Prosthetic implant with biplanar angulation and compound angles   

Abstract: A prosthetic implant, and more particularly, with a prosthetic implant having biplanar angulation and that can be inserted into a disk area generally straight using a posterolateral approach.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 12/336,753, filed Dec. 17, 2008, which is incorporated herein by reference and made a part hereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a prosthetic implant, and more particularly, with a prosthetic implant having a biplanar angulation to permit insertion straight along a diagonal angle into a disk space.

2. Description of the Related Art

Spinal fusion is a commonly performed procedure. In a typical spinal fusion operation, a surgeon places a mechanical container, commonly known as a cage, between at least two adjacent vertebrae of the spine. This container contains or is later filled with bone graft which eventually incorporates into the adjacent vertebrae and creates a solid fusion. Interbody cages are placed in the disk space following removal of the disk. The cage can be surgically placed via several approaches, such as anteriorly through the abdomen, posteriorly through the spinal canal, posterolaterally through the neuroforamen of the vertebra, and transversely from a side of the spine. A goal of the surgical approach is to minimize trauma to adjacent structures and incision size.

A challenge to the placement of cages is the attainment of proper fitment between the adjacent vertebrae. It is important that a cage surface fits flushly against the endplates of the adjacent vertebrae. If a cage fits poorly, the cage could loosen, causing poor fixation and potential re-operation. The disk space, where the cage is placed, is not parallel. The space is angulated such that it is wider anteriorly than posteriorly. This angulation is termed lordosis.

Several cage designs have been proposed in the prior art. Brantigan (U.S. Pat. No. 4,834,757) describes a square shaped cage which is impacted in between vertebrae. Michelson (U.S. Pat. No. 5,015,247) describes a straight threaded cage which is screwed into the disk space. Brantigan (U.S. Pat. No. 5,425,772) and Michelson (U.S. Pat. No. 6,302,914) describe a cage with a built in single-plane lordotic angle to improve fitment between adjacent vertebrae. These cages are designed for posterior or anterior placement.

The placement of cages from posterior, lateral, and anterior approaches raise concerns about potential impingement upon important anatomical structures. Such structures are the spinal canal, the spinal nerves, and the abdominal vasculature, respectively. The posterolateral approach, also called the transforamenal approach, is gaining popularity as the preferred approach for the placement of intervertebral fusion cages. Typically, cages designed for this approach are “banana shaped,” as exemplified by Varga, et al (U.S. Pat. No. 6,579,318).

A significant difficulty with banana-type cages is that their placement requires cage rotation at the time of placement to seat the cage in place. The cage is inserted at a 45 degree lateral angle into the disk space (the maximum angle limited by anatomical structures) and is then rotated a further 45 degrees within the disk space for proper placement. This rotational step is difficult in that it occurs blindly inside the disk space. Incomplete rotation frequently occurs, resulting in poor cage fitment, with potential loosening and reoperation.

If a Brantigan (U.S. Pat. No. 4,834,757) cage were inserted in a diagonal or non-straight trajectory, it would not have flush contact with the adjacent vertebrae due to the lordotic angle of the disk space. Furthermore, a standard lordotic cage, such as Michelson (U.S. Pat. No. 6,302,914), would have its lordotic angle in the incorrect orientation for proper fitment if placed diagonally.

What is needed is a cage that can be placed via the posterolateral approach in a straight manner and that does not require a further rotation for placement. Desirably, such a cage will be placed at a straight angle relative to an anterior-posterior axis and, preferably, at a diagonal or angle, such as approximately 45 degrees and reside in a diagonal configuration within the disk space.

SUMMARY

Accordingly, one object of the invention is to provide a cage having a biplanar angulation.

Another object of the invention is to provide a cage that has a biplanar angulation and that may be inserted straight into a disk space, at an angle or diagonally relative to the anterior-posterior axis of the spine.

Still another object of the invention is to provide a cage having a biplanar angulation and that minimizes or eliminates the need for rotation after the cage is inserted into the disk space.

Yet another object of the invention is to provide a cage having lateral slots or channels for insertion of a tool or instrument to facilitate placement of the cage.

