Surgery – Instruments – Stereotaxic device
Reexamination Certificate
2000-01-21
2002-03-12
Thaler, Michael H. (Department: 3731)
Surgery
Instruments
Stereotaxic device
C005S622000
Reexamination Certificate
active
06355049
ABSTRACT:
This invention relates to head fixation apparatus primarily but not exclusively for use in stereotactic procedures for diagnosis and treatment of the brain.
A number of different imaging techniques are available for diagnosis and monitoring of neurological conditions including computerised tomography, positron emmision tomography, magnetic resonance imaging, magnetic resonance spectroscopy, and digital subtraction angiography. It is often desirable that imaging be carried out periodically and for images from different types of apparatus to be integrated or correlated. A problem in each case arises in repeatably positioning the patient's head in a precise location relative to each imaging apparatus and defining a co-ordinate system enabling different apparatus to be used to image the same image plane.
A number of stereotactic surgical techniques are based on imaged information and it is also a common requirement for stereotactic procedures such as biopsies to be carried out at the same location within a patient's head on a number of separate occasions over a long term period of treatment. Examples of such surgical procedures would be the biopsy of a tumour and the draining of cysts.
It is known to provide head fixation apparatus comprising frame means attachable to stereotactic surgical and or imaging apparatus and fixation means for fixing the frame means onto a patient's head in a substantially reproducible manner such that the location of anatomical features and their corresponding images can be spatially defined with reference to the frame means.
The co-ordination of stereotactic imaging and surgical procedures has for example been achieved by means of head fixation apparatus in which a frame means is a rigid metal frame fixed to a patient's head so that a three dimensional coordinate system can be defined with reference to the frame. Biomedical images can then be characterised with reference to this coordinate system and the co-ordinates used as control parameters for stereotactic procedures. A guide for a surgical probe can for example be attached to the frame and used to guide the probe to co-ordinates within the brain which have been calculated from an image that may have been produced sometime earlier at a different location having the appropriate imaging facilities.
For satisfactory correlation to be achieved it is necessary that the fixation means by which the frame means is fixed to the patient's head provides precise and repeatable location of the frame means with reference to the patient's fixed anatomical features i.e. the skull bones.
It is known for the fixation means to comprise rods or screws which penetrate holes in the patient's skull and which support a frame means in the form of a base ring. Imaging apparatus or stereotactic surgical instruments may then be connected to the base ring. A number of disadvantages are associated with this fixation means, primarily because of its invasive nature which requires sterility and anaesthesia and results in patient trauma. The reproducibility available with this technique is also limited because the bore holes become obstructed by debris and will heal over in time preventing long term relocations.
A number of non-invasive techniques have been proposed of which GB-2164856 (Laitinen) discloses fixation means for a reference frame comprising two ear plugs and a naison support. A disadvantage of this apparatus is that the ear plugs and naison support each contact relatively soft tissue so that to minimise movement of the frame means a degree of force needs to be applied to the ear plugs and naison support which is uncomfortable for the patient and prevents the apparatus being tolerated for more than about 20 minutes. This factor makes the apparatus unsuitable for the prolonged studies demanded in some imaging techniques such as positron emmission tomography. A further disadvantage is that the particular apparatus disclosed is insufficiently robust to serve as a secure base for surgical instruments.
It is also known to mould a helmet conforming to the shape of the top part of a patient's head using either thermosetting material or fibreglass/resin techniques and to inset metallic supports into the helmet upon which to mount a frame. Such systems are described by T. Greitz et al in Neuroradiology 19, 1-6(1980).
This publication discloses the use of a dental mould in conjuction with a fibreglass bandage to provide a mouth piece receiving an impression of the patient's upper incisor teeth.
A disadvantage of such skull cap techniques is their inherent lack of reproducibility due to the presence of soft tissue between the cap and the skull. The skin in this area is also not firmly fixed to the skull and tends to allow movement of the cap. In the case of a skull cap in which a mouth piece is provided having an impression of the upper incisors it is found that cap movement tends to be pivotal about the incisors. Consequently this technique has not been found to be practicable in general use.
It is also known to provide fixation apparatus where reference is made to the patient's teeth as in the case of the Rand-Wells stereotactic device referred to in Radiology Volume 74 No. 1 pages 86 to 87 January 1960. Although not disclosed in this publication the Rand-Wells device in use includes a mouthpiece having a U-shaped tray into which dental cast material is received to make a cast of the patient's upper teeth. Subsequent to alignment with the teeth three pointed screws are fastened to the skull through the skin such that a framework is rigidly and precisely fixed to the head. The Rand-Wells device has been used for procedures in which radio active seeds are implanted into the pituitary gland through the nasal cavities. The invasive nature of the screws leads to the disadvantages of other invasive techniques discussed above.
According to the present invention there is disclosed apparatus for use in stereotactic diagnosis and treatment comprising frame means, or frame assembly, and fixation means, or fixation member, for repeatably and reproducibly fixing the frame means to the patient's head such that locations within the head are spatially definable with reference to the frame means, wherein the fixation means comprises a cast of the patient's upper teeth and or palate, the fixation means further comprising support means for rigidly connecting the cast to the frame means and biassing means non-invasively engageable with the head and operable between the head and the frame means and or the fixation means to bias the cast into positive contact with the upper teeth and or palate.
Preferably the fixation means comprises a cast comprising a U-shaped portion indented with an impression of substantially all of the patient's upper teeth if any.
An advantage of such an arrangement is that the teeth provide the most rigid point of non-invasive location on the skull and are able to withstand comfortably considerable firm pressure particularly when distributed over the complete set of teeth.
Advantageously the cast has a contact surface which in use engages in intimate contact the inner and inferior aspects of all of the patient's upper teeth.
It is thereby possible to make the cast conform to the numerous contours provided by the patient's teeth so that the cast locates in a unique position. This also avoids the problem of the undercut provided by the incisor teeth in that a cast which also fitted intimately over the entire inner and outer surface of these incisor teeth would not be removable without splitting the cast.
Preferably the contact surface further engages the outer aspect of the molar and premolar teeth.
Additional locating points are thereby established without preventing the cast from being removed since these teeth in general do not include an undercut.
The cast may include also a bridge portion conforming to the palate and forming a continuous bridge between the arms of the U-shaped portion.
The hard palate is also capable of comfortably taking high
Sherwood Services AG
Thaler Michael H.
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