Intrabody distraction device with a screw working in traction

An intra-corporal expandable device incorporating a screw operating under traction. A first elongated part (1) receives a second telescopic part (2). Each of these parts comprises links (61), (62) to the organism at a first end (11), (21) and is linked to a rod (3) comprising at least one thread at a second end (12) and (22). The rotation of the rod (3) controlled by means (4) causes a relative displacement of the two parts (1) and (2). The rod (3) is thus assembled between two ends (12) and (22) which come closer when the device is elongated, the length of the loaded rod (7) is reduced when the device is elongated and the length of loaded rod (7) operates only under traction. The device according to the invention is intended in particular for the production of osseous lengthening nails and growth prostheses.

FIELD

The present invention concerns intra-corporal expandable devices, such as bone lengthening nails, bone transport nails, spinal distraction rods or growth prostheses.

BACKGROUND

Several intra-corporal expandable devices including, notably, those described in documents U.S. Pat. No. 3,976,060, Proc Inst Mech Eng [H]. 1989; 203(2): 97-102., WO 01/78614, DE 85 15 687 U1 or U.S. Pat. No. 6,336,929 include a first elongated part, a second part assembled telescopically relative to the said first part, first links to the organism at a first end of the said first part, second links to the organism at a first end of the said second part, a rod with at least one thread, the rotation of which causes displacement of the second part relative to the said first part, means for controlling the rotation of the said rod and links between these components. However, in all these known devices the said rod is assembled between the said first end of the said first part, and the second end of the said second part opposite the said first end of the said second part. The said rod is thus assembled between two ends which move apart when the device is elongated, the loaded rod length increases when the device is elongated and the loaded rod length operates under compression when the device is elongated. As a consequence, the length of the elongation is limited by the buckling height of the said rod under the applied load, the volume devoted in the said device to the said rod and to the tapping with which it cooperates which does not contribute to the robustness, notably under deflection, of the said devices, is substantial and, above all, the torque required to rotate the said rod is also substantial, which determines the dimensioning of the means to control the rotation of the said rod accordingly, and restricts usage in practice of certain means which are simple and reliable but of limited power, such as direct magnetic transmission without amplification between two permanent magnets, for example as described in document U.S. Pat. No. 6,336,929.

SUMMARY

The present invention proposes to remedy these disadvantages. Indeed, in the intra-corporal expandable device according to the present invention which comprises a first elongated part, a second part assembled telescopically relative to the said first part, first links to the organism at a first end of the said first part, second links to the organism at a first end of the said second part, a rod with at least one thread, the rotation of which leads to the displacement of the said second part relative to the said first part, means for controlling the rotation of the said rod and links between these components, the said rod is assembled between two ends which come closer when the said device is elongated, the second end of the said first part opposite the said first end of the said first part and the second end of the said second part opposite the said first end of the said second part.

Thus the loaded rod length is reduced when the device is elongated and the loaded rod length operates under traction when the device is elongated.

The links between the said rod and the said second end of the said first part and the links between the said rod and the said second end of the said second part which may comprise, respectively:a pivot and a tapping,a tapping and a pivot,a first tapping in a first direction and a second tapping in the direction opposite the said first direction; in this case the said rod contains a first thread able to cooperate with the said first tapping at one end, and a second thread able to cooperate with the said second tapping at the other end.

Moreover, according to the present invention, the said means to control the rotation of the said rod can be of all types, but preferentially consist of a driven permanent magnet assembled coupled with the said rod so that its magnetisation direction is roughly perpendicular to the axis of rotation of the said rod and, outside the organism, of a magnetic driving field source rotating roughly around the axis of the said rod. Advantageously the said driven permanent magnet is a neodymium magnet able to tolerate the sterilisation temperatures of the said intra-corporal expandable device according to the present invention and the said magnetic driving field source rotating outside the organism is at least one neodymium magnet which is rotated roughly around the axis of the said rod, whilst keeping one of its poles constantly turned towards it. Equally advantageously, the speed of rotation of the said magnetic field will be able to be less than one rotation per minute. The diameter of the said rod will, for its part, advantageously be less than 4 mm.

