Setscrew and setscrew insertion tool for improved rod alignment

Abstract

To provide an orthopedic tool and system including a pedicle screw, a rod and a corresponding set screw.SOLUTION: A set screw 31, 32 for threadable engagement with a head 21 of a pedicle screw 11, 12 for holding a spinal rod 7 has a spinal rod facing side and a set screw driver facing side, and includes an opening on the set screw driver facing side for engaging with the set screw driver, and a convex surface on the rod facing side, where an apex of the convex surface substantially coincides with a rotational central axis of the set screw.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This patent application claims priority to International Patent Application No. PCT / IB2019 / 052451, filed March 26, 2019, the contents of which are incorporated herein by reference in their entirety.

[0002]

[0002] The present invention relates to orthopedic surgery, and more specifically to orthopedic tools and systems including pedicle screws, rods and corresponding set screws. The present invention also relates to instruments used to manipulate these elements, and methods of using these elements. [Background technology]

[0003]

[0003] In the field of orthopedics and implant instruments and systems for orthopedic surgery, more specifically for spinal fixation of the spine, a set screw is used to push down a rod- or bar-shaped device and attach it to the head of a pedicle screw. The process of pushing a spinal rod towards and down the head of a pedicle screw is also called rod reduction. Before attaching the rod to the head of the pedicle screw, the pedicle screw is attached to the vertebra with a bone anchor, a threaded bone engagement part or a bone screw in order to fasten the pedicle screw to the vertebra of a patient or organism. For this purpose, as an example, for several adjacent vertebrae for vertebral fixation, a pedicle screw is attached to the vertebra for each vertebra, and then several pedicle screws are mechanically fastened towards each other by using a rod placed in a groove or U-shaped opening formed by the pedicle screw head to form a row of pedicle screws in the spine. This makes it possible to provide the mechanical support required for spinal stabilization for spinal fixation in a patient or organism.

[0004] For example, U.S. Patent No. 10,058,355, the entirety of which is incorporated herein by reference, describes an orthopedic implant kit that provides a pedicle screw, a corresponding set screw, a rod, and tools for manipulating the same, including a screw extender for holding the pedicle screw, and a set screw driver for tightening the set screw to the head of the pedicle screw. As another example, U.S. Patent No. 8,795,283, the entirety of which is incorporated herein by reference, describes another type of kit orthopedic surgical system for surgical intervention for spinal stabilization, including a pedicle screw with a head for receiving a rod, and tools necessary for the surgical intervention. In yet another example, U.S. Patent No. 8,262,662, the entirety of which is incorporated herein by reference, provides a system and method for delivering a spinal connector spinal anchor site into the spinal column. In one embodiment, a spinal implant and access device is provided that includes a U-shaped receiving member, a bone engaging member, an extension member, a spinal rod, and a set screw.

[0005]

[0005] Similar orthopedic spinal surgery concepts, tools and devices for attaching rods to pedicle screws via set screws have been proposed as described above, e.g., in U.S. Pat. Nos. 5,129,388, 5,147,360, 5,520,689, 5,536,268, 5,720,751, 5,817,094, 5,882,350, 5,984,923, 6,056,753, U.S. Pat. No. 6,113,601, U.S. Pat. No. 6,183,472, U.S. Pat. No. 6,258,090, U.S. Pat. No. 6,454,768, U.S. Pat. No. 6,648,888, U.S. Pat. No. 6,740,086, U.S. Pat. No. 7,618,442, U.S. Pat. No. 8,308,782, U.S. Pat. No. 8,876,868, U.S. Patent Application Publication No. 2006 / 0025771, and U.S. Patent Application Publication No. 2018 / 0289397, all of which are incorporated herein by reference in their entirety.

[0006]

[0006] However, the prior art tools still present certain problems due to misalignment of the spinal rod relative to the pedicle screw head when the surgeon or operator of the spinal surgery tool needs to attach the rod to the pedicle screw by a set screw. Therefore, despite all the solutions currently proposed in the related prior art spinal surgery tools, highly improved methods, systems and devices for spinal surgery are highly desirable. Summary of the Invention

[0007] According to one aspect of the present invention, there is provided a set screw for threadably engaging a head of a pedicle screw for retaining a spinal rod. Preferably, the set screw has a spinal rod-facing side and a set screw driver-facing side, the set screw driver-facing side including an opening for engagement with the set screw driver and a convex surface on the rod-facing side, the apex of the convex surface being substantially coincident with a central axis of rotation of the set screw.

[0008] According to another aspect of the present invention, there is provided a set screw for threadably engaging a head of a pedicle screw for retaining a spinal rod. Preferably, the set screw has a spinal rod-facing side and a set screw driver-facing side, including an opening on the set screw driver-facing side traversing the set screw from the spinal rod-facing side to the set screw driver-facing side, and an annular surface on the rod-facing side surrounding the opening, the annular surface having a chamfered or curved surface.

