CA2221456C - Method and device for fixing the human head - Google Patents

Abstract

The invention concerns a method and device for fixing the human head during neurosurgery and the like, which are of simple design and simplified application, respectively.
The device comprises: a base plate (1); at least one support element (4) which can be detachably mounted on the base plate (1) and has base holders (5, 15) which can each be positioned freely on the base plate (1); a base rod (7, 17) secured on the base holder (5, 15) with at least one hinge joint (9, 19); a projecting holder rod (8, 18) secured to the hinge joint (9, 19), a detachably mounted upper jaw cross-plate (27) being provided at the end of the holder rod (8, 18); and an upper jaw impression tray (30) which can be mounted on the upper jaw cross-plate (27) and can be fixed on the upper jaw by a vacuum.

Description

Specification Method and Device for Fixing the Human Head The invention relates to a method and a device for fixing the human head.
In many branches of human medicine or of medical research, 15 secure fixing of the head of a patient or of a test subject is necessary. This is of the greatest importance especially in the field of head surgery and of ear, nose and throat surgery.
Through the use of imaging computer technology in diagnosis and therapy, the requirements for accuracy and reproducibility 20 have risen, both in the establishment of a spatially defined point in or on the human head and in the fixing of the head itself.
The most widely known methods for fixing the human head are briefly described below:

a) Fixing the head with adhesive tape:
The head of the patient lies in the rear position on a foam ring. Adhesive tapes stretched across the forehead and 30 upper and lower jaw fix the head 5 on to a base. The disadvantages of this are the following points:
- through the strong pulling of the adhesive tapes, pressure points, displacements and/or skin swellings can occur;
10 - once the retaining elements (adhesive tapes) have been removed, renewed positioning in exactly the same place is scarcely possible any more, and this is particularly disadvantageous in stereotactic operations and in radiotherapy;
15 - the head cannot be fixed sufficiently; the movement of the head can be restricted too little, particularly in a sideways direction (towards the side).
20 b) Fixing the head with a face mask:
The head lies in the rear position in a pre-formed shell and the face is covered by a mask, which has been individually prepared previously and is laterally anchored.
25 On the basis of skin displacements on the bones of the face, however, there is very slight movement between the face and the mask so that it is not possible to achieve extremely accurate fixing of the head, the following points also being negative:
30 - the operation area in the region of the face is not accessible, since it is largely covered;

2 5 - swelling of the skin under the mask which sits tautly;
- the complete covering of the face is a strain on the patient;
- high costs and expenditure of time.

c) Fixing the head by clamping it;
The head of the patient is clamped by fixing screws from several sides into a metal ring. The disadvantages of this 15 are:
the operation areas of the head and the back of the head are largely covered and thus they are not accessible or only accessible with difficulty;
- high costs of the metal ring;
20 - different positions of the patient for different types of intervention are only possible to a limited extent;
- displacements of the skin occur frequently.
d) Fixing of the head by screwing down of the skull:

The head of the patient is screwed down at a plurality of points via a metal ring. The disadvantages of this are the following:
- screwing on to the skull bones represents an 30 invasive method and is thus only possible and justified in certain indications;

3 5 - the psychological strain on the patient is considerable;
- the method can only be applied to a limited extent to certain positions of the patient.
10 e) Fixing of the head via the teeth (the so-called Gill Thomas-Cosman mount as per GB-A-2 213 066);
An impression of the teeth of the upper jaw is here placed into the mouth (cemented) and tightened via a 15 crossbar on a ring shaped holding device running at nose height against a support at the back of the head. The result of this is that the position of the head of the patient has to be adapted by force, i.e. using considerable force, to pre-set connection points. Through the necessary 20 cementing onto the teeth of the upper jaw, this device cannot be used on elderly, toothless patients. In addition, the following points are disadvantageous:
- different operation areas are not accessible because of the holding frame which takes up so 25 much space (e.g. in ENT-surgery an endoscope cannot be led in through the nose);
- the positioning of the head of the patient is complicated and difficult, thus time consuming and a great strain on the patient.

