KNEE JOINT PROSTHESIS SET AND INSTRUMENTS

Description

[0001] The invention relates to a set of knee joint prostheses, specifically the femoral components of the knee joint prostheses. The femoral component of a knee joint prosthesis works together with a tibial component; these two components essentially form the knee joint prosthesis. The set includes knee joint prostheses in various sizes.

[0002] Knee joint replacements for the total replacement of a natural knee joint have long been known. Typically, a knee joint replacement consists of a femoral component and a tibial component, which are implanted by the surgeon at the distal end of the femur and, respectively, at the proximal end of the tibia. The femoral component interacts with the tibial component to replicate the hinge function of the natural knee joint. To this end, the two components typically each have a joint piece and a stem for anchoring. Such knee prostheses are also referred to as total knee prostheses.

[0003] Such a knee joint endoprosthesis is disclosed, for example, in EP 0 410 237 A1. It comprises a femoral component with a shaft for anchoring in the medullary canal of the femur. The shaft tapers towards its proximal end.

[0004] For hip joint endoprostheses, it is known to provide a prosthesis set with prostheses, each comprising a stem in different sizes (WO 98 / 42279 A1). The stem has an oval cross-section in the proximal region and tapers to a circular cross-section towards the distal end. For different sizes, the stem is enlarged / reduced in essentially the same proportions.

[0005] Knee joint prostheses are available in several sizes to accommodate different patient anatomical conditions. While mass-produced modular knee joint prostheses offer components that are comparatively inexpensive and available in a variety of sizes, adaptation to specific anatomical conditions is often unsatisfactory. It may therefore be necessary to embed and fix the prosthesis in the medullary canal of the femur with cement. However, this frequently results in insufficient long-term stability. Loosening of the cement may occur, meaning the stem of the femoral component is no longer securely anchored in the femur. In many cases, particularly in cases of condylar bone loss, the stem is usually crucial for load transfer and essential for guiding the prosthesis. If it becomes loose, it can no longer fulfill any of these functions, resulting in the prosthesis failing.Revision surgery is then necessary. This problem can be addressed by custom-fabrication of the stem to adapt to the specific anatomical conditions. This can be done after a CT scan of the femur to determine the individual shape of the medullary canal and then shape the stem. However, this would require a custom-made design. While this has the advantage of a good fit and thus high long-term stability, it is very complex.

[0006] The invention is based on the object of combining the advantages of the two different approaches.

[0007] The solution according to the invention lies in the features of the independent claim.

[0008] Advantageous further training is the subject of dependent claims.

[0009] In a knee joint endoprosthesis set comprising modular knee joint endoprostheses in various sizes, wherein each knee joint endoprosthesis comprises a tibial component for anchoring to a proximal end of the tibia, a femoral component for anchoring to a distal end of the femur, wherein the femoral component comprises a joint element for articulated interaction with the tibial component and a shaft designed for anchoring in a medullary canal of the femur, wherein the set comprises shafts in various sizes, the invention provides that in the femoral component, a shape of the shafts is selected such that it tapers from a distal end facing the joint element to a proximal, free shaft end and is designed with an oval cross-section at the distal end and with a round cross-section at the proximal, free shaft end,wherein an ovality determined by the oval cross-section increases with increasing size of the shafts with respect to its degree of ovality, wherein the degree of ovality of the ovality is determined by a ratio of its longer to its shorter axis.

[0010] The invention recognizes that a shaft design with variable cross-section as claimed allows for particularly good adaptation of the various sizes to the anatomical conditions of the femur and its medullary canal. The oval shape at the distal end, combined with the transition to a round shape at the free end, results in a rotationally secure and firm fit of the femoral component in the bone. The shaft thus advantageously becomes load-bearing and not only performs a guiding function, as is predominantly the case in the prior art, but also ensures the holding and fastening function. This advantage can be used to create a set, whereby a comparably secure anchorage can be achieved with shafts manufactured in a few predetermined sizes in series, something that was previously predominantly reserved for custom-made products adapted to the specific anatomy of the patient.This results in significantly improved tolerability and long-term stability of the prostheses. The risk of complicated revision surgeries is reduced, especially for obese patients, who experience shows are particularly at risk of implant loosening.

