FR2624720A1 - Implant for osteosynthesis device, in particular for the spine - Google Patents

Abstract

This implant comprises a part 1 intended for bone anchoring, and a body 2 for fastening on to a rod 3, having a channel 6 emerging on the posterior part of the said body, delimited by two lateral branches 8 and open on either side of the body in order to receive the rod 3; the implant comprises a tapped cap 9, adapted to be able to be screwed on to a thread 12 of the lateral branches 8 in order to lock the rod 3 in translation and in rotation, and a locking screw 13 which can be screwed into an internal boss 15 of the cap 9 with its tip 13a driven into the rod 3. This arrangement considerably simplifies the instrumentation necessary, since all the implants used are of the type with posterior opening, by virtue of the cap fixed on to the posterior end.

Description

 The subject of the present invention is an implant for an osteosynthesis device, in particular of the spine, of the type comprising a part intended for bone anchoring and a body for fixing on a rod, in which is formed a channel opening onto a posterior part of said body and delimiting two lateral branches.

 The bone anchoring part can be, for example, a screw or a suitably made blade.

 The bodies of known implants are either closed, or open posteriorly, or open laterally.

These implants have the following disadvantages:
- the number of elements necessary for instrumentation is very high, due to the existence of three different types of body;
- the bodies open posteriorly between the obligation to use intracanal blockers, as described for example in French patent 2,545,350 (83 07,450), constituting additional instrumentation elements which must be placed beforehand on the rod .
- It is relatively difficult to introduce the rod into implants with closed bodies;
- Implants with open bodies must be oriented in a precise manner, which constitutes a troublesome constraint for the practitioner in the case of the use of screws;
- the multiplicity and complexity of the elements used require the implementation of significant ancillary equipment;
- the manufacture of the elements of these implants is difficult and expensive, and their ablation also difficult, in particular because of the obligation to execute cuts.

 The object of the invention is to propose an implant free from these drawbacks.

 According to the invention, the body of the implant has a channel opening onto a posterior part of said body, delimiting two lateral branches and open on either side of the body so as to be able to receive the rod, and the implant comprises on the one hand a tapped cap, adapted to be screwed onto a thread formed on the lateral branches constituting the rear end of the body by closing the channel on this side, and so that its two diametrically opposite edges bear on the rod, and d 'on the other hand a needle screw can be screwed into a corresponding threaded hole formed in the cap so that its tip enters the rod, which is thus blocked in translation and in rotation by the two edges of the cap and by the screw.

 The implementation of this cap makes it possible to reduce the type of body necessary to a single one, namely a body open posteriorly, which considerably reduces the number of elements necessary for the osteosynthesis device, by removing for example the intracanal blockers. of the prior art recalled above.

 The needle screw can be operated independently of the cap, its needle coming into the rod, and ensures the security of the fixing by acting as a nut brake.

Other features and advantages of the invention will appear during the description which follows, given with reference to the accompanying drawings which illustrate two embodiments thereof by way of non-limiting examples
- Figure 1 is a longitudinal elevational view of a first embodiment of the invention in which the implant comprises a screw for bone anchoring;
- Figure 2 is a side elevational view of the cap of the implant of Figure 1;
- Figure 3 is a top view of the cap of Figure 2;
- Figure 4 is an elevational view of a second embodiment of the implant according to the invention in which the bone anchoring part is a hook;
- Figure 5 is an elevational view with partial cutaway, of the implant of Figure 4 fixed on a rod of an osteosynthesis device;
- Figure 6 is a view in a sagittal plane of vertebrae, one of which is fractured;
- Figure 7 is a view in a frontal plane of the fracture of Figure 6 reduced by an osteosynthesis device provided with implants according to the invention;
- Figure 8 is a view in the sagittal plane of the device of Figure 7.

 The implant shown in Figures I to 3 is intended to be part of an osteosynthesis device, in particular of the spine.

 It comprises a part intended for bone anchoring, constituted in this example by a screw 1, known per se and which will therefore not be described, and a body 2 for attachment to a rod 3 whose surface is smooth or provided with roughness such as diamond tips.

