CRANIAL BOLT

Abstract: A cranial bolt is disclosed for connecting one or more elongate, flexible members such as catheters with the interior of the skull, wherein the bolt comprises a hollow shank having one threaded end and a second end opposite said threaded end for receiving one or more elongate members, each said member being retained in said second end and communicating with a passageway in the shank extending to the threaded end.

Description: Cranial Bolt This invention relates to cranial bolts or screws and systems for monitoring physiological functions in human and animal brains. Cranial bolts are frequently used for temporarily securing a catheter to the skull, the catheter being used for monitoring intercranial pressure in the intensive care of patients who have suffered head injuries. In one procedure a catheter is introduced into the brain through a hollow bolt and the intercranial pressure measured by means of a sensor in the tip of the catheter. The catheter may be inserted into various parts of the brain. Where it is introduced into a cranial ventricle, the catheter may also be used to draw off cerebral spinal fluid (CSF) in order to alleviate pressure increases or to analyse samples of the CSF. Existing cranial bolts are bulky and typically incorporate a Luer lock or other device for fixing the catheter securely to the bolt. More recently interest has arisen in measuring a number of physiological parameters in the brain during intensive care. If a number of securing devices, such as Luer locks are incorporated in the bolt, it becomes even more bulky and awkward to use. It is now proposed to provide a cranial bolt in which one or more tubes (or a single multi-lumen catheter) are fixed directly into a hollow shank foraiing the body of the bolt and individual passageways are provided within the shank for passing probe(s) or tube(s) into desired positions in the brain. According to one aspect of the invention there is provided a cranial bolt for connecting one or more elongate, flexible members, such as tubes, cables, filaments or the like, with the interior of the skull, said bolt comprising a hollow shank having one threaded end and a second end opposite said threaded end for receiving one or more elongate members, each said member being retained in said second end and communicating with a separate passageway in the shank extending to the threaded end. Conveniently the tube or tubes or other elongate member are fixed into the end of the shank with adhesive. It will be appreciated that instead of fixing a plurality of individual catheters into the second open end of the shank, a multi-lumen catheter could be fixed into the end of the shank and probes or smaller tubes fed through respective lumens and passageways into the brain. The term 'multi-lumen catheter' is used here in a broad sense and may comprise a bundle of individual tubes which are gathered together, e.g. by enclosing them in a common external sheath, or held together by a non-tubular gathering device such as a series of external rings or a spring-like coil. Alternatively, the multi-lumen catheter may be a catheter in which two or more lumens are extruded integrally so that externally the catheter appears to be a single tube. Whatever the particular construction selected, the individual lumens are split out of the assembly at the point where the catheter enters the shank and individual connections are made to passageways therein. Similarly, at the end of the assembly remote from the shank, the lumens are split out of the assembly and individual connections made to appropriate devices, e.g. via Luer locks. Although the shank may be manufactured from plastics material, e.g. an engineering plastic such as polycarbonate, the shank is preferably made from metal. Some plastics are hard enough to cut a thread in the skull but metals do this more efficiently. Titanium or its alloys are preferred because they are non-magnetic and interfere less than other materials in magnetic scanning procedures. The bolts of the present invention are designed to make use of the n inimum of metal. In order to facilitate manipulation of the bolt and manually screwing the bolt into the skull while nrinimising the amount of metal employed in manufacturing the bolt, a metal shank is preferably received within a plastics body member which may be moulded with wings or other projections to permit the member to be gripped and the shank screwed more easily into a hole in the skull. Preferably the shank is generally cylindrical and preferably formed with a central axial passageway and a further passageway or passageways disposed around the central passageway. The central passage preferably has a larger cross-section than the further passageways and may be used for example, for draining CSF fluid. The further passageways are preferably angled with respect to the central passageway. For example, they may be inclined at an angle between about 3 and 15° (such as about 5 to 10°) to the longitudinal axis of the shank. In order to avoid the danger of the catheters kinking, particularly at or close to the point where they enter the shank, a kink-resistant catheter construction is preferred. Flexible tubes can be made kink-resistant by stiffening them with a spring, such as a coil spring. The spring may be metal or plastic but preferably is a tubular metal coil spring, and the wire from which it is made preferably has a generally flat cross-section. In order to miriimise flow disturbance or contamination of fluids in the tube, the spring is preferably embedded or encapsulated in the wall of the tube or is