WO2006120437A1

WO2006120437A1 - External fixator and distractor

Info

Publication number: WO2006120437A1
Application number: PCT/GB2006/001706
Authority: WO
Inventors: Martin Elloy; Peter James Raffan
Original assignee: Fixator Innovations Limited
Priority date: 2005-05-10
Filing date: 2006-05-09
Publication date: 2006-11-16
Also published as: GB0509491D0; GB2425958A

Abstract

A transfixion pin clamp comprises (i) a collet having jaws, a tapered portion and a threaded portion, (ii) a body having a hole therethrough sized to receive at least the threaded portion of the collet and having means for the attachment of one or more frame members, and (iii) a nut sized to index the threaded portion of the collet, wherein in use a transfixion pin may be placed within the jaws of the collet, the body placed about the collet and the nut threaded onto the collet and tightened to move the body onto the tapered portion of the collet thereby tightening the jaws about the transfixion pin.

Description

EXTERNAL FIXATOR AND DISTRACTOR

Field of Invention

The present invention relates to a pin clamp for use in external fixator and distractor devices useful in aiding the healing of bone fractures and the like. In particular, although not exclusively, the present invention relates to a collet type pin clamp and its use in securing transfixion pins.

Background to the Invention

Fractures of the long bones may be treated by means of internal fixation devices such as pins, plates and screws. These are applied to the broken bones once the fragments have been properly aligned and then fixed to maintain that alignment while healing takes place.

Bone fragments can be difficult to align prior to the application of an internal fixation device because of the considerable force usually needed to stretch the soft tissue contraction that normally accompanies displaced fracture. The services of a strong assistant to the operating surgeon are often required. Another way to facilitate realignment or reduction of a fracture is to use devices known as fracture tables or reduction machines. Usually clamps or pins are secured to the limb or directly to the bone fragments and then manipulated and locked in the desired position while the internal device is being applied.

An alternative system for fracture fixation, known as an external fixator, comprises an adjustable frame clamped to transfixion pins that are screwed into appropriate positions in the fractured bone. By adjusting the frame attached to the pins, realignment of the bone fragments can be achieved. The frame and clamps may be locked in position to function as an external fixator. Such external fixators are often complex and have a number of joints which have to be secured against loss of position. The result is usually a bulky and costly construction that impedes radiographic checks on the quality of reduction.

EP 1312316 teaches a transfixion pin securing device having a portion that is fitted about a pin and then secured to the pin using a crimped band. The band requires a crimping tool to effect attachment. The crimping secures the pin irreversibly to the device and so adjustment requires the removal of the band and the crimping of another band about the device.

It is an object of the invention to overcome the disadvantages associated with the art or to at least provide the public with a useful alternative.

Summary of the Invention

In a first aspect, the invention provides a transfixion pin clamp, comprising a collet having jaws moveable between a clamping position, in which the jaws are closed around and clamp a transfixion pin, and an open position, in which the jaws are open and the pin can be removed axially from the collet. In typical use two or more clamps are part of a fixator or distractor apparatus and are held spaced apart by a frame, each clamp being clamped to a pin attached to a bone. The clamps can be attached and released without disturbing the pins or any other fixing apparatus attached to the pins.

In an embodiment, the invention provides a transfixion pin clamp, comprising (i) a collet having jaws and a tapered portion and (ii) a body having a hole therethrough sized to receive a part of the tapered portion of the collet and having means for attachment of one or more frame members, wherein in use a transfixion pin may be placed in the jaws, the body located about the collet and urged further onto the collet so as to tighten the jaws about the transfixion pin.

In use, the body hence acts on the collet to close the jaws to clamp the pin in place. A fastener is optionally provided which co-operates with the collet and body to fasten and release the clamp. In one embodiment the body and fastener are in threaded engagement and turning the fastener fastens or releases the clamp. In a further embodiment the collet and fastener are in similar threaded engagement.

The fastener can be or' comprise a nut or canulated screw. Threaded portions can be provided on one or more of the collet, body and/or fastener.

In a particular embodiment of the present invention there is provided a transfixion pin clamp comprising (i) a collet having jaws, a tapered portion and a threaded portion, (ii) a body having a hole therethrough sized to receive at least the threaded portion of the collet and having means for the attachment of one or more frame members, and (iii) a nut sized to index the threaded portion of the collet, wherein in use a transfixion pin may be placed within the jaws of the collet, the body placed about the collet and the nut threaded onto the collet and tightened to move the body onto the tapered portion of the collet thereby tightening the jaws about the transfixion pin.

