Device and method for inserting a prosthetic knee

[0002] The present invention relates to a device and to a method which allow a surgeon, when implanting a total endoprosthetic knee joint, to execute resection of the femur and of the tibia in an extremely precise manner.

[0003] The exact position of the resection lines on femur and tibia is of crucial importance for a long useful life of a total endoprosthetic knee joint. To date, resection has been extremely demanding, even for an experienced surgeon, since it is necessary, by means of the operation, to create the normal bearing surfaces according to the predetermined geometry of the endoprosthesis, in so doing to align the normal bearing surfaces according to the desired mechanical leg axes, if appropriate also correcting pathological defects of position, and in addition to take into account the position and the effect of the ligaments and muscles which are present. The alignment of tibia and femur is usually carried out by visual examination with the possible use of intramedullary or extramedullary aids, in which case an additional problem is that access to the operating field is often made difficult. These marginal circumstances can cause stressful situations even for surgeons with considerable experience.

[0004] A total endoprosthetic knee joint consists of a component secured to the femur and of a component secured to the tibia. Before the total endoprosthetic knee joint can be implanted, the adjoining bone areas of the femur and of the tibia must be appropriately resected in order to create normal bearing surfaces corresponding to the geometry of the endoprostheses. The frontal surfaces of the tibia and of the femur are usually resected. At least the femur is additionally provided with a so-called dorsal cut and a ventral cut since the femoral part of total endoprostheses is usually unshaped. The instruments generally supplied by manufacturers of prosthetic knees do not allow the necessary bone cuts on femur and tibia to be made with the required precision.

[0005] A further important requirement, however, is to ensure that those components of the prosthetic knee which slide on each other during flexion and extension of the knee are always in the correct position relative to each other, i.e. that the mechanical leg axis can deviate by not more than 3° varus or 3° valgus from the physiological bone axis, the deviation preferably being less than ±2°. In addition, it must also be borne in mind that the flexible connection between the two components is caused by ligaments and muscles, insofar as these are preserved upon implantation of the prosthesis. This requires equilibration of the ligament apparatus, ensuring good stability of the knee joint both in extension and in flexion.

[0006] The known instruments for implantation of total endoprosthetic knee joints generally comprise the following means:

[0007] means for aligning the tibia relative to the femur in order to obtain the desired leg axis position;

[0008] means for producing the desired tensioning of the knee ligaments;

[0009] means for performing resection of tibia and femur, in the form of sawing jigs which serve to guide a saw blade.

[0010] Such an instrument is known from the printed specification EP 0 322 363 A1. This instrument uses an extramedullary means for alignment of tibia and femur (extramedullary alignment system) and has the disadvantage that the alignment of the femur can be determined only with the aid of an X-ray apparatus. In addition, the reference system for the bone cuts is put in place by sight, said reference system additionally making access to the operating field difficult.

[0011] A further instrument is known from the printed specification EP 0 691 110 A2. This instrument uses an intramedullary means for alignment of tibia and femur (intramedullary alignment system) and has the disadvantage that a guide bar is in each case needed for mutual fixation of tibia and femur, said guide bar being introduced into medullary space of the tibia and femur, respectively. This intervention in the medullary space can cause thromboses and embolisms, with a possibly fatal outcome.

[0012] The object of the present invention is to make available a device and a method for localizing resection cuts on the femur and on the tibia for preparing an implantation of a total endoprosthetic knee joint, which method can be performed easily and in a reliably reproducible manner.

[0013] This object is achieved with a device having the features of claim 1, 15 or 23. The dependent claims 2 to 14, 16 to 22, and 24 to 36, relate to further advantageous embodiments of the device according to the invention. The object is also achieved with a method having the features of claim 37.

[0014] In an advantageous embodiment, the device according to the invention comprises a reference device consisting essentially of a base part which can be detachably locked in the distal area of the femur and of a reference body which is connected to the base part in an articulated and/or displaceable manner, which reference body has means defining a system of coordinates X, Y, Z, where the alignment of the reference body can be accurately positioned relative to the femur and where an actuating means acting between the reference body and the base part is provided for fixing the mutual position thereof, and where the means defining the system of coordinates X, Y, Z are designed for aligned attachment of working means such as a sawing jig, a base bar or a measurement device.

[0015] An advantage of this device is that the reference device is connected securely to the femur and is preferably aligned in the direction of extent of the weight-bearing axis of the femur, and that all the cuts on femur and tibia are carried out aligned relative to this reference system so that resection cuts or resection surfaces can be formed on the femur and tibia with very great precision and in a defined alignment.

[0016] The reference device can be secured on the femur by a large number of differently designed means, for example with bone screws, or with gripper arms which at least partially enclose the femur and can additionally have spikes which penetrate into the femur for improved anchoring.

[0017] In another advantageous embodiment, the device according to the invention comprises a reference device which can be secured extramedullarly and detachably in the distal area of the femur and whose alignment can be accurately positioned relative to the femur, and comprising a tibial splint which can be secured extramedullarly and detachably on the tibia, where the alignment of the tibial splint can be accurately positioned relative to the tibia, and comprising a securing device which securely connects the reference device and the tibial splint in a detachable manner.

