Patent Description:
Kambin's triangle is an anatomical corridor situated in the neural foramen which can be used to access critical structures in a variety of spinal procedures. Kambin's triangle is known as a safe space for carrying out percutaneous procedures, being a clean access route to the intervertebral disc. It is considered safe because it lacks important vascular and/or neural elements. However, it has the problem that space is limited at some points (<NUM>-<NUM>) and that it is delimited on one side by a nerve root. In endoscopic and/or percutaneous operations there is therefore a danger of damaging the nerve root, either by involuntary cutting during a cutting operation in an articular process to create more space, or by pressure on the nerve applied by the endoscopic devices (for example, the cannula), which may cause dysaesthesia or inflammation of the nerve. This has limited the viable operations that can be done by an approach via the neural foramen.

Document <CIT> discloses a dilator unit provided with a shield for the nerve. The object of the shield is to protect the nerve root during percutaneous operations which use the neural foramen as an access route. The unit comprises an elongate dilator shaft and a shield. The transverse cross sections of the shaft and shield are complementary and form a circle. The elongate dilator shaft has the function of placing the shield in position. In use, the unit is positioned in the disc space at the required position and rotated to a point at which the outer surface of the shield is adjacent to the nerve root. At this point, the dilator shaft may be withdrawn, leaving the shield in place. An object pursued in this document consists of allowing a box or cage to be placed in the intervertebral space which prevents damage to the nerve root.

The dilator unit of document <CIT> has a circular transverse cross section which is formed by the dilator shaft and the shield, which are in contact with one another. The unit has at the centre of its transverse cross section an opening corresponding to a passage for receiving a guide wire or thread. The dilator shaft and the shield come in contact along two planar surfaces perpendicular to one another. The shield has recesses in each of said perpendicular planar surfaces. Corresponding projections of the dilator shaft are arranged in said recesses. The arrangement of the perpendicular surfaces and the consequent perpendicular arrangement of the recesses allows shaft and shield to slide along the longitudinal or axial axis of the unit, but any movement in another direction is prevented, and both elements are therefore interlocked. The outer surface of the shield occupies approximately <NUM>° of the <NUM>° of the outer circumference of the unit.

A problem with this device of document <CIT> is that it does not leave enough space to be able to operate afterwards, as the shield significantly reduces the space once positioned. This reduction in space still limits the possibilities and, in particular, the introduction of an intervertebral box or cage is not viable.

Document <CIT> discloses an apparatus and a method for dilation and retraction of tissues during spinal surgery. The apparatus comprises a dilator assembly which includes a plurality of slidingly dilators (up to three different dilators). This system allows to provide an intermediate amount of dilation of tissues in an anatomical anterior direction, and additionally minimize or avoid dilation of soft tissues in anatomical posterior direction as sequential dilators are advanced over a first positioned dilator.

An object of the present invention is to disclose a series of means that allow a shield for protecting the nerve root to be placed without having the drawbacks of the prior art. The invention is set out in independent claim <NUM>, whilst further advantageous embodiments of the invention are set forth in the appended dependent claims.

In particular, the present invention discloses a dilator for percutaneous spinal surgery which comprises a main elongate dilator body and an elongate shield for protecting the nerve root, the main dilator body and the shield each comprising mutually complementary contact surfaces and in which the main body and the shield define a peripheral surface of the dilator in such a way that main body and shield define a transverse cross section of the dilator, it being possible for the main body and the shield to slide one relative to the other along an axial axis of the dilator, the dilator also comprising a through-hole for receiving a guide wire, in which said hole is placed eccentrically with respect to a combined transverse cross section of the main body and of the shield.

The eccentric placement of the hole allows, after the removal of the main body, a guide cable to be used which had been housed in said hole in order to carry out bone cutting operations without having to move or apply pressure to the shield, which could cause damage to the nerve root.

The present invention also discloses a dilator for percutaneous spinal surgery which comprises a main elongate dilator body and an elongate shield for protecting the nerve root, the main dilator body and the shield each comprising mutually complementary contact surfaces and in which the main body and the shield define a peripheral surface of the dilator in such a way that main body and shield define a transverse cross section of the dilator, it being possible for the main body and the shield to slide one relative to the other along an axial axis of the dilator, the dilator also comprising a through-hole for receiving a guide rod, in which the transverse cross section of the dilator is oblong or elongate in shape, the shield being arranged on one of the elongate faces of the transverse cross section.