[0011] The invention is credited with recognizing that the degree of ovality is crucial for the sizing of the shafts. This departs from previous approaches, which typically used shaft length as the determining parameter for size. The fact that this allows a particularly good fit to be achieved with a manageable number of sizes is completely surprising.

[0012] Below, some of the terms used are explained: The ML direction is understood to be a direction running from medial to lateral. It runs perpendicular to the sagittal plane of a body. It is therefore a transverse direction. In anatomy, it is also referred to as the transverse axis and thus largely corresponds (though not necessarily exactly) to the axis for the flexion movement of the knee joint.

[0013] An ML dimension is understood to be a dimension in the ML direction, for example an extension of the ovality in the ML direction.

[0014] The AP direction is defined as a direction running from anterior to posterior, i.e., from the front to the back of the body. This direction is perpendicular to the frontal plane of the body. In anatomy, it is also known as the sagittal axis and is perpendicular to the sagittal plane.

[0015] An AP dimension is defined as a measurement in the AP direction, for example, the extension of ovality in the AP direction. All of the aforementioned directional specifications refer to the installed (implanted) state of the endoprosthesis.

[0016] Ovality is determined by its oval cross-section. The size of the ovality depends on the size of the cross-section. The degree of ovality of an ovality is, as stated, determined by the ratio of its longer to its shorter axis, for example, the ratio between its ML dimension and its AP dimension. The larger this ratio, the greater the degree of ovality and the greater the deviation from circularity.

[0017] A round cross-section is understood to mean an essentially circular design.

[0018] An equivalent diameter is defined as the diameter for a circular shape and the average diameter for a non-circular shape. Any undersize, which may occur with stems designed for cemented implantation compared to stems of the same size designed for cementless implantation, is not taken into account when determining the equivalent diameter.

[0019] According to the invention, an ovality design is provided in which the degree of ovality differs between shafts of different sizes, specifically such that the degree of ovality increases with increasing shaft size. This exploits the surprising discovery that it is advantageous to vary the ovality in a defined manner across the different sizes. This is expediently done in such a way that the ovality is not the same shape between the different sizes (and then only differs in size), but that the ovality is deliberately variable in shape. It is a merit of the invention to have recognized that it is the degree of ovality in particular that offers a very excellent correlation to the different shaft sizes. With this design, the invention departs from previous approaches, which predominantly used the shaft length as the decisive parameter for the size.Even the stem thickness alone is not used as a decisive parameter for size. The current state of the art contains no indication of creating a set of stems of different sizes for knee joint prostheses, with each size having a different, distinct degree of ovality. The fact that a particularly good fit can be achieved with a manageable number of sizes is completely surprising.

[0020] Preferably, the oval cross-section has an ovality such that its major axis lies in the ML direction and its minor axis in the AP direction, with the ratio of the long axis to the short axis preferably being in the range between 1.1 and 1.4. With this special configuration of the ovality in the surprisingly narrow range of the axial ratio, as recognized by the invention, an outstandingly good fit can be achieved. This can be further enhanced by making the ovality elliptical.

[0021] The knee joint endoprosthesis has a modular design, with stems of different sizes being provided that can be optionally connected to the joint component.

[0022] Preferably, the stems each have a circumferential surface designed to engage an inner wall of the medullary canal. Additionally or alternatively, the stems can each have such a circumferential surface that corresponds to a conical transition body between an oval, particularly elliptical, cross-section at one end and a circular cross-section at the other end. This allows for a large-area contact area, which leads to favorable load introduction into the bone and pressure distribution across the bone. The load-bearing capacity and long-term stability can thus be improved.

[0023] The stems are designed to have an elastic modulus in the range of 70 to 120 GPa, especially when made of cementless titanium. This puts them within the physiologically favorable range and can ensure good force transmission to the bone while preventing bone degeneration, which could easily occur with an otherwise unsuitable elastic modulus (Wolff's transformation law).

