AU706871B2

AU706871B2 - Intramedullary fixing device

Info

Publication number: AU706871B2
Application number: AU30193/95A
Authority: AU
Inventors: Roger Churchward; John William Owen
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-08-22
Filing date: 1995-08-22
Publication date: 1999-06-24
Anticipated expiration: 2015-08-22
Also published as: AU3019395A

Description

-la- INTRAMEDULLARY FIXING DEVICE The present invention relates to an intramedullary fixing device and more particularly to a fixing device for use with the humerus.

Fractures of the shaft of the humerus are usually treated non-operatively. However certain of these fractures do need surgical treatment, particularly fractures arising from tumor deposits. The management of these fractures without surgery requires the use of braces and slings for many weeks and may also require a period of hospitalisation. Use of an internal fixation device within the medullary cavity enables the fracture to be stabilised relatively quickly. Previously proposed intramedullary fixing devices for the internal fixation of pathological fractures such as these comprise a stainless rod mounted within the cavity and spanning the zone of the fracture. If the bone destruction is extensive, rotation of the bone at opposite sides of the fracture can occur and in these 9 15 circumstances the rod can be locked to the bone above and below the fracture by means of cross pins extending through the rod to lock the bone against rotation relative to the rod. However cross pinning the humerus does raise some problems because access to the ".'.humerus is not easy and also there are major nerves and vessels around the arm which can 9eeo easily be hit by the cross pins. Hitherto, cross pins used for this purpose have been of 20 small diameter threaded with a low profile thread which bites into the bone tissue; the cross bores in the stainless rod through which the cross pins extend are not threaded.

Although for structural reasons it is desirable for the pin to be a close fit within the cross bore, if the cross bore is matched closely to the outer diameter of the pin it becomes extremely difficult to insert the pin. Accordingly the cross bore is usually enlarged to a diameter which enables easier insertion of the pin, although this does, as a consequence, lead to the possibility of movement occurring between the bore and the pin and in some circumstances this movement can result in breakage of the small diameter pin arising from movement of the pin against the edges of the bore under the applied stress.

According to the present invention, there is provided an intramedullary fixing SR e device comprising a rod for location within the humerus and cross-bores extending through 990408,p:\oper\rshfiing-device.cap, 1 -2the rod for receiving cross pins for anchoring the rod to the bone at opposite sides of a fracture, each said cross bore having an internally-threaded portion and a convergent entry portion leading into the threaded portion, and each said cross pin comprising a head and a shank which is threaded to engage the internal thread in the bore, the convergent entry portion of the bore facilitating insertion of the pin into the threaded portion of the bore, and the head of each pin includes adjacent the shank a seating portion adapted to seat firmly within the convergent entry portion of the cross bore when the cross pin is in full engagement with the rod.

In a preferred embodiment of the invention, the shank being threaded adjacent the head and the distal end portion of the shank is unthreaded. Preferably, the distal end of the shank is of rounded form to facilitate cooperation with the entry section of the bore during insertion of the pin into the bore. The proximal and distal ends of the rod will each have at least one such bore for receiving a cross pin and each may have up to three such 15 bores. Advantageously, the rod is solid.

9 An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a side view, partially in cross-section, of a fixing device in accordance 20 with a preferred embodiment of the invention in association with a jig for manipulating the device; and Figure 2 is a section to an enlarged scale of the upper end portion of the fixing S. device.

I

In accordance with a preferred embodiment of the invention, an intramedullary fixing device for use in the humerus comprises a solid rod 2 of a suitable material such as stainless steel, with cross bores 4 and corresponding cross pins 6 which lock in a very stable manner within the cross bores 4, whilst the bores 4 are formed to facilitate insertion of the pins 6 even within the restricted access provided within the area of the humerus.

More particularly and as shown in Figure 2, each cross bore 4 is internally threaded at 4a over the majority of its length. The entry portion 4b of the cross bore 990412,p:\oper\rsh,fixing-device.cap,2 4 is of substantially larger diameter than the threaded bore 4a and converges to the diameter of the threaded bore 4a in order to provide an entry guidance section leading to the threaded bore 4a. The pin 6 comprises a head 8 and a relatively small diameter shank 10 which is threaded at 10a only in its part adjacent to the head 8, the distal end 10b of the shank 10 being of rounded form. By way of non-limiting example, the shank 10 can have a diameter of about 3 mm and the head 8 a diameter of about 6 mm. Insertion of the pin 6 into the cross bore 4 is facilitated by the convergent guidance section 4b which centres the unthreaded portion of the shank 10 relative to the threaded portion 4a of the bore 4 so that when the threaded portion 10a of the shank 10 adjacent the head 8 meets the threaded portion 4a of the bore it is in correct alignment relative to the threaded portion 4a and can be screwed into the threaded portion 4a to provide a very firm and stable anchorage.

It will be noted from the drawing that the length of the threaded portion 10a of the Sshank 10 is substantially equal to the depth of the threaded bore 4a so that the 15 portion of the shank 10 projecting beyond the rod 2 is itself entirely unthreaded. It will also be noted that the distal end 8a of the head 8 is of frusto-conical shape corresponding to the form of the convergent guidance section 4b of the bore 4 so that when the pin 6 is screwed into the bore 4, the tapered portion 8a of the head 8 is seated firmly within the guidance section 4b of the bore 4 which further assists in providing a very stable anchorage of the cross pin 6 within the rod 2.

