CA2088066A1

CA2088066A1 - Artificial vertebra

Info

Publication number: CA2088066A1
Application number: CA002088066A
Authority: CA
Inventors: Mohamed I. Rasheed
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-07-24
Filing date: 1991-07-24
Publication date: 1992-01-25
Also published as: AU8098091A; ATA155790A; EP0540559A1; AT394307B; JPH06500711A; WO1992001428A1

Abstract

Abstract The subject matter of this invention is a spinal prosthesis for the replacement of one or more destroyed vertebrae, with two supporting plates which lie close to the end surfaces of adjacent healthy vertebrae. The supporting plates have spikes for providing an anchorage in these adjacent vertebrae and are connected by a spacer, the length of which can be adjusted. This spacer (9) is arranged off-center relative to the longitudinal axis of the spinal prosthesis (1), which is defined by the centers of the supporting plates (4), and has two rails (7,8) with meshing teeth (14) along the surfaces that face each other.
The rails (7,8) are connected to each other by means of a screw (17). Between the supporting plates (4), a recipient site for the implant (32) consisting of a natural and/or artificial material is left open. The subject matter of this invention also includes a device for handling this spinal prosthesis, in particular for inserting the spinal prosthesis into the spinal column.

Description

~88`~

~ h~ preaent ~nvention concerns a ~pinal prasthesis for subs~itution of one or more de3troy~d ~rt~brae, ~rlith two sUpporting plates for the install~tion ~n supportin~ surr~ces of ~ac-2nt ~althy vert~brae, whereby the ~uppor~cing plates feature anchorin~ mean~ for 3~racing in ~hese vertebrae al~d ar~
conneceed ky and rigidly ~ttached to at l~st on~ spacer whcse length is ad~ustabl~.
~ urther ~ehis inv~ntion concerns a de~rice ~or handling ~his spin~ 1 pr~-~th~3is .
1~ one or more b~d or d~troy~ r~,ebrae must be removed fro~ the spinal colu~nn, it might, be b~cau~e th~ v~rtebrae ~ro a~ectcd s~ith met~tas s, ~ m~ght ke due to Qpidu~al spinal column metasta3~s or du~ to ~unct~onal ~nstability of the spinal column. ~o date it was rc~uired to remo~e ~'ne bad or de~tro,-ed vert~rae complQtely rrOm the splnal column and to impl~et: ~ prosthesi~ betweerl the remaining good vertebr~ o~ the Spi na 1 columr~ .
For length-adjustr~ent:, spinal pro~h~s~s or ele~nts of the spinal p~osthes~q with di~ferent ~-xQd i~ngth3, ~cr xamplo, were used, whereby the ad~usts~ent, at the ~paC~ ~o b~ bridg~d durlng the operaCion t~rc~ugh m-asur4~nt o~ the gap b-twQcln ~he remain~ng ~ertebrae ~nd cQl~ction ~ the sui tabl.Q proethe~3is or a suit~ble connec~ing ~lement, is carried cut wi~h th~ asficmhly of .he prosth-sis during th~ operation. A m~l1t~ ele~cnt pro~the~i~
~it~ conn~ct~ng p~ec~s of different le~gths, for ~x~mpl~ is ~escribed in ~S-PS 4 ~99 086 A di~advantage o~ thi~ well-~:nown )rosthe~1~ 18 its compl~cat~d design of m~ny ~le~ents and the s~ward ~anipulation during impl~nt~tion. ~he EP-PS O 179 695 :nd the DE-~S ~ 365 873 describe ~imil~r splnal prothese~ ~ith a -ix~d l~ngth.
oth~rwls-, th~ spinal prosthe~i~ can b~ individually m~e 3uring the operation, as ln the cas~ o~ the ~lloplastic vertebra epl~c~ment de~cribed in DD-PS 2~5 ~16. Dis~d~ranta~eoUa with ~his, howe~er, i~ th~t this ve~tebra replacen~nt i5 connecte~ 'cO
~rly one screw an~ a wir~ pin in the adjacent g~od ~ertebrae.
~rle cylindr~c~ haped metal-she~ting ~acket with perforation~ ~n ~~e jacXet ~all, ~hown in EP-A O 268 llS, ~l~o made in~ividually during the operation, which is filled with bone pieces and/or bone cement, has the disadvantage that the bone cement, while hardening, reaches local temperatures which can lead to the necrosis of the surrounding tissue.
Furthermore spinal protheses are also well-known, whose length can be adjusted through different methods. Spinal protheses, adjustable in length, are described in US-PS 4 657 550, US-PS 4 553 273 and DE-OS 37 29 600. These concern layouts, in which the distance between two supporting elements i5 adjustable by means of a central spinal pinion. The block-shaped supporting elements, described in US-PS 4 553 273, on which the spinal pinion rests, are embedded into recesses that are preferably polygonal, provided each time in ad~acent vertebrae.
As a result, a disadvantage here also is that the recessQs must be made during the operation, which makes necessary a time-cQnsuming and complicated procedure. The recesses must be cut into the adjacent vertebrae with precision as per the dimensions of the supporting elements, since otherwise there is no secure attachment. The angular supporting elements, described in DE-OS
37 29 600, are screwed together only from the side with bone screws without attachment to the supporting surfaces of the vertebrae. Another possibility of the attachment of the supporting elements is described in US-PS 4 657 550, namely the connection through spikes in the adjacent vertebrae. However, all these developments have the disadvantage that with the provision of a central length-adjustable spacer no implant can be used.
Further DE-Al 30 23 942 describes a spacer for the prosthesis vertebra replacement and a tool for the implantation of the same. Again, no implant can be used and the tool consists of a pincer-like device with specially designed shank pincers and a catch for holding its bracing position.
One problem to be solved by this invention is to create a length-adjustable spinal prosthesis which does not have the disadvantages of the above-mentioned well-known spinal protheses, but can centrally house and, if necessary, fasten an implant, and through which just elements of destroyed vertebrae also can be replaced. That is, the whole vertebra does not always have to be removed, if it is only partially severely damaged. Thus, if "adjacent vertebrae" are mentioned, the remaining healthy portions of partially removed vertebrae thus are also meant.
Further, such vertebrae or vertebrae elements are understood with "healthy vertebrae (elements), n which, in the opinion of the surgeon, are capable of ensuring enough support for the implanted prosthesis.
In accordance with this invention, this problem is solved in such a way that the spacer is fitted off-center with regard to f5 ,J ~ ~,J ~

the longitudinal axis of the spinal prosthesis which is defined by the centers of the supporting plates, whereby between the supporting plates an open recipient site for an implant made of a natural and/or artificial material, is left. The off-center configuration of the spacer makes it possible to insert an implant in a stable prosthesis that can be adjusted to different lengths. As a result, the strain of the prosthesis configuration can be relieved considerably, since the implant also can take on a considerable portion of the pressure that rests on the spinal column. Naturally every suitable artificial replacement can form the implant. However, a natural bone implant is preferred, best taken from bones of the individual's body or one tan implant]
made of bone bits and cement. In any case, with the present invention, the amount of the exogenous material implanted into the patient's body can be reduced to a minimum.
In a preferable embodiment of the invention, the bracers are spikes. After implanting the spinal prosthesis and discontinuing the extension of the patient's spinal column, necessary for the operation, these spikes automatically penetrate the adjacent vertebrae.
The preferred application of a supporting plate with at least one perforation makes possible, with the use of a bone implant, the natural growing together of bone material within the spinal column through the supporting plates. Should several of these perforations exist, an especially fortified stabilization of the prosthesis results after the intergrowing. In addition, this also ensures the possibility of a just partial removal of vertebrae and the safe connection with the remaining healthy vertebrae elements.

