Patent Description:
The present invention relates to orthopedics and more precisely to orthopedic tools and systems including pedicle screws, rods and corresponding set screws. The invention also relates to instruments which are used for manipulating these elements.

In the field of orthopedics and implant tools and systems for orthopedic surgery, more specifically spinal fusion surgery for a spinal column, set screws are used to push down and attach a rod-type or bar-type device to a head of a pedicle screw. The process of pushing down the spinal rod towards and into the head of pedicle screw is also called rod reduction. Before attaching the rod to the head of the pedicle screw, the pedicle screw is attached to a vertebrae with a bone anchor, threaded bone-engaging part or bone screw for fastening the pedicle screw to the vertebrae of a patient or living being. For this purpose, as an example, for several adjacent vertebrae for vertebrae fusion, for each vertebra a pedicle screw is attached thereto, and thereafter, several pedicle screws are mechanically fastened towards each other by the use of the rod that is placed in a groove or U-shaped opening that is formed by the pedicle screw head, forming a row of pedicle screws in the spine. This allows to provide for the mechanical support needed for spinal stabilization for spinal fusion in a patient or living being.

For example, <CIT> describes an orthopedic implant kit that provides for a pedicle screw, a corresponding set screw, a rod, and the tools to operate these, 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, <CIT> describes another type of kit orthopedic surgery system for surgical intervention for spinal stabilization, including pedicle screw with a head for receiving a rod, and tools necessary for the surgical intervention. In yet another example, <CIT>, provides for a system and method for delivering a spinal connector spinal anchor sites in a spinal column. In one embodiment, a spinal implant and access device is provided that includes a U-shaped receiver member, a bone-engaging member, an extension member, a spinal rod, and a set screw.

Similar orthopedic spinal surgery concepts, tools and devices have been proposed as discussed above, for attaching a rod to a pedicle screw via a set screw, for example <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>.

<CIT> relates to polyaxial bone anchors that include a retainer for holding a shank within a receiver, the retainer being in at least two discrete pieces and cooperating with a variety of inserts, some of which independently lock the polyaxial mechanism.

<CIT> relates to a set screw for uses with spinal implants to attach an elongated member to a bone. The set screw has a body with a lower portion. An external thread is on the lower portion wherein at least a portion of the external thread is on the lower portion wherein at least a portion of the external thread has a variable pitch. The set screw will engage a receiver member by a predetermined longitudinal distance before encountering the variable pitch of the external thread on the set screw. A pre-selected torque value for seating the set screw is achieved at this predetermined longitudinal distance of thread engagement by the set screw into the receiver member.

European Pat. No. <CIT>, also published as <CIT>, relates to a pedicle screw fixation system. A locking mechanism for locking a rod in a screw and rod fixation assembly includes a cap having a sidewall and a locking element extending from at least a portion of the sidewall. Locking mechanism cooperates with a receiver component for a spinal fixation rod to lock the rod in the receiver without requiring application of torque.

<CIT> relates to an implant for insertion on or into a bone of a patient and for receiving a rod member in an open channel formed between two arms of a head thereof. A closure for closing the channel and capturing the rod in the open channel. The closure included an axially projecting dome that is positioned to engage and abut against the rod in use. The closure also includes guide and advancement structure that joins with mating guide and advancement structure in the bone screw head.

European Pat. No. <CIT>, also issued as <CIT>, relates to a fixing device for a surgical anchor member. The fixing member comprises a control device connected to a connecting portion in turn connected to a shaft having, at one of its ends, coupling units for connecting the fixing device with a fastening element adapted to be coupled in a respective fastening seat of a surgical anchor member. The device further comprises centring means for coupling the fastening element with the respective fastening sear of the surgical member.

However, the state of the art tools still present specific problems when a surgeon or operator of the spinal surgery tools needs to attach the rod to the pedicle screw by means of the set screw, that are due to misalignment of the spinal rod relative to the pedicle screw head. Therefore, despite all of the solutions currently proposed in the state of the art related spinal surgery tools, strongly improved methods, systems and devices for spinal surgery are strongly desired.

According to the present invention, a set screw for threadable engagement with a head of a pedicle screw for holding a spinal rod is provided. Preferably, the set screw has a spinal rod facing side and a set screw driver facing side, and includes an opening at the set screw driver facing side for engaging with the set screw driver; and a convex surface at the rod facing side, an apex of the convex surface substantially corresponding with a rotational central axis of the set screw.

