A method for computer assisted determination of values of correction parameters for positioning a medical device relative to a target structure or to a reference base. The method includes a numerical procedure that includes the steps of:
|
1. A method for computer assisted determination of values of correction parameters for positioning a medical device in spatial relation to a target structure comprising the steps of:
A) obtaining a medical image of the medical device and the target structure by means of using a radiographic device, wherein the medical device comprises a cylindrical reference means that is surrounded by material of the medical device, and wherein the cylindrical reference means has a different density than the surrounding material of the medical device;
B) determining an actual first position of the medical device with respect to a local system of coordinates fixed with respect to the radiographic device by calculating a position of the cylindrical reference means with respect to the local system of coordinates by means of using a numerical procedure using a computer and the medical image;
C) calculating an actual first position of the target structure in spatial relation to the medical device by using the computer;
D) retrieving a desired second position of the medical device in spatial relation to the target structure;
E) calculating values of one or more correction parameters between the actual first position and the desired second position of the medical device in spatial relation to the target structure by means of using the computer; and
F) positioning the medical device in the desired second position in spatial relation to the target structure using the values of one or more correction parameters calculated in step E);
wherein the numerical procedure comprises the steps of:
i) automatically detecting a projection of the cylindrical reference means in the medical image and determining a minimum of four characteristic landmarks within the projection of the cylindrical reference means;
ii) generating a virtual geometric representation of the cylindrical reference means;
iii) determining virtual projection points representing said characteristic landmarks using the virtual geometric representation of the cylindrical reference means; and
iv) iteratively determining the position and orientation of the cylindrical reference means by matching the virtual projection points of the virtual geometric representation of the cylindrical reference means with the minimum of four characteristic landmarks within the projection of the cylindrical reference means
v) i) automatically detecting a lens-shaped projection of the cylindrical reference means in the medical image and determining two points of intersection and the a first and second apex of the lens-shaped projection of the cylindrical reference means;
vi) ii) generating the a virtual geometric representation of the cylindrical reference means with the diameter d, the longitudinal axis, the center and the height h;
vii) iii) determining the virtual projection points representing the two points of intersection and the first and second apex using the virtual geometric representation of the cylindrical reference means; and
viii) iteratively iv) determining the position and orientation of the cylindrical reference means by matching the virtual projection points of the virtual geometric representation of the cylindrical reference means with the two points of intersection and the first and second apex of the lens-shaped projection;
and additionally comprising the step of transmitting the values of the correction parameters to a robotic positioning device, wherein the positioning of the medical device in the desired second position relative in spatial relation to the target structure is effectuated by means of using the robotic positioning device.
2. The method according to
B1) detecting at least a portion of an imaged target structure which is received by a projection of the target structure into the medical image by means of using the radiographic device.
3. The method according to
A1) obtaining at least a second medical image of the medical device and of the target structure by means of using the radiographic device, wherein the optical axis of the radiographic device when obtaining the at least one second medical image is adjusted at an angle with respect to its position when obtaining the first medical image.
4. The method according to
A2) determining a position of the local system of coordinates for the at least one second medical image in spatial relation to the position of the local system of coordinates for the first medical image.
5. The method according to
6. The method according to
7. The method according to
8. The method according to
9. The method according to
10. The method according to claim 1 9, wherein under step D) the desired second position of the medical device relative to the target structure is retrieved from a second set of digital data using the computer.
11. The method according to
13. The method according to
14. The method according to
15. The method according to
positioning of a radiographic device with an optical axis, a focal point and an image sensor with an image field in spatial relation to the medical device and the target structure so that at least a portion surrounding the cylindrical reference means of the medical device and a relevant portion of the target structure are projectable into the image field of the image sensor.
16. The method according to
17. The method according to
18. The method according to
providing the medical device comprising the cylindrical reference means, wherein the cylindrical reference means has a longitudinal axis, a height h and a center; and
attaching the medical device to the target structure in a first static position.
19. The method according to
planning the desired second position for the medical device in spatial relation to the target structure and storing the planned second position as a second set of digital data on a data storage of the computer.
