GB1601591A

GB1601591A - Screw extracting device

Info

Publication number: GB1601591A
Application number: GB3997077A
Authority: GB
Original assignee: Chas F Thackray Ltd
Current assignee: SSL CC Services Ltd
Priority date: 1978-05-31
Filing date: 1978-05-31
Publication date: 1981-11-04

Description

(54) SCREW EXTOCTZG DEVICE (71) We, CHAS. F. THACKRAY LIM1TED, of P.O. Box 171, Park Street, Leeds, LS1 1 RQ, West Yorkshire, a British company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed,to be particularly described in and by the following state ment: This invention relates to devices for extras ting sCrews, especially, but not exclusively surgical screws from bone in the case where the screw head has broken off.

The present standard procedure for extracting the body of a surgical screw (normally a self-tapping screw), where the screw head has broken off, is to mill out a core of bone around the screw body. Conventional tools are inadequate for gripping the remaining exposed screw and, if it is left in, it is an embarrassment for the ensuing surgical operation.

The present invention is a device for gripping and removing a screw which, when applied to the removal of a screw body from bone, allows the screw to be extracted with little inconvenience.

According to the present invention there is provided a screw extracting device comprising a wire having at least a helical portion, and means for effecting engagement of said helical portion of the wire onto an exposed portion of the screw thread and for rotating said helical portion of the wire to effect a grip on the screw and then to rotate the screw.

Preferably a single tool is provided for effecting engagement of the helical wire onto the screw thread and also for rotating the helical wire. Preferably this tool includes means for aligning the helical wire longitudinally with respect to the longitudinal axis of the screw.

Preferably the helical wire is held to a por-tion of the tool so that rotation of this portion will tend to rotate the helical wire relative to the screw.

Preferably the wire includes both a helical and a straight portion, the tool including means for trapping the straight portion to hold it stationary relative to the tool. In one embodiment of the present invention the trapping means includes a nut which is located on a threaded portion of the tool and which is arranged so that it can be rotated relative to the tool to trap the straight portion of the wire against the body of the tool. In an alternative embodiment in accordance with the present invention the trapping means includes a sleeve slidable on the tool and arranged to trap the straight portion of the wire between the sleeve and the body of the tool.

Preferably the tool is provided with means for indicating when a sufficient number of turns of the screw thread have been engaged by the helical wire.

Embodiments of the present invention will now be described by way of examples only and with reference to the accompanying drawings, in which Figure 1 is å side elevation of the mill cutter (not forming part of the present invention); Figure 2 is a longitudinal cross-section of a screw extracting device in accordance with thq present invention; Figure 3 is a side elevation of the screw ex extracting device of Figure 2; Figure 4 is an end elevation óf the screw extracting device of Figure 2; Figure 5 is a side elevation of another screw extracting device in accordance with the present invention; and Figure 6 is a longitudinal section through the screw extracting device of Figure 5.

Referring to Figures 2 to 4, a screw extrac- - ting device in accordance with the present inyen- tion includes a tempered wire 1 having a helical portion la and, extending from one end of the helical portion la, a straight portion lb. The device also includes a tool 2 to be used- together with wire 1. In an alternative embodiment, the tempered wire 1 may be replaced by a helical spring wire having a non-helical portion of wire integral therewith.

Tool 2 includes an elongate body 3 having a central bore within which is accommodated a rod 4 which is slidable within the central bore and which acts as a depth gauge.

Near one end of body 3 the central bore opens out to a short section 5 of slightly greater diameter, section 5 in turn opening to a short tubular section 6 which is provided with a cut out portion 6a and which extends to the end of body 3.

Extending from a position at the junction of sections 5 and 6 longitudinally along the body 3 of tool 2 is a slot 7.

Slot 7 terminates at its other end adjacent a clamp 8 mounted on body 3 of tool 2. Adjacent the other side of clamp 8 and located on a threaded portion of body 3 is a clamp nut 9 which may be turned relative to body 3 in order to cause clamp 8 to move axially relative to body 3.

Body 3 of tool 2 is provided with a recessed portion 12 extending across slot 7 to enable a suitable implement such as a screwdriver to be inserted under the wire to assist in the removal thereof.

Rigidly attached to the end of body 3 remote from section 6 is a handle l O.

The above described device may be used for extracting the body of a surgical self tapping screw, the screw head having broken off leaving the body lodged in bone. In order to effect the extraction, the first stage is to remove any obstruction such as bone plate. A mill cutter such as that shown in Figure 1 is then placed over the top of the screw body, carefully aligned and bone is cut through the proximal cortex.

