PIN CLAMP

The present invention relates to a fixator for use in external fixation of bone fractures. In particular, the present invention relates to a fixator pin clamp and protective cap.

Various different fracture repair systems are in common use to manage unstable fractures of bones. These include external fixator systems using a scaffold of fixator members, e.g. metal rods or beams, and clamps, and internal fixator systems, for example the bone plate and screw system and the interlocking nail system.

The main advantages of the external fixator system are that it allows adjustments to fracture alignment and loading during and after surgery. It is a system that can be applied without approaching the fracture site. Also, the ability to use a minimally invasive, closed application technique preserves surrounding soft tissue, minimizes damage to the bone's blood supply and optimizes the biological environment at the fracture site for bone healing,

A known external fixator has three basic elements, regardless of the device or system used. These are transfixion pins of various sizes that are screwed into the bone and left protruding through the skin, rigid connecting beam or beams, on the outside of the skin, to bear the load and pin clamps to connect the beam(s) to the pins.

The pins are placed into or through sound bone on either side of the fracture site. However, the position of the pins is governed by the presence of muscle and other soft tissue, blood vessels and nerves. Wherever possible, the pins are placed in 'safe corridors' in the soft tissue and may emerge from the skin at different angles and in different planes. Moreover it has been shown that pins at various angles are more effective in supporting the bone fragments.

The choice of pin angles is limited, in many external fixators, by the design of the pin clamp and the use of rigid beam elements. Most external fixators of this type employ straight rigid beam elements and the choice of pin angles are limited to those that can be achieved by rotation of pin clamps around the beam axes. In a few cases beams are bent prior to use. Also most of the existing pin clamp designs require a degree of dismantling to fit to a beam or to be threaded onto the beam from one end. The latter is not always possible in the case of bent beams.

Patent application PCT/GB2007/001372 describes a mouldable beam that allows pin clamp positions other than along a straight axis. However this precludes the use of pin clamps that must be threaded onto the beam from one end and a pin clamp that can be fitted directly to any point along the beam without dismantling would be useful in this case and of advantage in others where bent beams are employed. It would be an advantage to do this without disturbing adjacent pin clamps. The surgery would be facilitated by a pin clamp that could be deployed without dismantling during which components could be dropped or misplaced. With currently available systems adding or removing pin clamps from a fixator construct can be problematic. A pin clamp that can be inserted or removed from between two others without loss of integrity of the pre-existing or remaining system and without dismantlement would be an asset. EP 0700664A1 describes a pin clamp that allows a connection to be made to the beam without disturbing the connection with the pin but this is somewhat complicated and relatively bulky.

Metal beam elements can obscure fracture sites under radiographic examination.

This problem is partly addressed by the introduction of reinforced polymer beams.

However these are generally used with pin clamps made of radio opaque materials, leaving a residual problem. A pin clamp made largely of radiolucent material would address this point.

It is, therefore, an object of the present invention to provide a device to connect fixator beams to transfixion pins that is sufficiently versatile to address one or more of these problems.

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

A fixator pin clamp of the invention has an open recess to accept a fixator beam element and a cam to clamp onto the beam.

The cam is preferably movable between a first position in which the beam can be moved into and out of the clamp and a second position in which the beam is held tight in the clamp. In an embodiment of the invention, set out in detail below, the cam is or comprises a rotatable cam member, and rotation thereof clamps and unclamps the beam. This provides a convenient means to operate the clamp, and the clamp can be provided with a finger-operated cam, able to be tightened onto the beam using the fingers of an operator without needing a tool such as a spanner.

Preferably, the cam is movable between a first position in which the beam can be moved into and out of the clamp in a direction perpendicular to the beam axis and a second position in which the beam is held in the clamp recess. Using a clamp having this arrangement a beam is easily moved sideways into the clamp, or the clamp moved onto the beam without needing to thread the beam through any part of the clamp. Instead, the beam can be moved sideways into jaws of the clamp. This facilitates assembly of fixator beam and pins around a fracture.

The clamp is for use in clamping transfixion pins onto a beam and hence generally comprises a clamping member which clamps or otherwise attaches to a transfixion pin and a clamping member that clamps a fixator beam. The transfixion pin clamping member suitably is or comprises a locking bolt. In example set out below the bolt has a hole or threaded portion to accept a pin. In use, the

- A - transfixion pin passes though a hole or notch in the head portion of the bolt. The bolt may pass through the clamp body and be tightened onto the body using a locking nut, thus tightening a pin, held across an upper portion of the body, onto the clamp.

Different sizes of transfixion pins may be used with the clamp and therefore the hole or notch in the head of the bolt is preferably large enough to accept the greatest pin size envisaged for use with the device.