Still, according to the present invention, a set screw for threadable engagement with a head of a pedicle screw for holding a spinal rod is provided. Preferably, the set screw has a spinal rod facing side and a set screw driver facing side, and includes an opening at the set screw driver traversing the set screw from the spinal rod facing side to the set screw driver facing side, and an annular surface at the rod facing side surrounding the opening, the annular surface being beveled or having a curved surface.

According to still another embodiment of the present invention, an orthopedic tool kit is provided, including a set screw and a set screw driver. Preferably, the set screw configured for threadable engagement with 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. In addition, the set screw includes an opening at the set screw driver traversing the set screw from the spinal rod facing side to the set screw driver facing side, and an annular surface at the rod facing side surrounding the opening. Furthermore, preferably, the set screw driver includes a shaft, and an engagement part for engaging with the set screw via the opening, wherein in an engaged position, a frontal portion of the engagement part is protruding from a spinal rod facing side of the set screw.

According to an example, a pedicle screw is provided, the pedicle screw having screw head with a U-shaped groove for accommodating a spinal rod. Preferably, a lower surface facing a lower surface of the spinal rod is forming a bottom of the U-shaped groove is semi-cylindrical, and has a curvature along a radial direction, the radial direction extending away from a center axis of the screw head, to provide for a smooth surface with less sharp edges towards the spinal rod.

The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description with reference to the attached drawings showing some preferred embodiments of the invention.

The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate the presently preferred embodiments of the invention, and together with the general description given above and the detailed description given below, serve to explain features of the invention.

The present invention is defined in claim <NUM> and claim <NUM> while preferred embodiments are set forth in the dependent claims. These methods do not form part of the invention.

Herein, identical reference numerals are used, where possible, to designate identical elements that are common to the figures. Also, the images are simplified for illustration purposes and may not be depicted to scale.

<FIG> shows a cross-sectional view of several pedicle screws <NUM>, <NUM>, or other types of back surgery screws, that are engaged with individual vertebrae V1, V2 of a spine of a patient or living being, and interconnected with a spinal rod <NUM> or support rod, and are held by corresponding set screws <NUM>, <NUM>, or fastening devices. As shown on the left side of this representation, an axis of longitudinal extension RA1 of spinal rod <NUM> is substantially perpendicular to a center axis HA1 of screw head <NUM> of pedicle screw <NUM>. Moreover, the bone anchor or threaded part <NUM> of pedicle screw <NUM> also defines a center axis SA1, that can coincide with center axis HA1 of screw head <NUM> in case of a mono-axial configuration, or can be different from center axis HA1 of screw head <NUM> in case of a poly-axial configuration. For illustration purposes, pedicle screw <NUM> is in a mono-axial configuration, but it is also possible to use poly-axial screws. <FIG> shows a cross-sectional view along axis of longitudinal extension RA1 of spinal rod <NUM>, depicting the U-shaped groove <NUM> or other type of cavity, opening, trench, depression, or mechanism in screw head <NUM> for accommodating spinal rod <NUM>. Screw head <NUM> has an internal threading <NUM> that is complementary or corresponding to an external threading of set screw <NUM>, <NUM>, so that the set screw <NUM>, <NUM> can threadably engage and be tightened relative to screw head <NUM>.

As shown on the right side of <FIG>, at least at some sections along the spinal rod <NUM>, it is possible that orientation of spinal rod <NUM> relative to screw head <NUM> is not perpendicular, for example angle α2 between axis of longitudinal extension RA2 of spinal rod <NUM> is not <NUM>° degrees or perpendicular to center axis HA2 or the thread axis of screw head <NUM> of pedicle screw <NUM>, but there is an inclination angle α2. Generally, as rod <NUM> is pre-bent before insertion and attachment to pedicle screws <NUM>, as an example, this misorientation can be a result of the bending of spinal rod <NUM> at one end, for example in case where the last pedicle screw <NUM> of a row or series of pedicle screws has the end of rod <NUM> is protruding upwards away from the spine. It is also possible that this deviation from the perpendicular arrangement is simply a misalignment between screw head <NUM> and rod <NUM> that cannot be easily corrected by the surgeon or operator, as the incision at the surgical location is not easy accessible or viewable, for example due to the minimal invasive surgical approach. Another reason for the misalignment is caused by the user, operator, or surgeon itself, when he attempts to tighten the set screw <NUM> to screw head <NUM>, via screw extender <NUM> and set screw driver <NUM>, as shown in <FIG>. While the alignment between spinal rod <NUM> and pedicle screw head <NUM> may initially be correct, the surgeon may have moved or titled the screw extender <NUM> laterally by a certain angle, and therefore has bent or moved the screw head <NUM> relative to rod <NUM>, to cause the misalignment. This is common in surgeries where the incision for the surgery is small and does not allow for an easy view of the pedicle screws <NUM>, <NUM> and rod <NUM>.

