WO2000018311A1 - Spinal osteosynthesis device with median vertebral hook - Google Patents

Abstract

This device comprises two longitudinal rods (7) adapted to be fixed on the spine and to extend respectively on each side of a section of the latter and, for a given vertebra (3), a hook (12) and two vertebral bearing means associated with said hook, which is adapted to bear against the median part of the vertebral posterior arch (20) between two longitudinal rods, the hook is provided with transverse rods (27, 28) for connection to the longitudinal rods and is made in two parts (13, 14) capable of being assembled to constitute the hook, namely a first part (13) comprising a body extended by a blade (16) which extends with a lateral off set relative to the body and is so profiled and adapted to be capable of bearing against a central region of the vertebral posterior arch (20), and a second part (14) forming a connector for connection with the first part, comprising a body integral with a transverse stem (21) insertable in a transverse bore in the body of the first part (13), means (41) being provided for fixing this rod in a detachable manner to the body of said first part (13). The invention avoids cutting the ligaments between the spinous processes to allow mounting hooks.

Description

SPINAL OSTEOSYNTHESIS DEVICE WITH MEDIAN VERTEBRAL HOOK

The present invention relates to a spinal osteosynthesis device, and more particularly, but not exclusively, a spinal osteosynthesis device having a median hook and vertebral anchorage supports of the type described in French Patent Application Serial No. 95 00 732 (No. 2 729 556) filed January 23, 1995; U.S. Patent No. 5 702 452 filed January 22, 1996; and French Patent Application Serial No. 98 12 243 filed September 30, 1998, the disclosures of which are hereby incorporated by reference.

BACKGROUND One type of osteosynthesis device comprises two longitudinal rods adapted to be fixed on the spine and to extend respectively on each side of a section of the latter. For a given vertebra, this device also includes a hook and two vertebral bearing means associated with the hook to bear against the median part of the vertebral posterior arch between two longitudinal rods. This hook is typically provided with transverse connection means to connect the hook to the longitudinal rods.

While such a median hook is satisfactory, it obliges the surgeon, for the purpose of placing it in position either over the lamina or under the lamina relative to the spinous process and to the vertebral arch, to first of all cut the upper and interprocess ligaments and one of the adjacent spinous processes for placing therein the body of the hook (the ligaments being the longitudinal fibrous mass which interconnects the spinous processes). At the end of the intervention, the surgeon must place the ligaments and the cut part of the spinous process back in position and then suture the whole. Cutting the upper and interprocess ligaments consequently destabilizes the spine superjacent to the segment provided with the instrumentation and moreover accentuates the invasive character of the intervention. Thus, there is a need for further contributions in the area of medical implant technology to address this shortcoming and/or other problems.

DISCLOSURE OF THE INVENTION

One form of the present invention is a unique hook implant. Other forms include unique spinal implant methods and devices. A further form is a unique transverse connection device for interconnecting two longitudinal members of a medical implant apparatus. In one variation, the longitudinal members are in the form of rods or bars that extend along opposite sides of the spine and the connection device is configured to interconnect the rods and engage at least one vertebra of the spine. The rods may be engaged to the spine by way of one or more anchorage members fastened therealong.

Still a further form is a spinal implant device that includes a median hook comprised of at least two parts to permit placing the hook in position without cutting the spinous process, the upper ligaments, and/or interprocess ligaments. The multipart hook may be connected between two longitudinal members connected to a patient's spine.

Among the objects of the invention is to place a median hook in position without cutting the spinous process or associated ligaments. Accordingly, in another form of the invention, a hook is made in two parts: a first part comprising a body extended by a blade, which extends from the body and is profiled and adapted to bear against a central region of the vertebral posterior arch; and a second part forming a connector for connection with the first part. The second part may include a body that is integral with a transverse stem adapted to be inserted in a transverse bore in the body of the first part. Also, means for fixing the stem to the body of the first part may be included.

