MXPA00011403A - Fiducial matching by means of fiducial screws - Google Patents

Abstract

The invention relates to a device for the referenced positioning of two reference points (11;14) situated on a fiducial screw (2) implanted into a bone. Said device comprises (A) a fiducial screw (2) which can be screwed into a bone (1) and has a longitudinal axis (9), a screw shank (10) and a screw head (22) provided with means (12) for receiving an instrument used to screw the fiducial screw (2) in and out;and B) a pointer (3) provided with at least three means (19) which are not positioned colinearly and emit electromagnetic or acoustic waves, where said pointer (3) has a front end (15), a rear end (16) and a longitudinal axis (9). C) The pointer (3) has means (20) at its front end (15) and the fiducial screw (2) at its head (22) which make it possible for the pointer (3) and the fiducial screw (2) to be joined in the direction of the longitudinal axis (9) and concentrically in relation to said axis (9). D) thanks to the known length (x) of the fiducial screw (2), the known length (y) of the pointer (3) and the means (20) described under C) it is possible to achieve a defined, local coordination between the reference points (11;14) on the fiducial screw (2) and the means (19) of the pointer (3) emitting electromagnetic or acoustic waves.

Description

EXACT COINCIDENCE THROUGH REFERENCE SCREWS DESCRIPTION OF THE INVENTION The invention relates to a device for taking as reference two fixed reference points on a reference screw implanted in a bone as defined in the preamble of independent claims 1 to 5, and with a method for creating a particularly dependent relationship of the reference points as set forth in the preamble of independent claim 11 A problem that frequently occurs in Computer Aided Surgery is, for example, a computer tomogram of the bones or body parts to be treated, is the starting point of the surgical intervention. It may be necessary to identify the finding of a position of a given point in the bone or part of the body associated with the surgical instruments and compare its position with that of the identical point on the computer tomogram To obtain minimal damage to the soft parts around the bone , the bone or also for example a vertebra, must be operated without exposing large surfaces of the parts to be treated (minimal invasive technology). In this regard, computer-assisted surgery is appropriate to align the patient's coordinate system in the particular operating room by the dynamic reference base of the position finding system with the coordinate system of the previously recorded tomographic image data, a coordinate transformation must be carried out, called "coincidence". 5 A more extensive description of computer assisted surgery includes an appropriate matching algorithm for such a coordinate transformation and is provided in L. P. NOLTE ET AL. CLINICAL EVALUATION OF A SYSTEM FOR PRECISION ENHANCEMENT IN SPINE SURGERY, CLINICAL BIOMECHANICS, 1995, VOL. 10, No. 6, PP 293-303. One way to match the patient's coordinate system in the operating room with the patient's image coordinate system is to use mechanical scanning devices such as those described illustratively in U.S. Patent 5,383, 5 (Buchholz). However, these known methods are excessively expensive in terms of time and present only obsolete precision. Another way to match the system of coordinates of the patient in the operating room is with the coordinate system of the image consists of identifying predetermined points using anatomical landmarks. When the parts of the body are only little exposed, this method is also difficult due to the access restricted virtual Often an endoscope should be used. In another method for aligning coordinate systems, so-called reference implants are used to unambiguously identify reference points. Such an appropriate method and apparatus is described in the United States document, 9 5.91 (Alien). This method includes the implementation of at least related reference points especially in a spatial relationship. A device for the preoperative determination of position data of endoprosthesis parts of an intermediate bone joint in relation to the bone which forms the intermediate bone joint is described in DE 29 70 393 AESCULAP. This known device comprises a measuring device for determining the position of the marking elements within a three-dimensional coordinate system, a data processing unit and a marking element, each for the two bones that form the bone joint . These marking elements consist of a screwed leg in a bone in the form of a bone screw and a T-shaped upper body constituted of markers that are separated from each other. All these known methods share the drawback of consuming too much time.

The object of the invention is the palliation. Its purpose is to create a device and method that allows to create a spatial relationship, for reference points in reference screws, between their positions in the coordinate system of the physical body and the positions of the identical reference points in the coordinate system of the image, and at the same time work with very little damage to the soft tissue around the bones (minimal invasive technology). The purpose of the device is to define two reference points on a reference screw and as a result, the method requires only two implanted reference screws. In addition, the image can be by X-ray or a computer tomogram stored digitally. The invention solves the problem by using a device to reference two reference points in a reference screw implanted in a bone, this device comprises the features of claim 1 or claim 5, and in addition a method, defined by the characteristics of Claim 11, to implement a spatial relationship between the reference points. In a preferred embodiment of the device of the invention, an indicator fixed with the marker means moves in a position and orientation defined especially precisely in relation to a fixed reference screw with the fixed reference points. A point of reference is the tip of the screw reference, and the other reference point is the head of the screw. The indicator is placed by inserting a bolt that fits snugly at its front end into the corresponding opening in the head of the reference screw. The opening in the reference screw therefore the tip are concentric with the longitudinal axis of the reference screw. The point in turn is concentric with the indicator. Consequently, the indicator and the reference screw are located on an axis defined by the reference points on the reference screw. The position of the indicator is defined in the direction of this longitudinal axis because the body of the indicator adjacent to the tip is of a diameter greater than the diameter of the tip and therefore makes contact with the head of the screw. For a given position of the marker means in the coordinate system, the position of the reference points on the reference screw in this way can be determined in the same coordinate system. The marker means may be in the form of emitters / detectors that emit or detect electromagnetic or acoustic waves. Depending on the class of emitters / detectors, the position of the marker means can be determined by an appropriate position detector. The position detector can also be part of a CAS system (computer assisted surgery) and can include computer image processing software.

