Patent Application
20090293883
The invention relates to a connecting device for connecting a ring-shaped frame, which is adapted for fixation to the head of a patient during neurological diagnosis, therapy or surgery, to a supplementary equipment, for positioning of the frame and the equipment in a predetermined relation to each other, wherein the frame comprises a connecting bore or hole and the equipment comprises a connecting pin for insertion into the hole in the frame during positioning.
During neurological diagnosis, therapy or surgery of the head of a patient, use is made of a ring-shaped frame, which is secured to the head by means of at least three pointed fixation pins which are tightened against the skull for fixation of the frame thereto.
However, when tightening of the fixation pins against the skull, which usually is accomplished by threaded fixation pins which are screwed into the skull, the frame will be deformed due to the large forces acting between the frame and the skull by means of the fixation pins. The deformation will be particular significant when, as is common practice today, using pin support members, which project upwards from the frame, with the fixation pins passed through the upper ends of each pin support member. Hereby the moment forces acting on the frame, will be considerable.
The deformation of the frame makes it more difficult to connect supplementary equipment, needed for the diagnosis, therapy or surgery, to the frame in a proper position. When performing diagnosis, therapy or surgery proceedings to the head, it is for obvious reasons extremely important that the area to be treated, is localized with a large precision, as well as that the treatment is performed in the proper area, which necessitates positioning of the equipment with large precision on the frame.
More precisely, when diagnosing and locating areas in the head to be treated, it is common practice to perform some kind of imaging of the head, e.g. by means of Magnetic Resonance Imaging, and for this purpose it is known in the art to place an indication box, having fiducials or reference markings, which are visible in the imaging method used, on the frame to be able to establish the frame position in the images. It is therefore important to be able to position the frame and the indication box in an as accurate defined relationship as possible. For this purpose it is known in the art to provide the frame with guiding and connecting holes or bores and the indication boxes with matching pins to locate the indication box correct on the frame. At least two bores and pins, respectively, are required for proper positioning. To enable firm holding of the indicating box onto the frame, there are generally also provided some other kind of fixation device such as one or more tensioning clamps.
However, as the frame is deformed during attachment on the head, a certain play must be provided between the holes in the frame and the pins on the indication box, in order to allow mounting and removal of the indicating box while the frame is attached to the head. Consequently, the frame and indication box are somewhat movable in relation to each other, which decreases the precision of the identified position during imaging.
Other types of supplementary equipment which might be desired to mount on a frame of this kind, is e.g. a graduated scale and/or a guide member for positioning and displaceable mounting of instruments for diagnosis, treatment or surgery, for example surgical instruments or needles for taking of samples or treatment. Furthermore, the frame is often used as a fixture for steady mounting of the patient's head to different kinds of equipments or apparatuses, such as image producing equipment, for image scanning of the head, or equipment for radiation treatment of chosen areas inside the head. The same problems as in connection with the indicating boxes above, applies also here, i.e. due to the deformations of the frame when attaching it to the head, it is necessary to provide a play between the holes and the pin in, order to allow mounting and removal of the equipment, with decreased accuracy of the equipment position as a result.
The object of the invention is to eliminate or reduce the above mentioned problems associated with prior art devices, and provide a connecting device for interconnecting a ring-shaped frame and a supplementary equipment with an enhanced precision. At least this object is achieved by a device according to claim 1.
Accordingly, the object is achieved by a device comprising connecting holes formed in the frame and connecting pins on the equipment, wherein each hole opens into a surface of the frame and has an enlarged portion, which preferably is outward diverging, closest to the surface and a cylindrical portion beyond the enlarged portion.