Helical wire 1 is then fitted into the tool 2 by positioning the helical portion la into section 6 of the body 3 of the tool, section 6 thereby aligning the helical portion of the wire along the longitudinal axis of the tool 2. The straight portion ib of the wire is then inserted into slot 7 and threaded along the slot up to the clamp 8. Clamp nut 9 is then rotated so as to cause axial movement of clamp 8, thereby trapping the portion Ib of wire 1 against the body 3 of tool 2.

In an alternative embodiment the clamp 8 is omitted so that it is the clamp nut 9 itself which traps the portion lb of wire 1 against the body 3 of the tool 2.

The tool 2 is then positioned with section 6 over the end of the body of the screw and its longitudinal axis aligned with the axis of the screw. With the end of the helical portion la of the wire 1 in contact with the end of the body of the screw, the handle 10 is turned clockwise and the resultant friction between the end of the wire 1 and the top of the screw causes the helical portion la of the wire 1 to open and engage into the screw thread. As the handle is turned the body 3 of tool 2 moves relatively towards the screw body and the top of the screw body engages the end of depth gauge 4. Depth gauge 4 is thus moved relatively towards handle 10. When the other end of depth gauge 4 projects beyond the end of body 3 which carries handle 10 the helical portion la of wire 1 has engaged with a sufficient number of turns of the screw body, for instance, about five or six turns.

The handle 10 is then turned anti clockwise causing the helical portion la of wire 1 to grip and turn the screw until it is fully extracted from the bone.

Once the screw body has been extracted, the wire 1 is disposed of together with the screw body engaged thereby. A new wire may be int serted in the tool ready. for its next use.

The device may be made of metal and can be dismantled so that cleaning and sterilisation is a simple operation. Preferably the wire is made of a metal with greater tensile strength than that of the screw so that if the screw remains lodged in the bone the part of the screw contained within the helical portion of the wire will shear rather than the wire itself.

The device may have shape and dimensions such that it is suitable for removing the screws used in surgery.

Referring to Figures 5 and 6, another embodiment of a screw extracting device in accordance with the present invention includes a tempered wire (not shown) similar to that described in connection with the embodiment of Figures 2 to 4 and a tool 21 to be used together with the wire. Tool 21 includes elongate member 23 having a relatively long shank portion 25 and integral therewith and extending therefrom a relatively short portion 27 of slightly greater diameter and carrying a handle 29.

Elongate member 23 has a central bore within which is accommodated a rod 31 which is slidable within the central bore and which acts as a depth gauge.

The end portion 33 of elongate member 23 is in the form of a short tube, integral with the rest of elongate member 23 and having a cut out portion 35.

Extending from section 33 in a direction towards handle 29 is a slot 37, the length of slot 37 being sufficient to accommodate the non-helical portion of the wire. As can be seen in Figure 6 slot 37 includes a curved portion 39 extending from section 33 of elongate member 23 to a straight portion 41 of the slot. In addition the slot is provided with a short extension 43 beyond the junction of the curved portion 39 and straight portion 41.

The tool also includes a metal sheath 45 which is slidable on elongate member 23.

Sheath 45 includes a portion 47 having a gently narrowing exterior end 49 and an approximately constant internal diameter. Integral with section 47 and extending therefrom is a section 50 of slightly greater diameter there being a stepped junction 51 between sections 47 and 50. At the end of section 50 and remote from section 47 the sheath 45 is provided with an integral annular flange 53. Finally sheath 45 is provided with an inner small lug 55 integral with section 47 and of dimensions such that it can be located in slot 37 for sliding movement therein.

Tool is further provided with helical spring 57 which may be located around elon- gate member 23 so that one end thereof abuts against the stepped junction 59 between sections 25 and 27 of elongate member 23 and the other end of spring 57 abuts against stepped junction 51 of sheath 45.

In use the device will initially be as shown in Figures 5 and 6, that is to say, not including the tempered wire. Tool 21 is gripped in the hand by means of handle 29 with the index and second fingers around flange 53 of sheath 45.

The sheath 45 may then be drawn towards handle 29 against the action of spring 57, thereby revealing slot 37. The tempered wire is then positioned with its helical portion in space 33 and its non-helical portion extending along curved portion 39 of slot 37 and to the end of straight portion 41 of slot 37. Flange 53 of sheath 45 is then released and the sheath will be urged by spring 57 in a direction away from handle 29. This movement will continue until the inner surface of sheath 45 engages the tempered wire in straight portion 41 of slot 37, the nature of the material of the wire and/or the diameter of the wire relative to the depth of the slot being such that the sheath will tend to clamp the wire between the sheath and the elongate member 23. The sheath 45 will, in any case, not be able to move in a direction away from handle 29 beyond the position where lug 55 engages the end of the tempered wire.

