Patent Description:
The present patent application describes surgical methods that use bone screws that can be attached to a bone, for example vertebra, and methods, devices, and systems for tightening or fastening a bone screw to a bone. The surgical methods are described to aid understanding the invention.

In the field of surgery where a surgeon or operator needs to attach or fasten a bone screw to a bone, for example for securing or fastening a bone, bone fragments, or different bones together, for example via a surgical incision to a living organism, often a first axis defined by an extension of the bone anchor part of the bone screw and a second axis defined by the screw driver of the fastening tool will become misaligned. Ideally, in case the screw head and the bone anchor of the bone screw are monoaxial, the first and the second axis should be maintained in axis with each other. The misalignment is usually the result of the poor view that a surgeon or operator has to the surgical site, or the very limited or non-existing view to the actual axis that the bone anchor has taken inside the bone. The misalignment can force the first axis of the bone anchor of its initially desired positioning and axis, thereby moving the bone out of the initial position. This can lead to problems of parasitic lateral torques, strains or stresses between the bone anchor of screw head, and the bone, that can remain even after a surgery. Also, surgeons tend to apply strong torques to the fastening tool whilst the first axis and the second axis are misaligned, so that the lateral strains are exacerbated.

For example, in the field of orthopedic surgery, <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 threadably tightening the set screw relative to screw head of pedicle screw. With this toolkit, it is possible that the threaded part of bone screw is fastened to a bone, e.g. vertebra, and as a connection between screw driver and screw head can be very rigid, any tightening of the bone screw out of the originally-defined first axis will lead to lateral strain that the bone will be subjected too. In addition, while an orientation of the screw head can be given by the orientation of the rod that is placed inside a groove of screw head, and ideally the rod should be arranged perpendicular to the axis defined by the screw head, by misaligning the axis defined by a set screw that is holding the rod inside the groove, for example with the set screw driver, the screw head can be subject to undesired lateral strains that will lead to a strain applied to a bone to which the bone screw is fastened to. These undesired lateral strains can lead to substantial problems post-surgery, and can be felt as chronic pain by the living being post-surgery, and can also lead to improper healing of the bone structures affected by the surgery. The lateral strains can also lead to overloading of implants which can in turn lead to material failures or implant loosening, for example post-surgery.

Therefore, there is a strong need for substantially improved solutions for providing bone tightening systems and orthopedic implant kits to surgeons, physicians, laboratory operators, in light of the above-discussed deficiencies. In addition, there is a strong need for providing tools or devices that can measure an axis of orientation of a bone fastening rod relative to a central axis of a head of a pedicle screw.

<CIT> discloses devices, systems, apparatus and methods for accessing the cervical spine via an anterior approach and implanting a spinal fixation member between two vertebrae of the cervical spine in the disc or intervertebral joint space, such as in an ACDF procedure. The delivery device includes a distal end that can be anchored to the spinal fixation member. Once anchored to the spinal fixation member, the delivery device is operable to both advance and attach the spinal fixation member within a cervical disc joint space.

<CIT> discloses a spinal implant that is configured for midline insertion into a patient's intervertebral disc space. The spinal implant may include structural guidance features to facilitate the angular approach of fixation elements into the apertures. The spinal implant may also be a configured with a tactile or visual feedback response feature to allow the user to know when the fixation elements are fully seated within the apertures.

<CIT> discloses an adaptable gripping device that is notably for operating the end of a screw. The device comprises a part mounted with limited sliding capability at the tip of the end of the operating device. The part has internal arrangements adapted to assure the temporary coupling of the head of the screw, in combination with the end. The part is adapted to be retractable for freeing, in a similar manner, the head of the screw.

<CIT> discloses a minimally invasive system including a bone screw and a tissue retractor having distal and proximal end portions and a partial pathway therebetween. The tissue retractor is removably couplable to the bone screw. An instrument has distal and proximal end portions and a hollow cavity and is removably couplable to the tissue retractor. A drive shaft has a diameter less than a diameter of the hollow cavity and is rotatable with respect to the instrument. A counter-torque handle has gripping and an interlock end portions with an instrument interface releasably positioned within the hollow cavity at the proximal end portion thereof and rotatably fixed thereto in an assembled configuration. The interlock end portion also includes an open-ended slot having a width greater than the drive shaft diameter such that the counter-torque handle is movable to and from the assembled configuration while the drive shaft is within the hollow cavity.

