WO2014184463A1

WO2014184463A1 - Bone screw for a protected arthrodesis device

Info

Publication number: WO2014184463A1
Application number: PCT/FR2014/051040
Authority: WO
Inventors: Noël GRAZIANI
Original assignee: Euros
Priority date: 2013-05-17
Filing date: 2014-04-30
Publication date: 2014-11-20
Also published as: FR3005565A1; FR3005565B1

Abstract

The invention relates to a bone screw (10) comprising a body (20) which is elongate along an longitudinal axis (A1) and supports at least one helical thread (30) and, at the rear end of said elongate body, a head (40) which has a recess (41) for receiving the end of a screwing tool. According to the invention, the helical thread has at least one notch (32) the shape of which is such that the joints between the notch and the helical thread form angles, one of which is acute and the other of which is obtuse, the joint forming an obtuse angle being the one located closest to the head.

Description

BONE SCREW FOR SAFETY ARTHRODESIS DEVICE

TECHNICAL FIELD TO WHICH THE INVENTION RELATES The present invention generally relates to the fixation of any implant on a bone of a patient.

It relates in particular to arthrodesis of the spine, that is to say the blockage of several vertebrae relative to each other.

It relates more particularly to a bone screw comprising, on the one hand, an elongated body along a longitudinal axis which carries at least one helical thread and, on the other hand, at one end of this elongate body, a head which has an imprint receiving the end of a screwing tool.

It also relates to an arthrodesis device comprising, on the one hand, a bone plate having at least two openings delimited by support edges, and, on the other hand, at least two bone screws as mentioned above.

BACKGROUND

Document FR2874316 discloses an arthrodesis device as mentioned above, comprising a bone plate and four spinal screws.

These spinal screws, once screwed into two cervical vertebrae of the spine of a patient, then allow to retain the bone plate against it. This device thus makes it possible to block these two cervical vertebrae with respect to one another.

As is stated in this document, in general, the major risk of arthrodesis devices is to see one of the spinal screws extract from one of the vertebrae, which can be very dangerous for the patient.

Indeed, during the surgical procedure, the spinal screws are screwed into the cancellous bodies of the vertebrae, which does not ensure a good maintenance of these screws in the vertebrae.

The arthrodesis device disclosed in this document FR2874316 is then specifically designed to prevent the spinal screws from being unscrewed.

Thus, each spinal screw comprises, between its head and its elongate body, a nut-shaped portion. The bone plate has meanwhile, along a portion of each of its openings, a slot which defines with this opening an elastic blade.

Thus, the elastic blade is adapted, at the end of screwing, to deform to allow the spinal screw to rotate (despite its nut-shaped portion) and then, after screwing, to press against one of the flanks of the nut-shaped portion of the spinal screw to lock it in rotation .

The major disadvantage of this arthrodesis device is that its implementation is difficult since it requires the surgeon a significant effort when it must deform the elastic blades every sixth turn of the spinal screws.

OBJECT OF THE INVENTION

In order to overcome the above-mentioned drawback of the state of the art, the present invention proposes a new bone screw, the shape of the thread of which alone ensures its locking in the spongy body of the patient's bones.

More particularly, it is proposed according to the invention a bone screw as defined in the introduction, wherein said helical thread has at least one notch whose shape is such that the junction areas between the notch and the helical thread form angles of which one is acute and the other is obtuse, the junction zone forming an obtuse angle being that closest to the head, and wherein the head has a peripheral groove laterally open.

Thus, it is understood that when the screw is screwed into the bone, the junction zone forming an acute angle is the one that meets the first bone. It is then inclined in such a way that it does not form an obstacle to screwing the screw.

The other junction zone then meets the bone. Its obtuse shape, which is a kind of ramp, does not form an obstacle to screwing the screw.

On the other hand, thanks to the invention, the junction zone which forms an acute angle has a hook function preventing the bone screw from being unscrewed.