[0009] According to yet another aspect of the present invention, there is provided an orthopaedic tool kit including a set screw and a set screw driver. Preferably, the set screw is configured to threadably engage a head of a pedicle screw for holding a spinal rod, the set screw having a spinal rod-facing side and a set screw driver-facing side. Further, the set screw includes an opening on the set screw driver-facing side that traverses the set screw from the spinal rod-facing side to the set screw driver-facing side, and an annular surface on the rod-facing side that surrounds the opening. Further, preferably, the set screw driver includes a shaft and an engagement portion for engaging the set screw through the opening, and in an engaged position, a front portion of the engagement portion protrudes from the spinal rod-facing side of the set screw.

[0010] According to yet another aspect of the present invention, a pedicle screw is provided having a screw head with a U-shaped groove for receiving a spinal rod. Preferably, the lower surface facing the lower surface of the spinal rod forms the bottom of the U-shaped groove and has a curvature along a radial direction that extends away from a central axis of the screw head and presents a smooth surface with less sharp edges towards the spinal rod.

[0011]

[0011] The above and other objects, features and advantages of the present invention, as well as the manner in which they are achieved, will become more apparent, and the invention itself will be best understood by considering the following description in conjunction with the accompanying drawings, which show several preferred embodiments of the invention.

[0012]

[0012] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate currently preferred embodiments of the invention and, together with the general description above and the detailed description below, serve to explain features of the invention. [Brief description of the drawings]

[0013] [Figure 1A] 1A-1C show different exemplary cross-sectional side views of several pedicle screws 11, 12 attached together via a spinal rod 7 within several vertebrae of a patient's or organism's spine to illustrate one of the problems encountered with prior art spinal surgery systems, devices and tools. [Figure 1B] 1A-1C show different exemplary cross-sectional side views of several pedicle screws 11, 12 attached together via a spinal rod 7 within several vertebrae of a patient's or organism's spine to illustrate one of the problems encountered with prior art spinal surgery systems, devices and tools. [Figure 1C]FIG. 1 shows different exemplary cross-sectional side views of several pedicle screws 11, 12 attached together via a spinal rod 7 within several vertebrae of a patient's or organism's spine, to illustrate one of the problems encountered with prior art spinal surgery systems, devices and tools, the figures showing a set screw 32 being tightened to the spinal rod 7 and screw head 22 by use of an exemplary screw extender 6 and set screw driver 20. [Figure 2A] 1 shows an exemplary diagram of a set screw 130 according to one embodiment of the present invention, the diagram showing a front view and a cross-sectional side view of the set screw. [Figure 2B] An exemplary diagram of a set screw 130 according to one embodiment of the present invention is shown, showing a transverse side cross-sectional view in the direction of the axis RA2 of the spinal rod 7. [Figure 2C] An exemplary diagram of a set screw 130 according to one embodiment of the present invention is shown, which shows the set screw 130 biasing against the spinal rod 7 inside the pedicle screw head 22 when the spinal rod 7 is diagonally inside the U-shaped groove 26. [Figure 2D] 1 shows an exemplary diagram of a set screw 130 according to one embodiment of the present invention, which shows an enlarged cross-sectional view of the set screw 130 without the opening 132 for illustrative purposes. [Figure 3A] An exemplary diagram of a set screw 230 and a corresponding shaft of a set screwdriver 200 according to another embodiment of the present invention is shown, the set screw 230 and the screwdriver 200 can form elements of an orthopaedic surgical tool kit or system, the diagram showing a side view of the set screw 230 and the corresponding set screwdriver device 200 engaged with each other. [Figure 3B]An exemplary diagram of a set screw 230 and corresponding shaft of a set screwdriver 200 according to another embodiment of the present invention is shown, the set screw 230 and screwdriver 200 can form elements of an orthopaedic surgical tool kit or system, the diagram showing a side cross-sectional view of the set screw 230 and screwdriver 200. [Figure 3C] An exemplary diagram of a set screw 230 and corresponding shaft of a set screwdriver 200 according to another embodiment of the present invention is shown, the set screw 230 and screwdriver 200 can form elements of an orthopaedic surgical tool kit or system, the diagram showing a side perspective view of the set screw 230 and screwdriver 200. [Figure 3D] An exemplary diagram of a set screw 230 and corresponding shaft of a set screw driver 200 according to another embodiment of the present invention, which may form elements of an orthopaedic surgical tool kit or system, is shown, showing a side cross-sectional view of the set screw 230 and corresponding set screw driver device 200 abutting or contacting the spinal rod 7 when the spinal rod 7 is not perpendicular to the axis HA2. [Figure 4A] An exemplary illustration of a set screw 200 alone without a corresponding set screw driver 200 is shown, with the illustration showing a side view. [Figure 4B] An exemplary view of the set screw 200 alone without the corresponding set screwdriver 200 is shown, along with a corresponding cross-sectional view showing details of the opening 232. [Figure 4C] An exemplary illustration of a set screw 200 alone without a corresponding set screwdriver 200 is shown, with the illustration showing a front perspective view. [Figure 4D] An exemplary illustration of a set screw 200 alone without a corresponding set screw driver 200 is shown, with the illustration showing a rear perspective view. [Figure 5A]An exemplary cross-sectional view of the screw head 22 of the polyaxial pedicle screw 21 and the set screw 230 engaged with a spinal rod 7 is shown, with the rod 7 being substantially perpendicular to the axis HA2 of the screw head 22, and the view shows that the set screw driver 200 is in contact with the rod 7 through the opening 232. [Figure 5B] An exemplary cross-sectional view of the screw head 22 of the polyaxial pedicle screw 21 and the set screw 230 engaged with the spinal rod 7 is shown, with the rod 7 being substantially perpendicular to the axis HA2 of the screw head 22, the view showing the stage after the set screw driver 200 has been pushed back against the set screw 230 and the set screw 230 has come into contact with the rod 7. [Figure 6A] An exemplary diagram of another embodiment of the present invention is shown, which shows a pedicle screw 311 having a U-shaped groove 325 for accommodating a spinal rod 7, in which the edge 327 of the cylindrical outer surface of the screw head 321 is not very sharp, and the diagram shows a cross-sectional view from the side perpendicular to the extension axis of the spinal rod 7 and the groove 325. [Figure 6B] An exemplary diagram of another embodiment of the present invention is shown, which shows a pedicle screw 311 having a U-shaped groove 325 for accommodating a spinal rod 7, and the edge 327 of the cylindrical outer surface of the screw head 321 is not very sharp, and the diagram shows a top view of the screw head 321. [Figure 6C] An exemplary diagram of another embodiment of the present invention is shown, showing a pedicle screw 311 having a U-shaped groove 325 for accommodating a spinal rod 7, in which the edges 327 of the cylindrical outer surface of the screw head 321 are not very sharp, and the diagram shows an exemplary cross-sectional view of the screw head 321 having a seat 326 for preventing multi-axial movement of the bone anchor 41 by downward pressure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014]

