The invention is directed to a template for treat¬ ment tools for the treatment of osseous structures and a method for the definition and reproduction of the positional relationship of a treatment tool rel¬ ative to an osseous structure.

Using image producing methods such as computertomo- graphy and computer-based image-processing systems, it is possible to record osseous structures of the living organism in slices by a non-invasive tech¬ nique, to reconstruct them three-dimensionally and to visualize them through an output medium. Further, such systems frequently permit already a three-di¬ mensional planning of surgical interventions with regard to incisions, drilling, puncture, positioning of individual implants or other surgical interven¬ tions. Intraoperatively, i.e. during the actual sur-

gical procedure, there often occur orientation prob¬ lems because no adequate technical means exist for a consequent, exact three-dimensional transfer of the steps of the intervention which have been planned with a waste of technical support. Therefore, the accuracy of execution depends exclusively on the experience, the three-dimensional perceptivity and the technical skill of the surgeon, which, depending on the type and the anatomical site of the interven¬ tion can involve extreme risks even with experienced surgeons. Generally, only freehand-guided instru¬ ments, two-dimensional tomographic images and pre- or intraoperative X-ray images are available.

For some interventions, standard tool guides have been provided. These are mostly cutting, boring or sinking templates for preparing and/or fixing the seat of a knee or hip joint prosthesis (as e.g. US 4,567,885, US 4,703,751, US 4,822,362, US 4,721,104, DE-33 39 259, EP 380 451, EP 415 837, EP 231 885, EP 228 339, DE 39 25 488, DE 79 14 280) or for reposi¬ tioning osteotomies in the region of the proximal head of the femur or tibia (e.g. US 4,565,191, DE 38 42 645, DE 32 11 153). The intraoperative posi¬ tioning of these templates relative to the bone is performed free-handed and even in case of special solutions allowing limited adaptation to the anatom¬ ical conditions, as e.g. in US 4,846,161, DE 34 47 163 or DE 40 16 704, can generally not be car¬ ried out exactly and clearly according to the plan¬ ning of the intervention. In some approaches, intra¬ operative measurement and positioning under X-ray control are provided. This causes an increased expo-

sure to radiation for the patient and the medical staff, prolongs the duration of the surgical inter¬ vention and again is just an indirect and not clear¬ ly defined transfer of the treatment strategy de¬ fined in the surgical planning.

There also exist devices for stereotactical inter¬ ventions. Principally, these devices can be divided into two categories. The first category comprises devices which, designed as rigid frames, are attach¬ ed directly (e.g. by screws) on/in the bone and are adapted for rigid mechanical coupling a posi¬ tioning or coordinate measuring syste; , with the reference points of said devices being τ&. roduced in a tomographic image (e.g. stereotaxic apparatuses as described in Riechert et al.: Beschrexbung und An- wendung eines Zielgerates fur stereotaktische Hirn- operationen, Acta neurochir., Vienna, Austria, Suppl. Ill (1955), 308; and in DE 37 17 871, DE 39 02 249 and EP 312 568). The second category com¬ prises methods wherein individual reference bodies (marking elements, at least three of them) are fixed in or on the bone or the overlying skin surface al¬ ready prior to tomographic scanning of the respec¬ tive part of the body and subsequently are imaged in the tomographic pictures. These reference bodies und markers are then detected, as to their position and orientation, through a mechanically rigid construc¬ tion or 3D coordinate measurement and evaluation for detection of the transformation relation between the coordinate systems of the bone structure, the tomo¬ graphic images and the environment (Adams et al.: A navigation support for surgery. In: Hohne et al.:

3D-Imaging in Medicine. Nato ASI Series F.; Computer and System Science Vol. 60, Springer, 1990; Kosugi et al.: An articulated neurosurgical navigation sys¬ tem using MRI and CT images. IEEE Transactions on Biomedical Engineering, Vol. 35, No. 2, Feb.1988).

Since the relative position of the reference bodies or points relative to the osseous structures is known or can be obtained from the tomographic imag¬ es, it is possible to use a 3D coordinate measuring or adjusting device, coupled to these reference bod¬ ies (or points) fixedly or through defined transfor¬ mation relationships, for the positioning of coordi¬ nate measurement pins or guide devices for punctur¬ ing cannulae and drills.

Generally, these methods suffer from the following disadvantages:

- The reference bodies (markings, frames, other devices) can be fixed on the skin surface only in special cases (in the skull region or in the region of palpable sites on osseous structures), and even there only with restricted accuracy.

- A fixing directly on or in the osseous tissue requires that the patient has to undergo an ad¬ ditional surgical intervention.

The reference bodies (and possibly the whole rigid device) must remain fixed to the patient in an unchanged position from the time of image pick-up to the surgical intervention. In case of

a non-rigid or non-physical connection, time- consuming (and again failure-prone) intraopera¬ tive measuring and aligning work has to be per¬ formed.

Generally, application is restricted to inter¬ ventions in the region of easily accessible os¬ seous structures and thus is normally unsuited for orthopedic surgery.

In the skull region, the systems described by Adams et al. and Kosugi et al. are suitable only with lim¬ ited accuracy as freehand-guided intraoperative 3D position measuring devices for navigational purpos¬ es. These systems rely or. artificial reference mark¬ ers on the skin surface. (Natural landmarks normally cannot be unambiguously identified as reference points, neither in the tomographic image nor in the site of the operation) No possibilities exist for the planning and storing of orthopedic interventions and, further, only freehand-guided measurement probes are available). Thus, these systems cannot be employed as suitable devices in orthopedic bone sur¬ gery.

