CA1150120A

CA1150120A - Hook assembly for engaging a spinal column

Info

Publication number: CA1150120A
Application number: CA000353350A
Authority: CA
Inventors: James S. Keene
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-06-04
Filing date: 1980-06-04
Publication date: 1983-07-19
Also published as: NZ193931A; FR2458271B1; GB2051581A; US4269178A; DE3021238A1; AU532978B2; JPS5636944A; FR2458271A1; AU5903880A; GB2051581B

Abstract

ABSTRACT OF THE DISCLOSURE
An apparatus used in the treatment of spinal fractures and scoliosis. A threaded rod carries 2 or more sleeves, each sleeve surrounding a portion of the rod and slidable along the entire length of the rod. Each sleeve engages a hook to inter-connect the rod with the hook. The hook includes a base for en-gaging the sleeve. The base has a bore therethrough which receives the sleeve, and a slot is located parallel to and communicating with the bore. The slot has a width which is greater than the diameter of the rod and less than the outside diameter of the sleeve so that the rod can be placed into the slotted base of the hook and held in position by the sleeve which is slipped over the rod and into the bore. A projecting hook portion is integral-ly connected with the base and is used to engage the bone of the spinal column. A locking system in the form of threaded nuts engages the rod securing the position of the sleeve so that the entire hook assembly may be held in place with respect to the rod. When hooks are faced toward each other on a rod, compression is achieved by advancing the threaded nuts. Likewise, distraction is achieved by reversing the hooks so as to be facing away from each other. The bore in the base may be tapered or may have a smaller portion to prevent the sleeve from sliding completely through the bore. Opposing openings are located on either side of the base for engagement by an instrument, such as a hook holder, to aid in the placement of the hook assembly before inter-connection with the treaded rod. Preferably, the hook assembly forms a part of a Harrington compression rod or a tensioning means which interconnects a Harrington distraction rod and a Harrington compression rod.

Description

The Lnvention gerleraLly relates to a device for the SUI--~Jical treatment of spinal fractures or for s-traightel-ing the SpillO
in the surgical treatmen-t for deviations of the spinal column, especially scoliosis. In particular~ the present invention re-lates to a hook assembly for a Harring-ton compress:ion rod, or a trar.sverse traction device which are affixed to -the spine.
The present invention will be illustrated by way of the accompanying drawings, in which:
Figure 1 is an illustration of a Harrington distrac-tion rod and a Harrington compression rod engaging the spinal column;
Figure 2 is a schematic illustration, from the rear, of an individual suffering from scoliotic curvature of the spinal column;
Figures 3 and 4 show a Cotrel compression rod and a Harrington distraction rod engaging the spinal column and tension-ed by a device disclose~ in French Paten-t No~ 2,244,466;
Figure 5 is a cross-sectional view of the hook assembly of the invention shown in the locked position;
Figure 6 is a side view of the hook and base portions of the hook assembly;
Figure 7 is a sectional view of the base of the hook assembly taken along lines 7-7 of Fig. 5; and Figure 8 is a perspective view showing the hoo}c assembly in position to be engaged.
Scoliosis is the lateral deviation of the spina] colnmn.
The spinal curvature which results Erom scoliosis is generally def:ined on -the basis of specific reference points. In partic~llar, the extreme upper and lower vertebrae and the most d:isplaced ver-tebra are of particular interest. The extreme upper and lower vertebrae are those which are -the most inclinded relative to thc median longitudinal axis of the torso. The two plalles withill wl-}ich -1- ~

the ex-treme upper and lower vertebrae can be found define the scoliotic angle. I`he most displaced vertebra is defined as the vertebra which is the farthest from the median axis of the torso.
When the scoliotic angle of curvature exceeds a given limit of approximately 35 - 50, it becomes necessary to consider surgical treatment of the scoliosis. The surgical treatment is known as arthrodesis and consists of fusing together the vertebrae of the scoliotic curvature, after correcting the scolio-tic cur-vature to the maximum possible extend. Such correction can be accomplished prior to the operation by continuous traction of the spine or by corrective plaster casts.