~a~ss~ ;~
s It is further useful if the perforations have a circular shape, since the production of the same is made easy as a result.
In accordance with a preferred embodiment of the invention, it is planned that, in an approximate continuation of the off-center spacer, connecting elements are connected to the supporting plates, which have at least one perforation for a bone screw that penetrates the end surfaces of the adjacent vertebra.
The selected length for the bone screw can be of a length that reaches into the spinal arch of the vertebra concerned. As a result, a secure fastening in addition is provided for the spikes which penetrate the healthy vertebra. It is also easily made possible to partially remove a bad or destroyed vertebra. With the use of a long bone screw, the spikes, provided for the connection in the adjacent vertebra, naturally must be fitted in such a way that the bone screw can be screwed through between these. The fact that these connecting elements are placed in approximate continuation of the spacer, also makes possible keeping the wound as small as possible, since the access to the screws of the connecting element and to the adjusting mechanism of the spacer results from the same side and is only slightly height-shifted.
The use of connecting elements in the construction of spinal prostheses is well known. Thus, connecting elements in spinal protheses with a fixed length are described in US-PS 4 599 086, in DE-OS 23 65 873 and in EP 179 695. While, in accordance with DE-OS 37 29 600, connecting elements are provided by angular supporting elements which, in turn, are connected by means of a central length-adjustable spacer. The connecting elements, described in DE-OS 23 65 873, are arranged along much of the ~ ;i 6 supporting plate's perimeter where tensions, eruptions and splintering in the bone can occur, due to several bone screws penetrating into the vertebra. A large wound perforation also must be provided, in order to screw the connecting elements around the vertebra. In DE-OS 37 29 600, on the other hand, only one connecting element on the vertebra, in the shape of the vertical element of an angular supporting element with a perforation for a bone screw is described. However, with a design of this type, a reliable connection of the vertebra is not provided with regard to the rotational force, since the supporting surface of the vertebra also is not directly connected to the horizontal element of the angular supporting element.
It is useful when the connecting elements opposite the spacer are shifted outward and connected to the supporting plates via connecting segments. As a result of this, a secure connection of the ad;acent vertebra is provided and, with that, the off-center spacer moves slightly underneath the supporting surface of the adjacent spinal vertebra, which is desirable for static reasons. Nevertheless, enough room remains for a possible implant.
As per another embodiment of the invention, the connecting elements which exhibit at least one perforation for a bone screw that penetrates the ad~acent vertebra from the side, are connected to the supporting plate on the side opposite the spacer of the supporting plates. As a result, the connecting area for the implant, in the case of an implanted prosthesis, is also accessible to the surgeon from the same side for possible connection like the bolted connection with the adjacent vertebrae. A length adjustment, though, must be carried out and ~8~

fastened during the implantation, or the access to it must result via a borehole through the implant, if one wishes to keep the wound small.
In a further preferred embodiment of this invention, it is planned that each connecting element exhibit two off-center perforations for two bone screws, penetrating the adjacent vertebra from the side. With this embodiment, if necessary, obstructing spikes can be left out within the area of the edge of the supporting plate for the penetrating of the bone screws into the vertebra.
By preference, spikes pointing into the recipient site for the implant are provided on the supporting plates for anchoring the implant. As a result, the use of bone cement (Palacos) for fastening, enclosing and filling spaces to a large degree is not necessary. With the hardening of bone cement, temperatures of up to 95C have been known to arise, which results in the burning of the surrounding tissue structures. The spikes, in accordance with the invention, secure a permanent fastening of the implant without the use of bone cement, especially for a bone implant.
In the above embodiment it is useful if the spikes are fitted in an arrangement of spikes provided for the connection on the adjacent healthy vertebra. The production of the spinal prosthesis thus is made considerably easy, since the spikes, in the shape of doubls cones, can be pushed into boreholes provided for this purpose in the supporting plates.
In this connection it is advantageous if the spikes are radially fitted near perforations of the supporting plates. The plates extend preferably in a section above and below the respective supporting plate and are symmetrically fitted, for ~ o ~

example, to the corners of an imaginary hexagon. The perforations (which actually are known from the DE-OS 37 29 600) lie inside the lateral edges of the hexagon. These perforations, roughly in the shape of boreholes or slots, make possible a growing together of the adjacent vertebrae with the spinal prosthesis and the implant firmly connected by the spikes. For this, the perforations described in DE-OS 37 29 600 make possible only an ingrowing of the vertebra's substance into the prosthesis, since this prosthesis features no possible attachment for an implant, especially for a bone implant.
Preferably the coned spikes have a length of 3 to 50 mm.
Since the spinal prosthesis can be used in patients of all ages and in all areas of the spinal column, it is advantageous to provide the size of the spinal prosthesis and with that also of the spikes in various different dimensions suitable for these varying applications. In the case of small children, a smaller size for the spinal prosthesis and the spikes is selected in accordance with the size of the adjacent vertebrae and the implant to be installed, as opposed to adults. In the case of a neck vertebra, for example, a different dimension for the spinal prosthesis also is selected, as opposed to the replacement of a lumbar vertebra. The spikes should be at least long enough to ensure that they can penetrate the roughly 3 mm thick layer that is connected to the vertebra~s end. The length of the spikes is practically unlimited, they can even penetrate the vertebra completely and can even penetrate right into the next vertebra.
However, this leads to a limited movement of the spinal column.
Therefore, if not intended for any other purposes, the length of the spikes should not exceed the height of the adjacent vertebra.