In one aspect, this invention comprises a fusion cage comprising a cage body having a plurality of surfaces, the plurality of surfaces cooperating to define a multi-planar angulation adapted to achieve substantially flush fitment in a disk space between adjacent vertebrae when the fusion cage is inserted in the disk space.

In another aspect, this invention comprises a method for fusing bones, the method comprising the steps of providing a cage adapted to be inserted into a disk area substantially diagonally or in an angled direction with respect to an anterior-posterior axis, the cage having a first surface lying in a first plane and a second surface lying in a second plane, and inserting the cage in the substantially diagonal or angled direction such that the first and second surfaces engage a surface of a first vertebrae and a second vertebrae substantially flush.

These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

FIG. 1 is a perspective view of a cage in accordance with one embodiment of the invention showing the cage placed in a disk space;

FIG. 2 is a view, taken along the line 2-2 in FIG. 1, showing the cage inserted straight and at a diagonal or an angle with respect to an anterior-posterior axis;

FIG. 3 is a perspective view showing various details of the cage shown in FIGS. 1 and 2;

FIG. 4 is another perspective view of the cage of FIG. 1;

FIG. 5 is a perspective view of the cage with various projection lines showing the dimensional relationships between the various line segments to illustrate the biplanar angulation or compound angles formed by the various surfaces of the cage;

FIG. 5A is view showing imaginary planes corresponding to the superior and inferior surfaces of the cage, showing their relative relationship and multi-planar or bi-planer angulation;

FIG. 5B is a view, taken in the direction of arrow A in FIG. 5A, showing the relationship of the planes and biplanar angulation of the surfaces;

FIG. 6 is a front view of the cage;

FIG. 7 is a rear view of the cage;

FIG. 8 is a side view of the cage shown in FIG. 1, showing the various relationships and dimensions and relative dimensions of the various corners of the cage;

FIGS. 9 and 10 are illustrative embodiments showing different multi-planar or biplanar angulations;

FIG. 11 is a cross-sectional view taken along the line 11-11 in FIG. 5;

FIG. 12 is a diagonal view taken along the line 12-12 in FIG. 5;

FIG. 13 is a sectional view taken along the line 13-13 in FIG. 5;

FIG. 14 is a fragmentary exploded perspective view of a portion of a cage and an insertion tool;

FIG. 15 is a perspective view of yet another embodiment of the cage of FIG. 1;

FIG. 16 is a front view of the cage;

FIG. 17 is a rear view of the cage;

FIG. 18 is a perspective view of the cage similar to FIG. 5;

FIGS. 19A and 19B are views similar to FIGS. 5A and 5B, respectively;

FIG. 20A illustrates a cage placed in a space between two disks;

FIG. 20B is a view taken along line 20B-20B of FIG. 20A;

FIG. 20C is a view taken along line 20C-20C of FIG. 20A;

FIG. 20D is a view taken along line 20D-20D of FIG. 20A;

FIG. 21A is a view similar to FIG. 20A showing use of another cage;

FIG. 21B is a view taken along line 21B-21B of FIG. 21A;

FIG. 21C is a view taken along line 21C-21C of FIG. 21A;

FIG. 21D is a view taken along line 21D-21D of FIG. 21A;

FIG. 22A is a view similar to FIGS. 20A and 21A;

FIG. 22B is a view taken along line 22B-22B of FIG. 21A;

FIG. 22C is a view taken along line 22C-22C of FIG. 21A;

FIG. 22D is a view taken along line 22D-22D of FIG. 21A; and

FIG. 23 is a is a perspective view of another embodiment of the invention.

DETAILED DESCRIPTION

Referring now to FIGS. 1-10, a prosthetic implant or fusion cage 10 is shown for insertion and use in a disk space or disk area 11 between a first vertebra 12 and second vertebra 14. In the illustration being described, the first vertebra 12 has a first or superior surface 12a and the second vertebra 14 has a second or inferior surface 14a, as best illustrated in FIG. 1. The cage 10 is inserted straight posterolaterally, also called a transforamenal approach, into the disk area 11 between the first vertebra 12 and second vertebra 14. As described and shown, the cage 10 is inserted on a diagonal or angled direction with respect to an anterior-posterior axis AP (FIG. 2), such as in the direction of arrow 16 as shown.