20. The method according to
G) displaying the values of the correction parameters between the actual first position and the desired second position of the medical device in spatial relation to the target structure on a display of the computer. A method for computer assisted determination of values of correction parameters for positioning a medical device in spatial relation to a target structure comprising the steps of:
A) obtaining a medical image of the medical device and the target structure using a radiographic device, wherein the medical device comprises a cylindrical reference means that is surrounded by material of the medical device, and wherein the cylindrical reference means has a different density than the surrounding material of the medical device;
B) determining an actual first position of the medical device with respect to a local system of coordinates fixed with respect to the radiographic device by calculating a position of the cylindrical reference means with respect to the local system of coordinates using a numerical procedure using a computer and the medical image;
C) calculating an actual first position of the target structure in spatial relation to the medical device by using the computer;
D) retrieving a desired second position of the medical device in spatial relation to the target structure;
E) calculating values of one or more correction parameters between the actual first position and the desired second position of the medical device in spatial relation to the target structure using the computer; and
F) positioning the medical device in the desired second position in spatial relation to the target structure using the values of one or more correction parameters calculated in step E);
wherein the numerical procedure comprises the steps of:
i) automatically detecting a lens-shaped projection of the cylindrical reference means in the medical image and determining two points of intersection and a first and second apex of the lens-shaped projection of the cylindrical reference means;
ii) generating a virtual geometric representation of the cylindrical reference means with the diameter d, the longitudinal axis, the center and the height h;
iii) determining virtual projection points representing the two points of intersection and the first and second apex using the virtual geometric representation of the cylindrical reference means; and
iv) determining the position and an orientation of the cylindrical reference means by matching the virtual projection points of the virtual geometric representation of the cylindrical reference means with the two points of intersection and the first and second apex of the lens-shaped projection; and
G) displaying the values of the correction parameters between the actual first position and the desired second position of the medical device in spatial relation to the target structure on a display of the computer.
21. The method according to claim 1 20, wherein the step of positioning medical device is manually positioned in the desired second position in spatial relation to the target structure is performed manually.
22. The method according to
23. The method according to claim 1 2, wherein the detection of at least a portion of an imaged target structure which is received by a projection of the target structure into the medical image by means of using the radiographic device in step C) is automatically performed.
24. The method according to claim 1 9, wherein the desired second position of the medical device in spatial relation to the target structure is automatically retrieved from a second set of digital data stored on the data storage of the computer.
25. The method according to
26. The method according to
|
1. Field of the Invention
The invention relates to a method for computer assisted determination of positioning parameters for positioning of a medical device relative to a target structure and to a medical device for use with the method.
The task of placing implants plays a key role in trauma and orthopedics as well as in several other medical disciplines. Not only with upcoming minimal invasive techniques, orientation in anatomical terrain is demanding and requires experience of the operator. Prolonged surgery time accompanied by intense radiation and poor surgical results are the consequence. Computer assisted surgery (CAS) concepts aim at easing surgical handling. They are generally based on a three step approach where in a first step medical imaging of the region of interest is required, secondly a virtual surgical plan of the operation is generated and in a third step the surgeon is reliably guided in executing the plan on the patient. Medical imaging is mainly performed by CT (Computed tomography), MRI (Magnetic resonance imaging) or radiography such as 3D isocentric scanning. On the costs of a considerable radiation dose, these technologies deliver highly defined 3D images for convenient planning but confront particularly the smaller clinics with a major investment. Moreover, in many hospitals CT or MRI are considered as a bottleneck in the clinical workflow. After the surgical planning costly and accident-sensitive tracking devices based on optical, mechanical, electromagnetic or acoustic principles are required in the operation room to interlink the patient with the operational plan. This step is called patient registration which is currently one of the most challenging issues in the field of computer aided surgery and influences significantly the overall accuracy of the surgical procedure. For tracking of anatomy and implants, reference bases need to be rigidly and in many cases invasively attached to several relevant elements. This is generally perceived as a time consuming and hindering necessity during surgery. Hence, a simplified assistance technology for reliably and efficiently performing medical interventions carries potential to significantly improve current surgical workflows.