For this form, openings can be provided in the bodies of the two parts of the hook for each receiving a bent bar for connection with the longitudinal rod, each body being in addition capable of receiving a screw for clamping to the connection bar. Additionally, the blade may extend with a lateral offset relative to the body, and the body of one or more parts comprising the hook may be positioned in a location readily accessible to the surgeon that reduces interference with the upper and/or lower interprocess ligaments. In this form, the end of the stem may include a bearing surface for engaging a transverse connection bar between the hook and a longitudinal rod. A bore for receiving the end of the connector stem may open onto an opening provided in the body for the bar and a second opening for a second connection bar may be provided in the body of the second part of the hook. As the end of the connection bar for the first part of the hook bears against the bearing surface of the stem of the second part, a clamping element (such as a screw) may be inserted in the body of the first part that permits, when it is tightened, fixing the connector to the first part of the hook and to the connection bar, thereby constituting the complete hook, the two parts of which however remain separable. With this arrangement of the hook in two parts, it is sufficient for the surgeon to provide in the upper and interprocess ligaments a small passage for the connecting stem between the two bodies of the hook without adversely affecting the rest of the ligaments or a spinous process. Consequently, when placing the hook in position, the lesion created in the upper and interprocess ligaments is reduced to a minimum, and, at the end of the intervention, the surgeon is no longer obliged to suture these ligaments.

In still another form, there is provided a method of treating a patent's spine that includes forming an opening in ligament tissue connected to a first and a second vertebra and attaching a median hook of the present invention to at least one of the first or second vertebra.

Other forms, embodiments, objects, features, benefits, aspects, and advantages of the invention will be apparent from the following description, with reference to the accompanying drawings which illustrate an embodiment thereof by way of a non-limitative example.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagrammatic elevational view of a spinal osteosynthesis instrumentation placed in position on a segment of the spine, one end of this instrumentation being provided with the vertebral anchorage and a transverse connection system according to the invention.

Fig. 2 is a partial perspective view to a larger scale of the anchorage and transverse connection system of Fig. 1, provided with the hook of the invention, and of the corresponding vertebra on which the hook of this system may be anchored. Fig. 3 is an exploded, front elevational view to a larger scale of an embodiment of the hook of the osteosynthesis device of Figs. 1 and 2, before the assembly of its two component parts.

Fig. 4 is a side elevational view of a first part of the hook in the direction of arrow K of Fig. 3. Fig. 5 is a diagrammatic elevational view to a larger scale of the vertebra of Fig. 2 and of the part of the hook comprising the anchorage blade, shown in the position over the lamina in the central part of the vertebral posterior arch. Fig. 6 is a rear elevational view of a spinal segment consisting of two vertebrae at the beginning of the surgical intervention for mounting the vertebral anchorage device according to the invention.

Fig. 7 is an elevational view in a sagittal plane corresponding to Fig. 6. Fig. 8 is an elevational view illustrating the mounting of the hook according to the invention between the spinous processes of two consecutive vertebrae in the position over the lamina.

Fig. 9 is a view similar to Fig. 8 illustrating insertion of a rod or bar for connection to a vertebral rod. Fig. 10 is an elevational view in a sagittal plane corresponding to Fig. 9.

Fig. 11 is a view of a spinal lumbar segment, to a smaller scale, equipped with an osteosynthesis device having two longitudinal rods interconnected by a pair of anchorage systems having hooks according to the invention.

MODE(S) FOR CARRYING OUT THE INVENTION The spinal implant osteosynthesis instrumentation 100 diagrammatically shown in Fig. 1 extends along a vertebral segment consisting of three vertebrae 1, 2, 3 interconnected by vertebral disks 4, 5, 6, and comprises two longitudinal rods anchored in the vertebral bodies at generally equal distances apart, in a standard manner, by means of bone anchorage elements or members, such as pedicle screws 8, represented diagrammatically.

