Abstract:
A medical clamp, in particular a spinal clamp, includes two clamp limbs connected to a grip part. The grip part executes a clamping movement of the clamp limbs and the clamp limbs are connected to the grip part in a releasable manner. The clamp permits particularly safe, minimally invasive percutaneous interventions, especially in the area of the spinal column. A device for using a medical clamp for providing a reference position for a positioning system for percutaneous interventions and a method for determining a reference position for a positioning system for percutaneous interventions, are also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority, under 35 U.S.C. § 119, of German Patent Application DE 10 2007 011 568.9, filed Mar. 8, 2007; the prior application is herewith incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The invention relates to a medical clamp, in particular a spinal clamp. The invention further relates to a device for using a medical clamp for providing a reference position for a positioning system for percutaneous interventions and to a method for determining a reference position for a positioning system for percutaneous interventions. 
         [0003]    Image-assisted interventions, in particular CT-assisted interventions, are nowadays part of clinical routine. In contrast to invasive surgical treatment, minimally invasive image-assisted interventions allow the operator to work with minimal injury to the patient. That does not just reduce the clinical costs. It also reduces the danger of complications and has a positive cosmetic effect. 
         [0004]    In order to carry out those image-assisted interventions, it is necessary to navigate medical instruments through the inside of the patient&#39;s body. The term navigation is understood as determining a position by a locating device, planning an access route to a target site and guiding a medical instrument to that target site along the planned access route. For that purpose, it is known to apply at least one reference marking (dynamic reference base (DRB)) to the patient&#39;s body. 
         [0005]    For example, that can involve optical markings (for example spherical reflectors detectable by a camera) or electromagnetic markings (for example coils excited in an electromagnetic field). The position of the medical instrument relative to the patient&#39;s body can be determined with the aid of the reference marking and thus used for the navigation. 
         [0006]    It has heretofore been customary for reference markings to be secured, for example affixed, to the patient&#39;s skin. In complex interventions, particularly in the area of the spinal column, that type of positioning of the reference markings is too imprecise for an exact navigation of the medical instrument. The reason therefor is that movements of the surface of the patient&#39;s body cannot be completely avoided. Reference markings therefore started to be secured directly to the patient&#39;s bone, for example by using nails or screws. In interventions on a patient&#39;s spinal column, the reference marking has heretofore been applied to exposed bones, for example to the spinous process, in most cases with the aid of clamps. All of those methods, however, require relatively invasive interventions in the patient, for which reason such a positioning of reference markings is complex and risky and, in addition, the above-mentioned advantages of a minimally invasive intervention are for the most part negated. 
       SUMMARY OF THE INVENTION 
       [0007]    It is accordingly an object of the invention to provide a medical clamp, in particular a spinal clamp, a device for providing a reference position and a method for determining a reference position, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and which permit particularly safe, minimally invasive percutaneous interventions, especially in the area of the spinal column. 
         [0008]    With the foregoing and other objects in view there is provided, in accordance with the invention, a medical clamp, in particular a spinal clamp, comprising two clamp limbs and a grip part connected to and releasable from the clamp limbs for executing a clamping movement of the clamp limbs. 
         [0009]    The clamp is the embodiment of a number of fundamental concepts, all of which are based on the understanding that the use of the clamping method can be retained if a medical clamp can be made available which satisfies the requirements of a minimally invasive intervention and also takes into consideration the point of view of safe positioning of a reference marking. 
         [0010]    According to a first underlying concept of the invention, the clamp has a modular construction in which the clamp limbs are connected to the grip part in a releasable manner. The fact that the clamp limbs can be released from the grip part means it is possible to use different clamp limbs, in particular those clamp limbs that are best suited for the individual case, i.e. the ones best suited to the specific anatomy. The modular construction of the clamp reduces the purchase costs, since the grip part only has to be purchased once. Instead of many different medical clamps, it is necessary to purchase just a single grip element and the necessary clamp limbs. 