 The body 2 comprises, starting from the end of the screw 1, a cylindrical part 4, a conical part 5 and a rear part of the open type, that is to say which has a channel 6 extending along the axis XX of the screw 1, opening onto the rear part, and open on either side of the body 2 in order to be able to receive the rod 3. The latter rests on a rounded bottom 7 of the channel 6, which is. on the other hand delimited by two lateral branches or banks 8 constituting the rear end of the body 2.

 The implant comprises a female cap 9 having a thread 11 adapted to be able to be screwed onto a corresponding thread 12 formed on the branches 8, and for? that its two diametrically opposite edges (9a) can bear, at the end of screwing, on the rod 3. On its side, the periphery of the cap 9 is also profiled to allow its screwing by a suitable key not shown, for example by a profile 17 with twelve sides (Figure 3) or an octagonal profile. In addition, the implant comprises a needle screw 13 which can be screwed into a threaded hole 14 formed in an internal revolution boss 15 of the cap 9, of axis XX, so that the needle 13a can be inserted into the rod 3. The boss 15 is dimensioned to be able to be inserted between the arms 8 while being practically in contact with them. Therefore, any bringing together of the two arms 8 during the screwing of the cap 9 is impossible.

 The needle screw 13 has an axial recess 16 profiled so as to be able to receive a not shown screwing tool, for example a hexagon profile.

 The thread 12 of the rear end of the body 2 on the one hand, the thread 14 of the boss 15 and the thread of the needle screw 13 on the other hand, have different threads. Finally, the anchor screw 1, the body 2, the cap 9 and the screw 13 are made of the same biocompatible material, for example steel according to the American standard 316 L corresponding to the AFNOR AS 1 Z2 CND 17.3 standard, the screw can be according to the "M3CH" standard.

 The assembly of the implant which has just been described is very simple: firstly introduce the rod 3 between the branches 8 in the channel 6 until it comes to bear against the bottom 7, then the needle screw 13 being engaged in the boss 15, the cap 9 is partially screwed onto the thread 12. The implant is loaded by detraction or compression or derotation, the assembly is then temporarily fixed by tightening the screw 13 by l 'tool corresponding to the profile of the housing 16, until the tip 13a enters the rod 3. Finally, we proceed to the terminal fixing by screwing the cap 9 to the bottom. Therefore, the tip 13a of the screw 13 driven by the cap 9 due to the difference in the two screw threads, sinks into the rod 3.

 At the end of these operations, the rod 3 is blocked both in translation and in rotation at three points, namely: the two edges 9a of the cap 9 and the tip 13a of the screw 13. Finally, the latter ensures the safety of fixing by acting as a nut brake.

 In the second embodiment illustrated in Figures 4 and 5, the implant is a hook 18 comprising a curved blade 19 for bone anchoring, known per se, and a body 21 formed of two lateral branches 8 connected to the blade 19 by a conical part 22 and delimiting between them the channel 6, the body 21 being similar to the body 2. The needle screw 13 allows the hook locking 18-rod 3 in all directions, as in the embodiment of Figures 1 to 3. Likewise, due to the difference in the two pitches, namely that of the internal thread 11 of the cap or capsule 9 and of the needle screw 13, there is no risk of the cap 9 being unscrewed when the needle screw 13 is blocked on the rod 3. The locking of the hook 18 on the rod 3 is carried out without blocker or safety lock, and the fixing of the rod 3 in the channel 6 is then extremely stable, as can be verified by mechanical tests.

 The installation of the hook 18 is carried out in the following manner: first of all, its implantation is carried out in the same manner as that of a hook with posterior opening closed by a cylindroconical blocker. This type of hook has a body hollowed out with a channel, half of which, on the side where the blade is installed, is cylindrical, and the other half conical. A blocker made up of a cylindrical-conical ring and surmounted by a square body, allows the hook to be blocked on the rod in level and in rotation. To obtain a strict immobilization of the hook opened in the bone support, a safety lock is put in place, and ensures with the blocker a fixing for a double bolting.

