Disc-shaped augment for a bone, especially a long bone

Description

[0001] The invention relates to a disc-shaped augment for filling bone defects, particularly at the end of long tubular bones such as the tibia. The augment is provided with a first side, a second side, an outer shell on the lateral sides, and an inner wall for a through-opening running from the first to the second side for an anchoring keel of an endoprosthesis arranged on the second side.

[0002] When implanting endoprostheses, especially joint endoprostheses, a problem sometimes arises that the bone receiving the endoprosthesis is damaged, especially in the area of ​​the end of the bone (bone head). The main reason for this is defects in the (cancellous and / or cortical) bone substance or surface, e.g., due to disease or injury, but increasingly also due to the explantation of an older prosthesis. To nevertheless create a sufficient base in the bone for anchoring the endoprosthesis, augments are typically inserted to fill the missing bone substance. It has proven effective to position them countersunk into the bone end so that they are surrounded by the cortical edge of the bone end, like a quiver.

[0003] Disc-like augments for use with the tibial component of a knee joint endoprosthesis are known, for example, from EP 1 360 950 B1. Two half-sided augments are provided below the tibial plate, arranged to the left and right of an anchoring keel. The augments lie flush against the underside of the tibial plate and, when installed, are secured there by means of a fixing screw. It has been shown that, while the augments are held in a defined manner in relation to the endoprosthesis, this does not hold them in relation to the bone head, which they are actually intended to support or whose bone defect they are intended to fill. A stronger relationship to the bone defect or to the space within the bone defect to be filled would be desirable.A further difficulty can arise after prolonged use if the augment grows into the bone over time, making it difficult or even impossible to remove the endoprosthesis with the augment, for example, during revision surgery. This poses the risk of further damage to the already sensitive bone head.

[0004] The invention is based on the object of creating an improved augment with which the aforementioned disadvantages can be avoided or reduced.

[0005] The inventive solution lies in the features of the independent claim. Advantageous further developments are the subject of the dependent claims.

[0006] In a disc-shaped augment for filling bone defects, in particular at the end of long tubular bones such as the tibia, with a first side, a second side, an outer shell on lateral sides and an inner wall for a through-opening running from the first to the second side for an anchoring keel of an endoprosthesis arranged on the second side, wherein the augment has a generally C-shaped configuration with two legs flanking the through-opening, the invention provides that a connecting piece between the legs is designed in a joint-like manner and interacts elastically with the legs, so that a frame is formed, and upon compression of the legs an outwardly directed restoring force is generated, wherein the legs are designed in a skeletal construction with a plurality of adjacent disc segments separated by slots, which are arranged on the frame via webs.

[0007] The elastic design of the disc-shaped augment allows it to be inserted and countersunk into a cavity surrounded by the cortex at the bone head. The disc-shaped augment rests with its outer surface against the inner surface of the cortex, and the compression of the limbs during insertion presses the advantageously porous structure on the outer shell against the inner surface of the cortex. The resulting pretension creates an intimate connection between the outer shell and the cortex.

[0008] Due to its skeletal design, the disc-shaped augment is not designed as a single unitary disc, but is divided into several adjacent disc segments. They are typically of the same thickness. The disc segments are attached to the frame via webs, which are elastic due to the connecting piece that interacts elastically with the limbs. This allows compression of the limbs without causing tension between the disc segments. The skeletal design enables particularly favorable compression and elastic behavior, which simplifies insertion of the augment into a recess created in the bone head and ensures increased fixation security. Surprisingly, if desired, it also provides sufficient sealing against bone cement, so that a continuous sealing plate is not necessary.A further advantage of the skeletal design is that augments of various sizes can be easily created by adding / enlarging or removing / reducing one or more disc segments, typically involving multiple disc segments, i.e., three or more. The skeletal design, with its numerous spaces between the disc segments and toward the elastic frame, not only allows for high compression but also promotes the ingrowth of bone material for long-term, stable fixation.

[0009] The invention thus combines two significant advantages. Firstly, it achieves favorable primary fixation, and secondly, it creates optimal conditions for the subsequent ingrowth of bone material and thus for a correspondingly solid, long-term, stable fixation. Furthermore, if necessary, the augment and its outer shell can be detached from the surrounding bone structure by compression, thus facilitating explantation.

[0010] Below, some of the terms used are explained: Compression of the legs refers to a movement of the legs toward each other, narrowing the space between them. This is also referred to as compression. Similarly, a movement in the opposite direction is called expansion.

[0011] An anchoring keel of an endoprosthesis is understood to be a structure which is intended for anchoring the endoprosthesis in a bone, in particular a medullary cavity of the bone, and which comprises a shaft and wing-like arms arranged laterally thereon.

