Compact external fixator

Field of application

This invention relates to an external fixator which can be used in the field of bone surgery and in particular for the treatment of fractures in small bones, such as fractures of the first metatarsal, the wrist, the heel, and in general fractures in the bones of small children.

State of the art

Small axial external fixators such as for example the external axial fixator model no. 30000 produced and marketed by the applicant and described and claimed in European patent no. 11,258 and in US patent 4,621,627 are known.

These known fixators generally comprise an elongatable central body with clamps attached to the longitudinal ends thereof by means of pins or bone bolts through corresponding ball joints which can be immobilised in a predetermined orientation. Each joint comprises a ball formation which is integral with a clamp or the central body and is acted upon by a locking bush pushed by an eccentric which can be rotated from the exterior by means of a suitable tool. The central body comprises two or more telescopic members which can move with respect to each other and which can be immobilised in the required position by means of suitable locking members. The form of fixator described above is produced in several sizes, one of which is used to reduce and stabilise fractures in small children and in the smallest bones of adults, such as for example the wrist or heel.

However, even this type of fixator has some recognised disadvantages, among which should be mentioned in particular the opacity of the central body to X-rays, which prevents multilateral X-rays examination of fractures during reduction and in the course of subsequent inspections.

Another disadvantage of known fixators lies in their bulkiness, due to the fact that the stop blocks and eccentric locking devices are placed between the central body and the corresponding clamps, and therefore increases the length of the fixator and the minimum distance between the bone bolts, reducing the possibilities for adjustment of the central body.

A further disadvantage lies in the relatively large weight of conventional fixators, especially when treating fractures of the wrist and in general fractures in small children and old people.

Yet another disadvantage lies in the possibility of relative torsion between the telescopic part of cylindrical shape about their longitudinal axis when these parts are not immobilised to allow limited movement of the stumps, and to accelerate new marginal growth in the fracture.

WO 9423662 discloses an external fixator whose central body comprises a male and a female member, both made of plastics material, i.e. an X-rays transparent material.

WO 94-06364 discloses an external fixator with two telescoping members with adequate X-ray transparency.

Description of the invention

The main object of the present invention is to eliminate the aforementioned disadvantages by providing an external fixator which permits X-ray examination of the fracture from all viewpoints, including therefore through the fixator, while showing, at the same time, reliable characteristics in respect of torsional rigidity and immobilisation of the orientation of the joints.

A further object is to provide an external fixator which is particularly suitable for the treatment of fractures in the small bones of adults and in general in. the bones of small children.

Another object is to provide a fixator which has the feature of being appreciably light.

These and other objects are achieved by an external fixator according to the appended claims.

Brief description of the figures

Further features and advantages will be more apparent in the light of the detailed description of a preferred but non-exclusive embodiment of the external fixator according to the invention which is illustrated by way of a non-restrictive example with reference to the appended table of drawings in which: <ul id="ul0001" list-style="none" compact="compact"><li>Fig.1 shows a general perspective view of an external fixator according to the invention fitted in the vicinity of an articulation of the wrist ;</li><li>Fig.2 represents a side elevation view of the fixator in Fig. 1 in the fully retracted position;</li><li>Fig. 3 illustrates a side elevation view of the fixator in Fig. 1 in the fully extended position ;</li><li>Fig. 4 shows a side view of a first detail of the above figures in partial cross-section along an axial longitudinal plane ;</li><li>Fig. 5 shows a side view of a second detail of the above figures partly in cross-section along an axial longitudinal plane;</li><li>Fig. 6 shows a view in transverse cross-section along the plane of the line VI-VI of the detail in Fig. 4 ;</li><li>Fig. 7 shows a view in transverse cross-section along the plane of line VII-VII in the detail of Fig. 5 ;</li><li>Fig. 8 shows a view in transverse cross-section along the plane of line VIII-VIII in the detail of Fig. 5 ;</li><li>Fig. 9 shows an exploded view in partial cross-section along an axial plane of a clamp in Fig. 4 ;</li><li>Fig. 10 shows a perspective view of a detail of the clamp in Fig. 9 ;</li><li>Fig. 11 shows a side view of the fixator of Fig. 1 coupled to a tensioning device ;</li><li>Fig. 12 shows a side view of the independent tensioning device of Fig. 11;</li><li>Fig. 13 is a front view of the tensioning device of Fig. 12.</li></ul>

Detailed description of a preferred embodiment

With reference to the aforesaid figures, an external axial fixator according to the invention, indicated in general by reference number 1, comprises a pair of clamps 2, 3 for securing bolts or pins V which have been first fixed by the surgeon in the stumps of the fracture, for example in the wrist joint, connected to a central elongatable body 4 by means of corresponding end joints 5, 6.

Central body 4 may be formed of two members, respectively one male member 7 and one female member 8, of an approximately cylindrical shape, having a circular transverse cross-section, which are telescopically coupled in such a way that they can slide over each other along a common longitudinal axis L varying the overall length of central body 4.

Clamps 2, 3 are preferably formed of corresponding principal portions 9, 10 of approximately prismatic or parallelepiped shape connected to corresponding plates 11, 12 by means of bolts 13, 14 to secure bone pins V.

According to the invention, telescopic members 7, 8 are at least partly X-rays transparent to allow viewing of the fracture even through central body 4. One of the telescopic members, in particular male member 7, is made of a material which is highly X-rays transparent.