However r it is during sur~ery that -the correction is completed and finaliæed. For this purpose, solid metallic rod with hooks is placed in the concavity of the curvature and a threaded rod with hooks is placed on the convexity of the curvature.
These rods straighten the spine and maintain the correction until arthrodesis is attained by means of autogenous bone gra~t. The implants used most often to correct curvature during surgery are known as the ~larrington distraction system and the Harrington compression system, illustrated in Figure 1.
The distraction system consists of two metallic anchoring devices 115 and 117 of the hook type which are attached to the vertebrae 4 which comprise the spinal column, generally referred to by reference character 1. A notched metal rod 115 serves as a stay and permits the spacing between the hooks 116 and 117.
One of the ends 118 of the rod 115 is usually notched in such a manner as to permit the distance between anchoring devices 116 and 117 to be adjusted by means of a spreading instrument.
Generally, the upper anchoring element 116 is intended for fas-tening toward the upper end of the spine and is hooked onto a dorsal vertebrae 9. ~sually, the hook of element 116 is directed upward and shaped in such a manner as to permit its insertion between the articular facets of two adjacent vertebrae.
The hook of element 116 penetrates into the interarticular space and is supported on the vertebrae.
Similarly, a lower anchoring element 117 is intended to be fastened at the lower end of the spine and is often supported on a lumbar vertebra 10. It is comtemplated that the hook associated with element 117 is directed downwardly and supported on the lima of the lumbar vertebrae between the spinous ~o process and the articular facet. In the illustrated example, vertebrae 9 and 10 are considered to be the extreme vertebrae.

:

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The compression system consists of two or more metallic anchoring devices 111 and 112 of the hook type which are attached to selected transverse processes of vertebrae 4 which are situated on the convex side of the scoliotic curvature. Threaded metal rod 113 serves as a stay and permits spacing between the hooks 111 and 112. Hooks 111 and 112 usually face each other and slide freely along threaded rod 113. These hooks are adjusted by means of nuts 114 so as to effect compression of the convexity of the scoliotic curvature. It is understood that more-than two hooks and nuts can be used to achieve the desiredamount of compression.
Thus, by the application of Harrington distraction and compression systems, the straightening of the scoliotic curvature can be effected and main-tained. Vertebral arthrodesis is then achieved by exposing the postexior arches of the vertebrae and attaching autogeneous spongy bone with the Harrington devices left in place.
Fig~ 2 is an illustration of a patient suffering from scoliosis schematically represented from the rear. The spinal column 1 is visible and indicated schematically by rectanyles or trapezoids. The patient illustrated in Fig. 2 exhibits a scoliosis invo]ving a deviation of the vertebrae to the right.
The scoliotic curvature can be defined on the basis of the top ver-tebrae 2 and the bottom vertebrae 3 of the deviation, and the vertebrae 4 which are located at the peak of the curvature. It is noted that the vertebrae 2 and 3 are those which are most ~ - 4 -.

l' ~ .L~3 strongly lnclined relati.ve to the medlan longitudinal axis M-M
of the body, while vertebrae 4 are those which are farthRst rom ; that axis. Angle a is ~hus a characterlskic of the scoliotic curvature. When the angle a exc~eds a limit of approximately 35 - 50~, it is of~en necessary to resort to arthrodesis and ~o install Harrington distraction and co~pre~sion rodtsystems, illustrated in Fig. 1.
However, the Harring~on distraction and compression systems are not totally effective in supporting the peak verte-brae 4 which are further away from the axis M-M than ~he other vertebrae and cannot fully accomplish straightening of the scoliotic curvature. Accordingly, transverse tens~oning devlces as lllustrated in Figs. 3 and 4 have been suggested by French l Patent No. 2,244,446. Such a transver3e tensioning devlce makes use of (1) a compression rod 11, similar to the ~arrington com-pression rod, and (2) a tensioning ele~ent 12. Obviou~ly, the intent of the Harrington dîstractîon rod 5 is to separate the vertebrae apart from each other. The basis of the tran~ver~e tensioning device is a tensioning element 12 which i8 supported by the compression rod 11 on the side of the vertebrae mos~ d~-placed by the curvature and connected to the other ~ide o~ th~
spine by the Harrington distraction rod 5. Preferably, tha ten-sioning means is adjustable so that the peak of the scollotic curvature can be pulled toward the digtraction rod 5,res~Lting in a better correction of ~he curvature and a better preservation of the correction obtained. I~ is con~emplated that a trjansver~e tensionlng device results in reductlon of the lateral displace-ment of the most dipIaced vertebrae, completion of the correctio~
obtained by he longitudinaL harrington distraction rod, ard - 5 - `