[0018] This embodiment according to the invention has the advantage that the tibia can be brought into a precisely defined position relative to the femur and can then be fixed in this position. The direction of extent of the resection cuts on the tibia can therefore be predetermined by the cutting device secured on the femur. The position of the tibia can be accurately adjusted relative to the femur, for example in order to correct the line of the mechanical leg axis. In one advantageous embodiment, the securing device is of U-shaped or rectangular design, so that the operating area on the knee is by and large freely accessible even when the securing device is in place.

[0019] In a further advantageous embodiment, the device according to the invention comprises a reference device which can be detachably locked on the distal area of the femur and whose alignment can be accurately positioned relative to the femur, and a cutting device which is movably connected to the reference device, in particular a sawing jig for guiding a saw blade, or a sawing device having a saw blade, where the alignment of the cutting device, in particular of the saw blade, is determined at least by the alignment of the reference device. It is possible to use cutting devices with very different cutting methods, for example saws, ultrasonic cutting devices, or use of lasers. The device according to the invention allows the cutting device to be guided in such a way that the cut extends in the intended direction. An advantageous method for generating the cut has proven to be the use of a saw.

[0020] In a particularly advantageous embodiment, the sawing device comprises a saw blade whose extent defines a saw blade plane, the sawing device being secured with a connection means on the reference device and on the adjustment device, and the connection means and the sawing device being designed in such a way that the saw blade is mounted so as to be displaceable exclusively in the saw blade plane.

[0021] This embodiment has the advantage that the alignment of the saw blade is predetermined so that the operating surgeon can concentrate exclusively on moving the saw blade toward the bone and executing the resection, in the certainty that the alignment of the resection plane is correct. This makes things considerably easier for the operating surgeon during resection since he can concentrate essentially on the cutting, and in so doing can concentrate on any obstacles such as ligaments, and without having to worry about the direction of extent of the saw.

[0022] The device according to the invention can also be driven by a motor. In addition, a computer can be provided which monitors or even controls the movement of the device and the cutting.

[0023] The method according to the invention for performing resection cuts on femur or tibia is carried out in particular by means of a reference device being fixed on the distal area of the femur and then aligned relative to the direction of extent of the femur, and by means of a sawing jig, for guiding a saw blade, or a sawing device with a saw blade, being connected displaceably to the aligned reference device and being guided in an alignment defining the direction of extent of the resection cut, and by means of the resection being performed with the saw blade guided in alignment.

[0024] The invention is described below with reference to illustrative embodiments. In the drawings:

[0025] FIG. 1ashows a perspective view of a base plate secured on the femur;

[0026] FIG. 1bshows a bottom view of a base plate;

[0027] FIG. 2ashows a side view of a reference device;

[0028] FIG. 2bshows a plan view of a reference device;

[0029] FIG. 2cshows a rear view of a reference device;

[0030] FIG. 3 shows a perspective view of a reference device secured on the femur;

[0031] FIG. 4 shows a perspective view of a control jig secured on the reference device;

[0032] FIG. 5 shows a perspective view of an alignment rod connected to the reference device;

[0033] FIG. 6 and FIG. 7 show perspective views of a tibial splint;

[0034] FIG. 8 shows a perspective view of a tibial splint to be checked using the alignment rod;

[0035] FIG. 9 shows a perspective view of a joint held at 90° flexion with a securing frame;

[0036] FIG. 10 shows a movement device secured on the reference device;

[0037] FIG. 11 shows a view of a movement device with a base bar and a measurement bar secured thereon;

[0038] FIG. 12 shows a view of a sawing jig secured on the base bar;

[0039] FIG. 13ashows a perspective view of a total system for inserting a knee prosthesis;

[0040] FIG. 13bshows a plan view of a reference device and a cutting device secured thereon;

[0041] FIG. 13cshows a detail view of a locking device;

[0042] FIG. 14 shows a diagrammatic view of a drive device controlled by a computer;

[0043] FIG. 15 shows a sagittal view of femur and tibia and their axes;

[0044] FIGS. 16a-16dshow a further illustrative embodiment of a base plate to be secured on the femur.

[0045] In the following, the same components are provided with the same reference labels.

[0046] An essential feature of the device according to the invention and of the method according to the invention for insertion of a total endoprosthetic knee joint is the use of a reference system which can be anchored on the femur 1. This reference system is used as a reference for all the maneuvers and method steps for aligning the tibia 2 relative to the femur 1 and for performing resection on the articular surfaces. In an advantageous embodiment, the reference system anchored on the femur 1 can be adjusted in its alignment relative to the femur 1 in order to align the reference system in particular such that it runs in the weight-bearing direction of the femur 1.

[0047] FIG. 1ashows a base plate 3 which has bores 3b, 3c, 3dfor receiving bone screws 4. As can be seen from the bottom view in FIG. 1b, the base plate 3 has three bearing surfaces 3awhich are spaced apart from each other and which come to lie on the femur 1 so that the three-point contact thus formed guarantees a tilt-free bearing on the femur 1. The base plate 3 additionally has an opening 3ffor receiving a bayonet catch and two alignment bores 3e, 3g. The bore 3badditionally has a countersink, as is shown in FIG. 1a.