4

5 - tightening and cementing the impression tray in the mouth is a strain on the patient, particularly when freeing the impression;
- the mount is expensive, particularly as ear plugs are also provided for fixing the head and straps 10 running over the skull cap and these further restrict the possible regions for operations;
- the patient's head can only be put in a limited number of positions, since the mounting frame extends as far as the nape of the neck and this 15 also means that particularly lateral regions of the back of the head are not accessible.
The purpose underlying the invention, therefore, is to create a method and a device for fixing the human head which avoids 20 the disadvantages mentioned, is simple in construction and application and at the same time to a great extent gentle on the patient; in addition, the device should make possible the exact application of calibration points (so-called markers) and maximum accessibility to operation areas.

This purpose is fulfilled with a device in accordance with the features of claim 1 or with a method according to claim 14 or 16.
In addition, an impression tray suitable for this method is claimed according to claim 17 and an operation simulation 30 method according to claim 23.

5 In contrast to the devices or methods described initially, on the device or the method according to the invention the fixing of the human head is essentially achieved through vacuum forces which act between the head to be fixed and an impression, taken individually from the respective person, of the upper jaw 10 or of the so-called hard palate (palatinum durum) and teeth as far as they are present. Freeing the impression from the upper jaw or the hard palate of the patient once the investigation or the treatment is finished, is possible by switching off the vacuum with very little application of force and is thus very gentle on the 15 patient. The fixing or fastening of the upper jaw impression tray likewise take place in an especially simple and easily reproducible way, which is gentle on the patient, via the application of vacuum.
20 Through this fixing by means of a vacuum, it can be ensured that, especially with toothless patients (e.g. accident victims) and even after an impression has been used several times, a secure connection by vacuum, remaining exactly the same, is always made possible. As a means of producing the vacuum, 25 simple vacuum pumps with an adjustable level of vacuum pressure, which may be controlled to monitor secure fixing of the impression, hose couplings and isolating valves may be used. To support the vacuum effect, by application of impression mass to the impression which is in fact

6 5 finished, flat hollow spaces or vacuum channels are produced or, by preference, are already formed in the impression, and a terminating connector can be inserted in the front upper jaw region of the impression and of the upper jaw impression tray.
In addition, this system is easy to clean in the sterilizer and the 10 running costs are low since for each individual patient only one impression from cheap impression material is used, whilst the remaining components of the fixing mount may be used again and again.
15 Through the support elements which are in the form of supports or columns and may be positioned in any place on the base plate, or through similar base holders with a plurality of swivel axes or ball ends, the patient's head is practically completely accessible to the doctor treating him, for any type of 20 intervention. What is essential here, is the slim rod-shaped design of the support elements which, however, are sufficiently stable and in contrast to the known massive metal rings can be positioned at any place on the base plate in such a way that they do not interfere with the planned intervention and can be 25 set in all co-ordinate axes or degrees of freedom.
Of particular advantage here is a counter-fixing device which is similarly constructed and thus capable of being positioned in various ways for the additional securing of the head of the 30 patient, particularly in

7 5 regions of the upper head area and the back of the head or in the shoulder area, the fixing of the head being secured especially on restless/conscious patients or where there is greater effect of force on the patient's head such as in working with bones or cartilage. In addition, this makes possible even 10 distribution of pressure and takes the stress off the patient.
Especially the shoulder fixing device is here of independent importance since through it, even without a vacuum, fixing of the patient's head by exercising counter-pressure to the upper jaw impression can be achieved with a stretching of the throat 15 region. This "stretching" process is particularly suitable for surgery in the throat region.
What is particularly advantageous, moreover, is the application of passive or active calibration points, which in modern medicine 20 establish reference points and reference planes on the practical application of imaging processes such as for example CT
(Computerized Tomography) or MRI (Magnetic Resonance Imaging). The claimed fixing device, makes it possible, after the preparation of an impression and the application of a calibration 25 rod to the upper jaw impression tray or to the upper jaw cross-plate securely connected thereto, to establish calibration points which can then be used with, or even without, further fixing of the patient's head in the imaging process (CT or MRI) then as reference points for further measures such as the

8 5 calibration of the patient in preparation for an operation or for operation simulation. This makes possible a new type of efficient operation preparation with a simulation of the planned intervention, since the operation instruments can be pre-set even without a patient being laid on them, and with the aid of 10 computer-generated virtual patient images, for instance, the direction of insertion and the length of instruments can be established, avoiding essential nerve passages or blood vessels which can be recognized on the computer-generated images.
When the patient is then added and the computer data 15 correlated with the calibration points or reference points, the operation can then be carried out relatively quickly.
Preferred embodiments, given by way of example, are described and explained in greater detail below with the aid of 20 the drawing. These show:
Fig. 1 - a device for fixing the head of a patient with a plurality of support elements, in plan view;
25 Fig. 2 - the device according to Fig. 1, in side view with the head of the patient shown diagrammatically;

