Abstract:
A device for punching out tissue areas from bone has a blade whose circumferential cutting edge corresponds to the contour of a tissue area that is to be punched out. The blade is composed of a plurality of blade segments that are each movable in an axial direction counter to the force of a spring.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates to a device for punching out tissue areas from bone, with a blade whose circumferential cutting edge corresponds to the contour of a tissue area that is to be punched out.  
         [0002]     Tissue punches of this kind, also called cartilage punches, are sold by the company Ars Arthro AG, 73728 Esslingen, Germany.  
         [0003]     Such punches are used, for example, in autologous chondrocyte transplantation (ACT), see DGU—Mitteilungen und Nachrichten 45/2002 1, “ACI und Tissue Engineering” under the auspices of the DGU and DGOOC.  
         [0004]     The hyaline articular cartilage of humans varies in thickness depending on topography. In the area of the patella, it can reach a layer thickness of 7 to 8 mm. Since the articular cartilage has no direct vessel or nerve attachments, it is nourished mainly through diffusion from the synovial fluid of the intraarticular space. The crosslinking of various matrix components to form the ground substance of the cartilage permits mechanical damping and almost frictionless sliding of the articular surfaces. At the cellular level, there is a complex structure of cartilage cells (chondrocytes), collagen fibres and proteoglycans. The healthy hyaline cartilage of an adult is able to tolerate loads that can amount to a multiple of the body&#39;s weight.  
         [0005]     Damage to the articular cartilage represents a major problem in routine traumatology and orthopedics. The limited healing capacity of the hyaline cartilage has long been recognized and is mainly due to its particular structure and anatomy.  
         [0006]     Damage to the articular surface, above all in the area of the load-bearing zone of the sliding surface of the joint, therefore entails increased risk of substantial joint damage in the sense of premature arthrosis. Known methods for biological reconstruction of full-thickness cartilage damage are in most cases suitable only for small to medium-sized defects. In cases of full-thickness cartilage damage, especially in the area of the knee joint, with a defect covering more than about 4 cm 2 , autologous chondrocyte transplantation (ACT) is therefore gaining increased clinical application.  
         [0007]     In this method, a specimen of cartilage is removed arthroscopically from a non-supporting part of the joint. The cartilage cells from the biopsy specimen are isolated and are cultivated in a cell culture.  
         [0008]     The cultivated cells are transplanted back into the cartilage defect zone during a second intervention.  
         [0009]     The defective tissue has previously been removed from the cartilage defect zone, for which purposes a device mentioned at the outset is used for the punching operation.  
         [0010]     In this so-called defect preparation, the edges have to be as smooth as possible and at right angles, specifically such that the prepared defect edges are delimited on all sides by stable cartilage. The defect base ought to reach as far as the subchondral bone. A cartilage punch corresponding to the size of the defect is applied and firmly pressed in. The contour of the circumferential cutting edge corresponds approximately to the contour of the tissue area to be punched out; this area can be circular, oval or of another shape. By means of a sharp spoon or a ring curette, the defective tissue area is scraped off (debrided) as far as the osteochondral zone.  
         [0011]     The biopsy specimen produced beforehand is then transplanted back into the area that has been prepared in this way.  
         [0012]     The known punches that are used have a continuous circumferential cutting edge that lies in one plane. The punches are usually made up of a hollow body, for example a tube, whose end edge extending approximately perpendicular to the longitudinal axis is ground down to form a cutting edge.  
         [0013]     In practical use, it has now been found that optimal defect preparation is not possible with blades of this kind, because in most cases the bone surface from which the tissue area is to be separated is not even. As has already been mentioned, such defects occur particularly in the area of the knee joint, where the bone surface is strongly curved.  
         [0014]     When a bone punch with a flat blade line is driven into a curved bone surface, this inevitably means that only some tissue areas can be incised to the optimal depth, while others cannot.  
         [0015]     Remedial measures, such as tilting the punch back and forward, does not provide the desired smooth edges prepared at right angles.  
         [0016]     It is therefore an object of the present invention to remedy this situation and to develop a device of the type mentioned in the introduction such that optimal defect preparation is possible.  
       SUMMARY OF THE INVENTION  
       [0017]     According to the invention, the object is achieved by the fact that the blade of the device for punching out tissue areas is composed of a plurality of blade segments that are each movable in an axial direction counter to the force of an elastic element.  