[0012] The first side of the augment is typically the one oriented inward, toward the bone's interior. The second side of the augment is typically the one oriented in the opposite direction, toward the bone's end.

[0013] The distance between the first and second sides of the disc segments determines the thickness of the augment. The frame can be thinner, but is preferably no thicker than the disc segments.

[0014] In the case of contour-similar objects, "undersized" means that the outer contour of one object runs within the outer contour of the other object, preferably with dimensions reduced by a certain absolute or relative amount.

[0015] A ridged structure is preferably understood to be a coarsely ridged structure, with a distance between individual ridge profiles of at least one millimeter. It has been shown that such coarse ridges create a reliable and long-lasting form-fitting fixation with bone cement.

[0016] In the case of the grooved structure, sharp-edged means that protruding areas of the groove are designed without rounded edges.

[0017] The porous structure preferably has a porosity in the range of 60% to 90% and / or an average pore size of 0.1 mm to 1.5 mm, in particular 0.4 mm to 1.0 mm. The thickness of the porous structure is preferably between 0.6 mm and 2.5 mm, with the thickness being dimensioned such that at least one layer of pores is provided deep within the material (i.e., not at the surface or cut through). This allows undercut structures to be formed in the pores.

[0018] Preferably, the first side of the disc-shaped augment is designed as a porous structure. This creates favorable conditions for bone ingrowth and thus good fixation of the augment at the large contact surface with which the first side lies flat against the bone. The edges are advantageously solid. Edges refer to the transitions between side surfaces, particularly from the first side to the lateral sides. This reinforces the edges, preventing the porous structure from breaking out.

[0019] The outer shell is designed as a porous, bone-inducing structure. This promotes bone ingrowth. Thus, the primary fixation achieved by compression can be supported by long-term fixation through the ingrown bone material.

[0020] The porous structure is advantageously designed in such a way that it comprises connected pores in the depth of the material. The porosity thus goes beyond superficial porosity and extends into the depth of the material. This creates cavities that are connected to one another, creating particularly favorable conditions for the ingrowth of bone material. The pores are advantageously dimensioned in such a way that they have a width of approximately 0.4 mm to 1.0 mm. This results in particularly favorable ingrowth behavior. It is expedient if the porous structure comprises at least one and up to three layers of pores in the depth, which typically means a preferred thickness of the porous structure of approximately 0.6 mm to 2.5 mm. This creates undercut structures in the pores that ensure a good holding effect when bone material grows in.

[0021] It is advantageous for the porous structure to have porous areas surrounded by a solid edge. This provides a clear boundary and prevents unwanted breakout of mechanically more sensitive porous material from the porous structure, particularly in the wheel area.

[0022] It is possible for the limbs, particularly with their disc segments, to be formed from a porous structure, with the second side expediently being provided with a cover plate. This results in a lightweight structure that is also almost completely open for the ingrowth of bone material. However, it is preferred for the limbs to have a solid (non-porous) core with pockets on the outer sides in which the porous structure is arranged. This allows defined zones to be created where the porous structure is present and where bone material should grow in. In addition, the limbs or augment become mechanically more robust and resilient. Further advantages of pockets with limited depth in terms of porosity are simpler production and easier cleaning.

[0023] The inner wall of the frame and / or disc segments is advantageously constructed from solid material. This prevents unwanted penetration of bone cement into the porous structure of the frame or disc segments. This also applies to lateral surfaces other than the outer shell, for example, to inner walls with slots or gaps between them.

[0024] Preferably, the slots are narrow enough to act as a gap seal for bone cement. This provides a simple and inexpensive way to achieve adequate sealing against bone cement. Preferably, the slots are a maximum of 0.7 mm wide, more preferably a maximum of 0.4 mm. Depending on the height of the disc segments and / or the viscosity of the bone cement, larger widths may be sufficient, or smaller widths may be necessary to achieve a sufficient sealing gap.

[0025] Advantageously, the lateral surfaces of the disc segments (usually their lateral outer sides or the side surfaces forming the slots) are solid, i.e., non-porous. This provides stiffening. Furthermore, the risk of unwanted penetration of bone cement into or through the slots is effectively counteracted. With such a solid design of the lateral surfaces, the width of the slots is no longer important. Preferably, the disc segments are solid, if necessary with pockets for a porous structure on the outer surface and / or on the first side.

[0026] It is advantageous if the frame is designed as a curved leaf spring. The stress resulting from compression is distributed across the elastic frame, resulting in even loading and thus greater resilience. It is particularly advantageous if the frame is designed as an outer edge that surrounds at least half of the entire disc segments, with the outer shell located on the outside. The frame thus borders the entire disc segments located on the inside of the frame. The frame can thus simultaneously form the outer shell with the porous structure.