The peripheral groove provided in the head is provided to receive a tongue of a bone plate. Since the bone plate is well fixed to the bone by several other screws, this tongue will prevent the screw from tearing axially from the bone.

It is therefore the combination of the notches and the peripheral groove that ensure the screw a good fixation in the bone.

Other advantageous and non-limiting features of the bone screw according to the invention are the following:

said elongate body has, at its junction with said head, a portion of length greater than 5 mm, which is substantially frustoconical of revolution around the longitudinal axis;

- said head has a peripheral groove laterally open, and possibly also backward (opposite the elongated body);

said head has, on the side of the elongate body, a sphere-shaped section of revolution about the longitudinal axis;

each notch has a dihedral shape;

at least two rows of notches aligned along axes parallel to the longitudinal axis are provided.

The invention also provides an arthrodesis device as defined in the introduction, with bone screws as mentioned above, whose elongated bodies are engaged through said openings and whose heads rest on said support edges.

Advantageously, there are provided movable tongues on said bone plate, which are automatically recalled through the openings.

Preferably, said tongues are formed with said bone plate.

According to another advantageous characteristic of the invention, said support edges have shapes of spherical sections.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT The following description with reference to the accompanying drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it can be implemented.

In the accompanying drawings:

- Figure 1 is a schematic perspective view of a bone screw according to the invention;

FIG. 2 is a schematic side view of the bone screw of FIG.

1;

FIG. 3 is a schematic perspective view of an arthrodesis device equipped with two bone screws such as that represented in FIG. 1;

- Figure 4 is a sectional view along the plane A-A of Figure 3; and

FIGS. 5 to 7 are cross-sectional views of the bone screw of FIG. 1 engaged in a bone, on which the bone screw is respectively represented during screwing into the bone, screwed into the bone to the outcome of the operation, and screwed into the bone one year after the operation. Figure 1 shows a bone screw 10 provided for anchoring in a vertebra of a patient's spine. This is therefore a spinal screw 10.

In the description, the terms "front" and "back" will be used relative to the direction of gaze of the surgeon implanting this spinal screw in the patient's spine. Thus, the back will designate the side facing the surgeon and the front will point to the side facing the patient.

Such a spinal screw 10 is used to secure any implant to the patient's spine.

Here, as shown in FIGS. 3 and 4, this spinal screw 10 is more particularly intended to be used in combination with other identical screws, in order to fix a bone plate 50 to several cervical vertebrae of the patient, for the purpose to block these vertebrae relative to each other (we speak of cervical arthrodesis).

As shown in Figures 1 and 2, the spinal screw 10 object of the present invention comprises a body 20 elongate along a longitudinal axis A1, which laterally carries a helical thread 30. This spinal screw 10 also comprises, at the rear end of this elongate body 20, a head 40 which has a cavity 41 for receiving the end of a screwing tool.

According to a particularly advantageous characteristic of the invention, the helical thread 30 has at least one notch 32 whose shape is such that the angles α1, a2 formed at the junctions between the notch 32 and the helical thread 30 are one acute and the other obtuse (see Figure 7), the obtuse angle being formed at the junction between the notch 32 and the helical thread 30 which is closest to the head 40 of the spinal screw 10.

Otherwise formulated, considering the two areas of the helical thread 30 which border the notch 32, the one closest to the head 40 forms an open corner at an obtuse angle, while the one furthest from the head 40 forms a open corner at an acute angle.

The edge 32B of the notch 32 closest to the head 40 thus forms a ramp, while the other edge 32A of the notch 32 forms a hook (see Figures 5 to 7).

In the embodiment of the invention shown in the figures, and in particular in FIG. 2, the body 20 has three distinct parts situated in the extension of each other, including a rear portion 21, an intermediate portion 22, and a front portion 23.

The front portion 23 is pointed so that a hole can be made in the corresponding vertebra of the patient. This front portion 23 is here substantially conical of revolution about the longitudinal axis A1.

