WO1992004875A1

WO1992004875A1 - Bone fixing device

Info

Publication number: WO1992004875A1
Application number: PCT/AU1991/000444
Authority: WO
Inventors: David Mark Allison
Original assignee: David Mark Allison
Priority date: 1990-09-24
Filing date: 1991-09-24
Publication date: 1992-04-02

Abstract

A bone fixing device is provided for fixing a plurality of bone fragments together. The device (2) comprises an elongate rod (4) which has a screw thread (6) formed along a first length (10) and, a cylindrical tube (8) which is threadingly engageable with the screw thread (6) on the rod (4). To use the device (2), a hole is formed to pass through bone fragment (34) and to penetrate bone fragment (36). The hole through bone fragment (34) has a diameter equal or greater than that of the threaded portion (10) of rod (4). A thread is formed in the hole in bone fragment (36) to engage thread (6). The rod (4) is inserted through bone fragment (34) and threadingly engages bone fragment (36). The tube (8) is threadingly engaged with the rod (4) and screwed to a position where a leading end (20) of the tube (8) can apply a force tending to compress bone fragments (34, 36) together. Excess length of the rod (4) and tube (8) can be cut off near a layer of skin (40) which overlies the bone fragments (34, 36). Cutting of the tube (8) and rod (4) effectively locks the tube (8) from unscrewing in reaction to the compressive force.

Description

BONE FIXING DEVICE

FIELD OF THE INVENTION

This invention relates to a bone fixing device for fixing a plurality of bone fragments together.

BACKGROUND OF THE INVENTION In order to assist healing of fractured, broken or severed bones it is advantageous for fracture surfaces of corresponding bone fragments to be placed in fitted contact and to be so held during the bone healing process. The most common way of ensuring such contact is, where practical, to apply a compressive loading to the bone fragments in a direction substantially normal to the fractured surfaces.

Bone screws are one known device for holding bone fragments together and applying a compressive loading thereto. There are two types of bone screws; those with heads and those without. The bone screws with heads apply a compressive force directly on the bony cortex (or surface) of an adjacent bone fragment. Bone screws without heads have threads at opposite ends separated by a shank devoid of thread. The threads at opposite ends have like handedness but different pitch so as to apply a compressive force to the bone fragments when tightened.

Both types of bone screws require exposure of at least one bone surface. In some circumstances, for example when fixing fractured smaller bones of the hands, the disturbance to soft tissue anatomy surrounding the bone fragments causes morbidity to such an extent as to make the use of bone screws inappropriate. Moreover, on many occasions bone fragments are simply too small to be fixed by presently available screws. A further deficiency with bone screws of the type having heads is that they are unable to be used to fix bone fragments through a joint surface, since the screw head would prevent correct mutual alignment of the joint surfaces. A further general inconvenience of bone screws is that the length thereof must be predetermined prior to use. .Another device for fixing bone fragments together is a Kirscher wire. Kirscher wires are pins, pointed at one or both ends, which can be drilled across bone fragments and fracture surfaces. Kirscher wires are particularly useful in fixing together smaller bone fragments and can be placed percutaneously, that is, through the skin and soft tissue thereby resulting in minimal disturbance to the soft tissue. However, Kirscher wires do not apply compression across the fracture surfaces and may cause distraction. Distraction may delay bone healing, cause healing to be less smooth and reduce the stability of the fracture during healing. The provision of threads at a leading end of a Kirscher wire assists in holding the bone fragments together, but as previously stated, does not cause compression.

Another means of fixing bone fragments is to use a thin threaded rod and apply a nut at one end to provide compression. However, pressure exerted on an adjacent skin layer can cause necrosis and while the pressure can be dissipated over a wider area by use of a washer between the nut and the skin layer, it has been found that this results in insufficient compression being applied to the fracture site. The nut may be applied directly to the bone cortex, however this necessitates soft tissue dissection.

SUMMARY OF THE INVENTION It is an object of this invention to provide a bone fixing device which attempts to alleviate at least one of the above described deficiencies in the prior art.

According to one aspect of the present invention there is provided a device for fixing a plurality of bone fragments together comprising: an elongate rod for penetrating said plurality of bone fragments and connecting said bone fragments together, said rod having a screw thread formed along at least a portion of its length; and, an elongate tubular member threadedly engageable with said screw thread; whereby, in use, said elongate tubular member can be screwed onto said rod to a position where an end of said elongate tubular member applies a force tending to compress said bone fragments together.