[0019] Wherever possible, the same reference numbers are used herein to designate identical elements common to the figures, and images may be simplified for illustrative purposes and not drawn to scale.

[0015]

[0020] FIG. 1A shows a cross-sectional view of several pedicle screws 11, 12, or other types of spinal surgical screws, engaged with individual vertebrae V1, V2 of a patient's or organism's spine, interconnected with a spinal rod 7 or support rod, and held by corresponding set screws 31, 32, or fastening devices. As shown on the left side of this figure, the longitudinal extension axis RA1 of the spinal rod 7 is substantially perpendicular to the central axis HA1 of the screw head 21 of the pedicle screw 11. Furthermore, the bone anchor or threaded portion 41 of the pedicle screw 11 also defines a central axis SA1, which may coincide with the central axis HA1 of the screw head 21 in the case of a monoaxial configuration, or may be different from the central axis HA1 of the screw head 21 in the case of a polyaxial configuration. For illustrative purposes, the pedicle screw 11 is of a monoaxial configuration, although polyaxial screws may also be used. 1B shows a cross-sectional view along a longitudinal axis RA1 of the spinal rod 7, showing a U-shaped groove 25 or other type of cavity, opening, long deep groove, recess, or feature in the screw head 21 for receiving the spinal rod 7. The screw head 21 has an internal thread 27 that is complementary to or corresponds to the external thread of the set screws 31, 32 so that the set screws 31, 32 can be threadably engaged and tightened relative to the screw head 21.

[0016]

[0021] As shown on the right side of FIG. 1A, at least in some parts along the spinal rod 7, the orientation of the spinal rod 7 with respect to the screw head 21 is not perpendicular, e.g., the angle α2 between the longitudinal extension axis RA2 of the spinal rod 7 is not 90° or perpendicular to the central axis HA2 or the thread axis of the screw head 22 of the pedicle screw 12, but an inclination angle α2 may exist. In general, as an example, the rod 7 is pre-bent before insertion and attachment into the pedicle screw 11, so that this incorrect orientation may be the result of bending of the rod 7 at one end, for example, when the last pedicle screw 12 of a row or series of pedicle screws has a spinal rod 7 with an end that protrudes upward and away from the spine. This deviation from a perpendicular arrangement may also be simply a misalignment between the screw head 22 and the rod 7 that cannot be easily corrected by the surgeon or operator, for example due to a minimally invasive surgical approach, since the incision at the surgical site is not easily accessible or visible. Another reason for misalignment is caused when the user, operator, or surgeon himself tries to tighten the set screw 31 to the screw head 21 via the screw extender 6 and the set screw driver 20, as shown in FIG. 1C. The alignment between the spinal rod 7 and the pedicle screw head 21 may be accurate initially, but the surgeon may laterally move or tilt the screw extender 6 by a certain angle, thus bending or moving the screw head 21 relative to the rod 7, causing misalignment. This is common in surgeries where the surgical incision is small and the pedicle screws 21, 22 and the rod 7 cannot be easily seen.