9 5 Fig. 3 - the device according tot Figs. 1 and 2 in front elevation looking from the body to the head of a patient not shown.
Fig. 4 - a preferred connected mount for calibration

10 points in plan view;
Fig. 5 - the mount for calibration points, in side view looking in the direction of arrow A in Fig. 4.
15 Fig. 6 - a side view similar to Fig. 2, however from the opposite side, with a base plate with a fixing device placed on it and a similarly formed counter-fixing device;
Fig. 7 - a fixing device similar to that in Fig. 3, however 20 viewed from the head to the body of the patient;
Fig. 8 - an upper jaw cross-plate in plan view in the longitudinal axis of the body, with holder rods attached to it to fix it on to a support element;

Fig. 9 - a support element in stand form with a base holder, a base rod and a holder rod with a hinge joint which can be centrally locked, in side view;

5 Fig. 10 - a support element as per Fig. 9 with a central adjusting screw, in front elevation.
Fig. 11 - a support element in the form of a stand as per Figs. 9 and 10, with base holder, telescopic holder and 10 base rods and ball and socket joints with a central locking device, in plan view;
Fig. 12 - a mount for calibration points similar to Figs. 4 and 5 with a screw fixing device, transverse distance rod 15 and a lateral distance rod;
Fig. 13 - an upper jaw impression tray, in perspective view;
20 Fig. 14 - the base plate according to Fig. 1, in outline, with extension plates in a modular form of construction;
and Fig. 15 - a preferred counter-fixing device for the 25 shoulder region in side view.
A base plate made of steel, which may be magnetised, and on to which further plate parts 1' (cf. Fig. 14) can be attached in a modular form of construction, is connected on its underside via 30 stable connections 2, here only indicated diagrammatically, for example

11 5 bolts, with an operating table. The base plate 1 can be adjusted to these connections 2 in respect of the operating table in a horizontal and in a vertical direction and can be twisted to a certain degree, there being a high degree of security ensured in each position. On the base plate 1 serving as reference base, a 10 head support ring 3 lies centrally (or a head support adapted to the shape of the head) and may be moved freely according to the position of the patient. When the head is laid back, the head rest ring 3 consists of a slightly compressible hard rubber ring on which the back of the head is bedded. Here, head rest rings 15 3 of different diameters and different thicknesses are available for the different sizes of head and different operating positions.
The head rest ring 3 or the shaped head rest are expedient for the even distribution of pressure and transmission of force from the head to the base plate 1 when the patient is on his side.
20 They increase the support surface, which results in a reduction of the surface pressure. The pre-shaped headrest is mainly used where the patient or the test subject is on his or her side.
To fix the patient's head, a plurality of support elements 4, which 25 may be freely positioned and are in the shape of stands, are provided here in the corner region of the base plate 1 as force-transmitting portions of the head holding device. These consist respectively of a base holder 5,15 and a preferably

12 5 screwed in base rod 7,17 securely connected thereto, and a holder rod 8,18 jointed to the latter, the reference number with the prefix "1" indicating in each case the same constructional element on the opposite longitudinal centre plane of the base plate 1. The holder rod 8 or 18 has at its end in each case one 10 fastening place 28 with a screwed locking device 10 for each end of a central upper jaw cross-plate 27.
The base holder 5,15 has an on/off switch 6,16 for strong permanent magnets built into the base holder, with which it can 15 be magnetically immovably anchored to any point on the base plate 1 which is magnetisable (or it can be freed). On an alternative pneumatic design, 6,16 indicated an actuating valve to activate a vacuum with which the base holder 5,15 can be held on to the base plate 1 by suction. On this version, the base 20 plate does not need to be magnetisable, thus a simple plastic plate can be used which, in addition, means that it can be easily used on the MRI-scanner. The base holders 5,15 can, however, also be pushed into corresponding bore holes 12 in the base plate 1 (cf. Fig. 10).