[0048] As is shown in FIG. 3, the base plate 3 is arranged in the vicinity of the condyles 1aand aligned on the femur 1 in such a way that the axis formed by the bores 3g, 3epreferably extends in the direction of the weight-bearing axis 19bof the femur 1. For this purpose, a drilling gauge is used to fit two Steinmann nails into the femur 1, approximately in the direction of extent of the weight-bearing axis 19b, and the base plate 3 is then placed on the femur 1 in such a way that a Steinmann nail in each case extends through the bores 3g, 3e. A drilling jig is then placed on the bores 3b, 3c, 3dof the base plate 3, after which holes are drilled in the femur 1 and bone screws 4 are then introduced, so that the base plate 3, extending in its longitudinal extent approximately in the direction of the weight-bearing axis 19b, is securely connected to the femur 1 by the bone screws 4.

[0049] In a preferred embodiment, the device according to the invention has a reference device 5 which can be connected securely to the base plate 3, the mutual position of base plate 3 and reference device 5 being adjustable in order to set the course of the resection lines on femur and tibia as exactly as possible. FIGS. 2ato 2cshow such a reference device 5 which has component elements whose alignments define a system of coordinates X, Y, Z, in relation to which system of coordinates all other maneuvers and cuts on femur 1 and tibia 2 are made.

[0050] The reference device 5 comprises a base part 5aon which a closure part 5cof a bayonet catch with pivot axis 5band actuating lever 5dis arranged. The base part 5ais connected to the base plate 3 in such a way that the lever 5dis brought into the position illustrated, after which the closure part 5cis introduced into the opening 3fand the locking part 5gis then introduced into the countersink of the bore 3b. The actuating lever 5dis then moved in the direction 5eso that the bayonet catch formed by the parts 5c, 3fis locked and the base part 5ais connected securely but detachably to the base plate 3.

[0051] A swivel plate 5his arranged on the base part 5aso that it can swivel about the swivel axis 5iin the direction 5k, the swivel plate 5hhaving two bores with internal threads for receiving a hexagon socket screw 51 in each case. These screws 51 are turned into the internal threads to such a depth that they bear on the base part 5a. The relative inclination between the base part 5aand the swivel plate 5hcan be set by the respective screw-in depth of the two opposite hexagon socket screws 51, as can best be seen from FIG. 2c.

[0052] A reference body 5ohaving longitudinal bores 5qcan be connected securely to the swivel plate 5hby means of screws 5r. The longitudinal bore 5q, also referred to as oblong hole, is designed wider than the shank of the screw 5r. With the screws 5rloose, the reference body 5o, on account of the lengthwise extent of the longitudinal bores 5q, can either be displaced in parallel in the direction of movement 5sor can additionally be displaced about the pivot axis 5tin the direction of movement 5u. Thus, the reference body 5ocan be arranged displaceably relative to the swivel plate 5h, and in particularly easily offset, and can be securely connected with the aid of the screws 5r. The reference body 5odefines, via the reference surfaces 5pand the forks 5mconnected securely to the reference body 5o, the alignment of the system of coordinates X, Y, Z which constitutes the reference coordinate system. As can be seen from FIG. 2c, a guide opening 5zis arranged in the reference body 5o, which guide opening 5zconstitutes a longitudinal guide extending in the X direction for a toothed rod 10a. The reference body 5ohas a worm gear 5wwhich is arranged in its interior and which comprises two perpendicular pivot axes 5y, with a knurled screw 5vbeing arranged on one pivot axis 5yand a worm being arranged inside the reference body 5o, and with a gear 5wbeing arranged on the other pivot axis 5yand a toothed wheel 5xprojecting into the longitudinal guide 5z, which toothed wheel 5xis intended to engage in the toothed rod 10a. The toothed wheel 5xcould also be arranged directly on an axis 5yof the knurled screw 5v, so that a worm gear 5wcould be dispensed with.

[0053] FIG. 3 shows a femur 1 onto which the base plate 3 is screwed. The reference device 5 is connected to the base plate 3 and can be released and removed at any time or put back in place by actuation of the actuating lever 5d. The longitudinal guide 5zextending in the X direction can also be seen in FIG. 3. In a further alternative embodiment, the reference device 5 could also be designed in such a way that, in addition to the swivel axis 5i, it can be swiveled relative to the base part 5ain a direction of movement 5fon a second swivel axis 5jextending perpendicular to the swivel axis 5i, in which case the swivel angle can again be set and fixed by means of screws. Dispensing with the swivel axis 5i, the reference device 5 could also have just the one swivel axis 5j.

[0054] FIG. 4 is a symbolic representation of the reference body 5ointo whose longitudinal guide 5zan insertion and holding part 6aof a control jig 6 is admitted. The control jig 6 comprises a holder 6bwith a transparent body 6darranged thereon, with grid lines 6e. The control jig 6 serves to align the swivel plate 5hin the direction of swiveling 5k. For this purpose, in the arrangement according to FIG. 3, the insert part 6ais introduced into the longitudinal guide 5zand, thereafter, the transparent body 6dwith holder 6b, mounted displaceably in the direction of extent of the holding part 6aor in the X direction, is displaced in such a way that the transparent body 6d, as indicated in FIG. 4, comes to lie directly before the femoral condyles 1a. The holder 6bis then fixed on the holding part 6awith the knurled screw 6c. The grid lines 6ein this case extend in the Y and Z directions of the system of coordinates defined by the reference body 5o. By appropriate turning of the screws 51, the transparent body 6dcan be turned about the swivel axis 5i. The position of the transparent body 6dcan also be adjusted by displacing the reference body 5oin the direction 5sor in the direction 5u. Thus, the position of the reference body 5oor the system of coordinates can be adjusted in the Y and Z directions with very great precision relative to the position of the condyles 1a.

