AU2008351158B2

AU2008351158B2 - Lock ring for an osteosynthesis device and osteosynthesis device including such ring

Info

Publication number: AU2008351158B2
Application number: AU2008351158A
Authority: AU
Inventors: Alexandre Worcel
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-12-13
Filing date: 2008-12-12
Publication date: 2014-01-23
Anticipated expiration: 2028-12-12
Also published as: CN101938947B; ES2559102T3; CA2708972A1; MX2010006447A; KR20100113484A; MY152698A; WO2009103886A3; CA2708972C; AU2008351158C1; JP2011505938A; BRPI0819917A2; EP2229111B1; HK1150952A1; AU2008351158A1; FR2924918B1; FR2924918A1; JP5279837B2; PL2229111T3; EP2229111A2; WO2009103886A2

Abstract

The invention relates to a blocking ring (20) for a threaded holding pin (18) to be screwed into a portion of a bone (14), said ring including a first portion (22) having an axial bore (24) for receiving said holding pin, the periphery of said first portion being threaded so as to interact with a holding plate (12), wherein said ring is characterised in that the same further comprises, as an extension to said first portion, a second deformable portion (28, 44) having a thickness lower than the first portion and having a similar axial bore (30, 46), and in that the shearing of the pin (18) and the ring at the join between the first portion (22) and the second portion (28) deforms the remaining portion (34) of the second portion (28) of the blocking ring (22) towards the pin (18) in such a way as to block the pin (18) in relation to the blocking ring (22) by crimping.

Description

WO 2009/103886 PCT/FR2008/001732 Lock ring for an osteosynthesis device and osteosynthesis device including such ring The present invention relates to a lock ring for a fixing pin designed to be screwed into a bone part. It also 5 relates to an assembly comprising not only such a ring but also a collar designed to be inserted into a hole in a fixing plate. Lastly, it relates to an osteosynthesis device. An osteosynthesis device comprises a fixing plate, at least two pins designed to be screwed into two bone parts, 10 and lock rings for anchoring the pins and thus fastening the fixing plate to the two bone parts. A major problem in this technical field is to devise an osteosynthesis device offering both efficient locking of the pins, to prevent them coming unscrewed when subjected to 15 mechanical stresses or vibrations, and easy unscrewing of the pin when the practitioner wishes to remove the osteosynthesis device. EP-1 583 478 discloses an osteosynthesis device in which the axis of the pin and that of the lock ring are at an 20 angle relative to each other. In that osteosynthesis device the holes of the fixing plate are threaded and receive an intermediate ring containing a threaded bore to receive a pin and a lock ring. In order to fit the osteosynthesis device, the 25 practitioner first drills the fixing plate at at least two points selected to enable it to be anchored to the bone part, wO 2009/103886 - 2 - PCT/FR2008/001732 and then drills this bone part with a drill bit guided perpendicular to the fixing plate. Next, he fits the intermediate ring and screws the threaded pin into the bone part to the desired length. He then places the lock ring onto 5 the pin and screws this lock ring into the intermediate ring. It can be seen that, because of the angular difference between the axis of the pin and that of the lock ring, the lock ring becomes increasingly wedged into the intermediate ring as it is screwed down. This provides an 10 irreversible locking of the pin relative to the fixing plate. That device is effective but has a number of drawbacks. In the first place, there is little tolerance in the angular interval between the pin axis and the lock ring axis. 15 Accurate manufacture of the intermediate ring is therefore required, resulting in a high cost of manufacture. In addition, although this angular interval results in effective locking, it has the disadvantage that this locking action begins as soon as the lock ring begins to be 20 screwed down. The lock ring can therefore sometimes fail to penetrate sufficiently into the fixing plate. Lastly, in the case of a thin plate (less than 3 mm, for example), the intermediate ring and the lock ring must be inserted partially into the bone part if the device is to be 25 properly anchored. This means that this prior art device cannot be used on the upper bones (arm, forearm, hands, wO 2009/103886 - 3 - PCT/FR2008/001732 wrist, face), which are too thin. It is an object of the invention to overcome the limitations of prior art osteosynthesis devices. The present invention achieves its object by 5 providing a lock ring for a threaded fixing pin designed to be screwed into a bone piece, said ring comprising a first part having an axial bore to receive said fixing pin, and the periphery of said first part being threaded to engage with a fixing plate; said ring being characterized in that it 10 further comprises, continuing on from said first part, a second part that is thinner than the first part and has a similar axial bore, this second part being deformable and thus able to lock, by deformation, said ring to said pin. In a preferred embodiment, the bore of the first part 15 of the ring is threaded. Advantageously, the first part of the ring has a cylindrical or frustoconical external form. The invention also relates to an assembly comprising a ring according to the invention and a collar, said collar 20 being designed to be inserted into a hole in a fixing plate, the collar having a threaded frustoconical bore corresponding to the thread on the ring, and a radial slot. The collar advantageously comprises a radial slot. In one particular embodiment, the collar has a convex 25 periphery designed to engage with a concave hole in a fixing plate.