         [0018]     These measures have the advantage that, by dividing the blade into individual blade segments, and by these each being acted on by the force of an elastic element, these blade segments can penetrate into the cartilage tissue independently of the other blade segments. If the bone area is curved in a dome shape, and if the blade is applied in the area of the dome, the corresponding blade segments can penetrate deeper into the cartilage tissue in those areas where the dome slopes down slightly farther.  
         [0019]     In other words, as far as their depth of penetration is concerned, the individual blade segments can adapt to the contour of the underlying (subchondral) bone surface. A punch line is thus generated that adapts automatically to the respective substructure of the bone. Since the blade segments are movable in the axial direction, a cutting edge is obtained that is reliably smooth and suitably at right angles. Through the choice of the number of blade segments, it is possible to create a blade line more or less adapted to the undulated substructure or bone surface. If the bone base is only gently undulated or curved, 5 or 10 blade segments may suffice for a blade line length of 10 cm for example, while more segments, for example up to 20 blade segments, can be provided for a strongly undulated surface.  
         [0020]     The blade line is thus optimally adapted to the anatomy of the bone surface, with the result that an optimal preparation of the defect is possible. The subsequent scraping off of the punched-out tissue area from the bone base is made much easier than in cases when some areas of the tissue are not incised or punched to the optimal depth, on account of the undulating geometry of the substructure of the bone.  
         [0021]     The elastic element can be made from an elastically deformable material.  
         [0022]     In one embodiment, the elastic element is designed as a spring, and the blade segment can be moved counter to the force of said spring.  
         [0023]     In another embodiment of the invention, the blade segments are received in a guide.  
         [0024]     This measure has the advantage that the blade segments are guided exactly in their axial reciprocating movement, so that particularly smooth and right-angled cuts can be made.  
         [0025]     In another embodiment of the invention, a blade segment can be acted on by the elastic element or spring in such a way that it can be pressed out past the distal edge of the guide.  
         [0026]     This measure has the advantage that a variable length section is present which at the same time also defines the maximum depth of penetration of the blade into tissue.  
         [0027]     This not only permits variable adaptation of the blade line to the contour of the bone surface from which the cartilage tissue is to be separated, but also limits the maximum depth of penetration, so as to rule out the possibility of the bone being damaged by inadvertently pushing the blade of the punch in too far.  
         [0028]     In another embodiment of the invention, the guide has an outer wall and, arranged radially inward from the latter, an inner wall, between which walls the blade segments are received.  
         [0029]     This measure has the advantage that the blade segments are guided in the radial direction by the wall and are also protected from being damaged. It is thus also possible for the individual blade segments to be arranged next to one another as Individual segments, since they are held and guided by the inner and outer walls and are additionally guided in the circumferential direction by an adjacent blade segment.  
         [0030]     This permits particularly safe handling.  
         [0031]     In another embodiment of the invention, the device is designed as a hollow body that is divided into at least two hollow body segments, at least one hollow body segment being axially displaceable relative to another.  
         [0032]     This measure has the considerable advantage that the punching operation can first be carried out, and one of the two hollow body segments can then be withdrawn axially, as a result of which sufficient space is created for scraping off the tissue from the bone with the spoon. Some of the blades are still pressed into the tissue, as a result of which this area serves as a support or abutment for the spoon, so that this scraping can take place such that the edges are not damaged by this scraping process.  
         [0033]     This results in particularly exact and smooth edges in the punched-out area.  
         [0034]     In another embodiment of the invention, the hollow body segment comprises the guide and the blade segments guided by the latter.  
         [0035]     The hollow body is thus composed of different blade units, of which at least one can be axially withdrawn as a complete structural unit, so that the operating surgeon has sufficient space to scrape off material with the spoon.  
         [0036]     In another embodiment of the invention, the blade segments of a hollow body segment are axially movable together in the guide.  
         [0037]     This measure has the considerable advantage that the blade segments of the hollow body segment that is withdrawn can be drawn back axially even further, so as to disappear completely in the guide, particularly between the inner and outer walls. This ensures that, when scraping out the tissue area, the operating surgeon cannot accidentally injure himself on the blades of the axially retracted hollow body segment.  
