CA2222025C

CA2222025C - Intervertebral disk stabilizer and instrument for reduction of spondylolisthesis

Info

Publication number: CA2222025C
Application number: CA002222025A
Authority: CA
Inventors: Madhavan Pisharodi
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-03-18
Filing date: 1996-06-06
Publication date: 2007-11-27
Anticipated expiration: 2016-06-06
Also published as: DE69623616D1; WO1996040016A2; US5653762A; JP3761196B2; ES2182985T3; WO1996040016A3; DE69623616T2; AU6090096A; EP0830116B1; CN1134243C; CN1192669A; EP0830116A2; CA2222025A1; JPH11510405A; MX9709599A

Abstract

A middle expanded, removable disk im-plant (22) with substantially rectangular cross--sectional shape with a minimal height (H) and a width (W) greater than the height which is de-tachably mounted to an applicator (52) for in-sertion into the anatomical region between two adjacent vertebrae (16, 18) from which a por-tion of the intervertebral disk has been removed. The implant is positioned by anterior-posterior movement in the disk space to the position in which both the expanded middle portion and the smaller diameter end (25, 36) portions of the im-plant engage the bodies (12, 14) of the adjacent vertebrae and then rotated to bring the sides (34) of the implant defining the height of the implant into engagement with the bodies of the adjacent vertebrae. A lock (24) is then secured to the im-plant to prevent further rotation thereof. In the event the adjacent vertebrae need to be aligned before fusion, an elongate implant (112) is pro-vided which is split longitudinally into side-by-side members (113, 114) movable relative to each other and which is inserted into the disk space between two misaligned vertebrae (133, 137). The members are provided with teeth (138) for engaging the adjacent vertebrae and the implant formed by the two side-by-side members is rectangularly-shapedin cross section, the height (H6) of the rectangularly-shaped cross section being less than the width (W6) so that the implant can be inserted between the adjacent vertebrae with the lesser, height dimension oriented in the same direction as the axis of the spinal column and the larg er width dimension at approximately a right angle to that axis. One member is then moved relative to the other from the first side-by-side position along the longitudinal axis of the implant to a second position in which the members are aligned with the respective, adjacent, misaligned vertebrae and the implant is rotated 90.degree. to engage the teeth to the bodies of the adjacent vertebrae. The two members are then brought back into the first side-by-side position to draw the vertebrae into alignment and the implant is rotated approximately 90.degree. to disengage the teeth from the vertebrae for removal from the disk space.