8 ~

If the supporting plates are circular, they can be easily produced by means of forming. A hexagonal shape is also sturdy and easily producible.
According to an advantageous embodiment of this invention, the off-center spacer can be adjusted in length in a ratchet-like manner. Mostly it is not known before the operation which precise length of the spinal prosthesis is needed. By means of a ratchet-like adjustment mechanism of the spacer, a guick and precise adjustment of the spinal prosthesis in the space to be bridged, between the two remaining healthy vertebrae, is guaranteed. The term "ratchet-like," used here, means that the spacer of the spinal prosthesis is adjustable in one direction, preferably by pushing it together, while a movement in the opposite direction is blocked by blocking devices. Here, in accordance with a shortening of the prosthesis, a readjustment of the length can result more or less automatically in the installed position after the patient's spinal column is no longer stretched.
The procedure during the operation with an adjustment of the prosthesis is roughly as follows: From data of previous examinations, X-rays and experience, the surgeon selects the appropriate dimension of the prosthesis. The spinal column of the patient is stretched and the destroyed vertebra(e) is/are removed. The length and the shape of the implant to be installed between the support plates of the prosthesis is determined and the intended or removed implant is cut to the required size. The implant is installed in the recipient site of the wide-open prosthesis outside the patient's body and the prosthesis is manually pushed together, and the spikes, fitted to the inside of ~8~

the supporting plate, penetrate the implant and secure it.
Subsequently, the prosthesis is installed between the remaining adjacent healthy vertebrae and the patient's spinal column is no longer stretched. Because this results in a considerable pressure on the vertebrae, the spikes on the inside of the supporting plate penetrate further into the implant and the spacer pushes together more or, in the case of a ratchet, locks "tooth by tooth." At the same time the spikes, provided on the outside of the supporting plates, penetrate the supporting surfaces of the adjacent vertebrae. When the supporting plates rest on the supporting surfaces of the adjacent vertebrae and the implant, bone screws are screwed through the perforations of the connecting elements for additional securing if needed.
In accordance with a preferred embodiment, the off-center spacer, (ratchet-like or not) is formed by two rails which are detachably connected to each other, each of which is connected to a supporting plate. This appears to be the simplest and most secure construction.
In this connection it is further advantageous if at least one of the rails has a guide for the length adjustment of the other rail. This prevents jamming of the two rails during the length adjustment.
It is useful if the guide is provided in the ends of the rails opposite the supporting plates. This layout ensures a secure guide for both rails even with a maximum perforation.
Further it is advantageous if the guide is formed by a brace which embraces the other rail. This brace is, even in a loose connection of the two rails, a measure for securing the other rail permanently.

In accordance with a preferred embodiment, the guide is formed by bending or angling one rail with the longitudinal edges flange-like on at least one element of its length. A guide of this type ensures that the two rails are guided precisely in a line in case of a loose connection.
It is also useful if the rails of the spacer are bent convex in a section at right angles to the longitudinal axis relative to the axis of the spinal prosthesis. ~his shape, which is particularly recommended, provides the prosthesis with greater strength in the longitudinal direction.
In this connection it is also advantageous if the connecting elements are also bent convex in a section at rights angles to the longitudinal axis relative to the axis of the spinal prosthesis. As a result, a better adjustment of the connecting elements to the adjacent vertebrae is also provided. If this form is additionally combined with circular support plates, the entire spinal prosthesis can be produced by means of forming.
Further, it is advantageous if the rails are provided with interlocking teeth on the sides facing each other. Thus, each time that a tooth snaps into place on one rail, the spacer on the other rail is locked into a certain position.
In this connection it is useful if with each rail, the edges of the teeth on the side facing the support firmly connected to the rail, vertically and diagonally drop away on the side facing the other supporting plate. ~eeth on the rails, made in this way, lead to the spacer being able to be pushed together.
However, an unintentional removal through the close fit of the vertical edges of the teeth with each other is prevented.