The highly X-rays transparent material may be a thermoplastic resin with an amorphous or semicrystalline structure selected from the polyethers, polysulphonates, polyoxymethylenes or polyetherimides.    Preferably female telescopic member 8 is constructed of a material which is substantially opaque to X-rays, such as for example an aluminium alloy, and has lateral walls of a relatively reduced thickness such as to be at least partly X-rays transparent.

From calculations and tests it has been possible to show that if a female telescopic member 8 is constructed with lateral walls of thickness S not exceeding approximately 1 mm then the central body as a whole becomes sufficiently X-rays transparent.

In order to prevent the relative rotation of telescopic members 7, 8 and therefore of bone clamps 2, 3 while the fixator is allowed to move, suitable anti-rotation means are provided. In particular, male telescopic member 7 has a flat 15 which extends over almost its entire length, leaving an end projection 16.

At the free end opposite clamp 3, female member 8 has a lateral projection 17 in which a partly threaded hole is provided to house a transverse screw 18 of which the smooth part acts together with longitudinal flat 15 of member 7 to prevent rotation of the latter about longitudinal axis L.

Appropriately, lateral projection 17 has a central slit 19 of predetermined length so as to provide the end of female member 8 with a certain amount of radial resiliency. Bolt 18 which passes through lateral projection 17 can tighten the end of female member 8 immobilising male member 7 in the required position. In addition to this, bolt 18 comprises an end stop with respect to end projection 16, preventing involuntary separation between member 7 and member 8.

It will be noted that the main prismatic portions 9, 10 of both clamps 2, 3 have axial through cavities 20, 21 with corresponding spherical restrictions 22, 23 which interact with ball joints 24, 25 fixed to corresponding telescopic members 7, 8 by means of locking screws 26, 27.    Locking cylindrical blocks 28, 29 are housed in through cavities 20, 21 and have at one end hemispherical seats 30, 31 acting against ball joints 24, 25 and at the opposite end cylindrical diametric seats 32, 33 facing outwards.

Transverse eccentric pins 34, 35 are rotatably supported at the distal ends of principal portions 9, 10 of clamps 2, 3 so as to interact with corresponding locking blocks 28, 29 on their diametric seats 32, 33. By rotating eccentrics 34, 35 hemispherical seats 30, 31 of the blocks are forced against the opposing ball joints 24, 25 in such a way as to immobilise them in the desired orientation.

A reduction in the overall length of the fixator is achieved through this arrangement of the eccentrics on the clamps, in particular towards their outer ends, making use of the structure of the clamp itself. Thus the maximum distance between the clamps, and therefore between bone bolts V, is less than in the past, permitting optimum use of the fixator for the wrist joint, and in general for small bones and in children.

In order to allow a distraction or compression of the fracture fixator 1 is provided with means for coupling to a tensioning device which is generally indicated with the reference number 36 and is clearly illustrated in Fig. 11-13.

Tensioning device 36 comprises a sleeve 37 with a longitudinal axis M which has a substantially cylindrical expansion 38 formed on the outer surface thereof and provided with longitudinal gripping grooves 39 and with a central hole 40 for insertion of a pin-like tool to allow rotation of the sleeve 37. The end portions 41, 42 of the sleeve are internally threaded with opposite threads to receive corresponding threaded rods 43, 44 carrying at the opposite ends thereof securing means 45, 46 for rigidly coupling with fixator 1. Securing means 45, 46 are essentially formed by approximately prismatic supports 47, 48 from which hook formations 49, 50 with centres equidistant from the axis M extend. Hook formations 49, 50 can be easily inserted into cylindrical grooves 51, 52 formed at the outer ends of telescopic members 7, 8 of central body 4 in such a manner that axis M of the tensioning device lays substantially parallel to axis L of the fixator 1.

Securing means 45, 46 are rigidly coupled to fixator 1 by means of corresponding screws 53, 54 passing through transverse holes of supports 47, 48 having axis directed towards the centres of their hook formations 49, 50.

The use of the fixator will be obvious in the light of the foregoing description.

After bolts V have been fitted into the stumps of the fracture, bolts 13, 14 and eccentrics 35, 36 in the clamps, together with stop screw 18 in the central body are released. After this the length of the fixator is adjusted in such a way that bolts V are inserted between plates 11, 12 and the principal portions 9, 10 of the clamps, bolts 13 and 14 and eccentrics 34, 35 are then screwed up immobilising the orientation of the clamps and screw 18 is screwed up to fix the length of the central body.

Once the fracture has been reduced a distraction or compression of the focus can be exerted by means of tensioning device 36, specifically by inserting hook formations 49, 50 into the cylindrical grooves 51, 52 of the telescopic members 7, 8. The sleeve 37 can be rotated acting either with the fingers on the expansion 38 or with a pin-like tool on the central hole 40 to bring threaded rods 43, 44 closer or further away as much as needed.

As a result of the X-ray transparency of the central body it is possible to perform the entire operation of reducing the fracture, exposing it to X-rays even from the side on which the fixator is located, with greater ease of handling and a reduction in exposure times.

The tensioning device can be coupled to the fixator in an extremely easy manner thanks to the open structure of the hook formation of the securing means that facilitates the use of the device even in a narrow space.    The fixator according to the invention is susceptible of many modifications and variants which fall within the scope of the appended claims. Dimensions, shapes and materials may be altered without going beyond the scope of the invention.