[0027] The webs are advantageously designed to be flexible. This allows the disc segments to move relative to the frame. This allows for lateral deflection of the respective disc segment, which can be particularly advantageous in cases of severe compression.

[0028] Preferably, at least one fastening hole for a fastening screw is provided in the frame and / or the disc segments. This allows for additional fixation of the augment to the bone, which can make a particularly valuable contribution to the primary fixation. Advantageously, the fastening hole has a solid hole casing. Such a solid hole casing provides stiffening to ensure the stability of the fastening hole even under the influence of the tightening force of the fastening screw. Furthermore, unwanted ingrowth of bone material can be prevented.

[0029] For the skeleton construction, it is expedient if the fastening hole is located in one of the disc segments. This disc segment is preferably not attached to the elastic frame by means of a narrow web, but rather by means of a wider bridge, which is further preferably at least half the width of the web (i.e. at least 1.5 times the width of a web). This achieves two advantages: firstly, it ensures effective fastening of the disc segment, which is additionally loaded by the fastening screw. Secondly, the wider bridge makes it possible to move the fastening hole closer to the edge and thus closer to the frame, which is a significant advantage, especially with small augments, due to the improved use of space. Multiple disc segments can also be provided with a fastening hole.

[0030] The through-opening is typically an elongated space for the anchoring keel of the endoprosthesis. The through-opening can be expediently open on one side. It is then located at the edge of the augment as a marginal opening. This is particularly advantageous when the augment is designed as a hemi-lateral augment. The term hemi-lateral refers to the dimensions of the endoprosthesis, the anchoring keel of which is guided through the through-opening of the augment. The endoprosthesis often only requires relining on one side, for example, if a bone defect is limited to one side of the bone head and the augment is therefore only needed there. It goes without saying that two hemi-lateral augments can also be provided to reline both sides.

[0031] The through-opening is typically rather small in relation to the dimensions of the augment, generally taking up less than half, frequently less than a third of the volume of the augment. This has the advantage that sufficient supporting material remains for the legs or the disc segments to ensure adequate underpinning. The through-opening is generally dimensioned such that it accommodates the anchoring keel, or possibly its wing-like outriggers, with minimal play. The minimal play is expediently dimensioned large enough to enable the desired compression, which leads to a reduction in the through-opening due to the elastic deflection of the frame, without striking the anchoring keel. The invention can also extend to augments that have a through-opening but not for an anchoring keel.

[0032] The outer shell is preferably not at a 90° angle to the first side or the second side. It has proven effective if the outer shell is tapered, preferably at an angle of 5 to 10° towards the first side. This allows for adaptation to the tapered outer contour of the bone, and thanks to this conicity, the augment can be inserted and removed more easily by compression than would be the case with a vertical outer shell.

[0033] Conveniently, outward-facing spikes are arranged on the outer shell. When implanted, they press into the surrounding cortex of the bone head, in which the augment is housed in a recess. This increases the security of fixation right from the start, thus providing improved primary fixation. When the augment's limbs are compressed for explantation, the spikes then automatically retract from the cortex, thus allowing the explantation to proceed.

[0034] A cover plate can be provided on the second side, which has a grooved structure as an interlocking for a cement connection. This can provide additional fixation and creates a cutting layer which, in the event of planned explantation, can be cut through relatively easily using a saw, thereby freeing the endoprosthesis from the augment and allowing it to be easily removed without tearing out any augment that may have grown deeply into the bone head. The grooved structure is advantageously designed with grooves. Conveniently, continuous grooves are provided, which are preferably oriented in a direction substantially transverse to the extent of the through opening. The grooves achieve particularly effective interlocking with an applied cement bed.The grooves should preferably have spacing and heights that are adapted to the flow and setting behavior as well as the grain size of the cement bed. Groove spacing in the range of 2 to 10 mm and / or a groove depth of 0.5 to 2 mm have proven successful, with the profiles bordering the grooves being approximately 0.5 to 3 mm wide.

[0035] The grooved structure can be designed with sharp edges. However, other alternative profile shapes are also conceivable, such as triangular or rounded corners.

[0036] It is advantageous if the grooved structure is produced using a wire EDM process. This allows for the efficient creation of almost any profile shape, including sharp-edged ones.

[0037] It is particularly useful if the augment is manufactured uniformly using an additive process, especially 3D printing. This allows even complex shapes in various sizes to be created with minimal or no complex post-processing. A combination with wire EDM is particularly useful for creating defined, sharply defined profiles, as mentioned above.

