US 20060116678 A1
The self-locking osteosynthesis device includes a plate equipped with holes for the passage of fixation screws. The invention is characterised in that, at least in the areas defining the screw holes, the aforementioned plate is made from a material having mechanical properties such that the periphery of the holes can be self-tapped by means of tapping screws which can be used to fix the plate.
1. Self-locking osteosynthesis device comprising:
a plate with holes for passage of fixation screws, said plate being comprised of a composite plate that contains holes having peripheries comprised of inserts comprised of a plastic biocompatible material having mechanical properties allowing a self-locking of the periphery of the holes by tapping screws used for fixation of the plate, the inserts being inserted into the holes provided in a remaining part of the plate comprised of metal.
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3. Device according to
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8. Device according to
tapping screws being comprised of a proximal part or head equipped with a conical threading tapping mechanism having a diameter that increases in the direction of the proximal end of the screws.
9. Device according to
a mechanism that prevents the rotation of the inserts engaged in the holes of the plate.
The invention relates to a self-locking osteosynthesis or osteotomy device of the type comprising a plate having an appropriate shape designed to be affixed on bone fragments using a screw to ensure their coaptation.
The coaptation of the bone fragments using plates of titanium or another material and screws in order to create an osteosynthesis is a common operation in bone surgery, for example, orthopedic surgery.
In order to obtain a good result, it is necessary that the plates or implants are screwed together permanently to the bone fragments assembled from the implants. It is thus a requirement that the screws can not unscrew and move back, to prevent any displacement of the implants relative to the bone fragments.
On the other hand, it would often be desirable to be able to choose the orientation of the screws relative to the plates and as a function of the positioning and the shape of the fragments to be assembled, which can improve the quality of the assembly.
In order to prevent the screws from unscrewing and moving back, it has been proposed (EP-0,345,133, FR-2,794,963) to house the locking instruments at the input of the screw holes into the plates, in order to eliminate any possibility of axial movement of the screws, after they are tightened in the bony material. For example, it is provided in the document EP-0,345,133, to use check screws that are outside-threaded and work together with a complementary threading arranged at the input of the holes of the screws that equip the plates, in a manner so that the head of the screws is wedged against a check screw and that the check screws can not move axially relative to the plates, this locking thus ensuring the permanent support of the plate on the bone fragments.
The devices proposed by several manufacturers represent at this time the solutions that are most certain in terms of locking. However, these relatively complex devices require the use of plates having a relatively sizeable thickness that is totally incompatible with a usage for operations on the bones of the hand or foot, for which the thickness of the plates must be as reduced as possible, taking into account the small size of the bones involved.
In the document EP-0.345.133, a device is again shown for connecting two elements such as an implant and a bone, according to which the implant comprises screw holes with axes oriented at an angle to each other, in a manner so that the screws going through these holes have orientations that are rigorously imposed by the direction of these axes. A device of this type can only be planned for the reduction of identical fractures, because otherwise it would be necessary to provide as many plate models as possible cases of fractures, which is practically impossible; in fact, it does not offer any possibility to choose the orientation of the screws as a function of the problems encountered in orthopedic surgery.
In the document WO-00/66012, a plate is described for osteosynthesis that can be locked, according to which the screws and the screw holes provided in the plate are equipped, respectively, with a locking threading and a sensible meshing profile allowing the introduction of the screws into the plate in an angled manner. The practical creation of a device of this type would be difficult and it seems its effectiveness has not been established.
In a general manner, in the field of osteosynthesis of small bones requiring the use of plates having small dimensions, the devices that are currently available on the market do not make possible an angular clearance between the screws and the plate, so that the screws thus have to be positioned perpendicularly to the plate. However, in certain cases, it would be desirable to be able to have one or more screws at an angle in order to use one or more of the better quality bones for tightening the screws.
The invention has the purpose of correcting the shortcomings mentioned above for osteosynthetic systems using plates and screws, notably because of the fact that the existing devices for serious orthopedics (treatment of serious traumatisms) can not be transposed to hand and foot surgery in which the dimension of the plates that can be used becomes considerably reduced.
According to the invention, this purpose is achieved using an osteosynthesis comprising a plate which is equipped with holes for the passage of screws for fixation of this plate onto a bone support. This device is notable in that the osteosynthesis plate is made, at least in the zones that define the screw holes, of a material that has mechanical properties to allow self-tapping of the periphery of the holes with the tapping screws used to fix the plate.
According to another characteristic arrangement, the osteosynthesis plate is made of a composite plate with hole peripheries comprised of inserts made of a plastic biocompatible material, and inserted into the holes in the remaining part of the plate which is made of metal.
According to another characteristic arrangement, the hole peripheries are comprised of inserts made of polyether ether ketone (PEEK), and the remaining part of the plate is made of titanium.
According to another characteristic arrangement, the head of the screws has a conical thread tapping mechanism.
By these characteristic arrangements above, the self-locking head of the screws drills its own helicoid receiving groove in the periphery of the holes in which they are engaged, in a manner so that the screws are then automatically locked in the plate when their head is tightened into its housing.
