GB2451227A

GB2451227A - External fixator pin clamp

Info

Publication number: GB2451227A
Application number: GB0712792A
Authority: GB
Inventors: Martin Arthur Elloy; Peter Raffan
Original assignee: FIXATOR INNOVATIONS Ltd
Current assignee: FIXATOR INNOVATIONS Ltd
Priority date: 2007-07-03
Filing date: 2007-07-03
Publication date: 2009-01-28
Also published as: GB0712792D0; WO2009004347A1

Abstract

An external fixator pin clamp comprises a clamp 1 having an open recess 1a to accept a fixator beam 5 and a cam 3 to clamp onto the beam 5. The clamp 1 may also comprise a locking bolt 2 that attaches a transfixion pin 4 by clamping it onto an external textured surface 1d of the clamp 1. The cam 3 may pivot on the bolt 2 and rotates about its axis. The transfixion pin 4 may pass through a hole 2a or notch in a head portion of the bolt. The cam surface may have a notch 3d on it which corresponds to the cross section of the beam 5. The clamp 1 may have a protective cap 8a which shields any moving parts and covers the free end of the transfixion pin 4. The clamp 1 may be made of plastics.

Description

EXTERNAL FIXATOR PIN CLAMP

The preseilt iflSs CfltiOfl relates to l tixaror for USC ifl external fixation of hone fractures. in prrticulti. the present in Ventioll relates to a Ii xator pin clamp and pro1ectie cap.

various different fracture repair s stems are in common use to manage unstable fractures of hones. These include external lixator systems using a scallok! ol hxaior members. e.g. metal rods or heanis. and clamps, and internal ti xator systems. for example the hone plate and scie' stem and the interiockin nail ssteiii.

The main advantages of the external tixator s\ stein are that it allows adjustnieiits to fracture alignment and loading during and after surger. It is a system that can he applied without approaching the fracture site. Also. the ability to use a minimally invasi e. closed application technique preserves surrounding solt [issue. minimises damage to the hone's blood supply and optimises the biological eii iiuiiiuent at the ii actuie site foi hone healing.

The external lixator has three basic cleiiient. regardless of the device or system used. These are transfixion pins of various si7es that are screwed into the hone and left protruding through the skin. ngid connecting beam or beams, on the outside of the skin, to bear the load IS and pin clamps to connect the heanus to the pins.

The 1i1S are placed into or through sound hone on either side of the fracture site. However.

the position of the pins is governed by the presence of muscle and other soft tissLue. blood essels and nercs. Wherecr possible. the pins are placed in safe corridors' in the soil tissue and max' emerge fromii the skin at different angles and in different planes. Moreover it has been shown that pins at various angles arc more effective in supporting the hone fragments.

The choice of pin angles is limited, in mans' external tixators. by the desigmi of the pin clamp and the use of straight. rigid beam elements. Mans' of the existing pin clamp designs also require a degree of dismantling to fit onto a beam, or have to he threaded onto the beam from oiie end. With currently a'ailahle s'vstems. inserting or removing pin clamps from between other pin clamps without loss of integrity of the pre-existing fixator construct, can he problematic. And pin clamps are generally made of radio opaque material that can interfere with radiological examination of the fractured bone.

It is. therefore. an object of the present invention to provide a device to connect fixator beams to translixion pins that is suiiicientlv ersatile to address these problems. is simple to use arid could he made largely of radiolucent material. In particular to take full advantage of the special characteristics of a mouldable beam as described in PCT/GB2007/00 1372.

According to the present invention, there is provided a clamp for connecting a transfixion pin to rigid beams for external fixation of hone fractures.

The present in'ention therefore provides a tixator pin clamp, which has a feature to accept a translixion pin by axial sliding and a second open laiure to directly accept a fixator heaiii element. The former feature has provision to temporarily hold its position on the pin whilst the beam is placed in position. The latter feature is provided with a cam for independently clamping the beam without compronlising the clamp attachment to the pin. Both features have a common final locking element. The clamping device provides for any angle between any pin and any beam l ing in an plane parallel to the pin. These features allow clamps to he attached to pins and then optimally aligned to accept a beam or beams to which they are finally clamped by means of a cam.

A prelen'etl embodiment of tills invention is described with reference to Figures I. 2. 3 and 4.

which arc isometric views.

Figure 1 shows the clamp and the pi-otective cap. Fig. I a shows an exploded ol the device comprising hod ( I). clamp bolt (2). cam (3). transfi xion pin (4). heani S). locking nLiI (6). sleeve (7). and protective cap (8): fig. lii sho s another \ icw ol hod' Coilipollent I I) llr additional claitv.

Figure 2 shows the device in an open position wit Ii tile beam ill place. Fig. 2a is an external \ ie and 11g. 2b a sectional iew through the i)laIle ol s\ inifletr) Figure 3 shos the clamp in a closed position. Fig. 3a is an external view of the device Fig. 3h is a sectional ie through the plane of svmilietr\.