2. Description of the Related Art
A computer assisted surgery system and a method for operating the same is known from US-A 2011/213379 BLAU ET AL. This known computer assisted surgery system essentially comprises a reference body which can be positioned in relation to an anatomical structure, a detector device for detecting the position of the reference body in relation to the anatomical structure and a computer suitably programmed for superimposing the anatomical structure with a virtual representation of a medical device, e.g an intramedullary nail, to modify the position of the reference body and to optimize the virtual position of the medical device, e.g. the intramedullary nail with respect to the anatomical structure.
The reference body can be fixed to a medical tool, e.g. a bore tool or to an intramedullary nail. The reference body is provided with a plurality of fiducial markers which are distributed over the reference body so that the position of the reference body can be determined from a single two-dimensional medical image. Alternatively, the reference body can be a medical tool having a unique geometry to identify the position thereof in a medical image. In another alternative embodiment an intramedullary nail can be the reference body because the intramedullary nail may have a unique form.
The method for operating the above computer assisted surgery system comprises the steps of:
One problem associated with the above described computer assisted surgery system and the method of using the same can be that the position of an implant or a surgical instrument is determined on the basis of a separate reference body comprising a plurality of markers which has to be attached to the implant or instrument in a defined position.
Furthermore, fiducial markers need a comparatively wide spreading for adequate tracking. This can be problematic since the field of view of a conventional C-arm is limited and the space for attachment of the markers is restricted. Furthermore, undesired overlapping in the projected medical image might occur. This wide spreading of the markers or targets is not required when using cylindrical reference means. Radiopaque markers must be embedded into a radiolucent structure like a carbon handle. The fiducial markers cannot be used e.g. on metallic implants. Producing radiolucent means equipped with radiopaque markers is more demanding than drilling holes into existing structures or even using existing holes.
Thus, there remains a need for an improved method and device for computer assisted surgery.
BRIEF SUMMARY OF THE INVENTION
It is an object of the invention to provide a method and a medical device permitting to position the medical device relative to a target structure or to a reference base by means of a computer, wherein the medical device comprises one or more reference means of simple and explicit shape, which are already present in an implant or instrument or which can be easily incorporated in an existing implant or instrument.
The invention solves the posed problem with a method for computer assisted determination of positioning parameters for positioning of a medical device comprising the features as hereinafter disclosed and claimed and with a medical device for use with the method comprising the features as hereinafter disclosed and claimed.
The advantages of the method for computer assisted surgery according to the invention are essentially that:
Moreover, known surgical navigation systems use position tracking technologies based on optical, electromagnetic or comparable principles. Reference to a targeted anatomical structure needs to be established by a work step called patient registration, interlinking a reference base of the tracking system with a radiographic image or a CT scan. By use of the method and device according to the invention this step can be omitted, since object tracking and registration of anatomical structures are performed by image processing of the same image. A further advantage is essentially to be seen therein that no additional tracking or imaging equipment is needed despite a conventional C-arm which is already available in the majority of clinics. Known surgical workflows can be maintained without additional training or additional qualified staff. Known surgical navigation systems provide real-time tracking of spatial movements of instruments operated in a free-hand manner. The proposed method and medical device provides rigid guiding of instruments or implants in static positions eliminating inaccuracies due to unconstrained manual instrument handling.
As used in this application the term “landmark” has the meaning of a distinctive feature marking a particular location of an object, e.g. detectable anatomical landmarks like a hole, a vertex, an edge or spherical aspects, e.g. a femoral head.
The term “C-arm” includes a medical X-ray image intensifier wherein the C-arm encompasses the X-ray source and an image intensifier, e.g. a fluoroscopic system or an electronic sensor permitting to display and to process the obtained medical image on a computer.
The numerical procedure used to determine the position of the cylindrical reference means with respect to a local system of coordinates generally performs the following steps:
Thereby, the position of several objects can be determined in relation to each other and to the anatomy of the patient. Defined surgical manipulation of the positions may then lead to a desired positioning of instruments and/or implants.