As a result thereof, when the surgeon or operator attaches spinal rod <NUM> to pedicle screw <NUM> with the set screw <NUM>, there are several problems that can arise. This is illustrated in on the right side of <FIG>, and further detailed in <FIG>, showing a schematic cross-section view of a screw extender <NUM> attached to pedicle screw <NUM>, where the set screw driver <NUM> is threadably engaging with inner threaded portion <NUM> of the screw extender <NUM>, the screw extender <NUM> attached to screw head <NUM> with engagement part <NUM>, to screw in the set screw <NUM> to lower the rod <NUM> into the U-shaped groove <NUM> provided by screw head <NUM>. As shown in <FIG>, angle α2 between axis of longitudinal extension RA2 of spinal rod <NUM> is not <NUM>° degrees or perpendicular to center axis HA2 of screw head <NUM> of pedicle screw <NUM>, but for illustration purposes in a range between <NUM>° and <NUM>°. Upon tightening set screw <NUM> within screw head <NUM> by set screw engagement part <NUM> of set screw driver <NUM>, in the variant shown a shaft that is in threadable engagement with an internal thread <NUM> of the screw extender <NUM>, an edge of the set screw <NUM> will contact an upper, outer surface point of spinal rod <NUM>, forming a single contact point CP1. Would the alignment be perpendicular, i.e. α2 = <NUM>°, a full front flat surface <NUM>, <NUM> of set screw <NUM>, <NUM> would come into contact with upper, round outer surface point of spinal rod <NUM>, forming a line of contact, and not a singular contact point CP1. This is shown on the left side of <FIG>, with pedicle screw <NUM>. This contact point CP1 will also be off-axis of the center axis HA2 of pedicle screw head <NUM>, by a distance OD1. The bending or misalignment of spinal rod <NUM> can be such that this contact point CP1 may be the only substantial mechanical contact point that acts on rod <NUM>, other than a minor lateral support contact by side walls of U-shaped groove <NUM>. In addition, due to the misalignment, in addition or alternative to contact point CP1, at the opposite lateral side of screw head <NUM>, spinal rod <NUM> will contact an edge of one end of the U-shaped groove <NUM>, to form a semi-circular contact line or arc CP2, instead of rod <NUM> being embedded in the semi-cylindrical lower surface of U-shaped groove <NUM>. This contact line CP2 will also be offset from the center axis HA2 of head <NUM> of pedicle screw <NUM>, by a distance OD2.

As the spinal rod <NUM> is held in place by several other pedicle screws <NUM>, <NUM> and corresponding set screws as shown in <FIG>, the tightening of set screw <NUM> with respect to screw head <NUM> may not provide enough compression or bending force to bend spinal rod <NUM> into a perpendicular arrangement with respect to screw head <NUM>, for example to realign it by pressing rod <NUM> against U-shaped groove <NUM>, as the spinal rod <NUM> is generally very stiff. In addition, this misalignment will causes stress onto one or more vertebra V2 that are affected by the misalignment via pedicle screw <NUM> and its bone anchor, and create lateral forces to the vertebra V2, as these can only move relative to other vertebra by a limited range. Also, in case a poly-axial pedicle screw <NUM> is used, the angular range of screw head <NUM> by axis HA2 relative to anchor <NUM> by axis SA2 may be not sufficient and is mechanically blocked to be able to compensate for the misalignment between rod by axis RA2 to screw head <NUM> by axis HA2, creating additional mechanical stress to affected vertebra V2.

The resulting undesired limited contact surface or region between rod <NUM> and screw head <NUM>, either by contact point CP1 at an lower edge of flat surface <NUM> of pedicle screw <NUM> with a point of the cylindrical surface of rod <NUM>, or by contact point or arc CP2 at the opposite lateral side of screw head <NUM>, for example by a semi-circular arc along an edge of U-shaped groove <NUM>, can lead to several problems.

