Lockable polyaxial screw

Abstract

The invention relates to a pre-assembled pedicle screw (1) comprising: - a screw (10) with a spherical head (11), - a socket (20) receiving the spherical head (11) in the manner of a ball-and-socket joint and having a location (21) for receiving a connection rod (50) connecting a plurality of pedicle screws (1), - a nut (30) intended to be screwed into the socket (20) in order to block the rod, - a ring (40) housed in the socket (20) and configured to bear against the spherical head (11), and having an impression (41) intended to receive a tool for manipulating the ring (40) between a position for releasing the spherical head (11) and a position for blocking the spherical head (11). According to the invention, the ring (40) is arranged between the spherical head (11) and the location (21) of the rod (50) within the socket (20).

Description

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, and more particularly concerns a pre-assembled polyaxial screw, i.e. in which it is the screw which is inserted from above into a sleeve, unlike a top-loading polyaxial screw in which it is the sleeve which snaps onto the head of the screw. Prior art

[0002] Generally speaking, 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 threaded nut adapted to screw into the pedicle screw and to hold a connecting rod in place.

[0003] These pedicle screws are most often polyaxial, that is to say 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 in relation to the direction of the connecting rod, before fixing the assembly. Indeed, the axis of the screw is rarely orthogonal to the axis of the connecting rod, and a polyaxial screw makes it possible to overcome this disadvantage.

[0004] Some prior art screws provide that tightening the nut locks both the rod within the socket and the orientation of the socket relative to the screw. These systems are mechanically simple because they comprise few parts. However, setting up the whole thing is difficult, as all the elements are mobile relative to each other during installation, and it is difficult for the practitioner to properly orient the elements according to the planned 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 blocking of the rod. However, before locking the rod with a nut, this system requires manually maintaining a pressing force on a lever in order to block the orientation of the socket, which is impractical.

[0007] Document WO2019 / 149483 describes another system for separately locking the orientation of the sleeve and the locking of the rod. However, this system has a large number of parts. In addition, the size of the head of the pedicle screw is increased, particularly in width.

[0008] Finally, each of these solutions requires the assembly of all the parts of the system (pedicle screws, connecting rods and then nut) before being able to proceed with adjustments and locking of the system. This has the disadvantage that once the screws are implanted, and when the connecting rod is assembled, the orientation of the sockets is not at all controlled, which prevents the connecting rod from being easily assembled within the sockets.

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

[0010] Also known are documents US2011 / 0152949 and WO2010 / 103198, the design of which can be further improved.

[0011] Also known are documents US2021 / 0052305A1, US2016 / 0361096A1, US2020 / 0054376A1, US2018 / 0193063A1 which are not entirely satisfactory and do not concern a pre-assembled polyaxial screw, but rather a top-loading polyaxial screw. Statement of the invention

[0012] One of the aims of the invention is to overcome the drawbacks of the prior art, by proposing a pre-assembled pedicle screw which is simple to design and use, and of reduced size.

[0013] For this purpose, a pre-assembled pedicle screw has been developed comprising: - a screw, or handle, with a spherical head, - a socket receiving the spherical head according to a ball joint, and having a location for receiving a connecting rod between several pedicle screws, - a nut intended 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 an imprint intended to receive a tool for manipulating the ring between a position for releasing the spherical head and a position for locking the spherical head, that is to say that the ring allows the orientation of the socket to be locked relative to the spherical head.

[0014] According to the invention, the ring is arranged between the spherical head and the location of the rod within the socket. That is to say, the rod rests on the ring, and the nut rests against the rod.

[0015] In this way, it is possible to manipulate the ring and bring it into its locking position on the spherical head, even before having placed the rod in the socket.

[0016] The orientation of the socket can therefore be carried out freely, while not all the elements of the system are yet present, which facilitates handling. Once the orientation of the socket is correct, it is possible to lock it so that the subsequent insertion of the connecting rod is not difficult, nor does it change the orientation of the socket.

[0017] The ring being coaxial with the nut within the sleeve, the size of the pedicle screw is not increased.

[0018] According to a first embodiment, the ring is threaded, which allows a simple and inexpensive design.

[0019] 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 manufacture of the sleeve is further facilitated.

[0020] In order to ensure optimal locking of the entire pedicle screw 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 rod, is transmitted to the spherical head instead of being absorbed by the connection between the ring and the sleeve. By "axial" is meant the measurement of the clearance along the axis of revolution of the sleeve.

[0021] In order not to hinder access to the screw when the ring is pre-mounted in the socket before the pedicle screw is inserted, the impression of the ring is through, the spherical head has an impression configured for its screwing by means of a tool, and the impression of the spherical head is of dimensions smaller than the inscribed circle of the impression of the ring. The term "inscribed" is used here in the geometric sense, that is to say that seen from above, the profile of the impression of the spherical head is contained in the largest circle tangent to the profile of the impression of the ring. The tool used to tighten the screw can therefore pass through the ring, and it is not necessary to remove the ring from the socket to tighten the screw.