It is specified that, in these figures, the same references designate the same elements, whatever the figure in which they appear, and however these elements are represented. Similarly, if elements are not specifically referenced in one of the figures, the reference can easily be found by referring to another figure. In all the figures the dimensions and proportions have been altered when this could facilitate understanding. In addition, when, according to the definition of the invention, the object of the invention comprises “at least one” element with a given function, the described embodiment may contain several of these elements.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

A preferred embodiment of the device represented inFIGS. 1 to 3includes:a first roughly tubular elongated part1which contains, at a first end11, links to the organism, consisting for example of a first hole61roughly perpendicular to the axis of the said first part1and intended to receive a screw, which is not represented, and at the second end12, opposite the said first end11, two longitudinal and diametrically opposite notches51,52. The said first end11can also contain unrepresented means for gripping, such as a thread and a slot, for example, the said device to facilitate its surgical implantation, in general in the medullar cavity of a long bone or along or as an extension of all or part of a long or flat bone, and also its explantation.a second, roughly cylindrical, part2the outer diameter of which is roughly equal to the inner diameter of the said first part1, with which it cooperates telescopically and which contains, at a first end21, links to the organism, consisting for example of a second62hole roughly perpendicular to the axis of the second part2and intended to receive a screw, which is not represented, and at the second end22, opposite the said first end21, and which still remains in contact with the said first part1, a tapping53roughly along the axis of the said second part2. Between the two ends, a longitudinal groove54opens diametrically out on either side of the said second part2. The width of the said groove54is roughly equal to the width of the said notches51,52made in the said second end12of the said first part1and the said tapping53opening on to the said groove54, and having a diameter appreciably less than the width of the said groove54.a rod3which contains at a first end31a thread of diameter and pitch equal to those of the tapping53of the said second part2, with which the said thread cooperates,links between these components consisting:of a roughly parallelepipedal supporting strip55able to be fit in the said two notches51,52made in the second end12of the said first part1in order to form a bridge between them. The said supporting strip55also contains, roughly in its middle, a hole551in which the said first end31of the said rod3can slide and rotate freely,of a supporting nut56which can be screwed on to the said first end31of the rod3.

The said supporting strip55and the said supporting nut56form a pivot between the said rod3and the said second end12of the said first part1.

In this preferred embodiment of the invention, the said means to control the rotation of the said rod3consist;of a cylindrical driven permanent magnet4with diametrical magnetisation coaxially coupled with the said rod3, for example by gluing using a silicone glue which is easily tolerated by the organism in a cylindrical cavity57coaxial with the axis of the said rod3and made in a cylindrical bulge33coupled with the second end32opposite the said first end31of the said rod3.of a magnetic driving field source rotating around the axis of the said rod3and unrepresented onFIGS. 1 to 3positioned outside the organism.

It can be noted that the said means for controlling the rotation of the said rod3can also consist of any other means known to the skilled man in the art such as an electric motor with or without gear reducer, and a current source inside or outside the organism, or a permanent magnet with a gear reducer and a rotating magnetic field source outside the organism, or a free-wheeling system able to transform the torques which may exist between the said first part1and the said second part2of the device when the patient rotates in a single direction of the said rod3. These said means may be able to drive the said rod3in one direction only or in both directions, according to requirements.

The various components of the said preferred embodiment of the device represented inFIGS. 1 to 3are assembled as follows: the said first end31of the said rod3is screwed into the said tapping53of the said second part2. As soon as the said first end31of the said rod3protrudes sufficiently beyond the said second part2in the said groove54, the said supporting strip55is slid into the said groove54and then slipped on, through its hole551, to the said first end31of the said rod3. The supporting nut56is then screwed on to the said first end31of the said rod3which protrudes beyond the said supporting strip55in the said groove54and locked definitively on the said rod3, for example using a laser weld at the end, or by crushing through the said groove54, causing an ovalisation of at least part of the said nut56and of the part of the said first end31of the said rod3which is located there. The system constituted in this manner is introduced into the said second end12of the said first part1, the said second end32of the said rod3and the said second end22of the said second part2firstly, until the said supporting strip55comes up against the said notches51,52of the said second end12of the said first part1. It is then possible to couple definitively the said supporting strip55and the said first part1, for example by means of a laser weld. The assembly of this preferred embodiment of the invention is thus completed.