[0055] The weight-bearing axis (WBA) 19bof the femur 1 extends in a known manner, as is shown in FIG. 15, through the center of the head of the hip 19cand through the center of the ankle joint 19e. The anatomical axis 19aof the femur 1 is inclined relative to this weight-bearing axis 19b. The line of the tibia 2 defines a mechanical axis 19d. In the position shown, the femur 1 and the tibia 2 show a flexion of 0°, and the weight-bearing axis 19band the mechanical axis 19dare congruent.

[0056] FIG. 5 shows an alignment rod 7 with which it is possible to align the reference body 5orelative to the position of the head of the hip 19c. The alignment rod 7 shall comprise an attachment block 7awhich can be secured by means of a knurled screw 7bto the fork 5m. A telescopic rod 7ewith end indicator 7fis mounted on the attachment block 7avia the hinge 7dwith pivot axis 7gand via the bracket 7cwith pivot axis 7h. The alignment rod 7 is designed and is arranged on the reference device 5 in such a way that the telescopic rod 7eextends substantially or as far as possible in the X direction and can be swiveled in the XY plane. The position of the reference body 5ois adjusted, with the screws 5rloose, by means of palpating, for example with the so-called two-finger method, the center of the head of the hip 19c, and the end indicator 7fof the telescopic rod 7eis then placed on the thigh 1cat this position, as a result of which the reference body 5ois aligned such that the projection of the X axis (in the sagittal direction) passes through the center of the head of the hip 19c. In addition, with the aid of the grid lines 6e, it is also possible to adjust the line of the X axis in such a way that the X axis passes through the center of the condyle 1a. Thus, in a sagittal view as shown in FIG. 15, the X axis is congruent to the weight-bearing axis 19b. The screws 5rare tightened and the position of the reference body 5orelative to the swivel plate 5his thereby fixed. Thus, by aligning the position of the reference body 5o, the reference system or the orthogonal axes in the X, Y and Z directions are defined.

[0057] The reference device 5 according to the invention has the advantage that all adjustments effected have been made to the reference device 5 and have as it were been stored in it. It is therefore possible to detach and remove the thereby adjusted reference device 5 from the base plate 3 via the bayonet catch 5b, in order to carry out further maneuvers on femur 1 or tibia 2. At a later stage the reference device 5 can again be secured on the base plate 3, in which case the axes extend in the X, Y and Z directions as previously defined and therefore do not have to be re-set.

[0058] An advantage of the reference device 5 is that the course of the axes X, Y and Z can be adjusted very accurately relative to the position of the femur 1 and of the condyles 1a. The reference device 5 could also be made simpler, with adjustment of the reference body 5orelative to the base plate 3 being possible only in one dimension or in two dimensions.

[0059] If separability between base plate 3 and reference device 5 is not necessary, then, in a further and simpler embodiment, it is possible for the base plate 3 to be omitted, in which embodiment the base part 5aof the reference device 5 is screwed directly onto the femur 1.

[0060] For aligning the tibia 2, a tibial splint 8 is provided, as illustrated in FIGS. 6 and 7. The tibial splint 8 is preferably secured on the tibia 2 in such a way that the tibial splint 8, in a sagittal view according to FIG. 15, is congruent with the mechanical axis 19dof the tibia 2. A tibial plate 8ahaving two bores 8bis anchored on the tibia 2 with two bone screws 8c. A bearing part 8dis connected to the tibial plate 8avia a lockable ball joint 8xand the connection part 8y. The ball joint 8xis arranged inside the body designated 8x. A tibial rod 8kopens into an end section 8hvia a stop part 8iand a limit stop 8e. In the loosened state, the tibial rod 8kcan be displaced in the direction of displacement 8f, and a screw 8gis connected to the bearing web 8dand, when tightened, fixes the tibial rod 8kto the body 8x, as a result of which the position of the tibial rod 8kis fixed in the direction of displacement 8f. At the end remote from the knee joint, a bearing part 8swith bearing 8tis placed on the lower leg 2aand fixed to the latter, for example with the aid of bandages. A displacement part 8ucan be displaced relative to the bearing part 8sin the direction of displacement 8wand can be fixed by a screw 8v. The tibial rod 8kopens into a displacement rod 8lwhich is mounted so that it can be displaced relative to the lengthwise direction 8nof the tibial rod 8kand can be fixed to the tibial rod 8kwith the aid of a knurled screw 8m. A pin-shaped holder 8o, which is arranged projecting from the displacement part 8u, can be introduced into a guide part 8pof the displacement rod 8l, can be adjusted in the direction of displacement 8r, and can be fixed with a knurled screw 8g. The described displacement possibilities of the tibial rod 8krelative to the tibial plate 8aand the bearing part 8sallow its course to be adjusted in such a way that the tibial rod 8k, in the sagittal direction, is congruent with the anatomical axis 19dof the tibia 2.