Preferably the clamp apparatus includes a bush which is adapted to fit about the pin and within the jaws of the collet. The bush can be of a split variety and have an aperture passing all the way through so the split can be opened and the bush passed over the pin before clamping. In this way, there is provided a transfixion pin clamp adapted for connection to or disconnection from a transfixion pin in a direction which is not substantially along the axis of said transfixion pin. The apparatus can thus be clamped onto an existing pin, or the apparatus removed without disturbing an overlying fixator. The bush may also be of a similar arrangement but sprung so that sides of the bush can be forced apart to locate the pin in the aperture and the sides will then spring back to grip the pin. In preferred embodiments the bush is of a circular cross section, more preferably the bush is of substantially spherical shape, allowing more flexibility in moving the pin relative to the collet.

In other embodiments the pin bush has two flat faces parallel to the plane of the split which are adapted to engage corresponding flat faces inside the jaws of the collet. Alternatively the pin bush may have prominences on the flat surfaces to engage corresponding recesses in the jaws of the collet.

The collet, body, nut and any other components used in the clamp may be made of any suitable material. In preferred embodiments the components are made of a radiolucent material which helps to prevent the clamp interfering with radiographical investigation of fracture reduction or repair.

The apparatus may include inside the collet an expander rod which when urged further into the collet opens the jaws to release the pin. One such rod, described in more detail below, has a tapered end capable of engaging a shoulder inside the collet and another end which passes through and protrudes beyond the collet. The rod is secured within the collet by a collar having a diameter large enough so as not to pass through the nut and adapted so that when the nut is loosened and wound back down the thread of the collet, it engages the collar pulling the expander rod into the collet where its tapered end indexes the shoulder inside the collet opening the jaws of the collet, thereby releasing the pin or the bush (and pin).

In preferred embodiments the collet is of substantially circular cross-section. The jaws of the collet may be sized to accommodate different sized transfixion pins so that the optimal sized pins can be used for the type of animal to be treated. The collet, body and nut may be of any scale; typically smaller for use on dogs and cats or larger for use on any larger animals, including humans

The diameter of the hole through the body of the pin clamp is preferably the same size or only slightly larger than the major diameter of the threaded portion of the collet. It is preferably smaller than the major diameter of the conical region of the collet. This ensures that, in use, the body can engage the tapered portion of the collet close to or at the point where the threaded portion of the collet ends and the taper begins.

In some embodiments the hole in the body of the clamp is tapered. In these embodiments the collet is caused to clamp the pin or bush by the interaction of an external taper of the collet with the internal taper of the body. Action on the fastener, e.g. when a nut is threaded onto the collet, drives the two tapers together locking the relative positions of the collet and the body.

The jaws of the collet may be adapted to provide re-entrant or leading geometry. In these embodiments a transfixion pin or bush is retained within the jaws by a combination of friction between the clamped surfaces and re-entrant geometry, which can only be released by separating the jaws of the collet. Where leading geometry is provided, forcible engagement and separation can be effected when the jaws are unlocked by a wedging action between the counter surfaces of the re-entrant geometry. This is effected in a direction substantially perpendicular to the bush pivot axis.

In a further aspect the invention provides a fixator or distractor device comprising one or more transfixion pin clamps according to the invention. The device can be comprised of two or more clamps attached via one or more frame members. A device with two or more frame members can include frame members in different planes.

The attachment of one or more frame members to the body of the clamp may be in the form of any suitable type of connection, for example a male or female screw thread, push fit or any other known attachment means. Preferred embodiments have a female screw thread into which frame elements having a corresponding male screw thread may be threaded. Other preferred embodiments have a hole through the body adapted to receive a rack. Hence, two clamps on the same rack can be moved relative to each other. These embodiments advantageously include means within the body to move the body relative to the rack such as a pinion in connection with a pinion driver. In preferred embodiments the pinion driver is in the form of a lobed handle. Further embodiments may include a means for locking the collet housing on the rack, such as a lever or locking pin. The lever or locking pin may be configured to lock into the pinion teeth or wedge the pinion shaft. Preferably, the locking mechanism is provided on the pinion. In one example the locking mechanism comprises a cam bearable against the surface of the pinion or the pinion drive shaft. In one particularly preferred embodiment the attachment means includes threads having an axis essentially perpendicular to the axis of the pin clamp. Two such threads may be provided diametrically opposed and have opposite handedness, i.e. one right-handed (RH) thread and the other left-handed (LH). In this embodiment adjacent clamp bodies are joined by connecting rods provided with RH thread at one end and LH thread at the other so that screwing in one direction causes adjacent bodies to separate whilst screwing in the other direction causes them to close together.

Clearly the relative angular position of the bodies can also be varied about the connecting rod axis.