[0017]

[0022] As a result, some problems may arise when the surgeon or operator attaches the spinal rod 7 to the pedicle screw 12 using the set screw 32. This is shown on the right side of FIG. 1A and in more detail in FIG. 1C, which shows a schematic cross-sectional view of the screw extender 6 attached to the pedicle screw 12, with the set screw driver 20 threadably engaging the female threaded portion 19 of the screw extender 6, which is attached to the screw head 22 using the engagement portion 21, and the set screw 32 is threaded to lower the rod 7 into the U-shaped groove 26 provided by the screw head 22. As shown in FIG. 1C, the angle α2 between the longitudinal extension axes RA2 of the spinal rod 7 is not 90° or perpendicular to the central axis HA2 of the screw head 22 of the pedicle screw 12, but ranges from 60° to 80° for illustrative purposes. When the set screw 32 is tightened in the screw head 22 by the set screw engagement 21 of the set screw driver 20, in the variant shown with a shaft threadably engaging with the internal thread 19 of the screw extender 6, the edge of the set screw 32 contacts the outer surface point of the upper part of the spinal rod 7, forming a single contact point CP1. If the alignment is vertical, i.e., α2=90°, the complete apical flat surfaces 33, 34 of the set screws 31, 32 contact the round outer surface point of the upper part of the spinal rod 7, forming a contact line, which is not a single contact point CP1. This is shown on the left side of FIG. 1A together with the pedicle screw 11. This contact point CP1 is also off-axis by a distance OD1 from the central axis HA2 of the pedicle screw head 22. The bending or misalignment of the spinal rod 7 may be such that this contact point CP1 may be the only substantial mechanical contact point acting on the rod 7, other than a small lateral support contact by the side walls of the U-shaped groove 26. Furthermore, in addition to or instead of the contact point CP1, due to misalignment at the opposite side of the screw head 22, the spinal rod 7 contacts the edge of one end of the U-shaped groove 26, forming a semicircular contact line or arc CP2, instead of the rod 7 being embedded in the semicircular underside of the U-shaped groove 26. This contact line CP2 is also offset from the central axis HA2 of the head 22 of the pedicle screw 12 by a distance OD2.

[0018]

[0023] Because the spinal rod 7 is held in place by several other pedicle screws 11, 12 and corresponding set screws, as shown in Figure 1A, tightening of the set screw 32 against the screw head 22 may not provide sufficient compressive or bending force to bend the spinal rod 7 into a perpendicular alignment relative to the screw head 22, for example to realign it by forcing the rod 7 into the U-shaped groove 26, since the spinal rod 7 is generally quite rigid. Furthermore, this misalignment will cause stresses in one or more vertebrae V2 affected by the misalignment through the pedicle screws 12 and their bone anchors, generating lateral forces in the vertebrae V2, since these vertebrae V2 can only move to a limited extent relative to the other vertebrae. Also, when a polyaxial pedicle screw 12 is used, the angular range of the screw head 22 along axis HA2 relative to the anchor 42 along axis SA2 may not be sufficient and is mechanically blocked to compensate for misalignment between the rod along axis RA2 and the screw head 22 along axis HA2, generating additional mechanical stress on the affected vertebra V2.

[0019]

[0024] The resulting undesirably limited contact surface or area between the rod 7 and the screw head 22, either by a contact point CP1 at the lower edge of the flat face 34 of the pedicle screw 32 with a point on the cylindrical surface of the rod 7, or by a contact point or arc CP2 on the opposite side of the screw head 22, for example by a semicircular arc along the edge of the U-shaped groove 25, can result in several problems.

[0020]

[0025] Firstly, due to the offset between the central axes HA2 of the screw heads, for example due to the offset distance OD1 or offset distance OD2, this mounting situation results in an undesirable lateral torque being applied to the bone anchor or threaded portion 41, which also generates a lateral tension in the bone structure of the vertebra V2 of the patient or organism. Any upward or downward pressure or movement exerted on the spinal rod 7, for example parallel or substantially parallel to the axis HA2, results in a lateral pressure of the bone anchor 41 on the vertebra V2, as shown by the arrow shown on the right side of FIG. 1B showing the vertebra V2. For example, after surgery, physical movements of the patient or organism may cause such pressure or movement on the spinal rod 7, which results in a strong lateral tension on the vertebra V2 via the bone anchor 41.

[0021]

[0026] Second, the limited surface area of ​​the contact points CP1, CP2, or both, can lead to undesirable cold welding that may occur during surgery. Such cold weld attachment can prevent further attachment or threading of the set screw 32 into the screw head 22, preventing proper attachment of the rod 7 to the pedicle screw 12.

[0022]

[0027] Third, the pressure caused by the offset distance OD1 or OD2 that is not on-axis with the central axis HA2 of the screw head may cause the set screw 32 inside the screw head 22 to be blocked when the user, operator, or surgeon is tightening the set screw 32 with the set screw driver. The occurrence of pressure off-axis of HA2 may result in a non-symmetrical different lateral pressure of the set screw 32 against the threads of the screw head 22, causing the set screw 32 inside the screw head 22 to be blocked. This may also lead to damage to the threads that may further block the set screw 32 against the screw head 22 and / or create additional undesirable friction during the rotationally threadable engagement between the set screw 32 and the screw head 22 that may lead to potential cold welding. Similar cold welding problems can arise with some of the prior art set screws that exhibit a pointed tip that allows for additional grip on the rod, as shown, for example, in U.S. Patent Application Publication No. 2018 / 0289397 or U.S. Patent No. 5,129,388, which references are incorporated herein by reference in their entireties.

