AU720999B2

AU720999B2 - A device for making a rigid transverse link between two rods for osteosynthesis of the spine

Info

Publication number: AU720999B2
Application number: AU23710/97A
Authority: AU
Inventors: Christian Baccelli; Regis Le Couedic; Eric Petreto
Original assignee: Stryker France SAS
Current assignee: Stryker France SAS
Priority date: 1996-06-03
Filing date: 1997-05-30
Publication date: 2000-06-22
Anticipated expiration: 2017-05-30
Also published as: MX9704076A; FR2749156A1; AU2371097A; JPH1080432A; DE811357T1; JP3934741B2; CA2206853A1; FR2749156B1; KR100386493B1; KR980000371A; NZ314986A; EP0811357A1; ES2142778T1

Description

-1- P/00/0011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD

PATENT

a

ORIGINAL

Name of Applicant: Actual Inventors: Address for service in Australia: Invention Title: STRYKER FRANCE S.A.

Christian BACCELLI; R6gis LE COUEDIC and Eric PETRETO CARTER SMITH BEADLE 2 Railway Parade Camberwell Victoria 3124 Australia A DEVICE FOR MAKING A RIGID TRANSVERSE LINK BETWEEN TWO RODS FOR OSTEOSYNTHESIS OF THE SPINE The following statement is a full description of this invention, including the best method of performing it known to us 111 A DEVICE FOR MAKING A RIGID TRANSVERSE LINK BETWEEN TWO RODS FOR OSTEOSYNTHESIS OF THE SPINE The present invention relates in general to devices for osteosynthesis of the spine, and more particularly to a device for making a rigid transverse link between two osteosynthesis rods extending in the longitudinal direction of the spinal column and anchored to the vertebrae.

Such transverse link devices are already known.

In particular, EP-A-O 446 092 discloses a transverse link device in which two hooks suitable for engaging on two longitudinal rods co-operate with locking screws and with a transverse bar to make a link that is simple and ••co practical to implement.

15 Nevertheless, it can turn out that the rods are insufficiently locked in the hooks when the device is subject to large lateral stresses. More precisely, the

S..

rods can slide out of the hooks, thereby eliminating the link, and that is totally undesirable.

20 Also, US-A-5 334 203 discloses a device for making a rigid transverse link between two rods for osteosynthesis of the spine, the device being of the type comprising two link-and-locking elements each comprising two branches separated by a central channel, each branch having a hook 25 shape defining a cradle for a longitudinal rod, and the two cradles facing respectively towards two opposite faces of the link-and-locking element so that each linkand-locking element can be engaged on a rod by the associated rod being received in its central channel, and can then be rotated to anchor the associated rod in the cradles of the two branches, the device further comprising a transverse link element extending between the two link-and-locking elements.

To provide locking for the assembly, that known device further comprises a relatively complex mechanical device including numerous different parts. This is disadvantageous in that installing the device is extremely fiddly, in particular because of the large number of parts that must be handled.

In addition, a major drawback of that known device lies in that it is necessarily preassembled before being put into place, and it is therefore very bulky, even though it must be fitted to the two longitudinal rods by movement that includes a substantial component in a direction perpendicular to the plane including the two rods.

This makes it necessary to destroy a large amount of the ligamentary structure that extends along the spinal column between the two rods.

Also, because of the numerous degrees of freedom of agog the preassembled device which are necessary to enable it 15 to be fitted to the particular configuration of the rods, the device can be awkward to mount.

Finally, and above all, that document states that the link-and-locking elements must initially be rotatably mounted on the transverse link element so that the device 20 can be convenient to use.

The present invention is based on the discovery that link-and-locking elements of the above-defined kind can make it possible to improve the qualities of a device having a simple transverse bar, as described in 25 EP-A-O 446 092, without being rotatably mounted on other portions of the device.

More precisely, it has been discovered that it is possible initially to mount the link-and-locking elements on the rod, and to rotate them before assembling the implant, it subsequently being possible to use a simple bar slid through the elements as the transverse link means.

The present invention thus seeks to mitigate the drawbacks of the state of the art and to provide a transverse link device which conserves the ease of use and the effectiveness of the link-and-locking elements of q 3 334 203 while also presenting the structural simplicity of the device of EP-A-0 446 092.

To this end, the invention provides a device as defined above, and wherein in that the transverse link element is constituted by a bar suitable for being slid longitudinally along the channels of the two linkand-locking elements once they are disposed substantially in alignment with each other, and in that a respective locking member is also provided suitable for co-operating with each link-and-locking element and for clamping said bar between the rod and the web of the channel to lock the assembly together.

Other aspects, objects, and advantages of the present invention appear more clearly on reading the following detailed description of a preferred embodiment thereof, given by way of example and made with reference to the accompanying drawings, in which: Figure 1 is a profile view partially in section of a transverse link device of the invention; 20 Figure 2 is a back view of the Figure 1 device; Figure 3 is an exploded perspective view of the three components of the device of Figures 1 and 2; and Figures 4a 4b, 5a 5b, and 6a 6b are fragmentary views respectively in profile and from behind 25 showing how the link device of Figures 1 and 2 is put into place.