Instrumentation 100 may be completed by one or more transverse connection devices (TCD) of a type known per se, such as the device 9 interconnecting longitudinal members in the form of rods 7. These TCDs may be, for example, the type described in French patent Nos. 2,645,427 of April 11, 1989 and 2,659,225 of March 8, 1990.

Instrumentation 100 is also provided with a system 11 providing a vertebral anchorage and a transverse connection between the rods 7, mounted on one of the vertebrae of the illustrated spinal segment, for example vertebra 3. System 11 will be described in further detail below with reference more particularly to Figs. 2 to 5.

System 11 extends along transverse axis 10, bridging rods 7. System 11 comprises a hook 12 of the median type and two vertebral bearing means associated with the hook 12 for a given vertebra such as the vertebra 3, namely pedicle screws 8, in the presently-described embodiment. Hook 12 includes two parts 13 and 14 that can be assembled during implantation to constitute a single functioning element. First part 13 comprises a body 15 extended by a blade 16 terminating in a bent bone anchorage nose 17. Blade 16 and bone anchorage nose 17 extend with a lateral offset relative to body 15. Further, blade 16 is profiled and adapted so that anchorage nose 17 can bear against a central region 20 of the posterior arch of the vertebra 3 and be inserted in the widest part of the medullary canal of the spine (as shown in Fig. 5 of the present invention). Second part 14 forms a connector for connection with the first part 13 and comprises a body 19 with transverse stem 21 adapted to be inserted in transverse passage or bore 22. Body 15 of first part 13 defines transverse bore 22.

Transverse bore 22 extends into and can extend through body 15 as illustrated. Stem 21 is configured for insertion into bore 22 on the side towards which the profiled blade 16 is offset (as shown in Fig. 3) so that when parts 13, 14 are assembled as shown in dot-dash lines 14a of Fig. 3, the anchorage nose 17 is situated in a substantially central position with respect to bodies 15, 19. When stem 21 connects body 15 and body 19 together, a gap 120 is defined between body 15 and 19 sized to receive posterior spinal tissue as more fully explained hereinafter. Bodies 15, 19 include respective openings 23, 24 extending throughout in a direction generally perpendicular to the longitudinal axis of stem 21 when bodies 15, 19 are assembled to one another. Opening 23 intersects bore 22. Openings 23, 24 extend along central axes that are approximately parallel to the longitude of rods 7 when instrumentation 100 is placed in position. Openings 23, 24 have a cross section adapted to receive the corresponding ends 25, 26 of two bent rods or bars 27, 28 providing a connection of hook 12 to the longitudinal rods 7. For the illustrated embodiment, bent bars 27, 28 comprise cylindrical ends 25, 26 connected substantially at a right angle to a respective bar 29, 31 having a substantially rectangular section adapted to be inserted in an inner passageway of a respective rod hook 32, 33. Hooks 32 and 33 are each configured to engage a respective one of rods 7 to be fixed thereto. It can be seen in Fig. 2 that the ends of the bars 27, 28, respectively, can project out of respective passages of hooks 32, 33 (such as end 28a of bar 28 extending through passageway 32a of hook 32). This arrangement permits spanning variable distances between rods 7 with system 11 according to the respective lengths of bars 27, 28. Screws 34, 35 are included that can be threaded into threaded holes 34a, 35a, of hooks 32, 33, respectively, to contact bars 29, 31 and clamp bars 29, 31 and rods 7 together. It should be understood that passages for receiving bars 29, 31, such as passage 32a, intersect the respective threaded holes 34a, 35a in hooks 32, 33. In this manner, the position of hook 12 between rods 7 may be selectively adjusted to the extent bars 27, 28 are of sufficient length.