Preferably, said end of the elongate tubular member is adapted to penetrate a layer of skin adjacent said bone fragments, whereby said force is applied below said layer of skin.

Preferably, said elongate tubular member includes a gripping means by which said elongate tubular member can be gripped when being screwed onto said elongate rod.

Preferably, said gripping means has a polygonal cross-section being receivable in a spanner or other hand tool. Alternatively, said gripping means includes a peripheral knurled ring. Preferably, said device further includes a second elongate tubular member threadingly engageable with said elongate rod, wherein said rod can pass through said bone fragments to a position where opposite ends of said rod can be accessed to allow said elongate tubular member and said second elongate tubular member to be screwed onto said rod from opposite ends in a direction toward each other to respective positions to apply a force tending to compress said bone fragments together.

Preferably, said rod and said elongate tubular member and/or second elongate tubular member are of indeterminate length, whereby after application of said device, lengths of said elongate rod, said elongate tubular member, and/or said second elongate tubular member extending away from said layer of skin can be cut off. According to another aspect of the present invention there is provided a method for fixing a plurality of bone fragments together comprising the steps of: providing an elongate rod having a screw thread formed along at least a portion of its length; forming a hole penetrating said bone fragments; inserting said rod into said hole to connect said bone fragments together; providing an elongate tubular member being threadingly engageable with said screw thread on said rod; and, screwing said elongate tubular member onto said rod to a position where an end of said elongate tubular member applies a force tending to compress said bone fragments together.

Preferably, in said screwing step, said elongate tubular member is screwed onto said rod to a position where said end penetrates a layer of skin adjacent said bone fragments whereby said force is applied below said layer of skin. Advantageously said end abuts a surface of an adjacent bone fragment.

Preferably, said step forming a hole comprises drilling a hole which penetrates said bone fragments. Preferably, said step of drilling a hole includes drilling a hole with a first length having a diameter equal or greater than that of said portion of said rod through all of said plurality of bone fragments except a bone fragment furtherest from said end of said tubular member, and having a second length penetrating said furtherest bone fragment of a diameter less than that of said portion of said rod whereby said thread can threadingly engage said furtherest bone fragment. Advantageously said elongate rod can be used as a drill bit for drilling the second length of said hole and tapping a thread therein.

Preferably, said method further comprises the step of locking said elongate tubular member from being unscrewed from said rod in reaction to said force.

Preferably, said step of locking comprises cutting off an excess length of said elongate rod and/or said elongate tubular member near said layer of skin, opposite said bone fragments.

BRIEF DESCRIPTION OF THE DRAWINGS One embodiment of the present invention will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a side view of an elongate rod of the bone fixing device;

Figure 2 is a longitudinal section view of an elongate tubular member of the bone fixing device; Figure 2a is a view from one end of the elongate tubular member illustrated in Figure 2; and,

Figure 3 is a perspective view in partial section illustrating the bone fixing device connecting a plurality of bone fragments together.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in the accompanying drawings a device 2 for fixing a plurality of bone fragments together comprises an elongate rod 4 which has a screw thread 6 formed along a portion of its length and an elongate tubular member in the form of a cylindrical tube 8 which is threadingly engageable with the screw thread 6 on the rod 4. The rod 4 has a first length 10 on which the screw thread 6 is formed, and an integral second threadless length 12 having a reduced diameter. Opposite ends 15, 17 of the rod 4 terminate in respective points 14 and 16. End 15 adjacent the first length 10 forms a leading end of the rod 4.

A first portion 18 adjacent a leading end 20 of tube 8 is provided with an internal thread 22. The leading end 20 is slightly tapered to have reduced width in a direction toward end 20. Extending from the first portion 18 is a second unthreaded portion 24 formed with an increased diameter to provide a sliding fit with the threaded first length 10 of the rod 4. An opposite end 26 of the tube 8 terminates in portion 28 having a hexagonal cross-section, (refer Figure 2a) .