         [0011]    A further underlying concept of the invention is to use clamp limbs that are individually adapted to the particular anatomy of the site of use (e.g. the vertebral body). In particular, clamp limbs are used that have L-shaped or Y-shaped clamping jaws. 
         [0012]    The Y-shaped clamping jaws are preferably used for particularly safe and rotationally stable fixation in the area of the lumbar spine. They are secured there to the spinous process. The Y-shape has the effect that the clamping force is distributed over a larger surface area, resulting in additional protection against twisting of the clamp. 
         [0013]    The L-shaped clamping jaws are particularly suitable for the upper region of the thoracic spine, since there the spinous processes are narrower and extend horizontally. 
         [0014]    A further underlying concept of the invention, when using straight clamping jaws, is to use a covering device which, during insertion of the clamp into the patient&#39;s body, covers the clamping jaws, which are often provided with points or edges. This avoids unnecessary damage to the tissue. 
         [0015]    With the objects of the invention in view, there is also provided a device for providing a reference position for a positioning system for percutaneous interventions. The device comprises the medical clamp according to the invention. 
         [0016]    With the objects of the invention in view, there is concomitantly provided a method for determining a reference position for a positioning system for percutaneous interventions. The method comprises providing the medical clamp according to the invention having a marking element, applying the medical clamp to a tissue part of a patient, and determining a position of the marking element with a contactless locating method. 
         [0017]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0018]    Although the invention is illustrated and described herein as embodied in a medical clamp, in particular a spinal clamp, a device for providing a reference position and a method for determining a reference position, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
         [0019]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0020]      FIG. 1  is a diagrammatic, front-elevational view of a medical clamp with a reference marking for use in a positioning system for percutaneous interventions; 
           [0021]      FIG. 2  includes first and second side-elevational views of a clamp limb with a straight clamping jaw, as depicted in  FIG. 1 ; 
           [0022]      FIG. 3  includes first and second side-elevational views of a covering device for a clamp limb, as depicted in  FIG. 2 ; 
           [0023]      FIG. 4  includes first and second side-elevational views of a clamp limb with a Y-shaped clamping jaw; 
           [0024]      FIG. 5  is a side-elevational view of a clamp limb with another Y-shaped clamping jaw; 
           [0025]      FIG. 6  is an enlarged, fragmentary, side-elevational view of a clamp limb with an L-shaped clamping jaw; and 
           [0026]      FIG. 7  includes a side-elevational view and a plan view of a clamp spike. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    The figures only show the invention diagrammatically and with its main component parts. All of the measurements are shown in millimeters. The indicated measurements are to be regarded as specific only to the example shown herein and serve only for purposes of illustration. All of the indicated measurements can be modified within the scope of the invention. 
         [0028]    Referring now to the figures of the drawings in detail and first, particularly, to  FIG. 1  thereof, there is seen a spinal clamp  1  according to the invention, which includes two clamp limbs  2  that are connected to a grip part  3 , with the grip part  3  being constructed to execute a clamping movement of the clamp limbs  2 . For this purpose, the grip part  3  has a first actuating limb  4  and a second actuating limb  5 , which are movable relative to each other. The two actuating limbs  4 ,  5  are connected to each other at one of their ends through a pivot joint  6  in the manner of a compass. This stable and simple construction ensures a high degree of safety against failure. 
         [0029]    End faces  7  of the grip part  3  that are directed away from the connection ends are spaced apart from each other when the clamp  1  is in an opened position, as shown in  FIG. 1 . This also results in a predetermined spacing of the clamp limbs  2 , which allows the clamp limbs  2  to be inserted into the patient&#39;s body through two skin incisions spaced apart from each other. The skin incisions simply have to be dimensioned in such a way that they are able to receive the clamp limbs  2 . Insertion of the grip part  3  into the body is not necessary. 