sandwiched between coaxial tubes which form the catheter. Catheters such as described in US Patents Nos. 5380304 and 5700253 and in our US Patent Application No. 09/093,934 are preferred, and their disclosure is specifically incorporated herein by reference. The invention is illustrated by the following specific description and accompanying drawings of cranial bolts in accordance with the invention, in which: Figure 1 is a perspective view of cranial bolt showing a member of catheters fixed to its receiving end, Figure 2 is a perspective view of the same bolt in an exploded view, and Figure 3 is a schematic, partly in section, showing one way in which the bolt maybe fitted to a patients skull. Referring to the drawings, the cranial bolt comprises a generally cylindrical shank 1 having a threaded lower end 2 for securing the bolt into a preformed hole in the skull 30, see Figure 3. The distal end 3 of the shank has a smaller diameter than the threaded portion 2. This is to prevent the passageways within the shank being occluded by uncut portions of the skull at the inner end of the hole which has been cut to receive the threaded end. This arrangement may also avoid the need to ream the hole in the skull after cutting a hole of appropriate size to receive the shank and therefore simplify installation of the bolt. The shank 1 is formed at its upper end with a shaped profile 4 adopted to engage in a hole 5 in a plastic body member 6. Body member 6 is formed with wing-like projections 7 to facilitate screwing the threaded part 2 of the shank into a preformed hole in the skull. Body member 6 may be moulded separately from the shank or moulded onto the upper part 4. At its upper end, the body member 6 is formed with a part 8 which is connectible with a flexible collar 9. Collar 9 may be manufactured from a flexible, resilient plastics material and is a push fit onto the end part 8 of the shank or moulded in situ onto the end of the shank. The collar 9 helps to prevent chafing of the tubes 21,22. Shank 1 is formed internally with a plurality of passageways. As seen best in Figure 2, one of the passageways 10 is larger than the other two 11. Passageway 10 preferably extends axially of the shank and is sized to house a drainage catheter. The passageways 11 may be disposed around the major passageways 10 and are designed to accommodate small catheters or probes for sensing parameters, such has oxygen concentration, carbon dioxide concentration, pH and temperature. Figure 1 illustrates one way in which tubes 20, 21, 22 are grasped together and anchored to the bolt fixed into the extension piece 9, by fixing with adhesive into the shank portion. The distal ends of the tubes 20, 21, 22 may be sealed into the passageways 10, 11. The tubes 20, 21, 22 may constitute tubular guides through which sensors or smaller catheters are fed to the desired site. This is illustrated in Figure 1 in which a catheter 23 is fed through tube 22, passes through the respective passageway in the shank and exits through the distal end of the shank. A Luer lock 24 is provided to maintain the catheter in the desired position after it has been located in the brain. A further alternative method of feeding probes or catheters into the bolt is to provide a multi-lumen tube which is fixed into the shank. Individual lumens are divided from the multi-lumen tube and aligned with passageways in the shank. Probes or catheters having diameters smaller than a lumen can then be fed into a respective lumen and passageway and into the brain through the distal end of the bolt. The tubes, 20, 21 and 22 are preferably kink-resistant, at least over the portion from the shank 1 to the Luer lock or locks 24. Because the tubes or catheters are grouped together in the flexible collar 9 and extend axialfy of the shank, the bolt has a minimum lateral spread. This is advantageous because a bolt which is bulky and has in-feed catheters extending from the bolt in various directions is more likely to be knocked or displaced accidentally during nursing or handling the patient. Figure 2 shows, in two scrap views, alternative arrangements for the location of the passageways through the shank. In practice it may be desirable to form the outer passageways 11 so that they are inclined at a small acute angle to the longitudinal axis of the shank. Preferably the angle is 3 to 15°, e.g., 4 to 8°. Figure 3 shows one method of fitting the cranial bolt into the skull 30. The scalp 31 is cut away for a sufficient distance to gain access to the skull and a hole is cut in the skull of a size which is just less than the diameter of the threaded part 2. The bolt can then be secured in the hole in the skull, by securing the threaded part into the skull. Once the bolt has been secured into the skull, catheters are passed through the guide tubes 20, 21 and 22 into the bolt and through the internal passageways in the bolt into the desired positions in the brain. Guide tubes 21 and 22 may be fixed e.g. by adhesive into the upper part of the bolt. When the bolt is to be removed, the catheters are first withdrawn and the bolt is then removed by unscrewing the shank. The bolt in accordance with the invention can be used to install single or multi- lumen catheters, sensors or drainage or sampling tubes into various parts of the brain, including the ventricles, sub-dural, epidural or parenchymal areas of the brain. Sampling tubes may include microdialysis catheters in which a saline solution is passed down one lumen and samples of chemicals in the brain are extracted through a second lumen via a membrane, and the extracted fluid analysed.