WO 2009/103886 - 4 - PCT/FR2008/001732 Lastly, the invention relates to an osteosynthesis device comprising a fixing plate having at least two holes, pins designed to be inserted into said holes for screwing into a bone piece, and lock rings or assemblies according to 5 the invention. Other features and advantages of the invention will become apparent on reading the description given below of one particular embodiment of the invention, given by way of indication, without implying any limitation, with reference 10 to the appended drawings, in which: - figure 1 shows schematically an osteosynthesis device, - figure 2 is a longitudinal section through part of an osteosynthesis device mounted on a bone part comprising a 15 ring in a first embodiment of the invention, - figure 3 shows the same device as in figure 1 following shearing of the lock ring and pin, - figure 4 is a longitudinal section through part of an osteosynthesis device mounted on a bone part comprising a 20 ring in a second embodiment of the invention, - figure 5 is a view along D of the device shown in figure 4. Figure 1 shows schematically an osteosynthesis device for fastening two bone parts 2a, 2b to a fixing plate 4. The 25 fixing plate 4 has holes for pins 6a, 6b, 6c, 6d, to pass through, on at least part of which is a thread 8a, 8b, 8c, 8d wo 2009/103886 - 5 - PCT/FR2008/001732 for screwing the pin into one of the bone parts. The osteosynthesis device has two pins per bone part but it will be understood that it could have only one pin per bone part in certain cases. It will be noticed that the pins can be 5 screwed in a direction perpendicular to that of the plane of the fixing plate 4. Pin 8b is an example of this. They can also be screwed at an angle to this perpendicular direction. Pins 8a, 8c and 8d are examples of this. Lock rings 10a, 10b, 10c, 10d are placed in the holes 10 of the fixing plate 4 to fasten the pins to this fixing plate. Embodiments of a lock ring according to the invention will now be described with reference to figures 2-5. Figure 2 illustrates part of an osteosynthesis device 15 comprising a ring in a first embodiment of the invention. This figure shows only one pin, but it will be understood that an osteosynthesis device comprises at least two pins in order to unite two boneparts. In figure 2, a fixing plate 12 is placed over a bone 20 part 14. The fixing plate comprises a hole 16 to receive a pin 18 and a lock ring 20. According to the invention the lock ring 20 comprises a first part 22 which has an axial bore 24 for the passage of the pin 18, which bore may or may not be threaded, the 25 periphery of the first part 22 of the lock ring comprising a thread 26 to enable it to be screwed into the hole in the wO 2009/103886 - 6 - PCT/FR2008/001732 fixing plate, and a second part 28, continuing on from the first part 22, but thinner than the first part, and having an axial bore 30 similar to that of the first part. The thickness of the second part 28 is selected to 5 suit the material of which the ring 20 is made, so that when the pin and the second part are sheared, the remaining part of the second part deforms and is pushed down against the top of the remaining pin, thus locking the pin relative to the fixing plate. 10 The osteosynthesis device is installed in the following manner. The practitioner drills the fixing plate at at least two points selected to enable it to be fixed to the bone parts. He then drills each bone part, using a drill bit guided perpendicular to the fixing plate. He next pre 15 positions the lock ring 20 by screwing it part of the way into the hole 16. He can also screw the lock ring 20 all the way into the hole 16, if for example the axial bore of the first part 22 of the lock ring is not threaded. The pin 18, whose bottom part comprises a thread 32, is then screwed into 20 the bone part to the desired length, the lock ring 20, or at any rate its second part, now having a secondary sighting function for guiding the pin as it is screwed in. If the lock ring 20 has merely been pre-positioned, it is now screwed fully into the hole 16. 25 The practitioner then shears off the pin 18 and the ring 20 approximately at the base of the second part 28 wo 2009/103886 - 7 - PCT/FR2008/001732 that is, at the junction between the first part 22 and the second part 28. A mark such as a slight groove can be provided at the periphery of the ring in order precisely to define the position of the shearing tool. 5 The remaining part 34 of the second part 28 of the lock ring 22 is deformed toward the pin 18 by the shearing action. The pin 18 is thus locked relative to the lock ring 22, and hence relative to the fixing plate 12, by a crimping action. 10 Consequently, when the practitioner shears the pin 18 and the ring 20 at the junction between the first part 22 and second part 28, using suitable pliers, the jaws of the pliers initially tend to squeeze the lock ring 20. As the jaws come together, they deform it and finally cut off both the lock 15 ring 20 and the pin 18. A sheared free edge of the second part is thus formed, making a remaining part 34 attached to the first part. Two diametrically opposite portions of this free edge are now pushed toward each other by the shearing action and roughly cover the sheared free end of the pin 18. 20 Thus deformed tightly around the pin 18, the remaining part 34 of the second part 28 of the lock ring 22 locks the pin 18 relative to the lock ring 22 by a crimping action. The situation now is that shown in figure 3, where elements identical to those in figure 2 are given the same 25 references. The lock ring according to the invention is wo 2009/103886 - 8 - PCT/FR2008/001732 particularly advantageous in that it offers excellent locking efficiency for small-diameter pins, with diameters of for example from 0.8 to 1.8 mm, which corresponds to the type of pin used on bone parts in the wrist, hand and face. 5 Thus, experiments have demonstrated a resistance to tension of more than 200 kg on a testing machine able to measure no more than 200 kg with a 4 mm diameter pin and a ring made of 316L surgical steel in which the second part has a thickness of 1 mm. In this test, the ring had no internal 10 thread. It will be appreciated that the re sistance to tension would be greatly increased with an internally threaded ring. This would provide in particular excellent resistance to tension, even with small-diameter pins. Clearly, the lock ring according to the invention is 15 also usable and effective with larger-diameter pins. Figure 4 shows a cross section through part of an osteosynthesis device that has a lock ring in accordance with a second embodiment of the invention, and figure 5 a top view along a direction D parallel to the direction of the pin 20 axis. The lock ring 36 comprises a threaded (thread 40) frustoconical first part 38 provided with an axial bore 42 and a second part 44, continuing on from the first part, comprising an axial bore 46 similar to that of the first part 25 38. According to the invention the thickness of the second part is chosen to suit the material used so that this second WO 2009/103886 - 9 - PCT/FR2008/001732 part is deformable and thus locks the pin, by deformation, when sheared off. The second embodiment of the invention differs from the first embodiment essentially in that the lock ring is 5 mounted on a collar 48 whose orientation in the orifice 50 of the fixing plate can be adjusted. For this purpose the collar has a convex edge 52 and the hole in the fixing plate 12 has a corresponding concave edge 54. The pin is installed in the same way as in the device 10 described with reference to figures 2 and 3. The practitioner first drills the plate at at least two points. He next forms the concave edge of the hole to permit the subsequent insertion of the collar. He then drills the bone part at the chosen angle using a drill bit. The collar 48 is next placed 15 in the hole in the fixing plate, its insertion being facilitated by the radial slot 50 in the collar 48. The lock ring 36 is screwed at least part of the way onto the collar 48 to immobilize its orientation and thus guide the pin 18. When the pin has been screwed in to the desired length, and 20 the lock ring has been screwed fully down onto the collar 48, the practitioner shears off the lock ring 36 and the pin 18 at the lower part of the second part 44 of the lock ring 36, thus deforming the residual part of this second part and thereby locking the pin 18. 25 As in the prior art, the lock ring in each of the embodiments described has one or more notches, such as the WO 2009/103886 - 10 - PCT/FR2008/001732 notches 56 visible in figure 5, to allow the practitioner, using a suitable screwdriver, to unscrew the pin/lock ring assembly when he wishes to remove the fixing plate from the patient.