In an embodiment of the invention shown in more detail below, the transfixion pin clamping member comprises a locking bolt that also serves to attach a transfixion pin by clamping it onto a textured surface of the fixator body by means of a locking nut. The textured surface may comprises a multitude of v-shaped grooves radiating from the axis of the bolt, suitably located on an upper surface of the clamp body. As the nut is tightened so the bolt is drawn into the body and the pin is tightened against the grooves and is held in place thereby.

In a preferred embodiment, the cam pivots on the bolt and rotates about its axis. Also preferably, the cam comprises a central hole through which the locking bolt passes. The resulting clamp can be made of a compact size and with relatively few components, as the bolt and the cam are substantially co-axial.

A fixator pin clamp of the invention may also comprise an elastomeric sleeve surrounding the diameter of the bolt head to grip a transfixion pin passing through its wall. In use a pin pierces the sleeve and passes through the notch or hole in the bolt head. Elasticity in the sleeve grips the pin, not as tight as a closed clamping member, e.g. when the nut is tightened, but sufficiently to resist movement of the pin due e.g. to gravity. Whilst the operator is assembling pins and clamps and beams, there is generally some minor re-adjustment needed of the pins in the clamps. The grip of the sleeve prevents pin or pins falling out before they are fully tightened, so by using the sleeve the operator does not have repeatedly to tighten the pins in position, so as prevent them falling out, then

loosen them to adjust their positions; instead the pins are adequately held in place by the sleeve until they are in final position, upon which they can be tightened just the once.

The body of a fixator pin clamp may have an open groove shaped to accommodate a fixator beam to allow the pin clamp to be placed directly onto the beam in any position along its length.

The cam surface may be shaped to give line contact with a significant portion of the beam cross-sectional profile.

A fixator pin clamp may be shaped to fit to a beam of circular cross section and its cam surface may have a notch formed by sweeping a segment of a circle. The cam surface suitably has a notch formed by sweeping a v cross-section.

A fixator pin clamp may be shaped to fit to a beam which has a rectangular cross section and in which the cam notch is of rectangular cross section. There may be no notch in the cam surface.

A fixator pin clamp may be designed to fit a beam of non circular and non rectangular cross section and which has a corresponding cam notch cross section.

In embodiments of the invention, the cam in one position gives unimpeded access for the fixator beam to the clamp body and in another position traps the beam in the body. In the one position, the clamp is open and in the another position it is closed. The cam or cam member may comprise an additional flange, which closes the entry passage for the beam into the clamp body, when the cam is rotated to its clamping position. The cam member may comprise a flange and the cam member may be movable between a first, open position in which the beam can be moved into and out of the clamp in a direction perpendicular to the beam axis and a second, clamped position in which the beam is held in the clamp and the recess is

closed by the flange. The flange portion may be in interference contact with the beam, when the nut and bolt are tightened. A portion of the flange is preferably adapted to be operated by hand, e.g. protrudes so it can be operated by a finger.

To limit the range of rotation of the cam, one or more stops are optionally provided in or on the clamp.

A fixator pin clamp may also comprise a protective cap, which shields any moving parts and covers the free end of the transfixion pin. The protective cap can envelop the fixed part of the body and have a flap which may be stretched over the cam and nut features and which have a tubular part with a diaphragm that can be penetrated by the transfixion pin to hold the flap in its closed position.

The body and/or cam can be made from plastic or metal. The protective cap can be made from an elastomeric material.

The present invention therefore provides a fixator pin clamp, which in specific embodiments has a feature to accept a transfixion pin by axial sliding and a second open feature to directly accept a fixator beam 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 compromising the clamp attachment to the pin. Both features can have a common final locking element. The clamping device can accommodate any angle between pin and beam. These features allow clamps to be attached to pins and then optimally aligned to accept a beam or beams to which they are finally clamped by means of a cam.

The invention is now illustrated in a specific embodiment, with reference to the accompanying drawings, in which:

Figure 1 shows the clamp and the protective cap. Fig. 1a shows an exploded view of the device comprising body (1), clamp bolt (2), cam (3), transfixion pin (4),

beam (5), locking nut (6), sleeve (7), and protective cap (8); fig, 1b shows another view of body component (1) for additional clarity.

Figure 2 shows the device in an open position with the beam in place. Fig. 2a is an external view and fig. 2b a sectional view through the plane of symmetry.

Figure 3 shows the clamp in a closed position. Fig. 3a is an external view of the device. Fig. 3b is a sectional view through the plane of symmetry.

Figure 4 illustrates a protective cap. Fig. 4a shows the cap alone in a closed position; fig. 4b shows the cap installed on the assembly; figs. 4c and 4d show the assembly with the cap open; and fig. 4e shows the cap alone in an open position.