Notice in FIGS. 3 and 4 that the cage 10 comprises a superior or top surface 18 and a generally opposing inferior or bottom surface 20. In the illustration being described, note that the surfaces 18 and 20 are serrated or comprise teeth 22 to facilitate preventing the cage 10 from loosening or becoming displaced after the cage 10 is placed in the disk area 11 between the first vertebra 12 and the second vertebra 14. The cage 10 is adapted or configured to comprise the surfaces 18 and 20 that cooperate to define a biplanar angulation and that cooperate to define multiple angles or at least one compound angle as described herein. The relative angulation between surfaces 18 and 20 facilitate full or flush surface contact between the vertebrae surfaces 12a and 14a and the surfaces 18 and 20, respectively, of the cage 10.

As illustrated in FIGS. 3 and 4, the surfaces 18 and 20 comprise an interior wall 18a and 20a, respectively, that define generally oval apertures or openings 24 and 26, for receiving bone graft material. Note that the cage 10 further comprises a front portion, surface or end 28 and a rear surface or end 30 as shown. The front portion, surface or end 28 comprises a plurality of angled surfaces 28c and 28d, as shown, that cooperate to define a nose, prow or angled frontal portion for ease of substantially straight or linear insertion and placement into the disk area 11 using a posterolateral or transforamenal approach.

The rear surface or end 30 comprises an interior wall 30a having a threaded aperture 40 for receiving an instrument or bone graft material after the cage 10 is inserted substantially straight or linearly into the disk area 11 using the posterolateral or transforamenal approach.

The cage 10 further comprises a side or third surface 42 and a generally opposing side or fourth surface 44 as shown. Note that the third surface 42 comprises a plurality of interior walls 42a and 42b that define apertures 46 and 48, respectively. Similarly, fourth surface 44 comprises interior walls 44a and 44b that define apertures 50 and 52, respectively, as shown. As illustrated, the apertures 46 and 48 are generally opposed to the apertures 50 and 52, respectively, and provide lateral openings adapted to permit graft material to be inserted into an open cage area 54 for fusing the vertebrae 12 and 14 together. Thus, it should be understood that the bilateral openings or apertures 46, 48, 50 and 52 facilitate insertion of bone graft material (not shown) and for bone ingrowth. The inferior and superior openings 24 and 26 further facilitate bone ingrowth.

The surfaces 42 and 44 each comprise a plurality of generally U-shaped walls or surfaces 42c, 42d and 44c, 44d, respectively, to define a first lateral slot 60 and a second lateral slot 62, respectively, for facilitating the placement of the cage 10 using an insertion tool or a surgical instrument 61 (FIG. 14). Notice that the lateral slots 60 and 62 are asymmetrical to allow for directional coupling to an insertion tool or surgical instrument 61. In this regard, notice that the slot 60 has a dimension D1 that is greater than a dimension D2 of the slot 62. The lateral slots 60 and 62 are adapted to receive a generally complementary shaped inter-fitting members or projections 63 and 65, respectively, of the insertion tool or surgical instrument 61.

The insertion tool or surgical instrument 61 has a hollow tubular portion 61 a that receives a rotatable shaft extension 67 having an end 69 that is threaded so that it can be screwed or threaded into the threaded aperture 40, as illustrated. During use, the surgeon would place the rotatable shaft extension 67 until the cage 10 becomes secured or fixed to the insertion tool or surgical instrument 61.

After placement of the cage 10, the rotatable shaft extension 67 is rotated counterclockwise from the cage 10. Note that the insertion tool or surgical instrument 61 or tubular portion 61 a may have indicia 71 for indicating to the surgeon or user the proper orientation of the cage 10, thereby reducing or eliminating the chance that the cage 10 would be improperly placed, for example, upside down into the disk area 11.

Referring now to FIGS. 3-10, the relative relationship of the surfaces 18 and 20, multiplanar or biplanar angulation and compound angle(s) they define will now be described. For ease of illustration, FIGS. 5-10 show various line projections or line segments corresponding to lines or segments between various boundary corners or points or edges of the cage 10. The points are identified and labeled with the letters A-F. The various relationships between and/or among the line segments and other segments will be used for ease of understanding to illustrate or demonstrate the biplanar angulation or compound angles of the cage 10 in this illustration. The “>” designation is understood to mean that a dimension of a segment is larger than the dimension of the segment(s) to which it is compared, “<” means the dimension is less, and “=” means the dimension of the segments is equal. For example, “CD>AB” means that the portion of the cage 10 associated with line segment CD comprises a dimension that is greater than the portion of the cage 10 associated with segment AB.