The reason why such a design of the holes and pins is advantageous in respect of the precision when interconnecting the frame and the equipment to each other, is that when deforming of an object, which in the case of a frame can be approximated to a beam, by applying a bending moment to it, one side of the object will be exposed to tensile stresses whereas the other side will be exposed to compressive stresses. Accordingly, due to the deformation, one side will be displaced in one direction and the other side will be displaced in the other direction. Somewhere there between, usually in the middle, the tensile forces, and the displacement, will accordingly be zero. This position is called the neutral layer. By locating the cylindrical portion of each hole in or near the neutral layer and make it appropriate short, this part of the hole will not, or at least to a small extent, be displaced and, consequently, no or only a small play has to be provided between the holes and the pins in order to compensate for the deformation and resulting displacement. By designing the holes with an enlarged portion closest to the opening in the surface of the frame, this portion of the frame will not affect the pin with a misalignment or bending moment, despite any deformation, and the equipment will be easy to mount and remove even when the frame is attached to the head.
Although the holes are designed as outlined above, in a preferred embodiment of the invention, the holes and the pins are located in positions where the deformation of the frame, when attached to a head, will be small or minimal. Such positions may be calculated by any calculation method known in the art, such as by the finite element method (FEM-analysis), or be measured upon loading of the frame.
Within the scope of the invention, it is envisaged that the pins may be cylindrical or have any other appropriate shape. However, according to a preferred embodiment, the pins are formed with a bulge or a ball having a cross sectional dimension which is equal to or slightly smaller than the cross sectional dimension of the hole, whereas a shaft portion of the pins has a smaller cross sectional dimension. By this, the contact surface between the hole and the pin will be advantageously small so that the risk that a possible difference in angle between the hole and the pin will cause a bending moment on the pin, is further reduced.
In a hereinafter described and in the drawings illustrated embodiment of the invention, the holes and the pins are directed perpendicular to a plane of the ring-shaped frame, i.e. the holes are formed in the upper and lower edge of the frame. However, the invention is not limited to that embodiment. On the contrary, the holes and pins may be arbitrary directed, according to desire and requirement, e.g. also in a direction in parallel to the plane of the frame with the holes opening through the lateral surfaces of the frame. Provisions may even be made to attach equipment from two opposite directions, e.g. from above and below, as is shown in an embodiment in the drawings. Besides such an embodiment, it is however not necessary for the holes to extend completely through the frame. On the contrary, the holes can also be terminated inside the frame.
Two holes and pins are normally required to position and prevent rotation of an arbitrary equipment with large precision in a predetermined location. In order to enhance the precision further it is advantageous to design the holes and pins such that the holes are either circular in cross section and the pins are oval, or the holes are oval in cross section whereas the pins are circular. In this way the hole and pin pair will contribute to the exact positioning in one direction only. One such hole and pin pair may preferably be combined with an ordinary hole and pin pair which restrain the movement in all directions. Hereby, the risk of stresses between the equipment and the frame, due to deformation of the latter, is further reduced.
The enlarged portion of each hole may have any arbitrary, appropriate form. In a preferred embodiment it is conical and diverging towards the frame surface, but it is to be understood that it need not be linearly diverging in a longitudinal section. On the contrary it can also have the form of a cylindrical hole with larger diameter in relation to the pin guiding cylindrical portion further inward in the frame.
The invention will hereinafter be described, by way of example, with reference to the accompanying drawings, in which:
Reference is first made to
When using the frame for imaging and diagnosing of areas inside the head, an indication box 5, having reference markings which are visible in the imaging method being used, can be mounted onto the frame as is indicated in
In
By adaptation of the cross sectional dimension of the pin 7 such that it is equal to or slightly smaller than the cross sectional dimension of the cylindrical portion 10 of the hole 6, it is possible to obtain a well defined position for the pin 7 in the hole 6, and consequently a well defined position of the indication box 5 on the frame 1. At the same time, the diverging portion allows for easy mounting and removal of the indication box, despite any deformation of the frame, since the deformation will affect the surface areas of the frame mostly, whereas the cylindrical portion, which is located in or in the vicinity of the neutral layer, as has been described hereinbefore, will be comparatively unaffected.
In
In
| Number | Date | Country | Kind |
|---|---|---|---|
| 0501002-0 | Apr 2005 | SE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE2006/000481 | 4/26/2006 | WO | 00 | 10/23/2007 |