~ 3 ~ J 12 It is advantageous also if each rail of the spacer is provided only with teeth in the margins connected to the two longitudinal edges. This embodiment is especially advantageous if the rails of the spacer are bent convex in a section at right angles to the longitudinal axis relative to the axis of the spinal prosthesis. Through the omission of the teeth inside the rails, the spring action is reinforced with the connection of the rails, since with teeth extending over the entire width of the rails, a greater radial rigidity of the rails is provided.
Further it is preferably planned that the two rails are connected to each other by means of a detachable fastener, for example a pin or a screw. In the case of loose detachable fasteners, the two rails are easily adjustable with it. If the prosthesis with the installed implant is then adjusted over its entire length, the fastener is simply tightened or locked and as a result presses the two rails of the spacer firmly against each other. With that, an unwanted length-adjusting of the prosthesis is practically impossible.
It is preferred also, if all elements of the fastener are permanently secured. This, for instance, can be achieved with a screw that is flattened rivet-like after its insertion at its end facing away from the head. Since this screw is relatively small and only loosely secured during the implantation of the prosthesis, the possibility exists that it and/or a possible lock nut is lost in the patient' 8 body. This i8 prevented as a result. With the use of another fastener, for example a pin, this pin can be firmly connected to one of the rails. In any case, it pushes through the other rail and can, for example, ~ J 13 exhibit a thread on the protruding section, onto which a nut is screwed. The pin's end then also can be flattened rivet-like, in order to make the nut permanent here.
Preferably the rails, in the case of a loose screw, are pressed spring-like together with a spring fitted under the screw head, for example a leafspring. At the same time this spring secures the screw. In this way, the rails of the spacer are already pressed together to a certain extent in the case of a loose screw, whereby an exact length adjustment of the prosthesis is made easy and a "rattling" of the rails is prevented. At the same time, an unwanted loosening of the screw is prevented through the spring action. At the same time the spring, for example, can be provided in the form of a helical spring or a bent leafspring.
It is useful also if, in the rail lying closer to the longitudinal axis of the spinal prosthesis, a threaded borehole for the attachment of the connecting screw is provided. Since the applied connecting screw must be small, owing to the dimensions of the prosthesis, it must only be tightened if the prosthesis with the installed implant was able reach its entire extension at the location of the patient's spinal column to be repaired. Then a threaded borehole is more advantageous than a lock nut. The tightening of the screw becomes easier, since no special procedure for the securing of the nut is needed.
In the rail lying further away from the longitudinal axis of the spinal prosthesis, a longitudinal groove, through which the connecting screw is screwed, can be advantageously provided.
This longitudinal groove makes possible an easy, fast and practically continuous adjustment of the spacer (to the extent ~ 14 that the teeth allow it to be "continuous"). Actually it is also possible to provide in one or ~oth rails lengthwise a number of boreholes at intervals next to each other. The length adjustment then comes about as a result, such that a screw is screwed into boreholes aligned with each other. However, this solution involves considerable additional expenditure during the production of the prosthesis, since all boreholes of the inner rail must be provided with internal screw threads. Also, the tooth interval must be coordinated with the interval of the boreholes, in order to guarantee a complete superimposing of the two boreholes.
It is advantageous also, if the head of the connecting screw is countersunk. Through this, a smooth outer side of the spacer can be obtained, which, with regards to a possible injury to the surrounding tissue, is useful.
As per a further embodiment, the rails of the spacer are spring mounted. As a result, they can be adjusted length-wise outside the patient~s body, so that no slipping results during the implanting. After the implanting of the prosthesis, the rails can glide together further with the kind of teeth provided on the rails, until the implant on the inside rests on the supporting plates. Here additional protection with an additional fastener, for example a screw, is possible, but not necessarily required for the suitable arrangement of the spring.
The rails can be held together especially with one or several of C-shaped leafspring clamp(s) which grip them on the outside. Leafspring clamps of such a type can be easily set up ~8~` 1S
and removed, whereby an easy perforation of the prosthesis is made possible, for example in the case of installing an implant with wrong dimensions.
In connection with this, with the use of two leafspring clamps, these are preferably provided on the longitudinal edges of the rails and locX each time into longitudinal slots provided on the outer surface of the outer rail and the inner surface of the inner rail relative to the longitudinal axis of the spinal prosthesis. Through this, they are secured against slipping and loosening and, on top of that, protruding elements can be avoided.
It is useful if, between the rails, a spacer in a hollow provided on the inner side of the outer rail is provided that, diagonal to the hollow in the extended position, is lowerable, adjustable and spring-loaded. A spacer of this type, which can possibly lock into a second, smaller hollow, makes possible an perforation of the spinal prosthesis in its extended pcsition without removing the leafspring clamps, for instance as in the case of an installed implant with the wrong dimensions.
The spacer may be formed by the vertical crosspiece of a T-shaped insert, the leg of which protrudes outward through a borehole provided in the outer rail. As a result, a simple adjustment of the spacer, both with the prosthesis in place inside the patient's body or outside the patient's body, is possible by means of an appropriately designed tool, for example, a suitable wrench.
It is also useful if adjoining and preferably connected walls are provided at right angles to the supporting plates so as to define at least a partial boundary or the recipient site between the supporting plates; in such a case, one wall may also be formed by one of the rails. Especially when a sufficiently large endogenous bone implant is not available, the surgeon is often forced to use several smaller bone fragments and to bond these with bone cement. It is in many cases useful for the recipient site to be surrounded by walls -- in such a case, all that needs to be done is to place the bone fragments as they are into the recipient site and to bond them with bone cement. In this context, the bone cement may be applied either after the prosthesis has been taken apart or, with the prosthesis installed in the gap that is to be bridged, the bone cement may be applied through the perforations especially provided for this purpose. It is best if the walls correspond to the shape of the supporting plates; thus, if the supporting plates are circular, the walls which define the recipient site should have a cylindrical shape.
In another useful embodiment of this invention, each supporting plate forms an integral unit with the rail, with which it is rigidly connected, and with the connecting element. This reduces the individual number of parts required for the spinal prosthesis. Thus, prior to application, the prosthesis can be easily and rapidly assembled.
In this case, the unit may be made entirely from one piece.
In particular, if the prosthesis is to have circular supporting plates and curved rails and connecting elements, it can be formed from a blank. This ensures that the unit is safely and sturdily built and that no subsequent weld, solder or screw connection is necessary. Connections as provided for by this invention cannot corrode inside the body of the patient as a result of the for~ation of a local cell, Shus eliminating the creation of wesk pointn. Th~ blank used m~y co~ist, for ex~mple, o~ a~loy steel, such as of (A)FM1~8 ~tQel ~U.S. Standard)~
Another p~o~lem ~o bo solved by this in~ention i~ ~o create a device for h~nd~iJ~g the spin~l prosthesis de~cri~ed above. For ~hi~ purp~se, a de~ic~ i8 used which cor.sists o~ two paral~el ~rms wlt~ inserts a~ worXing parts, a minimum o~ one g~de element, and an adi~t~n~ eiement. During a cop~n~r ad~ust~ent, -he guide sle~ent gu ~ dea ~he arms o~ the de~lcc parallol to ~ach ot~,~r, an~ t~o adjuetin~ eleme~t m~kes it pos~ible ~or th~
distanc~ betweQn the two ar~.s to ~e adjusted and boreholes are pr~vid~ in tha insert~, thr~ugh which scre-.ls protrua~ thae can ~e tightened in thr~.~ds provide~ in on~ p~rf~ra~ion in each o~
~he conne~tlnq ele~ents in order to att~ch the spinal prosthe8is.
~his type of device considerably simplifies the implan~aSion, the e~-p~nsion, and optionally tne ronlo~al or t~e spinal prosthesl~
accord1ng ~o thia in~ention, ~hich is g~ner~l~y quite ~mall, by using an insert for attaching the ~pinal pro~thesl~. ~he use of s~rews for fastenir~y the s~inal prosthesis to th~ inserts make~ a s~cure and easily -emoved connection possible. Inserts ~or othQr purposes, for example, ~Gr p~epunchinq the holes for the ~pikes, furth~r ~ liry the surgery.
lt is recommended that the guide eleme~t and the ~djusting t.l~ment co~sist o~ rods and th.~t th~ a~ju~ting e~ement be ~rmed .~y ~ th~ead on a rod. By me~n~ o~ the thread, tne di~ta~ce ~et~e~n the arm~ c~n be simply And ~ontinuously ad~u~t~d. lt ls al~o possible to ad~u~ ~he ~is~ance by pro~idlng one rod with ~h~o oppositely orie~ted threa~ hc two oppositely orient~d thread segmQnts of this rod mesh With the correspondi~g t~reads in ~h~ arms.
To ensure a s~cure guidance e~n in ca~es in which t~
stres~ or str~ n i~ rel~tively h~h, it i5 useful for the quide ~1Q~nt to bQ for~ed by t~o parallel rods, pre~er~ly on~ ~n each s~e of the adjusting dBvice~

~8~ 18 Ac~ording eo another p~e~er~cd em~odim~nt o~ thls inv~ntion, a ~easurin~ device for d~termining the distance between tbe ~w~
arms i~ ~lso avai~abl~. T~is simplifi~ th~ selection o~ t~e si2e of the spinal prosthesig and th~ prefabrication o~ the implant since it allows the surgeon to determine the distance between the remaining vertebrae rapidly and precisely.
A spinal prosthesis with connecting elements and perforations in the connecting elements can be connected by means of screws to the inserts that hold the screws so that the screws protrude through boreholes in the inserts and rest in threads which are provided in the boreholes of the ~onnecting elements of the spinal prosthesis. The use of screws to attach the spinal prosthesis to the in~erts allows a secure and readily detachable connection.
In ~noth~r pre~r~ed p~acti~al exa~ple o~ this d~viee, the ~ide, which ~aces th~ spinal prosthesis, o~ the in~erts sorroesponds to the outer sh~pQ o~ ;h~ conn~cting ele~ents Or t~e sp~n~l pr~3the~is, and the lnserts Ar~ pr~ferably r$gidly att~hed to t~e arms. This Jn~ur~ that thQ part~ o~ the spinal prosthe~l g, w~ich ~3 attaohed to ~h~ a~m~ of the device, can b~
accur3tely guided when the de~ice is be$nq expanded and that thQ
spac~r ~f th~ spinal p~o~thesi~ is kept ~rom ~amming.
This invent~on will be explalned b~low on the basis of pre~erred praCtical ex~mple~ that are illustrated in the d rawin~s ~
Figure 1 ~hows An axonometr$c erploded view o~ a ~pin~l prosthesis.