         [0038]     In another embodiment of the invention, the springs of the blade segments are supported on a common support that is axially displaceable between the walls.  
         [0039]     This measure has the advantage that the blade segments, either of the entire hollow body or only of the axially movable hollow body segment, can be moved to and fro in a single displacement by means of the aforementioned movement, for example in order to be drawn back into the guide for protection.  
         [0040]     This additionally has the advantage that during storage, or during preparation for an operation, the blades are initially set back behind the distal edge of the device and are pushed out only at the time of the actual punching procedure.  
         [0041]     This protects the sometimes very thin blade segments from damage and at the same time protects the operator from injury when preparing the operating equipment.  
         [0042]     In another embodiment, the device comprises a spoon for removing the punched-out area of tissue.  
         [0043]     This measure has the advantage that the geometry of the spoon can in each case be adapted to the geometry of the hollow body, so that this makes a further contribution to optimal removal of tissue.  
         [0044]     It will be appreciated that the aforementioned features and those still to be explained below can be used not only in the respectively cited combination, but also in other combinations or singly, without departing from the scope of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0045]     The invention is described and explained in greater detail below on the basis of a selected illustrative embodiment and with reference to the attached drawings, in which:  
         [0046]      FIG. 1  shows a longitudinal section through a distal end portion of a punching device according to the invention,  
         [0047]      FIG. 2  shows a plan view of the distal end area of the device from  FIG. 1 , illustrating its oval contour,  
         [0048]      FIG. 3  shows a greatly enlarged perspective and partially cut away view of a circumferential portion of the distal end area of the device from  FIG. 1 ,  
         [0049]      FIG. 4  shows a highly schematic representation of the use of the device in a defect preparation on a knee joint,  
         [0050]      FIG. 5  shows a greatly enlarged detail of the defect preparation, and the area bordered by a circle shows a still further enlarged representation of the blade segments penetrating into the hyaline articular cartilage, and  
         [0051]      FIG. 6  shows a perspective partial view of the device according to the invention from  FIG. 5 , with a hollow body element axially retracted so that the punched-out area of cartilage can be removed using a spoon.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0052]     In FIGS.  1  to  6 , a device for punching out tissue areas is designated in its entirety by reference number  10 .  
         [0053]     In its distal end area, the device  10  has a hollow cylindrical body, shown in  FIG. 1 , with an elliptical cross section, as can be seen from the sectional view in  FIG. 2 .  
         [0054]     The hollow cylindrical body  12  has an outer wall  14  and, arranged radially inward from the latter, an inner wall  16 .  
         [0055]     The outer wall  14  is composed of two elliptical half-shells  18  and  19 , and the inner wall  16  is composed of corresponding half-shells  20  and  21 . A blade  22  is received in the gap between outer wall  14  and inner wall  16 .  
         [0056]     The assembly composed of outer wall  14  and inner wall  16  thus serves as a guide for the blade  22 .  
         [0057]     As can be seen in particular from  FIG. 3 , the blade  22  is composed of a multiplicity of blade segments  24 ,  24 ′.  
         [0058]     Each blade segment  24  is composed of a hollow cylinder segment that is beveled at the distal end with a downward slope, as viewed from radially outward to radially inward. The higher edge of the bevel  28  thus forms a cutting edge  26 .  
         [0059]     The blade segments  24  are designed and arranged in such a way that they completely fill the space between the outer wall  14  and the inner wall  16  in the circumferential direction, the blade segments  24 ,  24 ′ being arranged lying next to one another, but in such a way that they can move in the axial direction, as is indicated by the double arrow  33 . It will be seen from the plan view in  FIG. 2  that twenty blade segments  24  are provided in total.  
         [0060]     At its end remote from the cutting edge  26 , each blade segment  24  is connected to an elastic element in the form of a spring  30 , which is supported on a support  32 .  
         [0061]     Each spring  30  is pretensioned in such a way that it tends to press a blade segment  24  out past a distal edge  25  of the hollow cylindrical body  12 .  
         [0062]     In  FIG. 3 , the blade segment  24  Is shown in its position of maximum extraction past the distal edge  25 .  
         [0063]     The adjacent blade segment  24  is driven in so far, or moved or pressed proximally in the axial direction, such that its cutting edge  26 ′ is flush with the distal edge  25 .  