The present invention concerns a bone screw tightening device according to claim <NUM>. Other advantageous features are found in the dependent claims.

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.

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 first representation showing the problem that can be caused by a parasitic strain S2 that is present between bone anchor <NUM> of bone screw <NUM>, for example when a surgeon or operator tightens screw <NUM> to bone V, for example via handles <NUM>, <NUM> and screw driver <NUM>. Specifically, in this variant, bone screw <NUM> may be a mono-axial screw where head <NUM> and bone anchor <NUM> are fixed to each other, and always have the same orientation relative to each other. In this respect, they are oriented along an axis HA1. Next, screw driver <NUM> is removably engaged with screw head <NUM> with engagement part <NUM>, and has an axis of longitudinal extension HA2. Screw head <NUM> is placed inside a surgical incision SI that allows to access screw head <NUM>. It is possible that operator or surgeon does not retain the axis of screw driver <NUM> HA2 in axis HA1 of bone screw <NUM> by an out of axis movement S1. As the connection between screw driver <NUM> and screw <NUM>, in this variant, does not allow for an angular change between HA1 and HA2, the movement S1 will cause strain S2 between bone anchor <NUM> of screw <NUM>, or will move bone V from its desired position, out of the orientation defined by axis HA1.

<FIG> shows a second representation showing the problem that can be caused by an operator or surgeon, specific to an orthopedic fixation system, where a pedicle bone screw <NUM> has already been fixed to a vertebra V by bone anchor <NUM>, for thereafter fixing adjacent vertebrae via pedicle bone screw <NUM> with a rod <NUM>. The problem can be caused when rod <NUM> is affixed or tightened to screw head <NUM> of pedicle screw <NUM> by a set screw <NUM> that can threadably engage with head <NUM>, and has a groove for accommodating rod <NUM>. In this situation, the pedicle screw <NUM> is a poly-axial or multi-axial screw, where head <NUM> and threaded part or bone anchor <NUM> can take different angular positions relative to each other, due to joint, engagement, or orientation mechanism <NUM>. In this representation, exemplarily bone anchor <NUM> and head <NUM> are shown to be aligned in the same axis, for example HA1 being equal to HA2, but these axes can also be oblique to one another, as a poly-axial screw is used.

For example, inside the surgical incision SI, when tightening set screw <NUM> to screw head <NUM>, rod <NUM> having an axis of orientation RA2 can be arranged non-perpendicularly to axis HA2 that is defined mainly by the orientation of screw head <NUM>. Due to the connection between screw head <NUM> and screw extender <NUM>, and screw driver <NUM> for set screw <NUM> via set screw <NUM>, screw driver <NUM> will have the same axis HA2. Once set screw <NUM> is tightened, and the axis HA2 and RA2 are not perpendicular to each other, as exemplarily shown in <FIG>, this can cause strain S1 to screw head <NUM> that will translate to strain S2 to vertebrae V, as rod <NUM> will abut against a side of groove of screw head <NUM>, and will not lie properly inside groove. As discussed above, in this variant, screw head <NUM> may be freely orientable relative to bone anchor <NUM> with an orientation mechanism <NUM> thereby forming a poly-axial screw, such that axis HA1 of bone anchor <NUM> and axis HA2 of screw head <NUM> may not coincide.

Due to the limited view provided by surgical incision SI to surgeon or operator, and in some cases the oblique position of axis RA1 rod <NUM> relative to an extension of the spine, it is possible that screw head <NUM> and its orientation HA2 cannot be oriented properly relative to rod <NUM> without additional help, to be ideally arranged perpendicular to RA2. Once set screw <NUM> is tightened, usually the poly-axiality of pedicle screw <NUM> is lost, and for this reason screw head <NUM> may not automatically orient itself perpendicularly to rod <NUM> simply by tightening set screw <NUM> to screw head <NUM> by set screw driver <NUM>. Accordingly, a device, system or method is desired that can measure the orientation of rod <NUM> relative to screw head <NUM> during the surgical procedure, so that the surgeon or operator can properly orient screw head <NUM> to be perpendicular or substantially perpendicular to rod <NUM>, before tightening set screw <NUM> to head <NUM>, for attachment of rod <NUM> to pedicle screw <NUM>.