relief o~ the load on the supporting vertebrae.
Generally, the ~ransverse tensioning devlces of the prior art have been comprised of compression rod 11 and ten~ion-ing element 12, ~he flrst of which is intended to be supported ¦ on two vertebrae 4 which are closest to the peak of the scoliotic curvature, and the second of which permits the flrst to be brought nearer to the metallle distrac~ion rod 5.
Compression rod 11 is generally comprised of a threaded rod 13, at one end v which is permanently astened a hook 14.
This rod 13 passes freely through anoth~r hook 15 which is held in place by nuts 16. Hook 15 slides along rod 13 and face~ hook 14. Hook 14 has a rounded and beveled end 17 which allows lt to be supported, from top to bottom, by the ~ransverse pro~e~se~
of the upper vertebra 4 of the peak, ater cu~ting of the costo-transverse ligament. Hook 15 passes from the bottom to top beneath the ~ransverse process of the lower vertebra 4 of the peak. Nut and locklng nut 16 permit hooks 14 and 15 to be brought closer to each other and to be tightened in such a way as to effect a firm transverge grip. Hook 15 is finally locked into position by means of a set screw S which ~ams the threads of rod 11. Hooks 14 and 15 are attached to the transverse pro-cesses of vertebra 4 which are situated on the conve~ side of the scoliotic curvature.
Tensioning element 12 comprises a threaded rod ~av- -~ng one end which is permanently fastened to hook 18. X1.~e ~d passes freely through another hook 19 which is held in place on the rod by nuts 21. Hook 19 is able to slide along the rod and faces hook 18. Hook 18 engages rod 13 and hook 19 engage~
Harrington rod 5. By screwlng nut and locking nut 20 along t~

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rod hooks 18 and 19 appro~c~ each ot~ler and the peak,vertebrae 4 are made to approach medlan axis M-M. This allows better correction of ~he scoliotlc curvature. ~ook l9 is finally locked into position by means of a set screws ~hich ~m ~he threads of element 12. It is noted that elements 11 and 12 are located at the pos~erior side of the spine, elemen~ 12 being in contact with the spongy graft 21 necessary for this arthrode~l~
so as to reinforce ~he solidi~y of he arthrodesis. -The surgical techniques used in employi~g the tran~-verse tractlon device illustated in Figs. 3 and 4 are outllned in more detail by Dr. Cotrel in his article entitled "New Techniques for the Treatment of Idlopathic Scoliosi.s>"
Internat~onal Orthopedics, Spring, 1978, pp. 247-~65.
The basic problems with the above described transver~e traction sys~em are as follows:
¦ 1. It ~s difficul~ to apply.

2. It requires the use of additional instr~lments other than those commonly available to spinal surgeons familiar with the Harrington proce-dure.

3. It provides for the use of tiny set screws to positively locate hooks 15 and 19 on e].ement~
11 and 12. Such set screws must be cut off flush with the hooks, thereby risking the los8 of a portion of a set screw in the human body.