The end of the helical portion of the wire is then placed in contact with the end of the body of a surgical self-tapping screw to be extracted from a bone and the body of the screw is extracted in the same way as that described in connection with the device shown in Figures 2 to4.

When the surgical self-tapping screw has been removed from the bone, then the screw and tempered wire may be removed from the tool 21 by pulling sheath 45 towards handle 29, thereby releasing the wire from its hitherto trapped position. Having removed the wire and screw the device may be easily dismantled for sterilising purposes although it should be noted that simply releasing flange 53 of sheath 45 will not result in the removal of the sheath from the tool. This is because spring 57 will urge sheath 45 in a direction away from handle 29 but only to a position where lug 55 of sheath 45 reaches the end of side junction 43 of slot 37, when further movement longitudinally of elongate member 23 is prevented. In order to dismantle the device the sheath has to be twisted relative to the elongate member so that the lug 55 passes along curved portion 39 of slot 37.

WHAT WE CLAIM IS: 1. A screw extracting device comprising a wire having at least a helical portion, and means for effecting engagement of said helical portion of the wire onto an exposed portion of the screw thread and for rotating said helical portion of the wire to effect a grip on the screw and then to rotate the screw.

2. A screw extracting device according to Claim 1 wherein a single tool is provided both for effecting engagement of the helical wire onto the screw thread and also for rotating the helical wire.

3. A screw extracting device according to Claim 2 wherein the tool includes means for aligning the helical wire longitudinally with respect to the longitudinal axis of the screw.

4. A screw extracting device according to any of the preceding claims wherein the wire includes both a helical and a straight portion, the tool including means for trapping the straight portion to hold it stationary relative to the tool.

5. A screw extracting device according to Claim 4 wherein the tool includes a body portion and the trapping means includes a member mounted on the body portion of the tool for rotation relative thereto, the member being arranged so that on rotation it will trap the straight portion of the wire against the body of the tool.

6. A screw extracting device according to Claim 4 wherein the tool includes a body portion and the trapping means includes a sleeve slidable on the body portion of the tool and arranged to trap the straight portion of the wire between the sleeve and the body of the tool.

7. A screw extracting. device according to Claim 1 and substantially as described herein.

8. A screw extracting device substantially as described with reference to Figures 2 to 4 of the accompanying drawings.

9. A screw extracting device substantially as described with reference to Figures 5 and 6 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Figures 5 and 6, that is to say, not including the tempered wire. Tool 21 is gripped in the hand by means of handle 29 with the index and second fingers around flange 53 of sheath 45. The sheath 45 may then be drawn towards handle 29 against the action of spring 57, thereby revealing slot 37. The tempered wire is then positioned with its helical portion in space 33 and its non-helical portion extending along curved portion 39 of slot 37 and to the end of straight portion 41 of slot 37. Flange 53 of sheath 45 is then released and the sheath will be urged by spring 57 in a direction away from handle 29. This movement will continue until the inner surface of sheath 45 engages the tempered wire in straight portion 41 of slot 37, the nature of the material of the wire and/or the diameter of the wire relative to the depth of the slot being such that the sheath will tend to clamp the wire between the sheath and the elongate member 23. The sheath 45 will, in any case, not be able to move in a direction away from handle 29 beyond the position where lug 55 engages the end of the tempered wire. The end of the helical portion of the wire is then placed in contact with the end of the body of a surgical self-tapping screw to be extracted from a bone and the body of the screw is extracted in the same way as that described in connection with the device shown in Figures 2 to4. When the surgical self-tapping screw has been removed from the bone, then the screw and tempered wire may be removed from the tool 21 by pulling sheath 45 towards handle 29, thereby releasing the wire from its hitherto trapped position. Having removed the wire and screw the device may be easily dismantled for sterilising purposes although it should be noted that simply releasing flange 53 of sheath 45 will not result in the removal of the sheath from the tool. This is because spring 57 will urge sheath 45 in a direction away from handle 29 but only to a position where lug 55 of sheath 45 reaches the end of side junction 43 of slot 37, when further movement longitudinally of elongate member 23 is prevented. In order to dismantle the device the sheath has to be twisted relative to the elongate member so that the lug 55 passes along curved portion 39 of slot 37. WHAT WE CLAIM IS:

1. A screw extracting device comprising a wire having at least a helical portion, and means for effecting engagement of said helical portion of the wire onto an exposed portion of the screw thread and for rotating said helical portion of the wire to effect a grip on the screw and then to rotate the screw.