Abstract:
An implant for partially replacing surfaces that are subject to stresses includes a base that is inserted into an area removed from a bone. The base includes at least one surface for replacing the removed area of the bone and an adapter for receiving the base. The system for inserting the implant includes an angle determining system that includes a set of elliptical plates having different diameters to determine the cutting angle of the implant to be utilized to replace the surface of the bone. The system also includes an oscillating drill with hollow drills that have beveled tips.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This. Application is a Section 371 National Stage Application of International Application No. PCT/DE03/01880, filed Jun. 5, 2003 and published as WO 03/103535 on 18 Dec. 2003, in German. 
     FIELD OF INVENTION 
     The present invention relates to an arrangement especially for the partial replacement of surfaces that are subject to stresses, e.g. the surfaces of a joint. However, it can also be used to replace jaw areas supporting chewing surfaces including teeth or pins. 
     BACKGROUND OF THE INVENTION 
     Until now, when joint surfaces became worn, it was usual to replace the entire joint or joint parts in toto with an endoprosthesis. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to create implants and an arrangement that allow partial replacement of surfaces that are subject to stresses, such as chewing or joint surfaces, without requiring the insertion of an entire endoprosthesis. 
     The novel implants and arrangements follow the principle that first the size of the defective joint surface section is determined, a drilling area is calculated within which the bone is removed with a special drilling device, the removed area of the bone also including the defective joint surface, and the removed bone area is subsequently replaced with an implant, e.g. with an inorganic base such as hydroxy apatite or with composite materials such as tricalcium phosphate with grafted bone or cartilage tissue or with a joint surface material or bone replacement material known in the prosthetics industry, such as ceramic or metals, particularly titanium alloys. 
     The implant according to the invention includes a spherical or axial base. An axial base is any base that has a longitudinal or symmetrical axis: Such bases are particularly cylinders with different footprints (circle, ellipse, polygon), cones, subrings or similar elongated bases. Spherical bodies do not have to have an exactly spherical shape. Its extension may be slightly different in all three spatial directions, e.g. ellipsoid, egg- or breadroll-shaped, etc. The base includes at least one surface that is formed as a joint replacement surface and/or has an adapter for accepting a surface element with such a surface. 
     In the rest of this document, joint surfaces will be used to designate other stressed surfaces as well, such as the chewing surfaces of a tooth. The base is inserted in an area of removed bone, from which the bone has been removed previously e.g. by drilling, punching, milling, via a laser and by other comparable removal techniques. The base is preferably held in place in the removed area by an interference fit, although other means of fixing with friction fit or positive locking, e.g. screwed, are also conceivable. The base may for example be cylindrical in shape and may support the joint surfaces directly or it may have an adapter for receiving such an element, such as a hole for receiving a tooth or pivot tooth or the frontal or peripheral part of the joint surface. 
     The implants according to the invention preferably include a cylindrical base with two frontal faces facing away from one another, of which the first frontal face or the periphery of the base preferably has a straight or curved surface at an angle not equal to 90 degrees to the axis of the cylinder, forming the joint surface to be replaced, and the second frontal face also has a preferably straight or curved surface at an angle not equal to 90 degrees to the axis of the cylinder, which closes with the bone periphery after it has been implanted. Instead of the surface, the base may also have an adapter for receiving one of the surface elements that contains the surface to be replaced, e.g. a joint surface element or tooth. However, the angle of the surface(s) may also be 90°. 
     The joint surfaces are preferably surface treated so that the natural joint surface structure is reflected as accurately as possible. Parts of the implant that come into contact with the bone or surrounding tissue may be coated and/or faced with antibiotics in a method known per se to prevent inflammations. In the same way, bone replacement materials may be manufactured from a correspondingly treated material, e.g. formed or sintered. 
     The implant preferably fits in the punched out or drilled out bone area in such a way that it is held by the interference fit. The cylindrical diameter of the implant is then preferably minimal, e.g. 0.01 to 0.5 mm larger than the drill hole in the bone. The fact that the forces acting on the joint surface are not transferred to the implant axially, but at a certain angle is advantageous for the interference fit. Of course, the cylindrical barrel of the implant may also be roughened or be provided with a clasping structure, e.g. a thread, which however is disadvantageous with regard to traumatizing the surrounding bone tissue. 
     The implant is preferably a single part, in other words it is produced from one material in one manufacturing step, which simplifies production. However, it may also be provided that the cylindrical base and the second frontal face are made from a conventional bone replacement material, while the first frontal face, which forms the joint surface is formed by a special joint surface material, such as special titanium alloys or ceramic. Alternatively, both frontal faces may also be made from a different material than the cylindrical implant base. 