[0024] Furthermore, the stems can advantageously be curved, specifically slightly curved with a curvature that has a radius of curvature of at least 1000 mm. With such a relatively slight curvature, a clear positioning of the stem and thus of the knee joint endoprosthesis as a whole in the bone can be achieved. The invention takes advantage of the fact that the medullary canal of the femur is typically not completely straight, but rather has a slight curve. By also having a curvature in the stem, a preferred position is created. For the surgeon, this means that the stem essentially positions itself. This not only ensures improved application and thus force transmission between the stem and bone, but also precise implantation. Any curvatures are preferably designed so that they are of different sizes in the AP direction and ML direction.It is particularly preferred if the stems are more strongly curved in the AP direction. This can even go so far that the stems have no curvature at all in the ML direction, i.e., are uncurved. In particular, the stems are preferably one-dimensionally curved; thus, there is only one plane of curvature. This results in a relatively simple basic shape that can be manufactured efficiently while still allowing for good, permanent fixation.

[0025] It is advantageous to design the stems as short stems with a length of less than seven times the equivalent diameter of the stem at the distal end. Such a short stem offers the advantage, on the one hand, of having a relatively large cone angle and thus enabling more universal adaptability; on the other hand, it offers the particularly valuable advantage for successful implantation and the patient's health that the short stem penetrates less deeply into the bone, thus reducing the risk of bacteria or other germs becoming deeply embedded in the bone. Therefore, the short stems are expediently designed even shorter, preferably with a length that corresponds to less than five times, but more preferably more than twice, the equivalent diameter at the distal shaft end.This further reduces the penetration depth of the prosthesis, while the minimum length ensures that a sufficiently large area is still available for force transmission and that adequate guidance is guaranteed.

[0026] The free end of the shaft is conveniently rounded in a dome shape. Such a shaft tip, roughly resembling a hemispherical shape, facilitates easier insertion and placement of the shaft into the medullary canal of the femur. Furthermore, such a design is atraumatic and protects the sensitive interior of the bone. It is particularly effective if the free end is rounded all around.

[0027] According to a further particularly advantageous embodiment of the invention, adapters are provided which connect the joint element to one of the shafts, wherein adapters of different lengths are preferably provided. A design of the adapters as plug-in adapters is expedient. In this way, by selecting a suitable adapter, a change in length can be achieved without the need for a different shaft. This allows a more precise adaptation to the respective anatomical conditions of the patient in a simple manner and without requiring additional sizes for the knee joint endoprosthesis set according to the invention. The adapters are advantageously designed to be angle-adjustable, specifically in such a way that they can be locked in their angular position. This allows a defined relative rotation between the shaft and the joint element to be set and secured.This also improves the adaptability of the inventive knee joint endoprosthesis set to the patient's specific anatomical conditions without requiring additional stem models for the set. For this purpose, the adapter is advantageously designed as a double cone or provided with multiple teeth. The latter offers the advantage of positive angle adjustment, while the former offers the advantage of continuous angle adjustment.

[0028] The knee joint endoprosthesis set expediently comprises both stems for fixation with cement and stems for cementless fixation. This allows for flexible response to different requirements. The stems for fixation with cement preferably have a predetermined undersize relative to the corresponding stems for cementless fixation. This makes it possible to exchange cementless stems of virtually the same size for cemented stems, even intraoperatively if necessary. The range of applications of the knee joint endoprosthesis set according to the invention is thus considerably expanded. The stems for fixation with cement can be provided with a smooth outer surface, which may be provided with a few grooves (maximum 5), whereas the stems for cementless fixation preferably have a grooved outer surface.Typically, a ridged surface consists of at least 16, preferably at least 20 ridges arranged axially along the circumference of the stem. The ridges increase the initial fixation security in cementless implantation, and the smooth design of the surface and the few grooves can correspondingly improve the cemented fixation.