[0061] Not later than after the tibial splint 8 has been applied, a tensioning instrument 20, of which an illustrative embodiment is disclosed in the printed specification FR 2 648 699, is inserted between the femur 1 and the tibia 2.

[0062] The tensioning instrument 20 is based on the principle of spreader forceps and serves to press the articular surfaces of the tibia 2 and of the femur 1 individually apart at the lateral and medial condyles in such a way that the desired alignment between femur 1 and tibia 2 is obtained. With the device according to the invention, the requirement that the weight-bearing axis 19bof the femur 1 should extend in the direction of the mechanical axis 19dof the tibia 2 can be easily satisfied by the alignment rod 7 indicating the line of the weight-bearing axis 19bbeing swiveled about the pivot axis 7hto the tibia 2. As the tibial rod 8kindicates the line of the mechanical axis 19dof the tibia 2, the tibia 2 can now be aligned by means of a corresponding adjustment of the tensioning device 20 in such a way that the tibial rod 8kin a sagittal view is congruent with the alignment rod 7. By adjustment to the tensioning device 20, the leg axis can also be set at a slight angle in the varus-valgus direction. It is thus possible intentionally to introduce an angle between the weight-bearing axis 19band the tibial axis 19d.

[0063] If the medial and lateral ligaments do not permit the spreading which is necessary for the desired leg axis position, known surgical interventions must be performed to release the tensioning of the ligaments by means of partial detachment at the points of adhesion to the bone. This must be done until there is suitable ligament tensioning in all flexion positions.

[0064] With the tensioning device 20 in place, the joint is then brought to a position of 90° flexion, as is shown in FIG. 9. In this position, the thigh and the lower leg rest on a suitable support. The femur 1 and the tibia 2 are then fixed relative to each other in this position of 90° flexion with the aid of a U-shaped securing bracket 9. The securing bracket 9 comprises a tibial splint holder 9avia whose knurled screw 9bthe end section 8hof the tibial rod 8kcan be securely clamped. The securing bracket 9 moreover comprises a bracket base part 9gand a bracket adjustment part 9cwhich can be adjusted in the longitudinal direction 9frelative to the bracket base part 9gand can be fixed by a knurled screw 9h. The tibial splint holder 9ais connected to the bracket adjustment part 9cin such a way that it can be slid in sliding direction 9eand it can be fixed by the knurled screw 9d. The bracket base part 9gis connected securely to a bracket transverse part 9iwhich has a recess 9kfor bearing on the reference body 5o. The bracket transverse part 9ican be connected securely to the reference body 5ovia a knurled screw 9l. The multiple adjustment possibilities of the securing bracket 9 allow the end section 8hof the tibial rod 8kto be connected securely to the reference body 5oin the predetermined position. After this step, the femur 1 and the tibia 2 are held securely in an exactly defined position relative to each other. In this position, the weight-bearing axis 19band the tibial axis 19dare preferably flush with each other, and the angle enclosed between them is 90 degrees. In a further advantageous embodiment, the securing bracket 9 could also be of rectangular design, with the tibial splint holder 9aand the bracket transverse part 9ieach being connected at both ends to a bracket base part 9gand to a bracket adjustment part 9c. Such a rectangular securing bracket 9 has increased stability compared with an embodiment according to FIG. 9.

[0065] The tensioning device 20 is then removed and the femur 1 and the tibia 2 are held as shown in FIG. 9. The securing bracket 9 according to the invention has the advantage that the femur 1 and the tibia 2 are held securely in a defined aligned position and that access to the operating field is not obstructed by the U-shaped design of the securing bracket 9.

[0066] FIG. 10 shows the arrangement according to FIG. 9, in this case additionally with a movement device 10 arranged on the reference device 5 and allowing a base bar 10g, and adapter parts 10hsecured thereon, to be moved in the X and Y directions. The movement device 10, also referred to as an adjustment device or an advance device, comprises an advance device 10ewhich is connected securely to a toothed rod 10a. This toothed rod 10ais arranged partially extending in the longitudinal guide 5z, the toothed wheel 5xof the knurled screw 5vengaging in the toothed rod 10ain order to move the toothed rod 10ain the direction of displacement 10bwhich corresponds to the X direction. Like the reference device 5 shown in FIGS. 2ato 2c, the advance device 10ehas a knurled screw 10fwhich drives a worm gear (not shown) which, via a toothed wheel arranged in a longitudinal guide, engages in a toothed rod 10cguided through the longitudinal guide, in order to move this toothed rod in the direction of displacement 10d. In the illustrative embodiment according to FIG. 10, the direction of displacement 10dis identical to the Y direction. The two movement axes or displacement directions 10b, 10dpreferably run at right angles to each other, although they can also be at another angle to each other. Advantageously, one direction of displacement 10bruns parallel to the weight-bearing axis 19b, whereas the second direction of displacement lad runs perpendicular to the weight-bearing axis 19b. Instead of being arranged on the reference device 5, the adjustment device 10 could also be arranged on the securing bracket 9, in which case the securing bracket 9 has a longitudinal guide 5zand a knurled screw 5vfor receiving and moving the toothed rod 10a.