The bone fixing device 2 is assembled by inserting the second length 10 of the rod 4 into the tube 8 from the leading end 20 so that the internal thread 22 can engage the thread 6 on the first portion 8 of the rod 4. One application of the bone fixing device is illustrated in Figure 3 in which the device 2 is used to fix a broken bone 30 in a patient's finger 32. The bone 30 is broken into bone fragments 34 and 36 and is surrounded by soft tissue 38 and a layer of skin 40. The bone 30 is fractured along a fracture site 42 with the bone fragments 34, 36 having substantially complementary fracture surfaces 44 and 46 respectively. A hole is drilled through the layer of skin 40, soft tissue 38 and penetrates bone fragments 34 and 36 so as to pass approximately at right angles to the fractured surfaces 44 and 46. The diameter of a length of the hole passing through bone fragment 34 is equal or greater than that of the threaded length 10 of the rod 4. This allows the rod 4 to be inserted without thread 6 engaging bone fragment 34 so that bone fragment 34 can slide along rod 4. A length of the hole passing through bone fragment 36 is made of a diameter less than that of the threaded length 10 of rod 4 to allow a thread to be tapped therein which can engage thread 6. The rod 4 is then inserted into the hole to connect bone fragments 34 and 36 together. Connection is achieved by the thread 6 which engages bone fragment 36. The tube 8 is screwed onto the first length 10 of the rod 4 to a position where leading end 20 applies a force tending to compress the bone fragments 34, 36 together. To tighten the tube 8 a

, spanner (not shown) can engage the hexagonal portion 28. In the above embod.iment, the hole formed through the bone fragment 36 is tapped so as to be engaged by the screw threads 6 on the rod 4. Conveniently, the hole can be tapped by using the rod 4 as a self-tapping drill bit. The point 14 at leading end 15 assists in piercing the skin 40, soft tissue 0 38 and bone fragment 36 when the rod 4 is used as a self- tapping drill bit.

Once the tube 8 has been tightened to produce the required compressive force on the bone fragments 34, 36 excess length of the tube 8 and rod 4 are cut off at a point at or 5 near the layer of skin 40. The cutting of the tube 8 and rod 4 effectively locks the tube from unscrewing in reaction to the compressive force. In an alternative embodiment the rod 4 can be formed to have thread 6 extending from near end 15 for a length approximately equal to the depth of penetration into bone fragment 36, with an adjacent unthreaded portion opposite end 15, extending for a length to pass through bone fragment 34 with thread 6 continuing thereafter for engaging tube 8. In this embodiment the drilling of a hole through bone fragment 34 and 36 and tapping of bone fragment 36 can be achieved simultaneously by using rod 4 as a drill bit which after use is left in situ for application of the tube 8. This simplifies the drilling step however a range of rods 4 must be provided having threaded and unthreaded portions of different lengths for different applications.

In a further embodiment of the invention, a second tube 8 is used and the rod 4 is passed wholly through the finger 32 so that opposite ends 15 and 17 are exposed whereby respective tubes 8 can be threaded onto the rod 4 from opposite ends and screwed in a direction toward each other to compress the bone fragments 34, 36 therebetween. In this embodiment no thread need be formed in the bone fragments 34, 36 and the thread 6 consequently does not engage the bone fragments 34, 36.

^■ Now that embodiments of the present invention have been described in detail, it will be apparent to those skilled in the relevant arts that numerous modifications and variations may be made without departing from the basic inventive concepts. For example, the rod 4 is illustrated as having first and second lengths of different diameter. However, the rod 4 may have a single uniform diameter and the screw thread 6 may extend for the whole length of the rod 4. The thread 6 can be any type of thread suitable for engaging the tubes 8 and, when necessary, the bone fragment 36. The rod 4 may also include a third length also of reduced diameter collinearly extending from leading end 14. The leading end 15 can be formed with any configuration suitable for penetrating skin, soft tissue and bone. Where the rod 4 is not used in a self-tapping manner the leading end 15 need not be furnished with a point 14 as shown in the illustrated embodiment.

The tube 8 may be formed with a constant internal diameter and provided with an internal thread for the whole of its length. Furthermore, whilst the elongate tubular member is in the form of a cylindrical tube 8 in the illustrated embod.im.ent, the tubular member can obviously be of any suitable cross-sectional shape. In addition, the hexagonal portion 28 need not be included or may be replaced by a portion of any other cross-sectional shape for receipt in a spanner or hand tool. Furthermore the leading end 20 need not be tapered as shown in the illustrated embodiment.

