External bone distractor has curved threaded rod with flats to prevent rotation of the spindle support carriages

EXTERNAL BONE DISTRACTOR

TECHNOLOGICAL BACKGROUND OF THE INVENTION

Replacing a missing bone fragment following tumor resection or major trauma often involves surgical techniques that promote the growth or development of the adjacent portion of healthy bone tissue.

One is to pull on the callus resulting from an osteotomy to lengthen it to a length corresponding to the bone loss.

This technique, considerably developed by the Russian practitioner Ilizarov, was initially used for long bones, or at least for bone fragments of generally cylindrical shape.

The external distractor described by this author in American patent US Pat. No. 4,978,348, published on December 18, 1990, seems to offer sufficient flexibility of use to be used both for restoring the shape of the hand, by stretching the hands. parts of phalanges remaining after amputation, only for reconstruction of the mandible, for example.

The system includes a set of threaded rods that can be assembled to match the shape of the bone or set of bone being treated. The threaded rods support spindle carriages whose adjustable spacings allow bone distraction. The pins of each of the carriages are clamped by a nut between washers threaded on a hollow bolt engaged on one of the rods. These have a flat part cooperating with the studs of the hollow bolts to immobilize the spindle holders in rotation with respect to the rods.

The device is simple, but the carriages being held along the rods by locknuts, two wrenches are necessary to move them. In addition, locking and unlocking a locknut requires relatively complex simultaneous handling of these two keys.

The external fixation system disclosed in the utility certificate application FR 2.671.479 in the name of the company Hit Medica, published on July 17, 1992, is based on the principle of the turnbuckle. The spacing of the two spindle holders is therefore simply obtained by operating the central part of the rod, the ends of which are threaded in the opposite direction.

Based on another principle, the device described in American patent US Pat. No. 4,848,368 published on July 18, 1989 in the name of R. Kronner is for its part manoeuvrable by a single wheel. In this case, the patient can perform the operation himself.

The previous two systems can be used for the distraction of straight, long or short bones, but they are not suitable for curvilinear bones such as, for example, the bones of the skull, the mandibles or the ribs.

A device specially adapted to the curved bone segments of the jaws, of the face or of the skull, is described in German patent application DE 195 03 609, published August 10, 1995 in the name of the company Normed Medizin Technik Vertriebs. The device is formed of several racks on which spindle carriages are fixed. The racks are articulated together so that the assembly externally matches the shape of the bone. A carriage can be moved along a rack by means of a screw engaged therewith.

The articulations between the racks comprise spherical connections, which has the advantage of making it possible to give any shape to the assembly. However, these joints have the major drawback of limiting the movement of the carriages.

It therefore emerges from the state of the art as described in the documents cited above that external bone distractors suitable for the reconstruction of curved bone segments, in particular bones of the jaw, face and skull, are known. , but that there is to date no osteogenic distraction device with characteristics that fully meet the needs of maxillofacial surgery.

GENERAL DESCRIPTION OF THE INVENTION

The present invention therefore relates to an external bone distractor comprising, in a known manner:

- a threaded rod comprising at least one flat,

- at least two carriages engaged on the rod and integral with the spindle holder,

- Guide means cooperating with the flat to block each of the carriages in rotation around the axis of the rod,

- Means for adjusting the position of each of the carriages along the rod.

The object of the invention is precisely a distractor of this type, the essential characteristic of which is that this rod is curvilinear.

Preferably, the rod more simply forms a planar curve.

Advantageously, the curve formed substantially matches the shape of the mandible. It is preferably made up of a 150 ° circular arc, the ends of which are extended by two straight segments.

According to an additional characteristic of the distractor according to the invention, the rod has at least two diametrically opposed flats preserving the thread in the vicinity of its neutral fibers.

In a particular embodiment of the distractor, the threaded rod has six diametrically opposed flats, machined so that the sides of the cross section of the rod, and their extensions, adjacent to the traces of the neutral fibers form a square.

Preferably, the guide means comprise at least one washer integral with each of the carriages engaged on the rod by means of an axial bore of section complementary to the cross section of said rod.

According to a variant of the external bone distractor according to the invention, these guide means comprise at least one pair of diabolos of axes of rotation integral with each of the carriages, arranged astride on either side of the rod and rolling on it. -this.

As for the adjustment means, they preferably comprise a knurled nut screwed onto the rod acting on each of the carriages by means of a bracket.

Advantageously, the guide means of a carriage have two positions: the direction of the spindle holder in one of the positions is perpendicular to the direction of the spindle holder in the other position.

Benefit will be gained from the fact that at least two of the carriages of the external bone distractor according to the invention are fixed, and that at least a third is movable along the rod.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1, 3 and 4 respectively show a schematic view from below, from the front and from the left, of the bone distractor according to the invention.