All the parts are made from a mechanically resistant material which is well tolerated by the organism such as 316L recast in a vacuum, certain titanium alloys, or high-resistance chrome- and cobalt-based alloys. Advantageously the surfaces of the parts, and particularly of the said rod3, are treated to limit friction and possible wear and tear. Treatments based on amorphous diamond-like carbon or tungsten disulphide are preferred. The combination of the small diameter of the said rod3, allowed by its assembly and its operation under traction, and of the low friction coefficient obtained due to the said surface treatments, allows the said rod3to be driven by a modest torque with regard to the applied load, and compared to what it would be if the said rod3had been dimensioned for operation under compression. The diameter of the said rod3is commonly between one and three millimeters and does not exceed four millimeters for an adult patient prosthesis, for example.

If the rod3has been designed with sufficient length, the maximum length variation potential of the said preferred embodiment of the said device according to the invention is roughly equal to the length of the said groove54of the said second part2minus the length necessary to accommodate the said supporting strip55and the said supporting nut56; otherwise it is the length of the said rod3which limits the said potential.

The operation of this preferred embodiment of the invention is clear: in the presence of a magnetic driving field perpendicular to the axis of the said rod3and rotating around this axis, the said cylindrical driven permanent magnet4coupled coaxially with the said rod3tends to become oriented in the said magnetic driving field applying a torque to the said rod3and causing it to rotate in the rotational direction of the said magnetic driving field if this torque is greater than the load torque of the said rod3under the load applied to it at the time when the magnetic driving field is activated. The said rotation of the said rod3is displaced in one direction or the other of the said second part2relative to the said first part1, depending on the thread direction of the said rod3and said tapping53, and thus the device according to the invention is elongated or shortened. The said second end12of the said first part1and the said second end22of the said second part2come closer when the device is elongated. The loaded length7of the said rod3is reduced when the device is elongated and the said loaded length7is under traction when the device is elongated.

Moreover, still referring to the said preferred embodiment of the device according to the invention represented inFIGS. 1 to 3, it is impossible to apply compression to the said rod3since it then slides into the hole551of the said supporting strip55, and the supporting nut56locks it only in the other direction, the other direction in which the rod3is subjected to traction.

The creation of a magnetic driving field favourable for rotating the said cylindrical driven permanent magnet4coupled coaxially to the said rod3and of the said rod3can be accomplished by any means, but preferentially by positioning outside the organism, at the height of the said driven permanent magnet4at least one other permanent driving magnet, one of the poles of which is directed towards the axis common to the said rod3and to the said driven permanent magnet4. The combination of two permanent driving magnets positioned such that the south pole of one is facing the north pole of the other, and such that the said driven permanent magnet4and the part of the organism which surrounds the said device are positioned between the two will produce an even greater motor torque, and may be preferred.

It is clearly stipulated that the embodiment of the invention represented inFIGS. 1 to 3is a preferred embodiment, but other embodiments conforming to the definition of the invention exist and will be able to be produced by the man skilled in the art. In particular the said rod3may be off-centre relative to the said first1and second2parts and the said first1and second2parts may have geometries other than a tube and a cylinder respectively, and each consist of several parts assembled by any means. Moreover, the said first end21of the said second part2may be on the side of the said first end11of the said first part1and the said second end22of the said second part2on the side of the second end12of the said first part1, unlike in the preferred embodiment represented inFIGS. 1 to 3. In this second configuration, the said second part2is constantly in full contact with the said first part1and grooves are made in the said first part1to allow linking to links to the organism contained by the said first end21of the said second part2along the entire elongation course of the said device.

Possibilities for Industrial Application

The present invention is particularly useful for the construction of any type of intra-corporal expandable device, and particularly medullar lengthening nails and long bones growth prostheses.