Neurosurgical instruments

Abstract

A catheter assembly for insertion into the brain. The assembly comprises a first length of tubing made of a first material. A second material surrounds the first length of tubing, the second material being more flexible than the first material and having a hardness of less than 50 Rockwell E. The second material provides damping to the first length of tubing.

Claims

1. A catheter assembly for insertion into a brain cortex, the assembly comprising: a catheter comprising a distal opening for delivery of therapeutic agents to the brain cortex at a target site; an inner element receiving the catheter; and a guide tube receiving the inner element, wherein: a length of the inner element received in the guide tube is movable axially relative to the guide tube and is stiffer than equivalent lengths of the catheter and the guide tube, and when the distal opening of the catheter is located at the target site, at least part of the inner element and at least part of the guide tube are located within the brain cortex.

2. A catheter assembly according to claim 1, wherein the inner element is made of stiff material.

3. A catheter assembly according to claim 2, wherein the stiff material is stainless steel.

4. A catheter assembly according to claim 2, wherein the stiff material is fused silica.

5. A catheter assembly according to claim 1, wherein the inner element is an inner tube.

6. A catheter assembly according to claim 1, wherein the catheter is a stiff-tipped catheter.

7. A catheter assembly according to claim 6, wherein the catheter comprises a fused silica tip.

8. A catheter assembly according to claim 1, wherein the catheter is made of PEEK material.

9. A catheter assembly according to claim 1, wherein the catheter is arranged to extend into the brain cortex beyond distal ends of the inner element and the guide tube.

10. A catheter assembly according to claim 1, wherein the length of the inner element received in the guide tube is longer than a width of the inner element.

11. A catheter assembly for insertion into a brain cortex, the assembly comprising: a catheter comprising a distal opening for delivery of therapeutic agents to a target site within the brain cortex; an inner tube receiving the catheter; and an outer tube receiving the inner tube, wherein the inner and outer tubes are arranged such that, when inserted in the brain cortex with the distal opening of the catheter located to deliver therapeutic agents to the target site: at least part of the inner tube and at least part of the outer tube are located within the brain cortex, and brain matter integrates into the catheter assembly between the catheter and the outer tube to aid formation of a seal between the catheter assembly and the brain cortex, which prevents reflux of the therapeutic agents, delivered into the brain cortex through the catheter, along the inner and outer tubes.

12. A catheter assembly according to claim 11, wherein the lengths of the catheter, the inner tube, and the outer tube are arranged such that the inner tube extends into the brain cortex further than the outer tube and the catheter extends into the brain cortex further than the inner tube.

13. A catheter assembly according to claim 11, wherein the catheter is made of material such that a distal portion of the catheter is stiffer than a proximal portion of the catheter.

14. A catheter assembly according to claim 11, wherein the catheter assembly includes an annular gap between the inner tube and the outer tube.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described by way of example with reference to the following drawings:

(2) FIG. 1 illustrates a side view of a guide tube;

(3) FIG. 2 illustrates a side view of an inner tube;

(4) FIG. 3 illustrates a side view of a catheter;

(5) FIG. 4A is a side view of the assembled guide tube, inner tube and catheter;

(6) FIG. 4B illustrates the assembled guide tube, inner tube and catheter inserted into the brain; and

(7) FIG. 5 a cross section of the ends of the catheter, inner tube and guide tube inserted into the brain.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(8) FIGS. 1-3 illustrate a guide tube, inner tube and catheter respectively according to the present invention.

(9) The guide tube 10 is shown in FIG. 1 and comprises a length of tube 12 with a hub 14 at one end. In this example it is made from a polyurethane plastic such as carbothane 55DB20. However, it may be made from any material which is biocompatible and sufficiently rigid at room temperature to maintain its central aperture. In this example, the tube 12 has an outer diameter of 0.6 mm and an inner diameter of 0.5 mm.

