OR ORTHOPEDIC CONDITIONS

TECHNICAL FIELD OF THE INVENTION

The invention relates to elements used to aid in treatment of musculoskeletal disorders or orthopedic conditions. Particularly, the invention relates to optimization of the characteristics and/or placement of elements used to aid in musculoskeletal disorders or orthopedic conditions such as repair of bone fractures using computer-implemented arrangements.

BACKGROUND OF THE INVENTION

Traditionally, treatment of musculoskeletal disorders or orthopedic conditions is conducted through a medical professional performing an analysis of the required measures to be taken through inspection of a patient or imaging data. Through this inspection, a practitioner may classify an injury and select the type of treatment that is required. It may be difficult in some cases to identify an injury and it may also be difficult for the proper treatment to be select even if the classification is correct.

In the case of bone fractures, for example implants and screws used in reparation of fractures and the locations into which they are placed with respect to the bone and the fracture, are selected by a medical professional based on previous experience. The current approaches may lead to selections that are not optimal, as each fracture is unique and may be complex, with several fractures and bone fragments. The practitioner cannot foresee how an implant will behave with movement of the bone and its surrounding muscles. There is also such a large combination of implants and methods for their attachment to the bone and the locations thereof, that it is not feasible for a human to accurately predict which combination would be the best choice for a given situation.

Also repair of e.g. a radius bone fracture is done by selecting either an implant and an orthopedic cast or an orthopedic cast alone. It is typically not certain if the treatment is successful, i.e., if the bone heals and holds its shape and position as planned.

Further, the design of custom elements, e.g. implants, cannot be executed so that an optimum selection is made regarding the material, dimensions, or other characteristics of the elements for a specific fracture in a specific bone with features that may be dependent on the entity within which it resides.

SUMMARY OF THE INVENTION

An object of the invention is to alleviate at least some of the problems relating to the known prior art. The object of the invention can be achieved by the features of the independent claims. One embodiment of the present invention provides an arrangement for optimization of location and/or characteristics of at least one element used to aid in treatment of musculoskeletal disorders or orthopedic conditions. The arrangement comprises at least one processor configured to receive three-dimensional digital imaging data indicative of subcutaneous tissue of a target entity. The at least one processor is additionally configured to create, using the imaging data, a computational model to represent one or more tissues and their possible fragments incorporating information involving a location related to a musculoskeletal disorder or orthopedic condition identified from said imaging data. The at least one processor is furthermore configured to optimize the location and/or one or more characteristics of the said at least one element with respect to at least one variable and generate an output to a user entity of the arrangement, indicative of the feasibility of the at least one element. The musculoskeletal disorder or orthopedic condition inspected by the arrangement involves fractured tissue and/or one or more tissue fragments and the computational model is created through performing a comparison between the three-dimensional imaging data related to a musculoskeletal disorder or orthopedic condition and data representing a generic model of corresponding tissue and as a result of said comparison, the computational model represents the fractured tissue and/or tissue fragment(s) in positions corresponding to their intact form.

There is also provided a method according to claim 12 and a computer program according to claim 14. Having regard to the utility of various embodiments of the present invention, reductions in expenses related to rehabilitation of musculoskeletal disorders or orthopedic conditions may be achieved. Errors made in treatment selections may reduce the amount of time required by a medical professional to treat a specific condition, as correct classification of an injury and selection of a suitable treatment strategy or element used to aid the treatment may be made more efficiently.

Errors made in classification of an injury may be avoided. Through an arrangement according to the present invention, a medical professional may gain more precise knowledge about the extent of an injury. For instance, the extent of fragmentation may be evaluated more accurately than through visual inspection of a patient or image data.

It may be advantageous for a medical professional to utilize an arrangement solely for purposes of obtaining a computational model that represents fractured tissue and/or tissue fragment(s) in positions corresponding to their intact form. In other words, an arrangement may be used to obtain a computational model of a patient's tissue where repositioning of tissue fragments, i.e., torn muscles or broken bones for instance, has been carried out.

Errors in e.g. placement of implants or their selection leads to reoperations to replace the implant, which further requires reserving expensive operating rooms and time of personnel required in the procedures. Operation expenses may additionally be reduced as time taken to perform surgeries can be decreased if operation instructions are given to the surgeon, and there is no need for further assessment at the time of the surgery.