[0023]

[0028] 2A-2D show different exemplary cross-sectional views of a set screw 130 according to an embodiment of the invention to alleviate the above-mentioned problems. As shown in FIG. 2A, which shows a cross-sectional view and a front view of the set screw 130, the set screw 130 does not have a flat surface 34 facing the rod 7, but has a front surface or face FF that forms a convex shape and is circularly symmetric about an axis HA2. In the illustrated variant, as shown in more detail in FIG. 2D, the central area or inner area IA of the front surface FF forms a first surface 135 with a curvature having a first radius R1, which curvature is defined in the radial direction of the cylindrical shape of the set screw 130, and the outer area or annular surface ring OA of the front surface FF forms a second surface 134 with a second curvature having a second radius R2 and an edge area 133 or annular surface ring edge area EA that is flat but has a chamfered edge. Furthermore, the rod 7 is shown to have a cylindrical smooth surface without indentations or notches. Preferably, the inner area IA has a greater curvature than the outer area OA, for example, the first radius is smaller than the second radius, but it is also possible to form a continuous sphere in which IA and OA have the same radius R1=R2. In one variant, starting from the center point or centre of the front surface, for both the inner area IA and the outer area OA, the change in radius of the front surface FF is gradual, i.e. it is smallest at the centre, and changes progressively to a greater radius towards the edge, for example by following an elliptical shape, in other words the shape of an ellipsoid, when viewed from a cross-sectional view, the apex of the ellipsoid being located at the centre of rotation of the front surface FF. In another variant, the entire front surface FF, including areas IA, OA and EA, is spherical, the gradient of the edge area EA being selected to match the flank or thread angle of the thread 137 of the set screw 130. In another variant, a sphere for the front surface FF is formed, for both the inner area IA and the outer area OA, with a constant radius of curvature, but still with a chamfered circular outer edge EA of the thread 137.This arrangement of the front face FF of the set screw 130, which presents a continuous convex or protruding bulge along the entire diameter of the set screw 130, covering the circular inner area IA, the annular outer area OA, and the annular edge area EA, also makes it possible to avoid any sharp edges, such as those formed by two perpendicularly arranged surfaces resulting in an edge angle of 90°, which may cut or otherwise damage the surface of the spinal rod 7, even if the spinal rod 7 is arranged at an oblique angle to the screw head 22. In this respect, the entire surface of the set screw 130 facing the spinal rod forms a convex volume protruding from a surface perpendicular to the thread axis of the set screw. The only sharp edges of the set screw 130 that are less than 90° are arranged on the side wall of the set screw 130 that has the crest of the thread 137, which are such that they cannot come into contact with the spinal rod 7 when the set screw 130 is threadably engaged with the head 22.

[0024]

[0029] Preferably, the radius of curvature R1, R2 is greater than the radius of the set screw of the pedicle screw 12, preferably about half, ±25%, of the diameter of the outer cylindrical surface of the screw head 22 of the pedicle screw 12 or the diameter of the set screw 130, more preferably at least twice the radius of the screw head 22 or at least twice the diameter of the set screw 130. Smaller radii are possible, but result in a set screw that is thicker and requires more space inside the patient or organism. The edge area EA preferably has no curvature, but is chamfered or otherwise shaped to match the flank of the thread 137 of the set screw 130, so as to keep the set screw 130 as thin as possible relative to the thickness TH, when viewed along the axis HA2, for example at an angle of 45°. Furthermore, the set screw 130 has an opening 132 or other type of removable attachment or engagement mechanism for engaging with a corresponding or complementary engagement portion 21 of the set screw driver 20. In the illustrated variant, a hexagonal socket head for the opening 132 is provided, but different types of removable attachment or engagement mechanisms between the set screw 130 and the screwdriver are also possible, including, but not limited to, fillister head, Torx head, spanner head with two or more drills, square head, clutch heat, multiple slot heads and corresponding complementary engagement tools or parts 21 by the set screwdriver 20. The set screw 130 is also designed to keep the overall profile low, which in the case of the set screw 130 means that the thickness TH is minimized to avoid needing a screw head 22 with a higher build, minimizing the space required within the patient or organism to protrude from the vertebrae, such that protrusion of the pedicle screw from the spine is reduced. Thus, according to one embodiment, the set screw 130 is designed as a one-piece such that the anterior FF is an integral part of the set screw 130 made of one piece of material without any moving parts attached or otherwise integrated with the convex anterior FF.Also, the distance OS between the root diameter of the thread 137 of the set screw 130 and the diameter of the outer annular area OA can be zero so that the width of the edge annular area EA matches the distance between the root and apex of the thread 137, but in a variant, the distance OS can also be positive so that the diameter of the outer annular area OA is smaller than the root diameter of the thread 137.

[0025]

[0030] As shown in FIG. 2B, which shows a side cross-sectional view in which the front FF set screw 130 engages with the spinal rod 7 arranged obliquely relative to the screw head 22, in other words, the angle α2 between the axis RA2 and HA2 is not 90°. This results in a contact point CP3 that is much closer to the central axis HA2 of the screw head 2 resulting in an offset distance OD3. Compared to the contact point CP1 shown in FIG. 1C, assuming that the misalignment angle α2 is substantially the same, the distance can be reduced by one third. This results in a significant reduction by one third of the undesired lateral torque applied from the bone anchor 41 to the vertebra V2 when the spinal rod 7 moves along the axis HA2.

