Patent Publication Number: US-2005115368-A1

Title: Screwdriver for bone screws

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates to a screwdriver for bone screws, especially for compression screws and locking screws on a bone nail. More particularly the invention relates to a flexible screw driver for use in surgery.  
      From DD 238 724 A1, a medical screwdriver is known, which embraces a screw head with positive and non-positive fit.  
      From DE 101 18 570 A1, a surgical drill is known, the shaft of which has a central longitudinal bore for a fibre-optical position transmitting device. The shaft of the drill has a clutch, upon which a drill head can be placed, a flexible shaft portion made from coiled spring steel directly adjoining to the clutch and a rigid shaft portion connected to the flexible shaft portion. A longitudinal continuous bore extends through the shaft with the rigid and the flexible shaft portions, into which bore a position transmitting device is introduced. Further, in DE 101 18 570 A1 it is proposed to insert a screwdriver or another tool into the clutch. With this drill, it has proven to be disadvantageous because it is hard to manipulate, especially when used as a screwdriver, and that it is difficult to clean after using thus requiring considerable expenditure of work.  
     SUMMARY OF THE INVENTION  
      The invention has as one aspect to create a screwdriver which avoids the aforementioned disadvantages and which allows safe operation by the surgeon.  
      According to the invention, this aspect is provided for by a screwdriver for bone screws, especially for compression and locking screws, having a handle, a shaft extending out from the handle, which shaft has a screw driving or other tool at a free end thereof. The shaft has a flexible portion and two rigid portions on either side of the flexible portion. The flexible shaft portion has a flexible element for transmitting torque. At least the flexible shaft portion is surrounded by an elastic protective hose or elastomeric sheath. The flexible shaft portion has a holding portion on each of its ends, respectively, the flexible element being held between the holding portions. Normally, the holding portions are solid. Preferably, the flexible element consists of a coiled wire, however, various other flexible shaft designs for torque transmission can be used such as a tube. If a tube is used the tube element can be provided with slits which run transverse to the longitudinal direction. The hose or sheath preferably consists of a biocompatible material such as silicone rubber. Preferably the diameter of the shaft in the flexible area is larger than the rigid shaft portions. The diameter of the connecting shaft between the handle and the flexible portion may have a diameter which increases moving towards the flexible portion in a conical form. Likewise, the shaft between the tool at the free end of the screwdriver or other instrument and the flexible region tapers towards the tool on the conical form. While the handle preferably is essentially circular, it may have a flattened side with the flattened side indicating a known orientation of the tool. Preferably, the flexible portion has a length which is less than half (½) but greater than one third (⅓) the total length of the instrument, i.e. between ½ and ⅓ of the length from the top of the handle to the free end of the instrument. The sheath may be rubber, plastic, or other elastomeric materials and may have a diameter of approximately 10 mm and a thickness of approximately 2 mm.  
      The screwdriver according to the invention is provided for bone screws, especially for compression screws and locking screws on bone nails. The screwdriver has a preferably longitudinal handle, with a shaft centrally extending out from the handle. A screw driving tool is provided on the free end thereof to match the drive on the screw. The shaft has a flexible shaft portion. According to a preferred embodiment of the invention, the shaft has two rigid portions provided on both sides of the flexible shaft portion. Preferably, the flexible shaft portion has on each of its two ends one holding portion, respectively, and a flexible element held between them. Preferably, the flexible element consists of a flexible tube element or of a helically coiled wire. At least the flexible shaft portion is surrounded by an elastic protection tubular cover or hose. The arrangement of the flexible shaft portion between two rigid shaft portions allows for a safe and precise handling, the surgeon having good control over the torque exerted. The flexible shaft portion with a flexible element creates the possibility for continuous bending of the shaft. The elastic protection hose, arranged at least across the elastic shaft portion, prevents the intrusion of blood and tissue into the flexible shaft portion and thus facilitates cleaning and disinfection of the screwdriver after use.  
      In the preferred embodiment of the flexible element as a flexible tube element, the latter is preferably formed by a metal tube, the outer wall of which presents slits which extend transversely to the longitudinal direction. Preferably, the protection hose consists of a biocompatible material, silicone being particularly suited.  