Returning to the description in the illustration of FIGS. 5-8, note that the line segment length C-D>A-B>E-F>G-H, and the area defined by ACDB in FIG. 5 is greater than the area GEFH. As illustrated in FIGS. 5-8, the dimension between the line segments A-C and B-D gets smaller when moving from line C-D to A-B. Likewise, the cage 10 has a compound or biplanar angulation so that a cross-sectional height dimension (as viewed in FIG. 5) of the cage 10 gets smaller from segment C-D as it moves to every other segment A-B, G-H and E-F.

FIG. 5A illustrates imaginary planes P1 and P2 in which the surfaces 18 and 20, respectively, lie. FIG. 5B shows a view taken in the direction of arrow A in FIG. 5A and generally perpendicular to the plane P2 showing the biplanar angulation or relative tilt (when viewed from left to right in the FIG. 5B and toward G-H). In the example, the surfaces 18 and 20 converge along both a longitudinal axis from a first point, such as the end 28, to a second point such as the rear surface or end 30. The planes P1 and P2 and surfaces 18 and 20 also converge in a direction from segment C-D to G-H in the illustration and also when viewed in a direction generally perpendicular to that longitudinal axis as shown in FIGS. 5-A, 5B and 5C. Thus, the cage 10 and surfaces 18 and 20 define numerous angles, such as angles BA1, BA2, BA3 and BA4 shown in FIG. 4. The angles are all different in the illustration.

Stated another way, the cage 10 comprises a longitudinal axis LA (FIG. 3) and a cross-sectional axis CSA (FIG. 3) that is generally perpendicular to the longitudinal axis LA. In the illustration being described in FIGS. 1-14, the cage 10 is symmetrical about a longitudinal horizontal plane LHP (FIG. 4) along the longitudinal center axis (FIG. 3), but is non-symmetrical in a longitudinal vertical plane LVP (FIG. 3). In one illustration, the cage 10 assumes a trapezoid (FIG. 11) in a vertical cross-sectional plane that is generally perpendicular to the longitudinal center axis, such as the imaginary plane along line 11-11 in FIG. 5. It should be understood, however, that the cage 10 could assume another shape, such as a trapezium (see FIGS. 15-19B), ellipsoid, circular, oval, arcuate or other shape. Other illustrative embodiments are shown in FIGS. 15-23 described later herein.

One important feature of the cage 10 is that the opposing surfaces 18 and 20 in the illustration provide, are arranged or are adapted to cooperate to define one or more compound angles or a biplanar angulation so that the surfaces 18 and 20 become in substantially flush contact with the surfaces 12a and 14a, respectively, when the cage 10 is inserted substantially straight or linearly on a diagonal or angle into the disk area 11 using a posterolateral or transforamenal approach and, if necessary, rotated as described herein.

FIG. 8 is an illustration corresponding to the embodiments of FIGS. 3-7 illustrating CD being greater than AB which is greater than EF which in turn is greater than GH. It should be understood, however, that the degree of the biplanar angulation or compound angle will be selected or changed and will depend upon the relative relationship or orientation between the disk surfaces 12a and 14a. Several other illustrative embodiments are shown in FIGS. 9-10. For example, FIG. 9 illustrates an embodiment wherein the cage 10 has dimensions such that the line segment CD>AB=EF>GH. FIG. 10 illustrates an embodiment where line segment CD>AB<EF>GH. As described later herein, the user will select the cage 10 having the desired biplanar angulation in response to the disk area 11 and the relative relationship of the vertebrae surfaces 12a and 14a. This selection and placement will now be described.