[0026]

[0031] Furthermore, since the surface of the front FF of the set screw 130 has a curvature that engages or abuts the spinal rod 7, which also has a curved outer surface and has the shape of a cylinder, the contact surface at the contact point CP3 is substantially larger than the contact surface formed by the sharp edge of the set screw 32, contact point CP1, for deformations shown with an edge angle of 90° or less, since there is a certain amount of deformation in the contact area between the spinal rod 7 and the front FF of the set screw 130. This can reduce or completely eliminate the cold welding problem at the contact point CP3. Furthermore, as shown in FIG. 1C, when the user, operator, or surgeon turns the set screw 32 relative to the screw head 22 via the set screw driver 20, the edge of the set screw 32 turns or rotates against the cylindrical surface of the spinal rod 7. Thereby, the edge can act like a knife and provide a cutting action by cutting a groove into the spinal rod 7 with the edge, thereby damaging the outer surface of the spinal rod 7. As in the variation shown in Fig. 2C, the front FF of the set screw 130, which is a curved surface, can be turned into another curved, cylindrical surface of the rod 7 to completely avoid this cutting. The front FF of the set screw 32 can also be hardened or coated with a hard surface to provide additional hardness to its body, such as, but not limited to, the use of a chrome-cobalt alloy or anodizing. The material used to manufacture the set screw 32 can be the usual material used for implant devices, such as, but not limited to, titanium, different types of titanium alloys of different grades, stainless steel, CrCoMo.

[0027]

[0032] According to another aspect of the invention, as shown in Figures 3A-3D, a set screw 230 is provided having a transverse opening or through hole 232 that completely transverses or intersects the central axis of the set screw 230, with at least a portion of the opening 232 serving as an engagement mechanism for engagement with the set screw driver 200. Furthermore, according to another aspect of the invention, the engagement tool or mechanism 220 of the set screw driver 200 is dimensioned such that when fully engaged with the set screw 230, the engagement tool 220 transverses the opening 232 by a distance DD from the outermost point of the set screw 230, protruding slightly outside the front face FF of the set screw 230. For example, the distance DD may be in the range of 0.05 mm to 0.5 mm, more preferably 0.1 mm to 0.4 mm. For example, as shown in Figures 3A-3C, the engagement tool 220 of the set screw driver 200 is shown fully engaged with the set screw 230, meaning that the engagement tool 220 is blocked or otherwise mechanically prevented from further introduction or traversal of the set screw 230, for example, by the abutment surface 231 of the set screw 230 and a corresponding surface or abutment ledge, or other mechanical means on the set screw driver 200. Other types of mechanical arrangements can be used to limit the penetration of the set screw driver 200 relative to the set screw 230. In this engaged position, the front end face 222 of the engagement tool 220 projects slightly outside the set screw 230 by a distance DD, with the highest or most protruding point of the front face FF of the set screw 230 as a circular edge 236, as shown in Figure 3B.Moreover, in this fully engaged position between the set screw 230 and the tool 200, the distance between the set screw 230 and the tool 200 is set such that the external thread 237 of the set screw 230 and the external thread of the set screw driver 200 are aligned with each other to form a common virtual thread helix, in other words both threads or threads are aligned such that the thread pitches match as shown in Fig. 1C, so that the set screw 230 and the tool 200 can move together by rotational threadable engagement through the internal thread 19 of the screw extender 6 without adjusting the position between the set screw 230 and the tool 200. Similarly, when the screw extender 6 is fully inserted into the head 22, the internal thread of the screw head 22 matches the distance to the internal thread 19 of the screw extender to provide a continuous virtual thread helix.

[0028]

[0033] In this embodiment, as shown in Figures 3C and 4C, the front surface FF of the set screw 230 is defined as the front surface FF that will face and engage the spinal rod 7 and includes an annular ring section 234 that is not flat, in other words not perpendicular to the central axis or axis of rotation of the set screw 230, but forms a slope toward the outer edge of the set screw 230 in a radial direction away from the central axis, and preferably also has a curved or spherical surface with a curved or spherical radius when viewed radially, as seen in Figure 4A. In this variation, the front surface FF includes a circular edge 236 that forms the part of the set screw 230 that is the most forwardly projecting or outermost part of the set screw 230, and a radially outermost chamfered annular edge 233 that forms part of the thread of the set screw 230. The slope or inclination angle of the annular edge 233 forming part of the thread is greater or steeper than the slope or inclination angle of a tangent arranged on the annular ring section 234, as shown by the dashed line in Fig. 4A, e.g. 45°, e.g. in the range of 15° to 30°. In variants in which the annular ring section 234 is annularly curved or has a spherical shape, the curvature or spherical radius is preferably more than half, ±25%, of the cylindrical outer diameter of the screw head 22 or the outer diameter of the set screw 230, more preferably at least twice the radius of the screw head 22 or at least twice the radius of the set screw 230.

