of the common diseases - cervical disc herniation. The presence of pre-prepared implants of different sizes - width, height and angulation is convenient, allows quick selection of the implant, which is closest to the needs of the patient, which reduces the operative time and reduces the risk of infections. The main disadvantages of the method are related to the lack of complete correspondence between the needs of the patient and the specific anatomy and the implants prepared in advance according to the average model. Therefore, the surgeon has to adapt the patient's anatomy to the implant. This in turn is the reason for the uneven distribution of load forces, reducing the contact surface and creating conditions for expulsion of the implant. For the same reasons, the fusion conditions are worse than with the proposed method with individually designed titanium implants.

Alternative solution 3: Implant with the possibility to change the size during the intervention.

Some of the implants for surgical treatment of diseases of the cervical spine have been developed with the possibility of changing the size and geometry. Such an example are telescopic implants, which are extended to the required size for the specific case. They are most often applied when it is necessary to replace the entire vertebral body. The advantages and disadvantages of this type of implant largely correspond to those listed in the previous alternative.

Alternative solution 4: An implant that is sized during the intervention.

This type of implant is used when it is necessary to replace the vertebral body. Most often they resemble a bent in the form of a tube titanium mesh. The mesh structure provides sufficient strength and at the same time allows relatively easy cutting of the implant to the required length. The process prolongs the operating time and is of unsatisfactory accuracy, which therefore creates risks of expulsion and risks of infection.

Individually designed titanium implants

With this type of implants, full compliance with the anatomical structures of the particular patient is achieved. Preliminary design allows to make the necessary adjustments in the shape and size of the implant. so that a maximum contact surface is provided after installation and

BG 67358 Bl maximum stability at restored normal anatomical relationships of the surrounding structures. As a result, optimal conditions for fusion are created. which is the purpose of this type of intervention. The presence of a pre-prepared individualized implant shortens the intervention time and consequently reduces the risk of infections. The above is a prerequisite for faster recovery of patients and in general - a better result of the treatment.

The presence of a stage for preoperative planning and production of the individualized implant can be considered as a disadvantage due to the need for more time. On the other hand, the whole process requires a more careful and detailed understanding of the needs of the particular patient and leads to the best for him, personalized solution.

None of the alternative methods listed above has the advantages listed in the proposed method.

Technical essence of the invention

The objective of the invention is to provide a method for creating personalized, meeting the specific, individual needs of the patient spinal implants for surgical treatment of diseases of the cervical spine by optimizing the bearing surface and anatomical relationships, which will find application in surgical treatment of diseases of the cervical spine. With this type of implants, full compliance with the anatomical structures of the particular patient is achieved. Preliminary design allows to make the necessary adjustments in the shape and size of the implant, so that after placement to ensure maximum contact surface and maximum stability in the restored normal anatomical relationships of the surrounding structures. As a result, optimal conditions for fusion are created. which is the purpose of this type of intervention. The presence of a pre-prepared individualized implant shortens the intervention time and consequently reduces the risk of infections. The above is a prerequisite for faster recovery of patients and in general - a better result of the treatment.

The presence of a stage for preoperative planning and production of the individualized implant can be considered as a disadvantage due to the need for more time. On the other hand, the whole process requires a more careful and detailed understanding of the needs of the particular patient and leads to the best for him, personalized solution.

The problem is solved by building a method that includes the following seven consecutive stages:

1. Scanning of the anatomical structures of the patient - most often by computed tomography or high-end 3D C-arm, which is significantly faster than computed tomography and can be easily used in patients with claustrophobia. as well as in patients weighing more than 150 kg (maximum weight for the masses of most computed tomography).

2. Preliminary preparation or Pre-preparation of the digital data for the anatomical structures of the specific patient, including filtration, segmentation and processing to create a three-dimensional CAD model (reconstruction) of the spine.

3. Creating a CAD model of the spine - on the basis of previously created 3D geometric models processing is performed, resulting in a solid geometric model, such as

Accordingly, actions are taken to simplify the model in order to reduce the amount of recorded information without reducing the accuracy of the description of the problem area - the interface between the vertebrae, where ..implanted newly built parametric model of cervical implant (cage) ).

4. Virtual adaptation of the parameters of the implant (cage), which performs and maintains the necessary correction of the spinal curvature - includes three-dimensional simulation of the location and analysis of the interface. At this stage, the assembly of the obtained solid model of the spine and a pre-designed parametric model of the cervical implant (cage), which is located in the gap between the vertebrae of the affected area, and the adaptation of the parametric model of the implant (cage) to the geometry of the bone system. of the spine by varying its parameters in order to achieve the necessary correction of the spinal curvature.