First, due to the offset between the central axis of screw head HA2, for example by offset distance OD1 or offset distance OD2, this attachment situation will lead to a lateral undesired torque that is applied to bone anchor or threaded part <NUM>, that in turn will create lateral tensions to the bone structure of vertebrae V2 of patient or living being. Any upward or downward pressure or movement that is exerted on spinal rod <NUM>, for example in parallel or substantially in parallel to axis HA2, will lead to a lateral pressures of bone anchor <NUM> to vertebrae V2, as indicated by the arrows shown on the right side of <FIG> showing vertebrae V2. For example, post-surgery, bodily movements of the patient or living moving could cause such pressures or motions to spinal rod <NUM>, which will lead to strong lateral tensions to vertebrae V2 via bone anchor <NUM>.

Second, the limited surface area of the contact points CP1, CP2, or both, can lead to undesired cold welding, that could even happen during the surgical operation. Such cold welding attachment could block further attachment or threading of set screw <NUM> relative to screw head <NUM>, and would prevent from properly attaching rod <NUM> to pedicle screw <NUM>.

Third, the pressure caused offset distance OD1 or offset distance OD2 that is not in axis with central axis of screw head HA2 could lead to a blocking of set screw <NUM> inside screw head <NUM>, when an user, operator, or surgeon is tightening the set screw <NUM> with set screw driver. The generation of a pressure that is off-axis of HA2 will lead to different and non-asymmetrical lateral pressures to set screw <NUM> to the threaded part of screw head <NUM>, that could lead to a blocking of set screw <NUM> inside screw head <NUM>. This in turn can lead to damage of the threads that can further block the set screw <NUM> to the screw head <NUM>, and/or create additional undesired friction between the rotational threadable engagement between set screw <NUM> and screw head <NUM> that could lead to potential cold welding. A similar cold welding problem can arise with some of the state of the art set screws that show pointed tips that permit additional grip to the rod, for example as shown in <CIT> or <CIT>.

<FIG> show different exemplary cross-sectional views of a set screw <NUM>, to alleviate the problems described above. As shown in <FIG>, showing a cross-sectional and frontal view of set screw <NUM>, set screw <NUM> does not have a flat surface <NUM> that faces the rod <NUM>, but has a frontal surface or face FF forming a convex shape and circular-symmetrical around axis HA2. In the variant shown, and as illustrated in more detail in <FIG>, a central area or inner area IA of frontal face FF forms a first surface <NUM> with a curvature having a first radius R1, the curvature being defined in a radial direction of the cylindrical shape of the set screw <NUM>, and an outer area or annular surface ring OA of frontal face FF forms a second surface <NUM> having a second curvature having a second radius R2, and an edge area <NUM> or annular surface ring edge area EA having a flat but beveled edge. Moreover, the rod <NUM> is shown to have a cylindrical smooth surface with no indentations or notches. Preferably, the inner area IA has more curvature than the outer area OA, e.g. the first radius is smaller than the second radius, but it is also possible that IA and OA form a continuous spherical surface with the same radius R1 = R2. In a variant, starting from a central point or center of the front surface, for both inner area IA and outer area OA, the radius change of frontal face FF is progressive, i.e. it is the smallest at the center, and progressively changes to a larger radius towards the edge, for example by following an elliptic shape when seen from a cross-sectional view, in other words a shape of an ellipsoid, with the vertex of the ellipsoid located at the rotational center of frontal face FF. In another variant, the entire frontal face FF including areas IA, OA, and EA are spherical, and the slope of the edge area EA is chosen to fit the flanks or thread angle of threading <NUM> of the set screw <NUM>. In another variant, for both the inner area IA and outer area OA form a spherical surface for frontal face FF, with a constant radius of curvature, but still having the beveled circular outer edge EA for the threading <NUM>. With this arrangement of frontal face FF of set screw <NUM>, showing a continuous convex or protruding bulge along an entire diameter of set screw <NUM>, covering circular inner area IA, annular outer area OA, and annular edge area EA, it is also possible to avoid any sharp edges, for example edges that are formed by two surfaces arranged perpendicularly which lead to an edge angle of <NUM>°, that could cut in or otherwise damage a surface of the spinal rod <NUM>, even if spinal rod <NUM> is arranged at an oblique angle relative to screw head <NUM>. In this respect, an entire surface of the spinal rod facing side of the set screw <NUM> forms a convex volume that protrudes from a surface that is perpendicular to the thread axis of set screw. The only sharp edges of set screw <NUM> of <NUM>° or less are arranged on the side walls of set screw <NUM> with the crests of the threading <NUM>, but these are such that they do cannot come into contact with spinal rod <NUM> when set screw <NUM> is threadably engaged with head <NUM>.