     If the base has an adapter for the surface element, the function of the base as a bone replacement substance may be optimized, while the received surface element may be optimized as a joint surface element. The selection of the material must be modified accordingly. All known screwed attachment methods or other positive locking techniques, friction or interference fit are suitable as adapter combinations. 
     The shape of the implant or joint surfaces, e.g. on at least one of the two frontal faces may be reproduced to match the drilled out or punched out bone part in a shape tracing method known per se, wherein it must be ensured that the diameter of the base is enlarged such that the implant base is held securely in an interference fit in the bone. 
     All commonly used implant materials and bone replacement materials are suitable for producing the implant. 
     An arrangement for inserting the implant according to the invention preferably includes an angle determination system in the form of elliptical plates. The shape of the elliptical plates corresponds to the intersecting plane through a circular cylinder at a given angle of intersection x relative to the plane perpendicular to the axis of the cylinder. The greater the angle of intersection, the longer the ellipse. The width of the ellipse is conserved through the diameter of the circular cylinder. Elliptical plates are provided, preferably with different diameters and different angles of intersection. The reason these elliptical plates have different geometries is so that a suitable elliptical plate may be selected to cover a defect in such a way that while it covers the defective joint surface area completely, at the same time it covers as little of the healthy joint surface as possible. When the correct elliptical plate has been found, the angle of intersection of the elliptical plate indicates the exact drilling angle and drilling diameter for the bone material to be removed and replaced, drilling in the corresponding angle and the corresponding diameter being set in such a way that drilling ends in the defective joint surface area. 
     To enable corresponding substitution of the bone material, the arrangement according to the invention further includes an angle guiding device that has a fixing extension for insertion between the joint surfaces. This fixing extension may be for example the angle determining arrangement or any other extension that enables the angle guiding device to be fixed between the joint surfaces. An angle adjusting device is linked to the fixing extension and includes a guide element or bore guide that either extends relative to the fixing extension at the angle defined by the elliptical plate or whose angle is adjustable to the angle of intersection defined by the elliptical plate. 
     The guide element on the angle adjusting device is arranged at the adjusted angle relative to the fixing extension and enables setting of a guide wire in the  30  operational area for fastening a bore guide, which enables a drill to be guided through the bone at the preset angle so that it ends exactly in the joint surface to be replaced. After setting the guide wire, the bore guide is fastened by the guide wire at the prescribed angle and distance from the defective joint surface, and then the tubular drill for removing the bone material is guided into the bone area to be cut away by this bore guide. 
     Instead of the guide element for setting the guide wire, the bore guide may also be provided on the angle adjusting device, in which case the tubular drill for removing the bone material is guided into the bone via the angle adjusting device itself. 
     A drilling arrangement for removing the bone material or for drilling the path includes a drill and/or a punch, which may be guided by a bore guide. The bore guide is held either by the guide wires or the angle adjusting device itself at a fixed angle relative to the joint surface section to be restored in such a way that the drilling axis ends in the center of the joint surface section to be replaced. 
     To create a clean cut that ends exactly in the plane of the joint surface, the drilling arrangement preferably includes an oscillation drill device that has a hollow tubular drill with a beveled tip, the bevel of the tip corresponding exactly to the drilling angle of the drill relative to the joint surface. The oscillation angle of the oscillation drill device is exceptionally small, preferably less than 10°, especially less than 5°. In this manner, it is possible to guide the drill via the drilling device or drilling machine directly to the joint surface, wherein the beveled tip lies exactly parallel to the joint surface, so that one edge of the drill is not already cutting into the facing joint surface when the opposite drill edge has just reached the joint surface. 
     The tubular drills themselves are preferably designed as thin-walled, hollow cylindrical drills whose beveled tips have a hard runner back, which is especially coated with grindstone or carbide trimming, especially with a diamond trimming, so that the sharpness of the drill is guaranteed even after frequent use and the bone tissue is traumatized as little as possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a set of elliptical plates for determining the drilling size and the drilling angle, 
         FIG. 2  shows an angle guiding device whose fixing extension is formed by an elliptical plate, 
         FIG. 3  shows an angle guiding device in which the fixing extension is configured for knee joints by a fixing mandrel, 
         FIG. 4  shows a bore guide, 
         FIG. 5  shows a bore guide with a tubular drill, 
         FIG. 6  shows a second perspective view of the bore guide with the tubular drill of  FIG. 5 , 
         FIG. 7  shows the side view of a two cylinder drill with beveled tip, 
         FIG. 8  shows a tubular drill with a beveled tip for manual operation, 
         FIG. 9  shows a schematic view of the advance of the tubular drill with beveled tip in the operation zone, 
       FIG.  10 / 11  shows a schematic representation of the punching and replacing of a defective joint surface area, and 
         FIG. 12  shows a perspective view of two implants implanted in a femur to restore sections of knee joints, 
         FIG. 13-16  shows additional embodiments of implants according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows three elliptical plates which are obtained from a circular cylinder by a diagonal cut. The angle determination from the elliptical plates then specifies the angle of intersection relative to a cross-sectional area to the cylinder axis. Accordingly, a large angle deviation from the cylinder cross section requires a correspondingly longer elliptical shape and a smaller deviation requires a correspondingly shorter ellipse. The width of the ellipse corresponds to the cylinder diameter. 