The intermediate portion 22 is here substantially cylindrical in revolution about the longitudinal axis A1, so that it enters effortlessly into the hole drilled in the vertebra of the patient.

The rear portion 21, which is located on the side of the head 40 of the spinal screw 10, has two substantially frustoconical portions 21A, 21B of revolution about the longitudinal axis A1. It thus comprises that, when the spinal screw 10 is screwed into the vertebra and the rear portion 21 of its body 20 enters the hole drilled in the vertebra, this rear portion 21 forces the pierced hole in the vertebra to expand.

Thus, since the hardest part of the vertebra is that located near its outer face, the rear portion 21 of the body 20 ensures good maintenance of the spinal screw 10 in the vertebra, by wedging.

In practice, only a front section 21 B of the rear portion 21 of the body 20 will penetrate into the patient's bone.

This frustoconical front portion 21 B has an apex angle of the order of 5 degrees. It extends over a length of about 8.5mm.

The other rear leg 21 A, which is not intended to enter the bone but which is only intended to make the junction with the head 40 of the screw, here has an angle at the summit of the order of 27 degrees . It extends over a length of about 1.5mm.

As shown in FIGS. 1 and 2, the threading 30 rises from the lateral face of the body 20. It has a simple thread and here forms seven turns around the body 20.

This threading 30 has a generally triangular profile inclined towards the rear.

The thread 30 thus has a front face strongly inclined rearwardly, at an angle β1 greater than 20 degrees, here equal to 25 degrees.

It has a rear face slightly inclined towards the front, according to a angle β2 less than 10 degrees, here equal to 5 degrees.

The "osteodynamic" profile of this thread 30 thus provides the spinal screw 10 a better grip, which makes tearing more difficult.

Here, as shown in Figure 1, there is provided, at each turn of the thread 30 around the body 20, three notches 32.

The different notches 32 are aligned in three rows 31 of axes parallel to the longitudinal axis A1.

These notches 32 all have substantially identical shapes.

Thus, as shown in Figure 7, each notch 32 has, seen from the front, a dihedral shape.

Each notch 32 thus has two flat flanks 32A, 32B which are connected by a bottom edge 32C. Alternatively, these two flat sides could rather be connected by a leave.

In this particular embodiment of the invention, the "angles α1, α2 formed at the junctions between the notch 32 and the helical thread 30 are one acute and the other obtuse" that:

the angle a1 formed between a first of the flanks 32A and the tangent to the thread 32 (at the point of junction between the threading 30 and this first flank 32A) is strictly less than 90 degrees, and that

the angle a2 formed between the second of the flanks 32B and the tangent to the thread 32 (at the point of junction between the threading 30 and this second flank 32B) is strictly greater than 90 degrees.

Thus, as shown in Figure 5, when the spinal screw 10 is screwed, the first and second flanks 32A, 32B of the notches 32 do not form an obstacle to this screwing. The second flank 32B of each notch 32 forms in particular a kind of ramp on which the spongy body of the bone 100 slides.

On the contrary, as shown in Figure 6, when the spinal screw 10 is unscrewed, the first flank 32A of each notch 32 forms a kind of hook which prevents this unscrewing by clinging to the spongy body of the bone 100.

As shown in Figures 1 and 2, the head 40 of the spinal screw 10 here has a particular shape.

It has a front portion 44 in the form of a ball section. This front portion 44 thus has a planar rear face 45 and a front face 43 in the form of a sphere of revolution portion about the longitudinal axis A1, which is connected to the body 20 of the spinal screw 10.

The front face of this front portion 44 of the head 40 of the spinal screw 10 thus forms a convex surface 43 adapted to bear against the bone plate 50 (see FIG. 4).

The head 40 of the spinal screw 10 also has a rear portion formed of four identical studs 46 which rise from the rear face 45 of the front portion 44 of the head and which delimit between them a cruciform impression 41.