Unless otherwise specified Figs.1a and 1b will be used as a key to identify the features below. The component parts comprise a body part (1) having a hole (1c) to accept the outer diameter (3a) of a cam part (3), and a concentric hole (1d) to accept the head portion of a threaded clamping bolt (2), which is surrounded by an elastomeric sleeve (7). The shaft (2b) of the clamping bolt (2) passes through a concentric hole in the cam part and is fitted with a locking nut (6). The head of the bolt has a cross hole (2a) of sufficient size to accept the largest transfixion pin (4) to be used in this application.

A transfixion pin (4) forcefully penetrates the wall of an elastomeric sleeve (7), located over the bolt head, and passes through a hole (2a) in the clamping bolt (2). The hole 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 transfixion pin (4) into engagement with a textured surface, in this illustration one of many radial grooves (1b), on the face of the body (1), thereby resisting rotation as well as further axial movement of the bolt within the body.

The body has a semi-cylindrical groove (1a), which matches the diameter of the beam (5), cut perpendicularly to the cam support surface (1c) and intersecting it.

This groove opens to the surface of the body opposite to the bolt head to form a hook feature. Jaws of the clamp are thus formed by the grooved body and the cam.

5 The cam (3) has a cylindrical surface (3a) with a circumferential notch (3d) of varying shape and at a varying depth, i.e. at varying distance from the pivot axis, so that, when assembled to the body in the closed position shown in Fig. 3, it complements the beam (5) and in the open position, shown in Fig. 2, which looks along the axis of the beam, the groove is not visible because it is clear of the

10 notch (3d). Thus free entry of a beam (5) into the body is possible. Referring to Fig. 1, additional clearance may be provided by a flattened area (3f) on the cam surface (3a). The cam also has a flange feature (3b), projecting only in a direction that makes face (3e) cover the beam when the cam is positioned as in Fig 3 but is clear of the beam when positioned as in Fig. 2. A projection (3c) from the flange

15 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 3b, thereby clamping it in the groove. In this position the flange feature (3b) on the cam covers the entry point for the beam into the body. Stop features (1e) and (1f) limit the torsional0 _ . movement of the cam.

When the nut (6) is finally 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 the 25 flange portion (3b) 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 (1a) and also resisting any further rotation of the cam.

The cam is supported by both the body surface (1c) and the beam (5). In this

30 configuration the bolt (2) is supported by the pin (4) and the cam (3). The pin, in turn, is supported by the textured surface (1b) of the body (1). The texture on this surface takes the form of grooves radiating from the bolt axis. Such grooves are

preferably V-shaped to effectively accommodate a variety of pin sizes. Alternative forms to the cam surface may be devised to have the same effect.

Contact between the flange feature and the beam may be omitted because the notch traps the beam.

Additionally the bolt feature may be used as a pivot for the cam negating the need for the cam support surface (1c) within the body. In that case a further surface may be provided on the body to support the shaft (2b) of the bolt.

Different beam cross sectional shapes may be used and the geometries of both the cam notch and the body groove may as a result be different. For example if the beam is of rectangular cross section, the cam notch is optional and the body groove may be of rectangular cross section.

Conventional machining processes can be used to produce the parts. However the cam and body parts may preferably be produced out of metal using the investment casting process or more preferably from plastic using the injection moulding process.

Pins may have to be trimmed by the surgeon to avoid excessive protuberance, which could result in sharp edges, which would thereby form a hazard. 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 preferred. Such a device is shown as (8) in Figures 1 and 4. This cap has a body section (8a), which encapsulates the body (1) of the clamp and is open on the aspect (8b) to allow unimpeded insertion of the beam (5) and access to features (6) and (3c) for actuation and locking of the cam. A second section (8c) has a flexural hinge to the first part at position (8d) so that it may be closed over the parts (6) and (3c) and onto the transfixion 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, which in use is forcibly penetrated by 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 (8f) partly surrounds the elements (3c) and (6), thereby helping retain the cap in position.

The pin clamp may be used are described with either a rigid or alternatively a mouldable beam element.

With a rigid beam, at least one transfixion pin may be inserted into the bone on each side of the fracture site, the fracture may then be reduced, pin clamps fitted to each pin and orientated to align the surfaces designed to accept the beam. The beam is then inserted into these two clamps and locked in position by actuation of the cam and tightening of the clamp nut (6). Further pin clamps may then be placed onto the beam and orientated to allow additional transfixion pins to be drilled through the pin clamp bolt head and into the bone. In these the elastomeric sleeves would be redundant. The cams are actuated to clamp on the beam before insertion of the transfixion pins, which would be finally locked by tightening the nut.

With mouldable beams, all transfixion pins may first be placed in desirable safe corridors, regardless to plane or orientation. Pin clamps may then be slid onto these pins and aligned to place the open notches on a track to accept the shape of a moulded beam. Alternatively the bar may be clamped in the first pin clamp and locally bent to successive pin clamps.

The invention thus provides a pain clamp and use thereof.