[0029]

[0034] As another variation, the annular ring section 234 is flat, in other words the surface defining the extension of the flat annular ring section 234 is perpendicular to the central axis of the set screw 230. This embodiment makes it possible to avoid the edge contact point CP5 as shown in FIG. 5B, and instead a linearly radially extending portion of the flat surface of the ring section 234 can contact the rod 7 in a direction parallel to the extension of the rod 7. For example, when the tip of the tool 200 comes into contact with the rod 7 at the contact point CP4, as shown in Fig. 5A, as a result of the screwing action of the set screw 230 by the tool 200 as a set screw driver, the tool 200 is pushed out of the set screw 230 by the force P, as shown in Fig. 5B, and instead of the small contact point CP5, due to the additional threadable engagement of the set screw 230 with the internal thread 27, the flat surface of the annular ring section 234 forms a contact line CL with the rod 7, assuming that the rod 7 is substantially parallel to the transverse extension axis of the U-shaped groove 26 of the screw head 322. Such a set screw 230 with a flat annular ring section 234 can be used when the rod 7 is not diagonally inside the U-shaped groove 26, as shown in Figs. 5A and 5B, but is more or less perpendicular to the screw. This may be contrasted with the use of a chamfered, curved, or spherical annular ring section 234 (non-flat) of the set screw 230, which is used when the rod 7 is at an angle to the U-shaped groove 26, as visualized in Figure 3D. These two different types of set screws 230 allow the surgeon or operator to selectively choose a flat or non-flat thread depending on the orientation of the rod 7 within the U-shaped groove 26 of the screw head 322.

[0030]

[0035] As seen in Figures 3B, 3D, and 4B, when the set screw driver 200 is fully engaged with the set screw 230, the apex of the tip 222 protrudes a distance DD from the outermost edge 236 of the front face FF of the set screw 230. Furthermore, the front tip face 222 itself is curved, and may be, for example, spherical, form a portion of an ellipsoid, or may be progressively curved with a smaller radius of curvature in the inner central portion and a larger angle of curvature in the outer annular section. As shown in Figures 3B and 3D, in this arrangement, the circular edge formed between the front tip face 222 and the side wall of the engagement tool 220 is within the opening 232 of the set screw 230, which may serve to avoid contact between the sharp edges and the spinal rod 7. As shown in Figures 3D and 5A, in this arrangement, the orientation of the spinal rod 7 represented by the screw head 22 and its longitudinal axis RA2 relative to the central axis HA2 can vary within a certain angular range, and the contact point CP4 between the set screw 230 and the set screw driver assembly 200 is between the front tip 222 and a surface point of the spinal rod 7. Assuming that RA2 and HA2 remain within a certain angular range, e.g., the front FF and the front tip face 222, no contact occurs between the front FF of the set screw 230 and the spinal rod while the user or operator tightens the set screw 230 with the set screw driver 200, and the protruding depth of the engagement tool 220 of the set screw driver 200 can also be designed to allow an angular variation of 70° to 110° of RA2 and HA2. The front tip face 222 of the set screw driver 200 can be made of hardened stainless steel.

[0031]

[0036] The contact point CP4 between the rod 7 and the set screw driver 200 allows a counter pressure or counter force P to be generated against the engagement portion 220 of the set screw driver 200, so that the set screw driver 200 is gradually pushed back and released from the set screw 230 as the set screw driver 200 tightens the set screw 230, and when gradually pushed back or released, the outermost surface of the set screw, which is the edge 236, contacts the spinal rod 7 to form a contact point CP5, as shown in FIG. 5B. As shown in FIGS. 5A and 5B, while threadably engaging the set screw 230 with the screw head 22, the front end surface 222 of the set screw driver 200 and the rod 7 first contact at the contact point CP4. Then, when the set screw driver 200 is gradually released from the set screw 230 by the push back caused by the force P, the tightening action brings the rod 7 and the set screw 230 into contact at the contact point CP5. This can be done so long as the rod 7 makes initial contact with the set screw driver 200 and not the set screw 230 .

[0032]

[0037] This presents several advantages to an orthopedic tool kit or system using such a set screw 230 having a transverse opening 232 and a corresponding set screwdriver 200, as described above. First, it is possible to generate a first contact point CP4 with the spinal rod 7 that minimizes the distance of CP4 from the central axis HA2 of the screw head 22 of the pedicle screw 21, even when the longitudinal axis RA2 of the rod 7 and the central axis HA2 of the screw head 22 are oblique to each other. Furthermore, the opposing force P of the set screwdriver 200 against the engagement portion 220 can significantly reduce the retention force generated during full engagement of the engagement portion 220 with the set screw 230, and the force required to remove the set screwdriver 200 from the set screw 230 can be significantly reduced.

[0033]

[0038] 6A, 6B and 6C show another embodiment of the invention, in which a screw head 321 for a pedicle screw 311 is presented, which allows to mitigate the sharp contact between the spinal rod 7 and the edge of the groove 25 of the head 22 of the pedicle screw 12, as shown in FIG. 1C, and can create a sharp contact edge angle of 90° at the cylindrical outer surface of the screw head at the contact point CP2 when the spinal rod 7 is at an angle to the head 22. As shown in FIGS. 6A and 6B, the screw head 321 has a groove 325 with a non-sharp edge 327 at the interface between the outer cylindrical surface of the screw head 321 and the semi-cylindrical surface formed by the groove 325, since a curvature along the radial extension of the groove 325 is provided, for example, by a radius R3. For example, the radius R3 can correspond to or be larger than the diameter of the screw head 321. This allows the edge angle of edge 327 to be reduced, for example to form an edge angle of 100° or more.