To sum up, it is to be noted that, presently, only relatively primitive intraoperative devices are available for a consequent transfer of an individually planned orthopedic-surgical interven¬ tion in osseous structures. Consequently, an indi¬ vidually adapted hip-joint endoprosthesis, to be implanted without cement, is rendered absurd by a freehand-guided cutting in the intraoperative prepa-

ration of the seat of the prosthesis. The technology of bone treatment has been lagging behind the tech¬ nology of implant manufacture. This has resulted in imprecise preparations of the seat of prostheses with point-shaped force transmission and movement between bone and prosthesis. The same applies to individually planned repositioning osteotomies (being nonetheless relatively uncritical in the region of tibia and femur) . For some considerably more complicated and critical interventions, e.g. in the region of the spinal column and the pelvis), there are no orientation and positioning devices available at all.

Further, efforts are being made to make use of robot technology for thus obtaining improved devices for faster, more accurate and less burdensome interven¬ tions also in the region of osseous structures.

Most of the known methods work after the above out¬ lined reference body principle with preoperative image acquisition and are principally impaired by the above mentioned disadvantages. The endeffector is moved and positioned by a robot or manipulator (cf. e.g. Kwoh et al.: A robot with improved abso¬ lute positioning accuracy for CT-guided stereotactic brain surgery. IEEE Transactions on Biomedical Engi¬ neering, Vol. 35, No. 2, Feb. 1988; Taylor et al.: Robot total hip replacement surgery in dogs. IEEE Engineering in Medicine & Biology Society 11th annu¬ al international conference 1989, pp. 887-889; Rein- hardt et al. : Robotik fur Hirnoperationen, Polyscope plus No. 6, pp. 1, 5-6).

Some methods are executed with intraoperative image acquisition (particularly biplanar X-ray projection images) and suitable targeting and calibrating de¬ vices which appear in the image. By use of the known relationship between the targeting device and the robot (the targeting device being fixed e.g. in the robot gripper) and the relationship - defined by intraoperative X-ray images - between the targeting device and the X-rayed part of the body (the "ob¬ ject", as e.g. an osseous structure), it becomes possible to transform positioning processes or move¬ ments, having been defined in the coordinate system fixed to the object, into movements or positional vectors in the basic coordinate system of the robot (cf. e.g. Lavallee: A new system for computer as¬ sisted neurosurgery. IEEE Engineering in Medicine & Biology Society 11th annual international conference 1989, pp. 887-889; Jakobi et al. : Diagnosegesteuerte Therapierobotertechnik - medizinische und biomedi- zinische Aspekte, Z. Klin. Med. 45 Vol. 6, 1990, pp. 515-519) .

In the region of soft tissues, the principal system- atics of a fixedly defined spatial relationship be¬ tween the image acquisition device and the position¬ ing device for the endeffector has already become established in two cases (extracorporal shock wave lithotripsy, i.e. ultrasonic tomographic imaging or bipolar X-ray imaging with selection of the intra- corporal target point in the image and semiautomatic positioning of the shock wave focus; mammabiopsy, i.e. bipolar X-ray imaging with identification of the target point in the image and semiautomatic po-

sitioning of the biopsy cannula). No comparable techniques are known in the field of orthopedic sur¬ gery of osseous structures.

In a further approach, it is tried to accomplish the identification and positional detection of osseous structures in orthopedic interventions by optical pattern detection and then, using a robot, to dis¬ play cutting paths by a laser beam, to position tool guiding devices, to perform work on the bone direct¬ ly etc. (Prasch: Computergestϋtzte Planung von chir- urgischen Eingriffen in der Orthopadie, Springer Verlag 1990). To this purpose, contours of the re¬ spective osseous structure which have been detected with the aid of a computer in biplanar intraopera¬ tive X-ray projection images, are compared to and, as far as possible, made congruent with 3D-CAD mod¬ els of this structure which have been reconstructed from tomographic images and stored in the computer. If the orientation of the basic coordinate system of the robot and that of the X-ray device relative to each other are known, the robot can be moved accord¬ ing to its programming made corresponding to the 3D model in the CAD system. In the above mentioned pub¬ lication, repositioning osteotomy is mentioned as an exemplary application. This system has not been re¬ alized yet.

In conclusion, it is to be stated that none of the above mentioned robot systems is suited for routine use in the field of orthopedic surgery of osseous structures. Systems which demand intraoperative X- ray images are disadvantageous for the above rea-

sons. Due to the inherent technical (including also safety measures), organizational and economic neces¬ sities, the use of robots has to be limited to sur¬ gical interventions which require spatially complex treatment movements which can be carried out only via narrow access openings, or to interventions which for some other medical or surgical reasons cannot or not efficiently be performed without the aid of manipulators and robots. (The much-quoted repositioning osteotomy in the femur or tibia region does not count among these).

It is an object of the invention to allow a treat¬ ment of osseous structures for any desired orthope¬ dic interventions (i.e. also complex and possible novel interventions) which is safe, fast, exact and is defined according to the surgical planning. The term "treatment" is understood to comprise not only the treatment of an osseous structure by suitable tools (cutting, boring, milling device) but also other forms of treatment such as e.g. invasive mea¬ suring and scanning of osseous structures by corre¬ sponding measuring devices.

For solving the above object, there are proposed, in accordance with the invention, a method according to claim 1 and a template according to claim 3 which is preferably produced according to claim 5.

By the invention, intraoperative measuring and posi¬ tioning periods shall be minimized by shifting them into the preoperative planning phase and working steps requiring X-ray imaging shall generally be

rendered unnecessary. For complex surgical interven¬ tions, quick and easy intraoperative access to a ma¬ nipulator or robot as a tool for assistance in the surgical intervention shall be made possible.

According to the invention, the central functional element is a so-called individual template by which parts of the surface of an arbitrary osseous struc¬ ture which is to be treated and is intraoperatively accessible to the surgeon, are copied as a negative image without undercut and in a mechanically rigid manner, so that the individual template can be set onto the osseous structure in a clearly defined po¬ sition and with mating-engagement.