(10) The guide tube is inserted into: the brain through an aperture (e.g. burr hole) in the skull created by the surgeon. Once the length of tubing is inserted into the brain, the hub can be attached to the patient's skull, for example by bonding into a burr hole in the skull using an acrylic cement. A wire may be used to guide the guide tube into place, as disclosed in WO03/07784. Before insertion, the guide tube is cut to a length short of the target. The distal end of the guide tube will typically fall several millimetres short of the target.

(11) The hub of the guide tube is preferably domed and has a cut out slit 16 which links the central aperture of the tube to a side of the hub.

(12) The inner tube 18 is illustrated in FIG. 2 and comprises two connected lengths of tubing, the distil tubing 20, which in this example has an outer diameter of 0.42 mm and an inner diameter of 0.2 mm and proximal tubing 22 which has a larger diameter. A stop element 24 links the proximal and distil tubing. The distal and proximal lengths of tubing are typically made of a polyurethane plastic, such as carbothane 85AB20, although other material could also be used. The stop element 24 is in this case also constructed using polyurethane plastic, such as carbothane 72DB20. Again other suitable materials may be used.

(13) The stop element 24 has a central body 26 which is generally cylindrical and a pair of diametrically opposed wings 28,30 each containing a countersunk hole 32,34 whereby the stop element may be screwed to the outer surface of the skull of the patient. The inner tube with distal and proximal lengths of tubing and stop element is described in more detail in WO03/077785.

(14) The stop element has two roles. Firstly, when the inner tube is inserted into the guide tube, the stop element abuts against the hub of the guide tube, thereby forming a stop and defining the length of the distil tubing which extends from the tubing of the guide tube. Secondly, the wings of the stop element are used to fix the inner tube to the skull of the patient.

(15) The role of fixing the inner tube to the skull of the patient may be accomplished by alternative means. For example, a pair of wings may be provided on the proximal tubing, for example by overmoulding onto the tubing. These wings may be provided with apertures to receive screws which when screwed into the skull fix the wings and proximal tubing in place. This arrangement allows one wing to be folded onto the other, so that a single screw is inserted through both apertures of the wings. This arrangement has the advantage that it causes some clamping of the catheter within the proximal tubing.

(16) The catheter 36 is illustrated in FIG. 3 and comprises a fine length of tubing 38 and is typically made from fused silica. Alternative materials may be used which are inert and have low viral binding properties. The fused silica typically has an outer diameter of 0.2 mm and an inner diameter of 0.1 mm. The catheter is provided at one end with a barb 40 which acts as a stop. This may be directly moulded onto the catheter and may be made from a polyurethane plastic such as carbothane.

(17) The barb 40 has a stepped cylindrical profile with a central aperture. A region of greatest diameter 41 has straight sides which form a stop against which the end of the proximal tubing abuts when the catheter is inserted into the inner tubing. On either side of the region of greatest diameter is a cylindrical portion 43 with a waisted 45 portion of decreased diameter. In use, tubing is pushed over the cylindrical portion until it abuts the region of greatest diameter 41. As the tubing passes over the waisted portion 45 it deforms to form a seal. As the catheter 36 is inserted into the inner tubing 18, the end of the proximal tubing 22 is pushed over one of the cylindrical portions 43. Connector tubing (not shown) which connects the catheter to a pump may be attached to the other cylindrical portion of the barb in the same manner.

(18) In order to perform neurosurgery, the surgeon needs, in the first instance, to understand the patient's neuroanatomy and hence identify the position of the desired target. This is normally achieved by fixing a stereotactic reference frame to the patient's head, elements of which can be seen on diagnostic images, and from which measurements can be made. The stereotactic frame then acts as a platform from which an instrument is guided to a desired target using a stereoguide that is set to the measured co-ordinates. Once an instrument is guided to the desired target treatment can begin. This is described in more detail in WO03/077784.