Figure 4 illustrates a protective cap. Fig. 4a shows the cap alone in a closed position: fig. 4h shows the cap installed on the assemhl: figs. 4c and 4d show the assembl with the cap I 5 open: and hg. 4e sho s tile cap aloile iii au opei Position.

unless otherwise specified Figs. Ia and lb will he used as a key to identify the features below: The component parts comprise a hod' part ( I) having a hole (Ic) to accept the outer diameter (3a) of a cam part 3). and a concentric hole ( Id) to accept the head portion of a threaded clamping bolt (2). which is surrounded by an elastomeric sleee (7). The shaft (2h) of' the clamping bolt (2) passes through a concentric hole ill the cam part and is titted with a locking nut). The head of the bolt has a cross hole (2a) of sufficient size to accept the largest transfixion pin (41 to he used in this application.

A translixion pin (4 lorceiuil penetrates tile wall of an elastomenc sleeve (7) passing through a hole (2a) in tile cialllpiilg bolt (2). Tile Ilole thus formed in the sleeve (7)is tight on the pin and thereby retains it in position. Tightening the nut (6) on the bolt (2) has the effect of pulling the translixion pin 4 into engagement with a textured surl'ace. in this illustration one of many radial grooves (1 h). on the face of tile body (I). thereby resisting rotatloil as well as further axial movement of the bolt v ithin the body.

The bod' has a semi-cylindrical groove I I a. which matches the diameter of the beam (5).

cut perpeildictilarly to the cam support surface (Ic) and intersecting it. This groove opens to the surface of the body opposite to the bolt head to form a hook feature.

The cam (3) has a cylindrical sLirface (3a) with a circumferential notch (3d) of' varying shape and at a varying depth. i.e. at varying distance Ironl tile pivot axis. so that. wileil assenlbled to tile body in the closed position shown in Fig. 3. it complements the beam (5) and in tile OCfl position. shown in Fig. 2. which looks along the axis of' the beam. the groove is not visible because it is clear oh the notcil (3d). Thus l'ree entry of a beam (5) into the body is possible.

Refernng to Fig. I. additional clearance iiia he provided by a flattened area (3f) on the cani surface (3a). The cam also has a flange feature (3h). projecting only in a direction that makes lace (3e) cover the beam when the cam is positioned as in Fig 3 hut is clear of' the beam when positioned as in Fig. 2. A projection (3c) fronl the flange face opposite (3e) gives manual purchase to rotate the cam. When the cam is rotated within the body through approximately 90°. a shallower portion of notch (3d) engages the beam with interference at point (9) in Fig 3h. thereb clamping it in the groove. In this position tile flange feature (3h) on the cam covers the entry point foi' the beam into tile both. Stop features (1 e) and 1f limit the torsional niovenlent of' the cam.

When tile nut (6) is hinaily tightened on the bolt (2). the pin (4). resting on the textured surface of' the body. prevents further axial movement of the bolt within the body so that the nut drives the cam part deeper into the body, forcing tile flange portion (3h) of the cam and the surface of the notch (3d) harder against the beam at points (9) and (10) respectively thereby further clamping it in the groove ( Ia) and also resisting any further rotation of the cam.

In a preferred embodiment, the earn is supported by both the body surface ( Ic and the heani (5. In this configuration the bolt (2) is supported h the pin (4) and the cani (3). The pin, in turn, is supported h) the textured sun ace ( I h ol the body ( I). In (he prelerred embodiment the texture on this sui-face takes the form of groo\ cc radiating from the bolt axiS. Such grooves are preferably V-shaped to effecti clv accoiiimodare a variety of pm sizes.

Altet-nati e fi'rms to the caiii surface iiiav he de iced to have the same effect.

Contact het een the f!ane feature and the beam may he omitted because the notch traps the beam.

AdditionaIl the bolt feature may he used as a pivot for the cam negating the need for the cam stipport surface ( Ic) within the both. In that case it v ould become desirable to provide a further surface on the body to support the shaft (2h) of the bolt.

is Difl'erent beam cross sectional shapes may he used. In v hich case Lhe geonletries olboLh the cam notch and the both' groove uuld be different. For example if the beam were of' rectangular cross section. the cam notch would he unnecessary ai the body groove would also need to he of rectangular cross section.

Although the geometr\ may look soniewhat complicated, conventional machining processes 2() can he used to produce the parts. However the cam and body parts may preferably he produced out of metal using the investment casting process or more preferably from plastic using the injection moulding process.

Pins may have to he trimmed by the surgeon to avoid excessive protuberance. which could result in sharp edges. which would thereby form a ha7ard. To protect the patient from this hazard and to prevent accidental adjustments to the clamps, a protective cap of elastomeric material that encapsulates the device is prehirred. Such a device is shovv n as (8) in Figures 1 and 4. This cap has a body section (Sah which encapsulates the body (I) of the clamp and is open on the aspect (Sb) to allow unimpeded insertion of the beam (5) and access to features (6) and (3c)for actuation and locking of' the cain. A second section (8c) has a flexural hinge to tl first part at position (Sd) so that it ma he closed over the parts (6) and (3c) and onto the transf'ixion pin (4). A tubular feature (8e) covers the potentially rough end of the pin (4).

