External bone distractor

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DESCRIPTION

External bone distractor.

Technological context of the invention

The replacement of a missing bone fragment after tumor resection or after major trauma often requires operative techniques that allow the growth or development of adjacent healthy bone tissue to be promoted.

One of them consists of pulling the bone callus resulting from an osteotomy to lengthen it by the length corresponding to the bone loss.

This technique, developed considerably by the Russian physician 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 US patent US 4,978,348, published on December 1, 1990, appears to offer sufficient flexibility of use to be put into practice both for restoring the shape of the hand, through stretching of the parts of the phalanges remaining after an amputation, as for the reconstruction of the jaw, for example.

The system includes a set of threaded rods that can be assembled to adapt to the shape of the bone or the set of bones treated. The threaded rods support spindle carriages whose adjustable separations allow bone distraction. The spindles of each of the carriages are tightened by a nut between washers threaded on a hollow screw hooked to one of the rods. These have a chamfer that cooperates with studs of the hollow screws to immobilize the spindle holders in rotation with respect to the rods.

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

The external fixator for osteosynthesis disclosed in utility model application FR 2,671,479 in the name of the company Hit Medica, published on July 17, 1992, is based on the tensor principle. The separation of the two spindle holders is thus obtained simply by maneuvering the central part of the rod whose ends are threaded in the opposite direction.

Based on another principle, the device described in US patent US 4,848,368, published on July 18, 1989 in the name of R. Kronner, is, as far as it is concerned, maneuverable by means of a single toothed wheel. The patient can in this case carry out the operation himself.

Both of the above systems can be used for distraction of straight, long, or short bones, but are not suitable for curvilinear bones such as the skull, jaw, or rib bones.

A device specially adapted to the curved bone segments of the jaws, face or skull is described in German patent application DE 19503609, published on August 10, 1995 in the name of Normed Medizin Technik Vertriebs. The device is made up of several racks on which the spindle carriages are fixed. The zippers are articulated to each other so that the assembly conforms externally to the shape of the bone. A carriage can move externally along a rack by means of a screw screwed into the rack.

The joints between the racks comprise spherical links, which has the advantage that the assembly can be given any shape. However, these joints have the great drawback of limiting the movement of the carriages.

A continuous curved threaded rail, which does not limit the movement of the spindle carriages, is disclosed in Japanese patent application JP 09-215699 (the preamble of claim 1 is based on this document), published on August 19, 1997 on behalf of the Nagoya Rashi Seisakusho Society.

According to the embodiment represented in the figures accompanying the application, the rail has a square straight section and has a thread on each of its edges. In the example of use indicated, the rail is fixed on the right side of a jaw and follows the contour of the jaw, from back to front, without exceeding the projection of the chin.

However, it seems technically impossible that the rail described in JP application 09-215699 can follow the contour of the jaw beyond the protrusion of the chin. The small radius of curvature at the chin level would obviously lead to a significant deformation of the threads of the rod, and would prevent the rotation of the nuts that control the movement of the carriages.

In fact, in the position represented in the figures illustrating application JP09-215699, the internal threads of the curve followed by the rod are necessarily compressed while the external threads separate.

It follows that the curved rail seems usable only for the repair of a lateral part of the mandible, as represented in the main figure, and certainly not for the distraction of the middle part of the mandible.

It therefore follows from the state of the art as described in the documents cited above that external bone distractors adapted to the reconstruction of curved bone segments are known, especially the bones of the maxilla, the face and the skull, but There is currently no osteogenic distraction device that has characteristics that fully meet the needs of maxillofacial surgery.

General description of the invention

The present invention thus relates to a bone distractor comprising in a known manner:

- a curvilinear threaded rod that has several diametrically opposed chamfers that preserve the thread of the rod along longitudinal bands,

- at least two carriages hooked to the rod and attached to some spindle holders,

- guide means cooperating with said chamfers to block, in rotation around the axis of the rod, each of the carriages,

ES 2 236 601 T3

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

The object of the invention is precisely such a distractor, the essential characteristic of which is that the longitudinal bands along which the thread is preserved extend only close to the neutral fibers of the rod.

According to a further characteristic of the distractor according to the invention, the number of these longitudinal bands is only two and they are diametrically opposed.

Preferably, the rod more simply forms a flat curve.

Advantageously, the curve formed conforms substantially to the shape of the jaw. This is preferably composed of a 150 ° arc of circumference, the ends of which are extended by two line segments.

In a particular embodiment of the distractor, the threaded rod has six diametrically opposed chamfers, manufactured in such a way that the sides of the straight section of the rod and its extensions, adjacent to the marks of the neutral fibers, form a square.

