Abstract:
A device and method for stabilizing a broken bone while it heals is disclosed. The device is preferably a metal rod that has a threaded portion. The device is positioned into a bone, such as a metacarpal bone, by forming an opening in the bone suitable for receiving the device, and inserting it into the opening wherein the threaded portion retains the device in position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application No. 61/671,021, filed Jul. 11, 2012. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a device implantable in a bone to stabilize it while it heals, and which is particularly suitable for use in a metacarpal bone. 
     BACKGROUND OF THE INVENTION 
     The palm of the hand is made up of bones called metacarpals, and a metacarpal connects each finger and thumb to the hand. Each finger and thumb is formed of bones called phalanges. The connection of the phalanges to the metacarpals is called a “knuckle” joint or metacarpophalangeal joint (MCP joint), and acts like a hinge when the fingers or thumb are bent. 
     In each finger, there are three phalanges that are separated by two joints called the interphalangeal joints (IP joints). The proximal IP joint (PIP joint) is the one closest to the MCP joint. The other joint closest to the end of the finger is the distal IP joint (DIP joint). The thumb just has one IP joint. The joints are covered on the ends with articular cartilage. 
     Damage to the metacarpal bone may occur as a result of a sprain or fracture. Typically, once the metacarpal bone is lined up after an injury it must be stabilized in position while it heals. 
     To stabilize a broken metacarpal bone, it is now known to use a non-threaded, smooth metal shaft (hereafter “nail”) positioned in the metacarpal bone to hold it in position while the bone heals. An opening is first formed in the metacarpal bone, wherein the opening extends through the fracture and the nail is positioned in the opening to provide lateral stability for the parts of the bone on either side of the fracture. After a certain period, a second surgery is required to remove the nail from the bone. Problems with the nail are that, because it is not anchored in the bone, it can migrate through the metacarpal bone and into surrounding tissue. Sometimes this can result in damage to soft tissue, such as a severed or damaged tendon or cartilage, and/or cause pain. Another problem with the nail is that, because it can migrate, a second surgery is required to remove it. Additionally, the proximal end of pins and nails can cause tendon irritation, tendon rupture or skin irritation and infection. 
     One potential solution to this problem is to insert a screw into the bone. A major problem with such a technique (which to the inventors&#39; knowledge is not utilized and is not prior art) is that the torque required to place a screw into the length of a metacarpal bone (which is a relatively thin, delicate bone) is high. Such a procedure would be lengthy, and there would be a possibility of bone damage, or damage to the driving head of the screw, which could prevent complete insertion into the opening formed in the bone. Current screws are not designed specifically for intramedullary placement. For instance, the current screws are frequently not long enough. 
     SUMMARY OF THE INVENTION 
     The present invention solves the problems associated with repairing a metacarpal bone by providing a device that is a unique combination of a nail and a screw, which has threads only along 30% or less of its length. In this manner, the device can be inserted into the bone without damaging the bone because it is only threaded into a small portion of an opening formed in the bone. Further, the device is anchored into the bone, which eliminates migration and eliminates the need for a second operation to remove the device. 
     The device may have a threaded portion at one or more of its first end, central portion, or second end, and the threaded portion is preferably no greater than 30% and preferably no greater than 20-25% the length of the device. In one embodiment, the threaded area is between 0.5 and 1.5 centimeters (“cm”) and most preferably about 1 cm long. 
     At its first end, or proximal end, the device includes a driving head capable of being driven by any suitable driver into the opening. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of one embodiment of a device according to the invention. 
         FIGS. 2-2C  illustrate one method of utilizing the device of  FIG. 1 . 
         FIG. 3  illustrates the device of claim  1  positioned in a metacarpal bone. 
         FIG. 4  is a side view of an alternate embodiment of a device according to the invention. 
         FIGS. 5-5C  illustrate one method for utilizing the device of  FIG. 4 . 
         FIG. 6  illustrates the device of  FIG. 4  positioned in a metacarpal bone. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Turning now to the figures, where the purpose is to describe preferred embodiments of the invention and not to limit same,  FIG. 1  shows an exemplary embodiment  10  of the invention. Device  10  may be formed of any suitable material, such as titanium steel, stainless steel or nitinol. Device  10  has a first end, or proximal end,  12 , a second end, or distal end,  14 , a shaft  16  with an outer surface  17 , and a center portion  18  between first end  12  and second end  14 . A cutting point  19  is at second end  16  and a driving surface  20  is formed in the top of first end  12 . 