[0022] In order to ensure that the orientation of the socket is locked, the ring has a spherical support zone intended to come into contact with the spherical head, and the support zone has an elastic portion.

[0023] Preferably, the elastic portion is defined by at least one cutout, for example longitudinal, on the periphery of the support zone. This embodiment makes it possible to simply give the desired elasticity to the ring, without changing its material which is preferably rigid.

[0024] In order that the ring cannot be removed from the socket, in order to avoid its accidental loss, the ring has first snap-fastening means inside the socket.

[0025] Preferably, the first snap-in means are at least one ramp, for example arranged between two cutouts, and intended to snap into a bore of the socket. This embodiment is simple to manufacture and implement.

[0026] To ensure that the ring is tightened throughout the installation of the connecting ramp and before the nut is firmly and finally tightened, the ring has immobilization means within the sleeve.

[0027] In order for the ring to be firmly immobilized, the immobilization means comprise second snap-fastening means cooperating with a part of the sleeve.

[0028] In order not to increase the size of the pedicle screw, the second snap-in means are formed on the threads of the ring.

[0029] For this same purpose, the ring has first snap-fastening means inside the sleeve, and the immobilization means comprise the first snap-fastening means. Brief description of the drawings

[0030] [Fig.1] is a perspective view, seen from above, of a pedicle screw according to the invention.

[0031] [Fig.2] is a sectional view of a first embodiment of such a screw.

[0032] [Fig.3] is a sectional view of a second embodiment of such a screw.

[0033] [Fig.4] is a perspective view of a first version of a ring fitted to a pedicle screw according to the second embodiment.

[0034] [Fig.5] is a top view of such a pedicle screw.

[0035] [Fig.6] is a front view of a second version of a pedicle screw ring.

[0036] [Fig.7] is a diagram of such a ring mounted in a socket of such a screw.

[0037] [Fig.8] is a perspective view of a third version of the ring.

[0038] [Fig.9] is a perspective section of a screw receiving such a ring.

[0039] [Fig.10] is a perspective view of a fourth version of the ring.

[0040] [Fig.11] is a partial perspective section of a screw receiving such a ring. Detailed description of the invention

[0041] With reference to Figures 1 to 3, the invention relates to a pre-assembled pedicle screw (1) comprising a screw (10) with a spherical head (11), and a sleeve (20) mounted in a ball joint connection on the spherical head (11). The ball joint connection between the sleeve (20) and the spherical head (11) can be locked in the desired orientation, by means of a ring (40) arranged in the sleeve (20), configured to come into tight contact with the spherical head (11).

[0042] Gripping means (22) for the sleeve (20) allow it to be immobilized when handling the ring (40).

[0043] It is then possible to mount a connecting rod (50) between several pedicle screws (1), at a receiving location (21) of the sleeve (20), which generally has a U shape. The connecting rod (50) is 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).

[0044] In this way, the practitioner can: - place the pedicle screws (1) on the patient's affected vertebrae, - properly orient the sleeve (20) of each screw (1), and lock the orientation by means of the ring (40) of each pedicle screw (1), - and finally mount the connecting rod (50) connecting the pedicle screws (1), before proceeding to fix the rod (50) using the nuts (30).

[0045] Thus, when installing the rod (50), the sockets (20) are held in position and the installation of the rod (50) is facilitated.

[0046] In practice, the ring (40) has a bearing surface (42) of a shape complementary to the spherical head (11), and an imprint (41) intended to receive a tool for manipulating the locking of the ring (40) between a position of release of the spherical head (11) and a blocking position bearing against the spherical head (11), by a kinematics of the helical connection type. Preferably, the imprint (41) is hollow. 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.

[0047] In a first preferred embodiment illustrated in Figure 2, the locking is obtained by a thread of the ring (40) cooperating with a tapping of the sleeve (20). In a second embodiment illustrated in Figure 3, the locking is obtained by a cam profile (47) of the ring (40) cooperating with a complementary profile of the sleeve (20).

[0048] 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 size of the pedicle screw (1).

[0049] The operation of the first and second embodiments, of the helical connection type, is similar: the rotation of the ring (40) in a first direction involves its descent 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 blocking the orientation of the sleeve (20) relative to the head (11). The advantage of the first method is that the ring (40) and the nut (30) can have the same thread, the manufacture of the sleeve (20) is therefore facilitated by the production of a single tapping, over the entire necessary height.