Preferably, the radii R1, R2 of the curvature is more than a radius of the set screw of pedicle screw <NUM>, and preferably, about the half of the diameter of an outer cylindrical surface of screw head <NUM> of pedicle screw <NUM> or the diameter of set screw <NUM>, ± <NUM>%, more preferably at least two (<NUM>) times the radius of screw head <NUM> or more, or at least two (<NUM>) times the diameter of set screw <NUM>. Smaller radii are possible, but would lead to set screws that are thicker and would require more space inside the body of the patient or living being. The edge area EA preferably does not have a curvature, but is beveled or otherwise shaped to match the flank of the threading <NUM> of the set screw <NUM>, to be able to keep the set screw <NUM> as thin as possible with respect to thickness TH, when viewed along the axis HA2, for example by an angle of <NUM>°. Moreover, set screw <NUM> has an opening <NUM> or other type of releasable attachment or engagement mechanism for engaging with corresponding or complementary engagement part <NUM> of set screw driver <NUM>. In the variant shown, a hexagonal socket head for opening <NUM> is provided, but different types of releasable attachment or engagement mechanism between set screw <NUM> and screw driver are also possible, for example but not limited to filister heads, torx heads, spanner head with two or more drills, square heads, clutch heats, multiple slot heads, and with corresponding complementary engagement tools or parts <NUM> by set screw driver <NUM>. Also, set screw <NUM> is designed to keep the overall profile low, and for the set screw <NUM> this means that the thickness TH is minimized to avoid needing screw heads <NUM> that have are higher build, to minimize the space requires inside the body of the patient or living being that protrudes from the vertebrae, so that there is reduced protrusion of pedicle screw from the spine. Therefore, according to an aspect, set screw <NUM> is designed as one piece, such that the front face FF is an integral part of the set screw <NUM> that is made of one piece of material, without any moving parts attached or otherwise integrated thereto, having the convex front face FF. Also, a distance OS between a minor diameter of the threading <NUM> of set screw <NUM> and a diameter of outer annular area OA can be zero, such that a width of the edge annular area EA matches with the distance between the root and the crest of the thread <NUM>, but in a variant, it is also possible that the distance OS is positive such that the diameter of outer annular area OA is smaller than the minor diameter of threading <NUM>.

As shown in <FIG> depicting a side cross-sectional view with frontal surface FF set screw <NUM> engaging with an obliquely arranged spine rod <NUM> relative to screw head <NUM>, in other words an angle α2 between axis RA2 and HA2 is not <NUM>°. This lead to a contact point CP3 that is much approached to the central axis HA2 of the screw head <NUM>, to an offset distance OD3. Comparing to the contact point CP1 shown in <FIG>, the distance could be reduced by a factor <NUM> (three), given that misalignment angle α2 is substantially the same. This will lead to a strong reduction by a factor <NUM> (three) of unwanted lateral torques that are applied to bone anchor <NUM> to vertebra V2, upon movement of spinal rod <NUM> along axis HA2.

Moreover, as a surface of frontal face FF of set screw <NUM> has a curvature that will engage or abut against spinal rod <NUM>, which has an outer surface that is also curved and has the shape of a cylinder, a contact surface at contact point CP3 will be substantially larger than a contact surface formed by contact point CP1 the sharp edge of set screw <NUM>, in the variant shown by an edge angle of <NUM>° or less, as there will be certain amount of deformation of an area of contact of spinal rod <NUM> and frontal face FF of set screw <NUM>. This can reduce or even entirely eliminate the problems of cold welding at the contact point CP3. In addition, as shown in <FIG>, an edge of set screw <NUM> will be turned or rotated against the cylindrical surface of spinal rod <NUM>, when a user, operator, or surgeon turns the set screw <NUM> via set screw driver <NUM> relative to screw head <NUM>. Thereby, the edge will act like a knife and can provide for a cutting action by cutting a groove into spinal rod <NUM> with edge, to thereby damage an outer surface of spinal rod <NUM>. As in the variant shown in <FIG>, a curved surface, frontal face FF of set screw <NUM>, is turned against another curved surface, cylindrical surface of rod <NUM>, this cutting can be entirely avoided. Frontal face FF of set screw <NUM> can also be hardened or coated with a hard surface, to provide for additional hardness relative to its body, for example but not limited to the use of a chrome-cobalt alloy or anodization. Materials used to manufacture set screw <NUM> can be the usual materials used for implant devices, for example but not limited to titanium, different types of titanium alloys with different grades, stainless steel, CrCoMo.