[0038] A cement-tight cover plate can be provided. Cement-tight means that no bone cement penetrates the cover plate. For this purpose, the cover plate can be designed with slit-like perforations throughout. This separates the bone cement applied to the top of the augment from the inner and lower areas of the augment, preventing bone cement from seeping in and interfering with the ingrowth of bone material. The cover plate does not impede the elastic behavior of the frame, including compression, and the relative mobility of the disc segments.

[0039] Advantageously, the porous structure is provided with a coating that promotes bone ingrowth, in particular comprising calcium phosphate, and / or with a biocidal coating, in particular comprising silver, in non-porous areas. This promotes the ingrowth of bone material at desired locations and prevents it from occurring at other locations where this is not desired, particularly for the purpose of easier explantation.

[0040] Preferably, at least one flexible hinge is provided on the frame, which is designed to enable additional compression of the legs and generate an outwardly directed restoring force. This creates a localized flexible hinge—in addition to the leaf spring-like deflection of the frame as a whole—which achieves greater compression, which is particularly effective even with lower forces. This allows a change in the spring rate of the elastic frame. This is particularly advantageous for small augments, as they would otherwise be too stiff due to their compactness. The term "localized" is understood here to mean spatially concentrated. Advantageously, several such localized flexible hinges can be provided in order to achieve a more even distribution of the additional compression and the force applied by the restoring force.Several bending hinges also promote largely shape-accurate compression.

[0041] It is expedient for the at least one flexible hinge to be formed by a local material weakening, in particular in the form of a groove, a slit and / or perforations. This allows flexible hinges to be created on the frame in a technically advantageous manner. The groove design offers the advantage that the groove base maintains the separation of the interior and exterior spaces caused by the frame. Slits offer the advantage that a lower flexural rigidity can be set, whereby with a correspondingly narrow design of the slits (for preferred widths see above) there is protection against unwanted cement flow. The design with round perforations in particular offers the advantage that it can be manufactured efficiently and also has the advantage of allowing subsequent adjustment by drilling additional holes if necessary. Round, in particular circular, perforations are therefore preferred.They also offer the advantage that, due to the lack of corners, they counteract load concentration and therefore enable favorable load distribution over the surrounding area of ​​the flexible hinge. Multiple slots and especially perforations can also be grouped together. This means that low restoring forces can be achieved, which is a significant advantage, especially for small augments. - Adjustments can also be made through the choice of material; for example, a titanium alloy such as Ti6Al4V is stiffer than pure titanium (e.g., titanium grade 2). Varying the width or depth of the groove or the length and width of the remaining webs between the slots / perforations also allow adjustments to the flexural rigidity of the flexible hinges. It is advantageous if there are several flexible hinges with different material weakening, so that they have different levels of restoring forces when compressed.This allows for a finer adjustment of the flexural stiffness, both in terms of hardness and location.

[0042] The invention further extends to an arrangement comprising an endoprosthesis, in particular a knee joint endoprosthesis, and the disc-shaped augment. An anchoring keel of the endoprosthesis is received in the through-opening, particularly in the implanted state. The disc-shaped augment is expediently designed in its outer contour similar to the endoprosthesis, in particular a tibial plate. However, it is undersized compared to the latter, i.e. it has somewhat smaller dimensions (in particular in the range of 2 to 6 mm along the outer surface). Thus, it can support the endoprosthesis, in particular the tibial plate, but still be received in a recess bordered by the cortical bone in the bone head.

[0043] The disc-shaped augment is advantageously designed to support either the left or right half of the endoprosthesis. This allows the augment to provide effective support when a bone defect is present only on one side of the bone head, thus avoiding the unnecessary removal of bone material on the other, healthy side.

[0044] The through-hole for accommodating the anchoring keel and its wing-like outriggers is designed with a defined clearance of preferably 1 to 3 mm. This clearance creates a gap between the anchoring keel and its wing-like outriggers and the legs of the augment, allowing for tolerance compensation and frame deflection through compression. In practice, this is a significant relief, as it prevents excessive compression and unwanted jamming of the augment and the anchoring keel with its wing-like outriggers.

[0045] The invention is explained below with reference to advantageous embodiments in the accompanying drawings. They show: Fig. 1 is a perspective view of a first embodiment of a disc-shaped augment; Fig. 2A, rear view of the legs and a sectional view from the medial side of the augment according toFig. 1 ; Fig. 3A-F different profile shapes for a ribbing; Fig. 4 a frontal view of the augment together with a tibial plate of a knee joint endoprosthesis; Fig. 5A, B top views of a first side of the augment in two different sizes; Fig. 6 an exploded view of the augment according to Fig. 1 with the knee joint endoprosthesis; Fig. 7 shows a perspective view of the arrangement of the augment on the knee joint endoprosthesis; Fig. 8 shows a top view of a first side of a second embodiment of a disc-shaped augment with bending hinges; and Fig. 9A, B show detailed views of variants for adjusting the bending stiffness of the bending hinges.