         [0030]    In order to open and close a clamp mouth  8 , the two actuating limbs  4 ,  5  can be moved towards and away from each other through a central drive mechanism  9 . The central drive mechanism  9  includes a threaded spindle  12  provided with a knurled disc  11  and is preferably constructed to be self-locking. Thus, when securing the clamp  1  to a bone, it is possible to achieve a particularly firm and reliable fixation, with the clamp  1  being unable to automatically come loose. Elements  13  to be provided in the actuating limbs  4 ,  5  for the purpose of taking up the threaded spindle  12  will not be discussed in any detail herein, since technical constructions provided for this purpose are known to persons skilled in the art. As an alternative to a knurled disc, it is also possible to use a star-shaped wheel. 
         [0031]    In  FIG. 1 , a position is shown in which the two clamp limbs  2  have already been moved slightly from a normal position, in which the two clamp limbs  2  are parallel to each other, and towards each other. The clamp limbs  2  are connected to the grip part  3  in an individually releasable manner. Thus, the clamp limbs  2  can also be individually replaced, for example in the case of a defect or the like, or if the anatomical situation so requires. The connection between the clamp limbs  2  and the grip part  3  is produced by snap-fitting, locking or clamping connections, for which non-illustrated corresponding receiving openings or connecting openings are provided in the lower end faces  7  of the actuating limbs. In this way, a simple but nevertheless very secure connection can be established. The drawings do not show securing elements that may be necessary on the clamp limbs  2 . The measures necessary for suitably securing the clamp limbs  2  to the grip part  3  will not be discussed in any detail below. 
         [0032]    A clamp limb  2  of the kind shown in  FIG. 1  has a straight clamping jaw  15 , i.e. one that extends parallel to a central longitudinal axis  17  of the clamp limb  2 , as seen in  FIG. 2 . The clamping jaw  15  has a length of 20.5 mm and is provided with fixing spikes  16  which are each offset by 1.5 mm relative to the central longitudinal axis or line  17  of the 76.5 mm long clamp limb, in order to achieve a better fixation to the bone tissue. The exact positioning of the fixing spikes  16  will be seen from the spacing dimensions indicated in  FIG. 2 . 
         [0033]    An example of a fixing spike  16  of this kind is shown in  FIG. 7 . A fixing spike  16  is preferably composed of a cylindrical shaft  18  and of a conical point  19  attached to the shaft  18 . The point  19 , at the site of attachment to the shaft  18 , has a greater diameter (in this case 1.99 mm) than the shaft (in this case 1.5 mm) and therefore forms a kind of barb. In the example shown, the total length of the fixing spike  16  is 3.75 mm, with a shaft length of 1.75 mm. As the clamp  1  is closed, the fixing spikes  16  bore into the bone being operated on and avoid slipping of the clamp  1 . 
         [0034]    The thickness of the clamp limb  2  in the area of the clamping jaw  15  is less than the thickness of its attachment area  21 . A bridge between the two skin incisions is preserved during use of the clamp  1  due to this tapering. The thickness of the clamp limb  2  decreases continuously in the direction of the clamping jaw  15  in a transition area  22 . In the area of the clamping jaw  15 , the thickness of the clamp limb  2  is only 1.75 mm. This prevents unnecessary damage to the tissue when introducing the clamp limbs  2  into the patient&#39;s body. The transition area  22  connects the proximal attachment area  21  of the clamp limb  2 , which attachment area  21  has a length of 34.6 mm, to the distally disposed clamping jaw  15 . 
         [0035]    In order to ensure a minimally invasive application of the clamp  1 , it is particularly advantageous to use a covering device  24 , as shown in  FIG. 3 , to protect the tissue during insertion of the clamp limbs  2  into the patient&#39;s body. The covering device  24 , which has an overall length of 75 mm, is constructed as a cylindrical sleeve  25  which is partially open to one side and which is pushed over the clamp limb  2  starting from a distal free end  26  of the clamp limb  2 . Each clamp limb  2  is assigned a covering device  24 . 
         [0036]    The covering device  24  has an annular abutment  27  at the proximal end. The abutments  27  firstly serve to ensure that the covering devices  24 , with respect to their displaceability in the longitudinal direction, assume an exactly defined position relative to the clamp limbs  2 . As the clamp  1  is closed on the bone, the abutments  27  also serve to indicate the exact (preferably identical) position of the two sleeves  25  on the end faces  7  of the grip piece  3 . 