[0067] In order to perform the resection of the femur and of the tibia, a sawing jig 11, as is illustrated in FIG. 12, is secured on the base bar 10gof the adjustment device 10, which sawing jig 11 has slots 11aextending at different angles in order to guide the saw blade 12 with saw teeth 12aexactly at the angles predetermined by the implant. FIG. 12 shows a resection cut made with the saw blade 12 on the tibia front 2b. Depending on the design of an endoprosthetic knee-joint, the resection cuts can be made at different angles. For this reason, different sawing jigs 11 are available, with the sawing jig 11 suitable for each particular case being secured on the base bar 10g. The sawing jig 11 additionally has bores 11bfor guiding a drill for the patellar channel. The sawing jig 11 can be brought into the required position by manually turning the knurled screws 5v, 10f. The sawing jig 11 is moved exactly parallel, so that exactly parallel resection surfaces can be produced on femur 1 and tibia 2. The toothed rods 10a, 10ccould have a scale, for example a scale engraved on the surface, from which scale the distance traveled can be read off. This is advantageous particularly in the case of manual movement or manual actuation of the knurled screws 5v, 10f. The possibility of a manual movement has the advantage that the device can still be used even if a computer or a motor fails, so that the operation can be continued even in such an emergency situation.

[0068] In a preferred embodiment, the knurled screws 5v, 10fare driven by a motor. FIG. 14 shows a diagrammatic representation of a drive device 17 according to the invention which is connected to and is controlled by a computer 16 via a two-direction data line 16c. The drive device 17 comprises an electric motor 17dwith a shaft 17c. Arranged on this shaft 17cthere is an angle disk 17eand a sensor 17ffor detecting the angle of rotation. The electric motor 17dis controlled by the computer 16 and the angle of rotation of the electric motor 17dis monitored by the computer 16 via the sensor signal 17f. The knurled screw 5v, 10fand the shaft 17care connected to each other via a flexible shaft 17awhich has an adapter part 17bat both ends. The flexible shaft 17ais preferably a metal wire. The arrangement according to FIG. 14 has the following advantages:

[0069] Operations on bone entail very strict demands with respect to sterility. For this reason, all objects near the operating field must have sterile properties. It would be considerably complicated to build a sterilizable electric motor which could be arranged directly on the movement device 10. The use of a metal wire, e.g. spring steel wire, has the advantage that the electric motor can be arranged, for example, one to two meters away from the operating field. The use of a spring steel wire string has in particular the advantage of a high modulus of elasticity and a low hysteresis effect. On account of the increased distance from the operating field, there are lesser requirements with respect to the sterility of the drive device 17. The shaft 17aaccording to the invention additionally has the advantage that it is sterilizable and, since it is easy to produce, can be designed as a disposable product. The drive device 17 also has the advantage that the knurled screw 5vcan be driven and its angle of rotation also monitored via the sensor 17f. The drive device 17 can also have a plurality of independent drives for flexible shafts 17a. The shaft 17acan be designed as a solid wire or as a hollow wire. Steel wires are preferably used, but wires of other metals or of plastic or composite material are also suitable. In a further advantageous embodiment, the drive device 17 with electric motor 17d, angle disk 17eand sensor 17fcould be arranged in or in place of the knurled screw 5v, in which case the drive device 17 is connected to a computer 16 via an electric control and data line 16c.

[0070] In a preferred embodiment, the movement device 10 according to FIG. 10 is driven by a drive device 17 according to FIG. 14, in which the knurled screws 15v, 10feach are connected to a shaft 17a. Thus, it is not only possible to move the base bar 10g, with adapter part 10hsecured thereon, in the X and Y directions, but also to measure the geometry of the condyles 1aat selected points as well as the tibial plateau. In the illustrative embodiment according to FIG. 10, a guide 10kfor a measurement probe 10lwith measurement tip 10nis arranged on the adapter part 10h. The guide 10kis mounted on the adapter part 10hso as to be displaceable in the direction 10m.

[0071] The geometry of a femoral condyle 1acan be measured for example in the following manner:

[0072] The base bar 10g, initially without an adapter part 10hsecured thereon, is moved so that the base bar 10gcomes into contact with the femoral condyle 1aon the front of the femur 1. This blocks the rotation of the shaft 17b, which can be detected by the sensor 17f. Thus, the position of the front of the femur 1 can be determined and stored by the computer 16. The base bar 10gis then moved away again and the adapter part 10hwith measurement probe 10lis arranged on the base bar 10g, as is shown in FIG. 10. The base bar 10gis then moved until the probe tip 10nof the measurement probe 10lcomes to bear on the femur 1 as illustrated. This position is stored by the computer 16. Then, as is shown in FIG. 11, the base bar 10gis moved away again and a further measurement probe 10lis assigned to the guide 10kfor the measurement probe and can be secured with a knurled screw 10p. If the measurement probe 10lis arranged in an eccentric position, the dorsal extent 1dof the condyles 1acan be measured by moving the base bar 10g. If the measurement probe 10lis arranged in a central position, the depth of the groove 10bcan be measured by moving the base bar 10g. The condyles can also be measured at several points by means of suitable configuration of the measurement probe. The measurement probe 10laccording to FIG. 11 could also be used to measure the entire width of the condyles 1a, with the probe tip 10nbeing brought into medial and lateral contact with the condyles 1a, in which case a scale is advantageously arranged extending on the adapter part 10hin its longitudinal direction and makes it possible to read off the lateral position of the probe tip, so that the total width of the femoral joint head can be determined on the basis of the measured medial and lateral extents of the condyles 1a. This width can be entered in the computer, for example manually, so that the geometric data of the femoral joint head are available to the computer for further calculations.