The device of the invention is relatively simple to use but allows easy adjustment of pin angles as well as fixture of the pins after adjustment without the need for bulky tools or extra parts.

In a further aspect the invention provides a method for distracting, fixing or securing a bone fracture in an animal (including a human) comprising using a transfixion pin clamp according to the invention.

The invention also provides a method for distracting, fixing or securing a bone fracture in an animal (including a human) comprising using a fixator or distractor device according to the invention.

In another aspect the invention provides a kit comprising a plurality of collets, bodies and nuts, and optionally transfixion pins, bushes and frame members, which can be assembled into a clamp or distractor of the invention.

In a further aspect the invention comprises a transfixion pin clamp for use in a bone distractor, the transfixion pin clamp comprising a collet having jaws, the jaws adapted for clamping a transfixion pin at an angle substantially perpendicular to the axis of the collet and for allowing adjustable angular positioning of the transfixion pin relative to the axis of the collet. Description of Drawings

The invention is now discussed with reference to the accompanying drawings in which:

Figure 1 : shows an exploded perspective view of a pin clamp according to one embodiment of the invention; Figure 2: shows a perspective view of three devices of the invention connected via frame elements;

Figure 3: shows a perspective view of a further embodiment of the device of the invention;

Figure 4: shows a section through the device shown in figure 3 on a plane through the axes of the pinion and the locking pin;

Figure 5: shows a section through the device shown in figure 3 in the plane of one face of the rack;

Figure 6: shows a section through the device shown in figure 3 in the plane of the top face of the body with the locking pin shown in a locked position; and

Figure 7: shows a section through the device shown in figure 3 in the plane of the top face of the body with the locking pin shown in an unlocked position.

Detailed Description

The pin clamp shown in Figure 1 comprises a bush (1), in the form of a split bush which is placed around the transfixion pin (2) which is to be secured. The bush fits over the transfixion pin by virtue of a split which passes substantially through its section but does not completely divide the bush and may be sprung open to fit onto the pin or clamped closed to grip it. The bush (and pin) is fitted inside the jaws of a split collet (3) having a portion with a tapering outside diameter and a threaded portion. To clamp the transfixion pin, a body portion (4) is placed over the collet and driven onto the collet by a nut (5) so that the jaws of the collet clamp down about the bush. The body portion (4) may be rotated about the collet axis prior to tightening of the nut (5) to give the desired alignment of the transfixion pin relative to the body or to another pin attached via the body portion.

The body (4) as shown in Figure 1 is adapted for the attachment of further devices engaging the limb to be secured. In practice two or more of the depicted devices can be used to align and/or fix portions of fractured bone by attaching the bodies of two or more devices together via frame elements.

Figure 2 shows three transfixion pins (2) secured in clamps according to the invention. The frame elements (8) attach to the body (4) of each apparatus and retain the clamps and therefore the transfixion pins in fixed relative geometry. The bodies can be connected together with frame elements adapted to allow the bodies to be brought closer together or further apart. The bodies may be positioned in a variety of angular relationships to one another so as to provide at least two more degrees of freedom to the relative positioning of the transfixion pins.

The device shown in Figure 1 has an expander rod (6) which fits inside the collet and has a tapered end capable of engaging a shoulder inside the collet. The expander rod is secured within the collet by a collar (7) having a diameter large enough so as not to pass through the nut (5). When the transfixion pin is in the clamped configuration and the nut (5) is tightened up against the body (4) of the apparatus, the expander rod merely sits inside the collet. When the transfixion pin is to be released from the collet, the nut (5) is loosened and wound back down the thread of the collet until it touches the collar (7). When further pressure is placed on the collar (7) it pulls the expander rod into the collet where the tapered end of the expander rod indexes the shoulder inside the collet opening the jaws of the collet, thereby releasing the bush (and pin).

The pin (2) can be clamped at any position along its length, at any angle about its axis and at any angle to the axis of the collet (3). Before locking, the collet can be set in any angular position about the collet axis relative to the position of the body

(4). The device of the invention therefore provides four degrees of freedom to adjustment of the body relative to the pin. The device may be used to arrange bones and then hold them in position while healing of the fracture takes place. The device may be clamped onto a pin in situ, without disturbing the pin. The device may also be used to hold the bones in place while another type of fixator is applied, and can then be removed from below the fixator.

The device shown in figure 3 has a hole through the body adapted to receive a rack (9). The device includes a pinion (11) inside the body (4) in connection with a pinion driving handle (10), to move the body relative to the rack. The nut (5) acts in the same way as discussed in other embodiments to close the jaws of the collet (3). In use the pinion driving handle (5) can be turned to contract or extend the gap between this device and others which may be mounted to the same rack. This allows the device to be used in the movement of transfixion pins relative to one another to gain desired bone geometry before fixing.