Stem 21 of part 14 has two portions of different cross sections, namely, in the illustrated embodiment, a first portion 21a adjacent to body 19 and a second portion 21b forming a terminal portion 21b. The cross section of the first portion 21a is larger than the cross section of the terminal portion 21b so as to define a shoulder 36 therebetween. In one embodiment, portion 21a is cylindrical while the terminal portion 21b is noncircular, for example of elliptical section, and can be inserted in the bore 22 whose contour includes a complementary noncircular portion 22a (see Figs. 4 and 5). One aspect of this noncircular arrangement of end portion 21b is to prevent any accidental rotation of the connector 14 relative to the first part 13 of the hook after insertion of the terminal portion 21b in the bore 22. As illustrated in Fig. 3, the length 1 of the terminal portion 21b of stem 21 can be arranged to be substantially equal to the width 1 of body 15, i.e., the length of bore 22 when bore 22 extends throughout body 15. Nonetheless, in other embodiments, a circular section may be desired and/or different dimensioning of terminal portion 21b relative to body 15 may be utilized.

Provided in the terminal portion 21b of the stem 21 is a bearing surface 37 shaped to engage an end 25 or 26 of the corresponding bar 28 or 27, which end is cylindrical in the illustrated embodiment. The bearing surface 37 is consequently formed by a cylindrical surface that is generally complementary to that of the end 25, 26, which comes to bear therein when the anchorage system 11 is assembled. It should be understood that bearing surface 37 can be provided in a variety of configurations, which may or may not be complementary to end 25 (26) of bar 28 (27). Such varying configurations include, for example, rectangular, square and triangular shaped indents. In addition, the bearing surface can include surface features, for example screw threads, teeth, and/or a roughened surface. In one alternative embodiment, bar 28 (27) includes a bearing surface similar in configuration to surface 37 described for stem 21. The bearing surface on bar 28 (27) can be provided either in addition to the bearing surface 37 of stem 21 or as an alternative to the bearing surface of stem 21.

Provided in each body 15, 19 is also a threaded hole 38, 39 opening onto the respective opening 23, 24, intersecting therewith. Holes 38, 39 are adapted to receive a threaded screw 41, 42 (Fig. 2) for locking the connection bars 27, 28 to the assembled parts 13, 14 of hook 12.

The blade 16 and its terminal nose 17 are so profiled as to be adaptable to the anatomy of the central region of the vertebral arch 20, either in a position over the lamina, shown in full line in Fig. 5, or in a position under the lamina or infralamina position, shown in dot-dash lines 16a, 17a in Fig. 5. The connection bars 27, 28 are of course oriented in consequence to adapt them to either of the two positions. If the blade 16 is placed in the position under the lamina, its geometry can be correspondingly modified relative to that for bearing over the lamina (Fig. 5) so as to be better adapted to the anatomy of the infralamina part of the vertebral posterior arch. Methods for placing in position a median hook 12 in a spinal osteosynthesis instrumentation, for example, on the lumbar part of the spine (Fig. 11), are illustrated in connection with Figs. 6 to 11. Per the illustration of Figs. 6 and 7, the surgeon cuts out in the upper and interprocess ligaments 43 between the spinous processes 44, 45, as required, a small opening 46 the section of which need only be large enough for the insertion of the connection stem 21. It should be appreciated that opening 46 has a posterior margin 46a defined by remaining ligament tissue (see Fig. 7). As shown in Fig. 8, with the aid of suitable tongs 47, 48, known per se, the surgeon positions the two parts 13, 14 on each side of the opening 46, by inserting through the latter the stem 21 whose end portion 21b is inserted in the bore 22 of the body 15 until shoulder 36 abuts against the latter. The bearing surface 37 is then placed in the extension of the cylindrical inner surface of the opening 23 so as to permit the insertion of end 25 of the transverse connection bar 28. At this stage of the assembly of hook 12, gap 120 is defined adjacent stem portion 21a between bodies 15, 19 and is sized to receive the tissue defining posterior margin 46a. The second bent bar 27 is also inserted by its end 26 in the opening 24, and the longitudinal and angular position of the bars 27, 28 are adjusted as needed.