4. Hook 18 of element 12 does not positlvely locate on element 11 and is subject to slippage.

I-t is an object of this lnvention to provide a hook assembly for use with a threaded Harrington compression rod which may be used for the treatment of scoliosis or spinal fractures, the hook assembly allowing a single surgeon to easily place the Harrington rod in position.
It is a further object of this invention to provide a hook assembly for a treaded Harrington compression rod which allows the hooks to be properly spaced on the Harrington rod.
It is a further object of this invention to provide a hook assembly for a Harrington compresssion rod which allows the hooks to be tilted and manipulated into position before engaging the rod and being retained on the rod.
It i5 another object of this invention to describe a hook assembly for use in combination with a Harrington compres-sion rod which obviates the need for a partial laminectomy, when hooks are being placed on the lamiriae.
It is a fur-ther objectof this invention to provide a hook assembly for use with a Harxington compression rod which has a radiused shoe on each hook which can be placed to clear the edge of the lamina before the rod is tightened to achieve compression or distraction.

I-t is another object of this invention to describe a hook assembly for use with a ~larrington distraction rod, a Harrington compression rod or a tensioning device interconnecti;ng such rods which includes a hook comprised of a base and projecting hook, the base having a bore therethrough for receiving a sleeve loca-ted on the rod.
I-t is yet another object of this invention to provide a hook assembly for a Harrington compression rod which allows the preliminary placement of the hook before engaging the rod.
It is a final object of the hook assembly of this invention to provide a system for use in combination with a Harrington compression rod which significantly reduces the surgical time required for installing such rods.
The basis of the invention is a hook assembly for use with a treaded rod to inter-engage the threaded rod wi-th a portion of the spinal column. The hook assembly includes a sleeve or bushing for engaying the threaded rod and surrounding a portion -thereof. A base engages the sleeve and has a bore therethrough for receiving the sleeve. A slot is provided in the base on the side or top thereof and is parallel to and communicates with the bore. The slot has a width which is greater than the diameterof the threaded rod so that the threaded rod may pass therethrough and less than the outside diameter of the sleeve so that the sleeve does not pass therethrough. A hook or shoe is integrally connected to and projects from the base. A locking system is employed to position the hook assembly with respect to the threaded rod so that the rela-:~ _ g _ -tive position of the hook asse-mb]y will remain consistent with respect to the threaded rod. In a preferred embodimen-t, the lockin~ sys-tem is a threaded nut which engages the threaded rod on one side of the sleeve and base. It is contemplated that one~
of the threaded nuts may be integrally attached to the sleeve to facili-tate placement of the sleeve. The bore in the base may be tapered so that -the bore engages the sleeve and does no-t com-pletely pass therethrough. Alternatively, the bore may have a smaller diameter poxtion which prevents passage of the sleeve completely therethrough. In addition, the base may be provided with opposing openings for engagement by an instrument, such as a hook holder.
In use, each base and hook are placed on -the spinal column and the rod is positioned ~lithin -the slot of each hook.
The sleeve or bushlng is then located within the bore in the base to secure the rod to the hook. The threaded nut is then turned do~n to achieve compression or distraction, and the en-tire hook assembly is held in position.

