Abstract:
Devices and methods are disclosed for the fusion of joints (particularly finger joints or toe joints) in a bent (or angled) position. The device is not cannulated, straight and inserted into the joint in its straight configuration. The device is configured to have a thicker portion at its proximal end than at its distal end. The device is preferably inserted into a finger joint that is already bent at an angle, and the thin, distal end is configured to screw into and attach to the bone of second joint thereby fusing the first joint to the second joint.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a device or method for the fusion of a joint, particularly the DIP joint of a finger, in a predetermined position. 
       BACKGROUND OF THE INVENTION 
       [0002]    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. 
         [0003]    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. 
         [0004]    The joints are covered on the ends with articular cartilage. Damage to the joints may occur as a result of arthritis, a sprain or fracture, and wherein the damage either directly or indirectly affects the articular cartilage. Typically, the joint does not line up the same after the injury and causes unusual wear on the articular cartilage, eventually damaging the articular surface and causing pain and loss of mobility. 
         [0005]    Typical methods of surgically treating a damaged joint include artificial joint replacement or fusion. Fusion (arthrodesis) is used to enable bones that make up a joint to grow together into one solid bone. Fusions are commonly used in the PIP or the DIP joints in the fingers because it is easier than replacing the joint and is an acceptable alternative to replacement in many cases. 
         [0006]    Existing methods of fusion are inadequate, such as (a) K-wire fusion, (b) or inserting a screw through the tip of the finger and through the joint to be fused because the joint is typically fused straight (i.e., without a bend in it), which is not a natural position for the joint of a finger during normal use. Herbert and Acutrack screws and their variants have been used, but by using these, the joint (DIP joint) and end of the finger are fused in a straight position, which is unnatural since the joint is normally bent during use. DIP fusions with angles can be performed but the process is technically demanding, so it is rarely performed. Additionally, the ability to angle the joint is limited and the bone purchase is poor. An example of prior art screws is shown in  FIG. 1 . 
         [0007]    Other techniques such as pin and tension band or cerclage wire do not adequately solve the problem of easily fusing a finger joint in a bent position. 
       SUMMARY OF THE INVENTION 
       [0008]    The descriptions of this invention herein are exemplary and explanatory only and are not restrictive of the invention as claimed. 
         [0009]    A device (or screw) for fusing a joint, particularly the DIP joint of a finger, comprises: (1) a first (or proximal) end, (2) a second (or distal) end, and (3) a middle portion between the first end includes a first threaded section and second end. The outer surface of the first end comprises a first threaded section, and the outer surface of the second end includes a second threaded section. 
         [0010]    A preferred device according to the invention is a straight screw, that tapers to a narrow diameter and point, which permits bent DIP fusion by crossing a bent joint and being threadingly received in the phalange P 3  and phalange P 2  on either side of the joint. The design can fit virtually any size finger because of its taper and narrow outer diameter 
         [0011]    If the device of the invention has a sharp tip, the tip punctures dorsal cortex of P 2  to firmly secure the device into phalange P 2  at the distal side of the joint. Known designs have relatively thick tips that cannot accurately or effectively be inserted into phalange P 2 . 
         [0012]    The device is preferably not cannulated, so it can taper to a tip, but optionally, the device can be cannulated. But, even if not cannulated, it uses cannulated insertional techniques which make it easy to place. 
         [0013]    The middle portion of the device is thicker than the tapered second end. It bridges the space between the phalanges forming the joint and the extra thickness provides strength to resist the device from bending or breaking during use of the hand. 
         [0014]    The first threaded section may have a different thread pitch, and different thread heights (as measured from the body of the device) than the second threaded section, or the first threaded section may have the same thread type and pitch as the second threaded section. The device may include a self-tapping feature at the distal end and a head at the proximal end adapted to receive an end of a driving tool, such as a screwdriver, Allen wrench or socket wrench. 
         [0015]    A feature to prevent rotation may be included. This may take the form of the head of the device being triangular, and/or a series of nonsymmetrical features along the device to impede rotation or a texture added to the device. To achieve the same purpose the device may have other features or asymmetry at the head like ridges, wings, or barbs. 
         [0016]    Features to allow radiographic visualization of the position of the device inserted into the body such as notches, markers, and/or fins may be included. Features that control the position of a device according to the invention independent of radiographic assessment, such as clocking devices added to the screwdriver tip, may be utilized. Further, a screwdriver may have external marks on the handle or body that indicate the position of the device when it is inserted into a patient. 
         [0017]    The joint may be bent at an angle of between 1 and 25 degrees, at an angle of between 1 and 45 degrees, or at an angle of between 1 and 60 degrees. The device may be between ½″ and 3″ long, or between ¾″ and 1¾″ long. The device may be between 1 mm to 5 mm in diameter at its thickest point, or about 3 mm in diameter at its thickest point. For larger joints, the screw may be larger. 
         [0018]    A preferred method of inserting a device according to the invention is to first bend the joint a predetermined angle, then use a K-wire to form the path through the phalanges P 2 , P 3  of the joint into which the device will be positioned. A drill with a cannulated tip to receive the K-wire is then used to drill an opening where the K-wire has been positioned. The drill and K-wire are then removed, and a device according to the invention is threaded into the opening. The distal end threads into and is received in P 2  and the proximal end in threadingly received in P 3 . 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  depicts a prior art screw used for joint fusion. 