These studs 46 extend at a distance from the edge of the rear face 45 of the front portion 44 of the head 40, so that they form a stall with respect thereto which delimits a peripheral groove 42 open on the side ( that is to say radially with respect to the longitudinal axis A1) and towards the rear.

Alternatively, it could be provided that this peripheral groove is formed by a groove provided recessed in the scope of the head of the spinal screw.

The function of this peripheral groove 42 will be detailed later in this presentation.

As was introduced supra, this spinal screw 10 is here intended to be used in combination with other identical screws, so as to be able to fix a bone plate 50 to at least two vertebrae of the patient's spine, to form a arthrodesis device 1.

As shown in FIG. 3, the bone plate 50 has a generally rectangular shape with rounded corners, with two small straight sides and two large concave sides facing each other.

It has a central opening 53.

As shown in FIGS. 3 and 4, the bone plate 50 here has four openings 51 located near its four corners respectively.

Each opening 51 is traversed by the body 20 of a spinal screw

10. Each opening 51 is further delimited by a bearing edge 52 against which rests the bearing surface 43 of the head 40 of the corresponding spinal screw 10.

The bearing edge 52 delimiting each opening 51 has a shape concave sphere section, of equal diameter, clearance, to that of the bearing surfaces 43 of the spinal screw heads 10. Each opening 51 also has a diameter strictly greater than that of the rear portions 21 of the spinal screw bodies 10 In this way, the spinal screws 10 are free to pivot and tilt relative to the bone plate 50, which facilitates their screwing into the patient's vertebra at the desired inclination.

According to an advantageous characteristic of the invention, the arthrodesis device 1 comprises, next to each opening 51, a tongue 60 movable on the bone plate 50, which is automatically biased through the corresponding opening 51 in order to retain the spinal screws 10 through openings 51 of bone plate 50.

In practice, as shown in FIGS. 3 and 4, these tongues 60 come into formation with the bone plate 50 and are deformable under stress so as to be able to release the passage of the spinal screws 10 through the openings 51.

These tongues 60 have semi-circular curved rod shapes, which run along half of the periphery of the openings 51 of the bone plate 50.

They are located in recesses 54 recessed in the rear face of the bone plate 50, and are attached by one of their ends to the edge of this recess 54. They are thus deformable in bending to move away from the openings 51. Their elasticity allows them to automatically return through these openings 51.

Thus, when a spinal screw 10 is engaged through one of the openings 51 of the bone plate 50, the bearing surface 43 of its head 40 bears against the corresponding tongue 60, which forces it to bend. The head 40 of the spinal screw 10 can then bear against the bearing edge 52 delimiting this opening 51.

When the span 43 of the head 40 of the spinal screw 10 bears against the bearing edge 52, the tongue 60 automatically returns to position at the rear of the head 40, which makes it possible to block the spinal screw 10 at through the opening 51 of the bone plate 50.

Thus, once the arthrodesis device 1 fixed by four spinal screws 10 to the vertebrae of the patient, the risk of extraction of one of the spinal screws 10 is almost zero since, on the one hand, the spinal screws 10 are designed to not be able to unscrew, and, on the other hand, if one of the spinal screws 10 was tearing out of the vertebra in which it is engaged, it would be retained in position by the corresponding tongue 60.

The manner in which the arthrodesis device is described will now be described.

1 is installed on the spine of a patient during a cervical arthrodesis operation anterior way.

During this operation, a first spinal screw 10 is engaged through a first opening 51 of the bone plate 50, so that the bearing surface 43 of its head 40 bears against the bearing edge 52 bordering this opening 51.

In this position, as shown in Figure 4, the tongue 60 is positioned in the peripheral groove 42 defined by the head 40 while remaining at a distance from the edge of the peripheral groove 42, so that the spinal screw 10 remains free of rotate and tilt.

Equipped with an instrument of the Phillips screwdriver type, the surgeon can then screw this spinal screw 10 into the vertebra of the patient.

As shown in Figure 5, this screwing is operated without difficulty thanks to the shape of the notches 32 of the thread 30.