Thereafter, the surgeon clamps together the two parts 13, 14 of the hook 12 and the bars 27, 28 on the latter by tightening the screws 41 and 42. Examples of these stages are illustrated in Figs. 9 and 10. The transverse connection bars 27, 28 are then locked on the longitudinal rods 7 by means of the hooks 32, 33. As previously explained, different distances separating rods 7 and variable positioning of hook 12 between the rods 7 may be accommodated by properly sized bars 27, 28. The instrumentation illustrated in Fig. 11 by way of nonlimiting example extends over the first four lumbar vertebrae L5 to L2 and is provided with two vertebral anchorage systems comprising a respective hook 12. A first hook 12 is illustrated as median hook/transverse connection device 12a mounted on the upper vertebra L2 in a position over the lamina, and a second hook 12 is illustrated as median hook/transverse connection device 12b mounted on the vertebra L4 in a position under the lamina. For each median hook/transverse connection device 12a, 12b, the corresponding hook 12 is connected to the rods 7 by the corresponding transverse bars 27, 28. The arrangement of the hook 12 in two parts 13, 14 which may be locked together has the advantage of avoiding the creation of a large lesion in the upper and interprocess ligaments 43 when placing the median hook in position. Indeed, the cutting of these ligaments which was previously necessary resulted in a destabilization of the spine superjacent to the segment provided with the instrumentation. As only the small opening 46 must be cut in the ligament 43 with the hook and the surgical method according to the invention, this surgery is much less invasive and substantially reduces destabilization of the superjacent segment. Other aspects of the present invention discovered from trials conducted on cadavers include that owing to the fact the hook 12 is trapped in its ligament opening 46, stability can be greatly improved relative to existing median hook arrangements. Also, the surgical technique may be simplified and the implantation/instrumentation mounting time may be shortened relative to procedures with other instrumentation. Nonetheless, it should be understood that it is not intended that the scope of the present invention be limited by or depend on any findings, theories, or mechanisms stated herein.

Furthermore, it is not intended that the scope of the present invention be limited to the described embodiments and indeed many other embodiments are envisioned, only a few of which are described as follows. In one other embodiment, stem 21 of part 14 and bore 22 of part 13 are interchanged such that first part 13 includes integral stem 21 and second part 14 defines bore 22 configured to receive stem 21 of part 13. Also, hook 12 can further be provided through the assembly of more than two parts. By way of nonlimiting example, connection stem 21 can be assembled to bodies 15, 19 as one or more separate pieces that are attached to the respective body by any suitable means known to those skilled in the art. In another nonlimiting example, the different cross-sectional portions of stem 21 can be provided through the assembly of a corresponding number of pieces.

Alternatively or additionally, different relative dimensions of terminal portion 21b of stem 21 for part 14 relative to the width of body 15 for part 13 may be utilized as would occur to those skilled in the art. In further embodiments, stem 21 may be provided with a single cross-sectional shape with or without a shoulder 36, or with more than two different cross-sections and/or more than one shoulder. Alternatives may include a different amount of offset of blade 16 and/or nose 17 relative to body 15 or the offset maybe absent. In still other embodiments, part 14 may additionally or alternatively include a hook blade or other vertebral engaging portion or member. Also, the connection bars 27, 28 can be attached to the bodies 15, 19 by means other than screws 42, 41. For example, the end portions of the bars can include threaded shanks provided with lock nuts bearing against the respective bodies 15, 19. In still other embodiments, the hook 12 is positioned between rods 7 by way of a single transverse bar or rod in place of bars 27, 28. Furthermore, besides pedicle screws 8, other types of vertebral engagement members or elements may be used to fix rods 7 of instrumentation 100 to the spine, such as other types of bone screws, bolts, hooks, and the like.

A further embodiment includes a method of medical treatment of a patent's spine, comprising: forming an opening through ligament tissue interconnecting a first and a second vertebra, a posterior margin of the opening being defined by the ligament tissue remaining after opening formation; mounting a median hook including inserting a transverse stem through the opening to interconnect a first body of the hook and a second body of the hook, a blade extending from the first body to engage a posterior region of a vertebra; positioning the median hook between a pair of longitudinal members extending along the patient's spine; and fixing the median hook to the longitudinal members. Optionally, this method may further comprise one or more of: positioning the blade over or under a lamina of one of the first and second vertebrae; inserting a portion of the stem through an opening provided in one of the bodies; and/or securing the stem to at least one of the bodies. Fixation to the longitudinal members may include fixing a transverse bar between the first body and one of the longitudinal members.