During a surgical procedure it should be understood that the cage 10 is inserted generally straight or linearly at an angle or on a diagonal trajectory relative to the anterior-posterior axis AP (FIG. 2) using a posterolateral or transforamenal approach. As mentioned, the cage 10 and the biplanar angulation or compound angle(s) defined by surfaces 18 and 20 will be selected and adapted depending upon the relative relationship between the surfaces 12a and 14a. In general, the angle Θ (FIG. 2) of insertion increases, the length differences between the segments EF-CD will be decreased and the length differences between the segments AB-GH will also be decreased or lesser. In one embodiment, the cage is being rotated from an angle parallel to the intervertebral lordotic angle to an angle perpendicular to the intervertebral lordotic angle. Segments EF-CD and AB-GH no longer have to conform to this lordotic angle in this trajectory and therefore their length differences are decreased.

As a size of the cage 10 increases, a length difference, for example, between segments EF-CD will be greater as the cage 10 gets larger because a larger amount of the lordotic angle is covered by the cage, and segments or dimensions AB-GH will also be greater. FIGS. 20A-20D, 21A-21D and 22A-22D further illustrate these concepts. All else being equal, larger cages 10 require larger segment differences. A tiny cage 10 covers very little length of the lordosis, so the difference in side length will be small.

In the illustration in FIGS. 20A-20D, a selected cage 10 is inserted using a posterolateral or transforamenal approach and rotated such that its longitudinal axis is generally parallel to the anterior-posterior axis AP as shown. In this illustration, the cage 10 may have a relatively large longitudinal angulation (the angulation BA3 associated with side 42) as illustrated in FIG. 20B. Note, however, that the surfaces 12a and 14a in the illustration are angled not only posterolaterally, but also slightly in a lateral direction (i.e., along a cross-sectional angulation that is generally perpendicular to the longitudinal axis of the cage 10), as illustrated in FIG. 20B. Given the slight angulation, the cage 10 may have only a slight cross-sectional angulation (that is, the angles BA1 and BA2, illustrated in FIGS. 20C and 20D, respectively).

FIGS. 21A-21D illustrate a similar relationship between surfaces 12a and 14a. However, note that the cage 10 is inserted and rotated or pivoted such that it is angled with respect to the anterior-posterior center line. In view of this positioning, note that the user may select a cage 10 wherein the surfaces 12a and 14a define the angle BA3 that is less than the angle BA3 associated with the embodiment illustrated in FIG. 20B. Note that the cross-sectional dimension (i.e., those angles BA1 and BA2 illustrated in FIGS. 21C and 21D) will be slightly larger than those corresponding angles illustrated in FIGS. 20C and 20D, as shown.

FIGS. 22A-22D show another extreme placement of the cage 10, wherein the cage 10 is situated such that its longitudinal axis is generally perpendicular to the anterior-posterior axis. In this position, note that the longitudinal angle is associated with the side 42 (that is, the angle BA3 in the illustration), but generally corresponds to the angle (labeled DA in FIG. 22B) defined by the disk surfaces 12a and 14a. Compare this cage 10 to the cage 10 in the illustration described earlier herein relative to the embodiment of FIG. 20B. Note the cage 10 is selected and adapted to conform to the relationship of the surfaces 12a and 14a as well as the position in which the cage 10 is going to be inserted into the disk area 11 between the surfaces 12a and 14a.

Continuing with the illustration, a cage 10 is shown in FIGS. 22A-22D, having a longitudinal angulation that is slight, as illustrated in FIG. 22B, given the lateral placement of the cage 10 in the disk area 11. However note that the cross-sectional angulation and angles BA1 (FIG. 22C) and BA2 (FIG. 22D) may be relatively greater when compared to the same angles illustrated in FIGS. 20C and 20D.

Advantageously, the implant, system and method provides means for adapting and selecting a cage 10 in response to the relationship between the surfaces 12a and 14a as well as the placement of the cage 10 using a posterolateral approach and the position of the cage 10 in the disk area 11. In some cases, it may be necessary to use a cage 10 having larger or smaller longitudinal angles BA3 and BA4 and smaller cross-sectional angles BA1 and BA2, while in other environments it may be desired to use a cage 10 having relatively larger cross-sectional angles BA1 and BA2 and smaller biplanar angles BA3 and BA4. The angles BA1 and BA2 can be changed relative to each other as can angles BA3 and BA4.

Thus, it should be appreciated that the invention provides a cage 10 having biplanar and angulation defining compound angles that can adapt to various environments such that the surfaces 18 and 20 provide a snug fit against the surfaces 12a and 14a, respectively.