.~
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The basic feature of the invention is -the connectincJ
means which forms the hook assembly as illus-trated in Fic~s. 5~~.
This hook assembly allows the placement of the hook with engage-ment of the spinal column before tbe hook and attached base are connec-ted to the threaded rod. The hook assembly further pro vides a positive interconnec-tion be-tween the base and hook por-tions and the threaded rod so that, in the locked position, pi-voting or other movement be-tween the threaded rod and base of the hook assembly is not possible.
Referring in more detail to the features of Fig. 5, it can be appreciated that threaded rod 35 is somewhat similar to rod 113 shown in Fig. 1. In particular, rod 35 is a threaded rod which interconnects two or moxe hook means for engacJing the spinal column or inter-engaging a Harrington compression rod and a Harrington distraction rod. I-t is, therefore, noted that the hook assembly of the inven-tion may be used as a par-t of a dis-traction rod, as part of a compression rod or as part of a ten-sioning means which interconnects a Harrinc~-ton distraction rod and a Harrington compression rod. In fact, the hook assem-Z~3 bly may be used on any surgical system in which engagement of a hook means is required. .
The threaded rod 35 carries a sleeve 32 whLeh ~urro~nds the rod and slides along the rod for free posltioning. The base portion 30 of the hook assembly is integrally connected to a hoo~ portion 31 which par~icularly engages the spinal column or rod which is to be the anchoring means. Bore 33a is longitudl-nally located within the base portion 30 and i5 sl~ed to accept the sleeve 32. Bore 33b is provided and has a diameter whioh is less than the outside diameter of the sleeve 32 so that the sleeve is prevente~ from completely passing through bore 33~
and through the base portion 3~ of the hook assembly. Alterna-tively, as shown in Fig. 6, the bore within the ba~e portion 30 may be tapered bore 33c whlch performs the same function as bores 33a and 33b.
A slot 34, as best shown in Figs. 7 and 8, is parallel ¦
to the bore 33a and in communica~ion with the bore 3~a to form an opening in the base 30. The size of the slot 34 in relation to the sleeve 32 and threaded rod 35 forms a critical feature o the invention. In the preferred embodiment, the ~lot 34 should form an opening within ~he base 30 so tha~ the wiclth of slot 34 is greater than ~he diameter of rod 35 but less than the out$Lde diameter of sleeve 32. The result of this cri~leEIl dimen~ion is that the slot 34 allows the rod 35 to be ~lipped into the hook a~sembly and ~hen the sleeve 31 is moved along the rod 35 to engage the hook assembly. Thi~ movement can be appreciated by .
referring to the dotted lines in Fig. 8. Once the basP
30 is in position around the sleeve 32 so that ~he sleeve 32 i8 located within bore 33a and ~but~ the shoulder between bore 33a and ~3b, locking nuts 36 may be turned to lock the position of -1.'1 S.'~
sleeve 3~, base portion 30 and integrally connected hook port~on 31 into positlon with respect to the threaded rod 35.
In an alternative embodlment~ it is contemplated that the sleeve 32 may be integrally connected to a locking nut 36 so that the particular position of the sleeve 32 is determined by the position of ~he locking nut to which it is connected. In some operations, this type of structure allows for the manipula-tion o~ the hook assembly ln a more efficient ashion.
. It is further contemplated that the base portion 30 of the hook assembly may be provided with engaging openings 37.
These opPnings, w~ich are opposing, are provided so ~hat the entire base por~ion 30 and integrally connected hook portion 31 ~OO~ &~
may be handled by a ~C~ LI~p tq~3=J~i or other convenient de-.
vice. These engaging openings are especially necessary when the apparatus being implanted is of an extremely small nature and manipulation of the base portion 30 and integrally connected hook portion 31 becomes dif~lcult with human fingers. It iB
also contemplated that other engaging means, not ~hown, may be provided on the base portion 31, such as notches, multiple openings, transverse bores, pro~ections or protrusions.
It is, therefore, apparent that the hook assembly al-lows for the engagement of the hook portion 31 by manipulation of the base portion 30 before the base portion is slideably en-gaged by the sleeve 32 carried by the threaded rod 35. Wieh the hook portion 31 engaged to an anchor, such as the splnal column, the threaded rod 35 may be slipped through the slot 34 and the sleeve 32 is then moved along ~he threaded rod 35 into thc bore 33a. With the threaded rod 35 and sleeve 3~ in place, the entire hook assembly is retained on the rod 35 by locking nut 36 and compression or distraction may be achieved by advancing the ,'1~l5~ Z~
locking nut in the proper direct-ion. This allows the surgeon to place each hook on the spine, tiltlng or manipulating the hook as required to achleve a good purchase. Thi3 often avoid~
the partial l~minectomy th~ ls sometimes necessary with the Harrington systems of the prior art.
Use of the hook assembly apparatus as descrlbed above for thP trea~ment of spinal fracture as compared with the prlor art devices has shown ~hat a thirty to forty minute reduction in ^ o~r.u~ o~
surgical time can be achievPd when ~r~x~i g racture cases.
It is contemplated that even more time could be saved in the performance of scoliosls cases.
Various changes may be made to the details of the invention, as disclosed, without sacrificing the advantages thereo or departing from the scope of the appended claims. For example, any hook style may be adapted to this design or the sleeve or bushing employed can have a square~ hexagonal or other shape. It is only necessary ~hat the internal shape of the sleeve be complemen~ary and corresponding to the external shape of the threaded rod and that the external shape of the sleeve be equivalent ~o or ~o~lementary with the internal ¦I shape of the bore and the base.
¦ Furthermore, although ~he present invention has bçen ,~ disclosed and dlscussed with particular regard to its excep-tional advantages in terms of devices for the treatment o ~pinal ~S fracture and scoliosi.s, it may be unders~ood that the invent~ on may be employed in several surgical a3 well as indu~trial ap-plications wherein a rod engages a portion by mean~ o ~ hQo~
which requires manipulation about the portion. In additon, al-though the preferred embodiment contemplates a me~allic ~truc-l ture, the invention may be comprised of any ~ui~ble form re-¦¦ taining material.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OF PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A hook assembly for inter-engaging a first rod and a second device including a second rod, a bone or a portion of a spinal column, said hook assembly comprising: a) sleeve means for engaging the first rod; b) base means for engaging said sleeve means and having a bore therethrough for receiving said sleeve means; and c) hook means connected to and projecting from said base means, said hook means for engaging the second device, said base means having a slot parallel with and communi-cating with said bore, said slot having a width which is greater than a diameter of the first rod and less than the outside diameter of the sleeve means.