So, after implantation of the hook, we insert the rod 3 in the channel 6, then we partially screw the capsule or cap 9 by means of a key adapted to the polygonal external contour 17, we then load (detraction or compression) by adjustment of the screwing of the cap 9. The implant is fixed by means of the key, the end of which is engaged in the profiled housing 16 of the needle screw 13, and finally the final locking of the cap 9 is carried out with the key previously used,
It should be noted that the hook 18 with posterior opening closed by the cap 9, is specially recommended when the insertion of the blocker or the safety lock is difficult or impossible (divergent hooks too close together, etc.).

 Figures 7 and 8 show the implantation of osteosynthesis instrumentation on vertebrae 10, one of which has a fracture 25 (Figure 6). This instrumentation comprises two devices 20 for securing and transverse traction (DTT) with transverse rods 22 and hooks 23 fixed on the rods 3. The instrumetation is supplemented by several implants 18 constituted by hooks with a cap 9 as described with reference to Figures 4 and 5, suitably distributed along the rods 3.

In addition to those mentioned above, the invention has the following advantages
- possibility of direct introduction of the rod 3 posteriorly to the body of the implant without requiring additional parts, such as intraductal blockers;
- possibility of carrying out compression and detachment (that is to say the extension of the spinal or bone part) without obligation of a precise orientation of the head in the case of screw implants, whereas a precise orientation is on the contrary imposed by the conical shape of the previous system;
- considerable simplification of training by reducing the different types of bodies used until now to a single type, opened later;
- correlative simplification of ancillary equipment;
- Simplification of manufacturing, the cap, the needle screw and the thread on the rear end of the body does not imply any particular manufacturing difficulty;
better fixation of the implant by fixing at three points on the rod, namely two opposite edges of the cap 9 and the needle screw 13;
- possibility of re-tensioning the device (when this becomes necessary due to the growth of a young subject) or easy ablation, the latter being especially necessary in trauma. Indeed, disassembly of the implant can be carried out very easily first by unscrewing the screw 13, then the cap 9;
- Finally, ease of introduction of the rod into the implant, contrasting with the current difficulty of introducing this rod into a closed body.

 The mounting methodology ensures the conservation of the profiled housing 16 of the screw 13 thanks to the fact that the main clamping force is exerted, not on this housing 16, but on the periphery 17 of the cap 9.

 Alternatively, the needle screw 13 can be offset.

Claims (5)

 1 - Implant for osteosynthesis device, in particular of the spine, comprising a part (1, 19) intended for bone anchoring and a body (2, 21) for fixing on a rod (3), characterized in that the body (2, 21) has a channel (6) opening onto a rear part of said body, delimiting two lateral branches (.8) and open on either side of the body so as to be able to receive the rod (3), and the implant comprises on the one hand a threaded cap (9), suitable for being screwed onto a thread (12) formed on the lateral branches (8) constituting the rear end of the body (2, 21) by closing the channel (6) on this side, and poub that its two diametrically opposite edges (9a) bear only the rod (3), and on the other hand a needle screw (13) which can be screwed into a corresponding tapped hole (14) formed in the cap (9), so that its tip (13a) enters the rod (3), which is thus blocked in translation and in rotation by the two edges (9a) of the cap (9) and by the screw (13).  2 - Implant according to claim 1, characterized in that the screw (13) is engaged in an internal boss of revolution (13) of the cap (9).  3 - Implant according to claim 2, characterized in that the needle screw (13) has a recess (16) profiled so as to be able to receive a screwing tool, and the periphery (t7) of the cap (9) is also profiled for allow its screwing by a corresponding key.  4 - Implant according to one of claims 1 to 3, characterized in that the thread (12) of the rear end of the body (2, 21) on the one hand, the threaded hole (14) and the thread of the needle screw (13) on the other hand, have different screw threads  5 - Implant according to one of claims 1 to 4, characterized in that the anchoring part (1, 19), the body (2, 21), the cap (9) and the needle screw (13) are made in the same biocompatible material.