[0029] In terms of size, the shafts are preferably staggered regularly according to the ML dimension. Grading in regular steps has proven to be effective. The regularity can be based, for example, on a series, in particular a linear series, a logarithmic series, or a geometric series. A regular gradation based on a module size is particularly preferred. The module size (a) corresponds to a size step between two immediately consecutive sizes; the smallest and largest sizes of the set are also determined based on the module size. This can be done, for example, in such a way that the smallest size corresponds to approximately 10 to 15 times the module size a (e.g., 13 a) and the largest size to approximately 20 to 30 times the module size a (e.g., 23 a).Thus, by specifying only one dimension, namely the module dimension a, a convenient gradation and thus selection of sizes for the shafts in the set can be achieved. It is particularly preferred if the shafts extend approximately in a size ratio of 1:2, and the module dimension a is preferably selected such that between 8 and 14, more preferably between 10 and 12, different sizes result.

[0030] An instrumentation set may be provided for implanting a femoral component of a knee joint endoprosthesis from the knee joint endoprosthesis set. As already described above, the femoral component of the knee joint endoprosthesis comprises a shaft and a joint element. The instrumentation set includes a tool for forming a cavity sized to receive the shaft at the distal end of the medullary canal of a femur, a gauge for producing a receptacle for the joint element at the distal end of the femur, a depth measuring device for determining a positioning of the shaft in the cavity created to receive the shaft, and an insertion instrument for implanting the femoral component at the distal end of the femur. The depth measuring device is designed to indicate a required length of the shaft and / or an adapter for attaching the shaft to the joint element.With this instrumentation, precise positioning of the stem in the bone can be achieved using the depth gauge. It goes without saying that the depth gauge is tailored to the various sizes of the set. This allows the surgeon to precisely position the stem in the cavity. This increases assembly accuracy and effectively counteracts the risk of knee joint prosthesis malfunctions.

[0031] Additionally, an angle measuring device can be provided. It is designed to determine the rotation angle of the stem within the medullary canal. This allows the angular position of a curved stem, which, as described above, assumes a preferred position in the medullary canal, to be detected and determined. This angle must also be adjusted for the stem of the knee joint endoprosthesis during implantation to achieve an optimal fit. Since the preferred direction can be rotated both to the left and to the right, with left and right alternating between medial and lateral depending on the side of the body, a separate indicator for the rotation direction of the stem within the medullary canal is expediently provided. This indicator significantly reduces the risk of confusing left and right, or medial and lateral, since only the indicator needs to be referenced and therefore observed.The indicator can, for example, be designed as a punched mark or another structural element on the angle measuring device. Advantageously, the depth measuring device and the angle measuring device are designed as a single combined element. This reduces the number of parts and simplifies handling.

[0032] Furthermore, a separate alignment gauge can be provided. It is expediently arranged at the transition between the joint element and the shaft, and it is designed to determine a relative rotation between the shaft and the joint element. This allows the angle determined by the angle measuring device for rotation of the shaft in the medullary canal to be monitored as a relative rotation between the shaft and the joint element, preferably by adjusting the relative rotation using the adapter. In this way, the shaft is precisely aligned so that the joint element is correctly oriented once the shaft has settled into its preferred position. This significantly simplifies and increases the reliability of the angularly accurate assembly of the knee joint endoprosthesis.

[0033] Furthermore, a single knee joint endoprosthesis from the knee joint endoprosthesis set according to the invention is described, but not claimed.

[0034] The invention is described below by way of example with reference to advantageous embodiments of the invention and the drawings. They show: Fig. 1 shows a perspective view of a knee joint endoprosthesis in the implanted state at the knee joint; Fig. 2a, b shows schematic frontal and lateral views of the femoral component of a knee joint endoprosthesis according to an embodiment; Fig. 3a, b shows a frontal and lateral view of a shaft of the femoral component according to the embodiment; Fig. 4 shows a cross-sectional view of a proximal shaft end along a line IV-IV in Fig. 3 ; Fig. 5Cross-sectional view of a distal shaft end according to a line VV in Fig. 3 ; Fig. 6a, a stem of the same size for cementless or cemented implantation; Fig. 7, a rasp suitable for the stems according to Fig. 6 ; Fig. 8a, bperspective views of the shafts according to Fig. 6a, b; Fig. 9 an adapter for arrangement between shaft and joint element of the femoral component; Fig. 10a, b, c adapters of different lengths combined with shafts of different lengths; Fig. 11a, b a perspective view of the adapter with detailed representation; Fig. 12a, b perspective views of a combined depth and angle measuring device; Fig. 13 a detailed representation of the depth and angle measuring device; and Fig. 14a-f representations of various steps for implanting the knee joint endoprosthesis according to the embodiment.