After calculation of the actual relative position of all elements, e.g. the medical device and the target structure with respect to each other the situation can be visualized on a display of a computer.
As used herein, the singular form “a”, “an” and “the” does not exclude plural references unless the context clearly dictates otherwise. For example, the term “a cylindrical reference means” or “at least one cylindrical reference means” or “a medical image” does not exclude a plurality of cylindrical reference means or a plurality of medical images.
The medical device may be a surgical instrument, e.g. an aiming device or an implant, e.g. an intramedullary nail or a surgical instrument rigidly attached to an implant.
The target structure may be a further surgical instrument or an implant, e.g. an intramedullary nail or an anatomical structure, e.g. a bone comprising characteristic and detectable landmarks like a hole, a vertex, an edge or spherical aspects, e.g. a femoral head.
The reference base may be the operating room, an operating table, a bone or bone fragment, the patient (non-invasive to the skin) or a pre-inserted implant. Generally everything can be used as a reference base which can be maintained in a static position in relation to the target structure or with, depending on the application, acceptable relative movement of the target structure.
An additional medical device may be a screw or a pin or comparable.
Further advantageous embodiments of the method and the device according to the invention can be described as follows.
In a special embodiment the method further comprises before step C) the step of:
B1) detecting at least a portion of an imaged target structure which is received by a projection of the target structure into the medical image by means of the radiographic device.
In a further embodiment of the method the radiographic device has an optical axis and a focal point and the method comprises the additional step of A1) obtaining at least a second medical image of the medical device and of the target structure by means of the radiographic device, wherein the optical axis of the at least one second medical image is adjusted at an angle with respect to its position when obtaining the first medical image.
In a further embodiment the method further comprises the step of A2) determining the position of the local system of coordinates for the at least one second medical image relative to the position of the local system of coordinates for the first medical image.
In another embodiment of the method a 2D-3D reconstruction is obtained from the at least one second medical image and the first medical image.
The spatial position of the medical device relative to the target structure can only be calculated from a single medical image if at least one constrain is known (e.g. the distance between the target structure and the medical device) is known which is the case in e.g. distal locking of an intramedullary nail. If the distance between the target structure and the medical device is not known at least a second medical image from a different view angle is necessary. Assuming that during acquisition of these at least two medical images the cylindrical reference means has not been moved, and both, the cylindrical reference means and the target structure are visible on the medical images the local system of coordinates for the first medical image and the one for the second medical image can be related to each other and the spatial position of the target structure can be obtained.
Preferably, the medical image includes a projection of at least a portion of the medical device including the cylindrical target and of at least a portion of the target structure.
In a further embodiment of the method the medical device is attached to the target structure or to a reference base in a first static position of the medical device relative to the target structure.
Preferably, the numerical procedure comprises the use of a virtual geometric representation of the cylindrical reference means.
In yet another embodiment of the method the cylindrical reference means is in a fixed position relative to the medical device.
In another embodiment of the method the detection of an imaged target structure is performed by using a first set of digital data. The first set of digital data may define a geometric representation or approximation of the target structure or of a specific aspect of the target structure.
In a further embodiment of the method the desired second position of the medical device relative to the target structure and/or the virtual geometric representation of an additional medical device is retrieved from a second set of digital data using the computer. The second set of digital data may be a data set defining a surgical plan or/and a data set defining a desired position of the medical device relative to the target structure only.
In again a further embodiment the method further comprises the step of determining the relation between the position of the local system of coordinates for the at least one second medical image and the position of the local system of coordinates for the first medical image in a global system of coordinates fixed to a set of cylindrical reference means.
In another embodiment of the method the target structure comprises an implant.
In another embodiment of the method the target structure comprises an anatomical structure.
In again another embodiment of the method the target structure comprises an instrument, tool and/or a further medical device comprising a cylindrical reference means.
In a further embodiment of the method the additional medical device comprises an implant, e.g. a bone screw, an instrument, a tool and/or a further medical device.
In a further embodiment of the method further comprising before step A) the step:
In another embodiment of the method the first set of digital data is pre-operatively stored on a data storage of the computer.