According to the present invention, as shown in <FIG> in a side view and schematic exemplary fashion, a screw driver <NUM> can be used that has one or more universal joints UJ1, UJ2, and a screw extender <NUM> can be used for removable attachment to a screw head <NUM> of a bone screw <NUM>. An exemplary universal joint UJ is shown in <FIG>. This may be a way to limit any parasitic lateral torques to screw head <NUM> and also to bone anchor <NUM> (threadbare part) by screw extender <NUM> and set screw driver assembly <NUM>. The mechanics set up would use two different universal joints (UJ1 and UJ2) and a simple joint (SJ1), as discussed below. The basic principle of operation is that the direction of extension of screw extender <NUM> (SA2) and the one set screw driver <NUM> are given by the orientation of screw head <NUM> (SA3) of pedicle screw <NUM>, and not by forcing the surgeon or operator to change the orientation SA3 manipulating the screw extender <NUM> and/or set screw driver <NUM>.

A universal joint UJ1 will connect the upper section <NUM> of the set screw driver <NUM> with the lower section <NUM>, so that the angular position of lower set screw driver axis SA2 is decoupled from upper set screw driver axis SA1, but by maintaining a fixed angular rotative connection with angles alpha1 and alpha5. <FIG> shows an exemplary compact universal joint UJ that could be easily integrated into a screw extender. This feature allows to add bendability to set screw driver <NUM> or other type of screw driver, whilst preserving a transmission of torque from handles <NUM>, <NUM> to set screw <NUM> or other type of bone screw, as the titanium or stainless steel set screw driver <NUM> is very stiff.

Moreover, in case a screw extender <NUM> is used, a portion of screw extender <NUM> below where the handles <NUM>, <NUM> can be located can also be made less rigid in a direction away from axis SA1 than the remaining part of the screw extender, but by substantially preserving torsional stiffness of screw extender, specially less rigid than the portion of the screw extender that engages with screw head <NUM> of pedicle screw <NUM>. Specifically, screw extender <NUM> can be made more bendable with respect to an axis SA1, but still preserves a relatively high torsional stiffness to transmit torque. For example, slots or openings OS to screw extender <NUM> in an area below attachment area of handle <NUM> can be such that lateral torques off the axis SA1 are much less strong when transmitted via screw extender <NUM>. Screw extender <NUM> could be made more bendable off the axis SA1 in this area by additional slots or other types of openings OS, the slots being perpendicular to axis SA1, for example as angularly alternating slots, or a softer material at this area could be used. This allows to add additional bendability to the screw extender <NUM> without impacting its function of guiding rods <NUM> and set screw driver <NUM>. This area is in an upper part of screw extender <NUM>, and therefore will only minimally impact its operation, i.e. the threadbare engagement between set screw driver <NUM> and screw extender <NUM>. Moreover, the area with openings OS or other element that provides lateral softness can be such that it lies in a range of the location where universal joint UJ of screw driver <NUM> will be located, when engaging with set screw <NUM>, or other type of bone screw <NUM>.

A second universal joint UJ2 can be arranged between handle <NUM> and upper section <NUM> of screw driver <NUM>. This allows to block rotation of angles alpha1 of upper section <NUM> of set screw driver <NUM> to angle of handle <NUM> (alpha2), but allows for free orientation of handle axis HA1 and upper set screw driver axis SA1. To avoid that the handle <NUM> can apply to much force through lateral movement, handle <NUM> can be biased by a biasing spring mechanism S1. This could also be done by a handle that can slip laterally without the biasing springs mechanism S1. This decouples substantially all of the parasitic movement from handle <NUM> to set screw driver <NUM> away from axis SA1. An additional biasing mechanism can be also added to cover the other direction, to be perpendicular to axis HA <NUM>. Similarly, handle <NUM> can have a simple joint SJ1 that allows for free up and down pivoting movement of handle <NUM>, but has also a biasing spring mechanism S2 allowing for lateral movements of handle <NUM> that will be attenuated with less torque to screw extender <NUM>. In a variant, simple joint SJ1 can also be implemented as an universal joint, similar to UJ1 or UJ2.

These elements with handles <NUM>, <NUM> and set screw driver <NUM> having universal joint UJ1, and possibly UJ2, the orthopedic pedicle screw tightening system, or other type of bone screw tightening system, is entirely mechanical and can be fully integrated into a toolkit. It is also universally applicable to different types of surgical tools, where a bone anchoring has been made, and could also be used for dental and other applications. It is still possible for the user to apply a parasitic torque, but this set up could strongly reduce such torque, probably by more than <NUM>% as compared to the current solution.