In still a further embodiment, a hook assembly for spinal osteosynthesis includes a first part with a first body and a blade extending from the first body to engage a vertebra. Also included is a second part with a second body. A transverse stem extends between the first body and the second body to interconnect the bodies in a spaced apart relationship along a transverse axis. This stem maintains a gap between the bodies that is sized to permit placement of vertebral ligament tissue therein, and the stem is selectively fastenable to one of the bodies. In yet another embodiment, a spinal osteosynthesis device includes a pair of longitudinal members extending along a patient's spine and a hook. The hook includes a first body with a blade extending therefrom to engage a vertebra of the patient's spine, a second body, and a transverse stem extending between the bodies to define a gap therebetween. The device also includes a pair of transverse bars adjustably fastened to the hook to connect the hook to the longitudinal members and position the hook between the longitudinal members.

In still another form, a bone engaging hook is variably positioned between longitudinal members that includes a stem connecting a first body and a second body on opposite sides of an opening through vertebral tissue. The stem has a cross section that is smaller than a cross section of the first body along a transverse axis.

All publications, patents, and patent applications cited in this specification are herein incorporated by reference as if each individual publication, patent, or patent application were specifically and individually indicated to be incorporated by reference and set forth in its entirety herein. Furthermore, French Patent Application No. 98 12 243 filed September 30, 1998, to which priority is claimed is hereby incorporated by reference in its entirety. While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes, modifications and equivalents that come within the spirit of the invention as defined by the following claims are desired to be protected.

Claims

1. Spinal osteosynthesis device, comprising two longitudinal rods adapted to be fixed on the spine and to extend respectively on each side of a section of the latter and, for a given vertebra, a hook and two vertebral bearing means associated with said hook, which is adapted to bear against the median part of the vertebral posterior arch between two longitudinal rods, said hook being provided with transverse connection means providing a connection between said hook and the longitudinal rods, characterized in that the hook is made in at least two parts capable of being assembled to constitute said hook, namely: a first part comprising a body in which a transverse bore is provided; and a second part forming a connector for connection with the first part, comprising a body, a transverse stem adapted to be inserted in a transverse bore in the body of the first part, means being provided for fixing said stem to the body of said first part, and a blade extending from one of said bodies and profiled and adapted to bear against a central region of the vertebral posterior arch.

2. Device according to claim 1, characterized in that there is provided in the end of the stem a bearing surface for a transverse connection bar between the hook and the associated longitudinal rod, an opening for receiving an end of said bar being provided in the body of the first part and opening onto said transverse bore, and second opening is provided for the second bar in the body of the second part of the hook.

3. Device according to claim 2, characterized in that said end of the connection bar is cylindrical and the associated bearing surface forms a semicylindrical notch.

4. Device according to claim 2, characterized in that the transverse bore of the body of the first part extends on each side of the opening for the bar onto which it opens, and has a noncircular section matching a corresponding profile of the end of said transverse stem.

5. Device according to claim 4, characterized in that the said noncircular portion and the profile of the stem are elliptical.

6. Device according to claim 2, characterized in that the stem consists of a first portion adjacent to the body and a second portion forming a terminal portion, and the first portion has a cross section larger than that of the second portion so as to define a shoulder capable of abutting against the body of the first part of the hook, and the length of the second portion is correlatively arranged to be substantially equal to the length of the transverse bore.

7. Device according to claim 2, characterized in that the blade of the hook is so profiled as to be adapted to the anatomy of the central region of the vertebral posterior arch in bearing over the lamina.