Description

WO 96/40016 PCT/iIS96109114 INTERVERTEBRAL DISK STABILIZER AND INSTRUMENT FOR REDUCTION
OF SPONDYLOLISTHESIS

The present invention relates to an intervertebral implant and a method of stabilizing adjacent vertebrae. More specifically, the present invention relates to rectangularly-shaped disk implants which are expanded in the middle portion used for spinal fusion. If necessary in treating the patient, the present invention also contemplates reduction of spondylolisthesis, e.g., alignment of the vertebrae comprising the spinal column. In this second aspect, the present invention relates to apparatus which is inserted into the space between adjacent, misaligned vertebrae, engages the bodies of the adjacent vertebrae, and pulls the vertebrae back into alignnient.
Disorders of the spinal column, especially in the neck or lumbar region, continue to be a challenging field of medicine. Classical treatments for conditions involving subluxation of one vertebrae upon another, resulting in misalignment of the spinal column, use screws which extend through a plate and which are tightened to draw the misaligned vertebrae back into alignment. However, such conditions often involve damage to the intervertebral disk, e.g., rupture or herniation, which may result in compression of a nerve root. If the herniation is large, compression may be bilateral. This condition is usually not corrected by re-aligning the vertebrae with a plate and screws such that surgical removal of the disk followed by fusion is often indicated after reduction of spondylolisthesis. The classical treatment for a ruptured disk is diskectomy, i.e., removal of the disk from between the vertebrae. In this process. all or a portion of the intervertebral disk is removed, leaving a defect which bothers the patient throughout the rest of their life. An additional procedure is to replace the disk space with a bone graft, usually bone chips cut from the patient's iliac crest, bringing about fusion of the vertebrae above and below the disk and eliminating the space between the vertebrae.
However, diskectomy with fusion is not ideal because the replaced bone does not have the function of the cartilaginous tissue of the disk, i.e. no cushioning effect, and has several complications. First, conventional bone plugs used to pack the disk space do not conform to the space of the disk because the disk space is wider in the middle and narrower at its anterior and posterior ends. For this reason, currently available bone plugs have only four contact points, i.e. at the front and back of the disk space. Secondly. access to the disk is from the side of the dorsal spine of the adjacent vertebrae, leaving a space that is "off-center" relative to the bodies of the adiacent vertebrae such that the stability of the implant is even more problematical than might be apparent from the limited contact resulting from the shape of the intervertebral space. Another complication is the possibility of infection or other conditions which may require the removal of the implant. Also, if the bone pieces do not fuse. they may eventually extrude out of the disk space, causing pressure on the nerve roots.
Various prosthetic disk plugs, or implants, are disclosed in the art, but all are characterized by limitations of not conforming to the shape of the disk space, lack of stability when inserted off-center, difficulty in precise positioning, inability to be removed. or other disadvantages. For instance, U.S. Patent No. 4,863,476 (and its European counterpart, EP-A-0260044) describes an elongated body divided longitudinally into two portions having a cam device for increasing the space between the two body portions once inserted into the disk space. However, that device is generally cylindrical in shape such that the only contact points are at the front and back of the disk space, creating increased likelihood of instability. The art also discloses intervertebral disk prostheses (e.g., U.S. Patent Nos.
3,867,728, 4.309.777. 4.863,477 and 4,932,969 and French Patent Application No. 8816184) which may have more general contact with the adjacent disks, but which are not intended for use in fusion of the disks. The art also includes spinal joint prostheses such as is described in U.S. Patent No. 4,759,769, which is again not indicated for use when fusion is the preferred surgical intervention.
There is, therefore. a need for treatment of conditions involving misalignment and fusion of the spinal column, as specifically for a device capable of aligning and stabilizina the vertebrae adjacent an intervertebral disk for use in spinal fusion.
These needs are met in the present invention by providing a vertebral disk stabilizer comprising an elongate implant having first, second, third, fourth, fifth and sixth sides providing said implant with a substantially rectangular cross-sectional shape of minimal height defined by the first and second sides and maximal width defined by the third and fourth sides, the third and fourth sides being arched from one end of said implant to the other end of said implant to provide the middle portion of said implant with a width larger than the width of the ends of said implant; one or more of said first, second, fifth and sixth sides defining surfaces for engaging a lock having a vertebrae-bearing surface formed thereon; and means for detachably mounting said lock to one end of said implant to prevent rotation of said lock relative to said implant.