Also shown is one configuration of locking pin (12) described in more detail below. The locking pin is fitted with a handle portion to facilitate rotation about its axis between the unlocked and locked positions. Other configurations are also possible.

Figure 4 shows a cross section of the pinion (11) and its attached driving handle (10). Also shown is one possible configuration of the locking pin (12), which has a cam form cross section so that when rotated from its unlocked position it interferes with the pinion driving handle (10) at a point (13) and wedges it against rotation.

Figure 5 shows the pinion in driving engagement with the rack so that rotation of the pinion causes relative movement of the body along the axis of the rack.

Figure 6 shows the locking pin (12) wedged against the outer diameter of the pinion driving handle (10) thus preventing rotation of the pinion.

Figure 7 shows the locking pin (12) in its unlocked position with no contact with the pinion driving handle (10). Alternatively the locking pin could be made to engage the pinion teeth to prevent rotation.

The invention thus provides a pin clamp and uses thereof.

Claims

1 A transfixion pin clamp comprising (i) a collet having jaws, a tapered portion and a threaded portion, (ii) a body having a hole therethrough sized to receive at least the threaded portion of the collet and having means for the attachment of one or more frame members, and (iii) a nut sized to index the threaded portion of the collet, wherein in use a transfixion pin may be placed within the jaws of the collet, the body placed about the collet and the nut threaded onto the collet and tightened to move the body onto the tapered portion of the collet thereby tightening the jaws about the transfixion pin.

2 A device according to claim 1 wherein it additionally includes a bush adapted to fit about the pin and within the jaws of the collet.

3 A device according to claim 2 wherein the bush is of a circular cross section.

4 A device according to claim 2 or claim 3 wherein the bush is of substantially spherical shape.

5 A device according to claim 2 wherein the pin bush has two flat faces which are adapted to engage corresponding flat faces inside the jaws of the collet.

6 A device according to claim 5 wherein the pin bush has prominences on the flat surfaces to engage corresponding recesses in the jaws of the collet.

7 A device according to any preceding claim wherein the hole through the body of the pin clamp is the same size or only slightly larger than the major diameter of the threaded portion of the collet and smaller than the major diameter of the conical region of the collet.

8 A device according to any preceding claim wherein the hole in the body of the clamp is tapered. 9 A device according to any preceding claim, comprising an expander rod inside the collet and having a tapered end capable of engaging a shoulder or conical seat inside the collet, the expander rod being secured within the collet by a collar having a diameter large enough so as not to pass through the nut and adapted so that, when the nut is loosened and wound back down the thread of the collet, it engages the collar pulling the expander rod into the collet where its tapered end indexes the shoulder or conical seat inside the collet opening the jaws of the collet, thereby releasing the pin.

10 A device according to any preceding claim wherein the components are made of a radiolucent material

11 A device according to any preceding claim additionally including a hole through the body adapted to receive a rack and means within the body to move the body relative to the rack.

12 A device according to claim 11, further comprising a locking mechanism for preventing movement of the body relative to the rack.

13 A device according to claim 11 or 12, wherein the means within the body to move the body relative to the rack is a pinion in connection with a pinion driver.

14 A device according claim 12 or 13, wherein the locking mechanism is provided on the pinion.

15 A device according to any of claims 12 to 14, wherein the locking mechanism comprises a cam bearable against the surface of the pinion or the pinion drive shaft.

16 A device according to any preceding claims wherein the means for attachment of one or more frame members to the body of the clamp comprises one right-handed

(RH) female thread one left-handed (LH) female thread. 17 A fixator or distractor device comprising one of more transfixion pin clamps according to a preceding claim and at least one frame element.

18 A method for distracting, fixing or securing a bone fracture in an animal, including a human, the method comprising using a transfixion pin clamp or a fixator or distractor device according to any one of the preceding claims.

19 A kit comprising any number of collets, bodies, and nuts, and optionally transfixion pins, bushes and frame members, which in combination make one or more devices according to any one of claims 1 to 16.

20 A transfixion pin clamp for use in a bone distractor, the transfixion pin clamp comprising a collet having jaws, the jaws adapted for clamping a transfixion pin at an angle substantially perpendicular to the axis of the collet and for allowing adjustable angular positioning of the transfixion pin relative to the axis of the collet.

21 A transfixion pin clamp for use in a bone distractor, the transfixion pin clamp adapted for connection to or disconnection from a transfixion pin in a direction which is not substantially along the axis of said transfixion pin.

22 A device substantially as herein described and claimed.

23 A method substantially as herein described and claimed.

24 A kit substantially as herein described and claimed.