S"A jig 12 is provided for manipulating the rod 2. For connection to the jig, the rod 2 has at its upper end 2a a tapered cross section with an internally-threaded bore 2b. The tapered section is also provided with one or more splines defining a longitudinal keyway 2c. The jig itself comprises a handle 14 which extends alongside the rod 2 and which carries a tubular head 16 of a diameter approximately equal to the diameter of the rod 2. At its lower end the tubular head 16 is internally tapered so as to receive the external taper of the upper end 2a of the rod 2, the lower end of the head 16 also including an inwardly-directed projection 17 which is adapted to slide into the longitudinal keyway 2c in the tapered end. The rod 2 is firmly, but releasably, attached to the head 16 by means of a pin 18 which extends downwardly through the head 16 into threaded engagement with the threaded bore 2b at the 950821,p:\oper\rshfixg-dvice.cap.3 -4upper end of the rod 2, so that by tightening the pin 16 the rod 2 will be drawn upwardly within the lower end of the head 16, with the tapered surfaces of the rod 2 and head 16 being in tight engagement, and with rotation of the rod 2 relative to the head 16 being prevented by engagement of the projection 17 within the keyway 2c. After setting the rod 2 within the humerus, the jig 12 can easily be released from the rod 2 by unscrewing the threaded pin 18 and withdrawing the head 16 axially away from the rod 2.

To set the rod 2 within the humerus, the bone is drilled substantially to the diameter of the head 8 of the cross pin 6 at the side of the bone adjacent the jig 12 and substantially to the diameter of the shank 10 of the cross pin at the opposite side. The cross pin 6 is then introduced and screwed firmly into the bore 4 in the rod 2, with the head 8 and projecting shank 10 thereby being located within the holes drilled into the bone. The very firm anchorage of the pin 6 relative to the rod 2 15 precludes the likelihood of breakage of the pin, while the initial insertion of the pin 6 is significantly facilitated by the design of the pin 6 and associated bore 2 in the rod.

The embodiment has been described by way of example only and modifications are possible within the scope of the invention.

950821,p:\oper\rsh,fiing-device.cap,4 THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:- 1. An intramedullary fixing device comprising a rod for location within the humerus and cross-bores extending through the rod for receiving cross pins for anchoring the rod to the bone at opposite sides of a fracture, each said cross bore having an internallythreaded portion and a convergent entry portion leading into the threaded portion, and each said cross pin comprising a head and a shank which is threaded to engage the internal thread in the bore, the convergent entry portion of the bore facilitating insertion of the pin into the threaded portion of the bore, and the head of each pin includes adjacent the shank a seating portion adapted to seat firmly within the convergent entry portion of the cross bore when the cross pin is in full engagement with the rod.

2. A fixing device according to claim 1, wherein the seating portion of the head of the pin is of a frusto-conical shape which corresponds to the shape of the entry section.

0,.

3. A fixing device according to claim 1 or claim 2, wherein the shank of each pin is threaded adjacent the head, the distal end portion of the shank being unthreaded.

4. A fixing device according to any one of claims 1 to 3, wherein the distal end of the shank of each pin is of rounded form to co-operate with the convergent entry portion of the bore during insertion of the pin.

0• A fixing device according to any one of claims 1 to 4, wherein the head of each pin has a substantially larger diameter than the shank.

6. A fixing device according to any one of claims 1 to 5, wherein at least one said bore is provided at the proximal and distal ends of the rod.

7. A fixing device according to claim 1 or claim 2, wherein when each pin is seated within its associated cross bore, the head of the pin projects to one side of the rod to engage within a hole drilled into one side of the bone, and a portion of the shank projects 990412,p:\oper\rsh,

Claims

8. A fixing device according to any one of claims 1 to 7, wherein the rod is solid.
9. A fixing device according to any one of claims 1 to 8, further comprising a jig for manipulating the rod, said jig including means for releasably attaching the jig to the proximal end of the rod, and a handle. A method of setting within the humerus, the rod of a fixing device according to any one of the preceding claims, comprising drilling one side of the bone with holes to a diameter substantially corresponding to that of the head of each pin, and drilling the opposite side of the bone with holes to a diameter substantially corresponding to that of the shank of each pin, and screwing the pins firmly into the cross bores of the rod, with the head and projecting shank portion of each pin being located within the holes drilled in the opposite sides of the bone.
11. An intramedullary fixing device, substantially as hereinbefore described with reference to the accompanying drawings. DATED this 12th day of April, 1999. JOHN WILLIAM OWEN and ROGER CHURCHWARD By their Patent Attorneys: DAVIES COLLISON CAVE 99042,p:\oper\rsh,fixing-device.cap,6 -7- ABSTRACT An intramedullary fixing device comprises a rod for location within the humerus, with cross-bores extending through the rod for receiving cross pins for anchoring the rod to the bone at opposite sides of a fracture. Each cross bore is internally-threaded to receive a partially threaded shank of the cross pin and has a convergent entry section which facilitates insertion of the pin into the bore. .i *4 e s 950821,p:\oper\rs,fxing-device.cap,7