The method of the invention creates a spatial relationship between reference points and is based on the concept that the reference screws implanted in the bone can be recognized in a three-dimensional image elaborated for example by computer tomography or in common bone x-rays. . If the reference points on the reference screws are measured in the image in terms of a corresponding system of coordinates and if the reference points on the reference screws are mounted on the physical body and are measured by the device of the invention in terms of another coordinate system, then the association of the positions of the reference points in the image with those of the real body makes it possible for any point in the image to be related by a transformation of coordinates with the point corresponding to the physical bone, and vice versa. By means of the method and the device of the invention, the alignment or coincidence of the coordinate systems can be implemented by means of only two reference screws implanted in the body. Usually the term "exact match" indicates the creation of a spatial relationship of reference points in reference screws, between their positions in the coordinate system of the physical body and the positions of identical reference points in the coordinate system in the image .

Additional advantageous embodiments of the invention are defined in the dependent claims.

Essentially, the advantages provided by the invention are those that thanks to the device of the invention and using the method of the invention, it is sufficient to implant only two reference screws for the exact coincidence of the coordinate system of the image with the actual system of coordinates, and where the bone segment that receives the implanted reference screws needs to be exposed in a minimum part (minimal invasive technology). The invention and its further developments are described below in relation to the various embodiments that are partially shown schematically. Figure 1 is a perspective view of one embodiment of the device of the invention, and Figure 2 is a side view partially in section of one embodiment of the device of the invention. The embodiment of the device of the invention shown in FIGS. 1 and 2 comprises a longitudinal axis 9 reference screw 2 and an indicator 3 having a front end 15, a rear end 16, a cylindrical body and a retainer 5. A cylindrical tip 7 is present at the front end 15, opposite the detent 5 of the indicator 3 and is concentrically insertable in a tight fitting within the opening 12 present in the head 22 of the reference screw 2 to receive a tool for screwing or unscrewing the reference screw 2. The cross section of the screw 7 is smaller than that of the body 4 of the indicator 3 and as a result, the axial position of the inserted indicator 3 is rigorously defined because the flange 17 bears on the rear end 13 preferably perpendicular to the longitudinal axis 9 of the screw 2 of This opening 12 concentric with the longitudinal axis 9 in the head 22 of the reference screw 2 can be threaded or placed internally with a hexagonal socket. If this opening 12 is internally threaded, the tip 7 of the indicator 3 can be screwed externally to allow a rigid detachable connection between the indicator 3 and the reference screw 2 Due to this concentric mounting of the indicator 3 and the reference screw 2, the axis 9 of the longitudinal indicator coincides with the longitudinal ee 9 of the reference screw 2, and as a result the Direction of the 3 cylindrical indicator is defined in relation to the reference screw 2 3 LED 6 (light emitting diodes) are mounted at the rear end 16 of the indicator 3 such that they are in a plane 18 which is perpendicular to the longitudinal axis 9 of the point 3 and can be located at the rear end 16 of this indicator 3 The LEDs are not colmeal As shown in Figure 2, the length (x) between the front end 14 forming a reference point and the head 22 of the reference screw 2 forming the second reference point and the length between the flange 17 and the plane 18 containing the LED 6, is determined accurately. When knowing the position of the LEDs 6 in relation to the coordinate system in the room, in addition to the coaxial and concentric alignment of the longitudinal axis 9 of the indicator 3 with the longitudinal axis 9 of the reference screw 2 and the axially defined position of the indicator 3 in relation to the reference screw 2 by means of the flange 17 on the body 4 of the indicator 3 which makes contact with the head 22 of the screw, in this way it is possible to determine the positions of the reference points defined by the front end 14 and the head 22 of screw in the same coordinate system in the room. In the embodiment of the device of the invention shown in Figure 1, the LEDs 6 can be activated by a cable 8. Other power supplies such as normal or rechargeable batteries are also possible. If at least the three means 19 non-collinear electromagnetic or acoustic wave generators are the LEDs 6 as shown in the embodiment of FIGS. 1 and 2, the spatial position found by the LED 6 in relation to a coordinate system can be implemented using locators of optical position, such as the optical position locator found on the market as OPTOTRAK ™. When the reference screw 2 of Figure 1 is screwed into a bone 1, the sites of the reference points defined by the forward end 14 and the head 22 of the screw of the physical reference screws 2 can be aligned, is to say, they can be matched in the two particular coordinate systems with the sites of the same reference points recorded at another time, for example by computer tomography in a three-dimensional image. In addition, an embodiment of the device of the invention can additionally comprise a position locator 24 which within the room includes at least two sensors 23 which detect the electromagnetic or acoustic waves emitted by the medium 19.