As shown in <FIG>, different mechanisms are shown that can be added or implemented to an already existing screw extender/screw driver system, for example but not limited to the one shown in <CIT>, that allows to reduce any strain on set screw or bone screw that is not specifically directed to torque that is applied for the tightening of the bone screw by a torque. Specifically, the strains that need to be reduced are the ones that are in any radial direction (<NUM> degrees) away from an axis of longitudinal extension of screw driver/screw extender SA1, or HA21, as the bone screw, see <FIG>, for example a mono-axial bone screw or a pedicle screw that is not being poly-axial anymore, will translate such lateral movements into a strain to the bone V. For this purpose, the system of <FIG> can add flexibly in terms of bendability, that allows to decouple an orientation of the element <NUM> of screw driver <NUM> that firmly engages with the bone screw head <NUM>, and the parts that will be handled by the surgeon when tightening the bone screw. Some of these mechanisms are shown as universal joints UJ1 and UJ2 at specific locations, and some of them as springs S <NUM>, S2, to provide for a spring-biased suspension to the handles for axes HA1, HA2. Another element is the softening of the screw extender in an upper area, for example with slots or openings OS, at an area where UJ1 is located of the screw driver is located, so that the screw extender can be bent together with the screw driver.

Of course it would be possible to implement the universal joints UJ as simple as possible, for example as elastomeric joints with no moving parts other than the bendable elastomer, or other types of simplified flexible couplings, for example double spring couplings. In this sense, the main function of transferring a tightening torque to the bone screw by preserving or substantially preserving the torsional stiffness of screw driver <NUM> and screw extender <NUM> if present, and at the same time providing a decoupling between the main axis of the bone screw and the main axis of the tightening elements is provided, and can be implemented with possible equivalents, such as universal joints, cardan joints, beam couplings, elastomeric couplings, jaw couplings, etc..

<FIG> show another variant of a handle <NUM> that can be used to engage with and hold screw extender <NUM> at a position relative to pedicle screw <NUM>, for holding screw extender <NUM>. A portion of screw extender <NUM> is shown with a side view on the left of <FIG>. Handle <NUM> includes a hand grip portion <NUM> that is configured to be held by the hand of a user, operator, or surgeon, a first frame <NUM> that is non-movably attached to hand grip portion <NUM>, a second frame <NUM> that is suspended along a first linear axis relative to first frame <NUM> by elastic elements <NUM>, <NUM>, in the variant shown the elastic elements <NUM>, <NUM> being a pair of springs, second frame <NUM> guided by a linear guiding structure that are located at side parts of first frame <NUM> and second frame <NUM>, allowing second frame <NUM> to linearly slide within a certain motional range inside first frame <NUM>, biased by the pairs of elastic elements <NUM>, <NUM>.

The linear guiding structure can be implemented as complementary guiding rails, a linear bearing structure, for example with a carriage and guide rail, telescopic slide, or sliding surface for reducing friction between first frame <NUM> and second frame <NUM>. Moreover, handle <NUM> further includes a central engagement element <NUM> for engaging with a corresponding engaging structure <NUM> of screw extender <NUM>, for example by having a circular opening with circularly-arranged engagement teeth or ridges (<NUM>).

Engagement element <NUM> is elastically biased relative to second frame <NUM> with two elastic elements, for example but not limited to a coil or leaf spring <NUM>, <NUM>, so that engagement element <NUM> can slide within a certain motional range relative to second frame <NUM> along a second linear axis that is substantially perpendicular to first linear axis. Moreover, a linear guiding structure such as but not limited to a complementary rail structure can be provided at side walls of engagement element <NUM> and side walls of second frame <NUM>, to guide the linear motion along the second linear axis.

With the linear suspension of second frame <NUM> relative to first frame <NUM> by an increasing first biasing force with springs <NUM>, <NUM> for an increased position of second frame <NUM> off a first central or neutral position, and with the linear suspension of central engagement element <NUM> relative to second frame <NUM> by an increasing second biasing force with springs <NUM>, <NUM> for an increased position of central engagement element <NUM> off a second central or neutral position, first and second central position corresponding of a location of central axis HA2 when handle <NUM> is engaging with screw extender <NUM> in two perpendicularly arranged directions, it is possible to minimize that a user, operator or surgeon urges screw extender off axis that is defined by axis HA1 defined by screw head of pedicle screw <NUM>, and the extension thereof by axis HA2 of screw extender <NUM> (see <FIG>).