Referring now to the drawings, Figure 1 is a lateral view of a portion of a human spinal column having the vertebral disk stabilizer of the present invention inserted therein and having a portion of the bodies of the vertebrae adjacent the implant shown cut away and/or in shadow lines to show the engagement of the vertebral bodies by the vertebral disk stabilizer.
Figure 2 is an exploded, perspective view of the vertebral disk stabilizer of Fig. 1.
Figure 3 is a top plan view of the implant of Fig. 1 having a handle mounted thereto in place of the lock shown in Fig. 2.
Figure 4 is an exploded, perspective view of a second preferred embodiment of the vertebral disk stabilizer of the present invention.
Figure 5 is a longitudinal, partial sectional view of a preferred embodiment of an apparatus for correcting misalignment of two adjacent vertebrae constructed in acoordance with the present invention.
Figure 6 is an end view of the apparatus of Fig. 5.
Figure 7 is a view similar to that of Fig. 5 but with the mandrel removed therefrom.
Figure 8 is an end view of the apparatus of Fig. 5.
Figure 9 is a side, elevational view of the mandrel of the mandrel after removal from the apparatus of Fig. 5.
Figure 10 is an end view of the mandrel of Fig. 5.
Figure 11 is a partially schematic, lateral view of a portion of the lumbar spine showing the use of the apparatus of Fig. 5 to align the fourth and fifth lumbar vertebrae.
Figure 12 is a top, plan view of an alternative embodiment of the apparatus of Fig. 5 showing the two halves of the body in their first, side-by-side position.
Figure 13 is a top, plan view of the apparatus of Fig. 12 showing the two halves of the body in the second position.
In more detail, a disk stabilizer constructed in accordance with the teachings of the present invention is shown implanted in a human spinal column in Fig.
1. The vertebral disk stabilizer, indicated generally at reference numeral 10, is implanted between the bodies 12 and 14 of two adjacent vertebrae 16 and 18, respectively, in the disk space (not numbered) from which a portion of the intervertebral disk 20 is renioved, i.e. by simple diskectomy and small laminotomy.
Referring now also to Fig. 2, the vertebral disk stabilizer 10 is comprised of an elongate implant 22, lock 24, and means for detachably mounting the lock 24 to one end 25 of the implant 22. In the presently preferred embodiment shown, the mounting means takes the forin of a bolt 26 passing through a bore 28 in lock 24, the threads of bolt 26 engaging complementary threads in the walls of the bore 30 in the end 25 of implant 22.
. In more detail, implant 22 is comprised of first and second sides 32 and third and fourth sides 34 defining a substantially rectangularly-shaped cross-section. The height H of the rectangularly shaped cross-section is defined by first and second sides 32 and the width W is defined by the third and fourth sides 34 and, as is apparent by comparison of H and W, the height of H of implant 22 is less than the width W.
As will be explained below, H is minimized to facilitate insertion of the second end 36 into. and positioning of implant 22 in, the disk space from which a portion of the intervertebral disk 20 was removed and W is maximized to provide the desired stabilization to adjacent vertebrae 16 and 18. Third and fourth sides 34 are arched from one end of implant 22 to the other to provide the portion of implant 22 intermediate the ends 25 and 36 with a width W' which is larger than the width W" at the ends 25 and 36. Because the sides 32 of implant 22 are substantially flat and the sides 34 are arched from one end 25 to the other end 36, implant 22 is described as being a biplanar, bi-convex implant. The bi-convex sides 34 of implant 22 are provided with a plurality of teeth 38 for biting into the adjacent vertebrae 16 and 18 as will be explained in more detail below. The end 36 of implant 22 is formed in a blunt, or rounded shape to reduce the likelihood of injury to the nerves of the spinal cord during insertion into the disk space.
In the preferred embodiment shown, lock 24 is substantially square wlien viewed from the end 40 along the axis of the bore 28 therethrough and U-shaped when viewed from the side. The inside surfaces 42 of the arms 44 of the U-shaped lock 24 are flat for contacting the first and second sides 32 of implant 22 to prevent rotation of lock 24 relative to implant 22 when lock 24 is mounted to implant 22 and secured thereto by bolt 26. The surfaces 42 are provided with a slot 46 for receiving a complementary-shaped key 48 to facilitate assembly of lock 24 to implant 22.
The slot 46 may also be located on the implant 22 and the key 48 may be located on the lock 24 without any difference in the function of those component parts. The bore 28 in lock 24 is aligned with the bore 30 in implant 22.
The sides of the square end 40 of lock 24 provide surfaces 50 for bearing against the bodies 12 and 14 of adjacent vertebrae 16 and 18 as also explained in more detail below. It will be recognized by those skilled in the art who have the benefit of this disclosure that the bearing surfaces 50 need not be flat and that the end 40 of lock 24 need not be square. Other shapes and configurations may be utilized as needed to insure that movement of lock 24 is limited by the bodies of the adjacent vertebrae 16 and 18. The purpose of the bi-planar, middle expanded, bi-convex implant 22 is to enable insertion of the implant 22 into the disk space and turning by approximately 90 to increase the disk height and stabilize the disk space.