The elongate shape combined with the eccentric arrangement of the hole allows for a shield which protects more space and which is not inserted excessively into Kambin's triangle, as this reduces the space that is subsequently available.

The present invention also discloses a dilator for percutaneous spinal surgery which comprises a main elongate dilator body and an elongate shield for protecting the nerve root, the main dilator body and the shield each comprising mutually complementary contact surfaces and in which the main body and the shield define a peripheral surface of the dilator in such a way that main body and shield define a transverse cross section of the dilator, it being possible for the main body and the shield to slide one relative to the other along an axial axis of the dilator, the dilator also comprising a through-hole for receiving a guide rod, in which the shield has a laminar or curved laminar shape.

The laminar shape avoids the presence of elements of the shield which are introduced into the available operating space.

Said features (eccentricity of the guide hole, oblong shape of the dilator and laminar shape of the shield) may be implemented individually in dilators, combined in pairs or all three combined together.

According to the present invention, the main body and shield do not need to be interlocked so as to only be able to slide in respect to one another in the axial direction. Preferably, the shield has no recesses for interlocking with the main body. This allows a slimmer shield to be obtained which therefore occupies less space. In addition, preferably, the shield also has no projections for interlocking. If it is decided to produce recesses or projections for interlocking between the main body and the shield, it is preferable to produce said recesses and projections at each end of the transverse cross section of the shield, thus leaving the central portion free and therefore affecting the thickness, which should preferably be the minimum possible, of the shield as little as possible.

According to the present invention, both shield and main body may have retention means to restrict - but not prevent - movement between shield and main body in a radial direction, said retention means being situated at both ends of the transverse cross section of the shield and which preferably comprise the shape of said ends which preferably have a curved shape. In this case, the retention means restrict movement by providing a resistance which can be overcome.

The present invention also discloses kits which comprise a dilator according to the present invention. The kit may also comprise a drill bit, or various drill bits of different diameters. The kit may also comprise a guide cable, for example a so-called "K-wire". The kit may also comprise known elements of transforaminal access systems, such as Tom Shidi needles (for example with a blunt tip, and/or a cutting tip and/or a drill) and controls for the various transcutaneous components.

The dilator according to the present invention may be used in various transcutaneous spinal operations with a transforaminal approach, including vertebral arthrodesis in general and with the installation of intervertebral box(es) or cage(s) in particular. Preferably, the dilator according to the present invention may be used in operations that involve cutting a portion of bone (typically from the articular process) to access the disc space. A typical sequence consists of inserting a guide cable, inserting the dilator along the guide cable and removing the main body of the dilator while leaving the shield. In this way the nerve root remains protected. Then additional operations may be carried out, such as bone cutting using a drill bit, cleaning and preparing the disc space and positioning and installing an intervertebral box/cage for arthrodesis.

For a better understanding, drawings are attached which show, as an example, an explanatory but nonlimiting embodiment of the object of the present invention.

The dilator <NUM> is made up of a main body <NUM> and a shield <NUM>. Both the main body <NUM> and the shield <NUM> have an elongate shape for use in percutaneous operations. Main body <NUM> and shield <NUM> have conjugate shapes such that the dilator <NUM> has a uniform outer lateral surface. More specifically, and as can be seen in <FIG>, the cross section of the dilator <NUM> - made up of the cross sections of the main body <NUM> and the shield <NUM> - has an elliptical or ovoid shape. The dilator <NUM> also has a longitudinal through-hole <NUM>, the object of which is to receive a guide (for example a K-wire) which will guide the trajectory of the dilator <NUM> inside the body of the patient. The hole <NUM> is situated eccentrically with respect to the centre of the cross section of the dilator. In particular, the hole <NUM>, which is in the main body <NUM>, is situated farther from the outer surface of the dilator <NUM> formed by the shield <NUM> than from an outer surface of the dilator <NUM> formed by the main body. The outer surfaces formed respectively by the main body and the shield are opposite one another. This offsetting of the hole makes it easier subsequently to create additional space by the positioning of a drill bit to cut the bone of one or both vertebrae.