      In a preferred embodiment, the diameter of the shaft is larger in its flexible portion than in the rigid portions.  
      The cross section of the shaft, between handle and flexible portion, increases towards the flexible portion in a conical form. Also, the cross section of the shaft between tool and flexible portion may taper towards the tool in a conical form.  
      In one preferred embodiment, the handle with an essentially circular cross section has one flattened side, the flattened side indicating the orientation of the screwdriver or other tool. Through this, the surgeon operating the screwdriver can obtain an impression of the orientation of the tool, even when the tool point is not visible or only partly visible.  
      For better handling of the screwdriver, it has proven to be particularly advantageous that the flexible portion has a length which accounts for less than half of the total length. Preferably, the length of the flexible portion with respect to the total length is longer than one third of the total length, however.  
      In the preferred embodiment, the rigid shaft portion with the screwdriver tool is shorter than the second rigid shaft portion.  
      In a preferred construction, the screwdriver tool is formed in one piece on the free end of the rigid shaft portion. The tool, of course, could be modular. In a functional construction, the holding portions and the flexible element have a diameter of approximately 10 cm, the hose having preferably a wall thickness of approximately 2 mm. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention will be better understood on reading the following detailed description of non-limiting embodiments thereof, and on examining the accompanying drawing, in which:  
       FIG. 1  is an elevation view of one preferred embodiment of the screwdriver according to the invention is hereinafter explained in more detail by means of the figure. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The single figure shows a medical screwdriver  10 , with a handle  12 , a first rigid shaft portion  14 , a flexible shaft portion  16  and a second rigid shaft portion  18 . The handle  12  has a flattened side  20 , which extends along the longitudinal axis of the shaft. The rigid and massively realised, preferably solid, shaft portion  14  juts out of the handle  12 , the diameter of which increases conically upon the transition to the flexible portion  16  in a region  22 .  
      The flexible portion  16  has on its two ends one holding portion  22  and  24 , respectively, between which a helically coiled wire, from spring steel e.g., is held. A protective hose  30  of elastic, biocompatible material is drawn on the portions  24  and  26  as well as over the flexible wire. In the represented preferred example, the protective hose is a hose from silicone material, having a wall thickness of approximately 2 mm.  
      Besides the represented variant, in which the flexible region  28  is made from a helically coiled wire, it is also possible to form the flexible region by a thin-walled metal tube, the outer wall of which is interrupted by slits standing transversely to the longitudinal axis, through which bending of the metal tube becomes possible. For example, see U.S. Pat. Nos. 6,337,142 and 6,416,517 the teachings of which are incorporated herein by reference. Alternatively, thin-walled profiled metal tubes may be used to create the flexible portion  16 . When using a metal tube, it is important that an almost continuous bending can take place within a predetermined range of angles.  
      The protection hose  30  preferably terminates on the shaft on its two ends flush with the outer walls  32  and  34 .  
      The rigid portion  18  adjoins to a conical portion  36  adjacent to the flexible region  16 . The tool tip  38  is formed on the rigid portion  18  and verges via a region  40 , which also enlarges conically, into the rigid region  18 .  
      The total length of the screwdriver according to the invention is composed of the length A of the rigid portion  18 , the length B of the flexible portion  16 , the length C of the rigid portion  14 , and the length D of the handle  12 . The length proportions are herein selected such that the rigid portion  18  with its length A is shorter than the rigid portion  14  with its length C (A&lt;C). The flexible portion  16  with its length B is longer than each of the rigid portions and the handle (B&gt;A, B&gt;C, B&gt;D). With respect to the total length (A+B+C+D), the flexible portion  16  has a length B which is smaller than half the total length ( 2 B&lt;A+B+C+D) and larger than one third of the total length ( 3 B&gt;A+B+C+D).  
      The represented screwdriver with flexible shaft is particularly suited for the driving of screws which are disposed on a bone nail, like compression or locking screws, e.g. The particular advantage is that the driving of the screw by hand does not have to proceed in a straight-lined prolongation of the screw axis. Thus, this prevents the space for the screwdriver handle from being blocked by the patients body, as is the case by the iliac wing upon the anterograde access in the femur.  
      Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.