The respective hinge joint 9,19 between the base rod 7,17 and holder rod 8,18 is fixed by means of a central screwed locking device 11 and is secured. On the modified version in the form of a stand, however, with

13 5 the same base holder 5,15 according to Figs. 9 to 11 the head if the patient is supported by telescoping holding tubes 22 as the base and holder rods 7, 8 and ball and socket joints 23 as the hinged joint 9. The end of the right or the left holder rod 8,18 in each case forms a contact point 28 for fastening on to the upper 10 jaw cross-plate 27. This cross-plate 27 is connected to an upper jaw impression tray 30 filled with an impression mass 31 (cf. Figs. 4 and 13) by means of a connection, especially a quick-setting adhesive, on its flat side. The ends of the upper jaw cross-plate 27 (compare Fig. 3) here leave the mouth area 15 of the patient approximately in the region of the corner of the mouth, however they can also be led towards the nose or towards the chin. The upper jaw cross-plate 27 can here also be mounted on one side as a cantilever.
20 The upper jaw cross-plate 27 consists for example of stainless chromium steel and has a thickness of approximately 2 mm. Its size and form are variable and can thus be well adapted to the respective requirements of the operation, for example can also consist of very strong carbon fibres. In the centre region 29 of 25 the upper jaw cross-plate 27 which runs transversely, a U-shaped space is cut out in order to lead in a tube, for example, or to gain space and an overview in the mouth region for surgery. The ends of the upper jaw plates at the fastening points 28 are, just like the whole

14 5 upper jaw cross-plate 27, adapted in size and form, particularly in their overhang, to meet the requirements of the respective procedure in the treatment intervention.
In Figs. 2 and 3 the device for fixing a patient's head is shown in 10 operating position. From this it is clear that the support elements 4 run from the point of introduction of the force on the upper jaw impression tray 30 like a portal or a bridge to the base plate 1, and, after the joints 9 or 23 have been stopped, take over the transmission of force in all directions in a stable

15 fashion. Here, however, the overall structural shape is slim, so that the operation or treatment area on the head is easily accessible for the doctor.
On stereotactic operations, however, reference points are 20 essential, the previously described structure of the fixing device or elements of same also being able to serve as a mount for calibration points 37 (cf. Figs. 4,5,8 and 12). This so-called calibration rod consists of a transverse distance rod 33 which is connected to the upper jaw impression tray 30 so as to be 25 secured against twisting and/or displacement. A lateral distance rod 34 is fastened on the transverse distance rod 33 by a screwed or clamping connection 35, 36 so as to be able to be adjusted and fixed into place. Marker pins serving as calibration points 37 can either themselves form the calibration points or 5 serve as carriers for markers (e.g. in the form of lead pellets).
However, as reference points or calibration points, other types of sensors can also be used, for example optical, radioactive or inductive transmitters. The marker pins can also be attached to any other point of the mount e.g. to the transverse distance rod 10 33 or to one of the holder rods 8,18 (cf. Fig. 8).
In Figs. 1 - 3 and in Figs. 6 and 7 a counter-fixing device 40 for the back of the patient's head is shown, such as is expedient particularly in operations where great force is used on the skull 15 (e.g. chiseling, milling). On an otherwise identical structure with base holders 5,15, base rods 7,17 and holder rods 8,18 etc., the counter-fixing device 40 has a plurality of adjusting screws 41 and counter-pressure discs 42 attached thereto. This counter-fixing device 40 is, however, not absolutely necessary for 20 procedures where no force is used such as radio-therapy, and thus the head of the patient is held only on the support element or elements connected to the upper jaw impression tray 30.
In Fig. 15 a shoulder saddle 52 is provided which is adjustable 25 in height as an alternative counter-fixing device 50 and this allows exact re-positioning. The shoulder saddle 52 is here mounted on a base rod 51, anchored on the base plate 1 by means of a plug-in connection 12 so as to be slideable and rotatable and

16 5 thus, when it has been placed on the patient's shoulders, an opposing force to the upper jaw fixing device can be applied and the spinal column here stretched in the throat region. This counter-fixing device 50 is thus especially expedient for procedures in the throat region. Additional counter-fixing 10 devices 50 can also be fixed to the lower jaw in any position.
The upper jaw impression tray 30 is shown together with connected holder-rods 8 in Fig. 8. A calibration point 37 can be attached to said holder-rods such that the patient can be 15 scanned with the unit shown here, this unit being held exactly, and so as to be capable of being re-positioned, by the vacuum applied to the lower jaw impression tray 30. Then the head of the patient can be determined by connecting the holder rods 8 with the support elements 4 for the operation, for instance 20 through inserting into a bearing eye 24, shown in the successive Figs. 9 to 11, through connecting the base holder 5 and stopping the joints 9 or ball or socket joints 23.
In Fig. 9 to 11 views of the preferred embodiment of the support 25 element 4 are shown, namely in the form of a stand known from precision engineering, these stands 21 being "lockable" by a central locking device 20 or being capable of being held rigid in one position. Here, through the activation of the locking device, a