In yet another embodiment of the method the second set of digital data is pre-operatively stored on a data storage of the computer. The second set of digital data can comprise a surgical plan of an osteosynthetic or orthopedic treatment including desired relative positions of the medical devices and/or target structures involved in the surgical plan.
In a further embodiment the method additionally comprises the step of transmitting the values of the correction parameters to a robotic positioning device.
In again another embodiment the method comprises the additional step of positioning the medical device in the desired second position relative to the target structure by means of the robotic positioning device.
In another embodiment the method comprises before step A) the steps of:
In another embodiment the method further comprises the step of:
In another embodiment the method comprises the additional step:
In a further embodiment the method comprises the further step of manually positioning the medical device in the desired second position relative to the target structure, preferably by using the displayed values of the correction parameters.
In again a further embodiment the method comprises the further step of positioning the medical device in the desired second position relative to the target structure by using mechanically adjustable devices and by using the displayed values of the correction parameters.
In another embodiment of the method the detection of at least a portion of an imaged target structure which is received by a projection of the target structure into the medical image by means of the radiographic device is automatically performed.
In another embodiment of the method the desired second position of the medial device relative to the target structure and/or the virtual geometric representation of an additional medical device is automatically retrieved from a second set of digital data stored on the data storage of the computer.
In another embodiment of the method the first set of digital data defines a geometric representation or approximation of the target structure or of a specific feature of the target structure.
In a further embodiment of the method the numerical procedure essentially comprises the steps of:
Preferably, the virtual geometric representation includes values for the height h, the diameter d and the position of the centre of the cylindrical reference means.
In another embodiment the device further comprises an attachment means permitting to attach the medical device to a target structure or to a reference base.
In another embodiment of the device the reference base is statically constrained with respect to the target structure.
In another embodiment the device comprises a guiding structure to receive and guide a surgical tool or implant. A surgical tool or implant can be a drill bit, a screw, guide wire, a screw driver, a tap, a scalpel, a cannula or comparable or any other object to be positioned within the patient's body along a specified path.
In again another embodiment of the device the guiding structure is positioned in a fixed position with respect to the cylindrical reference means.
In a further embodiment of the device the guiding structure is positionable in a desired position with respect to the cylindrical reference means.
In another embodiment the device comprises a mechanical means for manually repositioning the medical device relative to the target structure or a reference base with respect to at least one degree of freedom. This mechanical means can be:
In another embodiment of the device the medical device is suitable to receive one or more additional medical devices to match a desired plan without repositioning the medical device itself. For example used for anatomical plating e.g. bone plates, screw lengths and/or screw orientation.
In a further embodiment of the device the actual first position of the medical device is indicated on at least one mechanical or digital scale. For example a mechanical rotational or translational scale attached to the medical device or a scale printed on an adhesive label stuck to the skin of the patient.
In a further embodiment of the device the actual first position of the medical device is transferred to the computer by wire connection or wireless transmission.
In another embodiment of the device the medical device additionally comprises a radiopaque structure visible in X-ray projections. The radiopaque structures can be aligned with virtual geometric representations of the radiopaque structures projected into the X-ray image.
In another embodiment the device comprises computer controlled actuators to position the medical device relative to the target structure in the desired second position.
In again another embodiment of the device the medical device comprises a surgical tool, preferably an aiming device. The aiming device can be attached to a reference base such as an implant, a bone, an operating table or to the skin of the patient or comparable.
In another embodiment the device the medical device comprises an insertion handle attachable to an implant.
In yet another embodiment the medical device comprises an orthopedic or osteosynthetic implant, e.g. an intramedullary nail.
In a further embodiment the medical device comprises a plurality of cylindrical reference means, preferably two or three cylindrical reference means in a known position with respect to each other. In case of circular cylindrical reference means at least a second circular cylindrical reference means is necessary to determine the position of an object with respect to six degrees of freedom. Furthermore, known distances between target centre points can be used to increase the accuracy of determining the position in a direction normal to the projection plane, particularly when using perspective projection.