         [0064]     The blade segment lying farther to the right of this in the illustration in  FIG. 3  is shown in an intermediate position between the two positions of the blade segments  24  and  24 ′.  
         [0065]     In the embodiment in  FIG. 3 , the spring  30  is integrally connected at one end to the support  32 , which again has a half-shell shape, and it is integrally connected at the other end to the blade segment  24 . This geometry can be obtained directly from solid material by means of a laser cutting operation.  
         [0066]     It is also possible to place a separate spring between the blade segment  24  and the support  32 , in which case corresponding guides have to be provided for the springs.  
         [0067]     FIGS.  4  to  6  show a manipulation of the device  10 , specifically the removal of a tissue area  40  of cartilage tissue  39  that covers a bone  38 , in this case the human femur, for example.  
         [0068]     As was mentioned in the introduction, the tissue area  40  to be removed is a defect area that is to be replaced by other tissue.  
         [0069]     The device  10  according to the invention is used here as a tissue punch in order to be able to remove this tissue area  40 .  
         [0070]     As can be seen from  FIG. 4 , the device  10  has a grip  42  that protrudes laterally from the hollow cylindrical body  12 .  
         [0071]     This is just one design example. If the operation is carried out by arthroscopy, that is to say through a trocar, the hollow cylindrical body  12  is accordingly longer, and a grip or a scissor-like maneuvering element is arranged at a greater distance from the removal site.  
         [0072]     However, this is a question of the particular design and of the type of intervention, that is to say whether it is a minimally invasive operation or an operation performed on an exposed knee joint.  
         [0073]     The handgrip  42  is in this case mounted on the outside of the half-shell  19 .  
         [0074]     On the opposite side, a bracket  44  protrudes from the other half-shell  18 , the purpose of which bracket  44  will be explained later in connection with  FIG. 6 .  
         [0075]     For the procedure referred to as a defect preparation, a device  10  with the desired geometry is chosen, in this case the geometry shown in  FIG. 2 , that is to say with an oval cross section. The cutting edge  26 , which is composed of the respective cutting edges  26  of the blade segments  24 , encloses an area of approximately 10 cm 2 . As can be seen in particular from  FIG. 5  and from the larger area enclosed by a circle, the device  10  is placed with its distal end on the cartilage tissue  39  that surrounds the bone  38 , specifically in the area of the defect, i.e. of the tissue area  40 .  
         [0076]     The device  10  is pressed into the cartilage tissue  39 , the individual blade segments  24  penetrating to the extent permitted by the surface of the bone  38 , i.e. the contour of the cutting edge of all the blade segments  24  adapts to the correspondingly curved contour of the bone  38 .  
         [0077]     The optimal depth of penetration is thus achieved in the area of each individual blade segment  24 , and, at the same time, a defect preparation is obtained in which the edges are very smooth and at right angles.  
         [0078]     The punched-out tissue area  40  is removed from the bone  38  using a spoon  48  (shown in  FIG. 6 ) with sharp edges, or a curette.  
         [0079]     The tissue area is scraped off as far as the osteochondral zone.  
         [0080]     To make this procedure easier, it is proposed that the hollow body segment  34 , as can be seen in  FIG. 6 , can be pulled off proximally in the axial direction. The bracket  44  makes this procedure easier.  
         [0081]     The hollow body segment  34  is thus composed of the half-shell  19  of the inner wall and the half-shell  18  of the outer wall, and of the corresponding blade segments  24  received between said walls.  
         [0082]     As has been explained in connection with  FIG. 3 , the springs  30  are pretensioned in such a way that they press the blade segments  24 ,  24 ′ out past the distal edge  25 .  
         [0083]     Since all the springs  30  of a hollow body segment are supported on a common support  32 , this opens up the possibility of drawing this support  32  further in the proximal direction between the half-shells  18  and  19 , so that the protruding parts of the blade segments  24  are drawn in between these edge areas, that is to say no longer extend past the distal edge  25 . This ensures that the operating surgeon does not injure himself while maneuvering the spoon  48 .  
         [0084]     This maneuvering involves the tissue area  40  being completely scraped off from the bone and removed using the spoon  48 , as shown in  FIG. 6 .  
         [0085]     Depending on the operating technique, an endogenous periosteal flap, for example one taken from the proximal tibia, is then fitted into the prepared defect area, or a suitably cultured biopsy is used.