17 5 piston presses on collet chucks, not shown, in the ball and socket joints 23 and fixes same. Tightening then occurs under fluid pressure (especially hydraulic) in the hollow holder tubes 22, such that all the joints 9 or 23 of respectively one support element 4 are simultaneously stopped or made rigid.

In Fig. 13 a perspective view of the upper jaw impression tray 30, with impression mass 31 filled into it is shown for clarification (indicated by dots.) On this "vacuum kit", a flexible strip 38, which by preference is stamped out f a thin rubber mat 15 in a U or star-shape, is laid into the impression mass 31 before the impression of the upper jaw or palate is taken, to create vacuum channels or pockets into which the vacuum is applied later. At the same time a connector piece 39 is also formed such that, once the jaw impression has been removed and the 20 impression mass 31 has hardened, the strips 38 can be pulled away either in several pieces or in one piece. In this way, flat pockets or channels are formed in the impression which is individual for each patient, and these form pressure chambers towards the upper jaw/palate when the vacuum is applied (cf.
25 Fig. 12) to the upper jaw impression tray 30 via the connector pieces 39. By monitoring the vacuum (approximately 0.2 atm) the exact seating of the impression tray 30 and thus the exact positioning can also be checked. Here standardized

18 5 impression trays 30 in a plurality of pre-fabricated sizes can also be used.
What is also of great importance is the possibility shown in Fig.
14 of expanding in modular fashion the base plate 1 with further 10 base plates 1' connected by means of transverse longitudinal or rotating guides 1 a, 1 b and 1 c. These base plates 1' can, just like base plate 1, have a large number of push in boreholes 12 arranged in grid form (and/or on the side edges 12') into which the base holders 5,15, the base rods 7,17 (or 51 in the case of 15 the shoulder counter-fixing device) can be inserted. Here the base plate 1' can then be moved in the shoulder area together with the counter-fixing device 50 in respect of the head longitudinal central plane around the rotatable guide 1c, in order to give the person carrying out the operation, for example, better 20 access to a certain cervical vertebra. It should be noted that it is possible to make reference back to the original stereotactic positioning e.g. by means of the marker pins 37 since the swivel movement (or even a translatory relative movement) is detected between the base plates 1 and 1' by scales or angle/length 25 measurement transmitters on the guides 1 a, 1 b, 1 c in all co-ordinate axes or degrees of freedom and thus the position of the patient can also be changed.

19 5 The practical application of the device according to the invention is now to be described below together with the calibration points 37 shown in Figs. 4, 5, 8 or 12 with the aid of CAS (computer-assisted surgery): CAS represents a navigational aid during operations. Before the operation, the patient is scanned using 10 CT or MRI. Then the individual steps are reconstructed (generated) as a 3D object with corresponding stereotactic space co-ordinates on the processing computer and transferred to a display or a monitor in the operating theatre. This virtual picture is calibrated in the operating theatre to the patient with 15 the aid of a passive mechanical arm coupled to the computer (e.g. similar to figure 12) and at the end of which a probe is located. Sensors on each of the 6 rotational axes of the arm inform the computer of the relative angles of the parts of the arm to one another, the computer being in the position of calculating

20 the stereotactic co-ordinates of the point of the probe. By moving through a plurality of points (e.g. anatomical points or through calibration points that are impenetrable by X-ray - so-called marker-characterised reference points) on the patient or on the calibration device and the corresponding correlation to 25 the reconstructed 3D object on the display, it is possible for the computer to fit this 3D object into this virtual space. The better the points moved through agree with the points correlated on the screen, the more exactly the virtual image and the head 5 of the patient agree with one another, which leads to great accuracy of the system. The person carrying out the operation can, during the operation, find his bearings with the aid of the reconstructed 3D object and a plurality of two dimensional images which always show the point of the probe.