     Cutting point  19  is preferred and helps cut through any bone left behind when the bone is drilled to receive device  10 , as explained below. Driving surface  20  in this embodiment has a Torx drive configuration, although any suitable driving configuration may be used. Other driving configurations that may be used include slotted, Pozidriv, Robertson, tri-wing, Torq-Set, SpannerHead, Triple Square and hex head. 
     Juxtaposed end  12  is preferably an outwardly-flared top portion  22 , which aids in forming a compression fit in the opening formed in the bone. 
     Extending length wise in outer surface  17 , preferably along the longitudinal axis of shaft  16 , are grooves  24 . As used herein, “extending length wise” means that each groove  24  is elongated and extends along the shaft with one end of the groove nearer the first end  12  and the opposite end of the groove nearer the second end  14 , but grooves  24  may be formed at an angle and not necessarily formed along the longitudinal axis shaft  16 , although that is preferred. Grooves  24  preferably have serrated edges that assist in boring the device  10  into and anchoring device  10  in the opening in a bone. Grooves  24  also may capture some debris left behind from the bone drilling process to create the opening created when device  10  is positioned into the opening. 
     Also formed in outer surface  17  is an annular ring or gap  26  and threads  28 . Annular ring  26  has an outer diameter smaller than the outer diameter of the other components of device  10  except for the cutting point  18 . The purpose of annular ring  26  is to collect debris that may be present or created when device  10  is inserted into the opening in the bone in order to make insertion of device  10  easier. Any suitable structure may be utilized for this purpose, and device  10  may have multiple annular rings  26 . 
     Threads  28  in this embodiment are juxtaposed second end  14 . Threads  28  extend outward from the outer surface  17  of shaft  16  by about 1-2 mm and are threaded into the opening formed in the bone. Any structure that can retain device  10  within a bone and prevent migration of deice  10  may be utilized for this purpose. 
     It is preferred that threads  28  are no more than 30%, and preferably no more than 25%, or about 15-25%, of the length of shaft  16 . This is to reduce the torque required to screw device  10  into a bone, particularly a bone such as a metacarpal because it is narrow and relatively fragile. If too much torque were needed to insert device  10 , the torque could damage the bone structure, or the driving surface  20  could be damaged, which could prevent complete insertion of device  10  into the opening. 
     Threads  28  could alternatively be juxtaposed first end  12 , at one or more locations along center portion  18 , or be at both first end  12  and second end  14 . Alternatively, the threads could be displaced at one or more positions along center portion  18 , and juxtaposed first end  12  and second end  14 . Any location of the threads is suitable as long as the threads in their entity do not exceed the percentage of the overall shaft length set forth in the claimed inventions, and anchor device  10  in the opening. 
       FIGS. 2-2C  depict a method for installing device  10  into a fractured metacarpal bone. In  FIG. 2 , the fracture in the bone is first aligned, and then a K-wire is inserted into the bone. A K-wire or pin is known I the art and is a sterilized, smooth steel pin used in orthopedics and other types of medical applications. It is available in different sizes as needed and provides structure, support and in one version has a diameter of about 0.040″. 
     In  FIG. 2A  a cannulated drill, using the K-wire as a guide, drills an opening into the metacarpal bone, wherein the opening extends through the fracture and provides enough space on each side of the fracture to properly position device  10 . 
     In  FIG. 2B , device  10  is rotatingly driven into the opening in the metacarpal bone. The outer diameter of the threads  28 , and in this embodiment all of the structures of device  10  except annular gap  26  and cutting point  19 , is slightly larger than the inner diameter of the opening in the bone. This provides bone material for threads  28  to thread into and provides a tight fit for device  10 . However, device  10  could function properly if only threads  28  were slightly larger than the inner diameter of the opening, the other structures of device  10  except cutting point  19  and annular gap  26  were about the same size or slightly smaller than the inner diameter of the opening. 
     In this embodiment, the threads are ultimately anchored in the distal side of the metacarpal bone, which is the end opposite the side of the bone through which the opening starts. The serrations on the grooves  24  perform a scraping function that enables device  10  to be driven deeper into the bone with less torque. Internal debris from the procedure may be captured in the grooves  24  and/or annular gap  26  to help reduce the torque required to properly position device  10 . 