According to the present invention, as shown in <FIG>, a set screw <NUM> is provided that has a traversing opening or through hole <NUM> that fully traverses or crosses through a center axis of set screw <NUM>, at least a part of the opening <NUM> serving as an engagement mechanism to engage with set screw driver <NUM>. In addition, according to another aspect of the present invention, the engaging tool or mechanism <NUM> of set screw driver <NUM> is dimensioned to slightly protrude outside of front face FF of set screw <NUM> by engaging tool <NUM> traversing the opening <NUM>, when fully engaged with set screw <NUM>, by a distance DD from the outermost point of the set screw <NUM>. For example, the distance DD can be in a range between <NUM> and <NUM>, more preferably between <NUM> and <NUM>. For example, as shown in <FIG>, the engagement tool <NUM> of set screw driver <NUM> is shown to be fully engaged with set screw <NUM>, which means engagement tool <NUM> is blocked or otherwise mechanically prevented from being further introduced or traversing the set screw <NUM>. , for example with an abutment surface <NUM> of set screw <NUM>, and a corresponding surface or abutment ledge or other mechanical means on set screw driver <NUM>. Other types of mechanical arrangement can be used to limit the penetration of set screw driver <NUM> relative to set screw <NUM>. In this engagement position, a front tip surface <NUM> of engagement tool <NUM> slightly protrudes outside of set screw <NUM> by a distance DD, taken the highest or most protruding point of the front face FF of set screw <NUM>, being the circular edge <NUM>, as illustrated in <FIG>. In addition, in this fully engaged position between set screw <NUM> and tool <NUM>, a distance between set screw <NUM> and tool <NUM> is set such that an outer threading <NUM> of set screw <NUM> and an outer threading of set screw driver <NUM> are aligned with each other to form a common virtual threading spiral line, in other words both threads or threadings will be aligned such that the threading pitch matches, as indicated in <FIG>, so that set screw <NUM> and tool <NUM> can be both together be moved by rotative threadable engagement through inner thread <NUM> of screw extender <NUM> without adjusting a position between set screw <NUM> and tool <NUM>. Analogously, which the full insertion of screw extender <NUM> with head <NUM>, inner thread of screw head <NUM> will match a distance to inner thread <NUM> of screw extender to provide for a continuous virtual threading spiral line.

In this embodiment, front face FF of set screw <NUM>, as shown in <FIG> and <FIG>, defined as the front face FF that will be facing and engaging with spinal rod <NUM> includes an annular ring section <NUM> that is not flat, in other words, not perpendicular to a central or rotational axis of set screw <NUM>, but forms a slope towards an outer edge of set screw <NUM> in a radial direction away from the central axis, and preferably also has a curved or spherical surface with a curve or sphere radius, also when seen in a radial direction, as can be seen in <FIG>. In this variant, front face FF includes a circular edges <NUM> that forms the portion of set screw <NUM> that is the most forwardly protruding or outermost part of set screw <NUM>, and a radially outermost beveled annular edge <NUM> that forms part of the threading of set screw <NUM>. A slope or inclination angle of annular edge <NUM> that forms part of the threading is larger or steeper, for example <NUM>°, than a slope or inclination angle of a tangent that is placed on annular ring section <NUM>, for example in a range between <NUM>° and <NUM>°, as indicated by the dashed lines of <FIG>. In the variant where annular ring section <NUM> is annularly curved or has a spherical shape, a curvature or sphere radius is preferably more than half of the outer cylindrical diameter of screw head <NUM> or the outer diameter of set screw <NUM>, ± <NUM>%, more preferably at least two (<NUM>) times the radius of screw head <NUM> or more, or at least two (<NUM>) times the radius of set screw <NUM>.

