Implant for osteosynthesis device in particular of the backbone

1. An implant for an osteosynthesis device, in particular for the spine, the implant comprising:

a first assembly comprising:

a fixing body for a bracing rod, said body being arranged to present a reception housing for receiving an anchor screw head, thereby defining a ball joint between the anchor screw and the fixing body;

a positioning ring for interposing between the anchor screw head and the bracing rod;

and a second assembly comprising a nut type system for fastening the bracing rod to the fixing body,

wherein

the first assembly has a positioning ring mounted in the fixing body with freedom to move in limited linear displacement and allowing the body and the anchor screw to rotate freely relative to each other in the absence of the bracing rod; and

the second assembly has a nut type system adapted on being screwed onto the body to bear against the bracing rod and move the positioning ring in linear manner so that on being tightened it clamps the bracing rod between said system and the positioning ring, and also clamps the anchor screw between the positioning ring and the fixing body;

wherein the positioning ring is guided to move with limited linear displacement relative to the fixing body by means of a guide peg co-operating with a complementary bore.

2. An implant according to claim 1 , wherein:

the fixing body has two side branches defining a channel between them that opens out on either side of the body in order to receive the bracing rod, the side branches having outside walls that are threaded; and

the fastening system comprises a nut adapted to be screwed onto the outside threaded walls of the side branches, the nut being fitted in its diametral zone with a shoe mounted to rotate freely and designed to come to bear against the bracing rod so that when tightened it clamps said shoe and the positioning ring.

3. An implant according to claim 1 , wherein the positioning ring presents a concave surface complementary to the bracing rod and is guided to slide in such a manner that the concave surface defines a portion of the reception channel for receiving the bracing rod so as to ensure that the bracing rod is positioned automatically between the side branches and on the positioning ring.

4. An implant according to claim 2 or 3 , wherein the positioning ring presents a through opening opening out between the side walls and over the head of the anchor screw in which there is provided a blind hole suitable for receiving a screw-driver tool passing through the opening.

5. An implant according to claim 1 or 2 , wherein the fixing body comprises:

a fixing head on which there stands the two side branches and in which there is arranged a cavity opening out at one end between the side branches and opening out at its opposite end;

the positioning ring mounted to move with limited displacement inside the cavity with its surface for receiving the bracing rod opening between the two side branches;

the head of the anchor screw mounted at least in part inside the cavity so that the positioning ring is interposed between said head and the body; and

a closure cup fixed on the fixing body on its inside face to close the cavity and having the anchor screw passing therethrough.

6. An implant according to claim 1 , wherein the positioning ring and the closure cup present partly-spherical bores so as to define the reception housing for receiving the head of the anchor screw.

7. An implant according to claim 1 , wherein the nut has a shoe of width adapted to co-operate with the nut to define on either side of the shoe two gaps serving firstly to receive the two pins of a tool for taking hold of the nut, and secondly to pass the side branches of the fixing body in order to enable said shoe to slide between the side branches.

8. An implant according to claim 2 or 7 , wherein the fixing body has two slots arranged facing each other in the inside walls of the side branches so that once the bracing rod has been installed they guide the pins of the tool on the fixing body and they enable the shoe to be indexed while out of sight between the side branches.

9. An implant according to claim 8 , wherein the nut has a shoe with two notches being formed on the side edges thereof, said notches opening out into the gaps and being designed to receive and position pins of the tool.

10. An implant according to claim 7 , wherein the nut has means enabling the shoe to be mounted by snap-fastening, which shoe is free to rotate relative to the nut once it has been mounted.

11. An implant according to claim 4 , wherein the positioning ring and the closure cup present partly-spherical bores so as to define the reception housing for receiving the head of another screw.