5. Physical construction of the cage.

6. Validation of the cage geometry.

7. Implementation in the patient through surgery.

Stage "Scanning of the patient's anatomical structures" begins with the capture of digital medical images using a computer tomograph or a high-end 3D C-shoulder from the problem area of the spine, using appropriate equipment, in a clinical setting.

This is followed by a "Pre-preparation" stage, in which digital "medical images" are translated into a surface polygonal STL format using specialized software. The STL format creates a closed surface model, allowing further processing by a three-dimensional modeler for the most accurate reconstruction of the existing bone system. At this stage, selection is made only of that part of the information that is important for the formation of the geometry of the cage. For example, in the case of identified problem areas in NW and C4, only those vertebrae and their adjacent vertebrae are selected for export in STL format.

The resulting STL file is not yet sufficiently suitable for processing in a three-dimensional CAD modeler, as it is essentially a superficial description of geometric objects.

The next step is "Creating a CAD model of the spine" - the goal is to rework the geometric model into a solid model, and accordingly take steps to simplify it, thereby reducing the amount of recorded information (for easier manipulation of the model ), without compromising the accuracy of the description of the problem area, the interface between the vertebrae, where the newly constructed pre-designed parametric model of the cervical implant (cage) is implanted.

The next step is "Virtual adaptation of the implant parameters (cage)". which is carried out by assembling the obtained solid model of the spine and a pre-designed parametric model of the cervical implant (cage) and its adaptation to the geometry of the skeletal system of the spine. Here is the most important procedure "Interface Analysis", consisting of changing the parameters of the pre-designed parametric model of the cervical implant (cage), as well as its location, to obtain the desired customized implant (cage). This procedure requires medical competence for the successful implementation of the geometry of the implant (cage) adapted to the specifics of the geometry of the two adjacent vertebrae, and it is during this procedure that the so-called

EN 67358 Bl "personalization", the implant being fully tailored to the specific clinical case. The step ends with the placement of some additional components, such as the markers in the cage, needed to identify the presence of an implant on radiography when it is made of non-metal.

The next stage "Physical construction of the cage" is related to the physical production of the cage, again using the STL form for transfer of the generated CAD model. The technology for the production of the implant is chosen. basically it is aimed at choosing between subtraction technologies or additive technologies with addition of material. Typically, material removal technologies are used in the fabrication of both non-metallic implants (eg PEEK) and those made of titanium alloys, while additive technologies (3D printing) are typical for the production of mainly titanium alloy implants.

At the stage of "Validation of the geometry of the cage" a review and metrological analysis of the produced physical sample is made and, if necessary, corrective actions are taken.

The final stage of "Implementation in the patient through surgery" involves the placement of the implant during the surgery.

The advantages of the proposed method for creating personalized implants, which will find application in surgical treatment of the patient in the cervical spine, are related to the ability to build a virtual and physical prototype of the spine and implant based on medical images of the patient through computed tomography methods or similar, such as the parametric construction of the CAD model of the implant allows it to be customized in real time to achieve the necessary correction of spinal curvature and validated virtually and physically, and then to be materialized through high-speed prototyping technologies. Preliminary design allows to make the necessary adjustments and adaptations in the shape and size of the implant, so that after placement to ensure maximum contact surface and maximum stability in the restored normal anatomical relationships of the surrounding structures. As a result, optimal conditions for fusion are created, which is the purpose of this type of intervention.

None of the alternative methods listed above have the advantages listed here.

Explanation of the attached figures

Figure 1 shows the original appearance of the imported medical images.

Figure 2 shows the division of the model into three parts - vertebra C4 (Fig. 2.a), vertebra C5 (Fig. 2.6) and their environment (Fig. 2.c) - visualized using the STL files generated for each part.

Figure 3a shows the initial view of the assembled components of fig. 2. in FIG. Z. to them is added a cage, modeled parametrically, and in fig. The parametric model of the cage is presented.

Figure 4 illustrates the possible actions of rotation / displacement of the vertebrae, related to the correction of the spinal curvature and its restoration in normal parameters for the particular patient, as well as the location of the cage between the vertebral bodies.

Figure 5 shows the assembled and modified cage around the vertebrae.

BG 67358 Bl

Figure 6 shows the assembly method and the markers themselves in cases where the cage material is non-metallic (eg PEEK).