[0073] The measurement probes 10lcan be configured in very different ways in order take account of the anatomical shape of the femur and to scan its surface. Thus, a measurement probe 10lcould also be designed in such a way that, arranged on the guide 10ksimilarly to FIG. 11, it allows the dorsal area of the femur 1 to be scanned.

[0074] In a preferred embodiment, the overall system for implanting a total endoprosthetic knee joint comprises a computer with a screen. The coordinates of the position of the measurement points of the femoral condyles determined using the measurement probes 10lare transmitted to the computer via the drive device 17, in which case the division of the angular wheel 17eand also the transmission ratio of the gear of the advance unit 10eare preset in the computer, so that the computer can calculate the distances of the individual measurement points in absolute coordinates and preferably in millimeters. A database with the geometric data of available knee-joint implants is also stored in the computer, and the computer compares these data with the measured data and proposes an optimally fitting knee-joint implant and represents this on the screen. In a preferred embodiment, as shown in FIG. 13a, the measured femur, the resection lines and the knee-joint implant to be fitted on the femur are illustrated on the screen. The surgeon checks the illustrated proposal and either confirms this proposal, moves the resection lines in their entirety, or chooses another knee-joint implant which appears to him to be more suitable. After the appropriate knee-joint implant has been chosen, the computer accesses a database in which all the geometric data of the implant are stored, in particular including the arrangement and course of the normal bearing surfaces of the implant and the corresponding resection lines. Based on these data, the computer determines which of a plurality of available sawing jigs 11 is to be secured on the base bar 11gin order to effect the previously determined cuts. It would be possible to provide just a single sawing jig 11 defining the angles of the respective resection lines. By providing different sawing jigs 11 whose cutting lines are adapted to corresponding implants, the resection lines on the femur can be cut according to the design and size of a particular implant. After the sawing jig 11 has been secured in place, the movement device 10 is driven by the computer in such a way that the sawing jig 11 is moved into the first cutting position. Then, as is shown in FIG. 12, the surgeon can insert the saw blade 12 into the respective slot 11aof the jig 11 and effect the cut. After the cut has been made, this can be communicated to the computer 16, for example by actuation of the foot switch 18, whereupon the computer 16 moves the device 10 and the sawing jig 11 to the next cutting position, so that the surgeon can effect the next cut. Since the computer 16 or sawing jig 11 defines precisely both the position of the cut and also its alignment, the resection cuts can be made very precisely according to the geometry of the implant which is to be fitted. This procedure greatly facilitates the work of the surgeon since he no longer has to worry about the position of the cut when cutting and can therefore devote all his concentration on the cut itself, in particular ensuring that no ligaments or other soft tissue parts are damaged during cutting. The device according to the invention also allows a less experienced surgeon to accurately cut the femur 1 and the tibia 2 without any problems and to fit the implant.

[0075] FIGS. 13a, 13b, 13cdisclose a complete system for implanting a knee prosthesis, which system no longer requires a sawing jig 11 since the position of the sawing device 14 and thus the position of the saw blade 12 are controlled and determined directly by the movement device 10.

[0076] As is shown in a side view in FIG. 13c, a pivot adjustment device 13qdesigned as a locking device 13ais arranged on the base bar 10gof the movement device 10. This locking device 13ahas locking positions 13ndistributed about its circumference, each locking position 13ndefining a preset swivel angle of the arm 13cin the direction of swiveling 13m. A knurled screw 13ballows the screw shank 13oto be raised and lowered. The pivot adjustment device 13qcould also have, instead of the locking device 13a, a drive motor making it possible to set a predeterminable pivot angle. Such a motor-driven pivot adjustment device 13qpreferably also comprises a pivot angle sensor which detects the pivot angle so that the angle, to be assumed, of the pivot adjustment device 13qcan be preset, for example, with the aid of a control device or a computer. As is shown in FIG. 13b, the arm 13cis connected to a second arm 13fvia a hinge moving in the direction of movement 13d, which second arm 13fis in turn connected to the third arm 13hvia a hinge moving in the direction of movement 13g. The third arm 13hforms on the one hand an axial attachment 13ifor the sawing device 14 and on the other hand a guide 13kwith slot 13lfor the saw blade 12. The holding arm 13 thereby formed allows the saw blade 12 to be guided or swiveled in one plane, preferably in the saw blade plane. The saw blade 12 forms a saw blade plane and is mounted so as to be displaceable in this plane. The arm 13 can be designed such that it has a spring force, so that when the saw blade 12 is brought toward the condyle 1a, an increasing restoring force acts on the sawing device 14. In order to generate such a spring force, torsion springs for example could be arranged in the hinges of the arm 13. In the illustrative embodiment shown, the guide 13kis connected securely to the arm 13h. However, the guide 13kcould also be articulated on the arm 13hvia a hinge, so that the guide 13kcould be swiveled toward the attachment 13i. By means of this measure, the saw blade 12 can penetrate deeper into the body which is to be cut.