According to the inventive method, there is used a split-field device (e.g. a computer or a nuclear spin tomograph) by which split images are produced of the layers extending through the body of the liv¬ ing organism and containing the osseous structure, and from these split images, data regarding the three-dimensional shape of the osseous structure and the surface thereof are obtained. In the preopera¬ tive planning phase, these data are used as a basis for defining, within the coordinate system fixedly positioned relative to the osseous structure, a rig¬ id individual template which, completely or by seg¬ ments (but at least by three intraoperatively clear¬ ly identifiable abutting points) , copies the surface of the osseous structure in such a manner that the individual template can be intraoperatively set onto these - then freely exposed - contact faces or points in exclusively one clearly defined position

in form-closed manner. Thus, when mounting the indi¬ vidual template, an individual abutting behavior is observed in all six spatial degrees of freedom. Therefore, quick and reliable identification and detection of position is possible intraoperatively. In the invention, the inter- and intra-individual variants of the shape of osseous structures, which pose a problem in other systems, guarantee a safe and clear intraoperative identification and detec¬ tion of position.

Further, the invention is characterized in that the cutting, boring, milling and other treatment steps which in the preoperative surgical planning phase are three-dimensionally charted in said coordinate system fixed relative to the osseous structure, can be clearly defined in or on the individual template in form of guide means or reference or flange en¬ gagement points for standardized tool guides, which can be performed directly in or on the template body relative to the bone. Intraoperatively, this situa¬ tion, which in surgical planning is precisely de¬ fined in three dimensions and simulated, is realized by simply setting the individual template onto the exposed surface of the bone. Time-consuming measur¬ ing and aligning work is thus shifted into the pre¬ operative phase. Working steps which involve intra¬ operative X-ray control can be omitted.

Using the template of the invention allows a treat¬ ment of osseous structures for any orthopedic inter¬ vention (i.e. also complex and possible novel inter¬ ventions) which is carried out in a safe, fast and

precise manner and is defined according to the sur¬ gical planning while it is not necessary anymore to intraoperatively check the orientation of the treat¬ ment tool. Intraoperative measuring and positioning periods are minimized by being shifted into the pre¬ operative planning phase and working steps requiring X-ray imaging have become unnecessary. For complex surgical interventions, a possibility is created for quick and easy intraoperative access to a manipula¬ tor or robot employed as an auxiliary tool in the surgical intervention.

The invention comprises the following features and characteristics:

1. By 3D reconstruction of a tomographically imaged object, particularly of the osseous structures of a living human, and by visualizing this re¬ construction on an output medium, particularly a computer monitor, and particularly by using a computer system or a computer-based display and construction system, there is generated a three- dimensional negative mold of parts of the indi¬ vidual natural (i.e. not pre-treated) surface of the osseous structure intraoperatively accessed by the surgeon.

2. The above negative mold can reproduce a cohesive region or a plurality of geometrically non-abut¬ ting partial segments of a bone surface and is constructed in a cohesive, mechanically rigid basic body (the individual template) . The over¬ all geometry of the basic body is also adapted

to the spatial conditions of the surgical access so that it will not overlap with any structure.

By use of the computer-based representation of the three-dimensional reconstruction of the os¬ seous structure, the treatment of the bone can be planned. For this treatment, any suitable tool guides, particularly drill sleeves, paral¬ lel guides, saw templates, 2D- and 3D-profiling milling devices can be provided. These tool guides, connecting elements, surfaces or points can be provided in/on the basic body of the in¬ dividual template, which relative to the 3D re¬ construction of the osseous structure are ori¬ ented or constructed in such a manner that the tool guides, which here can be coupled (releasably or non-releasably) in a mechanically rigid manner, will effect a three-dimensional guiding of the treatment tools or measuring de¬ vices exactly as provided by the surgical plan¬ ning.

According to the course of procedure described above under item 3, also the basic body of the individual template can have connecting ele¬ ments, surfaces or points arranged thereon, which can be releasably coupled in mechanically rigid manner to the gripper piece of a manipula¬ tor and thus preoperatively define the position of the gripper piece of the manipulator relative to the three-dimensional reconstruction of the osseous structure.

5. Prior to the intervention and starting from the home position described above under item 4, a spatial treatment or moving program for the gripper piece of the manipulator can be defined in the gripper piece coordinate system in a spa¬ tially determined relation to the three-dimen¬ sional reconstruction of the osseous structure and be programmed in a computer-based procedure.

6. Further, prior to the intervention and starting from the home position described above under item 4 and also in a spatially determined rela¬ tion to the three-dimensional reconstruction of the osseous structure, it is possible that, for the gripper piece of the manipulator, a desired spatial and chronological dependence on the 3D position and the mechanical 6D impedance can be defined in the gripper piece coordinate system and be programmed in a computer-based procedure.

7. The basic body of the individual template men¬ tioned above under item 2., comprising the nega¬ tive mold, the connecting elements, surfaces or points is produced preoperatively by use of a computer-based manufacturing device (particular¬ ly by NC milling and/or stereolithography) . Dur¬ ing the preparation of the surgical procedure, the tool guides provided in the surgical plan¬ ning are preoperatively mounted on the basic body of the individual template.

8. During the surgical intervention, the above treatment steps defined in the phase of surgical

planning can be exactly transferred since, rela¬ tive to the osseous structure, the tool guides can be brought exactly into the positions de¬ fined during the surgical planning phase (i.e. the manipulator gripper piece can be brought into the home position defined in the surgical planning phase). To this purpose, the individual template with the faces of the negative mold is set under mating engagement onto the then ex¬ posed bone surface, which is done without any further intraoperative devices (particularly without measuring devices such as 3D measuring arms or the like) and without intraoperative measuring and positioning work.

When optionally using a manipulator, the moving program defined during the preoperative planning phase in the computer system through gripper and workpiece coordinates, or, respectively, the 6D impedance variation space defined in the same manner, is converted after the intraoperative mounting of the individual template coupled to the gripper piece, and then will be available during the surgical intervention.

10. As outlined under item 9 above, the treatment and moving program defined under item 5 can be automatically reproduced in an exactly defined manner relative to the osseous structure or be manually released by pieces. The moving and treatment space defined according to items 6 and 9 is intraoperatively reproduced in an exactly defined manner relative to the bone through the

spatial and chronological dependence on the var¬ iation of the mechanical 6D impedance of the manipulator guided by the surgeon on its gripper piece.