[0035] A knee joint endoprosthesis in the implanted state at the knee is in Figure 1This is a partial view showing a portion of the thigh around a knee joint 91. The (upper) proximal end of a tibia 92 and the (lower) distal end 93 of the femur are visible. The natural knee joint has been replaced by a knee joint prosthesis comprising a tibial component 2 and a femoral component 3 that interacts with it in an articulated manner.

[0036] The knee joint prosthesis as a whole, as well as its tibial and femoral components 2 and 3, are modular in design. The structure of femoral component 3 is explained below. Femoral component 3 and its main components are shown in Figure 2 , which is a frontal view in Figure 2a and a view from lateral in Figure 2bThe femoral component 3 inserted at the distal end of the femur 93 comprises, as its main components, a joint element 4, a shaft 5, and an adapter 6. The joint element 4 has outwardly facing condylar elements 42 for articulated interaction with the tibial component 2. The condylar elements 42 are arranged on a box-like main body 41, which at its proximal end comprises a coupling piece 43 for connection to the shaft 5.

[0037] The shaft 5 is connected to the joint element 4 via an adapter 6. In the illustrated embodiment, this is a pin-like adapter 6, which is provided with a double cone. It is inserted with its distal end into the coupling piece 43 and with its proximal end into a corresponding receptacle 56 (see Figure 9) is inserted on the shaft 5. The generally conical-shaped shaft 5 is inserted into a medullary canal (medullary canal) of the femur 93, which is widened accordingly to accommodate the shaft 5. The shaft 5 can be held in the medullary canal 93 by a press fit in the case of cementless implantation or secured with cement (not shown). The implantation and fixation of a femoral component of a knee joint endoprosthesis as such are basically known and therefore need not be explained in more detail.

[0038] The shaft 5 is modular in different sizes. Examples of different sizes of the shaft 5, 5' and 5" are shown in Figure 10a, b, c The shaft 5 according to the invention is shaped in a special way. Figure 3a A frontal view of the shaft 5 is shown. It shows a straight conical shape with a thicker distal end 51 and a thinner proximal end 52.

[0039] The proximal end 52 is rounded to facilitate insertion of the shaft 5 into the medullary canal of the femur 93 and to reduce traumatic effects. A representation of the proximal end 52 is shown in Figure 4 Accordingly, the cross-section 54 at the proximal end 52 is circular. A representation of the distal end 51 is shown as a cross-sectional view in Figure 5 shown. Accordingly, the cross-section 55 at the distal end 51 is oval, specifically elliptical. The shorter axis 55a is located in the AP direction, and the longer axis 55b is located in the ML direction. A lateral surface 53 of the shaft 5 is thus not conical, but forms a transition surface between an elliptical and round cross-section.

[0040] In a lateral view, the shaft 5 is also tapered, but in this plane it is not straight but rather has a slight curvature, as visualized by the center line 50 shown in dashed lines in Figure 4b. The radius of curvature R is relatively large, resulting in a slight curvature. In the illustrated embodiment, the radius of curvature R is 1500 mm.

[0041] Various alternatives for the design of the shaft 5 are in Figure 6 They relate in particular to a version of the stem 5 for cementless implantation (see Figure 6a ) and a version of the stem 5* for cemented implantation (see Figure 6b ). The two shafts 5, 5* differ in the design of their lateral surface 53 and in their width.