In addition, engaging structure <NUM> of screw extender <NUM> and engaging element <NUM> of handle <NUM> are formed such upon their mutual engagement with each other, for example by sliding opening of engagement element <NUM> of handle <NUM> to engaging structure, they are configured to be oriented freely within a certain angular range to each other, but still fully lock a rotation of screw extender <NUM> relative to handle <NUM> around axis HA2. This can be implemented by an engaging structure <NUM> having a spherical or ball-like engagement element with engagement ridges or grooves, for example but not limited to a ball hex or ball torx structure, with an at least partially surrounding beveled edge <NUM> limiting a downward placement of handle <NUM> to screw extender <NUM>. Edge <NUM> can be made of a continuous surrounding structure, or by two or more knobs around outer cylindrical surface of screw extender <NUM>. In a variant, it is possible that central engagement element <NUM> has a curved structure while engaging structure <NUM> is cylindrically shaped, for allowing a certain range of angular motion of handle <NUM> relative to axis HA2. This this mechanism between handle <NUM> and screw extender <NUM>, with engaging structure <NUM> and central engagement element <NUM> allows for angular tolerance between handle <NUM> and screw extender <NUM> for holding pedicle screw <NUM>, and thereby is functionally equivalent to a universal joint, but also allowing for easy removability.

<FIG> shows an exemplary embodiment of a handle or knob <NUM> that can be centrally placed onto an end of screw driver <NUM>, <NUM>, for tightening a pedicle screw <NUM>. For example, handle or knob <NUM> can be rotated around axis HA2 when in operative connection with screw driver <NUM>, <NUM>, by one hand of user, operator, or surgeon, to turn screw driver <NUM>, <NUM> relative to screw extender <NUM>, while the other hand can hold screw extender <NUM> with handle <NUM>. Handle <NUM> includes an outer ring or holder <NUM> that can have plurality of knobs or protrusions <NUM> radially arranged around an outer circumference, or other arrangement to increase a holding friction with a hand of a user, and has an inner rectangularly-shaped opening accommodating a sliding frame <NUM>. Sliding frame <NUM> is located linearly suspended inside the opening by means of two pairs of elastic elements <NUM>, <NUM> on each side, for example coil or leaf springs, along for a force-biased linear motional range along a first axis. Sliding frame <NUM> can be linearly guided by side walls of opening and frame, for example with a corresponding rails structure, or other type of linear bearing structure. Moreover, a central engagement element <NUM> is located inside a rectangularly shaped opening of sliding frame <NUM>, biased on each side by an elastic element <NUM>, <NUM>, allowing a linear motional range along a second axis that is perpendicular to the first axis.

Central engagement element <NUM> can have an opening in the shape of a rotary torque tool, for example a hex structure, torx structure, or other type of tool engaging structure for applying a torque to a screw driver <NUM>, <NUM>. For example, central engagement element can be a non-traversing opening having a floor that limits an engagement depth with spherical engagement element <NUM> of screw driver <NUM>, <NUM>. As shown on the left side of <FIG>, an upper end of screw driver <NUM>, <NUM> is shown, having a spherical engagement element <NUM> for engaging with central engagement element <NUM> of handle or knob <NUM>, for example but not limited to a hex ball, hex torx, or other type of tool that allows for an free angular orientation range between handle <NUM> and screw driver <NUM>, <NUM>, but at the same time allowing for a transmission of a torque around axis HA2 to screw driver <NUM>, <NUM>. In this respect, central engagement element <NUM> and spherical engagement element <NUM> have the functional equivalent of an universal joint, but with the possibility of easily removing handle <NUM> from screw driver <NUM>, <NUM>. It is also possible that handle <NUM> is equipped with a torque limiting device, for example a breakable pin, or a torque ratchet. In a variant, instead of using helical springs <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, it is possible to use other types of elastic elements, for example but not limited to elastomeric cushions, suspension pistons, elastic cords, leaf spring arrangements, plate springs, volute springs, in both a push or a pull configuration, providing for a force to restore the respective frames or sliders to a neutral position.