[0050] Preferably, the blocking is reversible, the rotation of the ring (40) in a second direction involving its rise within the sleeve (20), therefore the release of the sleeve (20). This reversibility allows the surgeon to properly orient the sleeve (20), if necessary, by trial and error.

[0051] The manipulation of the ring (40) is done using a tool inserted into an imprint (41) of the ring (40).

[0052] In both embodiments provided, 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).

[0053] In practice, the first functional clearance (j1) is measured on 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) which 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 socket (20).

[0054] 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).

[0055] This has several advantages. First of all, in the unlikely event that the surgeon has 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.

[0056] Then, it is possible to use the ring (40) only for pre-locking the head (11), by means of a limited tightening force, while a greater tightening force guaranteeing the locking of the assembly is provided by the nut (30). This makes it possible to reduce the height of the imprint (41) of the ring (40), and therefore the height of the ring (40), because the dimensioning for the matting of the imprint (41) with a moderate clamping force requires a smaller surface area. The space requirement of the pedicle screw (1) can thus be optimized.

[0057] In order for a bearing surface (42) of the ring (40) to perfectly match the geometry of the spherical head (11), the ring (40) has at the bearing zone (42) an elastic portion (43), the elasticity of which is greater than the rest of the ring (40). By elasticity, it is meant that its diameter can vary in response to a force exerted on said portion.

[0058] With reference to Figure 4, this elasticity is preferably provided by cutouts, for example longitudinal (44) distributed around the periphery of the support zone (42). This solution is particularly suitable for rings (40) made of metallic materials.

[0059] To facilitate operations during surgery, the pedicle screw (1) is preferably delivered with the ring (40) pre-assembled in the sleeve (20). The support zone (42) of the ring can, thanks to its shape complementary to that of the spherical head (11), participate in the definition of the ball joint connection, the pre-assembly of the ring (40) is preferably in a configuration close to the blocking of the locking of the head (11).

[0060] That is to say that in the case of a threaded ring (40), the latter is not left more than one thread from its locking position, and is on the contrary screwed as close as possible to the head (11), while leaving the orientation of the sleeve (20) free relative to the head (11). Otherwise, in the event that the surgeon forgets to lock the ring (40) before mounting the rod (50), the second set (j2) risks not being able to fulfill its role.

[0061] In order to avoid accidental loss of the ring (40), it preferably has first snap-fastening means (45) against the sleeve (20).

[0062] Figure 4 shows an embodiment in which these first latching 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 socket (20). The direction of snap-fastening of the means (45) is parallel to the axis of revolution of the socket (40).

[0063] So that the prior assembly of the ring (40) does not hinder access to the imprint (12) of the screw (10), with a view to its manipulation by a tool, the ring (40) has an imprint (42) which is through, and of dimensions greater than those of the imprint (12) of the screw (10), and in particular of dimensions greater than the inscribed circle of the imprint (12).

[0064] Referring to Figure 5, it can be seen that the inscribed circle (C4) of the imprint (42) of the ring (40) is of greater diameter than the circumscribed circle (C1) of the imprint (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.

[0065] The indentations are preferably of the hexagonal or hexalobular type (six-pointed star-shaped), which allow efficient transmission of torque from the tool to the ring (40) and nut (30).

[0066] Figures 6 and 7 illustrate an embodiment in which the first snap-fastening 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), in a snap-fastening direction parallel to the axis of revolution of the sleeve (40).

[0067] 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 two-thread helix; - each net is made up of five ramps (45i to 45s).

[0068] In this way: - when assembling the ring (40) with the sleeve (20), the first two ramps (451) fit into the bore (23) and ensure the securing of the mounting of the ring (40), preventing its accidental loss; - when in use, the ring (40) is tightened in order to lock the orientation of the socket (20), the ring (40) descends within the socket (20) and the second ramps (452) will in turn be inserted into the bore (23), and so on. From this In this way, the successive ramps (45) guarantee that the tightening carried out on the ring (40) is maintained, because they prevent it from rising by unscrewing.

[0069] This embodiment of the ramps (45) constitutes a means of immobilization (46) of the ring (40) within the sleeve (20).

[0070] In Figure 7, we see the last ramp (45s) inserted in the bore (23) and preventing the untimely unscrewing of the ring (40).

[0071] This embodiment does not, however, prevent the possibility of adjusting the orientation of the sleeve (40) several times if necessary, since the force applied to the ring (40) by a tool is sufficient to cause the ramps (45) to come out of the bore (23).

[0072] In the illustrated embodiment, the upper face of the ramps (45) is inclined parallel to the angle helix (p). The contact between the ring (40) and the sleeve (20) is a point or an edge, depending on the depression of the ring (40). In an alternative embodiment not illustrated, the ramps (45) are offset in height to form the 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).