[0042] Reference is now made to Figure 7, which represents a rasp 13 (or a compressor). This is a tool for creating a cavity to receive the stem 5 in the femur 93. During the creation of the cavity, the medullary canal of the femur 93 is widened to the extent that it is dimensioned to receive the stem 5. This refers to both the dimensions in terms of width and depth as well as the curvature (i.e. the rasp 13 is curved in the same way as the stem 5). This is done with great precision in order to achieve a precise fit of the stem 5. For the stem 5 intended for cementless implantation, this means that the cavity is only widened to the extent that a press fit for the stem is achieved. In concrete terms, this means that the tool used to widen the cavity, such as the one shown in Figure 7 shown rasp 13, has a slightly smaller width than the corresponding shaft 5, namely by a press fit dimension 57 (in Figure 7visualized by the dashed line on each side of the rasp 13). An example of such a press fit dimension is 0.2 mm on each side. If the stem 5 is inserted into the cavity created with an undersize during implantation, this results in a press fit that ensures secure anchoring even without cement. To increase the security of the fixation, it is expedient for the outer surface 53 to have a knurling. The knurling is provided with a large number of grooves 59, in the illustrated embodiment 24 grooves, as shown in Figure 8a. This results in a tight fit, both in terms of initial fixation and in terms of long-term stable fixation.

[0043] The stem 5* intended for implantation with cement differs in the design of its surface and its width. The surface is not provided with a ribbing, but with a few grooves 59*. As shown in Figure 8b, three grooves are preferably provided, distributed equidistantly around the circumference of the surface 53 with an angular separation of 120°. In terms of width, the stem 5* intended for implantation with cement is reduced by an undersize 58, at least in the area of ​​the surface 53. The undersize 58 represents the thickness of a cement mantle with which the stem 5* is to be anchored in the medullary canal of the femur 93. As an example, Figure 6ba cement mantle thickness of 1 mm is shown, corresponding to a distance between the dashed and dash-dotted lines. Furthermore, the stem 5* is not intended for press-fit attachment, so its width is further reduced by the press-fit dimension 57. This reduction offers the advantage that one and the same rasp 13 can be used to create the required cavity, regardless of whether a stem for cemented implantation 5* or a stem for cementless implantation 5 is ultimately used. Thus, a uniform rasp can be used for each stem size in the set, regardless of the attachment method.

[0044] The shaft 5 is arranged on the joint element 4 by means of the adapter 6. The adapter 6 is designed as a double cone with a proximal cone 61 and a distal cone 62, which are integrally connected via a cut-out area 60. The cone 61 is to be inserted into a corresponding receptacle 56 at the distal end of the shaft for a conical connection, and the distal cone 62 is to be inserted into a corresponding receptacle of a conical connection on the coupling piece 43 of the joint element. The adapter enables a largely free angular adjustability between the shaft 5 and the joint element 4, and this angular position is locked by plugging the conical connections together using the adapter 6. Furthermore, a locking screw 65 is optionally provided, which secures the adapter 6 on the shaft side. A locking device on the joint side can be provided accordingly (not shown).A representation of the angle variability between shaft 5 and joint element 4 using adapter 6 is shown in . Figure 11a As symbolized by the double arrow, the angular position of the shaft 5 can be freely changed. In a detailed illustration in Figure 11b the transition between the shaft 5 in front of the adapter 6 can be seen, whereby an angle marking 85 is attached to the shaft 5 to visualize an angular position.

[0045] The shafts 5 are available in different sizes and lengths. There are standard length shafts, as in Figure 10b shown, short shafts 5', as in Figure 10a shown, and long shafts 5", as in Figure 10cFor example, the short shafts can be 30 mm shorter and the long shafts 30 mm longer than the normal length shaft 5. The adapters 6 are also conveniently available in different lengths, whereby the length of the adapters varies by a lesser amount than the length of the shafts 5. For example, a short adapter 6' can be 5 or 10 mm shorter than a normal length adapter 6, or a long adapter 6" can be 5 or 10 mm longer than a normal adapter 6. Thus, by using a suitable adapter, a fine adjustment of the length can be achieved, in addition to the angle adjustability and locking function already described.