11. The guide means of the template for limiting the movement of a treatment device during the treat¬ ment of an osseous structure as provided by the surgical planning allows e.g. vertebral osteo¬ tomy using a vertebral-osteotomy template with a rear contour analogous limitation for the cut¬ ting depth. This limitation for the cutting depth, which requires a guide path for the guide means which corresponds to that limiting edge of the cut through the osseous structure which fac¬ es away from the template, can guarantee suffi¬ cient accuracy by exact positioning and guidance of the tool simply by employment of an (individ¬ ual) template conforming with the osseous struc¬ ture in mating engagement.

12. The consideration of the spatially diametrical bone surface with respect to the "rear contour analogous limitation for the cutting depth" by which, when guiding the cutting, the rear bound¬ ary of the bone is considered corresponding to the projected cutting curve and the rear side of the bone, and is not exceeded by the saw blade. What is again of functional importance here is the use of an individual-template basic body so as to exactly and clearly position the cutting depth limitation during the surgical interven¬ tion.

13. 3D copying milling device for the cleansing of medullary space or for the milling of predeter¬ mined shapes in osseous structures, character¬ ized in that the geometrical data provided for the 3D copying milling device reproduce individ¬ ual geometrical conditions of the thre ^~ .-dimen¬ sional reconstruction of the tomographically imaged osseous structure. Also here, it is func¬ tionally important to use an individual-template basic body so as to exactly and clearly position the 3D copying milling device during the surgi¬ cal intervention.

Embodiments of the invention will be explained in greater detail hereunder with reference to the draw¬ ings. Throughout the Figures, identical reference numbers are used for identical parts in the differ¬ ent embodiments. The Figures show some exemplary embodiments which are merely provided for explaining the invention but, due to the various possible ap¬ plications of the invention, cannot depict the in¬ vention in an all-inclusive manner.

Figs. 1 to 5

show a first embodiment of the invention with an individual template, adapted to a vertebra, for guiding a tool, which in this case is a drill for application of bores for pedicle ^" screws into the vertebra,

Figs. 6 to 8

show a further embodiment of an individual template and its intraoperative handling and use,

Fig. 9 shows an individual template which is an al¬ ternative to the embodiment according to Figs. 6 to 8,

Figs. 10a to lOd

show a further embodiment of an individual template for hip-joint individual endopros- theses,

Fig. lOe

shows an alternative to the individual tem¬ plate according to Figs. 10a to 10d,

Figs. 11a to lid

show a further possible application of an individual template for use in scoliosis correction by repositioning osteotomy in the region of individual vertebrae,

Fig. lie

shows a further possibility for using an individual template for scoliosis correction by repositioning osteotomy in the region of individual vertebrae,

Fig. 12 shows the use of an individual template for osteotomy in the region of the thoracic limb,

Figs. 13a to 13d

show a further individual template for prep¬ aration of a prosthesis seat of a knee-joint head prosthesis.

Figs. 14a to 14c

show an individual template provided with a copying milling device,

Fign. 15 and 15b

show an example of the use of an individual template for robot-assisted treatment of osseous structures,

Figs. 16a to 16e

show a further example of the use of an in¬ dividual template for robot-assisted treat¬ ment of osseous structures,

Fig. 17 shows a further example of robot-assisted treatment,

Fig. 18 is a flow chart for illustrating the method of computer-aided and computer-integrated alignment of treatment tools for the treat-

ment of osseous structures in orthopedic surgery, and

Fig. 19 is a flow chart for illustrating the method for alignment of treatment tools for the robot-assisted treatment of osseous struc¬ tures in orthopedic surgery.

Figs, la, lb, 2a, 2b, 2c, 3a, 3b, 4, 5a, 5b, 5c show an individual template 4 for application of two bores in a vertebra. Each of the bores serves for the mounting of a pedicle screw which shall be screwed trough the (left or right) pedicle into the body of the vertebra, -as it is usually done for the anchoring of a fixateur-intern within a scoliosis operation. For reasons of stability, the screw shall be secured in the cortical substance (i.e. the out¬ er, more compact osseous layer). On the other hand, the bore and the screw shall injure neither the spi¬ nal cord extending in the adjacent spinal canal nor the spinal nerves issuing from the intervertebral canal, and penetrate through the cortical substance of the ventral side of the vertebra only so far that it does not yet ventrally issue from the boy of the vertebra. According to these requirements, the bores are preoperatively clearly defined in space by the entrance and end points and the diameter, and the screw is defined by the diameter and the length, which is done e.g. using CT images.

The method of the invention will be described here- under by way of an example which also stands for other, comparable interventions:

The vertebra and the regions of the structure rele¬ vant for the surgical planning (the osseous struc¬ ture 17 in general) are scanned by a tomographic method as already described, are reconstructed in three dimensions, and the thus obtained 1:1 model is visualized by a suitable medium (e.g. CAD system). Also a model of the osseous structure 17 made from any mechanically rigid model material, which has been produced in the master mold technique by machining or any other desired production method (from UV curable polymer material, e.g. by means of stereolithography), can serve as a basis for the further method steps described hereunder. Methods for the construction of an individual template e.g. by means of a physically rigid model of the osseous structure (e.g. of plastics, wax or metal) and by a plastically deformable, curable material which is machinable in the cured condition, can be used for modelling and producing an individual template.