     The set of elliptical plates to be provided includes different angles as well as different diameters, so that all sizes of joint surface defects may be covered with the elliptical plates. The elliptical plates are arranged over the defective joint site in such a way that the entire defective joint surface but at the same time as little of the healthy joint surface as possible is covered. The angle and width, in other words the diameter of the elliptical plate, determine the drilling angle and the diameter of the drill that will be used to remove the bone material. The removal of the bone occurs at the angle specified by the elliptical plate relative to the joint surface, the drilled or punched cylinder area ending in the defective joint surface, This drilled or cut out or punched out bone area is replaced afterwards with naturally-based bone replacement material such as hydroxy apatite, or by ceramic or metallic implant materials e.g. with a titanium base, wherein the end of the bone replacement material projecting into the joint surface then replaces the defective joint surface that was cut out. 
     Instead of the elliptical plates, it is also possible to determine the correct angle of intersection and drilling diameter for the bone material to be removed by measuring the length and the width of the defective site. 
     Additionally, the system according to the invention for partial joint surface restoration includes an angle guiding device which either enables the drill to be guided through the bone at the desired angle relative to the joint surface, or the guide wires to be set to which a bore guide may be attached, the bore guide then having the task of guiding the drill in the appropriate manner. The drill hole is set in such a way that it passes through the bone in the previously determined distance and angle and ends at the defective site, so that the defective site in the joint surface is removed from the bone by the drilling process. 
     For this purpose, angle adjusting device  20  has a fixing extension  22 , which in this case is formed by an elliptical plate from  FIG. 1 , an angle adjusting mechanism  24  and a guide  26  for setting guide wires in the bone. In addition, angle adjusting device  20  has a handle  28  at its back end for better handling. Fixing extension  22  is preferably secured detachably in angle adjusting device  20  so that different fixing extensions may be used in angle adjustment device  20 , as is shown in exemplary manner in  FIG. 3 , in which fixing extension  30  is configured for used in the knee joint by a fixing mandrel.  FIG. 3  also shows a guide wire  32 , which is set in the bone by guide element  26  to fix a bore guide to the bone, the bore guide being shown in  FIG. 4 , for example. 
     Bore guide  40  includes a contact area  42  for attaching to the bone and two guide holes  44 ,  46  through which guide wires  32  may pass. The guide wires are set in the bone e.g. via the angle adjusting device  20  of  FIGS. 2 and 3 . Bore guide  40  is formed entirely as a hollow cylinder with an inner cylinder area  48 , in which a drill is guided as shown  FIGS. 5 to 8 . Bore guide  40  also includes a swiveling sleeve  50  that has clamping elements (not shown) for fixing a guided drill into a defined position. 
       FIG. 5  shows a bore guide  40  together with a tubular drill  60 , which has a diamond tip  62 . Tubular drill  60  has very thin walls and a hollow interior, to that the bone material is only cut in the footprint area of tubular drill  60 , while the material to be removed remains inside the inner cavity of the drill. Trauma to the tissue is thus kept to a minimum. 
       FIG. 6  shows a diagonal front view of the same arrangement with bore guide  40  and tubular drill  60 . 
     If the bone is to be drilled at an offset angle, an oscillation drilling device with a small oscillation angle of no more than 10°, especially no more than 5° is preferably used. In this case, the tip of tubular drill  64 ,  66  is preferably beveled  68 ,  70  so that the elliptical surface of the drill head that is formed by the bevel ends exactly on the plane of the joint, which ensures that when the bone material is removed, i.e. punched out, the edge of the drill does not cut into the tissue between the joint surfaces or into the intact joint surface opposite. With the small oscillation angle in conjunction with the bevel of the tubular drill adjusted to the angle of intersection, it is thus ensured that the front end  68 ,  70  of the drill ends exactly at the plane of the joint. If the punched out material is still hanging on by a few fibers, a set  80  of hand drills  82  to  86  ( FIG. 8 ) is preferably provided, whose beveled tips  88  to  92  exactly match the inclined surface of drills  64 ,  66  of  FIG. 7  and have the exact elliptical shape of the elliptical plates of  FIG. 1 . With manual drills  82  to  86 , the punched bone material may thus be gently released from the operation field. 