The invention provides possibilities for treatment using also reverse engineering, in which the outcome of previous cases may be utilized to aid in treatment strategy or element selection. This possibly leads to increased knowledge on healing by using a patient-specific computational model and simulation combined with a trauma case library containing representative patient cases and models.

Added potential benefits arise from reductions of ailments of the patients. For example, smaller elements used in treatment of musculoskeletal disorders and orthopedic conditions could be used through utilization of the present invention, as with the current state of the art, e.g. implants that are larger than necessary may be installed for treatment of bone fractures as a precaution to ensure that the bone fragments are kept in the desired positions. This may potentially lead to reductions in used materials, further reducing expenditures, or increased wear comfort for patients. Additionally, ossification may be enhanced or decrease of bone strength avoided, as an implant may advantageously bear smaller loads.

An arrangement may also be used to design custom elements, such as implants, casts, screws, pins, or nails to be used in a specific circumstance. This may further increase wear comfort for patients, as standard available elements may be excessively large. Also, as a computational model may be obtained where tissues are repositioned to places corresponding to their intact form, elements may be designed or optimized for that particular case. Elements may be selected to retain the tissue at the repositioned locations.

Design of elements could occur in circumstances where commercial implants/solutions do not offer clinical improvement. In some cases for example deformation of an implant may cause a need for reoperation in a patient, even though the same implant would have been optimal in a similar case in another patient due to individual differences in bone characteristics. An arrangement according to the present invention may take into account individual traits of the patient, such as age to name an example, which can affect the choice of element to be used. Different materials may also be tested through the arrangement.

Many different types of conditions may be treated or inspected utilizing the present invention. In one embodiment, the arrangement may optimize an element to be used for treatment of a torn or otherwise damaged tendon, muscle or other tissue structure. The shape of an element and/or its material may be considered.

Embodiments of the invention are not restricted to a specific species, and may be utilized in relation to treatment of musculoskeletal disorders or orthopedic conditions of, for example, any mammal. Any tissue may also be considered, such as bones, tendons, or muscles. In the case of bones, any bone may be considered, such as the mandible, carpal, metacarpal, tarsal, metatarsal, tibia, femur, ilium, ischium, pubis, humerus, ulna, radius, orbita, or zygoma bone. Optimization incorporates analysis of the configuration of at least one element, where the configuration refers to a location and/or inherent characteristic (e.g. material, shape, elasticity, or other such property or properties) of the at least one element, and an output may indicate the feasibility of said configuration.

The exemplary embodiments presented in this text are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this text as an open limitation that does not exclude the existence of unrecited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific example embodiments when read in connection with the accompanying drawings.

The previously presented considerations concerning the various embodiments of the system may be flexibly applied to the embodiments of the method mutatis mutandis, and vice versa, as being appreciated by a skilled person.

BRIEF DESCRIPTION OF THE DRAWINGS

Next the invention will be described in greater detail with reference to exemplary embodiments in accordance with the accompanying drawings, in which:

Figure 1 illustrates an exemplary arrangement according to one embodiment of the invention,

Figure 2 depicts imaging data that may be visualized that can be stored in an arrangement according to one embodiment of the invention,

Figure 3 illustrates a 3D model that may be visualized and can be stored in an arrangement according to one embodiment of the invention, Figure 4 shows a generic model that may be visualized and can be stored in an arrangement according to one embodiment of the invention,

Figure 5 depicts a computational model that may be visualized that can be stored in an arrangement according to one embodiment of the invention, and

Figure 6 shows procedures that may be performed by an arrangement according to one embodiment of the invention.

DETAILED DESCRIPTION

Figure 1 shows an exemplary embodiment of the arrangement 100. A processor 102 receives input data 104, comprising imaging data and optionally additional data. Computational algorithms 106, for example to be used in creating an individual computer aided design model of a tissue from the imaging data and for performing optimization through simulations are provided to the processor 102, along with simulation models 108. The simulation models 108 may be e.g. dynamics models comprising information regarding for instance movement of a bone or bones and possibly surrounding muscles, or possibly alternatively or additionally static models comprising information on how loads cause stresses in a system. The processor 102 may also have access to databases 1 10 and 1 12, comprising information regarding generic tissue models and elements, respectively. In some embodiments, the processor 102 may be comprised in an electrical device 1 14, comprising at least a display, or be connected to said electrical device 1 14 via a network connection 1 16. The processor may reside in a remote server or the simulations may be executed through cloud computing. The arrangement 100 may also comprise a user interface 1 18.