It is preferred that one end of the tubular section is closed by a thin membrane. vvhicli would he lbrcihlv penetrated h' the pin thereby creating friction to grip the pin and a capacity to accept pins of different diameters. In section (8c). a cup like feature (Sf) would partly surroLind the elements (3c) and 6. thereby helping retain the cap in position.

To illustrate the utility of the proposed invention, two ways in which it can be used are described for use with either a rigid or alternativel a mouldahie beam element: With a rigid beam. at least one transfixion pin may he inserted into the hone on each side of' the fracture site. the fracture may then he reduced. pin clamps fitted to cacti pin and orientated to align the surfaces designed to accept the beam. The beam would then be inserted into these two clamps and locked in position by actuation of the cam and tightening of' the clamp nut (6). Further pin clamps could then he placed onto the beam and orientated to allovv additioml transfixion pins to he drilled through the pin clamp bolt head and into the bone. In these the elastomeric sleeves would he redundant. The Cams would he actuated to clamp on the beam before insertion ol' the transIxion pins, which vould he lnallv locked by tightening the nut.

With motildable beams, all transfixion IflS may first he placed in desirable safe COrri(lOfs.

regai'dles to plane or orientation. Pin clamps may then he slid onto these pins and aligned to place tI open iiotche on a track to accept the shape of a moulded heani. Alternatively the bar ma he clamuped in the tirt pin clamp and locally bent to successive pin clamnp.

Claims

1. A fixator pin clamp, which has an open recess to accept a fixator beam element and a cam to clanip onto a beam.

2. A tivator pin clamp according to claim I that uses a locking bolt that also serves to attach a transfixion pin by clamping it onto a textured surface of the fxator body by means of a locking nut.

3. A fixator according to claim 2 in which the cam pivots on the bolt and rotates about its axis.

4. A fixator pin clamp accot-ding to claim 2 in hich the transli xion pin passes though a hole or notch in the head portion of the bolt.

5. A tixator pin clamp accoiding to claim 2 in which the textured surface comprises a multitude ot v-shaped grooves radiating lroiii the axis of the 1)011.

6. A fmxator pin clamp according to an\ of the above claims in v hicim tl�^e hole or iiotch in the head of the bolt is large enough to accept the greatest pin size envisaged for use with the device.

7. A lixator pin clamp according to claims 2 to 6 kiLh an clastomeric sleeve surrounding the diameter of the bolt head to grip a transfixion pin passing through its vall.

8. A fixator pin clamp according to any of the previous claims in which its body has an open groove shaped to accommodate a lixator beam to allow the pin clamp to he placed directly onto the beam in any position along its length.

9. A fixator pin clamp according any of the previous claims in which the cam surface is shaped to give line contact with a significant portion of the beam cross-sectional profile.

10. A fixator pin clamp according to any of previous claims. shaped to fit to a beam of circLllar cross section and in which the cam surface has a notch formed by sweeping a segment oh a circle.

11. A fixator pn clamp according to claim 10 in which the cam surface has a notch formed by sweeping a v cross-section.

12. A fixator pin clamp as in any of claims I to 9 shaped to lit to a beam. which has a rectaiigular cross section and in which the cani notch is of rectangular cross section.

13. A fixator pin clamp according to claim 12 with no notch in the cam surface.

14. A fixator pin clamp according to any of claims I to 9 designed to fit a beam of non circular and non rectangular cross section and which has corresponding cam notch cross section.

15. A fixator pin clamp according to any of the previous claims, in which the cam in one position gives unimpeded access lbr the tixator beam to the clamp body and in another position traps the beam in the body.

16. A tixator pin clamp as in an previous claim in which the cam has an additional Ilange. which closes the entry passage br the beam into the clamp body. hen the cam is rotated to its claiiping position.

17. A fixator pin clamp according to any previous claim. which incorporates stops to limit the range of rotation of the cam.

18. A fiator pin clamp as in claim 16. in hich the flange portion is in interference contact with the beam. when the nut and bolt are tightened.

19. A fixator pin clamp according any of the previous claims, which has a proteCtie cap.

which shields any moving parts and covers the free end of the transfixion pin.

20. A fiator pin clamp according to claim 19 which has a protective cap vhich envelops the fixed part of the body and has a flap which ma he stretched over the cam and nut features and which ha' a tubular part with a diaphragm that can he I)enetrated h the transfixion pin to hold the flap in its closed position.

21. A fixator pin clamp according to any of the previous claims where the hod is made tioiii plastic.

22. A tixator pin clamp according to any of the pre ious claims where the cam is made from l)IastIC.

23. A fixator 1fl clamp according to clainis an\ pre iou' claim in which the body is iiiade ol metal.

24. A pin clamp according to claiiiis an previous claim in which the cam in iiiade from lucia I.

25. A fixator pin clamp according to claim 19 or 20. in which the protective ap is niade Irom an clasiomeric nialerial.

26. A fixator pin clamp as described in th hods' of this patent specification and shown in the diagrams.