Surgical instrument to measure an intervertebral space

The invention is a surgical instrument for measuring an intervertebral space. On the distal end of a handle of the instrument there are at least two measurement plates, whereby an interval between the measurement plates, and an angle enclosed by the measurement plates, are adjustable.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from European Patent Application No. 08 007 694.6, filed Apr. 21, 2008, the entire contents of which are herein incorporated fully by reference.

FIGURE FOR PUBLICATION

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a medical device for measuring spatial relationships between anatomical structures. More specifically, the present invention relates to a surgical instrument for measuring an intervertebral space in a precise manner so as to allow for optimal restoration of a damaged area.

2. Description of the Related Art

In prosthetics for intervertebral disks, it is customary to use so-called intervertebral prostheses as disk replacements. Such intervertebral prostheses are inserted between the vertebral bodies as part of an operation, replacing the defective disks removed earlier. To ensure that the original mobility and function of the spinal column is optimally restored, it is necessary that the damaged intervertebral space be reconstructed with optimal precision, and that the dimensions and positioning of an intervertebral prosthesis be chosen in optimal fashion. As a rule, intervertebral prostheses of the type mentioned consist of two prosthetic plates, each connected with a vertebral body. In some versions, between the prosthetic plates, a prosthesis core is placed, on which the prosthesis plates glide and assume the damping function of the removed disk. In determining the dimensions for an intervertebral prosthesis to be inserted, especially the area of the prosthetic plates, the overall height of the intervertebral prosthesis and an angular setting of the surfaces of the prosthetic plates facing the vertebral bodies to each other are decisive.

The related arts teach that the measurements of the intervertebral prosthesis are taken preoperatively using X ray or CAT imagery, and during the operation are verified after removal of the disk by test use of implants. Implant measurements are verified by inserting a test implant between the vertebral bodies mechanically spread apart from each other; the spreading is released; and then, using an X ray image, the register form of the implant is checked.

What is not appreciated by the prior art is that it is necessary to spread the vertebral bodies multiple times to remove and re-insert the test prostheses for insertion and checking of the intervertebral prostheses. On the one hand, this takes up a large part of the time for surgery; and, on the other hand, it necessitates unnecessary mechanical loads on the patient's spinal column.

Accordingly, the inventors recognize a need for an improved surgical instrument for measuring an intervertebral space in a precise manner so as to allow for optimal restoration of a damaged area

ASPECTS AND SUMMARY OF THE INVENTION

An aspect of the present invention is to make available a surgical instrument to measure an intervertebral space, by which it is possible to determine the dimensions for an intervertebral prosthesis to be inserted more quickly and more simply, and in a manner that is easier on the patient.

The present invention relates to a surgical instrument for measuring an intervertebral space. On the distal end of a handle of the instrument there are at least two measurement plates, whereby an interval between the measurement plates, and an angle enclosed by the measurement plates, are adjustable.

According to an embodiment of the present invention there is provided a surgical instrument for measuring an intervertebral space. The surgical instrument comprises a handle having a distal end. At the distal end there are provided at least two measurements plates, shown without limitation as a first and a second measurement plate. There is an interval between the first and the second measurement plates wherein the interval is adjustable. Also defined, is an adjustable angle (discussed below as α, but not limited thereto) enclosed by the first measurement plate and the second measurement plate.

The advantage of the present invention is that owing to both the interval and enclosed angle being adjustable, only one spreading procedure is necessary to insert the surgical instrument; with it, due to the adjustability of the interval and the angle enclosed by the measurement plates, an in situ variation of the size is possible, so that through a one-time insertion of the surgical instrument, the exact fit of various implant dimensions can be checked and then immediately an intervertebral prosthesis with the correct dimensions can be inserted.

It is advantageous if, simultaneous with the implant dimensions, it is also possible to determine the depth at which the implant is placed, proceeding from the anterior side of the vertebral body via a movable deep stop. Such a deep stop can, for example, be determined by means of a cover surrounding the handle, which can for example be implemented by a cylindrical cover that can be screwed via an outer thread. The advantage of a cylindrical cover that surrounds the entire handle, is that only a single stop is present, and thus with a single adjustment the stop can be determined simultaneously for the two vertebral bodies between which the intervertebral prosthesis is to be mounted.

