WO2025243258A1 - Osteosynthesis unit comprising an elastically deformable element - Google Patents

Abstract

Osteosynthesis unit comprising an osteosynthesis device having at least one through hole, at least one screw having a threaded body and a head with a profile converging towards the threaded body, an elastically deformable insert engaged within the at least one hole, and comprising a longitudinal cavity through which the screw in use extends, and having such cavity a profile converging in the direction of insertion of the screw, and such insert having a longitudinal cut defining an interruption of the peripheral surface of the insert so that, when the head of the screw is engaged in the cavity, a load applied to the screw elastically expands the insert generating an elastic reaction force which closes the radial clearances between the head of the screw and the insert.

Description

“OSTEOSYNTHESIS UNIT COMPRISING AN ELASTICALLY DEFORMABLE ELEMENT”

DESCRIPTION

FIELD OF THE INVENTION

The present invention relates to the field of osteosynthesis devices, and in particular to an osteosynthesis unit comprising an osteosynthesis device, e.g. a plate, an intramedullary nail, a femoral stem of a hip prosthesis, at least one screw for fixing the osteosynthesis device to a bone portion of the patient, and an elastically deformable insert interposed in use between the screw and the osteosynthesis device.

STATE OF THE ART

In the osteosynthesis device sector, there are widely used commercially available solutions that include a plate and a plurality of screws, generally made of metal, e.g. titanium alloy, which are used together to fix a bone fracture in a patient. Some common devices include a plate and a plurality of orientable screws, e.g. through a ball joint arranged in the holes of the plate, so as to be able to fix the plate to the patient's bone portion by orienting the screws according to different inclinations, thus allowing the fracture to be stabilized in multiple directions, especially when complex. Other commercially available devices include a plate and a plurality of non-orientable screws, in which the plate has one or more raised portions which in use are the only parts of the plate in contact with the patient's bone portion. These devices are designed to minimize the surface area of the plate in contact with the patient's tissues, so as to reduce irritation and damage due to the assembly of the plate, thus promoting the healing process and reducing the risk of post-operative complications. However, both of the solutions described above have numerous disadvantages. For example, during an osteosynthesis surgical operation, the screws are fixed to the patient's bone using a screwing device. Since this is an operation performed manually by the surgeon, a typical problem in these interventions is the plastic deformation of the screws due to high temperatures or mechanical stress, for example due to overheating during insertion due to the heat generated by friction between the screw and the bone or due to excessive tightening force, even a generation of splinters and debris that detach from the head of the screw. This determines both possible post-operative complications, e.g. infections, and a significant difficulty in removing the screws once screwed together with the plate on the patient's bone, extending the operating times, in addition to the fact that the screws are difficult to reuse if it is necessary to reposition them once screwed into the patient's bone portion, i.e. due to plastic deformation. It is therefore an ever-present need to create simple and compact solutions, through which it is possible to minimize the problems indicated above and above all not cause plastic deformation of the screws during the intervention.

PURPOSE AND SUMMARY OF THE INVENTION

The present invention has the purpose of satisfying at least in part the above- mentioned needs, wherein such purpose is achieved by means of an osteosynthesis unit according to claim 1.

According to a preferred embodiment of the present invention, an osteosynthesis unit with a simplified construction configuration is presented, through which it is possible to avoid a plastic deformation of the components defining the unit during the fixing of the same on the patient's bone portion, e.g. due to an excessive clamping force applied by the surgeon on the unit. To achieve this result, such a unit comprises an osteosynthesis device, e.g. an intramedullary plate or nail or a femoral stem of a hip prosthesis, having at least one through hole, at least one screw having a threaded body and a head with a convergent profile with a rectilinear generatrix towards the threaded body. According to an aspect of the present invention, such an osteosynthesis unit further comprises an elastically deformable insert, which in use is engaged inside the at least one hole. In particular, the insert has a longitudinal cavity through which the screw in use extends, and this cavity has a convergent profile with a rectilinear generatrix in the direction of insertion of the screw, i.e. in the same direction of convergence of the screw head. In this way, when the screw head engages inside the cavity of the insert, the respective perimeter surfaces come into contact. According to a further aspect of the present invention, in order to be able to block the angular position of the screw with respect to the osteosynthesis device, e.g. a plate, and ensure the anti -unscrewing function when the screw is in place, the insert has a longitudinal opening, preferably a cut, defining an interruption of the perimeter surface of the insert itself, i.e. when the insert is disassembled from the osteosynthesis device, the cavity is radially accessible through this longitudinal opening. In other words, the cut passes from the outside of the insert to the internal cavity of the same. The edges defined by the cut may or may not be in mutual contact with each other when the insert is not subjected to any external force. According to the invention, this construction device is exploited so that when the head of the screw engages the cavity, screwing the screw elastically expands the insert, generating an elastic reaction force that closes the radial clearances between the head of the screw and the insert, without therefore causing the detachment of splinters and debris due, for example, to excessive tightening force on the screw. Furthermore, it should be noted that this construction configuration not only provides a function of blocking the rotation of the screw with respect to the osteosynthesis device, e.g. an intramedullary plate or nail or a femoral stem of a hip prosthesis, when the latter is in place, i.e. the anti -unscrewing function, but also facilitates the extraction of the screw when the latter is removed. In particular, the elastic reaction force acting on the screw head has a component consistent with the direction of unscrewing, thus generating a thrust on the screw head that facilitates its extraction from the hole of the osteosynthesis device, and can advantageously be reused if a new positioning of the screw is necessary.

DESCRIPTION OF THE DRAWINGS

The construction and functional characteristics of the osteosynthesis unit may be better understood from the detailed description that follows, in which reference is made to the attached figures that represent a preferred and non-limiting embodiment thereof, in which:

• Fig.l shows an exploded view of an osteosynthesis unit according to a preferred embodiment of the present invention;

• Fig.2 shows a sectional view of the unit of Fig.l according to a variant that is not the subject of the attached claims;

• Fig.3 shows an exploded sectional view of an osteosynthesis unit according to a further preferred embodiment of the present invention;

Fig.4 shows a sectional view of the unit of Fig.2.

DETAILED DESCRIPTION OF THE INVENTION

According to a preferred embodiment of the present invention, Fig.l shows an exploded perspective view of an osteosynthesis unit D that can be used during a surgical operation to fix bone segments of a fracture in a patient. In particular, such a unit comprises an osteosynthesis device 1, preferably but not limited to a plate, preferably metallic such as for example titanium alloy, on which at least one through hole 2 is made, preferably a plurality of through holes. In the embodiment shown in Fig.l, the osteosynthesis device 1 is a plate, but in further preferred variants it can be an intramedullary nail or a femoral stem. Furthermore, to be fixed on a bone portion of the patient, the osteosynthesis unit D comprises one or more screws 3 that can be inserted into each hole 2. In particular, the screw 3 has a threaded body 3a and a head 3b, preferably hollow, on which it is possible to engage a tool (not shown in the figure) to screw the screw onto the bone portion of the patient and rigidly fix the plate to that bone portion. According to a first aspect of the present invention, to counteract the unscrewing of the screw 3 once in place, the osteosynthesis unit D comprises an insert 4 that in use is engaged in the hole 2. In particular, this insert comprises a longitudinal cavity 5 defining a through hole, inside which the screw 3 is inserted to screw the plate 1 onto the bone portion of the patient. Furthermore, the longitudinal cavity 5 is shaped so as to house the head of the screw 3b and preferably define a shape coupling with it at least at the end of the tightening, so that the head of the screw does not protrude from the plate once mounted. According to the invention, to engage the head of the screw 3b and the longitudinal cavity 5 of the insert 4 in contact, the latter both have a convergent longitudinal profile with a straight generatrix towards the direction of insertion of the screw 3 in the hole 2, i.e. respective truncated-conical surfaces, so that when the tightening is finished, the head 3b is drowned in the cavity 5 and its perimeter surface is in contact with the surface of the cavity.

It is evident that the head of the screw 3b can slide axially inside the cavity of the insert, as there is no thread. The screw is equipped with a single thread intended to grip exclusively on the patient's bone portion.

When the head of the screw 3b comes into contact during tightening with the surface of the cavity 5, due to the convergent shape of the respective profiles, the head of the screw 3b exerts a force on the surface of the cavity 5 having a radial component that generates a pressure on the insert 4. The surface of the hole 2 exerts a reaction force opposite to that applied on the insert 4, and such as to counteract the radial deformation of the insert itself, so that further advancement of the screw 3 inside the cavity is blocked, i.e. having the head of the screw 3b a portion in which the corresponding cross -section is greater than that of the cross-section of the cavity. According to the invention, the insert 4 has a longitudinal cut 6 defining an interruption of the perimeter surface of the insert itself.

An axial view of the insert resembles an expansion washer. Therefore, the same insert can be defined as “expanding”, since the pressure exerted by the head of the screw in the cavity of the insert causes it to expand. In fact, the insert 4 is made in such a way as to be elastically deformable under the action of a force exerted by the head of the screw 3b, and these construction characteristics are exploited in such a way as to facilitate in use the completion of the tightening of the screw to block both the plate 1 to the bone portion but also to counteract the unscrewing of the screw 3 once in place. In particular, on the basis of these construction measures, when the head of the screw 3b is engaged in the cavity 5, screwing of the screw 3 causes an axial movement of the head of the same screw, which, by interference, imposes an elastic deformation of the insert 4, in particular it expands elastically, not being able to move axially itself, by interference with the plate 1, increasing the circumferential width of the longitudinal cut 6, while the screw 3 can thus advance, screwing itself further into the bone portion of the patient. When the screw tightening is completed, the insert 4 is elastically deformed, applying an elastic reaction force against the screw head which closes the radial clearances between the screw head and the insert. Advantageously, this condition thus favors the locking of the angular position of the screw 3 with respect to the plate 1 when the latter is in operation, i.e. anti-unscrewing function. Preferably, as shown in Fig.1-2, the osteosynthesis unit D can comprise a longitudinally hollow spacer 7, e.g. a bushing, which in use is mounted in hole 2 in a manner interposed between plate 1 and insert 4. In particular, insert 4 in use is rigidly engaged in spacer 7, and the latter is used to fix plate 1 in a manner spaced from the patient's bony portion in order to minimize contact of the plate on the patient's anatomical part, reduce irritation and damage to the surrounding soft tissues and post-operative complications, thus promoting the patient's healing process. In particular, this spacer has a first flanged longitudinal end 7a which in use abuts against a portion of the surface of the plate 1. On the first longitudinal end 7a a circumferential recess 7b is made which is used to define a bearing surface for a first flanged longitudinal end 6a of the insert 4. Based on this construction configuration, in use the insert 4 is engaged inside the spacer 7 with the first flanged longitudinal end 6a engaged inside the circumferential recess 7b, e.g. defining a shape fit. As can be easily understood, the flanged ends of the insert 4 and the spacer 7 have the function of counteracting the axial movement of the same towards the bone portion of the patient when the screw 3 is tightened. To distance the plate from the bone portion, the spacer 7 has a longitudinal extension, i.e. parallel to the axis of hole 2, which is greater than the thickness of plate 1, thus presenting a second longitudinal end 7c protruding from hole 2. In use, this second longitudinal end 7c is brought into contact with the patient's bone portion, thus leaving plate 1 spaced apart and this promotes tissue ventilation. Preferably, insert 4 also has a longitudinal extension greater than the thickness of plate 1, e.g. equal to the length of the spacer. Furthermore, to counteract axial movement in the direction of extraction of screw 3 from hole 2, e.g. when osteosynthesis unit D is in operation and it is necessary to remove a screw, second longitudinal end 7c has a flanged edge 7d having a diameter greater than that of hole 2, so that in use this edge abuts against a portion of the surface of plate 1, ensuring the function of counteracting the axial movement indicated above. Furthermore, to facilitate the assembly phase of the spacer 7 inside the hole 2, the second end 7c has a convergent profile from the flanged edge 7d towards the tip of this end, and the spacer 7 is made in such a way as to be elastically deformable in a flexural manner when it is mounted inside the hole 2. In this way, when the second end 7c is inserted into the hole 2, the convergent profile of the same facilitates the insertion of the spacer 7 inside the hole 2, and said spacer deforms elastically by flexing towards the axis of the hole while it is pushed longitudinally inside it. When the second end 7c comes out of the hole 2, due to the elastic reaction force, the spacer 7 returns to the configuration before insertion into the hole 2, and the flanged edge 7d is positioned facing and in contact with a portion of the surface of the plate 1. It should be noted that on the basis of this construction configuration the screw 3 is installed parallel to the axis XI of the hole 2, i.e. when the screw 3 is in operation the axis of the screw coincides with the axis XI. It is also possible to envisage a simplified construction variant in which the spacer 7 is not present, in which for example the plate 1 is made in such a way as to have a portion protruding from the hole 2 made as a single piece together with the plate, e.g. by milling, through which it is possible to obtain an effect comparable to that provided by the spacer 7.

According to the invention shown in Fig.3-4, the osteosynthesis unit D has a construction configuration in which it is possible to angularly orient the screw 3 with respect to the plate 1. The reference numbers to the parts common to the embodiment of Fig.1-2 remain unchanged. To achieve this result, the insert 4 has a rounded external perimeter surface 4a, e.g. a spherical segment with two bases, and the spacer 7, or the hole itself, has a longitudinal recessed portion 7e defining a housing seat for the rounded perimeter surface 4a. On the basis of this construction configuration, the insert 4 is rotationally movable within the housing seat 7e, so that in use the plate 1 and the insert 4 are relatively rotationally movable with respect to each other, i.e. the X2 axis of the screw can be angularly distanced from the XI axis of the hole 2. Preferably, in this embodiment the perimeter recess 7b is absent since the housing seat 7e is shaped so as to block the axial movement in both directions when the insert is in place. Thanks to the presence of the longitudinal cut 6 on the insert, its assembly inside the spacer 7 is facilitated, for example the insert 4 can be inserted by pressure and, deforming elastically, enters the cavity of the spacer 7 and then expands again when it engages in the housing seat 7e, defining with the same e.g. a shape coupling. When spacing is foreseen, without changing the shape of the plate 1, it is possible to eliminate the spherical joint to obtain the solution shown in figure 2 which is not the subject of the attached claims.

Preferably, it is also possible to provide for a further simplified construction variant (not shown in the figure) in which, in this case too, the spacer 7 is not present, for example, the recessed portion 7e is obtained on the surface of the hole 2 to house the rounded surface 4a of the insert, and to obtain an effect comparable to that provided by using the spacer 7. Finally, it should be noted that the construction configuration of the osteosynthesis unit D indicated above not only favours the blocking of the rotation of the screw with respect to the plate 1 once in place, i.e. the anti-unscrewing function, but also facilitates the extraction of the screw when the latter is removed. In particular, the elastic reaction force applied by the insert on the head of the screw 3b has a component consistent with the direction of unscrewing, generating a thrust on the head of the screw that facilitates extraction from the hole 2.

It is worth highlighting that the longitudinal cut 6 on the insert allows the insert to expand, not only creating a reaction towards the screw, but also obtaining the blocking of the angular orientation of the screw 3 with respect to the plate 1. In other words, with a minimum of three components: the screw, the insert and the plate, it is possible to obtain the angular blocking of the screw with respect to the plate due to the penetration of the same screw into the bone portion of the patient due to the elastic dilation of the insert.

As clarified above, the presence of the spacer is completely optional, but in any case, if present, the device would consist of just four components.

Another advantage of the present invention is that the friction surfaces, i.e. the perimeter surface of the screw head and the internal surface of the insert cavity, being smooth, as generated by a rectilinear generatrix, do not produce microparticles, when they rub against each other, limiting the risk of contamination of the patient.

Claims

CIAIMS

1. Osteosynthesis unit (D) comprising:

- An osteosynthesis device (1) having at least one through hole (2),

- At least one screw (3) having a threaded body (3a) and a head (3b) with a profile converging towards the threaded body with a first rectilinear generatrix,

- An elastically deformable insert (4) engaged inside the at least one hole (2), and comprising a longitudinal cavity (5) through which the screw (3) in use extends, and having such cavity a convergent profile with a second rectilinear generatrix in the direction of insertion of the screw, and such insert having a longitudinal cut (6) defining an interruption of the perimeter surface of the insert so that, when the head of the screw (3b) is engaged in the cavity (5), a screwing of the screw elastically expands the insert (4) generating an elastic reaction force which closes the radial clearances between the head of the screw and the insert, wherein the insert (4) has a rounded perimeter surface (4a) so as to define a ball joint.

2. Unit (D) according to claim 1, wherein the insert (4) has a rounded perimeter surface (4a) so as to define a ball joint.

3. Unit according to claim 1, wherein said threaded body comprises the single thread of the screw.

4. Unit according to any of the preceding claims, wherein said elastic expansion of the insert is adapted to block an angular position of said ball joint.

5. Unit (D) according to any of claims 1 - 4, further comprising a spacer (7) mounted inside the at least one hole (2) interposed between the osteosynthesis device (1) and the insert (4), such spacer further having a first longitudinal end (7c) protruding from the hole (2) so that in use such end is in contact with the patient's body and the osteosynthesis device (1) is spaced from it.

6. Unit (D) according to claim 5, wherein the first longitudinal end (7c) is elastically deformable in a flexural manner and has a flanged edge (7d) having a diameter greater than the diameter of the hole (2), and such first end having a convergent profile extending from the flanged edge in the opposite direction to the osteosynthesis device (1).

7. Unit (D) according to claim 5, wherein the spacer (7) is made as a single piece with the osteosynthesis device (1).

8. Unit (D) according to any of the preceding claims, wherein the osteosynthesis device (1) comprises a plate.

9. Unit (D) according to any of the preceding claims 1 to 7, wherein the osteosynthesis device (1) comprises an intramedullary nail.

10. Unit (D) according to any of the preceding claims 1 to 7, wherein the osteosynthesis device (1) comprises a femoral stem.