In a variant shown in <FIG>, a helix tube, or other type of flexible rod, can be used for screw driver <NUM>, or portions thereof, for example at locations of UJ1 and UJ2. This is another device that allows to preserve torsional stiffness around the axis HA2 or SA1, and at the same time allows for bendability off axis HA2 or SA1. Specifically, a double helix tube can be used, with the two helixes running opposite each other that provides strong torsional stiffness.

Next, with <FIG> an exemplary device <NUM> is described that allows to measure an angle between axis HA2 of screw extender <NUM> and screw head <NUM>, and axis RA2 of rod <NUM>, or determine whether HA2 and RA2 are perpendicular to each other, so that the surgeon or operator can correct an orientation of screw head <NUM> relative to rod <NUM> by moving the screw extender <NUM>. This can be done during the surgery, where bone anchor <NUM> is already fully attached or fastened to vertebra bone V, and can therefore be done through the surgical incision, by a device <NUM> that can be slid over the screw extender <NUM> into the surgical incision.

Basically, as shown in <FIG>, device <NUM> is a tubular element that is hollow, for example has a hollow interior cylindrical cavity that has an inner diameter DIA slightly larger than an external diameter of the screw extender <NUM>, so that device <NUM> can be slid over screw extender <NUM>, for example when none of handles <NUM>, <NUM> are attached to screw extender <NUM>, as shown in <FIG> where device <NUM> has been slid over the screw extender <NUM>, and shown in <FIG> as a cross-sectional view, showing device <NUM> arranged around screw extender <NUM>, and optionally screw driver <NUM>. Tubular device <NUM> can have other cross-sectional shapes, for example hexagonal, square, polygonal etc., as long as it is hollow and can be slid over the screw extender <NUM>. At a front face of tubular device <NUM>, the circular front edge includes two protrusions, ridges, or edges E1, E2 arranged at <NUM>° from each other. One protrusion E1 has grooves, is dented, or saw-toothed, or has other type of mechanical irregularities <NUM> facing from front face, that can generate a vibration to tubular device <NUM> if the protrusion E1 is slid and pressed against spinal rod <NUM>, while the other protrusion E2 is smooth, so that no vibration occurs when protrusion E2 is slid and pressed against spinal rod <NUM>. Preferably, seen from a center axis of tubular device <NUM> in a radial direction, protrusion E1 is arranged with grooves <NUM> in an angular range covering the circular front edge between preferably <NUM>° to just under <NUM>°, more preferably between <NUM>° to <NUM>°. In addition, while the protrusions E1 and E2 are axisymmetric to each other, rotated relative to each other by <NUM>°, the dented protrusion E1 does not protrude as far away from front face of tubular element <NUM> as the non-dented one E2, for example by a distance difference AD. In other words, protrusion distance D1 of dented protrusion E1 is smaller than protrusion distance D2 of non-dented protrusion E2, for example by a difference of <NUM>.

As shown in <FIG>, operator or surgeon can slide tubular element <NUM> over screw extender <NUM>, for example after removing or before placing handles <NUM>, <NUM>, and can fully insert tubular element <NUM> to make sure it touches at least one upper surface of spinal fixation rod <NUM>, at least on one side of screw head <NUM>. This can be done to a screw extender of an orthopedic implant kit as exemplarily shown in <CIT>. Thereafter, surgeon or operator can rotate tubular element <NUM> manually, as indicated by the rotative arrow ROT, for example with his thumb and index finger, pressing tubular element slightly against rod <NUM>. In a first case, where rod <NUM> is substantially perpendicular to screw head <NUM>, which means axis HA2 is perpendicular to axis RA2, which is the desired orientation of rod <NUM>, the rotation ROT of tubular element <NUM> relative to screw extender <NUM> will not cause any vibration, as the teeth <NUM> are arranged slightly recessed, by a distance difference AD, and both protrusions E1 and E2 are asymmetrical to each other.

However, in a second case where rod <NUM> is not perpendicular to screw head <NUM>, which means axis HA2 is not perpendicular to axis RA2, which is an undesired orientation of rod <NUM> relative to head <NUM>, the manual rotation ROT of tubular element will cause teeth <NUM> to engage on a surface of rod <NUM>, to cause a vibration and possible a ratcheting noise that can be manually sensed and heard by surgeon or operator. This will happen as soon as the relative offset distance of rod <NUM> on each side of the screw head <NUM> exceeds the distance difference AD, which is caused by the oblique angle that exceeds a certain threshold.