As alluded to earlier herein, the cage 10 could assume different shapes, such as trapezium, ellipsoid, circular, oval, arcuate or other shapes. In this regard, and as described earlier herein, the embodiment of FIGS. 1-14 illustrate a cage 10 that is generally symmetrical about the longitudinal horizontal plane (FIG. 4). FIGS. 15-19B illustrate another embodiment, similar to the embodiment in FIGS. 1-14 wherein the cage 10 is not symmetrical about the longitudinal horizontal plane as illustrated in FIGS. 15-17. The parts in this embodiment are the same or similar to the parts in the embodiments of FIGS. 1-14 and those same or similar parts have been identified with the same part numbers, except that a prime mark (“ ”) has been added to the part numbers of the embodiment shown in FIGS. 15-19B.

In this illustrative embodiment, the cage 10 is not symmetrical about the longitudinal horizontal plane LHP illustrated in FIGS. 16 and 17, and the surfaces 18, 20, 42 and 44 cooperate to define a trapezium in cross-section as shown.

As illustrated in FIG. 18 and as with the embodiment being described earlier herein, various relationships between the segments may be defined. For example, as illustrated in FIGS. 15-18, the line segment KL is greater than IJ is greater than MN is greater than OP and the area defined by IKLJ in FIG. 18 is greater than the area OMNP. As with the prior embodiment, these various dimensions and relationships may be changed, modified or adapted to the particular environment or disk area 11 in which the cage 10 is going to be used.

FIGS. 19A-19B are similar to the imaginary planes shown in FIGS. 5A and 5B. These planes, however, show the non-symmetry of the surfaces 18 and 20 about the longitudinal horizontal plane. By comparison, note the planes P1 and P2 illustrated FIG. 5B show the planes P1 and P2 being generally symmetrical about the longitudinal horizontal plane. As with the prior embodiment, the cage 10 in FIG. 15 is also asymmetrical about the longitudinal plane.

FIG. 23 illustrates yet another embodiment of the invention illustrating a different shape of the cage 10 having biplanar angulation. In this embodiment, the surfaces 18 and 20 are bowed, convex or arcuately shaped as shown. Similar parts are identified with a double prime mark.

Thus, it should be understood that the cage 10 is selected and/or adapted to comprise a biplanar angulation and to permit a posterior-lateral insertion into the disk area 11. The cage 10 is selected or adapted such that it will provide a flush fitmet in a lordotic disk space when placed diagonally via a posterolateral approach. Advantageously, the cage 10 provides biplanar angulation to allow for full surface contact with the surfaces 12a and 14a of the adjacent vertebrae 12 and 14, respectively, when placed at the angled or diagonal trajectory. Note that the cage 10 is inserted in the angled or diagonal trajectory and that the superior and inferior cage surfaces 18 and 20 are in flush or substantially flush engagement with the surfaces 12a and 14a.

It should be understood that while the embodiments illustrated in FIGS. 1-10 show a polygonal or multi-sided shaped cage 10, the cage 10 could take other configurations, such as elliptical, circular or the like. The important feature is that the cage 10 is adapted to provide a biplanar angulation of surfaces 18 and 20 that cooperate to define a compound angle or a biplanar angulation that facilitate a generally or substantially flush fit against surfaces 12a and 14a, respectively, of the vertebrae during generally straight insertion using a posterior lateral approach.

During use, the insertion tool or surgical instrument 61 (FIG. 14) is screwed to the cage 10 as illustrated in FIGS. 1 and 2, the cage 10 is placed using a posterolateral or transforamenal approach and inserted into the disk area 11 (FIG. 1) in a generally straight or linear manner. In the illustration being described, the cage 10 provides means and apparatus that can be placed via a posterolateral approach in a relatively straight manner which reduces or eliminates the need to rotate the cage 10, which can reduce or minimize incorrect orientation or impingement upon important anatomical structures, such as the spinal canal, spinal nerves, abdominal vasculature. The surgeon may use the insertion tool or surgical instrument 61 (FIG. 14) inserted into the lateral slots 60 and 62 to facilitate placement and proper positioning. Note that the nose or front portion 28 of the cage 10 is adapted to facilitate insertion into the disk area 11. The cage 10 may be pivoted or rotated to a proper position as suggested in FIGS. 20A-22D. Graft material may be inserted in a conventional manner into the cage 10. Typically, the graft is placed prior to the insertion of the cage. The cage 10 is then placed using a posterolateral or transforamenal approach and rotated or pivoted if necessary. Thereafter, the patient is closed and the procedure is finished in a conventional manner.