The successful application of this method is only guaranteed if exact fixing of the patient' head and thus of the calibration is provided. As described initially, known systems are at the present time not in a position of registering exactly movements 15 made by the patient. Even on a system with active head-movement registration, fixing in order to control aiming devices is unavoidable. Thus, at the present time with known fixing methods, it is necessary before each use of the probe to check the head position by moving through corresponding calibration 20 points. On each head movement, therefore, subsequent calibration is necessary. The results are, amongst other things, considerable lengthening of the operation time. Moreover, a change of position between checking of the calibration and application of the probe for planning orientation and navigation 25 can have important consequences for the patient because this mistake is not detected by the system and thus faulty interpretation can result. Thus the reliability of the whole system is limited. For the calibration, a sufficiently large and easily accessible area of skin

21 5 is necessary. This is needed for the marker calibration on which a plurality of markers is applied to the skin. The surface calibration, on which the areas of skin serving for the subsequent calibration may not be displaced by the application of the mount, severs to improve the marker calibration. By 10 displacing the skin and/or the markers attached to same in relation to the head, a correlation of the real head of the patient to the 3D object reconstructed from the CT-data cannot be carried out with the desired and necessary precision. This is true both for marker calibration and for surface calibration. With 15 all these known methods, therefore, there was an unsatisfactory situation.
In contrast with this, in the application of the device or method according to the invention the following procedure is followed:
20 first of all, an upper jaw impression is taken from the patient by means of the upper jaw impression tray 30 and the impression mass 31 filled into same. If this is done shortly before the CT-scan, then, after the setting of the calibration device 33 to 37 consisting preferably of carbon fibres, the patient can be 25 scanned by CT without the impression tray 30, held only by vacuum, being removed and without the application of the additional head mount. Here, the calibration device 33 to 37 is so adjusted by pushing or swinging the distance rods 33,34 that the marker pin 37 located on the screwed mount 36

22 5 (generally pellets made of material that is impenetrable by x-ray are used) is found in the scanned region. Here no active holding by the patient is necessary and thus the mouth area is accessible for insertion of tubes.
10 This kind of reversible fixing of the head in the initial position is especially sensible with CT-scans for surgery involving soft parts since these can be displaced depending on the respective position. It is however often expedient to scan the patient (and thus the calibration device 33 to 37) fixed in the head support 15 shown in Figs. 1 to 3. A positive side effect of this exact fixing of the head during the CT-scan is the avoidance of movement artefacts that often occur. After the CT examination the support element 4 and the vacuum are released and the impression tray 30 (together with the calibration device 33 to 37) is taken away.
20 This can be stored for a later operation.
Here the following procedure is taken: after the impression tray 30 has been inserted into the mouth area, the latter is connected with the cross-plate 27 which is in moveable contact 25 with the already-described support elements 4 of the head mount. Then the impression tray 30 carrying the impression for the individual patient or a pre-fabricated one is pressed on to the teeth or on to the hard palate and fixed there by means of a vacuum. Then, once the operator

23 5 has convinced himself, by checking the vacuum, of the correct position of the impression tray 30 and thus also of the calibration device 33 to 37 connected thereto, the head fixing mount is fixed by stopping (making rigid) all the hinged connections 9, 19 between holder rods 8, 18 and base rods 7, 10 17 and by anchoring (activating the magnets or the negative pressure source by means of switches 6,16) of the base holders 5, 15 on the base plate 1 or 1'.
On the subsequent step of the operation, which can take place 15 over a shorter or longer period of time, the impression tray 30 in combination with the calibration device 33 to 37 is fitted to the upper jaw of the patients head in the manner already described for the CT-scan and fixed onto the base plate 1 through the application of vacuum to the impression tray 30 as well as 20 stopping the support elements 4 on the base plate 1. Now the necessary calibration points on the calibration device 33 to 37 for the CAS procedures can be moved through and thus a correlation be made between the real head of the patient and the virtual 3D image stored after the scan. What should be 25 particularly stressed is the fact that the calibration points in the form of marker pins 37 are immovable in relation to the head of the patient. Through the application of the head-fixing mount in combination with the calibration device 33 to 37, maximum accuracy can thus be achieved with stereotactic procedures of 30 this kind.