         [0037]    The abutment  27  is provided with lateral openings  28  for receiving an actuating pin  29 . The pin  29 , which is disposed perpendicular to a central longitudinal axis  31  of the sleeve  25  in the assembled state, serves as an actuating element for turning the sleeve  25  about its central longitudinal axis  31 . In the open position of the sleeve  25  shown in  FIG. 1 , the pins  29  protrude from the plane of the drawing in the direction of the observer. The abutment  27 , which is 5 mm wide, is adjoined at its bottom by a first closed sleeve part  32  measuring 22.5 mm in length. Thereafter, the sleeve  25  is opened by omission of one half of the sleeve. This opening  33  of the sleeve  25  results in a trough-shaped shield  34  formed by the remaining half of the sleeve and measuring 47.5 mm in length. This shield  34  also forms a distal end  23  of the sleeve and has a semicircular shape at that end in order to avoid unnecessary tissue damage during insertion of the clamp limb  2 . 
         [0038]    The dimensions of the clamp limb  2  and the covering device  24  are adapted to one another in such a way that the sleeve  25  can turn without difficulty around the clamp limb  2  in the assembled state. 
         [0039]    The two covering devices  24  provided on a clamp  1  can also be actuated independently of each other, i.e. they can be moved independently of each other from a first position, in which they preferably completely cover the clamping jaw  15  of a clamp limb  2 , to a second position, in which they do not cover the clamping jaw  15  of the clamp limb  2 . 
         [0040]    The principle of the covering device is not limited to clamp limbs  2  with straight clamping jaws  15 . Clamp limbs with differently shaped clamping jaws can also be protected in this way. 
         [0041]    Instead of the clamp limbs  2  provided with a covering device  24 , other clamp limbs can also be used with the grip part  3  shown in  FIG. 1 . For example, a clamp limb  36  measuring 35 mm in length and having a Y-shaped clamping jaw  37  is shown in  FIG. 4 . Clamping arms  38  of the Y-shaped clamping jaw  37  are angled symmetrically with respect to a central longitudinal axis  39  of the clamp limb  36  and have a maximum width of 12 mm at their distal end. The fixing spikes  16  provided there are then spaced apart from one another by 9 mm. The clamping arms  38  between them preferably enclose an angle of approximately 55° to 75°. An angle of approximately 60° to 70° has proven particularly advantageous for secure fixing. The clamp limb  36  shown in  FIG. 4  has fixing spikes  16  disposed along a midline or midlines  41  of the clamping jaw  37  and the clamping arms  38 . The exact dimensions of this clamp limb  36  and the positioning of the fixing spikes  16  will be seen from the measurements indicated in  FIG. 4 . 
         [0042]      FIG. 5  shows another clamp limb  42  with a Y-shaped clamping jaw  43  which, in addition to a wider shape of the clamping jaw, is distinguished by the fact that, instead of the fixing spikes, it has been provided with fixing edges  45  or teeth that protrude obliquely outwards from the surface of the clamping jaw  43  and extend at right angles to a central longitudinal axis  44  of the clamp limb  42 . 
         [0043]    Alternatively, it is possible to use clamp limbs  46  with L-shaped clamping jaws  47 , as is seen in  FIG. 6 . These preferably enclose an angle of approximately 20° to 90° with a central longitudinal axis  48  of the clamp limbs  46 . An angle of approximately 40° to 70° has proven particularly advantageous for secure fixing. Fixing spikes  16  are provided in this case too and disposed along a midline  49  of the clamping jaw  47 . 
         [0044]    Both the grip part  3  and the clamp limbs  2  are preferably made of stainless and acid-resistant steel. However, if large parts of the clamp  1  are made of a radioparent material, the number of metal artifacts in an imaging method can be reduced. Preferred materials are polyether ether ketone, glass fiber, carbon-fiber-reinforced polyether ether ketone, carbon and ceramic. For example, the actuating limbs  4 ,  5  of the grip part  3  and the clamp limbs  2  can be made entirely of one of the above-mentioned non-metals. In addition, all of the elements of the clamp  1  are preferably made of a sterilizable material, in such a way that they can be reused after one application. 