(19) The guide tube is inserted into the brain using the secured stereoguide and fixed in place as described above. FIGS. 4A and 4B illustrate the assembled guide tube 10, inner tubing 18 and catheter 36. FIG. 4A is the assembly outside the skull and FIG. 4B is the assembly with the catheter inserted into the brain 42. FIG. 4B illustrates the hub 14 of the guide tube 10 fixed in place in a hole in the skull 44 by bone cement 46. The inner tube is inserted into the guide tube by inserting the distil tubing 20 into the guide tube 10 until the stop element 24 abuts the hub 14 of the guide tube. The stop element 24 thus acts as a stop to control the amount the length of the inner tubing which is inserted into the brain. The catheter 36 is inserted into the inner tube and is pushed through until its barb abuts the end of the proximal tubing 22 of the inner tubing.

(20) Once the guide tube, inner tube and catheter are all inserted, the proximal tubing containing the catheter extending out of the skull from the hub of the guide tube are bent through 90 degrees so that the stop element lies flat against the skull, as illustrated in FIG. 4B. This is then fixed in position using screws 48 passing through the countersunk holes. The cut out slit 16 in the hub 14 of the guide tube allows this 90 degree bend. Further clamping may be provided by additional fixing means on the inner tube (such as wings over moulded on the inner tube) through which screws may be attached to the skull.

(21) The length of guide tube, inner tube and catheter are arranged so that the inner tube extends into the brain further than the guide tube (e.g. 10 mm) and the catheter extends into the brain further than the inner tube (e.g. 10 mm).

(22) With the guide tube, inner tube and catheter all in place, the catheter can be connected to a pump (not shown) via connector tubing which connects to the barb of the catheter.

(23) This arrangement has the advantage that it minimizes vibration of the catheter this is described in more detail below with reference to FIG. 5, which shows an enlarged view of the end of the catheter, inner tubing and guide tube inserted into the brain.

(24) When the guide tube is inserted into the brain it will fill with cerebro spinal fluid (CSF). The amount of cerebro spinal fluid in the guide tube will vary along its length. When inner tube and catheter are inserted into the guide tube, an annular gap 50 is created between the tubing 12 of the guide tube and the distil tubing 20 of the inner tubing and this annular gap will contain the cerebro spinal fluid. In this example the annular gap 50 is approximately 0.01 mm. As therapeutic agent is pumped to the end of the catheter and into the brain tissue, some backflow may occur along the cuter surface of the catheter and inner tubing and some therapeutic agent in this backflow may pass by capillary action into the annular gasp between the inner and cater tubing. The fluid between the inner tubing and guide tube has a damping action and reduces vibration of the catheter and inner tubing. Thus this arrangement of concentric tubing and an annular gap between the tubing creates a damping effect.

(25) In this embodiment the catheter is made from a relatively stiff material, i.e. fused silica, whereas the inner tubing is made from a more flexible material (i.e. carbothane 85AB20). The use of a more flexible material in the inner tubing than the catheter also provides a damping effect, thus reducing or eliminating vibration of the inner and outer tubing.

(26) In an alternative embodiment, the fused silica catheter could be over moulded with a more flexible substance, such as a polyurethane plastic to create the same effect.

(27) The Thermedics Carbothane PC-3572D-B20 Polycarbonate based polythurane Biomedical Elaster has a hardness of 71 shore D. Materials with a stiffness of less than 50 Rockwell E provide sufficient damping.

(28) Another suitable material is PEEK optima (manufactured by INVIBIO) which has a Rockwell (M) hardness of 99 (in its granular form).

(29) The guide tubs is also made of a more flexible material than the catheter (i.e. carbothane 85AB20) and this also contributes to the damping effect.

(30) The inner tube is not essential to the invention and the catheter may toe inserted directly into the guide tube. The flexible material of the guide tube and the annular gap between the guide tube and catheter both provide damping to the catheter.

(31) The inner tube may be fabricated from a stiff material, for example having a modulus of elasticity of greater than 30 GPa. For example fused silica, which has a modulus of elasticity of 35-40 GPa or stainless steel suitable for surgical instruments or implant surgery which has a modulus of elasticity of 190-200 GPa. With a stiff inner tube, the damping is provided by the fluid in the annular gap between the catheter and the inner tubing. Alternatively, catheter may be inserted directly into a guide tube, without an inner tube, in which case the guide tube may be fabricated from a stiff material having the properties described above.