With this device <NUM>, it possible to easily detect, without necessary visual feedback, with a very simple mechanism, whether rod <NUM> is not arranged perpendicularly to screw head <NUM>, and if surgeon or operator detects the non-perpendicularity, with screw extender <NUM>, screw head <NUM> can be brought into the desired position by orienting screw extender <NUM> that is attached to screw head <NUM>, before set screw <NUM> is tightened, for example before the polyaxiality of pedicle screw <NUM> is lost or limited.

Next, with <FIG> another device <NUM> is described that allows to measure the angle between axis HA2 of screw extender <NUM> and screw head <NUM>, and axis RA2 of rod <NUM>, or determine whether HA2 and RA2 are perpendicular to each other, so that the surgeon or operator can correct an orientation of screw head <NUM> relative to rod <NUM> by moving the screw extender <NUM>. In comparison to device <NUM>, the present device includes electronics and a power supply to measure the distance actively, by the user of distance measurement sensors <NUM>, <NUM> that are arranged at a front face of device <NUM>, or arranged such that they can measure a distance of the respective sensor <NUM>, <NUM> to spinal rod <NUM>, on each side of screw head <NUM> of pedicle screw <NUM>. Sensors <NUM>, <NUM> can be exemplarily implemented as, but are not limited to, optical, acoustical, ultrasonic, capacitive or inductive distance measurement sensors. <FIG> illustrated the device <NUM> that is placed over screw extender <NUM> showing, on the left side, rod <NUM> perpendicularly arranged to screw head <NUM> (the desired position), and on the right side, rod <NUM> not perpendicularly arranged to screw head <NUM>. Sensors <NUM>, <NUM> can measure a distance D11 and D12 on each side of screw head <NUM>, to determine whether the distances are equal, to see if perpendicularity is present. Signals from sensors <NUM>, <NUM> can be processed by a microcontroller that is powered by a battery, and a result of the comparison of the measured distances D11 and D12 can be indicated to the user for example by optical, acoustical, haptic, or vibratory means, for example via two lights <NUM> that can show perpendicularity, for example with a green light, or non-perpendicularity, with a red light, for example LED <NUM>. I a variant, the signal can be acoustical, for example with speaker <NUM> that indicates an acoustic low frequency signal for perpendicularity, and an acoustic high-frequency signal for non-perpendicularity.

With <FIG>, shows another variant, where detection sensors <NUM>, <NUM> having a semi-circle contact surface are arranged on each half of the circular front surface of device <NUM>. Moreover, device <NUM> has an arrow, line or other imprint or indication <NUM> that shows the desired rotative position of device <NUM> once placed on screw extender <NUM>, so that device <NUM> can be approximatively aligned to an axis of longitudinal extension of rod <NUM>, for example along the incision that usually is substantially parallel to rod. Indicator of orientation can also be implemented with small knobs, lump, or protuberances <NUM>, <NUM> to show orientation of device <NUM>. Front surfaces of detection sensors <NUM>, <NUM> can detect contact or close proximity to rod <NUM> on each side of screw head <NUM>, for example by sensors <NUM>, <NUM> arranged like buttons that can be pressed, or for example by a capacitive measurement to detect close proximity of rod <NUM>.

Claim 1:
A bone screw tightening device comprising:
a screw driver (<NUM>),
wherein the screw driver (<NUM>) includes, along an axis of longitudinal extension, at least one device (UJ1, UJ2) for providing for radial bendability and at a same time preserving torsional stiffness along an axis of longitudinal extension of the bone screw (<NUM>),
characterized in that the bone screw tightening device further includes a screw extender (<NUM>) for removable attachment to a screw head (<NUM>) of the bone screw (<NUM>) and for holding the bone screw (<NUM>) and accommodating the screw driver (<NUM>), and
in that the at least one device (UJ1, UJ2) for providing radial bendability is located along the screw driver (<NUM>) and located inside the screw extender (<NUM>) when the screw extender (<NUM>) is attached to the screw head (<NUM>) of the bone screw (<NUM>), or at an upper section (<NUM>) of the screw driver (<NUM>) outside of the screw extender (<NUM>) when the screw extender (<NUM>) is attached to the screw head (<NUM>) of the bone screw (<NUM>).