Preferably, the guide means comprise at least one washer attached to each of the carriages hooked to the rod by means of axial reaming of a complementary section of the straight 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 rotational axes integral with each of the carriages, arranged on horseback to both parts of the rod, and which roll on it.

As for the adjustment means, these preferably comprise a knurled nut screwed onto 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.

The benefit will be obtained that at least two of the carriages of the external bone distractor according to the invention are fixed and at least a third is mobile 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 contains the distractor according to a preferred embodiment of the invention.

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

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

Description of the preferred embodiments of the invention

References to figure 1 and figure 2 will serve to explain the general principle of the invention based on a model of apparatus adapted to mandibular reconstruction by progressive bone distraction.

Figure 1 represents in a simplified way a view from below of the distractor 1. There are carriages 2 that support spindle holders 3 hooked to a threaded rod 4.

Unlike known devices, which include one or more rectilinear rods, this threaded rod 4 is continuous and its shape conforms substantially to the shape of the jaw on the outside.

It comprises a front section 5 in the shape of an arc with a circumference of 150 ° and a radius of 70 mm, as well as two lateral sections 6 made up of rectilinear segments of 90 mm in length.

Figure 2 shows in section (section AA) the other essential characteristic of the threaded rod 4. Six chamfers 7, 8 included in a threaded rod according to the ISO M6 standard, which only preserve the thread 9 in the vicinity of the neutral fibers of the rod 4, that is, the fibers of the rod 4 that do not undergo neither extension nor compression and which are therefore located close to each of the two planes tangential to the rod 4 which are parallel to the plane in which said rod extends. Each preserved part 9 of the threading therefore preserves the nominal characteristics of the profile of the rods and the pitch of the threaded rod 4 and can, consequently, cooperate with a nut of the corresponding dimension. This nut, as will be explained in relation to Figures 5 and 6, will constitute means for adjusting the position of a carriage 2 along the rod 4.

As shown in Figures 3 and 4, the carriages 2 are capable of holding the spindle holders 3, either in a perpendicular position to the plane of the distractor 1 (carriages 2 in the front section 5), or in a parallel position (carriages 2 in the front section 5). side sections 6).

To do this, the carriages 2 are guided on the rod 4 and locked in rotation thereon 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 portions 9 of the threading in the vicinity of the neutral fibers, and their extensions in fact form a square BCDE.

In a first preferred embodiment of the distractor 1, a carriage 2 is attached to two aligned washers 10 whose axial reaming 11 is square in section, as shown in Figure 5b, that is, complementary to the rod 4 on which they are hooked. . The carriage 2 can therefore slide on the threaded rod 4, but only has two positions in axial rotation, at 90 ° from each other, depending on the way in which it has been threaded onto the rod 4.

According to a variant embodiment shown in Figures 6a and 6b, the channel 12 with a square section in which the threaded rod 4 circulates inside a carriage 2 is obtained by means of two pairs of aligned diabolos 13. The diabolos 13 are clamped in four cylindrical housings of the solid that constitutes the carriage 2, which allows the threaded rod 4 to slide when guided.

The carriage is represented without the cover, so that these diabolos 13 are made visible in FIG. 6a.

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

The free space left in the solid of the carriage 2, between the washers 10 or the diabolos 13 to accommodate

ES 2 236 601 T3 A knurled nut 14 screwed onto the rod 4, forms a stirrup 15 that transmits the movements of this nut 14 to the carriage 2.

This can be easily manipulated by the patient himself. A ratchet makes the number of fractional turns made noticeable.

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

These very light and simple structures of carriages 2 therefore make it possible, according to the views of the distractor 1 according to the invention of Figures 1, 3 and 4, to ideally place the spindles 17 in the most conducive places of the jaw to carry out good port a bone distraction without incident.

The profile of the path of the carriages 2, adapted in the best possible way to the shape of the jaw, makes the distraction particularly progressive.

It is conceived that the rod 4 serving as a rail must be kept attached to the jaw by means of spindles of two carriages 2 fixed to the minimum. At least a third carriage is mobile to effect bone transport.

The advantages of the curved shape of the threaded rod 4 are easily extrapolated to cases other than that of the jaw; a rod with dimensions and profile adapted to those of the skull would form the basis of a distraction equipment for the cranial box.

It is not necessary to explain that the invention is not limited solely to the above technical specifications, given by way of example; on the contrary, it encompasses all other possible variants of implementation.

In particular, the means 10, 13 for guiding the carriages 2 or for adjusting their positions 14 set forth above are not limiting. Any other mechanical means implemented for the same purposes is a possible variant that does not depart from the inventive concept of the external bone distractor, the characteristics of which are specified below.