Advantageously, the prosthetic implant or fusion cage 10 provides many advantages, some of which include: a fusion cage wherein the plurality of surfaces cooperate to define a biplanar angulation; a fusion cage wherein the cage body has a first surface generally opposed to a second surface, the first and second surfaces cooperating to define a compound angle and defining a biplanar angulation; a fusion cage wherein the at least one of the first or second surfaces are arcuate or convex in cross-section; a fusion cage wherein the first surface and the second surface converge along a longitudinal axis and in a direction generally perpendicular to the longitudinal axis, the first and second surfaces cooperating to define the compound angle; a fusion cage wherein the first surface lies in a first plane and the second surface lies in a second plane, the first and second planes being non-parallel in cross-section along a longitudinal axis and in cross-section along an axis generally perpendicular to the longitudinal axis; a fusion cage wherein the cage body comprises a longitudinal plane along a longitudinal axis and a cross-sectional plane along a cross-sectional axis that is generally non-parallel to the longitudinal axis, the cage body being non-symmetrical about either of the longitudinal plane or the cross-sectional plane; a fusion cage wherein the cage body comprises a first surface and a second surface coupling the plurality of surfaces, the first surface defining a first surface area and the second surface defining a second surface area, wherein the first and second surface areas are different; a fusion cage wherein the cage body defines a trapezoid or trapezium in a cross-sectional plane that is generally perpendicular to a longitudinal axis; a fusion cage wherein the trapezoid or trapezium gets smaller along the longitudinal axis from a first end to a second end; a fusion cage wherein the cage body defines a second trapezoid or trapezium in a second cross-sectional plane that is generally perpendicular to a longitudinal axis, the cross-sectional plane and the second cross-sectional plane being different in shape or area; a fusion cage wherein a first surface of a first vertebrae cooperates with a second surface of a second vertebrae to define the disk space, the cage body comprises a top defining a top surface for engaging the first surface of the first vertebrae and a bottom surface for engaging the second surface of the second vertebrae, wherein the cage body is adapted to cause the top and bottom surfaces of the cage body to engage the first and second surfaces substantially flush after the fusion cage is inserted into the disk space at an angled or diagonal trajectory; a fusion cage wherein the cage body comprises at least one channel or slot generally parallel to a longitudinal axis of the cage body, the at least one channel or slot being adapted for receiving an insertion instrument; a fusion cage wherein the cage body comprises at least one aperture adapted for receiving an insertion instrument; a fusion cage wherein the insertion instrument comprises indicia to facilitate proper placement of the fusion cage; a fusion cage wherein the plurality of surfaces comprise a first surface that lies in a first plane and a generally opposed second surface that lies in a second plane, the first and second surfaces cooperating to define a compound angle; a fusion cage wherein the compound angle is adapted to cause the first and second surfaces to engage the first and second vertebrae substantially flush when the fusion cage is inserted at an angled or diagonal trajectory into a disk area; a fusion cage wherein each of the plurality of surfaces comprises an opening, the cage body having at least one of a longitudinal slot or an opening adapted to receive a surgical instrument; a fusion cage wherein the cage body comprises a longitudinal axis and a cross-sectional axis, each of the first and second surfaces cooperating to define a first angle along the longitudinal axis and a second angle along the cross-sectional axis, each of the first and second angles being an acute angle; a fusion cage wherein the first and second angles are different; a fusion cage wherein the cage body is adapted such that when it is inserted substantially diagonally or angled with respect to an anterior-posterior axis, the first and second surfaces engage the first and second vertebrae substantially flush; a fusion cage wherein the first and second vertebrae cooperate to define a second compound angle, the second compound angle being adapted so that the first and second surfaces engage the first and second vertebrae substantially flush when the cage body is inserted into s disk area substantially diagonally or angled with respect to an anterior-posterior axis; a fusion cage wherein the first and second angles are different; a fusion cage wherein the cage body comprises a shape that is polygonal and non-circular in any plane; a fusion cage wherein the plurality of surfaces comprises a first planar surface and a generally opposed second planar surface, the cage body is