2. The hook assembly of claim 1 further including a lock means cooperating with said base means and sleeve means for engaging the first rod and locking the relative portion of the base means and sleeve means with respect to the first rod.

3. The hook assembly of claim 1 wherein the bore in said base means is tapered.

4. The hook assembly of claim 1 wherein the bore in said base means has a portion with a diameter which is less than the outside diameter of the sleeve means, thereby forming a shoulder against which the sleeve means abuts.

5. The hook assembly of claim 2 wherein said lock means is a pair or threaded nuts for engaging the first rod on a side of the base means and sleeve means.

6. The hook assembly of claim 5 wherein said base means further includes an opening for engagement by an instru-ment.

7. The hook assembly of claim 5 wherein one of said threaded nuts is attached to said sleeve.

8. An apparatus for engaging a spinal column compris-ing: a) a rod, b) a bushing surrounding a portion of the rod;

c) a base for engaging the bushing and having a bore therethrough for receiving the bushing, and d) a hook connected to and pro-jecting from the base, said hook for engaging a portion of the spinal column, said base having a slot parallel with and com-municating with the bore in said base, said slot having a width which is greater than the diameter of the rod and less than the outside diameter of the bushing.

9. The apparatus of claim 8 wherein said rod is threaded and at least one threaded nut in the form of a locking means engages the rod on a side of the base to lock the relative position of the base with respect to the threaded rod.

10. The apparatus of claim 9 wherein one of said threaded nuts is attached to said bushing.

11. An apparatus for engaging a second device includ-ing a second rod, a bone or a portion of a spinal column, said apparatus comprising: a) a rod; b) a sleeve means slidable along the length of said rod for engaging said rod; c) base means having a first and second end for engaging said sleeve means and having a bore extending therethrough from said first end to said second end for receiving said sleeve means; said base means having a slot parallel with and communicating with said bore, said slot having a width which is greater than the diameter of said rod and less than the outside diameter of the sleeve means; d) means for preventing said sleeve means from sliding out of said bore through said second end when said sleeve means is received within said bore through said first end; e) hook means connected to and projecting from said base means; and f) locking means cooperating with and independently moveable relative to said base means and said sleeve means and along said rod for engaging said rod, said locking means having a width greater than the inner diameter of said sleeve means.

