Metacarpal bone stabilization device

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.

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' 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.

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. 1shows an exemplary embodiment10of the invention. Device10may be formed of any suitable material, such as titanium steel, stainless steel or nitinol. Device10has a first end, or proximal end,12, a second end, or distal end,14, a shaft16with an outer surface17, and a center portion18between first end12and second end14. A cutting point19is at second end16and a driving surface20is formed in the top of first end12.

Cutting point19is preferred and helps cut through any bone left behind when the bone is drilled to receive device10, as explained below. Driving surface20in 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 end12is preferably an outwardly-flared top portion22, which aids in forming a compression fit in the opening formed in the bone.

Extending length wise in outer surface17, preferably along the longitudinal axis of shaft16, are grooves24. As used herein, “extending length wise” means that each groove24is elongated and extends along the shaft with one end of the groove nearer the first end12and the opposite end of the groove nearer the second end14, but grooves24may be formed at an angle and not necessarily formed along the longitudinal axis shaft16, although that is preferred. Grooves24preferably have serrated edges that assist in boring the device10into and anchoring device10in the opening in a bone. Grooves24also may capture some debris left behind from the bone drilling process to create the opening created when device10is positioned into the opening.

Also formed in outer surface17is an annular ring or gap26and threads28. Annular ring26has an outer diameter smaller than the outer diameter of the other components of device10except for the cutting point18. The purpose of annular ring26is to collect debris that may be present or created when device10is inserted into the opening in the bone in order to make insertion of device10easier. Any suitable structure may be utilized for this purpose, and device10may have multiple annular rings26.

Threads28in this embodiment are juxtaposed second end14. Threads28extend outward from the outer surface17of shaft16by about 1-2 mm and are threaded into the opening formed in the bone. Any structure that can retain device10within a bone and prevent migration of deice10may be utilized for this purpose.

It is preferred that threads28are no more than 30%, and preferably no more than 25%, or about 15-25%, of the length of shaft16. This is to reduce the torque required to screw device10into a bone, particularly a bone such as a metacarpal because it is narrow and relatively fragile. If too much torque were needed to insert device10, the torque could damage the bone structure, or the driving surface20could be damaged, which could prevent complete insertion of device10into the opening.

Threads28could alternatively be juxtaposed first end12, at one or more locations along center portion18, or be at both first end12and second end14. Alternatively, the threads could be displaced at one or more positions along center portion18, and juxtaposed first end12and second end14. 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 device10in the opening.

FIGS. 2-2Cdepict a method for installing device10into a fractured metacarpal bone. InFIG. 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″.

InFIG. 2Aa 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 device10.

InFIG. 2B, device10is rotatingly driven into the opening in the metacarpal bone. The outer diameter of the threads28, and in this embodiment all of the structures of device10except annular gap26and cutting point19, is slightly larger than the inner diameter of the opening in the bone. This provides bone material for threads28to thread into and provides a tight fit for device10. However, device10could function properly if only threads28were slightly larger than the inner diameter of the opening, the other structures of device10except cutting point19and annular gap26were 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 grooves24perform a scraping function that enables device10to be driven deeper into the bone with less torque. Internal debris from the procedure may be captured in the grooves24and/or annular gap26to help reduce the torque required to properly position device10.

FIGS. 2D and 3show device10in the metacarpal bone after the K-wire has been removed. Since device10is anchored in the metacarpal bone, there is no need for a second operation to remove it.

FIG. 4shows an alternate embodiment of the invention, device100. Device100is in all respects the same, and made from any suitable material and is inserted in an opening in a bone, as device10except that device100includes helical grooves123. Helical grooves123assist in reducing torque and help to rotatingly drive device100into an opening in the bone when force is applied to the driving surface120. Grooves123also collect debris as device100is being inserted, which, like annular gap26, helps reduce the pressure against the outer surface117of shaft116and thus reduces the force required to position device100into the opening in the bone. Longitudinal grooves124preferably have serrated edges and are the same as previously described grooves24except that they are intermittent because they are intersected by helical grooves123.

The structures and functions of the following components of device100have the same structures and functions of the components listed below with respect to device10: first end, or proximal end,112, and first end12; second end, or distal end,114and second end14; shaft116and shaft16; outer surface117and outer surface17; center portion118and center portion18; cutting tip119and tip19; driving surface120and driving surface20; flared tip122and flared tip22; and course threads128and course threads28.

Referring toFIGS. 5-5C, a method of positioning device100into a bone is depicted. The positioning method is the same as that described with respect to device10except that debris collects in helical grooves123and there is no annular gap16(although device100could also include one or more annular gaps16).

Specific exemplary embodiments of the invention are described below:

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; andd. a driving surface at the first end.

The device of example 1 wherein the device is comprised of one or more of nitinol, stainless steel and titanium steel.

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.

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.

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.

The device of any of examples 3-5 that has three or more grooves.

The device of any of examples 3-6 wherein at least one of the grooves has serrated edges.

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.

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.

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.

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.

The device of any of examples 1-11 wherein there is a cutting surface at the second end.

The device of any of examples 1-12 that further includes one or more helical groves along at least part of the shaft.

The device of example 13 wherein at least one of the helical grooves has serrated edges.

The device of any of examples 1-14 wherein the threads are juxtaposed the second end.

The device of any of examples 1-14 wherein the threads are juxtaposed the first end.

The device of any of examples 1-14 wherein the threads are on the center portion.

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.

The device of any of examples 1-18 that includes a plurality of annular gaps on the outer surface of the shaft.

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.

The method of example 20 wherein the device is comprised of one or more of nitinol, stainless steel and titanium steel.

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.

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.

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.

The method of any of examples 22-24 wherein the device has three or more grooves.

The method of any of examples 22-25 wherein at least one of the grooves has serrated edges.

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.

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.

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.

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.

The method of any of examples 20-30 wherein the device includes a cutting surface at the second end.

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.

The method of example 32 wherein at least one of the helical grooves has serrated edges.

The method of any of examples 20-33 wherein the threads are juxtaposed the second end.

The method of any of examples 20-33 wherein the threads are juxtaposed the first end.

The method of any of examples 20-33 wherein the threads are on the center portion.

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.

The method of claim 32 wherein each of the helical grooves has serrated edges.

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.