As of another variant, annular ring section <NUM> is flat, in other words a surface that defines the extension of the flat annular ring section <NUM> is perpendicular to a central axis of set screw <NUM>. This embodiment allows to avoid edge contact points CP5 as shown in <FIG>, and instead a linearly and radially extending portion of flat surface of ring section <NUM> can contact rod <NUM>, in a direction that is parallel to the extension of rod <NUM>. For example, upon making contact with tip of tool <NUM> with contact point CP4 at rod <NUM>, as a result of the threading action of set screw <NUM> by tool <NUM> as a set screw driver as shown in <FIG>, tool <NUM> is pushed out from set screw <NUM>, by the force P, as shown in <FIG>, and with the additional threadable engagement of set screw <NUM> with internal threading <NUM>, instead of small contact points CP5, the flat surface of annular ring section <NUM> will make a contact line CL with rod <NUM>, given that rod <NUM> lies substantially parallel to an axis of lateral extension of U-shaped groove <NUM> of screw head <NUM>. Such set screw <NUM> with a flat annular ring section <NUM> could be used in the cases where the rod <NUM> does not lie obliquely inside U-shaped groove <NUM> but is somewhat perpendicularly arranged to the screw, as shown in <FIG> and <FIG>. This can be in contrast to the use of a beveled, curved or spherically-shaped annular ring section <NUM> (non-flat) of set screw <NUM>, used in a case where rod <NUM> lies obliquely to the U-shaped groove <NUM>, as visualized in <FIG>. These two different types of set screws <NUM> allow a surgeon or operator to selectively choose flat-faced or non-flat faced screws depending on an orientation of rod <NUM> inside U-shaped groove <NUM> of screw head <NUM>.

As can be seen in <FIG>, <FIG>, and <FIG>, when set screw driver <NUM> is fully engaged with set screw <NUM>, an apex point of tip <NUM> is protruding from outermost edge <NUM> of frontal face FF of set screw <NUM> by a distance DD. In addition, a front tip face <NUM> itself is curved, for example it can be spherical, can form part of ellipsoid, or can be progressively curved with a smaller curvature radius at an inner central section, and having a larger curvature angle at an outer annular section. As shown in <FIG> and <FIG>, with this arrangement, an circular edge that is formed between front tip face <NUM> and side walls of engagement tool <NUM> lies within the opening <NUM> of set screw <NUM>, and this can serve to avoid the contact of a sharp edge with spinal rod <NUM>. As shown in <FIG> and <FIG>, with this arrangement, an orientation of spinal rod <NUM> expressed by its longitudinal axis RA2 with respect to screw head <NUM> and central axis HA2 can vary within a certain angular range, and the contact point CP4 made between set screw <NUM> and set screw driver assembly <NUM> will be between front face tip <NUM> and a surface point of spinal rod <NUM>. No contact will be made between front face FF of set screw <NUM> and spinal rod, while the user or operator is tightening set screw <NUM> with set screw driver <NUM>, given that RA2 and HA2 remain within a certain angular range, for example front face FF and front tip face <NUM>, as well as protrusion depth of engagement tool <NUM> of set screw driver <NUM> can be designed to allow for an angular variation between <NUM>° and <NUM>° of RA2 and HA2. Front tip face <NUM> of set screw driver <NUM> can be made of hardened stainless steel.

The contact point CP4 between rod <NUM> and set screw driver <NUM> allows to create a counter pressure or counter force P against engagement part <NUM> of set screw driver <NUM>, so that set screw driver <NUM> will be progressively pushed back and released from set screw <NUM>, upon the tightening of set screw <NUM> with set screw driver <NUM>, and with the progressive pushing back or release, the outermost surface of set screw, being edge <NUM>, will come into contact with spinal rod <NUM>, to form contact points CP5, as illustrated in <FIG>. As illustrated by <FIG> and <FIG>, an initial first contact that is made by front tip face <NUM> of set screw driver <NUM> with rod <NUM> with contact point CP4, while threadably tightening set screw <NUM> to screw head <NUM>. Thereafter, with the progressive release of set screw driver <NUM> from set screw <NUM> by a pushing back with force P, by the tightening action, contact between rod <NUM> and set screw <NUM> will be made with contact points CP5. This can be done as long as rod <NUM> is in initial contact with set screw driver <NUM> and not the set screw <NUM>.