Particularly the method based on a computer-assisted CAD model will be described hereunder:

The osseous structure 17 (i.e. the vertebra) is re¬ produced in a CAD system as a computerized model. For example in the region of the transverse process¬ es and the vertebral arc (Fig. 2) (or also of the transverse process and the processus spinosus) (Fig. 5) or of the processus spinosus and the vertebral arc or ... ) parts of the bone surface which are intraoperatively accessible to the surgeon are de¬ fined in the model as contact faces 1 for the indi¬ vidual template 4. After reversal of the normal line

of the surface (Fig. 3: 2 and 3), the defined con¬ tact faces 1 are used (as a negative, a "cast", "re¬ production") for a basis for the individual template 4 to be constructed in the coordinate system fixed relative to the model. To this effect, the contact faces 1 are first connected to a mechanically rigid construction adapted to the environment and the de¬ sired overall function, i.e. to the individual tem¬ plate body, so that the individual template 4, via the conventional surgical access (Fig. 4: sketch of a dorsal surgical access in an intervention for sco¬ liosis correction), can be set directly onto the exposed bone surface in a clearly defined manner as provided by the invention, without colliding with other structures in the surgical region. To achieve this, the individual template 4 is of such a config¬ uration that e.g. the contact faces 1 are defined without undercut and that, possibly, recesses 5 (cf. Fig. 5) are provided for structures in the vicinity of the contact faces 1. Thus, the individual tem¬ plate as a whole is adapted to the surgical site. Further, in this individual template, the tool guide, i.e. the drill guide, is mounted directly on the template body 6. To this purpose, two bores 7 are provided in the body of the individual template, on whose bore axes 8 there are arranged the entrance and end points 9,10 of the bores defined in the bone model according to the surgical planning, and which are provided with drill sleeves 11 which are each unambiguously positionable in the bores. With a known drill length 12, these drill sleeves define drill depths and diameters which, in length and in¬ ner diameter, are exactly adapted to the surgical

planning. Further, in or on the individual template body, there are provided bores, threaded bores or other receiving portions for connecting elements, allowing fixation of a universal gripper 14, which can also be reusable, or e.g. of a holding arm 15 which is fixed to the operation table and can be freely positioned and locked. Additionally, clamping devices or screw connections (e.g. 19) can be pro¬ vided for intraoperative fixation of the individual template 4 onto or to the osseous structure 17.

After generation of a corresponding machine program, the individual template 4 is produced by machining on a NC milling machine, favorably from plastics, e.g. plexiglass (PMMA) or also other materials, e.g. metal, or by a master mold technique, e.g. by ste- eolithography (or a similar procedure as de¬ scribed e.g. in Eusemann, Schnell zum Modell durch Rapid Prototyping, VDI nachrichten No. 17, April 26, 1991, p. 26 and in DE 39 33 142) from UV curable polymer. When machining is provided, e.g. in case of the pedicle-screw individual template 4, use can be made of a largely prefabricated semi-finished prod¬ uct which in NC treatment simply has to be provided with the contact faces 1 and the bores 7 each of which are individually defined. During the surgical intervention, the drill sleeves 11 are brought quickly and in a precisely defined manner into that position relative to the bone 17 which before has been determined in the surgical planning; according to the invention, this is accomplished by setting the individual template 4 onto the vertebra (i.e. onto the contact faces in the region of the trans-

verse processes and the vertebral arc). As provided by the invention, the bores 7 can be generated di¬ rectly by insertion of the drilling tool into the drill sleeves 11, wherein the diameter 16 and the entrance and end points 9,10 of the bores in the osseous structure of the vertebra 17 are defined by the preoperative planning and can be clearly repro¬ duced intraoperatively.

The usefulness of semi-finished products has to be examined depending on the respective surgical inter¬ vention. Semifinished products specifically suited for the intervention can be stored, in the CAD sys¬ tem, as a Macro (also parametrically) in libraries together with standard tool guides, standard tools, surgical fixing elements such as screws, fixateur- intern or -extern, other osteosynthesis instruments, grippers and holding arms up to robot and manipula¬ tor libraries. Also the storage of libraries with physiological or pathological osseous structures as well as standard surgical accesses in the CAD com¬ puter system can be of advantage. Then, in the phase of surgical planning, the mentioned individual com¬ ponents can be combined with each other, adapted to each other and positioned relative to each other in any desired manner in the coordinate system fixed relative to the computerized model of the osseous structure. By a clearly defined mechanical connec¬ tion and positioning of the individual components relative to each other and to the basic body of the individual template, which relative to the osseous structure has a clearly defined spatial position because of the contact faces, also the spatial posi-

tion and orientation of the individual components relative to the bone is known and can be clearly reproduced intraoperatively by mounting the individ¬ ual template.

Figs. 6a, 6b, 7a, 7b and 8 illustrate an embodiment of the method exemplified by the use of the princi¬ ple of the individual template in a repositioning osteotomy in the region of the trochanter minor. The contact faces 1 of the mechanically rigid template body 6 of the individual template 4 clearly define the position of the template relative to the osseous structure 17. Thereby, also the position of the cut¬ ting planes according to the surgical planning (Fig. 7) can be intraoperatively reproduced by mounting the individual template 4. The individual template 4 can optionally be provided with a universal gripper 14. Also a fixation (nails, screws and the like) 19 on the bone 17 can be optionally performed. Further, through a drill sleeve 11 and a bore 7, the bore defined in the surgical planning (Fig. 7) and having the bore axis 8 and the entrance and end points 9,10, can be intraoperatively reproduced for fixing a fixateur-intern 21 as shown in Fig. 8. Fig. 9 shows an alternative simple individual template 4 (only saw template) for repositioning osteotomy.