In an exemplary embodiment that is depicted in figures 2-5, the invention is utilized in reparation of a bone fracture. It is clear to a man skilled in the art, however, that also other musculoskeletal disorders and orthopedic conditions may be considered.

According to an embodiment of the invention, imaging data 200 depicted in Figure 2 is provided, which is preferably three-dimensional imaging data obtained by a method such as computed tomography, magnetic resonance imaging, or ultrasonic scanning. The imaging has been performed on a target entity 208 so that tissue, such as at least a part of a tissue 202, such as a mandible bone, which is intended to be treated can be identified therefrom. In the case of bone fractures, a possible fragment or fragments 206 of the bone 202, and a possible fracture or fractures 204 that are intended to be treated can also be advantageously identified from the imaging data 200. The location 204 may also refer to a location related to some other musculoskeletal disorder or orthopedic condition.

Referring to Figure 3, in one embodiment, the arrangement 100 may create a 3D model 300, which comprises points in three-dimensional space to represent an initial model of the damaged bone 302, including information involving the fragment(s) 206 from the imaging data 200. In other embodiments, the 3D model 300 may not be created.

Embodiments may also provide a generic model 400 (or a generic computation grid), shown in Figure 4, comprising points in three-dimensional space to represent a generic model of intact tissue 402 corresponding to the tissue 202 identified from the imaging data 200. In the exemplary case shown in the figures, a generic model of a mandible bone 402 corresponds to the bones 302 and 202 in the 3D model 300 and imaging data 200, respectively. The generic model 400 may in some embodiments include also other entities in addition to the fractured bone 202, 302, (or other treated tissue) such as teeth in the case of a mandible bone.

In some embodiments, the 3D model 300 and/or the imaging data 200 are compared to the generic model 400 in order to create, as depicted in Figure 5, a computational model 500 (or a patient-specific computation grid), comprising points in three-dimensional space to represent an individual model of the one or more tissues, such as fractured bones 202, 302 and their possible fragments 206 in positions corresponding to their intact form, giving computational model features 502 (bone) 506 (fragment), and 504, which gives a location of a fracture 204 identified from said imaging data 200.

The arrangement 100 may incorporate into the computational model 500 a fracture surface 512 for each of the fractures 204 that may be identified from the imaging data 200. The fracture surface 512 may comprise information regarding a surface on which a fracture may be considered to lie in in the computational model 500. Also other surfaces, such as articular surfaces, may in some embodiments be identified from the imaging data 200 and incorporated into a computational model 500.

500 may also comprise data regarding material and surface properties of the tissues, such as bone(s) and/or fracture(s). The potential 3D model 300 and computational model 500 may be created automatically by the arrangement 100 or contribution of a user of the arrangement 100 may be utilized. The computational model 500 may also be generated without using a 3D model 300, using only the imaging data 200 and the generic model 400.

The imaging data 200, the 3D model 300, the generic model 400, and/or the computational model 500 may be visualized through the user interface 1 18 to a user of the arrangement 100. In an embodiment of the invention, the user, for example a technician, may through the user interface 1 18 indicate the location(s) of, e.g., the fracture(s) 204 from the imaging data 200, from which the arrangement 100 determines the corresponding locations from the generic model 400, and then, from the data regarding the 3D model 300 and the generic model 400, creates the computational model 500 correspondingly incorporating information regarding the location of the fracture 504 and possibly a fracture surface 512. The aforementioned input of a user is optional, as the arrangement 100 may also operate independently to create data 500 and optionally 300.

In some cases, the arrangement 100 may automatically or utilizing input from a user, identify through the imaging data 200 ("point and click" -type identification of reference points) and possibly a generic model 400, measurements of bones, muscles or other tissue. Also angles relating to tissues may be measured, such as the orientation of an articular surface with respect to another articular surface. Measurements regarding the distance between e.g. different tissues, parts of tissues, or articular surfaces, may also be determined. For example, distances between bone endings may be measured.