[0077] The sawing device 14 has a hand grip 14awhich, in order to reduce excessive torques caused by the maneuvering, can be swiveled in the direction 14gabout the axis 14hrelative to the holding arm 13. The hand grip 14acould also be mounted so as to swivel about a pivot axis 13p. The hand grip 14athus serves to initiate movement in the direction 14cand in the direction of swiveling 14dabout the axis 13p. As a result, the position of the hand grip 14ain the vertical direction of swiveling is independent of the position of the saw blade 12. As is shown in FIG. 13c, the holding arm 13 can be inclined relative to the base bar 10gby turning the arm 13cabout the pivot axis 13eof the locking device. Otherwise the position of the saw blade 12 is determined by the movement device 10 controlled by the computer 16. Since the saw blade 12 is designed relatively long in the direction of extent 14c, the guide 13kis preferably provided with a slot 13lin order to guide the relatively thin saw blade 12 in a defined position and in order to avoid bending of the saw blade 12. Since the holding arm 13 together with the sawing device 14 could exert relatively great forces on the movement device 10 or base plate 3, a frame 15 is provided in the illustrative embodiment shown in FIG. 13a, which frame 15 comprises a cable winder device 14fand a cable 14ewhich has the task of generating a counterforce F compensating at least for the force of gravity of the sawing device 14. The frame 15 comprises a boom 15a, a vertical bar 15b, an underframe 15cand wheels 15d. The device 14bfor controlling the sawing device 14 is also arranged on the frame 15. The computer 16 with screen 16aand keyboard 16bis also secured on the frame 15. The drive device 17 is additionally secured on the frame 15, the two knurled screws 5v, 10fbeing driven via the flexible shaft 17afrom the drive device 17.

[0078] The holding arm 13 shown could also be designed with sensors making it possible to detect the angles in the movement directions 13d, 13gand 13min order to determine the exact position of the saw blade 12 or in order to measure the position and geometry of the condyle 1awith a probe head arranged in place of the saw blade 12.

[0079] FIGS. 16ato 16ddisclose a further illustrative embodiment of a base plate 3 or base device 3 which can be anchored on the femur 1. This base device 3 comprises a base platform 3h, with longitudinal axis 3s, on which four legs 3i, 3kare arranged so as to be displaceable in direction 3l. The legs 3i, 3kcan be displaced on grooves 3oextending in direction 3l. A shaft 3nwith external thread engages in an internal thread of the legs 3i, 3k. The shaft 3nhas a screw head 3pwhich is accessible from the side. The thread in the leg 3iis designed as a lefthand thread, and the thread in the leg 3kis designed as a righthand thread, with the thread of the shaft 3nbeing adapted accordingly for engagement. Thus, while the screw head 3pis being turned, two legs 3i, 3karranged alongside each other in each case move either toward each other or away from each other. The shaft 3nhas, at the center, a cylindrical part section 3mwhich is greater than the diameter of the shaft 3nand which is arranged in an interspace 3rof the base platform 3h, and which, in displacement direction 3l, bears on the base platform 3hwith slight play on each side and thus fixes the position of the shaft 3nrelative to the base platform 3hin direction 3land therefore serves as centering element 3m. FIG. 16bis a side view showing two opposite legs 3i, 3kwhich, on the opposing inner surfaces, have tips 3qwhich project in displacement direction 3land are intended to penetrate into the femur 1. As is shown in FIG. 16d, the base device 3 is secured on the femur 1 by means of this device initially being placed on the femur 1 in the line of extent of the femoral axis 19a, and the opposite legs 3i, 3kthen being moved toward each other by turning the shaft 3nuntil the tips 3qpenetrate into the femur 1 and the base device 3 is firmly connected to the femur 1. In an advantageous embodiment, the shaft 3nhas a screw head 3pat both ends, so that the shaft 3ncan be optionally actuated from either of the two legs 3i, 3k. An advantage of the illustrated embodiment of a base device 3 is that after it has been secured on the femur 1 it extends in the direction of the femoral axis 19aand in the direction of the intramedullary cavity of the femur 1. Thus, the base device 3 has an intramedullary line of direction, but without using an intramedullary body.

[0080] The two recesses 3b, 3fare designed in the same way as in the base plate 3 according to FIG. 1aand serve to secure the reference body 5 by means of a bayonet catch. FIG. 16cis a plan view showing the arrangement of the recesses 3b, 3fon the base platform 3h. The two lower recesses 3b, 3fdefine a straight line 19bwhich intersects, at an angle α, the straight line 19a, 3srunning through the center of the base platform 3h. This angle α is preferably in the range of 6±2 degrees. With the base device 3 secured on the femur 1, the straight line 19acorresponds to the line of the anatomical axis 19aof the femur 1. Statistical studies have shown that the weight-bearing axis 19bdeviates by approximately 6 degrees from the line of the anatomical axis 19a, so that the axis 19bshown in FIG. 16ccorresponds approximately to the line of the weight-bearing axis 19bwhen the base device 3 is fixed on the femur 1. The base device 3 has two pairs of recesses 3b, 3f, the pair arranged above the straight line 19a, 3s, as shown in FIG. 16d, being used on the femur 1 of a right leg, and the lower pair being used on the femur 1 of a left leg, in order to approximately define the line of the weight-bearing axis 19bwhen the anatomical axis 19aof the femur 1 has been determined.