[0034]

[0039] In this arrangement, when the spinal rod 7 is at an angle to the head 321, the contact point between the rod 7 and the groove 325 can be somewhere on the outer area OA3 or the inner edge area EA3, which are radially curved with a radius R3, as shown in FIG. 6B, instead of on the edge 327, the outer area OA3 being defined as the radially outer area of ​​the groove 325 of the head 322 at the edge 327, and the inner edge area EA3 being defined as the radially inner area of ​​the groove 325 at the inner edge 329. This also reduces the offset distance OD2 between the rod 7 and the contact point CP2, which is now near the axis HA2, as defined in FIG. 1C. The radius curvature R3 can be arranged such that at the inner edge 329 the edge angle is 90°, in other words the tangent to the surface EA3 at the edge area 329 is perpendicular to the central axis HA2 of the screw head 322. In a variant, the edge region EA3 is flat when viewed in cross section, which means that it forms a semi-cylindrical surface, perpendicular to the central axis HA2 of the screw head 322, and the curvature of the radius R3 starts in the outer region OA3. This makes it possible to provide a semi-cylindrical contact surface for contacting the rod 7 when it is perpendicular to the central axis HA2. As another variant, the radius R3 gradually increases with increasing radial distance, for example so that the radius R3 of the outer region OA3 is greater than the radius R3 of the edge region EA3. For example, the radius R3 at the outer edge 327 of the outer region OA3 can be such that the edge angle at the edge 327 is greater than 120° or greater than 135°.

[0035]

[0040] In the variant shown in FIG. 6A, the bone anchor 42 and the head 322 are arranged as a polyaxial screw that can be blocked as a pedicle screw 312. The upper connecting element or head 44 of the bone anchor 42 and the groove 325 are arranged in such a way that in any possible angular position of the bone anchor 42 relative to the screw head 322, the bone anchor cannot contact the spinal rod 7. This is done by maintaining a minimum distance OD5 between the heads 44 of the bone anchors 42 that is not zero. In the variant shown, the imaginary spherical surface formed by the partly spherical heads 44 of the polyaxial bone anchor 42 does not reach or otherwise protrude beyond the height defined by the inner edge 329 of the edge area EA3. If a monoaxial screw is used, the distance OD4 is preferably greater than 0.

[0036]

[0041] It is also possible that the lower part of the screw head 322 includes additional elements, for example an additional seat, ring or compression element 326 for engaging the head 44 of the bone anchor 42 placed in the groove 325, as shown in Figs. 3D, 5A, 5B with sharp edges and in cross section in Fig. 6C. For example, such pedicle screws capable of blocking polyaxiality by such mechanisms are described in US Pat. Nos. 5,882,350, 6,113,601 and 6,660,004, which references are incorporated herein by reference in their entirety. Another variation is the Medtronic™ CD Horizon Solera pedicle screw system that allows such blocking, having a blocking ring or seat that biases against the spherical head of the pedicle screw. Downward pressure of the set screw 3 against the spinal rod 7 on the element 326 blocks the angular position between the bone anchor 42 and the head 322. In such a variation, the surface of the screw head 322 forming the spinal rod-facing side of the groove 325 and the surface of the seat facing the spinal rod 7 can be continuously trimmed, for example, so that the surfaces are flush with one another, are substantially semi-cylindrical, and have a curvature in radial extension from the central axis HA2 as described above, ensuring that there are no sharp edges facing or otherwise contacting the spinal rod 7, even if the spinal rod 7 is at an angle to the axis HA2. For example, the surface of the element 326 can have a flat surface, as seen at edge 329 in the cross-sectional view of FIG. 6C, and then curve in the medial-lateral section toward edge 327 so that when the spinal rod 7 presses down on the element 326, for example, in compression, the surface of the U-shaped groove 325 facing the rod 7 and the surface of the element 326 facing the rod 7 are continuous, such that the radius of curvature of the edge of the element 326 matches the adjacent area of ​​the surface of the U-shaped groove and the surfaces are aligned with one another.

[0037]

[0042] Although the present invention has been disclosed with reference to certain preferred embodiments, numerous modifications, variations, and changes to the described embodiments, and their equivalents, are possible without departing from the scope and spirit of the present invention. Accordingly, it is intended that the present invention not be limited to the described embodiments, but rather be accorded the broadest reasonable interpretation in accordance with the language of the appended claims.

Claims

1. a set screw for threadably engaging a head of a pedicle screw for retaining a spinal rod, said set screw having a spinal rod opposing side and a set screw driver opposing side; an opening on the opposite side to the set screwdriver for engaging with the set screwdriver; a convex surface facing the spinal rod, the apex of the convex surface being substantially aligned with a rotational center axis of the set screw; A set screw.

2. 2. The set screw of claim 1, wherein the radius of curvature of the convex surface is smaller at the central axis of the set screw compared to the radius of curvature of the convex surface in a peripheral region of the central axis.

3. The set screw of claim 1 , wherein the convex surface is an integral part of the set screw, the convex surface being configured to directly engage a surface of the spinal rod.

4. 2. The set screw of claim 1, wherein the convex surface of the set screw is hardened relative to the body of the set screw.

5. 10. The set screw of claim 1, wherein an entire surface of the set screw facing the spinal rod defines a convex volume.

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