[0073] Figures 8 and 9 illustrate another embodiment of the immobilizing means (46) of the ring (40), which are pawls, advantageously arranged at one end of the cam profiles, or threads (47) of the ring (40).

[0074] When the ring (40) is tightened, the pawls (46) progress within the thread of the sleeve (20), until it exits where they are released and come to cooperate with a stop (24), when the ring (40) is sufficiently tightened.

[0075] Knowledge of: - the value of the first axial functional clearance (j1), 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).

[0076] In this mode, the mobility of the ratchet (46) is substantially parallel to the axis of revolution of the socket (40).

[0077] Machining (48) makes it possible to give the necessary elasticity to the portion of the thread (47) defining the ratchet (46).

[0078] Figures 10 and 11 illustrate another embodiment of the immobilization means (46) in which the mobility of the pawl (46) is substantially radial relative to the axis of revolution of the socket (40).

[0079] In a similar manner to the previous mode, the pawls (46) progress within the threading of the sleeve (30) until they come to cooperate with a stop (24) of the sleeve (20).

[0080] This method 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 method, because it is sufficient to provide a radial hole (25) passing through the sleeve (20) at the desired location.

[0081] 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).

[0082] In all cases, the immobilizing means (46) prevent the untimely disassembly of the ring (40), but do not prevent the intentional disassembly of the ring (40) using a tool exerting a force on the imprint (41).

[0083] The pawls (46) can be arranged on the sleeve (20), and the stop (24) can be arranged on the ring (40).

[0084] Furthermore, the pedicle screw (1) may be shaped differently from the examples given without departing from the scope of the invention, which is defined by the claims.

[0085] According to a non-illustrated embodiment, the first means for snapping the ring (40) are an added element preventing its disassembly from the sleeve (20), such as a pin or an elastic ring, but is however not preferred because this would increase the number of parts.

[0086] Furthermore, the technical characteristics of the different embodiments and variants mentioned above can be, in whole or in part, combined with each other. Thus, the pedicle screw (1) can be adapted in terms of cost, functionality and performance.

Claims

Claims [Claims 1] Pre-assembled pedicle screw (1) comprising: - a screw (10) with a spherical head (11), - a socket (20) receiving the spherical head (11) according to a ball joint, and having a receiving location (21) of a connecting rod (50) between several pedicle screws (1), - a nut (30) intended to be screwed into the socket (20) to block the rod, - a ring (40) housed in the socket (20) and configured to bear against the spherical head (11), and having an imprint (41) intended to receive a tool for manipulating the ring (40) between a position for releasing the spherical head (11) and a position for locking the spherical head (11), characterized in that the ring (40) is arranged between the spherical head (11) and the location (21) of the rod (50) within the socket (20). [Claims 2] Pedicle screw (1) according to claim 1, characterized in that the ring (40) is threaded. [Claims 3] Pedicle screw (1) according to claim 2, characterized in that the ring (40) and the nut (30) have the same thread. [Claims 4] Pedicle screw (1) according to one of the preceding claims, characterized 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). [Claims 5] Pedicle screw (1) according to one of the preceding claims, characterized in that the imprint of the ring (40) is through, the spherical head (11) has an imprint (12) configured for its screwing by means of a tool, and the imprint (12) of the spherical head (11) is of dimensions smaller than the inscribed circle of the imprint (41) of the ring (40). [Claims 6] Pedicle screw (1) according to one of the preceding claims, characterized in that the ring (40) has a spherical bearing zone (42) intended to come into contact with the spherical head (11), and the bearing zone (42) has an elastic portion (43). [Claims 7] Pedicle screw (1) according to claim 6, characterized in that the elastic portion (43) is defined by at least one longitudinal cutout (44) on the periphery of the support zone (42). [Claims 8] Pedicle screw (1) according to one of the preceding claims, characterized in that the ring (40) has first snap-fastening means (45) inside the sleeve (20). [Claims 9] Pedicle screw (1) according to claims 7 and 8, characterized in that the first latching means (45) are at least one ramp intended to latch into a bore (23) of the sleeve (20). [Claims 10] Pedicle screw (1) according to one of the preceding claims, characterized in that the ring (40) has immobilization means (46) within the sleeve (20). [Claims 11] Pedicle screw (1) according to claim 10, characterized in that the immobilization means (46) comprise second snap-fastening means cooperating with a part of the sleeve (20). [Claims 12] Pedicle screw (1) according to claim 11 taken in combination with claim 2, characterized in that the second snap-fastening means are formed on threads (47) of the ring (20). [Claims 13] Pedicle screw (1) according to one of claims 10 to 13, characterized in that the ring (40) has first snap-fastening means (45) inside the sleeve (20), and the immobilization means (46) comprise the first snap-fastening means (45).

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