[0046] In Figure 121 shows a combined depth measuring device 7 and angle measuring device 8. It comprises an approximately trapezoidal base plate 70 with a central opening 74. A shaft of an implantation instrument, in particular a shaft 14 of the rasp 13, or of a drill, can be inserted through this opening 74. This shaft is provided with markings 75 at a defined location. The depth measuring device 7 has a half-shell-like attachment 72 that surrounds half of the opening 74. A depth marking 73 is arranged on an upper side of the attachment 72. An angled contact surface is formed on a rear side 77 of the base plate 70. During implantation, this contact surface is placed onto the shaft 14 of the rasp 13 inserted into the created cavity in the femur 93 and is brought into contact with an end surface at the distal end of the femur 93. The base plate 70 thus assumes a defined position relative to the femur 93.The depth of the rasp 13 in the cavity in the femur 93 can then be read by means of the marking 75 on the shaft 14 of the rasp 13 in relation to the depth marking 73 on the depth measuring device 7.

[0047] The angle measuring device is constructed accordingly. It uses the same base plate 70. An angle scale 80 is provided for this purpose. It is also arranged bordering the opening 74, specifically at its upper end. Furthermore, an indicator 82 is provided, which can be designed as a punched opening. This indicates the direction of rotation, namely either toward the indicator 42 or away from it (as a replacement for perspective-dependent and thus confusing left- or right-turn indications). The angle scale 82 works together with a marking reference 81 on the shaft 14 (see Figure 13). This takes advantage of the fact that the rasp 13 is curved in the same way as the shaft 5. This means that the shaft 5 will align itself in the cavity created by the rasp 13 in the same way as the rasp 13. This means that the rasp 13 can be used as a type of trial implant. However, a standalone problem implant can just as easily be provided. Using the angle scale 80, the angular position of the rasp 13 in the cavity in the femur 93 can now be determined using the marking 81 on the shaft 14 and the indicator 82. With the information thus obtained for depth and angular position, the shaft 5 can be mounted on the joint element 4 in the correct angular position and the prosthesis can be inserted into the cavity created in the femur 93 with the correct depth.

[0048] The individual steps of implantation are described in Figure 14shown. In a first step 14a, access to the medullary canal in femur 93 is opened and initially drilled using an awl or drill bit 11. The medullary canal is widened using the rasp 13, thus creating the cavity to receive the shaft 5. To set a specific depth, a stop plate 12 is expediently provided, which is attached to the shaft 14 of the rasp 13 (see Figure 14b). This, in conjunction with a corresponding thickening 15 on the shaft 14 of the rasp 13, ensures that the cavity is not widened beyond a certain depth. The medullary canal is then gradually widened in the known manner until cortical contact is achieved in the medullary canal. Rasps 13 of various lengths are conveniently available; this allows, if the fit with the smallest rasp is not sufficiently secure, a rasp of the same size (width) but with a longer length to be selected in order to establish secure cortical contact in the medullary canal. Such rasps of the same width (size) but different lengths are available as rasp 13' and rasp 13" in Figure 14c shown.

[0049] Gauges can then be set in a manner known per se, one of which is shown as gauge 16 in Figure 14d. The required cuts are then made at the distal end of the femur in a manner known per se. To finally determine the required adapter length, the depth measuring device 7 is used. It is attached to the shaft 14, and the depth is measured in the manner described above. Depending on the depth, an adapter 6 of the appropriate length can be selected. This allows for fine adjustment of the depth. Furthermore, the angular position of the cavity and thus of the shaft 5 to be attached in the femur 93 can be determined in the manner described. By means of an alignment gauge 88, which is temporarily arranged at the transition between the shaft and the joint element of the femoral component 3 (preferably a separate trial prosthesis is used), a rotation angle between the shaft 5 and the joint element 4 is set (see Figure 14e). This angle is finally used to fit the shaft 5 onto the adapter 6 and secure it using the conical connection. The femoral component 3 with joint element 4 and shaft 5 is thus correctly adjusted in length and (rotation) angle. It can then be implanted into the prepared location at the distal end of the femur 93 using an insertion tool 18 (symbolically shown) (see Figure 14f ).