[0046] The invention is explained below using an example of an augment for a knee joint endoprosthesis, more precisely for an augment arranged on the upper (proximal) bone head of the tibia. The augment is to be distinguished from the prosthesis, i.e. the augment is not an element of the actual prosthesis. The augment strengthens the bone and thus increases or improves its ability to absorb the prosthesis. Augments according to the invention can of course also be provided at the other (distal) end or on other bones. The augment 1 preferably consists of a titanium alloy (e.g. Ti6Al4V) or pure titanium (e.g. Titanium Grade 2), and can expediently be produced by an additive process (3D printing). However, it can also consist of another biocompatible material, for example a metallic material such as cobalt-chromium-molybdenum (CoCrMo), stainless steel (stainless steel) or even a plastic material, such asPolyetheretherketone (PEEK).

[0047] The augment 1 of the presently explained embodiment is intended to be arranged below the tibial component 9 of a knee joint endoprosthesis, as shown in Figure 4is shown. The knee joint endoprosthesis comprises a femoral component (not shown) to be arranged on the femur bone (not shown) and the tibial component 9 to be arranged at the proximal end of a tibial bone 99. This comprises a tibial plate 91, which is arranged in a laterally extended manner on a resected bone head of the tibia. The first (distal) side 92 of the tibial plate 91 is designed to rest on the surface of the bone head of the tibia 99. On the opposite second (proximal) side (upper side) of the tibial plate 91, a receptacle 90 is provided, in which a bearing piece (not shown) of the knee joint endoprosthesis is to be arranged. Depending on whether the tibial component is intended for cemented or cementless implantation, the tibial plate 91 is optionally provided on its first (distal) side 92 with a porous structure for the ingrowth of bone material in order to enable optimal fixation during cementless implantation.

[0048] For securing the tibial plate 91, an anchoring keel 8 is provided, which projects distally. It has a shaft piece 82 and a distally adjoining cone piece 81. The cone piece 81 is designed to accommodate, if necessary, a plug-in stem protruding into the medullary canal of the tibia 9. Laterally, a wing-like extension 83 is connected to the shaft piece 82 on both the left and right sides, at the free end of which a clamping sleeve 84 is arranged. The wing-like outriggers 83 act as support arms for the tibial plate 91. The tibial plate 91 can thus be connected to the anchoring keel 8 at three points, namely centrally to the shaft piece 82 and on the left and right sides with the clamping sleeves 84 arranged at the free ends of the wing-like outriggers 83. For this purpose, two screw holes 94 are provided on the left and right on the tibial plate 91, which are aligned with the respective clamping sleeve 84.

[0049] How Figure 4 As shown, the wing-like arms 83 do not lie flush against the underside 92, but are held at a defined distance. For this purpose, a central support collar 93 is provided on the underside 92, against which the shaft piece 82 rests. Spacer inserts 96 with an external thread 97 are screwed into the screw holes 94 (see Fig. 6 ), which establish a defined distance from the clamping sleeves 84. In this way, together with the central support collar 93, a defined distance is set between the underside 92 of the tibial plate 91 and the wing-like arms 83 of the anchoring keel 8. This is highlighted there by the ellipse shown with a dotted line.

[0050] An exploded view is shown in Figure 6shown. The main components are the augment 1 and the tibial plate 91 with its anchoring keel 8. As already described above, assembly is carried out by attaching the anchoring keel 8 with a shaft piece 82 using the central screw 95 at the bottom of the distal side 11 of the tibial plate 91. In addition, spacer inserts 96 made of titanium material with an external thread 97 are screwed into the screw holes 94 and thus determine a defined distance between the wing-like arms 83 and the distal side 92 of the tibial plate 91. For additional fastening and support, further fastening screws 98 are provided, which are passed through the respective spacer insert 96 and engage in an internal thread of the respective clamping sleeve 84 and thus clamp it against the spacer insert 96.In this way, a defined distance is set between the wing-like arms 83 and the distal side 92 of the tibial plate 91.