symmetrical about a diagonal axis across the first planar surface; a fusion cage wherein the fusion cage is symmetrical about a longitudinal horizontal plane; a fusion cage wherein the fusion cage is asymmetrical about a longitudinal horizontal plane; a fusion cage wherein the fusion cage is asymmetrical about a longitudinal vertical plane; a fusion cage wherein the fusion cage is asymmetrical about a longitudinal vertical plane; a fusion cage wherein the at least one aperture defines a plurality of lateral slots; a fusion cage wherein the plurality of lateral slots comprise different dimensions to receive a plurality of projections, respectively, of a surgical instrument, the plurality of projections being adapted or sized to generally complement a size of the plurality of lateral slots; a method for fusing bones wherein the method further comprises the step of providing a cage having the first and second surfaces that cooperate to define a compound angle to provide a biplanar angulation; a method for fusing bones wherein the method further comprises the step of providing a cage having a cage body comprising a longitudinal plane along a longitudinal axis and a cross-sectional plane along a cross-sectional axis that is generally perpendicular to the longitudinal axis, the cage body not being volumetrically symmetrical about either of the longitudinal plane or the cross-sectional plane; a method for fusing bones wherein the method further comprises the step of providing a cage having a first surface and a second surface and a first side and a second side coupling the first and second surfaces, the first side defining a first side area, the second side defining a second side area, wherein the first and second side areas are different; a method for fusing bones wherein the method further comprises the step of providing a cage that defines a trapezoid or trapezium in a cross-sectional plane that is generally perpendicular to a longitudinal axis; a method for fusing bones wherein the method further comprises the step of providing a cage having a first surface generally opposed to a second surface, the first and second surfaces defining a compound angle and cooperating to define a biplanar angulation; a method for fusing bones wherein the method further comprises the step of providing a cage with the first surface lying in a first plane and the second surface lying in a second plane, the first and second planes being non-parallel and defining a plurality of acute angles; a method for fusing bones wherein the inserting step occurs during a posterolateral approach; a method for fusing bones wherein the method further comprises the step of providing a plurality of different sized cages from which a user selects the cage; a prosthetic implant system wherein the fusion cage has a plurality of slots and the insertion tool comprises a plurality of projections adapted for receiving in the plurality of slots; a prosthetic implant system wherein the plurality of slots have different dimensions and the plurality of projections generally complement the shape of the plurality of slots; a prosthetic implant system wherein the fusion cage comprises a threaded aperture, the insertion tool comprising a threaded member for screwing into the threaded aperture to secure the fusion cage to the insertion tool; a prosthetic implant system wherein the insertion tool comprises indicia to facilitate proper placement of the fusion cage; a prosthetic implant system wherein the fusion cage has a plurality of slots and the insertion tool comprises a plurality of projections adapted for receiving in the plurality of slots; a prosthetic implant system wherein the plurality of slots have different dimensions and the plurality of projections generally compliment the shape of the plurality of slots; a fusion cage wherein the plurality of surfaces cooperate to define a biplanar angulation; a fusion cage wherein the cage body has a first surface generally opposed to a second surface, the first and second surfaces cooperating to define a compound angle and defining a biplanar angulation; a fusion cage wherein the at least one of the first or second surfaces are arcuate or convex in cross-section; a fusion cage wherein a first surface and a second surface converge along a longitudinal axis and in a direction generally perpendicular to the longitudinal axis, the first and second surfaces cooperating to define a compound angle; and a fusion cage wherein a first surface lies in a first plane and a second surface lies in a second plane, the first and second planes being non-parallel in cross-section along a longitudinal axis and in cross-section along an axis generally perpendicular to the longitudinal axis.

While the method herein described, and the form of apparatus for carrying this method into effect, constitute preferred embodiments of this invention, it is to be understood that the invention is not limited to this precise method and form of apparatus, and that changes may be made in either without departing from the scope of the invention, which is defined in the appended claims.