Also the cutting plane which forms basis of the con¬ struction of e.g. hip-joint individual endopros- theses can be exactly reproduced by means of the in¬ dividual template. Figs. 10a to lOd show an embodi¬ ment for a corresponding individual template 4. (Fig. 10 again shows a simplified alternative). As

will be described hereunder with reference to this embodiment and as shown in Figs. 10a to lOd, the in¬ dividual template 4 can also be the basis for fur¬ ther, additional individual templates 27 which need not have contact faces 1 to the osseous structure 17 but are (rigidly) connected to the basic individual template 4 by defined flange engagement points 28. By use of such flange engagement points 28, also other additional devices, e.g. a parallel guide 26, can be coupled. Also a rear contour analogous limi¬ tation 24 of the cutting depth can be provided in/on the individual template 4 or/and the addition¬ al individual template 27. To this purpose, the cut¬ ting contour of the rear side of the osseous struc¬ ture 17 with the respective cutting plane 20 is re¬ produced in such a manner in the individual template 4 (or, respectively, in the additional individual template 27) in the form of the rear contour analo¬ gous limitation for the cutting depth that the saw 25, guided in parallel, whose housing is rigidly connected to a guide pin (or guide cam) which slides along the rear contour analogous limitation for the cutting depth, cannot move beyond the boundary of the osseous structure in rearward direction. When mounting a fixateur-intern 21, the bores 19 applied for the fixation of the individual template can be utilized, if desired (Fig. lOd) .

Figs. 11a to lie illustrate, by way of example, the method of a scoliosis correction by a repositioning osteotomy in the region of individual bodies of the vertebrae. Further, the method of the rear contour analogous limitation 24 of the cutting depth, an

alternative option of a parallel guide 26 for the sawing tool 25 and the method for mounting a fixateur-extern through a ventral access (Fig. He), are explained in greater detail. In the method of the scoliosis correction by a repositioning osteotomy in the region of individual vertebrae, it is provided according to the invention that, in the surgical planning phase, clearly defined bone wedges are cut from also defined bodies of the vertebrae, the spinal column as a whole is aligned and is temporarily fixed by known methods of osteosynthesis (from ventral and/or dorsal, Fig. He). Thus, completely new possibilities for operation and therapy are opened for scoliosis therapy, since, in the above manner, a scoliosis correction can be effected up to an angle of about 45° (according to Cobb) (Fig. lid) without a lasting stiffening of the spinal column (and without destruction of the inter- vertebral discs due to the therapy) .

In addition to the contact face 1 between the indi¬ vidual template 4 and the body 17 of the vertebra, a rear contour analogous limitation 24 for the cutting depth and a saw 25, being guided exactly parallel in the respective cutting plane, are required. The whole design and the manufacture are performed, as already described, on the basis of tomographic imag¬ es of the spinal column and assisted by a computer, in the CAD system, and manufacture is carried out by one of the above mentioned manufacturing methods. Two guide pins 23, rigidly connected to the housing of the sawing tool 25, are moved along two guides, i.e. the rear contour analogous limitations 24 for

the cutting depth. These will image the form of the rear side of the body 29 of the vertebra in such a manner that, when cutting is executed with a saw blade guided in parallel according to Fig. 11a, the tip of the saw blade exactly follows the rear sur¬ face of the body of the vertebra and linearly cuts through the cortical substance. To this effect, the geometry of the sawing tool 25 along with the guide pins 23 and the geometry of the saw blade must be known in the phase of surgical planning. Further, a cutting plane 20 must be defined, and a correspond¬ ing parallel guide 26 of the saw tool 25 has to be provided intraoperatively. A parallel guidance can be safeguarded e.g. in' the manner shown in Figs. 11a to lie.

The individual template 4 can be optionally fixed, as shown at 19, on the body of the vertebra and be provided with a universal gripper 14. If a universal parallel guide (as shown e.g. in Fig. 10b) is to be employed, corresponding flange engagement points 28 have to be defined in the surgical planning phase. In this case, a sole rear contour analogous limita¬ tion 24 for the cutting depth, accordingly having a sole guide pin 23, will be sufficient.

Fig. He shows a method by which a fixateur-extern for alignment and temporary fixation of the spinal column after a ventral repositioning osteotomy in the region of individual bodies of the vertebrae, can be fixed solely through the ventral access and can be mounted in a non-invasive manner from dorsal. To this effect, bores 7 are formed from ventral

through the body of the vertebra and the pedicles by use of an individual template 4 and drill sleeves 11. Then, a surgical threaded bar 30 is screwed into each of these bores until the head 32 of the threaded bar is flush with the ventral surface of the body of the vertebra. The threaded bars 30 are characterized in that each of them comprises a mandrel-like tip 31 which, when the threaded bars 30 are screwed into place, penetrate the layers of tissue dorsally abutting the vertebra, and in the screwed condition project so far beyond the dorsal surface 33 of the body that a fixateur-extern 22 adapted to them can be fixed to them and, thus, alignment and fixation of the spinal column can be performed from dorsal. Further, the threaded bar 30 is characterized in that a screwing tool can be applied in the region of the head 32 of the threaded bar (e.g. an internal hexagon), while, however, the head 32 of the threaded bar has a smaller diameter or the same diameter as the inner diameter of the thread. Thus, the threaded bar can be removed from dorsal. Additional ventral fixations of the bodies of the vertebrae to the purpose of osteosynthesis can be performed by use of fixateur-intern (clamps, plates and so on; possibly also by absorbable material) as commonly used to that purpose.

As a further example, Figs. 12a and 12b schematical¬ ly illustrate an application of the method using the individual template with alignment and definition of the cutting planes 20 and rear contour analogous limitation 24 for the cutting depth as performed in osteotomy in the region of the thoracic limb. The

line 24 of the body 6 of the individual template corresponds to that edge of the cutting plane through the osseous structure 17 of the thoracic limb which is facing away from template 4.

Figs. 13a to 13c schematically show an individual template 4 for the preparation of the seat for the knee-joint head prosthesis illustrated by way of example in Fig. 13d. The intraoperative procedure is as follows: The individual template 4 is set onto the bone 17 in a defined manner, abutting the con¬ tact faces 1. The drill sleeve 11 is inserted, and the bore with the bore axis 8 is formed in the bone. Subsequently, the drill sleeve is removed again. Then, the cut is formed along the cutting plane 20a. Then, the cut 20b can be performed free-handed at a right angle to cut 20a. (To this effect, also an additional template 27 can be provided). Thereafter, the groove (cut 20c) is milled or sawed (according to the geometry of the prosthesis), and then, cut 20d is formed along the lower edge of the individual template 4.