The purpose of lock 24 is to lock implant 22 against instability when in the vertical position so as to maintain the disk height thereafter.
Referring now to Fig. 3, there is shown an applicator 52 mounted to the end 25 of implant 22. In the embodiment shown, applicator 52 is mounted to implant by screwing the threaded end 54 thereof into the threaded bore 30 in implant 22.
When the end 54 of applicator 52 is screwed all the way into the bore 30, so as to prevent relative movement therebetween, implant 22 is inserted into the disk space and rotated therein using applicator 52 as explained below. Applicator 52 is detached froni implant 22 by rotating in the opposite direction while rotation of implant 22 is restrained.
The use of the stabilizer 10 of the present invention in, for instance, a method of lumbar intervertebral disk stabilization, or "LIDS," is illustrated in Fig.
1. Surgery is performed as in a simple diskectomy and the intervertebral disk 20 is exposed through a small laminotomy. The disk material is removed and any nerve root compression is corrected. The posterior longitudinal ligament (not shown) and disk cartilage are removed until the surface of the bodies 12 and 14 of adjacent vertebrae 16 and 18. respectively, are exposed above and below the disk space.
Using spreaders such as those disclosed in International Application No.
PCT/US95/00347, the vertebrae 16 and 18 are distracted to open the disk space, and once the desired "spread" is achieved, the middle portion of the disk space is packed with cancellous bone chips (not shown). Because the posterior longitudinal ligament is left intact to the opposite side and to the center of the disk space, the bone chips are held in place in the disk space.
An implant 22 having a height H and width W selected to fit the disk space is then mounted on applicator 52 by screwing on to the threaded end 54. The appropriatelv-sized implant 22 is then inserted into the disk space using the applicator 52 with the implant 22 oriented so that the top and bottom thereof, i.e., the first and second sides 32, engage the bodies 12 and 14 of adjacent vertebrae 16 and 18. respectively. Using the applicator 52, implant 22 is then moved further into (or back out of) the disk space in an anterior-posterior direction so as to enable the implant 22 to be positioned in the disk space at a position in which the expanded, middle portion and the smaller width ends 25 and 36 of the third and fourth sides 34 of implant 22 contact the respective lower and upper surfaces of the bodies 12 and 14 of the adjacent vertebrae 16 and 18 when rotated by approximately 90 using the applicator 52. To facilitate this rotation, the corners of the implant 22 between the first and second surfaces 32 and the third and fourth surfaces 34 are rounded as shown at 35, the rounded corners 35 effectively acting as planes, or ramps, to lever the adjacent vertebrae 16 and 18 apart during rotation. The respective lower and upper surfaces of the vertebral bodies 12 and 14 are slightly concave such that the larger width middle portion W" of implant 22 allows the implant 22 to engage substantially more of the respective surfaces of the vertebral bodies 12 and 14 than conventional prosthetic devices, thereby providing increased stability to the fusion once further rotation of implant 22 in the disk space is prevented as described below.
Once the implant 22 is positioned in the disk space, the applicator 52 is detached by unscrewing and backed out of the incision in the patient. Lock 24 is then inserted through that same incision and, using the slot 46 and key 48, the bore 28 in lock 24 and bore 30 in implant 22 are aligned and the bolt 26 is inserted and tightened to secure lock 24 to the implant 22. Securing the lock 24 to implant 22 in this manner prevents relative rotation between lock 24 and implant 22 and the bearing surfaces 50 of lock 24 bear against the bodies 12 and 14 of the adjacent vertebrae 16 and 18 to prevent rotation of the lock 24 relative to the adjacent vertebrae 16 and 18 against which the bearing surfaces 50 bear. The bearing surfaces 50 bear against the cortical end plates of the respective vertebral bodies 12 and 14, which are comprised of non-cancellous bone, and which provide a hard, relatively smooth surface. The end 40 of lock 24 is preferably supplied in a plurality of different sizes and shapes other than the square shaped end 40 shown in the figures so as to allow the surgeon to select an appropriately sized and shaped lock which provides a close fit with the space between vertebral bodies.
If necessary, a small amount of a physiologically compatible adhesive of a type known in the art is applied over the cancellous bone chips just medial to the implant to close off the remaining portion of the opening into the disk space.
The patient should be able to ambulate soon after the LIDS procedure because of the stability imparted to the spinal column by the implant of the present invention.
Before narrowing of the disk space occurs, the cancellous bone chips will have started the fusion process.