           [0020]      FIG. 2  is a perspective, side view of a device (or screw) according to the invention. 
           [0021]      FIGS. 3A-3B  show the fingers of a hand bent in a normal cascading position. 
           [0022]      FIG. 4  shows a device according to the invention position in and fusing a DIP joint of a finger. 
           [0023]      FIG. 5  shows a screw according to the present invention inserted into the DIP joint and fusing it into a bent position. 
           [0024]      FIG. 6  shows a screw according to the present invention inserted into a DIP joint and fusing it in a relatively straight position. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0025]    A device or method according to the invention allows for the fusion of joints in the finger (particularly the DIP joint) in a bent (or angled) position, which is more natural when using the hand. For a finger joint, fusing the joint in a bent position allows for the patient to be able to better grip things after a successful procedure and fusion of a joint. In certain embodiments, a device for the fusion of small finger joints preferably allows for one or more of various angled positions, and the particular angle may differ for different joints. The device is preferably a screw for fusing together bones or a joint, and most preferably is used for fusing bones or a joint in a finger or toe. 
         [0026]    With reference to  FIG. 2 , in one embodiment, the device is a screw  10  that has a first end  12  having a first threaded portion  14 , and a driver head  16 . It also has a central portion  20 , which is substantially cylindrical and preferably of a single diameter. It preferably has a second  22 , which has second threaded portion  24 , and as shown is tapered to a tip  26 . Screw  10  may have a cannula (not shown), but in this embodiment does not have one so that tip  26  is narrow and relatively sharp. 
         [0027]    In one embodiment, end  16  is adapted to receive a Phillips head screw driver, but any suitable adaptation is possible, such as a slotted, Torx, Pozidriv, Robertson, tri-wing, Torq-Set, Spanner Head, Triple Square, or hex configuration, or any other configuration capable of pushing or screwing the device  10  into an opening, particularly one in the end of a finger DIP joint, or a toe, in order to fuse a joint. In certain embodiments, an end of the device may be adapted to be self -tapping by utilizing tip  26  and second threaded portion  24 , but it is not limited thereto. 
         [0028]    As illustrated in  FIGS. 3A-6 , an angle is formed in the joint before device  10  is inserted into the joint and the angle is determined according to any desired fusion position. The angle could be between about 5 and 70 degrees and most preferably between about 15 and 45 degrees. 
         [0029]      FIGS. 3A-3B  illustrate preferred, optimal angles for setting the different small joints in a typical hand utilizing a device according to the invention. However, different hands and different people may require different fusion angles, which can be accommodated by the invention. In some embodiments, the flexed position for the PIP joints is about 40-55 degrees, the DIP joints may vary from about 0-20 degrees, the MCP joints may vary from about 25-40 degrees, and the IP joint is typically about 20 degrees. 
         [0030]    In some embodiments, the device material is one or more of titanium stainless steel, or plastic, but the device is not limited to these materials. The device may be comprised of any material(s) capable of fusing a finger joint, and rigid enough to prevent a patient from straightening it during ordinary use. 
         [0031]    The length of the device, such as screw  10 , depends on the size of the joint and phalanges, but is preferably between ½″ and 2″ and most preferably between ¾″ and 1½″. In many embodiments, the maximum diameter of the device is the outer diameter of the highest thread, which may be between 1 mm and 5 mm, and most preferably about 3 mm. 
         [0032]    First threaded section  14  should be long enough and of sufficient diameter such that when inserted into a bore in a phalange, the threads grip the bone in P 3  and do not allow screw  10  to twist without applying torque to end  16 . Second threaded section  24  should be long enough and of sufficient diameter such that when inserted into a bore formed in phalange P 2 , the threads  28  grip P 2  and do not allow screw  10  to twist. The diameter of second section  22  tapers down from middle section  20  to tip  26 . The diameter of first section  12  is preferably constant and may be equal to, less than, or greater than that of middle section  20 . 
         [0033]    A preferred method of inserting a device according to the invention is to first bend the joint a predetermined angle, then use a K-wire to form the path through the phalanges P 2 , P 3  of the joint into which the device will be positioned. A K-wire or pin is a sterilized, smooth stainless steel pin used in orthopedics and other types of medical applications. It comes in different sizes as needed and provides structure support, and one size has a diameter of about 0.040″. A drill with a cannulated tip to receive the K-wire is then used to drill an opening where the K-wire has been positioned. The drill and K-wire are then removed, and a device according to the invention is threaded into the opening. The distal end threads into and is received in P 2  and the proximal end in threadingly received in P 3 . 
         [0034]    The bored hole into which the screw  10  fits preferably has an internal diameter that is preferably the size of the screw minus the width of the threads. The pitch and height of the threads of first section  12  are preferably smaller than those of threads  28  in second section  22 . In a preferred embodiment, the pitch is  1 mm/revolution distal with a smaller pitch in the proximal section. The diameter of the screw maximal is preferably 2.5 mm. The diameter of the screw minor is preferably 1.8 mm. The thread height is preferably about 0.3 mm. 
         [0035]    One or more orientation marks may be incorporated into a screw  10  of the present invention. For example, an orientation marker may be placed at or near tip  26 , or on central portion  20 , allowing the surgeon to know when screw  10  is in the proper position. The orientation marker may be an indentation stamp or may be cast into screw  10  or may be a mark made with a surgical marker. 
         [0036]    Having thus described preferred 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.