Embodiments of the arrangement 100 may be used to identify fracture surfaces 512 or other surfaces related to a musculoskeletal injury and possibly additionally in order to analyze behavior of the related tissues. Also, the identification of surfaces related to injuries may be used to classify injuries. An arrangement 100 may also optionally be utilized solely, as an embodiment of its own, for the purpose of identification of surfaces, angles, or distances related to a musculoskeletal disorder or orthopedic condition.

In an embodiment of the invention, an arrangement 100 may automatically classify an injury and report this to a user. In one embodiment, the arrangement 100 may be used exclusively for this purpose. Classification may also refer to indication of an extent or severity of an injury, such as extent or fragmentation of e.g. a bone.

In some embodiments, an arrangement 100 may be used for injury classification and additionally or alternatively for obtaining a computational model 500 where tissue fragments are in positions corresponding to their intact form. Thus, it may be advantageous to obtain a computational model 500 that for instance a medical practitioner may use to gain information about a bone fracture or other injury. It may be useful for the practitioner or other user entity to be able to identify a correct/suitable placement for the displaced tissue that may correspond to its placement in intact form. An arrangement 100 may, in one embodiment, be utilized solely for this purpose.

Obtaining a computational model 500 with one or more tissue fragments 206 in positions corresponding to their intact form may be done through a comparison between the imaging data 200 and the generic model 400. The comparison process may comprise obtaining a transformation of a generic model 400 to correspond to the situation/positioning of tissue indicated by imaging data 200. A 3D model 300 may be created in an intermediate process in order to obtain the transformation of the generic model 400. The comparison process may additionally comprise repositioning of one or more tissue fragments that are displaced in the transformation of the generic model to correspond to their positions in intact tissue form.

The comparison, i.e., transformation and repositioning, may be carried out in a variety of ways. In one approach, at least the repositioning may involve shape recognition of the fracture surfaces on both sides of the fracture 204, and corresponding reference points between the surfaces may then be found and the tissue fragment or fragments 206 may be moved into its anatomically correct place. The repositioning may be carried out using an automatic alignment algorithm based on point cloud matching of the fracture surfaces on both sides of the fracture 204. The comparison or at least the involved repositioning may also be done by performing a mirroring operation of the corresponding tissue area from the intact side of the patient anatomy with respect to the patient's saggital plane, i.e., by assuming symmetry with respect to the saggital plane.

In the comparison, obtaining the transformation of a generic model 400 may involve alignment of the generic model 400 with the largest intact part of the patient tissue that may be identified from the imaging data 200 after which the one or more fragments also identified through the imaging data 200 may be repositioned into their intact positions using e.g. the aforementioned methods.

Additionally, in some embodiments, the classification may be used to determine, by an arrangement 100, a treatment strategy, which may be reported to a user. For example, the classification of a fracture may indicate if a preferred treatment strategy for the particular fracture in question is related to use of a cast or if surgery and an implant is a more viable alternative. Thus, an arrangement 100 may suggest or select from different element types an element or elements that are optimal with regard to the disorder or injury.

The preferred treatment related to injury classification may be obtained through a database, which may in some embodiments be created through data obtained by the use of an arrangement 100.

According to an embodiment of the invention, initial information regarding the location and characteristics of elements may be incorporated into the computational model 500. Exemplary elements are shown in Fig. 5, where an implant 508 and screws 510 for its attachment to the bone 502 and fragment 506 are depicted. The elements selected to be used may also be for example pins, casts, or splints.

The initial information may be created automatically by the arrangement 100 or may be obtained through input of a user, through for example the user indicating through a user interface 1 18 the location in which one or more elements 508, 510 should be placed initially.

In an exemplary embodiment, the 3D model 300, generic model 400, and computational model 500 are obtained through generation of a 3D computation grid. The arrangement 100 may, according to one embodiment, perform procedures as illustrated in Figure 6 to optimize the element(s) 508, 510 and their locations. Input data is received in 600, where the input data comprises three-dimensional imaging data 200 and optionally additional data. The additional data may be related to for example the age or gender of the target entity 208. Using the input data, a generic model 400 may be selected in 602. An initial 3D model 300 may be created in 604 using the input data. A comparison 606 may be performed between the 3D model 300 and a generic model 400, after which a computational model 500 may be created in 608 through utilization of a computational algorithm 106. Alternatively, the computational model 500 may be created by a computational algorithm 106 by comparing the imaging data 200 with the generic model 400, without the use of a 3D model 300.