The stabilizer 10 is also used to advantage to perform, for instance, a posterior lateral intertransverse fusion. The implant 22 is inserted into the region of the disk space from which a portion of the disk has been removed as described above with the lock 24 and the posterior lateral fusion performed. Because the implant 22 provides stability to the spine until the posterior lateral fusion is solid, the patient is generally able to ambulate soon after surgery. This procedure also prevents the narrowing of the disk space, which is a common problem with posterior lateral fusion.
Removal of the implant 22 is accomplished with relative ease compared to conventional implants. The bolt 26 is screwed back out of implant 22 and lock 24 is pulled out of the disk space. Applicator 52 is re-inserted and screwed into the bore 30 in iinplant 22 and used to rotate implant 22 by approximately 90 , causing the first and second sides, having minimal height, to contact the bodies 12 and 14 of adjacent vertebrae 16 and 18 so as to allow posteriorly-directed movement of the implant 22 out of the disk space.
An alternative embodiment of the implant of the present invention is shown in Fig. 4 in which the first and second sides 32' of implant 22' are substantially flat but not parallel along their longitudinal axes. The resulting wedge shape of the implant 22' facilitates insertion into the disk space, the rounded end 36 reducing the likelihood of injury to the nerves of the spinal cord during insertion into the disk space. Likewise, comparison of the widths W', W", and W"' of implant 22' will show that the width W' of implant 22' at the end 36' is less than the width W"' at the end 25'. Both widths are less than the width W" in the middle, expanded portion of implant 22'. In another alternative embodiment (not shown) which provides additional resistance to forward or backward movement of implant 22 in the disk space. the teeth 38 located closest to the end 25 of implant 22 (e.g., the teeth in the distal portion of implant 22) are slanted toward the end 25 and the teeth 38 closest to the end 36 of implant 22 are slanted toward the end 36. The teeth in the middle portion of implant 22, e.g., between the two sets of slanted teeth, are oriented vertically.
Referring now to Figs. 5-13, there is shown an apparatus for aligning adjacent vertebrae constructed in accordance with the teachings of the present invention. The apparatus. indicated generally at reference numeral 110, is comprised of an elongate handle 1 1 I and an elongate body 112. The body 112 is comprised of first and second side-by-side members 113 and 114, respectively, the first member 113 being integrally mounted to handle 111 and the second member 114 being movable relative to the first member 113 in the direction of the longitudinal axis of the shaft 115 of handle 111. Means, in the form of the teeth 138, is provided on body 112 for selectively engaging the adjacent vertebrae 133, 137 when the body 112 is inserted therebetween to prevent relative movement between the respective first and second ni eni bers 113 and 114 and the adjacent vertebrae 137 and 133 to which the first and second members 113 and 114 are engaged.
The shaft 115 of handle 111 is provided with a longitudinal bore 116 tllerethrough having a mandrel 117 positioned therein, the second member 114 being niounted to mandrel 117. At the end opposite first member 113, the shaft 115 is provided with a tubular barrel 118 having a collar 119 positioned therein.
Collar 119 is also provided with a longitudinal bore 116', the longitudinal axis of which is aligned with the longitudinal axis of the bore 116 in mandrel 117 which is provided xvith a set of threads 120 for receiving the threaded end 121 of mandrel 117.
Collar 119 is retained within barrel 118 by the keeper 122 which is retained on the end of barrel 118 by screws 123. An adjustment knob 124 is integrally mounted to collar 118 by screws 126. As a result of this construction, when mandrel 117 is rotated by turning adjustment knob 124, the second member 114 moves relative to first member 11 3 from a first position in which the members 113 and 114 are in side-by-side, parallel relationship to each other to a second position along the longitudinal axis of the shaft 115 of handle 111 in which the two members remain parallel to each other hut are no longer side-by-side as shown in Fig. 11. Referring to Figs. 7-10, it can be secn that one surface of first member 113 is formed in the shape of a half round hollo\v 127 for receiving the round mandrel 117 for retaining the two members and 114 in tight, parallel, side-by-side relationship when second member 114 is moved from the first position to the second position.