24 5 In conclusion, the advantages of the device according to the device are summarised:
- exact fixing of the head with space-saving construction;
- maximum freedom of vision and movement in the area of the operation for the person carrying out the operation;
10 - positioning of the head in variable positions for use in different kinds of operations;
- no invasive intervention is needed to fix the head;
- no displacements of the skin, and thus of the position, cased by the mounts;
15 - the possibility of attaching instruments of the most varied kind, e.g. an endoscope, to the mount as well as its suitability for virtual 3D endoscopy;
- definition of exact calibration points by the calibration device attached to the upper jaw or palate which can at 20 the same time be used as a component of the fixing mount;
- the conditions of the fixing by the base holders which are freely movable on the base plate are adapted to the individual features of the patient's head and not the other

25 way round, i.e. the patient's head being forced into the devices;
- simple handling, which also saves time, through the application of a vacuum and thus particularly gentle on the patient and hygienic.

Claims (16)

Claims:

1. Device for fixing the human head, consisting of:
- a base plate (1) - at least one support element (4) which is detachably mounted on the base plate (1), with respectively a base holder (5,15) which is positioned freely on the base plate (1), - a base rod (7,17) attached to the base holder (5,15) with at least one hinged joint (9,19), - a projecting holder rod (8,18), attached to the hinged joint (9,19), there being provided on the end of the holder-rod (8,18) a detachably mounted upper jaw cross-plate (27) and - an upper jaw impression plate (30), which is attached to the upper jaw cross-plate (27) and which is fixed to the upper jaw by means of a vacuum.

2. Device according to claim 1, characterised in that the upper jaw impression tray (30) is connected to the upper jaw cross-plate (27) by means of a screwed locking device (10,28) or an adhesive.

3. Device according to claim 1 or 2, characterised in that on the base holders (5,15) hinge connections (9,19), swivellable through many axes, are provided in the form of stands (21) with a central locking device (2C).

4. Device according to one or claims 1 to 3, characterised in that the base plate (1) is attached to an operating table so as to be adjustable.

5. Device according to one of claims 1 to 4, characterised in that the base plate (1) and/or portions of the support element (4) including the upper jaw impression tray (30) are formed, at least in sections, of material through which X-rays may pass.

6. Device according to one of claims 1 to 5, characterised in that the base plate (1) has markings and/or plug-in holes (12) to re-position the detached base holder (5,15).

7. Device according to one of claims 1 to 6, characterised in that the base holders (5,15) are configured as magnetic mounts or as pneumatic mounts.

8. Device according to one of claims 3 to 7, characterised in that the hinge connections (9,19) of the stands (21) are stopped by means or fluid pressure.

9. Device according to one of claims 1 to 8, characterised in that the base rods (7,17) and/or holder rods (8,18) or stands (21) are configured as carrying and receiving devices for medical equipment, especially endoscopic equipment, wound clasps, hand-rest surfaces or stereotactic navigational aids.

10. Device according to one of claims 1 to 9, characterised in that a counter-fixing device (40, 50) is provided with which a counter-pressure to the upper jaw impression tray (30) is exerted on the human body via adjustable surfaces (42, 52,).

11. Device according to one of claims 1 to 10, characterised in that on the base plate (1) a headrest ring (3) or an anatomically shaped headrest is provided.

12. Device according to one of claims 1 to 11, characterised in that at least one adjustable calibration rod (33, 34, 35, 36) is provided to establish the position of calibration points (37) which are attached to the upper jaw impression tray (30) and/or to the upper jaw cross-plate (27).

13. Device according to one of claims 1 to 12, characterised in that flexible strips (38) are inserted with a vacuum connecting piece (39) into the impression mass (31) filled into the upper jaw impression tray (30) and these strips are formed so that they are withdrawn after the impression mass (31) has hardened, to form vacuum channels.

14. Method of fixing the human head characterised in supporting the head from a base plate (1) and attaching an impression carried by an impression tray (30) to an upper and/or lower jaw and fixing the impression to the upper and lower jaw by a vacuum.

15. Method according to claim 14, characterised in scanning a patient with an imaging scanning device with only said impression tray (30) attached and calibration rods (33 to 37) connected to said base plate (1) and only thereafter connecting the impression tray (30) to a support element (4).

16. Method for fixing the human head by means of at least one support element and a jaw impression fastened to same and adapted to the patient, characterised in exerting counter-pressure to an impression tray (30) by means of a counter-fixing device (40, 50) with surfaces (42, 52) that counter-pressure to the impression tray (30) carrying the jaw impression is exerted by means of a counter-fixing device (40, 50) with surfaces (42, 52).