The main body <NUM> also has a pointed distal end <NUM>. As can be seen in <FIG>, the main body <NUM> has a recess for receiving the shield, along which the shield can slide. However, it is possible for the main body and the shield not to be interlocked, so that the relative movement in a radial direction may be completely allowed, or not totally prevented.

The shield <NUM> has a curved laminar shape in cross section. The laminar shape helps achieve a shield that is as slender as possible. More specifically, the shield <NUM> is formed in cross section by two main surfaces, an outer surface which forms part of the outer surface of the dilator <NUM>, and another inner surface parallel thereto, as well as two ends which form a connection between both main surfaces. For the shield to be more slender, both main surfaces are parallel to one another. In addition, the shield does not have attachment recesses on said main surfaces, which allows for an even more slender shield. In addition, in the case shown, neither do the ends <NUM> of the shield <NUM> have recesses for interlocking with the main body. It is not necessary to interlock the main body <NUM> and the shield <NUM> to prevent any movement between the two. If thought appropriate, the ends <NUM> could have projections for interlocking (not shown in the figure) or alternatively could be given a shape that restricts, but does not prevent, movement in a radial direction.

The shield may have a shank <NUM> for handling. The shank may take various shapes. In general, the instruments have been shown diagrammatically and any necessary connection and/or handling elements may be arranged at the distal and/or proximal ends thereof.

As shown diagrammatically in <FIG>, the box is introduced using percutaneous means. An endoscopic cannula <NUM> has been shown in <FIG> which approaches the intervertebral space by the anterior route.

<FIG> show diagrammatically a procedure for placing the dilator. The method may begin (<FIG>) by placing a guide cable <NUM> (K-wire) in position by a transforaminal approach. The guide cable <NUM> is positioned opposite the intervertebral disc <NUM> situated between the vertebrae <NUM>, <NUM> or alternatively penetrates therein. From here, said cable will serve as a guide for introducing the dilator with the corresponding shield <NUM> thereof facing towards the nerve root <NUM> that is to be protected, as shown in <FIG>. Next, the main body <NUM> of the dilator is removed, being made to slide with respect to the shield <NUM>, which remains in position, protecting the nerve root <NUM>. As can be seen in <FIG>, the guide cable <NUM> also remains in position. From the arrangement in <FIG>, the required transepidermal operation by transforaminal approach may begin. <FIG> show a possible operation. To illustrate the operations, the endoscopic cannula that would protect the elements that are introduced, depending on what is required in each case, has not been shown in the figures. <FIG> shows how a drill bit <NUM> is introduced in order to cut part of the inferior vertebra <NUM>. It would also be possible to cut part of the superior vertebra, or both vertebrae, depending on requirements. The object of cutting is to gain space for subsequent operations. Since, in order to make the cut, the drill bit has to project from the surrounding cannula (not shown in the figures), the shield <NUM> acts as a barrier which prevents cutting and/or compression of the nerve root <NUM>. <FIG> shows the cut portion <NUM>. In this case, the cut portion corresponds to the superior articular process of the inferior vertebra <NUM>. It will be noted that the fact that the hole in the dilator is in an eccentric position with respect to the centre of the cross section of the dilator facilitates being able to cut part of the vertebra without having to move the shield <NUM> from its position, as this would result in applying pressure to the nerve root <NUM> and causing dysaesthesia.

The drill bit <NUM> is then removed and it is now possible to carry out the necessary operations. If a considerable amount of bone has to be removed, it is possible to introduce two or more drill bits sequentially using an increasingly large drill bit diameter.

It is then possible to introduce a tool <NUM> (clamp and/or cutter, extractor, etc.) to clean the interior of the disc <NUM>, which leaves the way clear to place a cage or box <NUM> to carry out intervertebral fusion. Using this system, it is possible to introduce percutaneously various types of intervertebral boxes or cages, the object of which is to fuse and/or separate two vertebrae by being interposed in the intervertebral space. <FIG> show an example of a box <NUM> which is made up of two bodies <NUM>, <NUM> having conjugate shapes. Each of the two bodies <NUM>, <NUM> is of a suitable size to enter through an endoscopic cannula which passes through Kambin's triangle, for which said body has a corresponding hole <NUM> for a guide cable. The parts are assembled together.

