US20100071432A1

US20100071432A1 - Method for production of bone plates, in particular of plates for vertebral osteosynthesis

Info

Publication number: US20100071432A1
Application number: US12/444,560
Authority: US
Inventors: Mohan Emmanuel
Original assignee: Implants International Ltd
Current assignee: Implants International Ltd
Priority date: 2006-10-04
Filing date: 2007-10-04
Publication date: 2010-03-25
Also published as: FR2906702B1; FR2906702A1

Abstract

A method for producing bone plates includes the following steps: using a sheet (1) of titanium or of titanium alloy having a thickness of 1.7 to 2 mm; determining the direction of the fibres of this sheet (1) and cutting out portions (3) of sheet (1) parallel to the direction of the fibres of this sheet (1); cutting out, from each portion (3) of sheet, bone plates or bone plate blanks (4), in such a way that a longitudinal direction of these plates or blanks (4) is parallel to the direction of the fibres of the sheet (1); curving the sheets, plates or blanks in a suitable manner and then finishing the plates or blanks (4).

Description

The present invention concerns a method for producing bone plates, in particular plates for vertebral osteosynthesis.
It is common to use a plate made in titanium or titanium alloy in order to maintain two vertebrae or more than two vertebrae in relation to each other, this plate being placed against the vertebral bodies of the vertebrae and being secured to the latter parts using screws.
A plate of this type must have a shape curved in the transverse direction in order to adapt to the curvature of the vertebral bodies, and a shape curved in the longitudinal direction, enabling it to adapt to the lordosis of the vertebrae. It also comprises holes allowing passage through it of its fastening screws, and can comprise slots, cut-outs, bores, openings, recesses or others.
The existing plates are, to date, systematically made from blocks or strips cut out of laminated or forged sheets from titanium or titanium alloy, having a thickness substantially larger than the thickness which a finished plate must have, the aforementioned curvatures being formed by machining of the mass of this strip. For example, strips which have dimensions of 150 mm long by 35 mm wide and 7 mm thick, cut out transversely in the sheets, are used to obtain a series of finished plates with a thickness of 2.5 mm.
This production method is considered mandatory in order to obtain a plate able to resist the repeated stresses this plate undergoes after implantation. For the same reason, it is considered mandatory that such a plate be approximately 2.5 mm thick.
The traditional method has the drawback of being long and costly to implement, given the machining work to be done and the quantity of material lost.
Furthermore, this method has the drawback of creating “dead zones”, i.e. zones in which the integrity of the material is altered by the aggressive machining of a significant quantity of this material and by the resulting heating. The resistance of the plates to fatigue is affected by this, also making a thickness of the plates of at least 2.5 mm necessary.
The aim of the present invention is to resolve all of these drawbacks.
Its main aim is therefore to provide a method for producing a bone plate, in particular a plate for vertebral osteosynthesis, which is easier and less expensive to implement than the method according to the prior art, without decreasing the resistance of the obtained plate.
Another aim of the invention is to provide a method making it possible to obtain plates having a more reduced thickness than the current plates with equal resistance, in particular a thickness which can be from 1.7 mm to 2 mm.
An additional aim of the invention is to provide a method which avoids the creation of “dead zones” in the obtained plate.
In order to achieve at least the main aim above, the method according to the invention comprises the following steps:

a) using a sheet of titanium or of titanium alloy having a thickness of 1.7 to 2 mm;
b) determining the direction of the grain flow of this sheet;
c) cutting out portions of sheet, parallel to the direction of the grain flow of this sheet, sized so as to make it possible to obtain a plurality of bone plates, these portions of sheet in particular being in the form of strips;
d) performing, in any order, operations d1, d2 and d3 below:
d1) shaping the portions of sheet, or plates or blanks obtained by operation d2, in particular by rolling or cold bending, in order to form a curvature of the portions of sheet or of the plates or blanks in the transverse direction and/or the longitudinal direction, in order to obtain one or several curvatures suited to the shape of the vertebrae and/or the lordosis of the vertebrae for which the plates being manufactured are intended;
d2) cutting out, in each portion of sheet, bone plates or bone plate blanks, such that a longitudinal direction of these plates or blanks is parallel to the direction of the grain flow of the sheet;
d3) piercing and, if necessary, cutting out or machining portions of sheet, or plates or blanks obtained by operation d2;
e) finishing the plates or bone plate blanks.

