WO2020178470A1

WO2020178470A1 - Polyaxial fixation device

Info

Publication number: WO2020178470A1
Application number: PCT/ES2020/070157
Authority: WO
Inventors: Víctor SALA RUIZ; Alejandro Torregrosa Ortiz
Original assignee: Industrial Medica Alicantina, S.L.
Priority date: 2019-03-06
Filing date: 2020-03-04
Publication date: 2020-09-10
Also published as: ES1227379Y; ES1227379U

Abstract

The invention relates to a polyaxial fixation device for fixing a bone fragment by means of a screw (3) with a threaded conical head, the screw axis (4) being inclined at an angle (α) with respect to the axis of a hole, wherein the polyaxial fixation device is configured by means of a plate (2, 2') comprising at least one hole (1) identified by means of an inner surface (7), which defines an interior diameter, from which surface projects a flat circular segmented thread that defines vanes (5) for receiving the thread of the head of the conical screw (3).

Description

POLYAXIAL FIXING DEVICE

DESCRIPTION

OBJECT OF THE INVENTION

The present invention relates to a polyaxial fixation device that allows fixation of a plate to a bone fragment by inserting a screw through a hole in the plate in a direction other than the nominal direction of the hole. The polyaxial fixation device is configured by means of a plate comprising at least one hole defined by an inner surface that incorporates an extension that, instead of being a continuous thread, forming a ring with a diameter smaller than that of the hole, is segmented, forming a series of blades intended to accommodate the screw thread that allow a wide play in the angle between the screw axis and the axis of the hole through which it is inserted. The plate can be a first plate, with a plurality of holes or a second plate, with a single hole, defined by an outer surface by which it is inserted into the first plate through an opening made in the first plate.

It finds special application in the field of surgical implants industry for bone joints using plates and screws.

TECHNICAL PROBLEM TO BE SOLVED AND BACKGROUND OF THE INVENTION

In the current state of the art, a variety of systems focused on the polyaxial attachment of plates to bone fragments are known.

These known techniques can be divided into four types depending on the fixing method used in order to carry out the polyaxiality of the joint.

A first method is known as a blocking plug. By this method, a screw is inserted through the hole in a plate at a set angle to thread into a bone fragment, and then an externally threaded plug is housed over the screw head and threaded into the hole.

A second method is known as point threaded loading. Using this method, the screw is inserted into a threaded hole in a plate, to be threaded into a bone fragment, with an inclination that can have a maximum angle given by the manufacturer, and is fixed on the plate by adjusting the thread of the threaded conical head of the screw in the thread of the hole, fixing the position of the screw to the plate .

A third method is the "cut-in", which consists of a threaded conical head screw with a hardness greater than. The screw is inserted through the hole in the plate to be fixed to the bone until the thread of the head contacts the thread of the hole which, being in an angled position, does not thread into it, but deforms it and, having the screw a higher hardness, the new defined position remains.

A fourth method is the expansion sleeve, similar to the previous method, but where a threaded sleeve is inserted into the hole of the plate, with a lower hardness than those of the plate and the screw, so that it is the sleeve that is deformed by the pressure of the screw head thread rather than the plate itself.

However, all these methods have drawbacks when it comes to practical execution in that the high pressure that is exerted between the different components causes deformations that usually end in cold melting or seizing problems, also due to the use of very similar materials, based on having a high resistance, which greatly hinders the subsequent extraction of the elements with which the union is carried out.

The present invention solves this problem that is not solved in the present state of the art, by means of a polyaxial fixation device that is configured by means of a piece, either a plate with one or more holes or a plate with a single hole, Washer type or similar, to be inserted in another of greater dimension, so that both manufacturing and marketing are more flexible, and can even avoid inventories. The device incorporates, on the inner surface of the hole, an extension, like a ring that, instead of being continuous, is segmented, forming a series of blades destined to receive the screw thread by different threads, according to the angle of inclination of the screw. screw with respect to the axis of the hole.

DESCRIPTION OF THE INVENTION

In order to achieve the objectives and avoid the drawbacks mentioned above, the present invention describes a polyaxial fixation device for the fixation of a bone fragment by means of a screw with a threaded conical head in which the axis of the screw can be inclined at an angle with respect to the axis of the hole.

The device is configured by a plate comprising at least one hole defined by an internal surface, configured by an internal diameter, which incorporates blades that protrude towards the internal zone, in the manner of a segmented, circular flat thread. The function of the blades is to receive the screw through the threads of the thread located in the conical part of the head.

The plate can be a first plate, with a plurality of holes, or a second plate, with a single hole, and defined by an external surface through which it is inserted into openings in the first plate, so that the holes in the first plate are those provided by the second plate.

The blades have a truncated pyramidal configuration, that is to say, with a trapezoidal section in two perpendicular planes, one perpendicular to the longitudinal axis of the hole and the other that contains it, the pyramid having a rectangular base and facing the interior of the hole. In this way, the blade is attached to the inner surface of the hole through the larger base of the pyramidal shape of the blades, leaving the smaller base of the pyramid as the innermost area of the hole.

Therefore, in a cross section that contains the axis of the hole, the blades have a trapezoidal shape that forms an angle defined by the difference between the angle between two consecutive threads of the screw thread, that is, of the thread profile. of the screw and twice the maximum deviation angle for which the fixing device of the invention can work. In this way, the blades make the fixation device perfectly adapted for the fixation of a plate to a bone fragment by means of a screw with a longitudinal axis that can have a deviation from the axis of the plate hole of up to this value. determined maximum deviation.

To configure a robust device, on the one hand the edges of the blades to the internal surface of the hole have radii according to the two perpendicular directions, both in a plane containing the axis of the hole and in the perpendicular. On the other hand, the blades have a trapezoidal cross section that is attached to the inner surface of the hole at the larger base.

The axis of the hole refers to the axis of revolution of the inner surface.

BRIEF DESCRIPTION OF THE FIGURES

To complete the description of the invention and in order to help a better understanding of its characteristics, according to a preferred example of its embodiment, a set of drawings is attached in which, with an illustrative and non-limiting nature, they have been represented the following figures:

- Figure 1 represents a plan view of an orifice of the device in a first plate of the invention.

- Figure 2 represents a perspective view of the device represented in figure 1.

- Figure 3 represents a sectioned perspective view of the hole of the device in a second plate.

- Figure 4 represents a side sectional view of a screw housed in the first plate.

- Figure 5 represents a side sectional view of a screw housed in the second plate inserted in the first plate.

Below is a list of the references used in the figures:

1. Orifice.

2. First plate.

two'. Second plate.

3. Screw.

4. Screw shaft

5. Blades.

6. External surface.

7. Internal surface.

to. Angle of inclination of the screw axis.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

The present invention relates to a polyaxial fixation device. In a preferred embodiment, as represented in Figures 1, 2 and 4, the polyaxial fixation device of the invention consists of a first plate (2) that incorporates a plurality of holes (1), each of them defined through an inner surface (7) from which a series of blades (5) extend as projections that extend inwards as if it were a circular flat thread in which a series of parts have been removed to be evenly segmented.

For the fixation of different fragments in a bone break, a first longitudinal plate (2) with holes (1) is preferably used according to this embodiment, so that the different holes (1) are positioned on different bone fragments. In this way, a screw (3) inserted in each of these holes (1) fixes the bone fragment corresponding to the first plate (2) and all the bone fragments are joined together by the first plate (2) through the corresponding screws (3).

To do this, in the holes (1) of the first plate (2) of the present invention, once positioned on the bone fragments to be fixed, the screws (3) are inserted.

An alternative form of embodiment consists of a second plate (2 ') that only incorporates a hole (1) and is defined by an external surface (6), like a bush, ring or similar, although it could have an external surface (6 ) with any geometry. The second plate (2 ') incorporates a single hole (1) with the blades (5). The second plate (2 ') is intended to be inserted into an opening of the first plate (2) so that the configuration of the first plate (2) with several holes (1) of the first embodiment is made more flexible so that A first plate (2) can be made with openings in certain positions where the screws (3) must be placed and where the second plates (2 ^' ) are to be positioned, which provides great flexibility in terms of manufacturing and marketing.

As shown in the figures, the inside diameter of the hole (1) incorporates a series of blades (5) whose function is to retain the screw (3). This retention is not carried out in the thread that the screw (3) incorporates in the shaft, but in the thread located in the conical head that incorporates the screw (3). In fact, the diametral distance between two blades (5) is greater than the nominal diameter of the screw (3), so the screw thread (3) may not touch the blades (5) until reaching the conical area of the head. For this same reason, as the conical head of the screw (3) enters the hole (1), the tightening torque between both elements increases.

Furthermore, as a safety measure so that the screw (3) cannot pass through the polyaxial fixation device and disengage from it, the inside diameter defined by the blades (5) is smaller than the diameter of the screw head (3).

On the other hand, the blades (5) have a truncated pyramidal configuration, that is, of trapezoidal section in two perpendicular planes, one perpendicular to the axis of the hole (1) and the other that contains it, the pyramid being directed towards the interior of the hole (one). In this way, the blade (5) is attached to the internal surface (7) of the hole (1) by the larger base of the pyramidal shape of the blades (5), leaving the smaller base of the pyramid as the innermost area of the polyaxial fixation device. In addition, preferably, the union of each of the blades (5) to the internal surface (7) of the hole (1), instead of being carried out by means of straight edges, presents radii of agreement, not only in the transverse plane , as represented in Figure 1, but also in the diametral plane, as represented in Figure 3. In this way, the accumulation of stresses is avoided, not only in the radial direction but also in the direction of the axis of the hole ( 1), once the blades (5) are subjected to efforts during the introduction of a screw (3), which gives it a much higher resistance.

These stresses suffered by the blades (5) are due, above all, to the polyaxial fixation for which the present invention is conceived, that is, to the angle (a) of the inclination with respect to the axis of the hole (1) that is usually present the screw shaft (4) when inserted into the polyaxial fixation device for bone fixation. Indeed, in situations in which the screw (3) has a zero angle (a) and is centered in the hole (1), the thread of the screw (3) does not have to touch the blades (5) and even when the thread of the conical head of the screw (3) comes into contact with them, the blades (5) are only going to act as guide elements for the thread.

However, in a polyaxial fixation with an inclination of the screw (3) of a certain angle (a), as shown in Figures 4 and 5, the blades (5) will not only have a screw guide function ( 3), but they will also be stressed by fixing the screw (3). In this way, the polyaxial system allows a screw (3) to be placed to fix a plate (2, 2 ') to a bone fragment in any direction within the maximum range defined by the manufacturer. By means of the fixing device of the present invention, this operation can be carried out a number of times much higher than that offered by the competition due to the absence of problems in terms of cold welding of the elements, because, in addition to not being The high pressures between components are necessary, as is done in the state of the art, elements of different materials are also used, making the combination of these two factors favor the absence of this problem.

The configuration of the blades (5), all independent and without any connection between them, gives the plate (2, 2 ') the property of being able to deform to support the fixing of the screw head (3), adapting the position of each blade (5) at the height of the thread of the head of the screw (3) required according to the angle (a) of inclination of the axis of the screw (4).

Thus, the present invention should not be limited to the embodiment described herein. Other configurations can be made by those skilled in the art in light of the present description. Accordingly, the scope of the invention is defined by the following claims.

Claims

1 Polyaxial fixation device for fixation of a bone fragment by means of a screw (3) with a threaded conical head, the axis of the screw (4) being positioned with an inclination that presents an angle (a) with respect to the axis of the hole, where the polyaxial fixation device is characterized in that it is configured by means of a plate (2, 2 ') comprising at least one hole (1) identified by an internal surface (7), which defines an internal diameter, from which a Circular and segmented flat thread that defines blades (5) intended to receive the thread of the conical head of the screw (3).

2. Polyaxial fixing device, according to claim 1, characterized in that the plate (2, 2 ') is a first plate (2) comprising a plurality of holes (1).

3. Polyaxial fixation device, according to claim 1, characterized in that the plate (2, 2 ') is a second plate (2 ^' ) that comprises a single hole (1) and is defined by an external surface (6) by means of which it is inserted into openings of the first plate (2) so that the holes (1) of the first plate (2) are provided by the second plate (2 ').

4 Polyaxial fixing device, according to claim 1, characterized in that the blades (5) have the shape of a truncated pyramid so that, both a section perpendicular to the longitudinal axis of the hole (1) and a section containing the longitudinal axis of the hole (1) have a trapezoidal configuration.

5. Polyaxial fixation device, according to claim 1, characterized in that the edges of the blade (5) joining the internal surface (7) of the hole (1) have radii in accordance.