[0051] Figure 1 shows a perspective view of the first (distal) side 11 of a first embodiment of an augment 1 according to the present invention. The augment 1 is shaped like a thick disc and has two legs 31, 32, which are elastically coupled in a joint-like manner via a connecting piece 30 at the common end of the legs 31, 32. This forms an elastic frame 39, which typically encompasses approximately three-quarters of the circumference of the augment 1. The legs 31, 32 are divided into disc segments 36, with a through-opening 2 arranged between the legs 31, 32, which is designed to receive an anchoring keel 8 of the tibial component 9. With the frame 39 and the disc segments 36, the augment 1 is designed in a skeletal construction.

[0052] The disc segments 36 are each arranged on the inside of the frame 39 via a web 37. Thus, narrow slots 34 are formed between the disc segments 36 and between the disc segments 36 and the inside of the wall of the frame 39, which provide space for relative movement of the disc segments 36 during compression / expansion. The width of the slots 34 can be dimensioned such that, taking into account the depth of the slots 34 predetermined by the thickness of the disc segments 36 of the augment 1, a gap seal is formed that effectively prevents the ingress of bone cement. These disc segments 36 can be finely adapted to the space requirements of the through-opening 2, which in turn is largely determined by the nature of the anchoring keel 8 of the prosthesis to be implanted.

[0053] A posterior view of Augment 1 and a medial sectional view are shown in the Figures 2A and Bshown. The rear view refers to the orientation of the augment 1 in the inserted state. Using anatomical terminology, this is a posterior view. A cement-tight cover plate 4 can be formed on the top of the augment 1, i.e. on the second (proximal) side in the exemplary embodiment. This does not hinder the elastic behavior of the frame 39, including the compression, and the relative mobility of the disc segments 36. The cover plate can be provided with a grooved structure 40 on its upper side. The grooved structure 40 can thus serve as an interlocking to a cement bed (not shown), which fills the space between the tibial plate 91 and thus ensures additional fixation. The grooves 40 can have a groove 42, wherein the individual grooves are separated from one another by raised profiles.The grooves can be oriented in a front-to-back direction, i.e., from anterior to posterior in the implanted state. The depth of the grooves 40 can be, for example, 1 mm, the width of the grooves approximately 3 to 4 mm, and the width of the raised profiles 41 approximately 1.5 mm. In the simplest case, the profiles 41 can have a rectangular cross-sectional shape, as shown in FIG. Figure 3A) or 3B ), with rounded or sharp corners, respectively, as a positive or negative profile. Alternatively, non-rectangular shapes are also possible for the profile, for example in the form of a symmetrical triangle or an asymmetrical, sawtooth-like triangle, as in Figure 3C ) or 3E). Furthermore, rounded profiles can also be provided, for example in the form of a semicircle as in 3D figure ) or asymmetrical in the manner of a quarter circle as in Figure 3F). This can be selected by the specialist depending on the requirements for the interlocking formed by the profiles 41 with the bone cement.

[0054] In Figure 2A , B it can also be seen that the respective lateral sides of the augment 1 are conical and taper towards the interior of the bone on the first side (in this case distally, downwards in the illustration). In the exemplary embodiment shown, the angle on each side is approximately 7°. Other angles can also be provided. The conical design not only simplifies insertion during implantation, but above all also removal of the augment 1 from the bone during explantation. It can also be seen that the frame 1 and the disc segments 36 have approximately the same thickness.

[0055] Reference is now made to the Figures 1 and 2B ). As in Figure 1As visualized by dashed lines, the first (distal) underside 11 of the augment 1 and an outer shell 15 on the lateral side 13 are each provided with a porous structure 5. In the illustrated embodiment, the porous structure is not continuous, but the legs 31, 32 have a solid core 33. Pockets 35 are provided on the corresponding surfaces of the legs 31, 32, in which the porous structure 5 is arranged. The pockets 35 have a depth of approximately 0.8 to 2 mm. Figure 2BSuch pockets are provided and shown on the first (distal) side 11 and laterally on the outer shell 15. In order to prevent undesired breakage of the porous structure 5, particularly at the edges of the augment 1, the edges between adjacent porous structures 5 at the transition from the distal side to the lateral side are provided with solid, i.e. non-porous, edges 50. This provides reinforcement there and prevents breakage of the porous structure 5. The width of these edges 50 is indicated by the two opposing arrows in Figure 1 visualized and is preferably about 1 mm to 2 mm.

[0056] Furthermore, radially outward-pointing spikes 16 can be arranged on the outer shell 15. After implantation of the augment 1, these drill into the surrounding cortex of the tibial head, thus additionally securing the augment 1 in its position.

[0057] The fastening hole 28 can be arranged in one of the disc segments 36. It is dimensioned such that a cancellous bone screw 29 can be inserted through this opening and tightened for additional fastening. For additional stiffening, the fastening hole 28 is provided with a solid perforated casing 27 as an inner lining. Such a cancellous bone screw 29 for additional fastening is Figure 7 shown.