       FIGS. 2D and 3  show device  10  in the metacarpal bone after the K-wire has been removed. Since device  10  is anchored in the metacarpal bone, there is no need for a second operation to remove it. 
       FIG. 4  shows an alternate embodiment of the invention, device  100 . Device  100  is in all respects the same, and made from any suitable material and is inserted in an opening in a bone, as device  10  except that device  100  includes helical grooves  123 . Helical grooves  123  assist in reducing torque and help to rotatingly drive device  100  into an opening in the bone when force is applied to the driving surface  120 . Grooves  123  also collect debris as device  100  is being inserted, which, like annular gap  26 , helps reduce the pressure against the outer surface  117  of shaft  116  and thus reduces the force required to position device  100  into the opening in the bone. Longitudinal grooves  124  preferably have serrated edges and are the same as previously described grooves  24  except that they are intermittent because they are intersected by helical grooves  123 . 
     The structures and functions of the following components of device  100  have the same structures and functions of the components listed below with respect to device  10 : first end, or proximal end,  112 , and first end  12 ; second end, or distal end,  114  and second end  14 ; shaft  116  and shaft  16 ; outer surface  117  and outer surface  17 ; center portion  118  and center portion  18 ; cutting tip  119  and tip  19 ; driving surface  120  and driving surface  20 ; flared tip  122  and flared tip  22 ; and course threads  128  and course threads  28 . 
     Referring to  FIGS. 5-5C , a method of positioning device  100  into a bone is depicted. The positioning method is the same as that described with respect to device  10  except that debris collects in helical grooves  123  and there is no annular gap  16  (although device  100  could also include one or more annular gaps  16 ). 
       FIG. 6  shows device  10  positioned in a metacarpal bone. 
     Specific exemplary embodiments of the invention are described below: 
     EXAMPLE 1 
     A device for repairing a bone, the device for being received in the bone and comprising:
         a. a shaft having a length and an outer surface,   b. a first end, a second end and a center portion between the first end and the second end;   c. threads on the outer surface, wherein the threads comprise 25% or less of the shaft length; and   d. a driving surface at the first end.       

     EXAMPLE 2 
     The device of example 1 wherein the device is comprised of one or more of nitinol, stainless steel and titanium steel. 
     EXAMPLE 3 
     The device of example 1 or 2 that has one or more grooves on the outer surface, the grooves extending length wise along the outer surface. 
     EXAMPLE 4 
     The device of example 3 wherein the shaft has a longitudinal axis and the one or more grooves on the outer surface extend along the longitudinal axis of the shaft. 
     EXAMPLE 5 
     The device of example 3 or example 4 wherein at least one of the one or more grooves extends at least half of the length of the shaft. 
     EXAMPLE 6 
     The device of any of examples 3-5 that has three or more grooves. 
     EXAMPLE 7 
     The device of any of examples 3-6 wherein at least one of the grooves has serrated edges. 
     EXAMPLE 8 
     The device of example 1 wherein the device has a center portion with an outer diameter and the threads have an outer diameter that is equal to or greater than the outer diameter of the center portion. 
     EXAMPLE 9 
     The device of any of examples 1-8 wherein the first end is flared outwards to provide a compression fit in an opening formed in a bone. 
     EXAMPLE 10 
     The device of any of examples 1-9 that further includes an annular gap between the second end and the first end, wherein the annular gap has a diameter, and the shaft on either side of the gap has a diameter, the diameter of the annular gap being less than the diameter of the shaft on either side of the annular gap, the gap for receiving debris generated when installing the device. 
     EXAMPLE 11 
     The device of example 10 wherein the annular gap diameter is 5-20% less than the diameter of the shaft on either side of the annular gap. 
     EXAMPLE 12 
     The device of any of examples 1-11 wherein there is a cutting surface at the second end. 
     EXAMPLE 13 
     The device of any of examples 1-12 that further includes one or more helical groves along at least part of the shaft. 
     EXAMPLE 14 
     The device of example 13 wherein at least one of the helical grooves has serrated edges. 
     EXAMPLE 15 
     The device of any of examples 1-14 wherein the threads are juxtaposed the second end. 
