Patent Publication Number: US-2009228011-A1

Title: Cranial perforator

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present application generally relates to devices for drilling holes in the cranium. 
     2. Discussion of the Related Art 
     In many surgical operations it is necessary to obtain direct access to the cranial cavity and the brain. To perform such operations, it is often necessary to drill holes through the skull bone. Since the bone is very hard, it is necessary to apply significant pressure to drill through the bone, but it is also necessary to stop the drill once the bone has been penetrated to prevent damage to the dura. 
     A very satisfactory cranial drill with an automatic clutch mechanism for disengaging the drill when it approaches the interior layers of the skull bone or as it breaks through the interior of the skull is described in U.S. Pat. No. 4,456,010, issued Jun. 26, 1984, and U.S. Pat. No. 4,830,001, issued May 16, 1989, both of which are assigned to the assignee of the present invention, and the disclosures of which are fully incorporated by reference in their entirety in this application. 
     The invention described in U.S. Pat. No. 4,456,010 incorporates a sleeve about the exterior of the drill for holding the varius parts of the drill together during use. Sleeve  70  includes a raised portion  74  extending circumferentially on sleeve  70 , partially thereabout and is axially aligned with a recess  14  on drill body  10 . Raised portion  74  may be deformed radially inwardly to engage recess  14  on drill body  10  to hold sleeve  70  and driver  50  on drill body  10 . Although that arrangement works satisfactorily, it was found that this prior drill could be improved by incorporating a retaining ring in slot  14  shown in the previous patent, assembling the sleeve  70  over drill body  10  and then affixing the retaining ring to the inside surface of the sleeve, preferably by means of ultrasonic welding, as taught by U.S. Pat. No. 4,830,001. 
     Both of these perforators have an inner drill and an outer drill, with the outer drill having an outside diameter that is about 14 mm. Surgeons have recently requested smaller size drills while still incorporating the internal clutch mechanism to selectively transfer rotational movement from the driver to the drill member so that the drill will automatically release when the drill penetrates the skull. In addition, surgeons have requested a drill profile that will permit the surgeon a clear view while drilling. 
     Accordingly, there remains a need for a perforator that can drill smaller size holes in the skull while still having a clutch mechanism to release the drill once the skull is penetrated and that also provide a clear view of the drilling site. 
     SUMMARY OF THE INVENTION 
     In one embodiment, an exemplary cranial perforator includes a generally cylindrical driver, a generally cylindrical drill member and a generally cylindrical sleeve therebetween. The driver is connected to the proximal end of the sleeve. The drill member is connected to the distal end of the sleeve. The sleeve has an internal clutch mechanism to selectively transfer rotational movement from the driver to the drill member. The drill member has an inner drill and an outer drill disposed about the inner drill. The inner drill has a distal end that has only two drilling flutes. A proximal end of the outer drill has a first predetermined diameter D 1 . A distal end of the outer drill has a second predetermined diameter D 2 , with the first predetermined diameter D 1  being greater than the second predetermined diameter D 2 . A transition from the first predetermined diameter D 1  to the second predetermined diameter D 2  is a smooth, preferably radiused curve. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       Various exemplary embodiments disclosed herein will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a cranial perforator in accordance with the present invention. 
         FIG. 2  is a side view of the cranial perforator with parts broken away; 
         FIG. 3  is a front view of the cranial perforator; 
         FIG. 4  is a side view of the distal end of the inner drill portion of the drill member; 
         FIG. 5  is a top view of the distal end of the inner drill portion of the drill member; 
         FIG. 6  is an enlarged front view of the inner drill portion of the drill member; and 
         FIG. 7  is a side view of the distal end of the inner drill portion of the drill member similar to  FIG. 4 , but taken from the opposite side. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the devices disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present application. 
     The present application generally provides devices for drilling holes in bone, especially the skull. An exemplary cranial perforator  10  is illustrated in  FIGS. 1-7 . Perforator  10  includes a generally cylindrical driver  12 , a generally cylindrical drill member  14  and a generally cylindrical sleeve  16  therebetween. Sleeve  16  has a proximal end  18  and a distal end  20 . Driver  12  is connected to the proximal end  18  of sleeve  16 . Drill member  14  is connected to the distal end  20  of sleeve  16 . Sleeve  16  has an internal clutch mechanism  22  to selectively transfer rotational movement from driver  12  to drill member  14  in a manner known to those skilled in the art. An example of such a clutch mechanism is disclosed in co-owned U.S. Pat. Nos. 4,456,010 and 4,830,001, the disclosures of which are hereby incorporated by reference in their entirety. 
     Drill member  14  has an inner drill  24  and an outer drill  26  disposed about inner drill  24 . Inner drill  24  has a distal end  28  having only two drilling flutes  30 ,  32 , which are preferably beveled and angled at about 15°. Thus, drilling flutes  30 ,  32  are adapted to cut human cranial bone. Outer drill  26  has a proximal end  34  and a distal end  36 . Proximal end  34  of outer drill  26  has a first predetermined diameter D 1 , as shown in  FIGS. 2 and 3 . Distal end  36  of outer drill  26  has a second predetermined diameter D 2 , also as shown in  FIGS. 2 and 3 . Distal end  36  of outer drill  26  has four drilling flutes  40 ,  42 ,  44 ,  46 . As shown, first predetermined diameter D 1  is greater than second predetermined diameter D 2 . The transition  38  from first predetermined diameter D 1  to second predetermined diameter D 2  is a smooth curve, and preferably a radiused curve. Transition  38  is disposed proximate to the proximal end  34  of outer drill  26 . In a currently preferred exemplary embodiment, the first predetermined diameter is about 9 mm so that a relatively small hole can be created in the skull. In a currently preferred exemplary embodiment, a ratio of the second predetermined diameter D 2  to the first predetermined diameter D 1  is about 0.64. Thus, perforator  10  in accordance with the present invention is capable of drilling smaller size holes in the skull while still having a clutch mechanism to release the drill once the skull is penetrated. The use of only two flutes on the inner drill in combination with four flutes on the outer drill allows for cranial bone removal without binding and provides a clean cut when drilling smaller size holes. In addition, the smooth curve transition to smaller diameter D 2  near the proximal end of the outer drill provides the surgeon with a clear view of the drilling site. 
     A person skilled in the art will appreciate that the various devices disclosed herein can be formed from a variety of materials. Moreover, particular components can be implantable and in such embodiments the components can be formed from various biocompatible materials known in the art. Exemplary biocompatible materials include, by way of non-limiting example, composite plastic materials, biocompatible metals and alloys such as stainless steel, titanium, titanium alloys and cobalt-chromium alloys, glass, and any other material that is biologically compatible and non-toxic to the human body. 
     One skilled in the art will appreciate further features and advantages based on the above-described embodiments. Accordingly, the disclosure is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.