An optimization with respect to one or more variables is performed in 610, which comprises specification of element parameters 612, simulation 614, analysis of results 616, and the optional repetition of 612, 614, and 616.

In 612, the element parameters to be specified may include, among others, dimensions and/or material of one or more elements 508, 510 and their locations. This parameter data is then incorporated into the computational model 500. The element(s) 508, 510 to be may be automatically selected from a provided database 1 12 or a user may specify them, either through the database 1 12 or by explicitly defining characteristics (dimensions and/or material, for instance) of the elements 508, 510. The location of the element(s) may also be determined automatically or manually by a user.

It may be specified in the beginning of the optimization 610, i.e., upon the first execution of 612, that an initial parameter, i.e. one or more characteristics of an element or elements 508, 510 or an initial location are to be kept constant.

In an embodiment of the present invention, after provision of the input data in 600 and selection of the generic model in 602, one or more dynamics simulations are performed in 618, involving e.g kinetics and/or kinematics of the tissue(s) 502, possible fragment(s) 506, and additionally possibly surrounding other tissues, through simulation models 108. In one embodiment a fracture involving the mandible bone is considered, and the simulation in 618 involves a dynamics model of the temporomandibular joint, lateral pterygoid, masseter, and temporalis muscles. Biomechanical functions such as a mastication cycle in the aforementioned case of the mandible bone, may be included in the simulation 618 through the simulation models 108. From the dynamics simulation(s) 618, a load case library may be created in 620. A simulation involving stress analysis may be performed in 614, utilizing provided computational algorithms 106 and simulation models 108. Information regarding loads and constraints on the tissue(s) 502, fragment(s) 506, and element(s) 508, 510, through utilization of data obtained from the load case(s) created in 620 may be used in the simulation 614, which may involve a static simulation model. From the simulation 614, displacements, stresses, and/or strains involving any of the components of the system represented by the computational model, i.e. tissue(s) 502, fragment(s) 506, element(s) 508, 510, or fracture surfaces, may be derived.

The simulation of 614 may also be utilized in evaluating different load case scenarios for optimization sequences to be performed for the element or elements 508, 510.

In the simulations of Fig. 6, the tissue(s) 502 and fragment(s) 506 may be regarded as moving separately with respect to each other through the computational model 500, with the element or elements 508, 510 possibly holding them together. Information regarding properties of the element materials may also be taken into account.

The duration of the simulations of Fig. 6 or the number of times a specific biomechanical function is performed in the dynamics simulation 618 may be implemented according to predetermined values or they may be specified by a user.

In 616, results of the simulation are analyzed, and the procedures 612 and 614 may optionally be repeated. The analysis 616 can be related to the variable(s) with respect to which the optimization is conducted, such as in the exemplary case, stresses exerted on the bone(s) 502, fragment(s) 506, and/or element(s) 508, 510, the displacement of the fragment(s) 506 with respect to the bone(s) 502, the potential amount of restriction to the movement of the bone(s) 502 and fragment(s) 506 with respect to other bone(s) or muscles involved in the simulations as compared to a reference case, or the possible deformation of the element material(s), for example. The analyzed variables may be predetermined or they may be given by a user. In some embodiments, the user may define the importance of some variable with respect to other possible variables.

Upon selecting to return to the step 612, the location or a characteristic of the element(s) 508, 510 or a combination thereof, may be varied. The characteristics or attributes may, for example, include dimensions, mass, or material of an element 508, 510. The aforementioned variations in characteristics can be specified by a user or conducted automatically by the arrangement 100. All attributes may be defined freely or elements 508, 510 may be selected from the database 1 12.

In the case of an implant 508 and screws 510, for instance the type of screws 510 used may be varied.

The database 1 12 may include commercially available elements from various providers, from which a user may advantageously thus select those which are feasible or available to the user.

If it has been indicated in the first execution of 612 that a parameter is to be kept constant, only other parameters are varied upon the possible return to step 612. These parameters that are to be varied may optionally be defined by a user. For example, a user such as a medical practitioner may then indicate an implant 508 that is to be used, and the arrangement 100 may then optimize the screws 510 to be used as well as the location of the specified one implant 508. In another exemplary use scenario, the user, for example a designer of implants to be used in certain bone fracture repairs, may specify the material to be used, and the arrangement 100 may optimize the dimensions of an implant 508.