Claims

1. Knee joint endoprosthesis set comprising modular knee joint endoprostheses in different sizes, each knee joint endoprosthesis comprising a tibial component (2) for anchoring at a proximal end of the tibia, a femoral component (3) for anchoring at a distal end of the femur, the femoral component (3) comprising a joint element for articulated cooperation with the tibial component and comprising a shaft (5) for anchoring in a medullary canal of the femur, the set comprising shafts in different sizes, wherein, in the case of the femoral component (3), a shape of the shafts is chosen such that it tapers from a distal end (51), facing toward the joint element, to a proximal free end (52) of the shaft, and is designed with an oval cross section at the distal end (51) and with a round cross section at the proximal free end (52) of the shaft, wherein an ovality defined by the oval cross section increases, with respect to its degree of ovality, as the size of the shafts increases, wherein the degree of ovality of the ovality is defined by a ratio of its longer axis to its shorter axis.

2. Knee joint endoprosthesis set according to Claim 1, wherein the oval cross section (55) has an ovality of the kind whose major axis (55b) lies in the ML direction and whose minor axis (55a) lies in the AP direction, wherein preferably a ratio of the long axis to the short axis lies in the range of between 1.1 and 1.4, and further preferably the ovality (55) is elliptical.

3. Knee joint endoprosthesis set according to either of the preceding claims, wherein the shafts each have a lateral surface (53) which is designed to bear on an inner wall of the medullary canal.

4. Knee joint endoprosthesis set according to any one of the preceding claims, wherein the shafts each have a lateral surface (53) which corresponds to a conical transition body between an oval, in particular an elliptical, cross section at one end and a circular cross section at the other end.

5. Knee joint endoprosthesis set according to any one of the preceding claims, wherein the shafts (5) are curved, preferably weakly curved with a curvature that has a radius of curvature (R) of at least 1000 mm, further preferably in the range of between 1200 mm and 1800 mm, further preferably of between 1400 mm and 1600 mm.

6. Knee joint endoprosthesis set according to any one of the preceding claims, wherein the curvature of the shafts (5) in the AP direction and ML direction is different, wherein preferably the shafts are more strongly curved in the AP direction, further preferably not curved in the ML direction.

7. Knee joint endoprosthesis set according to any one of the preceding claims, wherein the shafts (5) are designed as short shafts with a length of less than 7 times an equivalent diameter at the distal shaft end, preferably less than 5 times, further preferably more than 2 times.

8. Knee joint endoprosthesis set according to any one of the preceding claims, wherein the free end (52) of the shafts has a rounded dome shape, wherein preferably the free end (52) is rounded all the way around.

9. Knee joint endoprosthesis set according to any one of the preceding claims, wherein adapters (6) are provided which connect the joint element (4) to one of the shafts (5), wherein adapters (6) are preferably provided in different lengths.

10. Knee joint endoprosthesis set according to Claim 9, wherein the adapters (6) can be locked at an adjustable angle with respect to a relative displacement between the shaft (5) and the joint element, preferably being provided with a double cone and / or multiple teeth.

11. Knee joint endoprosthesis set according to any one of the preceding claims, wherein shafts (5*) for fastening by means of cement and shafts (5) for cementless fastening are provided, wherein the shafts for fastening by means of cement each have a predetermined undersize (58) relative to the corresponding shafts for cementless fastening.

12. Knee joint endoprosthesis set according to Claim 11, wherein the shafts (5*) for fastening by means of cement have a smooth lateral surface or are provided with preferably a maximum of five furrows (59*), and / or the shafts for cementless fastening have a corrugated lateral surface.

13. Knee joint endoprosthesis set according to any one of the preceding claims, wherein the sizes of the shafts (5) are preferably graded regularly according to the ML dimension, specifically preferably on the basis of a module dimension corresponding to a size step between directly successive sizes of the knee joint endoprosthesis set.

14. Knee joint endoprosthesis set according to Claim 13, wherein the size of the shafts extends approximately in the range of 1 to 2, and the module dimension is preferably chosen such that there are between 8 and 14, further preferably between 10 and 12, different sizes.