         [0045]    The clamp  1  according to the present invention has a reference marking  51  with reflectors  52  disposed in a star shape for use in an optical positioning system for percutaneous interventions. For example, the reflectors  52  are constructed in such a way that they are suitable for detection with an infrared camera. The reference marking  51  is connected to the grip part  3  of the clamp  1  by a securing device  53 . The securing device  53  includes a coupling plug  54  onto which a coupling piece  55  of the reference marking  51  can be fitted. A longitudinal axis  56  of the coupling plug  54  is preferably placed as far as possible away from a central longitudinal axis  57  of the clamp  1 , that is to say the axis of symmetry of the clamp. In the case of a reference marking  51  made of metal, this eccentric configuration reduces the metal artifacts in the imaging method, because the reference marking  51  is set away from the operating area. 
         [0046]    The coupling piece  55  allows the reference marking  51  to rotate in such a way that the reflectors  52  are located in a position desired for navigation, which once again reduces the occurrence of metal artifacts. 
         [0047]    The application of a medical clamp  1  according to the invention to a bone, for example to the spinous process of the spinal column, is described below. A clamp  1  with straight clamping jaws  15  and with a covering device  24  is used, by way of example. The patient is placed in the customary abdominal position. After sterile washing of surgical standard, the position of the required skin incisions is determined, for example with the aid of CT. The skin incisions are at most 1 to 1.5 cm long and are directly above the spinous process. After blunt cutting or exposure without cutting, the clamp limbs  2  of the spinal clamp  1  can be introduced through the skin incisions into the patient&#39;s body. 
         [0048]    Before insertion, the covering device  24  is turned inwards in such a way that the clamping jaws  15  are covered and the fixing spikes  16  cannot lodge in the soft tissue and damage it. After checking the position of the clamp  1  through the use of the CT, the clamp  1  can be closed tight. The clamp mouth  8  is closed through the knurled disc  11 , which is constructed in this case as a rotatable grip. 
         [0049]    Once the modular clamp  1  has been secured to the patient&#39;s bone by a minimally invasive procedure, the position of the reference marking  51  fixed on the clamp  1  is determined with the aid of a contactless locating method and is used to navigate a surgical instrument or the like for surgery of the spinal column. Details concerning the structure and mode of functioning of the individual components of such a positioning system, in particular for collating and comparing data from the reference system on one hand and from the (CT) image data on the other hand, are known from the prior art and do not need to be dealt with any further herein. 
         [0050]    After the navigation has been concluded, the clamping action is cancelled by simply turning the knurled disc  11  back. The wound can be closed according to surgical standard. 
         [0051]    All of the features set forth in the description, in the attached claims and in the drawing may be important to the invention either individually or also in any desired combination with one another. In particular, the embodiments relating to the L-shaped clamping jaws  47  enclosing a particular angle with the central longitudinal axis  48  of the clamp limbs, the clamp limbs  36  having Y-shaped clamping jaws  37 , and the clamping arms  38  of the Y-shaped clamping jaws  37  being angled preferably symmetrically with respect to the central longitudinal axis  39  of the clamp limbs  36  and between them enclosing a particular angle, can also be realized separately, i.e. independently of the embodiments described in the other claims, and in themselves each represent protectable inventions. At the same time, the embodiments relating to the covering device  24  being constructed as a tubular sleeve  25  which is at least partially open to one side, the covering device  24  being disposed on the clamp limb  2  in such a way that, in a first position of the covering device  24 , the clamping jaw  15  of the clamp limb  2  is preferably completely covered by the covering device  24  and, in a second position of the covering device  24 , the clamping jaw  15  of the clamp limb  2  is not covered by the covering device  24  and each clamp limb  2  being assigned a covering device  24 , and the covering devices  24  being actuatable independently of each other, can also be realized separately, i.e. independently of the embodiments described in the other claims, and in itself also represents a protectable invention.