The surgeon then repeats this operation with three other spinal screws 10, taking care each time to screw these screws sufficiently into the vertebrae of the patient, so that the rear portions 21 of the bodies 20 of these spinal screws 10 engage and block in these vertebrae.

As shown in Figure 6, the shape of the notches 32 of the thread 30 then makes it possible to prevent the spinal screws 10 from being unscrewed.

Over time, as shown in FIG. 7, the soft body of the bones 100 will progressively engage in the notches 32 of the spinal screws 10 and will calcify which, in the long run, will ensure a very rigid fixation of the spinal screws 10 in The vertebrates.

The present invention is not limited to the embodiment described and shown, but the art can apply any variant within his mind.

It could thus be provided that the threading of the spinal screw has a double helix. It could also be provided that the head of the spinal screw has an imprint not cruciform, but rather hexagonal or flat.

It could also be provided that the threading of the spinal screw has only one notch, in which case the risks of unscrewing would however be greater than in the mode shown in the figures.

It could also be provided that the bone plate has a greater number of spinal screw openings, for example twelve in number, to be able to attach to a larger number of vertebrae.

It could also be provided to use the spinal screws to secure an implant other than a bone plate, for example an intervertebral connecting rod. In this variant, it may be provided that the head of the spinal screw has a different shape, to be easily attached to the connecting rod. An example of such a connecting rod is presented in document FR2942951.

According to another variant of the invention, provision could be made to use the screw on a bone that does not belong to the patient's spine. It could be used on the pelvis of a patient, in combination with a bone plate and with other screws, to repair a fracture of the pelvis.

Finally, it could be provided that the notches in the thread of the spinal screw have different shapes, for example in the form of an arc. In this variant, we mean by "the angles formed at the junctions between the notch and the helical thread are one acute and the other obtuse" that:

the angle formed between the tangent to the notch and the tangent to the thread (at a first point of junction between the thread and this notch, the one furthest from the screw head) is strictly less than 90 degrees , and

- The angle formed between the tangent to the notch and the tangent to the thread (at the second point of junction between the thread and this notch, the one closest to the screw head) is strictly less than 90 degrees.

Claims

1. Bone screw (10) having an elongated body (20) along a longitudinal axis (A1) which carries at least one helical thread (30) and at one end of said elongate body (20) a head (40) having an impression (41) for receiving the end of a screwdriver,

characterized in that said helical thread (30) has at least one notch (32) whose shape is such that the junctions between the notch (32) and the helical thread (30) form angles (α1, a2) of which one is acute and the other is obtuse, the junction forming an obtuse angle (a2) being the one closest to the head (40), and in that said head (40) has an open peripheral groove (42) laterally.

2. bone screw (10) according to the preceding claim, wherein said elongated body (20) has, at its junction with said head (40), a portion (21) of length greater than 5 mm, which is substantially frustoconical of revolution around the longitudinal axis (A1).

3. bone screw (10) according to one of the preceding claims, wherein said head (40) has, on the side of the elongate body (20), a bearing surface (43) in the form of a spherical portion of revolution around the l longitudinal axis (A1).

4. bone screw (10) according to one of the preceding claims, wherein each notch (32) has a dihedral shape.

5. bone screw (10) according to one of the preceding claims, wherein there is provided at least two rows (31) of notches (32) aligned along axes parallel to the longitudinal axis (A1).

6. Arthrodesis device (1) comprising:

a bone plate (50) having at least two openings (51) delimited by support edges (52),

at least two bone screws (10) according to one of the preceding claims, whose elongated bodies (20) are engaged through said openings (51) and whose heads (40) rest on said support edges (52), and

- tabs (60) movable on said bone plate (50), which are automatically biased through the openings (51).

7. arthrodesis device (1) according to the preceding claim, wherein said tabs (60) are formed with said bone plate (50).

8. arthrodesis device (1) according to one of claims 6 and 7, wherein said bearing edges (52) have shapes of spherical sections.