~88~

~ iguro ~ shows a ~ottom vi~w of the lowe~ outer half o~ the spir,al prosShesis t~s shown in Figure 1) relative to th~
longitudinal axis o~ t~ spi~l p~ost~esis Of Figure 1.
~ ig~re ~ pre~ents an ~xono~Qtric ~ w of an assembl~d and s{~rin~ oad~d spinal prosthes~J acsGr~ing to one of the practlcal exa~ples.
~ igurc 4 shows a top vSe~ of the upper ~nner~ half (~s showrl in FigurQ 3) of the ~pin~l prc~theYi~ o~ Figur~ 3.
Fig~re 5 ~how-o a top vi~w o~ a 'o~er (outer) half of tho spinal prosthesis accordin~ to Flgur~9 3 and ~.
~ igure ~ shows a ~or~20~tal ~nd vertio4l projection of a spac~r for th~ spir,al prosthesis show~ in Figur~ S.
Fi~Ur~ ~ presents an aXonometri~ view o~ a dlffer~nt ~pin~l pro~t~esl~ with a circular ~uppo~t.ing surfac~.
Figure 8 shows a partial view of a modified lower (outer) half of a spinal prosthesis according to another practical example.
Figure 9 shows an axonometric view of a modified upper (inner) half of the spinal prosthesis.
Figure 10 is a diagrammatic lateral view of an installed spinal prosthesis according to Figure 1 with an installed implant.
Figure 11 shows an axonometric view of an assembled spinal prosthesis of a different practical example in which the recipient site for the i~plant is surrounded on all sides by walls.
Figure 12 is a top view of the upper half (as shown in Figure 11) of the spinal prosthesis.

~8~B~ ~

Figure 13 is a top view of the lower half (as shown in Figure 11) of the spinal prosthesis.
Figure 14 shows an axonometric view of an assembled spinal prosthesis of yet another practical example.
Figure lS shows an axonometric view of anothe~ ~odified upper (inner) half of the spinal prosthesis.
Figure 16 shows an axonometric view of yet another modified lower (outer) half of the spinal prosthesis.
Figure 17 shows a horizontal projection of a detail shown in Figure 16.
Figure 18 is a lateral view of a device for handling the spinal prosthesis.
Figure 19 is a top view of the device of Figure 18, and Figure 20 shows a different insert.
Figure 1 illustrates a spinal prosthesis 1 which consists substantially of two parts or halves, each of which forms an integral unit 2,3. Each of these units 2,3 substantially consists, for example, of a hexagonal supporting plate 4 (any other shape is possible as well) which is connected via a connecting segment 5 to a connecting element 6 which is preferably attached at a right angle. On the other side of connecting segment S, rails 7 and 8 extend preferably in the vertical direction and facing away [from the connecting æegment].
These two rails 7,8 form a spacer 9, the length of which i8 adjustable (see details below). Between the supporting plates 4 lies the recipient site for the implant. On the sides, this recipient site is only partly enclosed by rails 7 and 8 while supporting plates 4 form the top and bottom surfaces of the recipient site. The length of this recipient site can be varied ~ ~ 8 ';~

by extending or shortening the rails. The attachment of the two rails 7 and 8 to each other determines the size of the recipient site and stabilizes it.
The supporting plates 4 have spikes 10 for anchoring the device in adjacent vertebrae (not shown) and spikes 11 for anchoring an installed implant (also not shown). These spikes extend in both directions and are arranged on the supporting plates at a certain distance from the rim or the edges. Spikes 10 and 11 may also be positioned differently, or they may have shapes and cross sections different from that shown. For artificial implants, in particular, spikes 11 which extend into the recipient site are not absolutely required; in fact, if especially hard implants are used, such spikes are not even useful.
The supporting plates 4 have perforations 12 which allow the implant that is located between the supporting plates 4 to knit with the adjacent vertebrae. Such perforations are of considerable advantage when an infiltration is desired. The number and shape of these perforations may vary; however, it is useful if at least two perforations are provided to ensure an intimate coalescence [of the implant with the adjacent vertebrae], thus ensuring that the prosthesis is securely held in place.
The connecting elements 6 have boreholes 13. These are provided for allowing the bone screws (not shown) to be screwed into the end surfaces of the adjacent vertebrae. These boreholes may also be threaded. Even though this type of connecting ~ ~ 8 g ~ ~ ~ 22 element is not necessarily reguired since the spikes 10 alone are able to ensure a secure connection, it contributes to a further stabilization.
Along the surfaces that face each other, the two rails 7,8 of spacer 9, the length of which can be adjusted, have teeth 14, the profile of which is vertical on the side which faces the supporting plate 4 that is connected to rails 7 and 8; on the other side, this profile slopes downward. Rail 8, which --relative to the longitudinal axis of spinal prosthesis 1 (as defined by the centers of the supporting plates 4) -- is considered the outer rail, has a longitudinal groove lS; the inner rail 7 has a threaded borehole 16. The longitudinal groove 15 is wide enough to ensure that the rod of a connecting screw 17 can fit through it and can be moved back and forth in the longitudinal direction. When the spinal prosthesis 1 is assembled, this connecting screw which is pushed through the longitudinal slot 15 is screwed into threaded borehole 16 against the spring action of a leaf spring 18 which is located between rail 8 and the head of screw 17 and which has rounded edges. The end projecting from the threaded borehole 16 can subsequently be flattened like a rivet, thus ensuring that it is undetachably retained in the rails. It is also possible to use rails 7 and 8, the inside surfaces of which are smooth; however, the means of attachment required in this case are considerably more complicated. Also, the surfaces of rails 7 and 8 that face each other may have any other meshing projections and corresponding grooves; however, rows of teeth are especially recommended.
As seen in Figure 2, the marginal region of longitudinal slot 15 in rail 8 of the outer integral unit 3 has a projection or shoulder 19 on which the leaf spring 18 and the lower surface of the head of the connecting screw 17 rest; thus, relative to the lower or outer surface of rail 8, the head of the connecting screw is countersunk.
The spinal prosthesis 1 shown in Figure 3 consists substantially of the same components as the spinal prosthesis shown in Figure 1. The difference is that the two rails 7,8 --having teeth 14 -- of the two halves 2,3 of spinal prosthesis 1 are connected to each other so as to be detachable. On the upper surface of the upper rail 7 and on the lower surface of the lower rail 8, longitudinal grooves 20 are provided near the longitudinal edges~ Two C-shaped spring leaf retainers 21 interlock with these longitudinal grooves in which they are held, thereby pressing rails 7,8 against each other. Thus, in the spinal prosthesis 1 shown in Figure 3, it is not necessary to connect rails 7,8 by means of a connecting screw 17 after the implant (not shown) has been inserted.
Figure 4 shows the upper integral unit 2 of spinal prosthesis 1 according to Figure 3, the connecting element 6 of which has a countersunk portion 22 (indicated by the broken line) near the borehole 13 for the bone screw so as to permit a countersunk attachment of the bone screw (not shown) which projects through the borehole 13. The borehole of unit 3 is similarly designed.
on the upper surface, which has teeth 14, of the lower (outer) rail 8, the lower integral unit 3 shown in Figure 5 has two intersecting rectangular grooves 23,23', which are positioned at right angles to each other, and a borehole 24 at the intersecting center of the two grooves. The depth of the two grooves 23,23' is not identical. In this particular practical case, for example, groove 23', which runs parallel to the longitudinal axis of the unit, is deep enough to be able to hold the entire crosspiece 25 (indicated by the broken line) of a T-shaped spacer 26 (see Figure 6). Thus, when the prosthesis is assembled, the teeth 14 of the two close-lying rails 7,8 are able to mesh. Groove 23, on the other hand, is considerably more shallow. When crosspiece 25 of spacer 26 (Figure 6) is pushed from the outside -- so as to counteract the effect of the spring leaf retainers 21 -- into the direction of the other rail 7 and is subsequently rotated 90, thus causing crosspiece 25 to come to rest in the shallower groove 23, teeth 14 of the other rail 7 rest on crosspiece 25 and are no longer able to mesh with teeth 14 of rail 8. This makes it possible for the spinal prosthesis 1 to be opened without removing the C-shaped spring leaf retainers 21, and the two rails 7,8 can slide past each other.
Figure 6 is a horizontal and vertical projection of Figure 5 and shows the spacer 26 with crosspiece 25 and a leg 25 with a hexagonal recess 28 in its front end. When the prosthesis is assembled, leg 27 projects through borehole 24 and can be easily turned from the outside by means of a suitable wrench.
Figure 7 shows a different practical example in which the supporting plates 4 of the two units 2,3 of the spinal prosthesis 1 have a circular shape. This shape allows units 2,3 to be fashioned from one piece, for example, by forming. Otherwise, spinal prosthesis 1 shown in Figure 7 is identical to that shown in Figure 1.
Figure 8 shows a partial view of a modification of rails 7 and 8 (in this case: rail 8) of spinal prosthesis 1; as seen, ~s~