8. Device according to claim 2, characterized in that the blade of the hook is so profiled as to be adapted to the anatomy of the central region of the vertebral posterior arch in bearing under the lamina.

9. Device according to claim 2, characterized in that there are provided in each body openings opening onto the openings and in which may be screwed threaded plugs for clamping of the connection bars and the stem of the connector in the body of the first part of the hook.

10. Device according to claim 1 characterized in that said blade extending from a body extends with a lateral offset relative to the body in which a transverse bore is formed.

11. A Median hook associated with vertebral bearing means and connection means for connection between said hook and said vertebral bearing means, said hook and the bearing means being intended for the same vertebra and for a spinal osteosynthesis instrumentation comprising two longitudinal rods adapted to be fixed on the spine, characterized in that said hook is made in two parts capable of being assembled to constitute said hook, namely: a first part comprising a body and a second part forming a connector for connection with the first part, comprising a body attached to a transverse stem adapted to be inserted in said transverse bore in the body of the first part, means being provided for fixing said stem to the body of said first part; and a blade which extends from one of said bodies and is profiled and adapted to bear against a central region of the vertebral posteria arch.

12. Median hook according to claim 11, characterized in that said blade extends with a lateral offset relative to said body.

13. A hook assembly for spinal osteosynthesis, comprising: a first part including a first body and a blade extending from said first body to engage a vertebra; a second part including a second body; and a transverse stem extending between said first body and said second body to interconnect said first body and said second body in a spaced apart relationship along a transverse axis, said stem maintaining a gap between said first body and said second body sized to permit placement of vertebral ligament tissue therein and being selectively fastenable to one of said first body and said second body.

14. The hook assembly according to claim 13, wherein said blade terminates with a bone anchorage nose offset along a transverse axis from said first body.

15. The hook assembly according to claim 13 or 14 wherein the blade is adapted to engage a central region of a vertebral posterior arch.

16. The hook assembly according to any of claims 13-15 wherein said first body includes a transverse bore adapted to receive a portion of said transverse stem.

17. The hook assembly according to any of claims 13-16 wherein said transverse stem is integral to said second body.

18. The hook assembly according to any of claims 13-17 wherein said transverse stem includes a first portion with a first cross section and a second portion second cross- section different than said first cross section to define a shoulder.

19. The hook assembly according to any of claims 13-18, further comprising a first bar and a second bar, and wherein said first body includes a opening receiving said first bar and said second body includes a opening receiving said second bar.

20. The hook assembly of claims 19, wherein said transverse stem includes a terminal portion defining a bearing surface shaped to engage one of said first bar and said second bar.

21. The hook assembly of any of claims 13-20 wherein said first body and said second body each include a threaded hole to receive a screw.

22. A spinal osteosynthesis device, comprising: a pair of longitudinal members extending along a patient's spine; a hook including a first body with a blade extending therefrom to engage a vertebra of the patient's spine, a second body, and a transverse stem extending between said first body and said second body to define a gap between said first body and said second body; and a pair of transverse bars adjustably fastened to said hook, said transverse bars connecting said hook to said longitudinal members and positioning said hook between said longitudinal members.

23. The device of claim 22, wherein said first part includes a first body and said blade is transversely offset from said first body.

24. The device of claim 23, wherein said second part includes a second body, said transverse stem is integral with said second body, and said first body includes and opening engaged by said transverse stem.

25. The device of claim 24, wherein said transverse stem has a cross section taken along an axis transverse to said longitudinal members between said first body and said second body that is smaller than a cross section of said first body along said axis.

26. The device of any of claims 22-25, wherein said transverse stem includes a terminal portion having a bearing surface shaped to engage one of said transverse bars extending from said hook to one of said longitudinal rods, said first part includes an opening for receiving an end of said one of said transverse bars.

27. The device of claim 26, wherein said end of said one of said transverse bars is generally cylindrical and said bearing surface forms a generally semicylindrical notch.

28. The device of any of claims 22-27, wherein said stem includes a first portion and a second portion defining a shoulder therebetween.