Claims: CLAIMS:- 1. A cranial bolt for connecting one or more tubes with the interior of the skull, said bolt comprising a hollow shank having one threaded end and a second end opposite said threaded end for receiving one or more tubes, each said tube being retained in said second end and communicating with a separate passageway in the shank extending to the threaded end. 2. A bolt as claimed in claim 1, wherein the tube or tubes are retained by fixing means within said second end. 3. A bolt as claimed in claim 2, wherein said fixing means is an adhesive. 4. A bolt as claimed in any one of the preceding claims wherein the shank is received within a plastics body member which has wing-like extensions to facilitate screwing the bolt into the skull. 5. A bolt as claimed in claim 4, wherein the plastics body member is moulded on the shank. 6. A bolt as claimed in any one of the proceeding claims wherein the shank includes a central passageway which is substantially co-axial with the axis of the shank and one or more further passageways which are disposed around said central passageway. 7. A bolt as claimed in claim 6, wherein the further passageways are angled outwardly with respect to said central passageway. 8. A bolt as claimed in claim 7, wherein the axes of the further passageways are inclined to the longitudinal axis of the shank at an an^le between about 3 and 15°. 9. A bolt as claimed in any one of the preceding claims wherein at least one of the said tubes comprises a catheter including a sensor for assessing a desired parameter. 10. A bolt as claimed in any one of the preceding claims wherein one or more of said tubes include an internal reinforcing spring which imparts kink resistance thereto. 11. A modification of the cranial bolt claimed in any one of the preceding claims wherein the bolt comprises a hollow shank which is threaded at one end and open at the other for reception of a multi-lumen catheter, said catheter being fixed into said open end and wherein the shank incorporates passageways corresponding to the lumens in the catheter, whereby an elongate flexible probe or tube can be passed through a respective lumen and passageway and be thereby guided into a desired position in the brain. 12. A cranial bolt for connecting one or more elongate, flexible members, such as tubes, cables, filaments or the like, with the interior of the skull, said bolt comprising a hollow shank having one threaded end and a second end opposite said threaded end for receiving one or more elongate members, each said member being retained in said second end and communicating with a separate passageway in the shank extending to the threaded end. 13. Use of a cranial bolt for securing a catheter to the skull by fixing the bolt into the skull and guiding the catheter through a hole cut in the skull, said bolt comprising a hollow shank which is threaded at one end for fixing to bone surrounding said hole and at a second end for receiving the catheter, said catheter being retained in said second end and communicating with a passageway in the shank extending to the threaded end.

Inventors: CRANE BARRY C, IRVINE MICHAEL P, MARKLE DAVID R, CRANE, BARRY, C., IRVINE, MICHAEL, P., MARKLE, DAVID, R.
Applicants: CRANE BARRY C, DIAMETRICS MEDICAL LIMITED, IRVINE MICHAEL P, MARKLE DAVID R, CRANE, BARRY, C., IRVINE, MICHAEL, P., MARKLE, DAVID, R.
Application year: 1999
Main classification: A61M1
IPC codes: A61B19, A61M1, A61M25