Using an individual template, almost any random de¬ vices can be brought into a clearly defined position relative to the osseous structure as provided by the surgical planning. Milling operations can be exactly planned and realized by a copying milling device which is set onto the osseous structure through a suitable individual template (and which can also reproduce geometries of osseous structures or re¬ flect them in some other manner).

Figs. 14a to 14c schematically show the cleansing of the space of the femural marrow from bone cement. The individual template 4 is intraoperatively set with the contact faces 1 onto the prepared bone. (Also for preparatory treatment, individual tem¬ plates can be provided) . The individual template 4 together with the additional device 41 coupled thereto by defined flange engagement points 28 de¬ fines the spatial orientation of the axis 42 of the milling device relative to the bone 17. The plan- parallel guide 36 of the additional device 41 limits the movements of the milling tool (or the milling head) in a plane perpendicular to the axis 42 of the milling device, and, further, the linear guide 37 of the additional device 41 limits the movements in the direction of the axis 42 of the milling device. The individual template 4 also comprises a cavity which, in the manner illustrated in Fig. 14a, is a copy 39 of the medullary space 40 but, as compared thereto, is enlarged in radial direction (relative to the axis of the milling device) by the factor of the difference of diameters (D _{GUI0E CAH} - D _{MILLING HEAD} ) . When the guide cam 23 is guided within this copy 39 of the medullary space, the medullary space is milled by the milling head 35 on the corresponding loca¬ tions. In the surgical planning phase, the overall individual template 4 along with the flange engage¬ ment points 28 for the additional device 41 - with the geometry of the milling tool 38 and the addi¬ tional device 31 being known, and on the basis of tomographic images of the osseous structure 17 and the medullary space 40 - is constructed and manu¬ factured in such a manner that, during the operation

and in the above described manner which is illus¬ trated in Fig. 14a, the whole medullary space 40 can be milled and the bone cement can be removed without injuring the compact outer structure of the bone. This method allows three-dimensional milling and cleansing of the medullary space in one working phase and in a clearly defined manner in accordance with the surgical planning.

Further applications are e.g. the triple reposi¬ tioning osteotomy of the pelvic bone, fixations in the region of the lumbosacral joint, and limited resections- of tumorous bone tissue.

The use of a robot or manipulator can be advan¬ tageous in case of very small access openings or spatially complex treatment processes (e.g. in tri¬ ple repositioning osteotomy of the pelvic bone or complex milling treatment) . Fig. 19 describes the principal method in diagrammatic form.

Figs. 15a and 15b show a first embodiment for the use of an individual template for robot-assisted treatment of osseous structures in orthopedic sur¬ gery. In the surgical planning phase, on the CAD system, the gripper 48 of a robot mechanics 49 stored in the macro library of the CAD system can be connected, with the contact faces 1, to the comput¬ erized model of the osseous structure 17 by a non- positive and torque-coupling connection to the in¬ dividual template 4. In doing so, the simulated po¬ sition of the robot gripper 48 in the coordinate system 43 fixed relative to the osseous structure 17

(or, respectively, the transformation relationship between the coordinate system fixed 44 relative to the robot gripper and fixed 43 relative to the osse¬ ous structure, when the individual template 4 is mounted on the bone 17 and is connected to robot gripper 48 in a defined rigid manner) is computed and stored as a starting position for simulation and program generation of the whole treatment procedure which, if desired, is performed with different treatment tools 47. The transformation relationship, changeable over time during the treatment procedure, between the robotic end effector 47 or the robot gripper coordinate system 44 and the coordinate sys¬ tem 43 fixed relative- to the osseous structure 17, is respectively planned, computed, simulated and stored or documented in the CAD system. This in¬ cludes the possibility of a positioning of laser pointers, tool guides, measuring probes, and of a direct treatment of the osseous structure by drills, milling devices, saws, lasers, ultrasonic applica¬ tors and others. Under the safety aspect, it would also be reasonable to define and program allowed and prohibited moving regions.

Using the individual template 4, fixed to the grip¬ per 48 of robot 49 according to the surgical plan¬ ning, the robot, during the surgical intervention, can quickly and reliably detect the spatial position of the osseous structure by the teach-in method (Fig. 15a). In the mounted condition of the individ¬ ual template 4, the parameters of the joint or the positional measuring data of the e.g. six axes of the robot 49 can be used for determining the trans-

formation relationship between the basic coordinate system 45 of the robot and the coordinate system 43 fixed relative to the osseous structure 17. On the basis of this transformation relationship, the treatment steps, defined during the surgical plan¬ ning phase in the coordinate system 43 fixed rela¬ tive to the osseous structure 17 (i.e. the transfor¬ mation relationship, changeable over time during the treatment procedure, between the robotic end effec¬ tor 47 or the robot gripper coordinate system 44 and the coordinate system 43 fixed relative to the os¬ seous structure 17), can the be computed after spa¬ tial fixation 46 (holding arm, other fixateurs- extern) of the bone in the basic coordinate system 45 of the robot. To this purpose, the transformation relationship, changeable over time, between the ro¬ bot gripper coordinate system 44 and the basic coor¬ dinate system 45 of the robot, and thus the movement of the endeffector 47 (or gripper 48, respectively) is computed in the basic coordinate system 45 of the robot. The intraoperative transfer of the treatment procedure can be carried out e.g. by robot-assisted positioning of tool guides, marking of cutting planes by laser beam, or also automatic treatment by robot-guided endeffectors, e.g. saws/drills/milling devices and so on. Further, the position of the treatment tool 47 relative to the osseous structure 17 can be intraoperatively displayed in the picture of the model on a computer monitor 57 and can be visually controlled by the surgeon.