This presents several advantages for an orthopedic tool kit or system that uses such set screw <NUM> with a traversing opening <NUM> and corresponding set screw driver <NUM>, as discussed above. First, it allows to make a first contact point CP4 with spinal rod <NUM> that minimizes a distance of CP4 from the central axis HA2 of screw head <NUM> of pedicle screw <NUM>, even in a case where longitudinal axis RA2 of rod <NUM> and central axis HA2 of screw head <NUM> are oblique to each other. In addition, the counter force P against engagement part <NUM> of set screw driver <NUM> allows to substantially reduce a retention force that is created between a full engagement of engagement part <NUM> with set screw <NUM>, and allows to substantially reduce a force necessary to remove set screw driver <NUM> from set screw <NUM>.

<FIG>, and <FIG> show an example, in which a screw head <NUM> for a pedicle screw <NUM> is presented, that allows to alleviate a sharp contact between spinal rod <NUM> and an edge at the groove <NUM> of head <NUM> of pedicle screw <NUM>, as illustrated in <FIG>, where a sharp contact edge angle of <NUM>° at the cylindrical outer surface of screw head can be created at contact point CP2, in a case where spinal rod <NUM> lies obliquely to head <NUM>. As shown in <FIG>, a screw head <NUM> has a groove <NUM> that has less sharp edges <NUM> at a an interface between the outer cylindrical surface of screw head <NUM> and the semi-cylindrical surface formed by groove <NUM>, as a curvature along a radial extension of groove <NUM> is provided, for example by a radius R3. For example, the radius R3 can correspond to a diameter of screw head <NUM>, or can be larger than the diameter. This allows to reduce edge angle of edge <NUM>, for example to form an edge angle of <NUM>° or more.

With this arrangement, when spinal rod <NUM> lies obliquely to head <NUM>, a contact point between rod <NUM> and groove <NUM> can be such that it does not lie on edge <NUM>, but somewhere on outer area OA3 that is radially curved with radius R3 or on inner edge area EA3, outer area OA3 defined as being the radially outer areas of groove <NUM> of head <NUM> at edge <NUM>, and inner edge area EA3 defines as being the radially inner areas of groove <NUM> at inner edge <NUM>, as shown in <FIG>. As defined in <FIG>, this will also reduce an offset distance OD2 between rod <NUM> and contact point CP2, which will now lie closer to axis HA2. The curvature by radius R3 can be arranged such that at inner edge <NUM>, the edge angle is <NUM>°, in other words a tangent to surface EA3 at edge area <NUM> is perpendicular to center axis HA2 of screw head <NUM>. In a variant, edge area EA3 is flat when seen in the cross-sectional view, which means it forms a semi-cylindrical surface, and perpendicular to center axis HA2 of screw head <NUM>, and the curvature with radius R3 starts at outer area OA3. This allows to provide for a semi-cylindrical contact surface for contact with rod <NUM> when rod lies perpendicular to center axis HA2. As of another variant, radius R3 progressively increases with an increased radial distance, for example such that radius R3 at outer area OA3 is larger than radius R3 at edge area EA3. For example, radius R3 at outer edge <NUM> of outer area OA3 can be made such that edge angle at edge <NUM> is more than <NUM>°, or more than <NUM>°.

In the variant shown of <FIG>, the bone anchor <NUM> and head <NUM> are arranged as a blockable poly-axial screw as the pedicle screw <NUM>. Top connecting element or head <NUM> of bone anchor <NUM> and groove <NUM> are arranged such that in any possible angular position of bone anchor <NUM> relative to screw head <NUM>, bone anchor cannot touch spinal rod <NUM>. This is done by preserving a minimal distance OD5 between head <NUM> of bone anchor <NUM> that is not zero. In the variant shown, a virtual spherical surface that is formed by partially spherical head <NUM> of poly-axial bone anchor <NUM> does not reach or otherwise protrude above a level that is defined by inner edge <NUM> of edge area EA3. In case a mono-axial screw is used, distance OD4 should be bigger than zero.

Claim 1:
A set screw (<NUM>) for threadable engagement with a head of a pedicle screw for holding a spinal rod, the set screw (<NUM>) having a spinal rod facing side and a set screw driver facing side, comprising:
an opening (<NUM>) at the set screw driver facing side entirely traversing the set screw (<NUM>) from the spinal rod facing side to the set screw driver facing side, the opening (<NUM>) including an engagement mechanism for engaging with a set screw driver (<NUM>) for threadably tightening the set screw (<NUM>) to a pedicle screw; and
an annular surface (<NUM>) at the rod facing side surrounding the opening (<NUM>).