For a mechanical implementation of the surgical instrument, it is advantageous if a first measurement plate is configured for adjusting the distance and a second measurement plate is configured for setting the angle enclosed between the measurement plates. The mechanical implementation in this case is unique, so that for the one plate, all that must be provided is a mechanism for height adjustment; and, for the other plate, a mechanism to adjust the plate angle.

A height adjustment can be effected for example with a spreader that can be configured like an accordion lift table. With this it is advantageous that such a spreader execute a parallel adjustment of the measurement plate without any additional tipping.

Preferably, such a spreader has two scissors-like members able to move relative to each other, of which one can be controlled using a coupling rod, whereby the other is pivoted by means of an axle.

Linear motion of the coupling rod can be generated with especial ease from a threaded rod's rotational motion via a threaded bushing, which is placed in the handle so as not to turn. Owing to such guidance it is possible with particular ease to precisely adjust small motion steps of the one scissors-like part via a thread with a small passage height. This can be done, for example, using a threaded rod that is placed in the handle. On a proximal end of such a threaded rod, then, for example, an operating lever or an appropriately configured rotary knob can be placed. The advantage of using a threaded rod to operate it is that through selection of the threading, a reduction can be attained simply for the adjustment path.

For adjusting the angle enclosed by the measurement plate, it is advantageous to provide a revolving mechanism. Such a revolving mechanism can be formed with particular ease by supporting the second measurement plate along an axis perpendicular to the longitudinal axis of the handle and parallel to the first measurement plate. It is especially advantageous if this axis is provided in a central area of the second measurement plate, so that owing to a swiveling of the second measurement plate, the centrally determined interval of the measurement plates does not change.

It is possible, with relative ease, to generate a swiveling motion of the second measurement plate from a linear motion using a connecting rod. Such a connecting rod converts a linear motion, for example that of a second threaded bushing, into a rotary motion, thus allowing the swivel motion of the second measurement plate.

The linear motion of the second threaded bushing, in turn, is easily to adjustable via a second threaded rod that also can be situated in the handle. An especially elegant solution is produced when the handle is shaped as a tube and the second threaded rod is placed in the first threaded rod, which is likewise configured as a tube. This solution is also particularly elegant for the threaded bushing. In this case, the second threaded bushing is placed concentric to the first threaded bushing and is placed so as to slide in it.

The overall surgical instrument is advantageously manufactured from biocompatible and sterilizable material such as stainless steel or titanium. The handle can, for example, be sprayed with a silicon rubber, to ensure better handling qualities.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to several embodiments of the invention that are illustrated in the accompanying drawings. Wherever possible, same or similar reference numerals are used in the drawings and the description to refer to the same or like parts or steps. The drawings are in simplified form and are not to precise scale. For purposes of convenience and clarity only, directional terms, such as top, bottom, up, down, over, above, and below may be used with respect to the drawings. These and similar directional terms should not be construed to limit the scope of the invention in any manner. The words “connect,” “couple,” and similar terms with their inflectional morphemes do not necessarily denote direct and immediate connections, but also include connections through mediate elements or devices.

FIG. 1ashows a top view of an invention-specific surgical instrument1for measuring an intervertebral space. The surgical instrument1has a handle10that consists of a handle grip12as well as a shaft11placed on handle grip12. At the distal end of handle10a plate holder13is situated, on which two measurement plates20,40(plate40shown inFIGS. 1b,2) are arrayed. At the distal end of handle10, behind measurement plates20,40, a movable and adjustable depth stop70is additionally placed, which in essence exhibits a turnable casing72that sits on an outer thread74of handle10, as well as a stop76connected with the casing76. In the distal area, a deep stop76completely surrounds surgical instrument1, so that by means of the stop76, it is simultaneously adjustable for one vertebral body found above and one below the measurement plates20,40.

At the proximal end of handle10, behind handle grip12, there is an operating device with a first operating lever32and a second operating lever52. The operating levers32,52act via respective rotating threaded rods31,51(as are more clearly shown inFIG. 5) placed in handle10on the adjustment mechanism placed in the distal area for measurement plates20,40.

FIG. 1bdepicts the surgical instrument fromFIG. 1ain a side view. In this side view, on the proximal end of handle10, the operating levers32,52are especially easy to perceive, are placed radially on threaded rods31,51(as are more clearly shown inFIG. 5) in handle10.

At the distal end of handle10, the depth stop70is turned until it reaches a distal end position, i.e., so that stop76lies immediately behind measurement plates20,40; while inFIG. 1a, it is in a proximal end position right at the transition of handle10to plate holder13.