With reference to Figures 1 and 2, there are shown two rods 10a and 10b for joining vertebrae together longitudinally, which bars are shown as being parallel to each other, but in practice they may occupy various mutual angles within limited angular ranges.

In conventional manner, these two rods are cylindrical and smooth. They are anchored.at various points to the vertebrae by means of well-known devices.

The transverse link device of the invention comprises a transverse bar 20, of rectangular section in this case, and two identical link-and-locking elements suitable for receiving locking screws More precisely, each element 30 comprises a generally diamond-shaped base 31, and two branches 33 and 34 extending parallel to each other from the base 31 from two opposite sides thereof.

Each branch is generally J-shaped, forming a hook, and defining a respective cradle 33a or 34a on its inside edge. The two cradles are open in two opposite directions. Each cradle lies under a sloping surface 36 which rises, i.e. goes away from the plane defined by the bottoms of the cradles, going outwardly. As explained below, this sloping surface serves to form a cam urging the associated rod 10a or 10b towards the bottom of said S 15 cradle when the element is rotated, thereby facilitating installation.

Between them, the two branches define a straight channel 35 whose web 35a is defined by the plane inside face of the base 31.

20 This channel is defined by two main inside faces 33c and 34c of the two branches and by two chamfered faces 33b and 34b adjacent to said main faces and situated at two opposite outlets of the channel, immediately behind the corresponding cradle, as can be seen in particular in "25 Figures 3, 4b, 5b, and 6b.

This disposition of the inside faces of the branches 33 and 34 makes it possible to define a path between the faces 33c and 34c suitable for receiving the respective rod 10a or 10b, with the chamfered walls 33b and 34b making it possible for the bar 20 to pass through after the elements 30 have rotated through an angle a (see Figure 5b) that is perceptibly smaller than It will be observed here that the width of the channel 35 between the faces 33c and 34c is selected to be slightly greater than the diameter of the rod 10a or while the width of the channel for the bar 20 placed perpendicularly to the rod is also slightly greater than the width of said bar, so as to leave a certain amount of angular play between the element 30 and the bar Finally, a through tapped hole 32 extends through the base 31 between its outside face and the web 35a of the channel.

A lock screw 40 is designed to be engaged in the tapped hole 32. It comprises a cylindrical body having an outside thread 41, a slightly bulging rounded tip 42, and a socket 43 for a tightening tool, e.g. a standard hexagonal socket.

The process of putting the above-described device into place is described below with reference to Figures S4a, 4b, 5a, 5b, 6a, and 6b.

Initially, one of the two elements 30 is placed on 15 one of the two rods 10a (or 10b), at substantially the same level so that the rod is received in the channel (Figures 4a and 4b). At this stage, the screw 40 can be premounted in its tapped hole 32.

~Thereafter, the element 30 is rotated (arrow Fl) 20 through an angle a, equal to 70' in this case, until it reaches an abutment position defined by the rod coming into contact with the bottoms of the cradles 33a and 34a in the two branches 33 and 34 (Figures 5a and 5b). It will be observed that during this movement, the sloping 25 top surfaces 36 of the element 30 act as cams to urge the rod 10a towards the bottoms of the cradles 33a and 34a.

The transverse bar 20 is then inserted through one or other of the two sides of the element 30, e.g. in the direction of arrow F2 in Figures 6a and 6b, so as to be engaged in the channel 35 of the element 30 between the rod 10a and the web 35a of said channel. It will be observed that the bar 20 is then positioned so as to leave free the region of the other rod 10b that is subsequently to receive the other element The other element 30 is then put into place on the other rod 10b by translation and then rotation, like the first element.

Finally, the bar 20 is slid so as to engage in said other element 30 in the same manner as in the first element, i.e. between the rod 10b and the top of the associated channel.

The two screws 40 are then tightened by means of a tool so as to lock said bar 20 between the rods and the webs 35a of the channels, the necessary reaction force being exerted on the rods by the curved free end portions of the branches 33 and 34.

This locking simultaneously provides mutual locking between the elements and the rods, such that an extremely simple procedure puts little stress on the surrounding **tissue and provides an extremely effective rigid oooo transverse link.

S 15 It will be observed that the thickness of the transverse bar 40 is selected to be such that on being tightened, the bar is capable of being curved somewhat.

This makes it possible for the device to accommodate situations in which the two rods 10a and 10b are not in 20 the same plane. Also, as mentioned above, the angular play of the bar 20 in the channels 35 serves to accommodate situations in which the two rods diverge or '"converge slightly in projection onto the transverse plane.

In this respect, it will be observed that the '-".rounded tip 42 of each screw 40 serves to accommodate mutually differing positions without compromising the quality of locking.

It will also be observed that the device of the invention makes it possible to provide a rigid link between the rods without undesirable transverse traction force being exerted on said rods.

Naturally, all of the component parts of the device of the invention are made of a biocompatible material such as stainless steel or a titanium alloy. Also, the shapes and dimensions of the parts, and in particular the 7 length of the bar 20 can be selected as a function of requirements.

The present invention is not limited in any way to the embodiment described above and shown in the drawings, and the person skilled in the art will be able to make any variant or modification thereto within the spirit of the invention.

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