teeth 14 are present only in the two longitudinal marginal regions 29,30 of the rails. In addition, in a section diagonal to the longitudinal axis of the spinal prosthesis, the rails have a convex curvature. To facilitate the production by means of forming, the center of curvature of the rail is located in the center of the supporting plates.
In Figure 9, yet another modification of the integral unit 2 of spinal prosthesis 1 is shown. In this embodiment, several sections along the upper or inner rail 7 have portions 31 which are bent or angled in the direction of rail 8 of the integral unit (not shown) and which form a guide for the other, namely the lower rail 8.
Figure 10 is a diagrammatic view of a spinal prosthesis 1 --in this case, the prosthesis shown in Figure 1 -- after the prosthesis has been installed. The bracket-like configuration of the spinal prosthesis 1 is particular obvious in this figure. In addition, an implant 32, which is located between the supporting plates 4, and two bone screws 33, which are screwed through the boreholes 13 in the connecting elements 6 into the side of the adjacent healthy vertebrae (e.g., 34), are also visible. Also, spikes 10 and 11, which penetrate the vertebrae 34 and the implant 32 are shown (indicated by the broken lines).
The spinal prosthesis 1 shown in Figure 11 consists substantially of the same components as the spinal prosthesis 1 shown in Figure 1. The difference here are walls 4' and 4" which are formed by the supporting plates 4 and which are adjacent to each other. These walls 20rm two telescopic boxes which surround the recipient site for the implant.

Figures 12 and 13 show a top view of the two halves 2 and 3 of the spinal prosthesis 1 of Figure 12 [sic] with walls 4' and 4 n .
The spinal prosthesis 1 shown in Figure 14 also consists substantially of the same components as the spinal prosthesis 1 shown in Figure 1, with the exception that the connecting elements 6 are located on the side of supporting plates 4 that is opposite to the spacer 9. Furthermore, the supporting plates 4 are circular, and in a section at a right angle to the longitudinal axis relative the longitudinal axis of spinal prosthesis 1, rails 7,8 of spacer 9 and connecting elements 6 have a convex curvature with a radius of curvature, the center of which coincides with the centers of supporting plates 4. These rails also form part of the walls of the recipient site. In this particular practical example, the outer rail (in this case: 7) has only one borehole for the rod of a screw which serves as a fastening means. Here, the movable part of the f~stening means, for example, the head of a screw or a nut, which is provided for loosening the longitudinal connection of the two rails 7 and 8, will come to rest preferably in a countersunk position on the lower surface (not visible) of rail 8. If, however, the device, with the implant installed, is to be locked into position or loosened, the implant must be perforated to allow a tool, such as a wrench, to be inserted.
Figure 15 shows yet another modification of the integral unit 2 of spinal prosthesis 1. In this case, for example, the upper or inner rail 7 in the end region on the opposite side of supporting plate 4 has one lateral projection 31a each along both long sides. These lateral projections project downward or are ~83~6-i angled in the direction of rail 8 of the integral unit 3 (not shown). The projections 31a form a lateral guide for the other, namely the lower rail 8. At the same time, the rail 8 (not shown) may of course also be fitted with such projections 31a. In addition, the ends of projections 31a may have hook-like extensions which hook onto rail 8.
Figure 16 shows another embodiment of the integral unit 3 of spinal prosthesis 1. In this case, the guide for the other rail 7 is formed by a bracket 31b which is located in the end region of the outer rail 8 and which embraces the other rail 7, allowing for a certain clearance (to enable the teeth of rails 7,8 to separate and slide past each other when an adjustment in length is made), after the device has been assembled. Bracket 31a, in addition to functioning as a guide, also serves to hold in position the two integral units 3, which make up the spinal prosthesis, at a time when the device is not yet permanently affixed.
Furthermore, unit 3 has a modified connecting element 6 with two lateral projections which have two lateral perforations 13 for the insertion of two bone screws (not shown). In this particular example, spikes 10 which project outward have been omitted since they interfere with the insertion of these bone screws (see also Figure 17).
Figure 18 shows a device 35 which is used during the operation in connection with the spinal prosthesis 1 (not shown).
Device 35 consists of two coplanar parallel arms 36 and 37 which are connected to each other by means of two parallel guide rods 40 and a preferably coplanar adjusting rod 41. The ends of arms 36 and 37 have threaded boreholes 46, to which replaceable inserts 38,39 can be attached by means of screws 47. These two inserts also have a borehole 48 for holding screw 47 in a countersun~ position as well as a borehole 43 for holding screws 42 which attach the spinal prosthesis 1 (not shown in this figure) via its connecting elements 6. The guide rods 40 are compressed into boreholes in arm 36; in boreholes 49 in arm 37, on the other hand, these guide rods can slide back and forth. In addition, the ends of guide rods 40 are fitted with stops 50. The adjusting rod 41 has a pressed-on knurled-head screw, a shoulder 51, and a threaded segment 44 which meshes with a threaded borehole 53 in arm 37. The segment between shoulder 51 and knurled-head screw 52 can freely rotate in a borehole 54 in arm 36. As the knurled-head screw 52 is turned in one or the other direction, the distance between the two parallel arms 36 and 37 is shortened or lengthened, thereby making it possible to open or close the spacer 9 of the spinal prosthesis 1 (not shown) when the spinal prosthesis is unscrewed. Furthermore, one of the guide rods 40 has a scale 45 by means of which the distance between the two arms 36 and 37 or the required size of the spinal prosthesis or of the implant can be measured.
The guide can be designed in many different ways. The simplest is a rotating rod which is also fitted with a thread for the adjusting device. If the structural height is sufficiently great, the guide rods need not necessarily project outward. As an alternative, no rods need to be used -- a slotted plate, in the slots of which the threaded rod can turn, is also possible.
The adjusting device may also be designed differently.
Figure 19 shows that the side of inserts 38 and 39 which faces the spinal prosthesis 1 corresponds to the circular shape of the connecting elements 6 shown in Figure 14. Another way of ensuring a proper fit might be possible by providing a corresponding recess in the front surface of the inserts. In addition, a groove 55 for holding a projection 56 on insert 38 is provided in the end of arm 36, which is one of many possible examples of how to provide additional torsional rigidity to the arm (in this case, 36).
Figure 20 shows a different insert which has outer spikes in correspondence with a supporting plate 4. This insert serves to punch holes into the adjacent vertebrae, thus preparing for the insertion of the spinal prosthesis.
These inserts may be attached in any conceivable manner to the arms of the device, for example, by means of a dovetailed groove and key. If none of the other applications are of interest and the only purpose is to hold the spinal prosthesis, the inserts shown in Figures 18 and 19 may also be connected to the arms so as to form one single piece. A variation of these inserts is, however, useful if for no other reason than the possibility of using an insert for the purpose illustrated in Figure 20. In addition, other useful inserts can be employed, for example, measuring inserts in connection with a scale between such inserts, etc.
During surgery, the device is used in the following way:
The gap to be bridged by the spinal prosthesis is determined by inserting device 35 into the spinal column, by expanding the device 35 by means of turning the knurled-head screw 52 until the outer surfaces of inserts 38 and 39 cone to rest along the end surfaces of the adjacent vertebrae, and by reading the distance A
on scale 45. Subsequently, device 35 is removed from the spinal ;~ ~o ~