FIG. 2shows the adjustment mechanism of the distally placed measurement plates20,40fromFIGS. 1aand1bin an enlarged cross-sectional depiction. For better visibility, the depth stop70is not shown in this depiction.

In the sectional depiction ofFIG. 2, in the right section of the drawing, the distal area of handle10is shown, to which plate holder13is attached. On plate holder13, via scissors-like mechanism27, which is movable according to the principle of an accordion-fold lift table, there is placed a first measurement plate20, whose interval relative to plate holder13and second measurement plate40is adjustable. Additionally, placed on plate holder13, placed over an axle43, is the second measurement plate40, which is situated at minimum in a position parallel to the first measurement plate20. Further, the inclination angle α of second measurement plate40is adjustable relative to first measurement plate20via a connecting rod42.

The scissors-like mechanism27of first measurement plate20is subject to linear control via a coupling rod22, (i.e., linear motion of threaded bushing24is transmitted via coupling rod22to a first scissors piece26aof scissors-like mechanism27). The scissors pieces26a,26bof scissors-like mechanism27are connected movably and turnably relative to each other. A first end of first scissors piece26ais pivoted in a first longitudinal hole28ain plate holder13and so as to slide along longitudinal axis L. A second end of first scissors piece26ais placed over an axle in first measurement plate20. A first end of the second scissors piece26bis placed over an axle in plate holder13, while a second end of second scissors piece26bis able to turn in a second longitudinal hole28b, and to slide parallel to longitudinal axis L in first measurement plate20. Coupling rod22acts on the first end of first scissors piece26aplaced in first longitudinal hole28aof plate holder13. Owing to a displacement of first scissors piece26aalong handle10's longitudinal axis L, the interval of first measurement plate20to plate holder13is changed according to the accordion lift table principle, thus altering the interval “a” (seeFIG. 2) of measurement plates20,40, that is defined relative to the first measurement plate20at the location of axis43.

The second measurement plate40is placed over a centrally placed axle43on plate holder13. A linear motion of second threaded bushing44is transferable into a tipping motion of second measurement plate40about axle43via a connecting rod42that engages on the proximal end of second measurement plate40. Support is provided for second measurement plate40in such a way that the interval is not changed by a tipping motion of second measurement plate40in a central area of measurement plate20.

The coupling rod22and connecting rod42are controlled by threaded bushings24,44placed in the handle10. The first threaded rod24is placed so as not to turn in handle10and configured as casing241, in which the second threaded bushing44sits. The first threaded bushing24is controlled via a first tube-shaped threaded rod31(not shown here, shown later inFIG. 5) and converts a turning motion of the first threaded rod31(not shown) into a linear motion along longitudinal axis L of first threaded bushing24, so that by turning the first threaded rod31(as is shown inFIG. 5), the height of first measurement plate20is controllably adjustable. In the first tube-shaped threaded rod31there is placed a second threaded rod51(as is also shown inFIG. 5), which second threaded bushing44controls. Second threaded bushing44is placed so as not to turn via a contact surface449in first threaded bushing25.

FIGS. 3ato3cshow various views of first threaded bushing24, as it is used inFIG. 2to control first measurement plate20.

FIG. 3ais a side view of first threaded bushing24, in which the structure of first threaded bushing24is easily perceived. First threaded bushing24essentially consists of a casing241, in which an inner thread243is placed. On the front side of casing241is a fork-shaped projection245with a borehole247in each of the anus, whereby the connection to coupling rod22can be made via borehole247. An outer thread of the first threaded rod (not shown) engages the inner thread243. The first threaded bushing24is supported by a bolt which engages into a longitudinal hole251situated on the circumference of casing241, and sits so as not to turn in a corresponding recess of handle10, so that rotation of first threaded rod51(as is shown more clearly inFIG. 5) due to engagement of threading evokes a linear motion of first threaded bushing24.

InFIG. 3b, the forklike extension245is easily recognized. The forklike extension245extends outside the thread diameter of bushing241, and through its fork-shaped design and the boreholes247, it offers a possibility to attach coupling rod22through an axis placement with an axis transverse to longitudinal axis L on threaded bushing24.

In the front view ofFIG. 3c, it is easy to perceive that projection245extends only in one half of the cylindrically formed threaded bushing24, and forms a contact surface249turned toward the central axis. In an assembled state, contact surface249stands in contact with a contact surface449of second threaded bushing44, and thus ensures they are positioned so as not to turn.