On the other hand, the osteosynthesis plate according to the invention allows a selective angulation of the screws relative to the axis of the holes of the plate, as a function of the requirements.
In addition to obtaining the results mentioned above that are very much of interest, the osteosynthesis device according to the invention provides several advantages:
it has a simple design so that it can be made in an economical manner;
it is easy to implement;
it is very reliable in its usage;
it can be used to ensure the locking of fixation screws of osteosynthesis plates having small sizes, which is not allowed by the systems currently proposed on the market.
This osteosynthesis device thus meets perfectly the expectations of surgeons in terms of ease of implementation and reliability of usage.
The above purposes, characteristics, and advantages, and still others, emerge better from the description that follows and the attached drawings in which:
Reference is made to the drawings in order to describe an embodiment example that is of interest, though in no way restrictive, of the self-locking osteosynthesis device according to the invention.
This device comprises a plate 1 equipped with passage holes 2 and fixation screws 3.
According to the invention, the plate 1 is made, at least in the defining zones of the passage holes 2 of the screws 3, of a material 4 that has the mechanical properties that allow a self-locking of the periphery of these holes using tapping screws for the fixation of the plate on the bone material.
The plate 1 can have any shape designed for the cases to be treated with reduction of fractures or restorative surgery; the shape shown in
In a preferred manner, the plate 1 is made up of a composite plate whose peripheries 4 of the holes 2 are made of a plastic biocompatible material, the remaining part or surface 5 of the plate being made of metal.
The peripheries 4 of the holes 2 can be made of a high-performance thermoplastic polymer. In a preferred and advantageous manner, the peripheries 4 of the holes 2 are made of polyether ether ketone (PEEK) that has very high mechanical properties and can be machined, like a metal.
The remaining part or surface 5 of the plates 1 can be made of stainless steel, and in a preferred and advantageous manner, it is made of titanium.
The solid fixation of the inserts made from the peripheries 4 of the holes 2 in the holes 6 arranged in the plate having a metal base 5 can be made by a technique of molding from a casting having the advantage of ensuring an intimate contact between the two materials.
However, in a preferred manner, the implementation of the inserts with PEEK 4 into the holes 6 of the metal plate 5 is done by means of a mechanical assembly. The inserts made of PEEK 4 are engaged, by deformation and pressure in the holes of the metal plate and are then held in these holes. For example, the inserts 4 can comprise a peripheral groove 4 a in which an upper edge 6 a of the holes 6 of the plate 1 come to engage, while the inserts are pushed into the holes. When the screws 3 are screwed in, the inserts 4 deform and are compressed between the edges of the holes 6 of the metal plate 5, which contributes to the solidity of the anchorage of these inserts in the metal plate.
A mechanism is provided to prevent any possibility of rotation of the inserts 4 in the holes 6 of the plate 5 when the screws are screwed into these inserts. This mechanism can, for example, be comprised of one or more grooves arranged in the inside cylindrical surface of the holes 6 of the plate 5, in parallel to the axis of the holes.
Using the mechanisms described above, the inserts 4 are solidly connected to the plate 1 without the possibility of axial movement or rotation.
The holes 2 have a conical shape. The large opening 2 a of the holes 2 accessible from the outside of the plate 1 comprise the input for them, while the small opening 2 b of the holes 2 opens onto the inside of the plate designed to be applied to the parts of the bone to be assembled. The conical wall 7 of the holes 2 of the inserts 4 is smooth and does not contain any threading before the use of the osteosynthesis plate.
The screws 3 that can be used for fixation of the osteosynthesis plate 1 described above comprise a proximal part or head 8 equipped with a conical threading tapping mechanism 9 having a diameter that increases in the direction of the proximal end of the screws.
These screws are, for example, the type described in the document WO 98/40024. They comprise a distal part 10 provided with a cylindrical threading 11, a proximal part or head 8 equipped with a conical threading tapping mechanism 9, and, preferably, a smooth intermediate section 12 arranged between the distal part 10 and proximal part 8.
The screws are made of any suitable biocompatible material and they can be advantageously of the “cannular” type, i.e. equipped with an axial canal 13 that extends from one end to the other of the screws, for the passage of a pin.
The nominal diameter of the cylindrical threading 111 of the distal part 10 of the screws is less than the diameter of the small opening 2 b of the holes 2, so that the distal part of the screws can go through the holes freely during the fixation of the osteosynthesis plate 1 on the bones.
The composite osteosynthesis plate according to the invention allows a tightening of the screws 3 at a certain angulation relative to the axes of the holes 2 of the plate.
On the right and left parts of the drawing, the osteosynthesis plate 1 is seen pressed against the bone pieces O1 and O2, by means of two screws 3 completely tightened, whose distal part 10 is tightened into the bone material 14 and whose proximal part 8 is tightened into the inserts 4 of the plate, the screws having different orientations and being locked using the devices described above.
On the central part of the drawing, a screw 3 is shown in the process of being tightened.
As indicated above, the invention makes it possible to obtain a locking of the screws eliminating any possibility of moving back after they are tightened in the bone material. This locking is all the more effective since the conical threaded head tapping mechanism of the screws produces a jamming effect resulting from the conical assembly of the screws and the inserts.