Alternatively, the optimization 610 may be conducted so that a predetermined amount of elements 508, 510 and parameters are specified, possibly selected from the database 1 12, and the simulation 614 is conducted for all of the one or more elements 508, 510 in the one or more possibly predetermined locations, either consecutively or in parallel, and the arrangement 100 may then in 616 analyze results of the simulations 614 to determine an optimized order of the specified elements 508, 510 and parameters with respect to one or more variables. In an embodiment of the present invention, the simulation 614 is conducted through finite element analysis.

In one embodiment, one or more of the procedures 600-624 illustrated in Fig. 6 that may be conducted by the apparatus 100 may be performed with the use of an algorithm that may utilize artificial intelligence.

In some embodiments, it may be possible to incorporate a form of reverse engineering into the optimization process, where the outcomes of previously realized element selections in identified injury cases are taken into account through information on healing of the fractures in a specific case. The information on healing may for instance be acquired through installing a measuring instrument on a cast or splint that measures the movement of a bone or limb that is being treated, said information being provided for use in the simulation 610 through creating a trauma case library in 622.

Computational models 500 may be used in other applications such as planning of a radius bone fracture treatment where a decision of implant or orthopedic cast usage is to be made. A database of computational models of similar patient cases may be used in pre-planning by using identified parameters such as fracture size, location or orientation with respect to primary loading and its direction combined with patient-specific data such as age and gender.

Preferably, in 624, the outcome of the analysis 616 is reported to a user through generation of an output. The output may be numerical, graphical, involve text, or be a combination of these. The output may also or alternatively comprise of a number of signals, files, or other forms of deliverables.

The output generation 624 may involve giving, through the user interface 1 18, optimum element(s) 508, 510 and their location(s). In some cases an element 508, 510 that is available in the database 1 12 should be bent or shaped for more efficient performance, and the output generation 624 may then involve instructions on how to modify the element 508, 510. The output may comprise information regarding the optimum choice, or a list of element(s) 508, 510 and location(s) may be provided, in which the order is optimized with respect to the predetermined variables. Also, for given elements 508, 510, the output may for instance specify locations for said elements that optimize certain variables, e.g. in the case of bone fractures locations which will result in minimum bone stress or, alternatively minimum displacement of the bone fragments.

The output generated in 624 may also comprise information regarding the variables with respect to which the optimization has been performed. For example, in conjunction with giving a specific optimized element or elements 508, 510 and location(s), the load on the element(s) 508, 510, bone(s) 502, and/or fragment(s) 506 associated with the given configuration may be given.

Comparison of elements 508, 510 and one or more associated variables may also be conveyed. For instance, the output may provide a graph depicting the magnitude of a variable such as relative movement of a bone 502 and a fragment 506 with different element configurations, such as an implant 508 in a specific location with varying types of screws 510.

In alternative embodiments, the arrangement may in 624 generate a computer-readable output. The output may then be mediated to a user entity. The user entity may be for example a robot intended to perform treatment such as surgery on the target entity using the data comprised in said output.

In some embodiments, the user interface 1 18 may display graphical instructions concerning the elements 508, 510 to be used and their locations to a user, such as a medical practitioner.

In yet one other embodiment, the treatment instructions, such as operating instructions, concerning the elements 508, 510 to be used and their locations may be provided to a user through augmented reality glasses.

Embodiments of the invention may also be used to optimize a treatment strategy. Using the imaging data 200 and a generic model 400, injuries and/or surfaces related to injuries and/or measurements related to tissues may be determined. Repositioning of tissues may be carried out, providing information on the displacement of tissues that may have occurred in relation to an injury. Outcomes relating to different types of elements, such as casts and implants, may be analyzed, and a preferred element or elements may be determined. The actual step of treatment, such as surgery, is preferably omitted from the scope of the presented solution and claims. In some embodiments the treatment may be carried out by personnel with necessary skills.

The invention has been explained above with reference to the aforementioned embodiments, and several advantages of the invention have been demonstrated. It is clear that the invention is not only restricted to these embodiments, but comprises all possible embodiments within the spirit and scope of inventive thought and the following patent claims.

The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated.