Lockable polyaxial screw

Abstract

The invention relates to a pedicle screw (1) comprising: - a screw (10) with a spherical head (11), - a sleeve (20) receiving the spherical head (11) via a ball joint, and having a receiving location (21) for a connecting rod (50) between several pedicle screws (1), - a nut (30) intended to be screwed into the sleeve (20) to lock the rod, - a ring (40) housed in the sleeve (20) and configured to bear against the spherical head (11), and having a recess (41) for receiving a tool to manipulate the ring (40) between a release position of the spherical head (11) and a locking position of the spherical head (11). According to the invention, the ring (40) is disposed between the spherical head (11) and the location (21) of the rod (50) within the sleeve (20). Figure for the abridged version: Fig. 3

Description

Title of the invention: Lockable polyaxial screw technical field

[0001] The invention relates to the technical field of pedicle screws used in dorsolumbar surgery. Previous art

[0002] Generally, a spinal implant comprises at least two pedicle screws intended to be screwed onto a variable anatomical element of the vertebra (lamina, pedicle, vertebral body), and a connecting system (plate or rod) joining the two pedicle screws together. It is well known to use a suitable threaded nut to screw into the pedicle screw and to hold a connecting rod in place.

[0003] These pedicle screws are most often polyaxial, meaning they have a spherical head connected to a sleeve by a ball joint, and the sleeve receives the connecting rod. In this way, it is possible to properly orient the sleeve of the polyaxial screw relative to the direction of the connecting rod before the assembly is fixed. Indeed, the axis of the screw is rarely orthogonal to the axis of the connecting rod, and a polyaxial screw overcomes this drawback.

[0004] Some prior art screws are designed so that tightening the nut locks both the shaft within the socket and the orientation of the socket relative to the screw. These systems are mechanically simple because they comprise few parts. However, assembling the device is cumbersome because all the components are mobile relative to each other during installation, making it difficult for the practitioner to properly orient the components according to the intended therapy.

[0005] In order to be able to separately lock the orientation of the socket relative to the spherical head, and the rod within the socket, different systems have been proposed.

[0006] Document EP3493755 describes a first system for separately locking the orientation of the socket and the locking of the rod. However, before locking the rod with a nut, this system requires manually maintaining pressure on a lever to lock the orientation of the socket, which is impractical.

[0007] Document WO2019 / 149483 describes another system for separately locking the orientation of the socket and the locking of the stem. However, this system has a significant number of parts. Furthermore, the overall size of the pedicle screw head is increased, particularly in width.

[0008] Finally, each of these solutions requires assembling all the system parts (pedicle screws, connecting rods, and then the nut) before adjustments can be made and to the locking of the system. This has the disadvantage that once the screws are inserted, and when mounting the connecting rod, the orientation of the sockets is not controlled at all, which prevents easy mounting of the connecting rod within the sockets.

[0009] It is therefore possible to propose improvements compared to existing systems, in terms of practicality and simplicity. Description of the invention

[0010] One of the aims of the invention is to overcome the disadvantages of the prior art, by proposing a pedicle screw that is simple in design and use, and of reduced size.

[0011] To this end, a pedicle screw comprising: - a screw, or handle, with a spherical head, - a socket receiving the spherical head via a ball joint connection, and having a location for receiving a connecting rod between several pedicle screws, - a nut designed to be screwed into the socket to lock the rod, - a ring housed in the socket and configured to bear against the spherical head, and having a recess intended to receive a tool to manipulate the ring between a position of release of the spherical head and a position of locking of the spherical head, that is to say that the ring allows the locking of the orientation of the socket with respect to the spherical head.

[0012] According to the invention, the ring is disposed between the spherical head and the location of the rod within the sleeve. That is to say, the rod rests on the ring, and the nut rests against the rod.

[0013] In this way, it is possible to manipulate the ring and bring it into its locking position of the spherical head, even before placing the rod in the socket.

[0014] The orientation of the socket can therefore be freely adjusted even before all the system components are in place, which simplifies handling. Once the socket is correctly oriented, it can be locked in place to prevent the subsequent insertion of the connecting rod from being difficult or altering the socket's orientation.

[0015] Since the ring is coaxial with the nut within the sleeve, the overall size of the pedicle screw is not increased.

[0016] According to a first embodiment, the ring is threaded, which allows for a simple and inexpensive design.

[0017] In this mode, the ring and the nut preferably have the same thread, that is to say that their threads have the same profile, the same pitch, and the same nominal diameter. The manufacturing of the socket is further facilitated.

[0018] To ensure optimal locking of the entire pedicle screw assembly by means of the nut, a first axial functional clearance between the ring and the spherical head is less than a second axial functional clearance between the ring and the sleeve. Thus, a tightening force transmitted from the nut to the ring, via the shank, is transmitted to the spherical head instead of being absorbed by the connection between the ring and the sleeve. "Axial" refers to the clearance measured along the axis of revolution of the sleeve.

[0019] To avoid obstructing access to the screw when the ring is pre-mounted in the sleeve before the pedicle screw is inserted, the ring's recess is through-hole, the spherical head has a recess configured for tightening with a tool, and the recess of the spherical head is smaller than the inscribed circle of the ring's recess. The term "inscribed" is used here in a geometric sense, meaning that, viewed from above, the profile of the spherical head's recess is contained within the largest circle tangent to the profile of the ring's recess. The tool used to tighten the screw can therefore pass through the ring, and it is not necessary to remove the ring from the sleeve to tighten the screw.

[0020] In order to guarantee the locking of the orientation of the sleeve, the ring has a spherical bearing area intended to come into contact with the spherical head, and the bearing area has an elastic portion.

[0021] Preferably, the elastic portion is defined by at least one cutout, for example longitudinal, on the periphery of the bearing area. This embodiment makes it easy to impart the desired elasticity to the ring, without changing its material, which is preferably rigid.

[0022] In order that the ring cannot be removed from the socket, in order to prevent its accidental loss, the ring has first snap-on means inside the socket.

[0023] Preferably, the first locking means are at least a ramp, for example disposed between two cutouts, and intended to lock into a bore of the socket. This embodiment is simple to manufacture and implement.

[0024] To ensure that the ring is tightened throughout the installation of the connecting ramp and before the nut is tightened firmly and definitively, the ring has immobilizing means within the sleeve.

[0025] In order to ensure that the ring is securely immobilized, the immobilization means include second ratcheting means cooperating with a part of the sleeve.

[0026] In order not to increase the bulk of the pedicle screw, the second locking means are formed on threads of the ring.

[0027] For this same purpose, the ring has initial snap-on means at the inside of the socket, and the immobilizing means include the first locking means. Brief description of the drawings

[0028] [Fig.1] is a perspective view, top view, of a pedicle screw according to the invention.

[0029] [Fig.2] is a cross-sectional view of a first embodiment of such a screw.

[0030] [Fig.3] is a cross-sectional view of a second embodiment of such a screw.

[0031] [Fig.4] is a perspective view of a first version of a ring equipping a pedicle screw according to the second embodiment.

[0032] [Fig.5] is a top view of such a pedicle screw.

[0033] [Fig.6] is a front view of a second version of a ring for a pedicle screw.

[0034] [Fig.7] is a diagram of such a ring mounted in a socket of such a screw.

[0035] [Fig.8] is a perspective view of a third version of the ring.

[0036] [Fig.9] is a perspective section of a screw receiving such a ring.

[0037] [Fig. 10] is a perspective view of a fourth version of the ring.

[0038] [Fig. 11] is a partial perspective section of a screw receiving such a ring. Detailed description of the invention

[0039] With reference to Figures 1 to 3, the invention relates to a pedicle screw (1) comprising a screw (10) with a spherical head (11), and a sleeve (20) mounted in a ball joint on the spherical head (11). The ball joint between the sleeve (20) and the spherical head (11) can be locked in the desired orientation by means of a ring (40) disposed in the sleeve (20), configured to bear tightly against the spherical head (11).

[0040] Gripping means (22) of the sleeve (20) allow its immobilization during the handling of the ring (40).

[0041] It is then possible to mount a connecting rod (50) between several pedicle screws (1), at the level of a receiving location (21) of the sleeve (20), which generally has a U-shaped form. The connecting rod (50) is itself held within the sleeve (20), orthogonally to the axis of revolution of the sleeve (20), by a clamping nut (30) mounted in the sleeve (20).

[0042] In this way, the practitioner can: - place the pedicle screws (1) on the relevant vertebrae of the patient, - orient the sleeve (20) of each screw (1) correctly, and lock the orientation using the ring (40) of each pedicle screw (1), - and finally mount the connecting rod (50) linking the pedicle screws (1), before proceeding to fix the rod (50) using the nuts (30).

[0043] Thus, when the rod (50) is installed, the bushings (20) are held in position and the installation of the rod (50) is facilitated.

[0044] In practice, the ring (40) has a bearing surface (42) with a shape complementary to the spherical head (11), and a recess (41) designed to receive a tool for manipulating the locking of the ring (40) between a release position of the spherical head (11) and a locking position against the spherical head (11), by means of a helical joint. Preferably, the recess (41) is concave. It is understood that the tool is not part of the pedicle screw (1) because it is not implanted and does not remain after the surgical procedure.

[0045] In a first preferred embodiment illustrated [Fig. 2], locking is achieved by a thread in the ring (40) cooperating with a tapped hole in the sleeve (20). In a second embodiment illustrated [Fig. 3], locking is achieved by a cam profile (47) of the ring (40) cooperating with a complementary profile of the sleeve (20).

[0046] The tool manipulating the ring (40) is introduced inside the sleeve (20) along its axis of revolution, which makes it possible not to increase the bulk of the pedicle screw (1).

[0047] The operation of the first and second embodiments, of the helical joint type, is similar: the rotation of the ring (40) in a first direction causes it to descend within the sleeve (20), against the spherical head (11). The functional play of the ball joint is eliminated by tightening the ring (40) against the head (11), thus locking the orientation of the sleeve (20) relative to the head (11). The advantage of the first embodiment is that the ring (40) and the nut (30) can have the same thread; therefore, manufacturing the sleeve (20) is simplified by producing a single tapped hole along its entire length.

[0048] Preferably, the locking mechanism is reversible, with rotation of the ring (40) in a second direction causing it to move upwards within the socket (20), thus releasing the socket (20). This reversibility allows the surgeon to properly orient the socket (20), if necessary, by trial and error.

[0049] The ring (40) is manipulated using a tool inserted into a recess (41) in the ring (40).

[0050] In both embodiments provided, a first axial functional clearance (j 1) between the ring (40) and the spherical head (11) is less than a second axial functional clearance (j2) between the ring (40) and the sleeve (20).

[0051] In practice, the first functional clearance (j1) is measured along a radius of the ball joint, as illustrated in Figures 2 and 3, but it is indeed the vertical component of the first clearance (j1) that must be less than the second clearance (j2), which is measured along the vertical axis. By convention, the vertical axis is defined by the axis of revolution of the bushing (20).

[0052] When tightened, the nut (30) presses on the rod (50), which in turn presses on the ring (40). Since the second functional clearance (j2) is greater than the first functional clearance (j1), the movement of the ring (40) along the vertical axis is not hindered by the sleeve (20), and the ring (40) can transmit the tightening force of the nut (30) to the spherical head (11).

[0053] This has several advantages. First, in the unlikely event that the surgeon had forgotten to lock the orientation of the sleeve (20) by means of the ring (40), then tightening the nut (30) is indeed capable of locking the entire pedicle screw (1), as in the solutions of the prior art.

[0054] Furthermore, it is possible to use the ring (40) only for pre-locking the head (11) by means of a limited clamping force, while a greater clamping force, ensuring the locking of the assembly, is provided by the nut (30). This makes it possible to reduce the height of the recess (41) of the ring (40), and therefore the height of the ring (40), since the dimensioning of the recess (41) with a moderate clamping force requires a smaller surface area. The overall dimensions of the pedicle screw (1) can thus be optimized.

[0055] In order for a bearing surface (42) of the ring (40) to perfectly conform to the geometry of the spherical head (11), the ring (40) has, at the bearing area (42), an elastic portion (43) whose elasticity is greater than that of the rest of the ring (40). By elasticity, it is understood that its diameter can vary in response to a force exerted on said portion.

[0056] With reference to [Fig. 4], this elasticity is preferably provided by cutouts, for example longitudinal cutouts (44) distributed around the periphery of the bearing area (42). This solution is particularly suitable for rings (40) made of metallic materials.

[0057] To facilitate operations during surgery, the pedicle screw (1) is preferably supplied with the ring (40) pre-assembled in the sleeve (20). Since the bearing area (42) of the ring, thanks to its shape complementary to that of the spherical head (11), can contribute to defining the ball joint, the pre-assembly of the ring (40) is preferably in a configuration close to the locking of the head (11).

[0058] That is to say, in the case of a threaded ring (40), it is not left more than one thread from its locking position, and is instead screwed as close as possible to the head (11), while leaving the orientation of the sleeve (20) free relative to the head (11). Otherwise, if the surgeon forgets to lock the ring (40) before mounting the rod (50), the second set (j2) may not be able to fulfill its function.

[0059] In order to avoid accidental loss of the ring (40), it preferably has first snap-on means (45) against the sleeve (20).

[0060] Figure 4 shows an embodiment in which these first snap-in means (45) are two diametrically opposed ramps, arranged on the elastic portion (43) of the ring (40), between two cutouts (44). These ramps are configured to snap into a bore (23) provided for this purpose in the sleeve (20). The snap-in direction of the means (45) is parallel to the axis of revolution of the sleeve (40).

[0061] In order that the prior assembly of the ring (40) does not hinder access to the recess (12) of the screw (10), for the purpose of its manipulation by a tool, the ring (40) has a recess (42) which is through, and of dimensions greater than those of the recess (12) of the screw (10), and in particular of dimensions greater than the inscribed circle of the recess (12).

[0062] With reference to [Fig. 5], it can be seen that the inscribed circle (C4) of the recess (42) of the ring (40) has a diameter greater than the circumscribed circle (Cl) of the recess (12) of the screw (10). In this way, the tool used to manipulate the screw (10) can pass through the ring (40) and the manipulation of the spherical head is easy.

[0063] The impressions are preferably of the hexagonal or hexalobular type (six-pointed star shape), which allow efficient transmission of the torque from the tool to the ring (40) and the nut (30).

[0064] Figures 6 and 7 illustrate an embodiment in which the first snap-on means (45) comprise several ramps arranged on the elastic portions (43) of the ring (40), between two cutouts (44). Each ramp (45) is configured to snap into the bore (23) of the sleeve (20), along a snap-on direction parallel to the axis of revolution of the sleeve (40).

[0065] However, the ramps (45) of the different elastic portions (43) are offset in height so as to define a helix of angle (p). In the illustrated mode: - the ring (40) has ten elastic portions (43); - the ramps (45) define a double-threaded helix; - each net consists of five ramps (45i to 455).

[0066] In this way: - when the ring (40) is assembled with the sleeve (20), the first two ramps (45i) are inserted into the bore (23) and ensure the secure assembly of the ring (40), preventing its accidental loss; - During use, the ring (40) is tightened to lock the orientation of the sleeve (20). The ring (40) descends within the sleeve (20), and the subsequent ramps (45) are then inserted into the bore (23), and so on. In this way, the successive ramps (45) ensure that the ring (40) remains tightened, as they prevent it from being pulled back out by unscrewing.

[0067] This embodiment of the ramps (45) constitutes a means of immobilizing (46) the the ring (40) within the socket (20).

[0068] In [Fig.7], we see the last ramp (455) inserted in the bore (23) and preventing the unintentional unscrewing of the ring (40).

[0069] This embodiment does not, however, prevent the possibility of adjusting the orientation of the sleeve (40) several times if necessary, because the force applied to the ring (40) by a tool is sufficient to bring out the ramps (45) from the bore (23).

[0070] In the illustrated mode, the upper face of the ramps (45) is inclined parallel to the right-angle helix (p). The contact between the ring (40) and the sleeve (20) is a point or an edge, depending on the depth of penetration of the ring (40). In an alternative mode not illustrated, the ramps (45) are offset vertically to form the right-angle helix (p), but the upper faces are horizontal: the contact between the ring (40) and the sleeve (20) is a portion of the upper face of the ramps (45).

[0071] Figures 8 and 9 illustrate another embodiment of the means for immobilizing (46) the ring (40), which are pawls, advantageously arranged at one end of the cam profiles, or threads (47) of the ring (40).

[0072] When the ring (40) is tightened, the pawls (46) progress within the thread of the sleeve (20), until its exit where they are released and come to cooperate with a stop (24), when the ring (40) is sufficiently tightened.

[0073] Knowledge of: - the value of the first axial functional clearance (j 1), defining the tightening to be applied; - the value of the pitch of the helical connection between the sleeve (20) and the ring (40); and - the starting position of the threads of this connection; allows you to determine where to place the stop (24).

[0074] In this mode, the mobility of the ratchet (46) is substantially parallel to the axis of revolution of the socket (40).

[0075] A machining (48) makes it possible to give the necessary elasticity to the portion of the thread (47) defining the ratchet (46).

[0076] Figures 10 and 11 illustrate another embodiment of the immobilizing means (46) in which the mobility of the ratchet (46) is substantially radial with respect to the axis of revolution of the socket (40).

[0077] In a manner analogous to the preceding mode, the pawls (46) progress within the threading of the sleeve (30) until they cooperate with a stop (24) of the sleeve (20).

[0078] This mode has the advantage of being able to use an added part such as a pin to make the stop (24): its positioning is easier compared to the previous mode, because it is enough to provide a radial hole (25) through the sleeve (20) at the desired location.

[0079] In these last two embodiments, the pawls (46) are advantageously arranged at the end of the threads (47), so as not to increase the size of the screw (1).

[0080] In all cases, the immobilizing means (46) prevent the untimely dismantling of the ring (40), but do not prevent the intentional dismantling of the ring (40) using a tool exerting a force on the imprint (41).

[0081] The pawls (46) can be arranged on the sleeve (20), and the stop (24) can be arranged on the ring (40).

[0082] Furthermore, the pedicle screw (1) can be shaped differently from the examples given without departing from the scope of the invention, which is defined by the claims.

[0083] According to an embodiment not illustrated, the first means for snapping the ring (40) is an added element preventing its removal from the sleeve (20), such as a pin or an elastic ring, but is not preferred because it would increase the number of parts.

[0084] Furthermore, the technical characteristics of the various embodiments and variants mentioned above can be combined, in whole or in part. Thus, the pedicle screw (1) can be adapted in terms of cost, functionality, and performance.

Claims

Demands

1. Pedicle screw (1) comprising: - a screw (10) with a spherical head (11), - a sleeve (20) receiving the spherical head (11) via a ball joint, and having a receiving location (21) for a connecting rod (50) between several pedicle screws (1), - a nut (30) for screwing into the sleeve (20) to lock the rod, - a ring (40) housed in the sleeve (20) and configured to bear against the spherical head (11), and having a recess (41) for receiving a tool for manipulating the ring (40) between a release position of the spherical head (11) and a locking position of the spherical head (11), i.e., a locking position of the orientation of the sleeve (20) relative to the spherical head (11), characterized in that the ring (40) is disposed between the spherical head (11) and the location (21) of the rod (50) within the socket (20),and the ring (40) is provided with a thread or a cam profile such that the rotation of the ring (40) in a first direction causes it to descend within the sleeve (20); and in that a first axial functional clearance (j1) between the ring (40) and the spherical head (11) is less than a second axial functional clearance (j2) between the ring (40) and the sleeve (20), and such that when the nut (30) is tightened, said nut presses on the rod (50), which in turn presses on the ring (40).

2. Pedicle screw (1) according to claim 1, characterized in that the ring (40) is threaded.

3. Pedicle screw (1) according to claim 2, characterized in that the ring (40) and the nut (30) have the same thread.

4. Pedicle screw (1) according to any one of the preceding claims, characterized in that the impression of the ring (40) is through, the spherical head (11) has an impression (12) configured for screwing by means of a tool, and the impression (12) of the spherical head (11) is of dimensions less than the inscribed circle of the impression (41) of the ring (40).

5. Pedicle screw (1) according to any one of the preceding claims, characterized in that the ring (40) has a spherical bearing area (42) intended to come into contact with the spherical head (11), and the area support (42) has an elastic portion (43).

6. Pedicle screw (1) according to claim 5, characterized in that the elastic portion (43) is defined by at least one longitudinal cut (44) on the periphery of the bearing area (42).

7. Pedicle screw (1) according to any one of the preceding claims, characterized in that the ring (40) has first snap-in means (45) inside the sleeve (20).

8. Pedicle screw (1) according to claims 6 and 7, characterized in that the first snap-in means (45) are at least a ramp intended to snap into a bore (23) of the sleeve (20).

9. Pedicle screw (1) according to any one of the preceding claims, characterized in that the ring (40) has immobilization means (46) within the sleeve (20).

10. Pedicle screw (1) according to claim 9, characterized in that the immobilization means (46) comprise second snap-in means cooperating with a part of the sleeve (20).

11. Pedicle screw (1) according to claim 10 taken in combination with claim 2, characterized in that the second snap-in means are formed on threads (47) of the ring (20).

12. Pedicle screw (1) according to any one of claims 9 to 11, characterized in that the ring (40) has first snap-in means (45) inside the sleeve (20), and the immobilizing means (46) include the first snap-in means (45).