The method according to the invention thus consists of determining the “grain flow” of the sheet, i.e. the orientation of the molecules of the material resulting from the lamination of the sheet, and cutting out the bone plates or the bone plate blanks such that the length of these plates or blanks is parallel to the grain flow of the sheet, these cutouts being done either before or after shaping of the strips or plates or blanks.
The applicant has indeed discovered that, in the traditional method, the grain flow of the sheet is systematically oriented transversely to the longitudinal direction of the bone plates obtained, the strips of sheets in which these plates are cut out themselves having been cut out transversely to the direction of the grain flow. This results in the unanimously accepted need, in order to obtain the appropriate resistance, to make bone plates whereof the curvatures are obtained by machining and the minimal thickness of which is 2.5 mm.
On the contrary, the method according to the invention makes it possible to obtain plates with the grain flow of the sheet oriented in the longitudinal direction of the obtained plates, which allows the use of sheets with a thickness limited to 1.7 to 2 mm and the shaping of the portions of sheet or of the blanks through relatively simple operations, in particular rolling or cold bending; the obtained bone plates have a resistance comparable to that of the 2.5 mm thick plates obtained according to the prior art, and do not involve the implementation of long and costly machining operations, which may also create alterations in the integrity of the material (“dead zones”).
The determination of the grain flow of the sheet in step b) can be done through a macrographic analysis of the surface of this sheet.
The cut-outs of the portions of sheet or of the plates or blanks in steps c) and d2) can in particular be done using a pressurized water jet machine, in particular of the numerical control type.
Water jet cutting is used rather than machining or laser cutting because it does not produce any cutting heat which would create particles able to crumble and which would unfavorably change the structure of the fibers around the cut-out sector of the material.
The transverse curvature produced in step d1 can in particular be generated by a radius of 80 mm and the longitudinal curvature can in particular be generated by a radius of 300 to 400 mm.
Preferably, in step d2, the cutout blanks comprise protruding legs allowing them to be immobilized on a suitable machine in order to perform all or some of the operations of step d3) and step e); the finishing operations of step e) then include the elimination of these protruding legs after performing the other finishing operations. Said suitable machine can in particular be a four- or five-axis shaping machine (the three Cartesian axes and one or two axes of rotation).
According to another possible embodiment of the invention, the method comprises the following steps:

- step a);
- step b);
- step c);
- step d1): formation of the portions of sheet only in the transverse direction;
- step d2);
- step d3);
- step d4): shaping of the plates or blanks obtained in step d2) in order to form a curve in the longitudinal direction, suitable for the lordosis of the vertebrae for which the bone plates are intended;
- step e).

The operations of step d3) (piercing and others) and d4) (longitudinal curvature) are therefore done on plates or bone plate blanks cut out in step d2).
According to another possible embodiment of the invention, the method comprises the following steps:

- step a);
- step b);
- step c);
- step d1): shaping of the portions of sheet in the transverse direction and in the longitudinal direction;
- step d3);
- step d2);
- step e).

The operations of step d1) (transverse and longitudinal curvatures) and d3) (piercings and others) are therefore done on the portions of sheet obtained in step c).
The method may comprise, after step d1 or d4, the performance of a macrographic analysis of the surface of at least one of the sides of said portion of sheet, or of said plates or blanks.
This analysis makes it possible to ensure that no surface flaws or cracks were created during these steps d1) or d4).

The invention will be well understood, and other characteristics and advantages thereof will appear, in reference to the appended diagrammatic drawing, illustrating, as non-limiting examples, portions of sheet during two possible implementations of the method it concerns.

FIGS. 1 to 4 are very diagrammatic views of portions of sheet according to a first embodiment of the method, and

FIGS. 5 to 8 are very diagrammatic views of portions of sheet according to a second embodiment of the method.

For simplification, parts or elements which are found identically or similarly in both of these embodiments will be identified by the same numerical references and will not be described again.
FIG. 1 illustrates a sheet 1 of titanium or of titanium alloy having a thickness of 1.7 to 2 mm whereof the fibers, diagrammed by dotted lines 2, are oriented in a determined direction (“grain flow”). This direction is that of the orientation of the molecules of the material resulting from the lamination of the sheet 1.
FIG. 2 shows a portion 3 of the sheet 1 dimensioned in order to allow obtaining of a plurality of bone plates, these bone plates being vertebral osteosynthesis plates. The portion 3 of sheet has been cut out parallel to the direction of the fibers of the sheet 1; it can, for example, be 160 mm long and 40 mm wide.
FIG. 3 shows blanks 4 of bone plates as they will be cut out in the portion 3 of sheet; they comprise a central part 4 a designed to form the osteosynthesis plate strictly speaking and, at each longitudinal end of this central part, a protruding leg 4 b pierced by a hole. These protruding legs 4 b allow the immobilization of the blanks 4 on a suitable machine for the performance of all or part of the piercing operations, and if applicable the limited cutting and/or machining operations of the blanks 4, and finishing operations for the bone plates. These finishing operations in particular include the elimination of the protruding legs 4 b.
It is essential to note that the blanks 4 are cut out such that the longitudinal direction of these blanks is parallel to the grain flow of the portion 3 of sheet.
FIG. 4 shows that the portion 3 of sheet was curved transversely before cutting out of the blanks 4, in particular by rolling or cold bending, such that these blanks 4 have, after cutting, a curvature suited to the shape of the vertebral bodies of the vertebrae for which they are designed to ensure mutual fastening. The radius generating this curvature can in particular be 80 mm.
The method corresponding to FIGS. 1 to 4 comprises the following steps:

- step a): use a sheet 1 of titanium or titanium alloy having a thickness of 1.7 to 2 mm;
- step b): determine the grain flow of this sheet, through a macrographic analysis of the surface of the sheet 1;
- step c): cut out, using a pressurized water jet machine with numerical controls, portions 3 of sheet 1, parallel to the grain flow of this sheet 1;
- step d1): shaping, by rolling or cold bending, portions 3 of sheet 1 in the transverse direction, as shown in FIG. 4;
- step d2): cutting out, using a pressurized water jet machine with numerical controls, blanks 4 in each portion 3 of sheet 1, such that a longitudinal direction of these blanks 4 is parallel to the grain flow of the sheet 1;
- step d3): placing blanks 4, using legs 4 b, in a shaping machine with four or five axes (the three Cartesian axes and one or two axes of rotation) then piercing, and if applicable, limited cutting and/or machining, of the blanks 4;
- step 4 d): shaping of the blanks 4 by rolling or cold bending in order to grant them a curvature in the longitudinal direction allowing them to be adapted to the anatomical lordosis of the vertebrae for which the bone plates are intended; this curvature is generated by a radius which can be from 300 to 400 mm;
- step e): finishing operations for these plates and obtaining bone plates by eliminating the legs 4 b.

FIGS. 5 to 7 correspond to FIGS. 2 to 4, respectively, showing a portion 3 of sheet 1 as previously stated, which is curved, then in which the blanks 4 are cut out.
In this case, however:

- the width of the portion 3 is smaller than that of the portion 3 of the preceding case, making it possible only to obtain a row of blanks 4.
- the portion 3 is bent longitudinally before cutting out the blanks 4, as shown by FIG. 8.

The method corresponding to FIGS. 5 to 8 comprises the following steps:

- step a) as previously stated;
- step b) as previously stated;
- step c) as previously stated;
- step d1): shaping of the portions 3 of sheet in the transverse direction and in the longitudinal direction;
- step d3): placement of the portions 3 of sheet in a shaping machine with four or five axes (the three Cartesian axes and one or two axes of rotation) then piercing, and if applicable limited cutting and/or machining at the appropriate locations;
- step d2): removal of the portions 3 of sheet from said machine and cutting out of the blanks 4 as previously stated;
- step e) as previously stated.

The operations of step d1) (transverse and longitudinal curvatures) and d3) (piercings and others) are therefore done on the portions of sheet obtained in step c).
Either of the aforementioned implementations of the method can comprise, after step d1 or d4, the performance of a macrographic analysis of the surface of at least one of the sides of the portion 3 of sheet, or of said blanks 4 in order to ensure that no surface flaws or cracks were created during these steps d1) or d4).
The invention thus provides a method for producing bone plates, in particular plates for vertebral osteosynthesis, having for determining advantages:

- being easier and less costly to implement than the method according to the prior art, without decreasing the resistance of the obtained plate;
- making it possible to obtain plates having a smaller thickness than the current plates with equal resistance, in particular a thickness which can be from 1.7 mm to 2 mm;
- avoiding the creation of “dead zones” in the obtained plate.

It goes without saying that the invention is not limited to the embodiment described above as an example, but that it extends to all embodiments covered by the appended claims.

Claims

1. Method for producing bone plates, in particular plates for vertebral osteosynthesis, characterized in that it comprises the following steps:

a) using a sheet (1) of titanium or of titanium alloy having a thickness of 1.7 to 2 mm;

b) determining the direction of the grain flow of this sheet (1);

c) cutting out portions (3) of sheet (1), parallel to the direction of the grain flow of this sheet (1), sized so as to make it possible to obtain a plurality of bone plates, these portions (3) of sheet in particular being in the form of strips;

d) performing, in any order, operations d1, d2 and d3 below:

d1) shaping the portions (3) of sheet, or plates or blanks (4) obtained by operation d2, in particular by rolling or cold bending, in order to form a curvature of the portions (3) of sheet or of the plates or blanks (4) in the transverse direction and/or the longitudinal direction, in order to obtain one or several curvatures suited to the shape of the vertebrae and/or the lordosis of the vertebrae for which the plates being manufactured are intended;

d2) cutting out, in each portion (3) of sheet, bone plates or bone plate blanks (4), such that a longitudinal direction of these plates or blanks (4) is parallel to the direction of the grain flow of the sheet;

d3) piercing and, if necessary, cutting out or machining portions (3) of sheet, or plates or blanks (4) obtained by operation d2;

e) finishing the plates or bone plate blanks (4).