InFIGS. 4ato4c, various views are shown of second threaded bushing44as it is used according toFIG. 2for controlling the revolving mechanism45.

FIG. 4ashows a side view of second threaded housing44. In this view, the design of second threaded housing44is perceived with particular ease. The second threaded bushing44essentially consists of a casing441, into which an inner thread443is placed. On the front side, proceeding from the casing441, extends a fork-shaped extension445, in which a borehole447is situated. The connection to the connecting rod42can be created via borehole447. As with the first threaded bushing24, the projection445is configured to be only half the radius of casing441, and forms a contact surface449there, which in an assembled state adjoins contact surface249of first threaded bushing24. Through the form-locked arrangement of these contact surfaces249,449is ensured a support of second threaded bushing44in first threaded bushing24so as not to turn.

FIG. 4bshows a top view of second threaded bushing44. In this top view, the fork-shaped projection445with a borehole447made in both legs of projection445is easily perceived. Through the boreholes447, in an assembled state, an axle in turn is run transverse to longitudinal axis L, by means of which the connecting rod42is supported, so that linear motion of threaded bushing44can be transmitted via connecting rod42to second measurement plate40.

FIG. 4cshows a front view of second threaded bushing44, in which the contact surface449formed by continuation445is especially well perceived.

The two measurement plates20,40are operated according to the design presented above through a rotational manipulation of one of the two (or both) operating levers32,52about handle10's longitudinal axis L. Manipulation of the first operating lever32, causes the tube-shaped first threaded rod31(as is more clearly shown inFIG. 5) to turn, which results in a translational motion of first threaded bushing24on the distal end of handle10. Due to the translational motion of first threaded bushing24, via coupling rod22, one of the scissors pieces26is moved so that with the scissors-like mechanism27, the interval “a” (as shown with the arrows) between measurement plates20,40is changed. Manipulation of second operating lever52causes a rotational motion of the second threaded rod51which is placed in the first threaded rod31. This rotational motion causes a translational motion of second threaded bushing44, which in turn, via connecting rod42, induces a tipping motion of second measurement plate40about axle43. In this way, the angle α enclosed by measurement plates20,40is adjustable.

Thus, during the surgical operation, after the spreading and removal of the disk, measurement plates20,40of surgical instrument1are brought into the intervertebral space, whereby a first basic adjustment is made according to values determined through X-raying or computer-aided tomography. Then, in a further X-ray image, the exact fit of measurement plates20,40of surgical instrument1(also thus the exact fit of a prosthesis prepared using the corresponding values), is checked. In case the desired exact fit is not attained, with the invention-specific surgical instrument1it is possible to undertake an adaptation of measurement and carry out another check of the exact fit in yet another x-ray image. No necessity exists to spread the spinal column to remove and again insert a test implant. In this way, it is now recognized that a substantial savings in time and cost is attained and, in particular, this makes possible an operation that is easier on the patient.

Turning next toFIG. 5, there is shown a partial cross-sectional view of the previously described handle grip12of the present invention wherein the first and second threaded rods31,51are more clearly depicted. At the proximal end of handle10(seeFIGS. 1aand1b), behind handle grip12, there is shown an operating device with first operating lever32and a second operating lever52. The operating levers32,52act rotationally via threaded rods31,51(as shown) placed in handle10on the adjustment mechanism placed in the distal area for measurement plates20,40(seeFIG. 1b). The operating levers32,52are placed radially on threaded rods31,51and perpendicular to longitudinal axis “L” and rotate in movement, translating the rotational movement down rods31,51to threads in respective bushings24,44to provide motion relative to the contact surfaces249,449and related coupling/connecting rods22,42.

In the claims, means or step-plus-function clauses are intended to cover the structures described or suggested herein as performing the recited function and not only structural equivalents but also equivalent structures. Thus, for example, although a nail, a screw, and a bolt may not be structural equivalents in that a nail relies on friction between a wooden part and a cylindrical surface, a screw's helical surface positively engages the wooden part, and a bolt's head and nut compress opposite sides of a wooden part, in the environment of fastening wooden parts, a nail, a screw, and a bolt may be readily understood by those skilled in the art as equivalent structures.

Having described at least one of the preferred embodiments of the present invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes, modifications, and adaptations may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.