Figure 7 shows the network of the STL file of the cage.

Figure 8 shows an exemplary implementation of a cage with rapid prototyping technology.

Figure 9 shows a cage assembled with the vertebrae, aimed at achieving correction of the spinal curvature.

An embodiment of the invention

The first stage of "Scanning the patient's anatomical structures" of the method of creating personalized implants involves the collection of medical images for the patient, which is performed in a clinical setting, and at this stage the preparation of tomographic data consisting of individual files.

The second stage of "Pre-preparation" includes preliminary preparation of digital data on the anatomical structures of the particular patient. This stage is associated with the processing of medical images to obtain a file in STL format of the area of interest. The initial view of the imported tomographic data is shown in fig. 1.

Here the model is divided into parts - most often into three: such as the C4 vertebra, the C5 vertebra and their surroundings. An STL file is generated for each part. This is shown graphically in fig. 2.

Then, at the stage "Creating a CAD model of the spine" the goal is to process the constructed surface geometric model to a solid one, and accordingly actions are taken to simplify it in order to reduce the volume of recorded information (for easier manipulation of the model). , without reducing the accuracy of the description of the problem area (the interface between the vertebrae, where it is expected to "apply the newly built cage").

The fourth stage "Virtual adaptation of the implant parameters (cage)" involves virtual prototyping of the vertebrae, in this case C4 and C5. Virtual prototyping of the vertebrae involves assembling the individual components (shown in Fig. 2) in such a way as to allow easy manipulation (rotation and movement relative to each other) for subsequent adjustment until they reach the required mutual position for normal spinal curvature ( Fig. 3a) and for adjusting to them the cage (Fig. 3b), modeled in turn parametrically (Fig. 3c).

At this stage, an analysis of the interface is performed, which consists of virtual articulation (movement) of the vertebrae (in this case C4 and C5), and in particular are related to the rotation / displacement of the cage relative to the vertebrae C4 and C5 so that a restoration of the normal spinal curvature was obtained, as well as the placement of the cage in the space thus formed between the C4 and C5 vertebrae. The parameters a, b, c and a of the cage are changed (Fig. 3c) in accordance with the established position of the vertebrae until the maximum contact surface between the cage and the vertebrae is reached.

Examples of possible actions are shown in fig. 4, where rotation of the C4 vertebra relative to C5 and displacement and change of the cage parameters is demonstrated. The cage itself is also modified during this step, as the parametric model allows a wide variation of its size and the achievement of different geometry. The assembled and modified cage is shown in the environment of the vertebrae in Fig.5.

It is possible to assemble markers to the constructed structure of the cage. This applies in cases where the material of the cage is non-metallic (eg PEEK). The assembly method and the markers themselves are shown in fig. 6. The markers themselves are short metal axes or balls that are used to recognize the cage on X-rays.

This stage ends with the construction of an STL file that will be used to make the cage. The geometry of the cage is relatively simple and the network of the STL file has the form shown in fig. 7.

The fifth and sixth stages are "Physical construction of the cage" and "Validation of the geometry of the cage", respectively. An example implementation of a cage with rapid prototyping technologies is shown in fig. 8, as additionally with the same technologies two vertebrae are made above and below the place of installation of the cage. In FIG. 9 shows the cage implanted between the vertebrae, aiming to achieve the necessary correction of the spinal curvature. The physical model created in this way allows to assess the contact (interface) between the cage and the vertebrae and to inspect and analyze the attachment and contact surfaces.

The last stage is "Implementation in the patient through surgery".

Application of the invention

Customized implants created by this method can be used in the surgical treatment of diseases of the cervical spine.

Claims (1)

Method for creating personalized implants for surgical treatment of diseases of the cervical spine, characterized in that on the basis of taken in clinical conditions tomographic data from the problem area of the patient's spine are built sequentially three-dimensional reconstruction of the skeletal system in CAD environment through surface and / or solid-state 3D model of the surrounding skeletal system of the affected area of the spine, based on which the geometry and taking into account the individual characteristics of the individual creates a virtual prototype of the spine, including three-dimensional models of the spine and pre developed three-dimensional parametric solid model of a typical for this area implant (cage), as the parameters of the solid model of the implant (cage), corresponding to the necessary correction of the spinal curvature, serve as initial parameters in its personalization to individual three-dimensional geometry to achieve maximum contactsurface between the cage and the vertebrae and ensuring successful fusion for each patient and subsequently for his physical production through materialization technologies with addition or removal of material