2. Method according to claim 1, characterized in that the determination of the grain flow of the sheet (1) in step b) is done through a macrographic analysis of the surface of this sheet (1).

3. Method according to claim 1, characterized in that the cut-outs of the portions (3) of sheet or of the plates or blanks (4) in steps c) and d2) are done using a pressurized water jet machine, in particular of the numerical control type.

4. Method according to claim 1, characterized in that the transverse curvature produced in step d1 is generated by a radius of 80 mm and the longitudinal curvature is generated by a radius of 300 to 400 mm.

5. Method according to claim 1, characterized in that, in step d2, the cutout blanks (4) comprise protruding legs (4 b) allowing them to be immobilized on a suitable machine in order to perform all or some of the operations of step d3) and step e); the finishing operations of step e) then include the elimination of these protruding legs (4 b) after performing the other finishing operations.

6. Method according to claim 5, characterized in that said suitable machine is a four- or five-axis shaping machine (the three Cartesian axes and one or two axes of rotation).

7. Method according to claim 1, characterized in that comprises the following steps:

step a);

step b);

step c);

step d1): formation of the portions (3) of sheet only in the transverse direction;

step d2);

step d3);

step d4): shaping of the plates or blanks (4) obtained in

step d2) in order to form a curve in the longitudinal direction, suitable for the lordosis of the vertebrae for which the bone plates are intended;

step e).

8. Method according to claim 1, characterized in that comprises the following steps:

step a);

step b);

step c);

step d1): shaping of the portions (3) of sheet in the transverse direction and in the longitudinal direction;

step d3);

step d2);

step e).

9. Method according to claim 1, characterized in that it comprises, after step d1 or d4, the performance of a macrographic analysis of the surface of at least one of the sides of said portion (3) of sheet, or of said plates or blanks (4).

10. Method according to claim 2, characterized in that the cut-outs of the portions (3) of sheet or of the plates or blanks (4) in steps c) and d2) are done using a pressurized water jet machine, in particular of the numerical control type.

11. Method according to claim 2, characterized in that the transverse curvature produced in step d1 is generated by a radius of 80 mm and the longitudinal curvature is generated by a radius of 300 to 400 mm.

12. Method according to claim 3, characterized in that the transverse curvature produced in step d1 is generated by a radius of 80 mm and the longitudinal curvature is generated by a radius of 300 to 400 mm.

13. Method according to claim 2, characterized in that, in step d2, the cutout blanks (4) comprise protruding legs (4 b) allowing them to be immobilized on a suitable machine in order to perform all or some of the operations of step d3) and step e); the finishing operations of step e) then include the elimination of these protruding legs (4 b) after performing the other finishing operations.

14. Method according to claim 3, characterized in that, in step d2, the cutout blanks (4) comprise protruding legs (4 b) allowing them to be immobilized on a suitable machine in order to perform all or some of the operations of step d3) and step e); the finishing operations of step e) then include the elimination of these protruding legs (4 b) after performing the other finishing operations.

15. Method according to claim 4, characterized in that, in step d2, the cutout blanks (4) comprise protruding legs (4 b) allowing them to be immobilized on a suitable machine in order to perform all or some of the operations of step d3) and step e); the finishing operations of step e) then include the elimination of these protruding legs (4 b) after performing the other finishing operations.

16. Method according to claim 2, characterized in that comprises the following steps:

step a);

step b);

step c);

step d2);

step d3);

step d4): shaping of the plates or blanks (4) obtained in step d2) in order to form a curve in the longitudinal direction, suitable for the lordosis of the vertebrae for which the bone plates are intended;

step e).

17. Method according to claim 3, characterized in that comprises the following steps:

step a);

step b);

step c);

step d2);

step d3);

step e).

18. Method according to claim 4, characterized in that comprises the following steps:

step a);

step b);

step c);

step d2);

step d3);

step e).

19. Method according to claim 5, characterized in that comprises the following steps:

step a);

step b);

step c);

step d2);

step d3);

step e).

20. Method according to claim 6, characterized in that comprises the following steps:

step a);

step b);

step c);

step d2);

step d3);

step e).