In a further embodiment of the device all cylindrical reference means are equally sized. Preferably, the longitudinal axes of all cylindrical reference means are parallel. A configuration with equally sized cylindrical reference means and/or an arrangement with parallel longitudinal axes configuration is easy to produce and allows for the largest possible corridor of view angles ensuring that all cylindrical reference means are visible in the medical images.
In another embodiment of the device the longitudinal axes of the cylindrical reference means are arranged at an angle with respect to each other in a defined manner. Preferably, the ratios of the height h to the diameter d of the cylindrical reference means are different. A arrangement of the cylindrical reference means with angled longitudinal axes and/or a configuration of the cylindrical reference means with different ratios h/d allows a unique allocation of each of the cylindrical reference means from its projection and eliminates the risk of numerical procedures converging to local minima and therefore to wrong solutions during iteratively matching virtual and actual projection landmarks.
The device according to the invention is preferably suitable for placement of an intramedullary hip implant.
The device according to the invention can be suitable for anatomical fracture reduction, particularly for adjusting rotational misalignment of fractured long bones.
The device according to the invention can be suitable for distal interlocking of intramedullary nails.
The device according to the invention can be suitable for anatomical plating of a bone, particularly of the proximal humerus.
The device according to the invention can be suitable for insertion of bone screws.
Several embodiments of the invention will be described in the following by way of example and with reference to the accompanying drawings in which:
The processing of the one or more medical images 50 can include:
Planning of the desired implant position on the basis of the taken medical images 50 can include the step of retrieving a desired second position of the medical device 1 relative to the target structure 10 and/or retrieving a virtual geometric representation of an additional medical device 3, e.g. bone screw 750 using the computer 32. Thereby, the desired second position of the medical device 1 relative to the target structure 10 and/or the virtual geometric representation of an additional medical device 3 can be retrieved from a second set of digital data using the computer 32. This second set of digital data can be pre-operatively established and stored on a data storage of the computer 32 and can include a surgical plan of an osteosynthetic or orthopedic treatment including desired relative positions of the medical devices 1 and/or target structures 10 and/or a virtual geometric representation of an additional medical device 3 involved in the surgical plan. This allows to retrieve the desired second position of the medial device 1 relative to the target structure 10 automatically or semi-automatically from the second set of digital data stored on the data storage of the computer 32.
The calculation of the required repositioning the elements relative to each other can comprise the step of calculating values of correction parameters between the actual first position and the desired second position of the medical device 1 relative to the target structure 10 and/or values defining a desired position of the additional medical device 3 relative to the medical device 1 by means of the computer 32. After calculation of the actual relative position of all elements with respect to each other the situation can also be visualized on the display 33 of the computer 32 in addition to the correction parameters.
The various steps of the method according to the invention as well as combinations thereof will be described in more detail in the below examples 1 to 5.
In
Another embodiment of the medical device 1 for a controlled placement of an intramedullary nail 110 as described with reference to
Intramedullary hip implants are frequently used for treatment of proximal femur fractures. An intramedullary nail 110 is inserted into the intramedullary channel of the femur and a hip screw 510 or blade is inserted through the intramedullary nail 110 into the femoral head 520 (
To simplify this procedure the medical device 1 according to the invention comprises an implant or a nail insertion handle 8 with cylindrical reference means 16. From two oblique (not necessarily orthogonal) X-ray images displaying the projections of the cylindrical reference means 16 as well as the projection of the femoral head 520 (approximated as perfect sphere) the spatial position of the femoral head 520 is derived with respect to the intramedullary nail 110. Correction values for adjustment of the nail insertion depth and for the nail rotation to achieve a central position of the hip screw 510 inside the femoral head 520 are depicted on a display 33 of a computer 32. In addition the current position of all relevant elements with respect to each other can be visualized on the display 33 as well. A reference scale 9 according
A common complication after intramedullary nailing of a long bone is malrotation of the injured limb. A bone fragment can freely rotate about the axis of an intramedullary nail 110. For the operator it is difficult to define the anatomical orientation of this fragment from a plain X-ray projection.