     EXAMPLE 16 
     The device of any of examples 1-14 wherein the threads are juxtaposed the first end. 
     EXAMPLE 17 
     The device of any of examples 1-14 wherein the threads are on the center portion. 
     EXAMPLE 18 
     The device of any of examples 1-14 wherein the threads are on two or more of the outer surface juxtaposed the second end, the outer surface juxtaposed the first end, and the center portion. 
     EXAMPLE 19 
     The device of any of examples 1-18 that includes a plurality of annular gaps on the outer surface of the shaft. 
     EXAMPLE 20 
     A method for repairing a metacarpal bone, the method comprising the steps of:
         a. drilling an opening in a fractured metacarpal bone, the opening extending through the fracture, the opening having an inner diameter;   b. placing a device into the opening, the device having a shaft with a shaft length and an outer surface, a first end, a second end and a center portion between the first end and the second end, and threads on the outer surface, the threads being 25% or less of the shaft length, the threads having a thread diameter, the thread diameter being greater than the inner diameter of the opening;   c. positioning the device into the opening by rotationally driving it using a driving tool, so that the device is positioned completely inside the opening on each side of the fracture in order to stabilize the bone.       

     EXAMPLE 21 
     The method of example 20 wherein the device is comprised of one or more of nitinol, stainless steel and titanium steel. 
     EXAMPLE 22 
     The method of any of examples 20-21 wherein the device has one or more grooves on the outer surface, the grooves extending length wise along the outer surface. 
     EXAMPLE 23 
     The method of example 22 wherein the shaft includes a longitudinal axis and at least one of the grooves on the outer surface extends along the longitudinal axis. 
     EXAMPLE 24 
     The method of example 22 or example 23 wherein at least one of the one or more grooves extends at least half of the shaft length. 
     EXAMPLE 25 
     The method of any of examples 22-24 wherein the device has three or more grooves. 
     EXAMPLE 26 
     The method of any of examples 22-25 wherein at least one of the grooves has serrated edges. 
     EXAMPLE 27 
     The method of example 20 wherein the device includes a center portion that has an outer diameter and the threads have an outer diameter that is equal to or greater than the outer diameter of the center portion. 
     EXAMPLE 28 
     The method of any of examples 20-27 wherein the first end of the device is flared outwards to provide a compression fit in the opening. 
     EXAMPLE 29 
     The method of any of examples 20-28 that further includes an annular gap between the second end and the first end, wherein the annular gap has a diameter, and the shaft on either side of the annular gap has a diameter, the diameter of the annular gap being less than the diameter of the shaft on either side of the annular gap, the annular gap for receiving debris generated when installing the device. 
     EXAMPLE 30 
     The method of example 29 wherein the annular gap diameter is 5-20% less than the diameter of the shaft on either side of the annular gap. 
     EXAMPLE 31 
     The method of any of examples 20-30 wherein the device includes a cutting surface at the second end. 
     EXAMPLE 32 
     The method of any of examples 20-31 wherein the device further includes one or more of helical groves along at least part of the shaft. 
     EXAMPLE 33 
     The method of example 32 wherein at least one of the helical grooves has serrated edges. 
     EXAMPLE 34 
     The method of any of examples 20-33 wherein the threads are juxtaposed the second end. 
     EXAMPLE 35 
     The method of any of examples 20-33 wherein the threads are juxtaposed the first end. 
     EXAMPLE 36 
     The method of any of examples 20-33 wherein the threads are on the center portion. 
     EXAMPLE 37 
     The method of any of examples 20-33 wherein the threads are on two or more of the outer surface juxtaposed the second end, the outer surface juxtaposed the first end, and the center portion. 
     EXAMPLE 38 
     The method of claim 32 wherein each of the helical grooves has serrated edges. 
     EXAMPLE 39 
     The device of claim 13 wherein each of the helical grooves has serrated edges. 
     Having thus described some embodiments of the invention, other variations and embodiments that do not depart from the spirit of the invention will become apparent to those skilled in the art. The scope of the present invention is thus not limited to any particular embodiment, but is instead set forth in the appended claims and the legal equivalents thereof. Unless expressly stated in the written description or claims, the steps of any method recited in the claims may be performed in any order capable of yielding the desired result.