[0058] In order to be able to bring the attachment hole 28 closer to the edge of the disc segment, preferably close to the surrounding frame 39, the web is expediently widened significantly at this point to form a bridge 38, which offers additional space to arrange the attachment hole 28 as close as possible to the frame 39. This can be advantageous, particularly for small sizes (but not limited to this), in order to achieve the greatest possible distance from the anchoring keel 8 and the bone cavity required to accommodate it for the purpose of better hold in the cancellous bone.

[0059] How to continue Figure 1As can be clearly seen, the through-opening 2 is divided into several areas. The largest area is typically occupied by a receiving area 22 at the edge of the through-opening for the shaft piece 82 of the anchoring keel 8, to which an elongated area 23 of the through-opening extends, which is typically designed to receive the wing-like boom 83. At the far end thereof, a circular receiving area 24 is typically provided for the clamping sleeves 84 at the free end of the respective wing-like boom 83. As can be seen particularly by a comparison with Figure 7 As can be seen, the through hole 2 with its areas 22, 23 and 24 is dimensioned to match the anchoring keel 8. This results in a mounting of the anchoring keel 8 with play, which in Figure 7is visualized by the two opposing arrows. It is dimensioned so large that there is sufficient clearance to the anchoring keel 8 with its outriggers 83 and sufficient space for compression of the legs 31, 32 and the frame 39 without the disk segments 36 striking the anchoring keel 8. It is Figure 7 example shown is about 1.5 to 2 mm.

[0060] The skeletal design with the elastic frame 39 and the disc segments 36 makes it easy to provide variants of the augment in larger or smaller sizes. The size and / or number of disc segments can be varied. For example, by omitting one of the disc segments 36 or by combining the disc segments 36, as shown in Figure 5B ), a smaller size of the augment 1 can be formed. Or it can be made by adding a disc segment 36', as shown in Figure 5A), or by enlarging the disc segments 36, as in Figure 8 shown, a larger size can be formed. In this way, synergistic effects arise when augments according to the invention are provided in an augment set of different sizes.

[0061] The porous structure 5 can be provided with a biocompatible coating 55, for example, made of calcium phosphate to further promote bone ingrowth. This applies to the porous structure 5 of all embodiments.

[0062] Several bending hinges 6 arranged on the frame 39 are shown by way of example in Figure 8shown. It is understood that the flexible hinges can be arranged on the other augments 1 shown. The flexible hinges 6 are formed on the outside of the frame 39. They are each formed by a groove 61 running through the outer casing 15 from the first to the second side, so that in the corresponding area only a relatively thin continuous strip remains in relation to the material thickness. This results in a local material weakening. The flexible hinges 6 lead to a reduction in the overall flexural rigidity of the frame 39. The extent can be adjusted by the type and number of flexible hinges 6.

[0063] A detailed view of one of the bending hinges 6 seen from the viewing direction as shown by the arrow marked "IX" is shown in Figure 9A, B). Each piece of the outer casing 15 is shown with a groove 61 in the center of the image. Optional slots 62 can be added, as shown in Figure 9A ), or perforations 63, as in Figure 9B). The slits 62 are preferably in a line in order to achieve a defined bending line; however, this is not mandatory. The perforations are clustered into two groups 63'. Between the slits 62 and the perforations 63, material areas remain whose combined width determines the flexural rigidity of the respective flexural joint 6. The smaller the width remaining, the less flexurally rigid the flexural hinge 6 formed in this way. The round design of the perforations 63 offers the advantage that it enables particularly fine adjustment and, by avoiding sharp corners, achieves a favorable course of the mechanical load lines. A notch effect, which is detrimental to long-term stability, can be reliably avoided in this way.

[0064] The following briefly explains the explantation of the implants from an endoprosthesis, in particular a knee joint endoprosthesis, and the disc-shaped augment 1. Reference is made to Figure 4and the saw slot shown there (see in particular the area marked by the dashed ellipse), into which a saw can be inserted during explantation. For explantation, the fastening screws 98 are first unscrewed and the spacer inserts 96 are also removed. The saw slot is now accessible from the side up to the shaft piece 82 in the middle of the tibial plate 91. The underside of the tibial plate 91 can thus be cut free using a saw (not shown). Finally, the central screw 95 is removed, and the tibial plate 91 can now be removed. In this way, the augment 1 with any cement layer arranged on it becomes accessible, which can then also be removed if necessary. If desired, the augment 1 can be explanted upwards by pressing the legs 31, 32 together.