The method and device according to the invention allow adjusting for example the orientation of a distal femur fragment with respect to the proximal femur fragment before locking the intramedullary nail 110 into place. A medical device 1 according to
Locking an intramedullary nail 110 distally in place is difficult since the intramedullary nail 110 deflects inside the intramedullary channel. The position of the distal interlocking holes 111 (
The method and device according to the invention permits to solve the above problem by use of a medical device 1 according to
Opposed to the advantages of simplifying a technically demanding procedure and reducing the required net X-ray exposure to a single X-ray, the disadvantage of this solution can be seen in the fact that it relates to a specific nail family. Several medical devices 1 need to be realized for several nail designs. Another embodiment of the medical device 1 according to the invention targets universal use for a variety of intramedullary nails 110. The medical device 1 comprises instrument guiding structures 5 for various interlocking patterns and allowing adjustment in one translational or rotational degree of freedom transverse to the nail axis in a plane normal to the drilling axis. Furthermore the medical device 1 is configured as an aiming device 7 and comprises as a mechanical means 6 a flexible and lockable arm with an attachment means 2 configured as an adapter section allowing attachment to various nail insertion handles 8. Before an intramedullary nail 110 is inserted into a bone, the medical device 1 is pre-calibrated by attaching it to the insertion handle 8, placing calibration bolts 13 (
The described procedures in examples 1-3 may be combined to assist an entire nailing procedure from a) proximal locking over b) anatomically adjusting the reduction of the fracture to c) distal interlocking. It appears furthermore reasonable to combine steps b) and c). A single medical device 1 and a single medical image 50 displaying the cylindrical reference means 16 of the medical device 1, the interlocking hole(s) 111 of the intramedullary nail 110 and the distal femur condyles is sufficient to define both, anatomical orientation of a distal femur fragment and alignment between drill and the interlocking hole(s) 111.
Particularly for fracture fixation at the proximal humerus accurate placement of fixation elements is of utmost importance. Especially in porotic bone, bone stock is limited and fixation failure is likely to occur. Screws should be placed close to the cortex which carries a risk for penetration of the screws into the articulation.
The method and device according to the invention permits to solve the above mentioned problem by use of a medical device 1 according to
A generic approach according to the invention for inserting and using surgical implants and instruments like screws, guide-wires, drill-bits or comparable items along a predefined path inside an anatomical structure is described in the following.
A medical device 1 e.g. according to
A) acquiring one single medical image 50 (schematically illustrated in the drawing plane of
B) determining the position and orientation of the cylindrical reference means 16 from said single medical image 50 using a numerical procedure executed with said computer 32, wherein said numerical procedure essentially comprises the steps of:
The above mentioned numerical procedure includes a numerical approach for calculating the position of the cylindrical reference means 16 and is based on the following mathematical relationships:
Numerical Approach to Determine the Spatial Position and Orientation of Circular Cylindrical Reference Means:
The procedure relates to the mathematical condition that the projection of the radiographic device 20 is based on an idealized central perspective. A punctiform X-ray source used as energy emitting source 29 sends rays from an origin of known distance H to the projection plane 49.
The procedure incorporates the following fundamental steps:
1. Automatic detection of the lens-shaped projection 42 of said cylindrical reference means 16 in said medical image 50 and determination of significant landmarks, i.e. two points of intersection 35, 36 and the first and second apex 37, 38 of the lens-shaped projection 42 of said cylindrical reference means 16 by use of image processing algorithms. Assumption: With h/H→0 the centre-line projection 51 approximates to the centre of projection 44.
2. Simulation of a virtual geometric representation of said cylindrical reference means 16 and of virtual projection points corresponding to the above mentioned landmarks.
3. Iterative optimization of the angular orientation and position of said virtual geometric representation by means of a numerical optimization routine and to determine the actual spatial position and orientation of the cylindrical reference means 16.
It should be understood that if the described procedure is performed on a single circular cylindrical reference means 16, five degrees of freedom can be obtained, since the cylindrical target 16 is rotation symmetric. Using two or more cylindrical reference means 16 allows constraining an object in 6 degrees of freedom.