column, and a suitable spinal prosthesis 1 is selected on the basis of the measured distance A. Next, the holes for the outer spikes can be prepunched into the adjacent vertebrae by means of the inserts shown in Figure 20. The spinal prosthesis 1 which is partially assembled is subsequently connected to device 35 by means of screws 42 which are screwed into perforations 13 (in this examples shown in the form of threaded boreholes) of the connecting elements 6; it is then inserted into the spinal column by means of device 35 where it is expanded to its proper length.
It is even better if the spinal prosthesis in the length measured is immediately attached to the inserts, thereby holding it in place. In this manner, the prosthesis can be safely secured in the spinal column without exertion of excessive force. After device 35 has been removed from the surgical incision, the bone screws are screwed through perforations 13 of the connecting elements 6 and the final length adjustment is made.
The favorite embodiment of spinal prosthesis 1 is the one shown in Figure 7; however, instead of the flat rails 7 and 8 shown in this figure, the rails with a convex curvature as shown in Figure 8 are used. The center of curvature of these rails lies in the center of each supporting plate 4. The two components 2 and 3 of the spinal prosthesis 1 are formed from one piece, and the double spikes 10,11, which are also obtained by forming, are inserted later.

Claims

1. Spinal prosthesis for replacing one or several destroyed vertebrae, with two supporting plates (4) which lie close to the end surfaces of adjacent healthy vertebrae, which have anchoring means (10) for anchorage in these vertebrae, and which are connected by and regidly attached to a minimum of one spacer (9), the length of which is adjustable, characterized by the face that the spacer (9) is attached off-center relative to the longitudinal axis of the spinal prosthesis (1) which defines the centers of the supporting plates (4), ensuring that a recipient site for holding an implant (32) consisting of a natural and/or artificial material is left open.

2. Spinal prosthesis according to Claim 1, characterized by the fact that the anchoring means (10) are spikes.

3. Spinal prosthesis according to Claim 1 or 2, characterized by the fact that the supporting plate (4) has a minimum of one perforation (12).

4. Spinal prosthesis according to Claim 3, characterized by the fact that the perforation (12) has a circular shape.

5. Spinal prothesis according to one of Claims 1 through 4, characterized by the fact that connecting elements (6), which have a minimum of one perforation (13) for a bone screw (33) which penetrates the side of an adjacent vertebra and which are approximate continuations of the off-center spacer (9), are connected to the supporting plates (4).

6. Spinal prosthesis according to Claim 5, characterized by the fact that the connecting elements (6) are attached via connecting segments (5) to the supporting plates (4) so as not to be flush with the spacer (9).

7. Spinal prosthesis according to one of Claims 1 through 4, characterized by the fact that the connecting elements (6), which have a minimum of one perforation (13) for a bone screw (33) which is screwed into the side of an adjacent vertebra, are connected to the supporting plates (4) on the side of the supporting plates (4) which lies opposite to the spacer (9).

8. Spinal prosthesis according to one of Claims 5 through 7, characterized by the fact that the connecting elements (6) have two off-center perforations (13) each for two bone screws (33) which are screwed into the sides of the adjacent vertebrae.

9. Spinal prosthesis according to one of Claims 1 through 8, characterized by the fact that the supporting plates (4) have spikes (11) which project into the recipient site and which serve to hold the implant (32) in place.

10. Spinal prosthesis according to Claim 9, characterized by the fact that the spikes (11) are arranged in continuation of spikes (10) which are provided for anchoring the prosthesis in the adjacent healthy vertebrae.

11. Spinal prosthesis according to Claim 9 or 10, characterized by the fact that the spikes (10,11) are radially attached next to the perforations (12) of the supporting plates (4).

12. Spinal prosthesis according to one of Claims 9 through 11, characterized by the fact that the spikes (10,11) are 3 to 50 mm long.

13. Spinal prosthesis according to one of Claims 1 through 12, characterized by the fact that the supporting plates (4) have a circular or a hexagonal shape.

