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

Description:
TECHNICAL FIELD 
     This invention relates to cranial bolts or screws and systems for monitoring physiological functions in human and animal brains. 
     BACKGROUND 
     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. 
     SUMMARY 
     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 forming 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 minimum of metal. 
     In order to facilitate manipulation of the bolt and manually screwing the bolt into the skull while minimising 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  25 , 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 minimise 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 U.S. Pat. Nos. 5380304 and 5700253 and in our U.S. patent application Ser. No. 09/093,934 are preferred, and their disclosure is specifically incorporated herein by reference. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is illustrated by the following specific description and accompanying drawings of cranial bolts in accordance with the invention, in which: 
     FIG. 1 is a perspective view of cranial bolt showing a member of catheters fixed to its receiving end, 
     FIG. 2A is a perspective view of the same bolt in an exploded view, and 
     FIG. 2B is a perspective, fragmented view of an alternate embodiment of the bolt, and 
     FIG. 2C is a perspective, fragmented view of another alternate embodiment of the 
     FIG. 3 is a schematic, partly in section, showing one way in which the bolt maybe fitted to a patients skull. 
    
    
     DETAILED DESCRIPTION 
     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 FIG.  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 FIG. 2A, 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 as oxygen concentration, carbon dioxide concentration, pH and temperature. 
     FIG. 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 FIG. 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 axially 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. 
     FIGS. 2B and 2C show alternate 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°. 
     FIG. 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  30  and a hole is cut in the skull  30  of a size which is just less than the diameter of the threaded part  2 . The bolt can then be secured to the hole in the skull  30 , by securing the threaded part  2  into the skull  30 . Once the bolt has been secured into the skull  30 , 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. The 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  1 . 
     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.