Iterative Determination of the Orientation of the Cylindrical Reference Means or of a Set of Cylindrical Reference Means
A virtual geometric representation of said cylindrical reference means 16 is generated with the known attributes d (diameter) and h (length). The virtual geometric representation of said cylindrical reference means 16 has one translational degree of freedom. It can slide along the central line 43, determined by the centre of projection 44 and the centre of said energy emitting source 29. Sliding position is controlled by Z (
Four virtual projection points representing said two points of intersection 35, 36 and said first and second apex 37, 38 are derived from the orientation of said virtual geometric representation of said cylindrical reference means 16.
A numerical optimization routine is used to find a global minimum for the deviations between said significant landmarks the actual projection points and the corresponding virtual projection points using three degrees of freedom (DOF) (α, β, Z) in order to carry out the optimized orientation of said virtual geometric representation of said cylindrical reference means 16. Due to the asymmetry of the lens-shaped projection 42 (segments b and c appear asymmetrically, due to the nature of a central projection) it is possible to calculate a unique solution for the orientation of the cylindrical reference means 16 from a single image.
The procedure can be extended by use of a plurality of circular cylindrical reference means 16 with known distances and alignment to each other. The entirety of all deviations between virtual and actual projection landmarks of all cylindrical reference means 16 is numerically minimized over said three degrees of freedom. This approach has the following advantages:
When aiming at reconstructing the position in space of a significant landmark within an X-ray projection, such as a vertex or edge of a bone or the centre of a femoral/humeral head, the previously described procedure can be used in the following way:
It should be understood that the procedure can be extended by increasing the number of oblique projections. More images allow more accurate 2D-3D conversion of more complex geometrical structures. However, this increases at the same time the complexity of the procedure and the radiation exposure to the operator, to the operating room personnel and to the patient.
While various descriptions of the present invention are described above, it should be understood that the various features can be used singly or in any combination thereof. The scope of the present invention is accordingly defined as set forth in the appended claims.
Windolf, Markus, Nötzli, Christoph Martin
Patent | Priority | Assignee | Title |
Patent | Priority | Assignee | Title |
5048103, | Mar 29 1989 | General Electric CGR S.A. | Method for the automatic resetting of images |
5368030, | Sep 09 1992 | IZI Medical Products, LLC | Non-invasive multi-modality radiographic surface markers |
6016439, | Oct 15 1996 | Biosense, Inc | Method and apparatus for synthetic viewpoint imaging |
20010044578, | |||
20020077540, | |||
20020077543, | |||
20040186347, | |||
20060064106, | |||
20080118138, | |||
20080234575, | |||
20090054910, | |||
20110028831, | |||
20110213379, | |||
20130072784, | |||
EP1491151, | |||
WO3105659, | |||
WO2003105659, | |||
WO2008071014, | |||
WO2010025575, |
Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
Jun 26 2019 | Synthes GmbH | (assignment on the face of the patent) | / | |||
Jul 18 2019 | AO Technology AG | Synthes GmbH | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 050652 | /0347 |
Date | Maintenance Fee Events |
Jun 26 2019 | BIG: Entity status set to Undiscounted (note the period is included in the code). |
Date | Maintenance Schedule |
Nov 30 2024 | 4 years fee payment window open |
May 30 2025 | 6 months grace period start (w surcharge) |
Nov 30 2025 | patent expiry (for year 4) |
Nov 30 2027 | 2 years to revive unintentionally abandoned end. (for year 4) |
Nov 30 2028 | 8 years fee payment window open |
May 30 2029 | 6 months grace period start (w surcharge) |
Nov 30 2029 | patent expiry (for year 8) |
Nov 30 2031 | 2 years to revive unintentionally abandoned end. (for year 8) |
Nov 30 2032 | 12 years fee payment window open |
May 30 2033 | 6 months grace period start (w surcharge) |
Nov 30 2033 | patent expiry (for year 12) |
Nov 30 2035 | 2 years to revive unintentionally abandoned end. (for year 12) |