When the first and second members 113 and 14 are in the first side-by-side position shown in Figs. 5 and 6, e.g., when the mandrel 117 is rotated to draw the end 136 of second member 114 against the end 154 of handle 111, the two members and 1 14 form an elongate body 112 having a shape which is similar to the shape of the nionolithic implant 22 shown in Figs. 1-4. Referring, however, to the body f'or the time being, when side-by-side, the two members 113 and 114 form a body 112 that is comprised of first and second sides 132 and third and fourth sides 134 providing a substantially rectangularly-shaped cross-section. The height H6 of the rectangularly-shaped cross-section is defined by first and second sides 132 and the width W, is defined by the third and fourth sides 134 and, as is apparent by comparison of H6 and W6, the height H6 of body 112 is less than the width W6.
As will be explained below, H6 is minimized to facilitate insertion of the second end 136 into. and positioning of body 112 in, the disk space from which a portion of the intervertebral disk 130 was removed and W6 is maximized to provide the desired stabilization to adjacent vertebrae 133 and 137. Third and fourth sides 134 are arched from one end of body 112 to the other to provide the portion of body intermediate the ends 125 and 136 with a width W'6 which is larger than the width W"t, at the ends 125 and 136. Because the sides 132 of body 112 are substantially flat and the sides 134 are arched from one end 125 to the other end 136, body 112 is described as being a biplanar, bi-convex body. The convex, or arched, sides 134 of body 112 are provided with a plurality of teeth 138 for biting into the adjacent vertebrae 133 and 137 as will be explained in more detail below. The end 136 of bodN- 112 is formed in a blunt, or rounded shape to reduce the likelihood of injury to the nerves of the spinal cord during insertion into the disk space.
Referring now to Fig. 11, the use of the apparatus 110 for reduction of spondylolisthesis is shown. In Fig. 11, the fourth lumbar vertebrae (L4) 133 is shown as having shifted anteriorally, leaving that vertebrae out of alignment with the fifth lumbar vertebrae (L5) 137 and the vertebrae comprising the sacrum 135. To correct this niisalignment, surgery is performed as in a simple diskectomy and the intervertebral disk (not shown) is exposed through a small laminotomy. Disk material is removed and any nerve root compression is corrected. The posterior lon~,~itudinal ligament (not shown) and disk cartilage are removed until the surface of the bodies 129 and 131 of the adjacent vertebrae (L4 and L5) 133 and 137, respectively, are exposed above and below the disk space.
Using spreaders such as those disclosed in International Application No.
PCT/US95/00347, the adjacent vertebrae 133 and 137 are distracted to open the disk space. The body 112 of apparatus 110, having the first and second members 113 and 114 initially in the above-described side-by-side relationship, is then inserted into the disk space with the top and bottom thereof, i.e., the first and second substantially planar sides 132. engaging the adjacent vertebrae 133 and 137 so that the teeth 138 f'oriiled on the third and fourth sides 134 of body 112 extend into the disk space %N-ithout engaging the adjacent vertebrae 133 and 137. The implant is oriented in the disk space so that, when rotated as described below, the first member 113 is the portion of the body 112 which contacts the body 131 of L5 137 and the second niember contacts the body 129 of L4 133. In other words, body 112 is oriented so 10 that first member 113 is positioned in close proximity to the body 131 of the vertebrae 137 which is aligned with the axis, or centerline CL, of the spinal column and second member 114 is positioned in close proximity to the axis of the body of the vertebrae 133 which is out of alignment. The body 112 of apparatus 110 is inserted until the middle portion of first member 113 is positioned adjacent the concavity in the upper surface of the body 131 of the L5 137. Using the adjustment knob 124. mandrel 117 is then rotated to advance the second member 114, e.g., the portion having the wider width W"6, anteriorally until the middle portion, e.g., the portion having the wider width W"6, of second member 114 is positioned adjacent the concavity of the lower surface of the body 129 of L4 133. As noted above, the wider nliddle portion W"6 of each of the members 113 and 114 comprising the body 112 of apparatus 110 provides maximal engagement of the concave shaped surface of the body of the vertebrae - when the body 112 is rotated by approximately 90 as described below. Depending upon the circumstances of each surgery, it may also be advantageous to "pre-adjust" the body 112 by advancing the second member 114 to the second position by the amount of the misalignment before inserting the body 112 of apparatus 110 into the disk space. The amount of slippage of L4 133 relative to L5 137 is calculated using known methods and/or estimated from X-ray films or other images.
