Screw and plate system for backbone osteosynthesis

Details Screw and plate system for backbone osteosynthesis Screw and plate system for backbone osteosynthesis

2000-05-23

2001-09-11

Reip, David O. (Department: 3731)

Surgery

Instruments

Orthopedic instrumentation

C606S064000, C606S075000

Reexamination Certificate

active

06287309

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to systems of the “plate” type for osteosynthesis of the spine.
Systems of this kind are known in the art and include at least two pedicular screws anchored in adjacent vertebrae to be treated and a connecting plate designed to connect the screwheads together in a rigid manner.
EP-A-0 441 084 in particular discloses a system of this kind in which each pedicular screw has a hexagonal section part for inserting the screw into the bone and on top of which is a threaded shank.
The plate has a plurality of oblong openings through which the various threaded shanks can be inserted and an open groove on its bottom face to prevent rotation of the hexagonal part of each pedicular screw, in order to prevent it coming loose.
Each pedicular screw is associated with a stirrup through which the threaded shank of the screw also passes and which straddles the top of the plate; finally, a nut is screwed onto the threaded shank to trap and immobilize the plate with the stirrup on top of it, between it and the hexagonal part of the screw.
Complementary raised patterns are provided on the top face of the plate and on the bottom face of the stirrup to prevent longitudinal sliding of the plate relative to the screw.
Although it is generally satisfactory, this fixing system nevertheless has certain drawbacks.
The raised patterns have to be provided to prevent sliding because the plate and the stirrup cooperate only via two plane faces in compression and so their absence would lead to the risk of entirely unacceptable relative movement of the vertebrae.
The machining required by these raised patterns significantly increases the unit cost of the plates and the stirrups.
Also, the raised patterns can impede fine adjustment of the system in that they allow only a particular number of discrete mutual positions of the plate and the stirrup, i.e. a particular number of discrete distances between the screws; moreover, if the nut is overtightened before the final tightening, mutual sliding of the plate and the stirrup during adjustments may be impeded.
Finally, the above prior art system requires the various stirrups to be attached to the top of the plate, before screwing on the nuts, which is irksome and entails the risk of incorrect positioning of the stirrups before tightening.
SUMMARY OF THE INVENTION
The present invention aims to alleviate the above drawbacks and to propose a plate-type connecting system in which the various components require much simpler machining, but which still offers excellent stability.
Another object of the invention is to propose a system which is simpler to fit because it avoids the irksome and unstable fitting of the stirrups before fitting the nuts.
A further object of the present invention is to propose a system which has some degree of elastic deformability, for improved distribution of the stresses between the various vertebrae.
The present invention therefore proposes a system for osteosynthesis of the spine, including at least two pedicular screws and a connecting plate adapted to connect the screws together in an essentially rigid manner, each screw having a bone anchor threaded part and a non-circular section head, as well as a threaded end shank adapted to cooperate with a nut, the plate having at least one opening adapted to have the threaded end shank of a screw passed through it and to be trapped between said non-circular section head and said nut, locking means being provided for preventing relative angular movement between the head of each particular screw and the plate, characterized in that the angular locking means include an attached member between said plate and said head of the particular screw and through which the threaded end shank of the latter passes, this member providing a first locking cooperation of shapes with said head and a second locking cooperation of shapes with said plate.
Preferred, but non-limiting, aspects of the system according to the invention are:
the first locking cooperation of shapes is a straddling of said non-circular section head by said attached member from above;
said attached member has two lateral legs delimiting between them a channel with straight edges whose width is slightly greater than the distance between two parallel flats of the head of said pedicular screw;
the second locking cooperation of shapes is a straddling of said plate by said attached member from below;
said attached member has two lateral columns defining between them a channel with oblique raised edges and said plate has lateral bevels adapted to bear against said oblique edges;
said plate bears only on said bevels of said attached member;
said attached member has a core which is generally disk-shaped with a central hole through it through which the threaded end shank of the pedicular screw can be passed;
the width of the attached member is substantially equal to that of the plate;
the system includes a set of pedicular screws and a set of plates which have different configurations of holes, with one slightly oblong hole of constant geometry and one or more elongate holes of different lengths;
the nut bears directly against the top face of the plate.
Other aspects, aims and advantages of the present invention will become more apparent on reading the following detailed description of one preferred embodiment of the invention, which is given by way of example only and with reference to the accompanying drawings, in which:


REFERENCES:
patent: 5728127 (1998-03-01), Asher et al.

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