When the parts are assembled, the guide holes are coaxial, one hole being a through-hole and the other having a thread <NUM> for receiving the endoscopic guide.

Assembly may be carried out, for example, by means of a set of respective conjugate recesses and projections situated at the contact interface between both parts. Said projections may preferably be perpendicular to the coaxial axis of said holes. Preferably, said holes are arranged on each of said conjugate projections.

The box also comprises a connection element in the form of a screw <NUM> which is fixed by means of a thread <NUM>, securing the parts <NUM>, <NUM>. The thread <NUM> may be fitted into respective threads in one or both parts <NUM>, <NUM>. Each of the two parts <NUM>, <NUM> has a through-hole <NUM>, <NUM> which has an inlet in the proximal area and an outlet in one of the bases for receiving a means of fixing to the adjacent vertebrae, for example, the screws or pins <NUM>, <NUM>, which have sharp projections. Each of the sharp pins <NUM>, <NUM> is arranged on one of the bases of the box, pointing in different directions.

The method (not claimed) of positioning the box <NUM> may be as follows:
First, a part <NUM> is positioned, being guided by an endoscopic guide which is threaded onto the corresponding thread <NUM> of the part <NUM>. Without removing the guide, the other part is positioned through the endoscopic cannula, said part also being guided by the endoscopic guide. This movement causes both parts to be held against one another, interlocking owing to the conjugate shapes thereof.

Next, the pins <NUM>, <NUM> are inserted, driving said pins into the adjacent vertebrae.

Finally, the screw <NUM> is slid along the endoscopic guide and then a tool is introduced to thread the screw <NUM>.

Next the threading tool, the endoscopic guide, which is unscrewed, the endoscopic cannula and the shield <NUM> are removed.

The installation method may be different from the one shown, and it is also possible to use different percutaneous and even non-percutaneous techniques. The order of the operations is also susceptible to changes. The introduction route is through Kambin's triangle made safe by the use of a shield for protecting the nerve root, which is preferably positioned by means of a dilator as shown above.

<FIG> shows how the box <NUM> would be positioned, typically at an angle owing to the transforaminal approach used for introduction thereof. However, in an intervertebral fusion operation typically two boxes <NUM> will be placed, one through the left neural foramen and the other through the right.

<FIG> shows an example of a marketable kit for carrying out transcutaneous operations which includes a dilator <NUM> according to the present invention, a guide cable <NUM> and at least one drill bit <NUM>, or a set of drill bits of different sizes. The kit may also comprise known elements of transforaminal access systems, such as Tom Shidi needles <NUM> (for example with a blunt tip, and/or a cutting tip and/or a drill and controls <NUM> for the various elements, etc.). In general, the heads for connection to the control of the different elements have not been shown in the figures so as not to complicate the illustrations. Nor has the use of the different endoscopic cannulas, employed as required and according to the judgement of the specialist doctor, been illustrated.

The dimensions of the dilator shown may vary depending on the type of vertebra to which said dilator will be directed. In the example, the transverse cross section of the dilator may be approximately <NUM> on the long axis and <NUM> along an axis perpendicular to said long axis. The shield may, for example, have a constant thickness of <NUM> and a length of <NUM> measured in the direction of said long axis. The through-hole of the dilator may be approximately <NUM> and may be arranged at a distance of at least <NUM> from the shield. The length of the dilator in the axial direction may be approximately <NUM>, and that of the shield, <NUM>.

The installation method may be different from the one shown, and it is also possible to use different percutaneous techniques and modifications to the one shown. The order of the operations is also susceptible to changes.

Claim 1:
Dilator for percutaneous spinal surgery with a transforaminal approach which comprises a main elongate dilator body (<NUM>) and an elongate shield (<NUM>) for protecting the nerve root, the main dilator body and the shield each comprising mutually complementary contact surfaces and in which the main body and the shield define a transverse cross section of the dilator, it being possible for the main body and the shield to slide one relative to the other along an axial axis of the dilator, the dilator also comprising a through-hole (<NUM>) for receiving a guide rod, characterised in that said hole is placed eccentrically with respect to a combined transverse cross section of the main body and of the shield.