Claims

1. A lock ring (20, 36) for a threaded fixing pin (18) designed to be screwed into a bone piece (14), said ring comprising a first part (22, 38) having an axial bore (24, 5 42) to receive said fixing pin, and the periphery of said first part being threaded to engage with a fixing plate; said ring being characterized in that it further comprises, continuing on from said first part, a deformable second part (28, 44) that is thinner than the first part and has a 10 similar axial bore (30, 46), and in that shearing the pin (18) and the ring (20) at the junction between the first part (22) and the second part (28) deforms the remaining part (34) of the second part (28) of the lock ring (22) toward the pin (18) in such a way as to lock the pin (18) with respect to 15 the lock ring (22) by a crimping action.

2. The ring as claimed in claim 1, characterized in that the bore (24) of the first part (22) of the ring comprises a thread (26).

3. The ring as claimed in either of claims 1 and 2, 20 characterized in that the first part (22) has a cylindrical external form.

4. The ring as claimed in claim 1, characterized in that the first part (38) has a frustoconical external form.

5. An assembly comprising a ring as claimed in claim 4 25 and a collar (48), said collar being designed to be inserted into a hole in a fixing plate (12), the collar having a WO 2009/103886 - 12 - PCT/FR2008/001732 threaded frustoconical bore corresponding to the thread on the ring, and a radial slot.

6. The assembly as claimed in claim 5, characterized in that the collar (48) comprises a radial slot (50). 5

7. The assembly as claimed in claim 6, characterized in that the collar has a convex periphery (52) designed to engage with a concave hole (54) in a fixing plate.

8. An osteosynthesis device comprising a fixing plate (12) having at least two holes, pins (18) designed to be 10 inserted into said holes for screwing into a bone piece (14), and lock rings (20, 36) as claimed in one of claims 1-3.

9. An osteosynthesis device comprising a fixing plate (12) having at least two holes, pins (18) designed to be inserted into said holes for screwing into a bone piece and 15 assemblies as claimed in one of claims 5-7.