Claims (1)

1. CLAIMS 1 A device for establishing as reference two reference points in a reference implant in a bone, this device comprises a) a msertable reference implant in a bone and having a longitudinal axis, a body and a head, and b) an indicator that is placed with an electromagnetic or acoustically effective means, arranged non-colmeally, the indicator has a front end, a rear end and a longitudinal axis, so c) the indicator is placed at its front end in the reference implant and placed on its head with the means that allows to assemble concentrically the indicator and the reference implant in relation to and in a manner defined in the direction of the longitudinal axis, characterized in that d) a defined spatial relationship can be derived between the reference points in the reference implant and the medium in the indicator that generates electromagnetic or acoustic waves from the known length of the ref implant erence, the known length of the indicator and the means mentioned in subparagraph c, and e) the reference implant is a reference screw, wherein the head comprises a means for receiving a suitable instrument for screwing or unscrewing the reference screw 2 as described in claim 1, characterized in that the medium emits waves electromagnetic or acoustic and this device additionally comprises a position locator comprising two sensors in the space that detect the electromagnetic or acoustic waves generated by the medium. Device as described in claim 1, characterized in that the means detects electromagnetic and acoustic waves and wherein the device additionally comprises a position locator that includes at least two spatially configured emitters that transmit electromagnetic or acoustic waves to the medium. Device as described in one of claims 1 to 3, characterized in that the means is configured in the indicator in a plane perpendicular to the longitudinal axis and between the flange and the rear end. Device as described in one of claims 1 to 3, characterized in that the means is formed in the indicator in a parallel plane and that it contains the longitudinal axis between the flange and the rear end. Device as described in one of claims 1 to 5, characterized in that the reference implant is a reference screw. Device as described in claim 6, characterized in that at its front end the indicator comprises a tip and an adjacent flange, and in that this tip can be received firmly in the receiving medium. instrument for screwing or unscrewing the reference screw and in which, when the initiator is inserted inside this means, and the flange makes contact with the screw head. 8. A method for creating a spatial relationship of reference points in a lifeless body in which a) at least three reference points are derived from the reference implants inserted in a three-dimensional body, b) is generated by at least one image of the three-dimensional body together with the reference implants inserted in the manner indicated in subparagraph a, c) the relation of the identical reference points is carried out in the manner indicated in subparagraph a in the physical body. which is exposed to at least one image that is obtained by subsection ad) the relationship is derived by measuring the image of subsection b and by measuring the physical body by means of subsection a, and e) the local measurement of the physical body is taken to performed by part a is implemented by a spatial measurement system that operates electromagnetically or acoustically, characterized in that f) the reference implants comprise reference points that lie at a known length along a given axis, and g) the position determination, each time of the two reference points present in the reference implant, is implemented by an indicator that is placed with at least three electromagnetically or acoustically effective means, arranged not colinearly, the indicator comprises a means at its front end, and the reference implant comprises a half in its head that allows the indicator and reference implant to be assembled concentrically and in a defined manner along the longitudinal axis, and h) a defined spatial relationship between the reference points in the reference implant and the middle in the Indicator can be derived from the known length of the reference implant, the known length of the indicator and the medium mentioned in part g. 9 A method to create a spatial relationship of reference points, where a) at least three reference points are derived from reference implants inserted in a three-dimensional body, b) at least one image of the three-dimensional body is created together with the reference implants inserted in the manner indicated in subparagraph a, c) the relation of the identical reference points is carried out in the manner in subparagraph a in the physical body which is exposed to at least one image obtained by subsection b that is established, d) the relationship is derived by measuring the image of subsection b and by measuring the physical body by subsection a, and e) the local measurement of the physical body carried out by subsection a is implemented. , by a spatial measurement system that operates electromagnetically or acoustically, characterized in that- f) the reference implants comprise reference points lying on a known length along a given axis, and g) is implemented ment of the position determination, in each moment of two reference points present in the reference implant, for a Indicator that is placed with at least three electromagnetically or acoustically effective means, arranged in a non-collinear manner, the indicator comprises a means at its front end and the reference implant comprises a means on its head that allows the indicator and the implant to be assembled. reference concentrically and in a defined manner along the longitudinal axis, and h) a defined spatial relationship between the reference points in the reference implant and the medium in the indicator can be derived from the known length of the reference implant, the known length of the indicator and the medium mentioned in subsection g. The method as described in any of claims 8 or 9, characterized in that the image is a three-dimensional computer tomogram obtained by computer and digitally recorded. The method as described in one of claims 8 to 10, characterized in that the measurement of the three-dimensional body is implemented by an optical position locator.