Once the first and second members 113 and 114 are approximately aligned with each of the adjacent vertebrae 133 and 137 by positioning the wide, middle portion of each member in the respective concavities of the vertebrae, using the barrel 118 of handle 111, the body 112 of apparatus 110 is rotated by approximately 90 to cause the teeth 138 formed on the surfaces 134 of first and second members 1 13 and 114 to engage the bodies 129 and 131 of the respective adjacent vertebrae 133 and 137 as shown in Fig. 11. Using the adjustment knob 124, mandrel 117 is then rotated in the opposite direction to draw second member 114 back into the first, side-bv-side, parallel relationship with first member 113, pulling the vertebrae to which it is engaged, i.e., L4 133, back into alignment with L5 137.
The diskectomy and laminotomy are preferably performed bilaterally. In other words, the above-described surgical procedure is performed to the side of the center line of the adjacent vertebrae such that the portion of the intervertebral disk which is removed is "off center" relative to the bodies 129 and 131 of the respective adjacent vertebrae 133 and 137. An identical surgery is performed on the other, or second. side of the center line of the adjacent verl:ebrae and the body 112 of a second apparatus 110 (not shown in the figures for purposes of clarity) is inserted into the disk space after that second procedure. The adjacent vertebrae 133 and 137 are then aligned by rotation of the respective adjustment knobs 124 of both apparatus until the vertebrae are aligned. In this fashion, the body 112 of one of the two apparatus 110 retains the adjacent vertebrae in alignment even after removal of the otlier implant.
Removal of the body 112 is accomplished by rotation by approximately 90 (preferably in the direction opposite the direction of rotation which was utilized to cause the teeth 138 to engage the respective adjacent vertebrae 133 and 137) so as to disengage the teeth 138 from L4fi133 and L5 137. While the body of the second apparatus remains in the disk space on the second side of the center line, an implant such as the implant 22 (see Figs. 1-4) is inserted into the disk space from which the body 112 was removed on the end of applicator 52 with the flat surfaces 32 adjacent the bodies 129 and 131 of adjacent vertebrae 133 and 137 and moved in an anterior-posterior direction so as to enable the implant 22 to be positioned in the disk space at a position in which the expanded, middle portion and the smaller width ends 25 and 36 of the third and fourth sides 34 of implant 22 contact the respective lower and upper surfaces of the bodies 129 and 131 of the adjacent vertebrae 133 and 137 when rotated by approximately 90 using the applicator.
After rotation, the applicator 52 is detached from the implant 22 by unscrewing and backed out of the incision. Lock 24 is then inserted through that same incision and, using the slot 46 and key 48, the bore 28 in lock 24 and bore 30 in iniplant 22 are aligned and the bolt 26 is inserted and tightened to secure lock 24 to the implant 22 all as previously described. Once the monolithic implant 22 is locked in place on the first side of the center line of the adjacent vertebrae 133 and 137, the body 12 of the second apparatus 10 on the second side of the center line, which has remained in place throughout the procedure, is then removed. The disk space is then packed with cancellous bone chips through this second side and a second monolithic implant 22 (also not shown) is inserted, positioned, rotated, and locked in its place in the same manner as described above. If necessary, a small amount of a pli}-siologically compatible adhesive of a type known in the art is applied over the cancellous bone chips just medial to the implants to close off the remaining portion of the openings into the disk space.
Referring now to Figs. 12 and 13, there is shown an alternative embodiment of the spondylolisthesis reduction apparatus, indicated generally at reference numeral 12 l 10a, of the present invention. Where possible, the component parts of apparatus 110a are labelled with the reference numeral (and the "a" designation) of the corresponding parts of the apparatus 1 1 0 . Apparatus II 0a is comprised of a handle 111 a and body 112a, the body 112a being comprised of first (fixed) and second (movable) members 113a and 114a, respectively. The second member 114a is nlounted to a mandrel 117a positioned in a longitudinal bore 116a in the shaft 115a by a swivel joint 140a and moves relative to first member 113a by action of the threads 121a formed on the outside surface of mandrel 117a on the threads 120a formed on the shaft 115a of handle 111 a. The body 112a of apparatus 110a is shaped in the same substantially rectangular cross-sectional shape as the body 112 of apparatus 110 and the component parts of apparatus 110a function in the same manner as the parts of apparatus 110.
Apparatus 110a also includes a plurality of fine serrations 142a formed on the opposed surfaces 144a and 146a of first and second members 113a and 114a, respectively. The serrations 142a act to resist longitudinal movement of second member 1 l4a relative to first member 113a.