12. The apparatus of Claim 11 wherein the means for preventing said sleeve means from sliding out of said bore com-prises the bore in said base means being tapered.

13. The apparatus of Claim 11 wherein said rod is threaded and said locking means comprises at least one threaded nut for engaging said rod and said base means.

14. The apparatus of Claim 11 wherein said rod is threaded and said locking means comprises a pair of threaded nuts for engaging said rod on one side of the base means and sleeve means.

15. The apparatus of Claim 11 wherein said base means further includes an opening for engagement by an instrument.

16. An apparatus for engaging a second device including a rod, a bone or a portion of a spinal column, said apparatus comprising: a) a rod; b) a sleeve means freely slidable along the length of said rod for engaging said rod; c) base means having a first and second end for engaging said sleeve means and having a bore extending therethrough from said first end to said second end for receiving said sleeve means; said base means having a slot parallel with and communicating with said bore, said slot having a width which is greater than a diameter of said rod and less than the outside diameter of the sleeve means; d) means for preventing said sleeve means from sliding out of said bore through said second end when said sleeve means is received within said bore through said first end, said means comprising the bore in said base means having a portion of the diameter of the bore which is less than the outside diameter of the sleeve means; e) hook means connected to and projection from said base means; and f) locking means cooperating with and independently moveable re-lative to said base means and said sleeve means and along said threaded rod for engaging said rod, said locking means having a width greater than the inner diameter of said sleeve means.

17. The apparatus of Claim 16 wherein said rod is threaded and said locking means comprises at least one threaded nut for engaging the said rod and said base means.

18. The apparatus of claim 16 wherein said base means further includes an opening for engagement by an instrument.

19. An apparatus for engaging a spinal column compris-ing: a) a threaded rod; b) a bushing surrounding a portion of the threaded rod and slidable on said rod for engaging said rod; c) a base having a first and second end for engaging the bushing and having a bore extending therethrough from said first end to said second end for receiving the bushing; said base having a slot parallel with and communicating with the bore, said slot having a width which is greater than the diameter of said rod and less than the outside diameter of the bushing; d) means for preventing said bushing from sliding out of said bore through said second end when said bushing is received within said bore through said first end; e) a hook connected to and projection from the base;
and f) locking means cooperating with and independently moveable relative to said base and said bushing and along said threaded rod for engaging said rod, said locking means comprising at least one threaded nut and said nut having a width greater than the inner diameter of said bushing.

20. The apparatus of claim 19 wherein the means for preventing said bushing from sliding out of said bore comprises the bore in said base being tapered,

21. The apparatus of claim 19 wherein said locking means comprises a pair of threaded nuts for engaging the rod on one side of the base and bushing.

22. An apparatus for engaging a spinal column compris-ing: a) a threaded rod; b) a bushing surrounding a portion of the threaded rod and slidable on said rod for engaging said rod;
c) a base having a first and second end for engaging the bushing and having a bore extending therethrough from said first end to said second end for receiving the bushing; said base having a slot parallel with and communicating with the bore, said slot hav-ing a width which is greater than the diameter of the rod and less than the outside diameter of the bushing; d) means for pre-venting said bushing from sliding out of said bore through said second end when said bushing is received within said bore through said first end, said means comprising the bore in said base having a portion of the diameter of the bore which is less than the out-side diameter of the bushing; thereby forming a shoulder against which the bushing abuts; e) a hook connected to and projecting from the base; and f) locking means cooperating with and inde-pendently moveable relative to said base and said bushing and along said threaded rod for engaging said rod, said locking means comprising at least one threaded nut and said nut having a width greater than the inner diameter of said bushing.

23. The apparatus of Claim 22 wherein said locking means comprises a pair of threaded nuts for engaging the said rod on one side of the base and bushing.