     After drilling out and removing the bone material, an implant  100  is then inserted into the bone  102 , as shown in  FIG. 9 , wherein the material of the implant is surface treated on the joint side frontal face  104  and on the outer side of the bone  106  thereof, in order to reproduce the shape and smoothness of the joint surface as naturally as possible, and also to match the outer surface of the bone as closely as possible to prevent trauma to the surrounding tissue. 
     The operation of boring with the oscillation drill device and the subsequent replacement of the punched bone area with an implant is shown schematically in  FIGS. 10 and 11 . 
       FIG. 10  shows a bone  102  with an upper joint surface  110 , e.g. corresponding to the ball-and-socket joint of the femur. With a hollow tubular drill  64  as shown in  FIG. 7  having a beveled tip  68 , the bone material to be removed is now punched out below the defective joint surface area  112 . If an oscillation drill device  65  with a small oscillation angle of approximately 5 degrees is used, bevel  68  remains approximately parallel to the surface of defective joint surface section  112 . Now when the beveled tip  68  of hollow cylinder punch  64  reaches surface  112 , it lies almost exactly on the plane of defective section  112  and only minimally traumatizes the tissue surrounding the joint. 
     As shown in  FIG. 11 , after the removal of the bone material  114  to be replaced, the resulting cylindrical drill hole in bone  102  is filled by an implant  100 , such has was shown in  FIG. 9  for example. 
     The implant includes a cylindrical base  116 , whose surfaces facing away  104  and  106  replace defective joint surface area  112  and the bone periphery. Frontal face  104  of implant  100  facing the joint is surface treated to reproduce the geometry and surface constitution of the surrounding joint surface area  110  as exactly as possible. Shape reproduction procedures that are known per se may also be used for reproducing the frontal face  104  of the surface joint from surface joint area  112  as accurately as possible. Frontal face  106  of implant  100  facing the bone periphery is also surface treated to create a homogeneous and tissue-tolerant closure with the surrounding bone surface. 
       FIG. 12  shows two implants  10   a ,  100   b , which are implanted in a knee joint of a femur  102 . Implants  100   a,b  are made from of a titanium alloy that is commonly used for joint implants. The first frontal faces  104   a,b  of the implants form a part of joint surface  112  and are surface treated in such a way that they exactly match the surrounding joint surface  112  and represent the joint in its original functionality. The implants are secured in the interference fit in the holes drilled out of bone  102 , so that they are restrained from axial movement even when the joint is stressed. Here it should be noted that the fact that frontal faces  104   a,b  of implants  100   a,b  are inclined at an angle not equal to 90 degrees relative to the cylinder axis of base  106   b  causes non-axial application of forces to the implant. In the figure, cylindrical base  106   b  of right implant  100   b  is clearly visible. 
       FIG. 13  is a highly schematic representation of an implant  120  with a cylindrical base  122 , in which joint replacement surface  124  is formed in the peripheral area of base  122 , in other words by removing material in the peripheral area. Frontal faces  126 ,  128  close with the periphery of bone  102  in the joint area. The implant is preferably made from titanium alloy, but it may also be made from consist of another of the bone and/or joint replacement materials cited. In particular, joint replacement surface  124  may be arranged on a component that is to be inserted separately in base  122 , which is a special joint replacement material. 
       FIG. 14  shows an implant  130  with a cylindrical base  132  that has an adapter for a joint surface replacement part  134 , on which joint replacement surface  136  is formed. Pins, screws, interference fit and others may serve as adapting means. The advantage of this embodiment resides in the fact that base  132  may be made from an optimized bone replacement material, while the joint surface replacement part  134  is optimized for the formation of the joint surface. 
       FIG. 15  shows a spherical implant  140 , which is inserted in a cylindrical drill hole in the joint area of bone  102 . Joint replacement area  142  has been created by removal from the sphere periphery. 
       FIGS. 16   a  and  16   b  show an implant  150  in the jaw bone  152 . The implant includes a circular cylindrical base  154 , which is inserted with its longitudinal axis horizontal and crosswise to the jaw bone. Base  154  has an adapter  156 , in the simplest case a drilled hole, in which a pin  158  is placed to receive a crown  160 . Base  154  is preferably made of bone replacement material with good tissue tolerance, which is capable of growing especially well into the bone. The pin and the crown may be made from conventional dental implant materials. 
     The bases shown in the above figures preferably have a circular cylindrical shape. However, they may also have other shapes such as a ball, a cone or a cylinder with non-circular base, etc. 
     The examples shown in the figures are intended purely to explain the object of the invention and not designed to modify the scope of protection, which will be defined in the following claims. 
     Naturally, it is possible to provide individual features of the invention separately or in combinations thereof, e.g. the guide wires. If the method is carried out so that the drilling axis prescribed by the arrangement approximately intersects the center of the defective joint surface, deviations of a few mm, e.g. up to 5 mm are tolerable.