Figure 2 shows an enlarged cross section of the threaded rod that comprises the distractor according to a preferred embodiment of the invention.

Figures 5a and 5b respectively show a top view and a front view of a first embodiment of one of the distractor spindle carriages according to the invention.

Figures 6a and 6b respectively show a top view and a front view of an alternative embodiment of one of the spindle carriers, the cover of which has been removed, of the distractor according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The references to FIG. 1 and to FIG. 2 will serve to explain the general principle of the invention based on a model of apparatus suitable for mandibular reconstruction by progressive bone distraction.

Figure 1 shows in a simplified way a bottom view of the distractor 1. We recognize carriages 2 supporting spindle holders 3 engaged on a threaded rod 4.

Unlike known devices, comprising one or more rectilinear rods, this threaded rod 4 is continuous and its shape on the outside substantially matches the shape of the mandible.

It comprises a front section 5 in the form of an arc of a circle of 150 ° and a radius of 70 mm, as well as two side sections 6 made up of rectilinear segments 90 mm long.

Figure 2 clearly shows in section (Section AA) the other essential characteristic of the threaded rod 4. Six flats 7.8 taken in a threaded rod to ISO M6 standard only preserve the thread 9 in the vicinity of the neutral fibers of the rod 4, that is to say the fibers of rod 4 which undergo neither extension nor compression. The preserved part 9 of the thread therefore retains the nominal characteristics of the profile of the threads and of the pitch of the threaded rod 4 and can therefore cooperate with a nut of the corresponding size. This nut, as will be explained in connection with Figures 5 and 6, will constitute a means of adjusting the position of a carriage 2 along the rod 4.

As shown in Figures 3 and 4, carriages 2 are able to hold spindle holders 3 either in a position perpendicular to the plane of distractor 1 (carriages 2 on the front section 5) or in a parallel position (carriages 2 on side sections S).

To do this, the carriages 2 are guided on the rod 4 and locked in rotation on the latter by guide means adapted to the particular shape of the section (Figure 2) of the threaded rod 4.

The sides 7 of this straight section adjacent to the preserved parts 9 of the thread in the vicinity of the neutral fibers, and their extensions, in fact form a BCDE square.

In a first preferred embodiment of the distractor 1, a carriage 2 is secured to two aligned washers 10, the axial bore 11 of which has a square section, as clearly shown in FIG. 5b, that is to say complementary to the figure. rod 4 on which they are engaged. The carriage 2 can therefore slide on the rod 4, but has only two positions in axial rotation, at 90 ° to each other, depending on how it has been threaded on the rod 4.

According to an alternative embodiment shown in Figures 6a and 6b, the channel 12 of square section in which the rod 4 circulates inside a carriage 2 is obtained by means of two pairs of diabolos 13 aligned. The diabolos 13 are journaled in four cylindrical housings of the solid constituting the carriage 2, which allows the threaded rod 4 to slide while being guided.

The carriage is shown with the cover removed, so as to make these diabolos 13 visible in Figure 6a.

As before, the carriage 2 can be oriented on the rod in two different ways.

The free space left in the mass of the carriage 2, between the washers 10 or the diabolos 13 to accommodate a knurled nut 14 screwed on the rod 4, forms a bracket 15 transmitting to the carriage 2 the movements of this nut 14.

This can be easily operated by the patient himself. A ratchet makes the number of fractions of a revolution made sensitive.

Cylindrical bores 16 are provided in the frames of the carriages to receive the rods of the spindle holders 3, which are immobilized by screws.

These very light and very simple structures of the carriages 2 therefore make it possible, in accordance with the views of the distractor 1 according to the invention of Figures 1, 3 and 4, to ideally place the pins 17 at the most suitable places of the mandible to carry out a bone distraction without incident.

The profile of the path of the carriages 2, best suited to the shape of the mandible, makes the distraction particularly progressive.

It is understood that the rod 4 serving as a rail must be kept integral with the mandible by means of the pins of two carriages 2 fixed at least. At least a third carriage is movable to carry out the transport of bones.

The advantages of the curved shape of the threaded rod 4 are easily transposable to cases other than that of the mandible; a rod of dimensions and profile adapted to those of the skull would form the basis of a cranial box distraction device.

As goes without saying, the invention is not limited solely to the above technical specifications, given by way of example;

it embraces, on the contrary, all the other possible variants.

In particular, the guiding means 10.13 of the carriages 2 or for adjusting their positions 14 described above are not limiting. Any other mechanical means used for the same purposes is a possible variant which does not depart from the inventive concept of the external bone distractor, the characteristics of which are specified below.