Claims

1. A disc-shaped augment for filling bone defects, in particular at the end of tubular bones such as the tibia, with a proximal side (12), a distal side (11), an outer sheath (15) on lateral sides and an inner wall for a through-opening (2), running from the proximal side to the distal side, for an anchoring keel (8) of an endoprosthesis (9) arranged on the proximal side, wherein the augment has a generally C-shaped form with two legs (31, 32) flanking the through-opening, characterized in that a connecting piece (30) between the legs (31, 32) is designed in the manner of a joint and interacts elastically with the legs (31, 32) so that a frame (39) is formed and an outwardly directed restoring force is generated upon compression of the legs (31, 32), wherein the legs are designed in a skeleton construction with a plurality of adjacent disc segments (36) separated by slots (34) and arranged on the frame via webs (37).

2. The disc-shaped augment according to claim 1, characterized in that the first side (11) is designed as a porous structure (5), wherein edges (50) are preferably designed to be solid and / or the outer sheath (15) is designed as a porous structure (5) promoting bone ingrowth.

3. The disc-shaped augment according to claim 2, characterized in that the porous structure (5) comprises pores connected to one another in the depth of the material, which preferably have a width of 0.4 to 1.0 mm, and / or the porous structure (5) has porous regions which are framed by a solid edge.

4. The disc-shaped augment according to any one of claims 1 to 3, characterized in that the legs (31, 32) have a solid core (33) on the outside of which pockets (35) are formed, in which the porous structure (5) is arranged.

5. The disc-shaped augment according to any one of claims 1 to 4, characterized in that the legs (31, 32) are formed from a porous structure (5), in particular with their disc segments (36).

6. The disc-shaped augment according to any one of the preceding claims, characterized in that the inner walls on the legs (31, 32) and / or the disc segments (36) are solid.

7. The disc-shaped augment according to any one of the preceding claims, characterized in that the slots (34) are dimensioned so narrowly that they act as a gap seal for bone cement, having preferably a maximum width of 0.7 mm, more preferably a maximum width of 0.4 mm.

8. The disc-shaped augment according to any one of the preceding claims, characterized in that the frame (39) is designed as an outer edge which surrounds at least half of the entirety of the disc segments (36), on the outside of which the outer sheath (15) is arranged.

9. The disc-shaped augment according to any one of the preceding claims, characterized in that at least one fastening hole (28) for receiving a fastening screw (29) is provided in the frame (39) and / or in the disc segments (36), wherein the fastening hole (27) preferably has a solid perforated sheath (27), wherein in particular the fastening hole (28) is arranged in one of the disc segments (36), and further preferably this disc segment (36) is arranged on the frame by means of a bridge (38) which is wider with respect to the webs (37).

10. The disc-shaped augment according to any one of the preceding claims, characterized in that the through-opening (2) is an elongate receiving space for an anchoring keel (8) and / or the through-opening (2) is open on one side and / or the through-opening occupies less than half, preferably less than a third, of the volume of the augment.

11. The disc-shaped augment according to any one of the preceding claims, characterized in that the outer sheath (15) is conically inclined, preferably tapering to the first side (11) at an angle of 5 to 10°, and / or radially outwardly directed spikes (16) are provided on the outer sheath (15), and / or the porous structure (5) is provided with a bone ingrowth-promoting coating (55), in particular comprising calcium phosphate, and / or is provided with a biocidal coating on nonporous regions.

12. The disc-shaped augment according to any one of the preceding claims, characterized in that at least one bending hinge (6) is provided on the frame (39), which hinge is designed to enable additional compression of the legs (31, 32) and to generate an outwardly directed restoring force, wherein preferably the at least one bending hinge (6) is formed by a local material weakening, in particular in the form of a groove (61), a slit (62) and / or perforations (63).

13. The disc-shaped augment according to claim 12, characterized in that if there are several bending hinges (6), these differ in terms of their material weakening, so that they have different restoring forces when compressed.

14. An arrangement of an endoprosthesis, in particular of a knee joint endoprosthesis, and the disc-shaped augment (1) according to any one of the preceding claims, characterized in that an anchoring keel (8) of the endoprosthesis (9) is accommodated in the through-opening (2).

15. The arrangement according to claim 14, characterized in that the disc-shaped augment (1) is similar in outer contour but undersized in relation to the endoprosthesis, in particular the tibial plate (91).

16. The arrangement according to claim 14 or 15, characterized in that the disc-shaped augment (1) is designed to support a left or right half of the endoprosthesis (9) on one half of the side, and / or in that the through-opening (2) for receiving the anchoring keel (8) and its wing-like extensions (83) is dimensioned with a defined free space of preferably 1 to 3 mm.