14. Spinal prosthesis according to one of Claims 1 through 13, characterized by the fact that the length of the off-center spacer (9) can be adjusted in a ratchet-like manner.

15. Spinal prosthesis according to one of Claims 1 through 14, characterized by the fact that the off-center spacer (9) is formed by two rails (7,8) which are detachably connected to each other and which are rigidly connected with one supporting plate (4) each.

16. Spinal prosthesis according to Claim 15, characterized by the fact that at least one of the rails (7 or 8) has a guide (31,31a,31b) for allowing a longitudinal movement of the other rail (7 or 8).

17. Spinal prosthesis according to Claim 16, characterized by the fact that the guide (31a,31b) is located in the end area of the rails (7 and 8) which lies opposite to the supporting plates (4).

18. Spinal prosthesis according to Claim 16 or 17, characterized by the fact that the guide (31a) is formed by a bracket (31b) which embraces the other rail (7 or 8).

19. Spinal prosthesis according to Claim 16 or 17, characterized by the fact that the guide (31) is formed as a result of the fact that at least a portion of the long sides of one of the rails (7 or 8) is bent or angled so as to form a flange.

20. Spinal prosthesis according to Claims 15 through 19, characterized by the fact that the rails (7,8) of the spacer (9) in a section at right angles to the longitudinal axis of the spinal prosthesis (1) have a convex curvature relative to this axis.

21. Spinal prosthesis according to Claim 20, characterized by the fact that the connecting elements (6) in a section at right angles to the longitudinal axis of the spinal prosthesis (1) have a convex curvature relative to this axis.

22. Spinal prosthesis according to one of Claims 15 through 21, characterized by the fact that the rails (7,8) have meshing teeth (14) along the surfaces that face each other.

23. Spinal prosthesis according to Claim 22, characterized by the fact that on each rail (7,8), the teeth (14) on the side, which faces the supporting plate (4) that is rigidly connected to the rail, have a vertical profile, and the teeth on the side, which faces the opposite supporting plate (4), have a slanting profile.

24. Spinal prosthesis according to Claim 22 or 23, characterized by the fact that each rail (7,8) of the spacer (9) is provided with teeth (14) only in the marginal areas (29,30) that are adjacent to the two long edges.

25. Spinal prosthesis according to one of Claims 15 through 24, characterized by the fact that the two rails (7,8) are connected to each other by means of a detachable fastening means, for example, a pin or a screw (17).

26. Spinal prosthesis according to Claim 25, characterized by the fact that all parts of the fastening means are undetachably held in place.

27. Spinal prosthesis according to Claim 25 or 26, characterized by the fact that, when the screw (17) is loosened, the rails (7,8) are spring-clamped to each other by means of a spring, e.g., a leaf spring (18), which is located under the head of the screw and which serves at the same to secure the screw (17).

28. Spinal prosthesis according to one of Claims 25 through 27, characterized by the fact that a threaded borehole (16) for holding the connecting screw (17) is provided in the rail (7) that is closer to the longitudinal axis of the spinal prosthesis (1).

29. Spinal prosthesis according to one of Claims 25 through 28, characterized by the fact that a longitudinal slot (15), which holds the connecting screw (17), is provided in the rail (8) that is located farther away from the longitudinal axis of the spinal prosthesis (1).

30. Spinal prosthesis according to one of Claims 15 through 29, characterized by the fact that the head of the connecting screw (17) is countersunk.

31. Spinal prosthesis according to one of Claims 15 through 24, characterized by the fact that the rails (7,8) of the spacer (9) are spring-clamped.

32. Spinal prosthesis according to Claim 31, characterized by the fact that the rails (7,8) are held together by one or several C-shaped spring leaf retainers (21) which embrace the rails from the outside.

33. Spinal prosthesis according to Claim 32, characterized by the fact that along the long edges of the rails, provision is made for two spring leaf retainers (21) which engage with the outer surface of the outer rail (8) relative to the longitudinal axis of the spinal prosthesis (1) and with longitudinal grooves (20) along the inner surface of the inner rail (7).

34. Spinal prosthesis according to one of Claims 31 through 33, characterized by the fact that a spring-loaded spacer (26), which fits into an indentation (23') located on the inner surface of the outer rail and which, when in an extended position, can be adjusted at a right angle to the indentation (23'), is provided between the rails (7,8)

35. Spinal prosthesis according to Claim 34, characterized by the fact that the spacer (26) is formed by the crosspiece (25) of a T-shaped insert, the leg (27) of which projects outward through a borehole (24) located in the outer rail.

36. Spinal prosthesis according to one of Claims 1 through 35, characterized by the fact that adjoining and preferably connected walls (4',4") are provided at right angles to the supporting plates (4) so as to define at least a partial boundary for the recipient site, with the possibility that one wall may be formed by one of the rails (7,8)

37. Spinal prosthesis according to one of Claims 15 through 36, characterized by the fact that one supporting plate (4) each forms an integral unit (2 or 3) with the rail (7 or 8), with which it is rigidly connected, and with the connecting element (6).

38. Spinal prosthesis according to Claim 37, characterized by the fact that the unit (2 or 3) is formed from one piece.

39. Device for handling the spinal prosthesis according to one of Claims 1 through 38, consisting of two parallel arms (36,37) with inserts (38,39) as working parts, a minimum or one guide element (40), and an adjusting element (41), with the arms (36,37) of the device being kept parallel to each other during a coplanar adjustment by means of the guide element (40) and with the adjusting element (41) allowing a controlled adjustment of the distance between the two arms (36,37), and with boreholes (43) provided in the inserts (38,39), through which boreholes (43) screws (42) protrude that can be tightened to fasten spinal prosthesis (1) in threads provided in one perforation (13) in each of the connecting elements (6) in order to attach the spinal prosthesis (1).

40. Device according to Claim 39, characterized by the fact that the guide element (40) and the adjusting element (41) are formed by rods and that the adjusting element (41) is formed by a thread (44,44') on a rod.

41. Device according to Claim 40, characterized by the fact that the guide element (4) is formed by two parallel rods that are preferably located on both sides of the adjusting element (41).

42. Device according to one of Claims 39 through 41, characterized by the fact that a measuring device (45) for measuring the distance between the two arms (36,37) is also provided.

43. Device according to one of Claims 39 through 42, characterized by the fact that, the side of the inserts (38,39) that faces the spinal prosthesis (1) corresponds to the external shape of the connecting elements (6) of the spinal prosthesis (1) and that the inserts (38,39) are preferably mounted on the arms (36,37) to resist torsion.

44. Device according to one of Claims 39 through 43 for spinal prostheses according to one of Claims 5 through 38, characterized by the fact that, if inserts (38,39) for attaching the spinal prosthesis (1) are used, the side of the inserts (38,39) that faces the prosthesis corresponds to the external shape of the connecting elements (6) of the spinal prosthesis (1) and that the inserts (38,39) are preferably mounted on the arms (36,37) so as to resist torsion.