While it is an advantageous feature of embodiments of the present invention that the rod 4 are tube 8 are formed of indeterminate length and cut at or close to a layer of skin 40 after the device 2 has been applied, it is possible to manufacture the rods 4 and tubes 8 of predetermined lengths and simply to select the appropriate length device 2 for the application at hand. .All such modification and variations are to be considered within the scope of the present invention, the nature of which is to be determined from the aforegoing description and the claims.

Claims

1. A device for fixing a plurality of bone fragments together comprising: an elongate rod for penetrating said plurality of bone fragments and connecting said bone fragments together, said rod having a screw thread formed along at least a portion of its length; and, an elongate tubular member threadingly engageable with said screw thread; whereby, in use, said elongate tubular member can be screwed onto said rod to a position where an end of said elongate tubular member applies a force tending to compress said bone fragments together.

2. A device according to claim 1 wherein, said elongate tubular member is adapted to penetrate a layer of skin adjacent said bone fragments, whereby said force is applied below said layer of skin.

3. A device according to claim 1 or claim 2 wherein, said elongate tubular member includes a gripping means by which said elongate tubular member can be gripped when being screwed onto said elongate rod.

4. A device according to claim 3 wherein, said gripping means includes a knurled ring.

5. A device according to claim 3 wherein, said gripping means is formed with a polygonal cross-section for receipt in a spanner or other hand tool.

6. A device according to any one of claims 1 to 5, wherein said end of said elongated tubular member is tapered to have a reduced width in a direction toward said end.

7. A device according to any one of the preceding claims further comprising, a second elongate tubular member threadingly engageable with said elongate rod, wherein said rod can pass through said bone fragments to a position where access can be gained to opposite ends of said rod whereby said elongate tubular member and said second elongate tubular member are screwed onto said rod from opposite ends in a direction towards each other to a position so as to apply a force tending to compress the bone fragments together.

8. A device according to any one of the preceding claims wherein, said rod, said elongate tubular member and/or said second elongate tubular member are of indeterminant length, whereby after application of said device, lengths of said elongate rod, said elongate tubular member and/or said second elongate tubular member extending away from said layer of skin can be cut off.

9. A method for fixing a plurality of bone fragments together comprising the steps of: providing an elongate rod having a screw thread formed along at least a portion of its length; forming a hole penetrating said bone fragments; inserting said elongate rod into said hole to connect the bone fragments together; providing an elongate tubular member being threadingly engageable with said screw thread on said rod; and, screwing said elongate tubular member onto said elongate rod to a position where an end of said elongate tubular member applies a force tending to compress said bone fragments together.

10. A method according to claim 9 wherein, in said screwing step, said elongate tubular member is screwed onto said rod to a position where said end penetrates a layer of skin adjacent said bone fragments whereby said force is applied below said layer of skin.

11. A method according to claim 9 or 10, wherein said step forming a hole includes drilling a hole which penetrates said bone fragments.

12. A method according to any one of claims 9 to 11 further comprising the step of locking said elongate tubular member from being unscrewed from said rod in reaction to said force.

13. A method according to claim 12 wherein, said step of locking comprises cutting off lengths of said elongate tubular member and elongate rod near said layer of skin, opposite said bone fragments.

14. A method according to any one of claims 9 to 13, further comprising the step of forming a gripping means on said elongate tubular member, by which said elongate tubular member can be gripped when being screwed onto said elongate rod.

15. A method according to claim 11 wherein said step of drilling a hole includes drilling a hole having a first length having a diameter equal or greater than that of said portion of said rod through all of said plurality of bone fragments except a bone fragment furtherest from said end of said tubular member and having a second length penetrating said furtherest bone fragment of a diameter less than that of said portion of said rod whereby said thread can threadingly engage said furtherest bone fragment.

16. A method according to claim 15 wherein, said elongate rod is used as a drill bit for drilling the second length of said hole and tapping a thread therein.

17. A method according to any one of claims 9 to 14 further comprising the step of providing a second elongate tubular member being threadingly engageable with said screw thread on said rod, wherein said inserting step comprises the step of inserting said rod into said hole to a position where access can be gained to opposite ends of said rod whereby the elongate tubular member and said second elongate tubular member can be screwed onto said rod from opposite ends in a direction toward each other to position perfect to apply a force tending to compress the bone fragments together.