Claims

WHAT IS CLAIMED IS:

1. A vertebral disk stabilizer comprising:
an elongate implant having first, second, third, fourth, fifth and sixth sides providing said implant with a substantially rectangular cross-sectional shape of minimal height defined by the first and second sides and maximal width defined by the third and fourth sides, the third and fourth sides being arched from one end of said implant to the other end of said implant to provide the middle portion of said implant with a width larger than the width of the ends of said implant;
one or more of said first, second, fifth and sixth sides defining surfaces for engaging a lock having a vertebrae-bearing surface formed thereon;
and means for detachably mounting said lock to one end of said implant to prevent rotation of said lock relative to said implant.

2. The stabilizer of claim 1 wherein the third and fourth sides of said implant are provided with teeth.

3. The stabilizer of claim 1 wherein said lock is provided with a substantially flat implant-bearing surface for contacting either the first or the second side of said implant to prevent rotation of said lock relative to said implant.

4. The stabilizer of claim 1 wherein the corners of said implant between the first, second, third, and fourth sides are rounded.

5. The stabilizer of claim 1 wherein the end of said implant opposite the end to which said lock is mounted is rounded.

6. The apparatus of claim 1 wherein said bearing surface is oriented at an angle of approximately 90° to the first and second sides of said implant when secured thereto.

7. The stabilizer of any of claims 1-6 in combination with an applicator for detachably mounting to said implant.