Figs. 15a and 15b schematically show the described method. The description of the geometry of the

treatment tool 47 in the coordinate system of the robot gripper 44 has to be known and has to be iden¬ tical with the one defined in the surgical planning. The same holds true for the transformation relation¬ ship between the robot gripper 48 or 44 and the in¬ dividual template 4 (among others, defined by the flange engagement points 28). The robot must be new¬ ly calibrated in each case prior to the operation. CAD models for preoperative simulation and off-line programming of diverse robots are available on the market.

Figs. 16a to 16e schematically show the method by way of example in connection with an operation for applying an individually adapted hip-joint prosthe¬ sis. Further, the Figures show other embodiments for individual functional elements, e.g. fixation of the individual template 4 to the bone 17a through a con¬ necting element 18, establishing a reference between the coordinate system 43 of the bone and the basic coordinate system 45 of the robot by use of a refer¬ ence bore 52 provided with an adjusting-spring groove, spatial fixation of the osseous structure 17 through flange engagement points 28 of the individu¬ al template 4. According to Fig. 16a, the individual template 4 is set with the contact face la onto the femur bone 17a and is fixed by two wires. The bone 17a and the individual template 4 are spatially fixed through flange engagement points 28 by means of a holding arm (or other fixateur-externs) 46 clampingly fixed e.g. to the operating table. The robot 49 whose gripper piece 48 carries e.g. a shaft end having a defined geometry and being provided

with an adjustment spring, detects the relative po¬ sition of the osseous structure 17 in the basic co¬ ordinate system 45 of the robot by the teach-in method through insertion of the referencing body (shaft end with adjustment spring) into the refer¬ encing bore 52 of the individual template 4. There¬ after, diverse treatment steps such as osteotomies and preparation of the medullary space are per¬ formed, according to the surgical planning, directly (by treatment tools) or indirectly (by laser point¬ ers, gauges and others) through the robot under per¬ manent control by the surgeon. (To these steps be¬ long, for instance, as shown in Fig. 16b, the posi¬ tioning of a simple universal saw template according to the cutting planes 20 defined in the surgical planning, performed by the robot 49, and, as shown in Fig. 16c, the treatment of the medullary space by a milling tool 47 guided by robot 49 according to the surgical planning) . Also the preparation of the acetabulum 51 can be carried out in a similar man¬ ner. To this purpose, the pelvis 17b is clampingly fixed from outside in the region of the palpable bone points as rigidly as possible and non-inva- sively. By an individual template 4b which in the region of the edge of the acetabulum can be mounted in a defined manner with the contact surface lb, the robot 49 determines the spatial position of the os¬ seous structure 17 in the basic coordinate system 45 of the robot. Then, the treatment, e.g. by means of a milling tool, is executed as defined by the surgi¬ cal planning. In this manner, it is possible e.g. to define an optimum thickness of the remaining bone and to avoid unintended perforation of the bottom of

the acetabulum. Fig. 16 just gives one example of the many possible applications of the instant method in the field of surgical treatment of osseous struc¬ tures.

The method for treatment of osseous structures by means of "virtual individual templates":

If, during the phase of surgical planning on the CAD system, the "allowed" moving range 50 for treatment tools is structured, defined and programmed with suitable precision in the coordinate system 43 fixed relative to the osseous structure 17, it is possible to define, on the basis of respective limitations of the moving space, respectively one access corridor 55 and, adjoining it, a "virtual" tool guide 56 aligned and positioned according to the surgical planning. In this manner, a reproducible treatment of the bone can be accomplished also in that the treatment tool (saw, drill, milling device or the like) is intraoperatively fixed to the gripper piece 48 of a passive, impedance-variable manipulator 49 and is manually moved by the surgeon. Fig. 17 serves for schematic illustration of the method. When ap¬ proaching, within the operation site, the osseous structure 17 to be treated, the surgeon is guided by defined impedance variations of the manipulator (in¬ crease of the impedance when performing movements in the direction of the limitation of the access corri¬ dor) until, directly before contact of the treatment tool with the osseous structure 17, movement is pos- i_ J -le only along the virtual tool guide ("virtual tplate") defined according to the surgical plan-

ning. The impedance variations can be effected or controlled by computer-assisted brake systems or actuators in the individual joints and degrees of freedom of the manipulator 49. For the force- and position-controlled system, there is required a 6D position and force-moment measurement (e.g. in the individual joints or through a 6D force-moment sen¬ sor 53 in the gripper piece 48 of manipulator 49).

The steps during the planning of the surgical inter¬ vention on the CAD system are the following:

Definition of the individual template 4 with the robot gripper piece 48 in the coordinate system 43 fixed relative to the osseous structure 17; manufacture of the individual template 4.

Definition, calculation and storage of the treatment procedure in form of an allowed moving space 50 in the coordinate system 43 fixed rela¬ tive to the osseous structure 17.

Intraoperative steps are:

Fixation 46 of the osseous structure 17.

Determination of the spatial position of the osseous structure 17 in the basic coordinate system of the robot by use of the individual template 4 mounted in the gripper piece 48 of the robot (shown in interrupted lines).

Transformation of the allowed moving space, de¬ fined in the surgical planning phase in the co¬ ordinate system 43 fixed relative to the osseous structure 17, into the basic coordinate system 45 of the robot.

Movement of the gripper piece 48 of the robot along with the treatment tool 47 by the surgeon; in doing so, counterforces and -moments (imped¬ ance variation) are generated by the manipulator in dependence on the position of the control points 54 and the forces and moments exerted by the surgeon; when the control points 54 reach the limiting faces- of the moving space, the vec- torial components of the applied forces and mo¬ ments which would lead to a movement of the con¬ trol points in vertical direction to the limit¬ ing faces of the moving space and out of the moving space, are neutralized by vectorially corresponding counterforces and -moments of the same amount. In the allowed moving space 50 and along its moving faces, the control points 54 (or the endeffector 47) can be moved freely or, respectively, assisted by a servo mechanism (i.e. with vectorially negative counterforces and -moments). Further, during the operation, the position of the treatment tool 47 relative to the osseous structure 17 can be displayed in the image of the model on a computer monitor 57 and can be visually controlled by the surgeon.