Abstract:
A positioning device for placing a prosthesis device in a spinal column of a living mammal, the device including at least one holding means for cooperation with the prosthesis device and for guiding thereof during positioning. The positioning device may also include fixing means for fixation with respect to at least one vertebra, where the fixing means includes locking means, which in a first, free state, allows adjustable movement of the holding device and thereby of the prosthesis device, and in a second, locked state, fixes the holding means and thereby the prosthesis device in a selected position. Embodiments of the disclosure also include Embodiments of the invention also include a system.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage entry of PCT/SE2006/000642, having an international filing date of May 31, 2006, which claims priority to Swedish patent application no. SE 0501253-9, filed Jun. 1, 2005. Each of the foregoing disclosures is expressly incorporated herein in its entirety. 
     FIELD OF THE INVENTION 
     The invention concerns a positioning device and a system for engagement with vertebrae in a spinal column including such a positioning device. 
     BACKGROUND OF THE INVENTION 
     For patients diagnosed with disc degeneration, surgical operations are performed more and more often. The most common operation for these patients today is fusion, where an ossified connection of vertebrae is obtained. Also, metallic connection devices can be used. Movability then ceases between the vertebrae in question but the patient will become free from pain. As the patient becomes more active and movable, the segments above and below the fused region will, however, be subjected to greater strains. The risk of new symptoms from surrounding segments thereby increases. 
     As an alternative to fusion, disc implants have been presented. A known disc prosthesis generally consists of two mutually articulated plates that are positioned between two vertebrae instead of the disc. The positioning of a disc implant results in eliminating the disc that causes pain, reinstating the distance between the vertebrae and reinstating movability between them. 
     In order to obtain sufficient certainty against a disc implant moving, over time, in an undesired manner from the intended position between two vertebrae, two mutually articulated plates of a previously known prosthesis are provided with different kinds of projecting engagement means, such as fin-shaped elements, pointed elements, pins and like plural projections for the engagement with the meeting surfaces of the vertebrae. 
     An operative method that is used for inserting a disc implant requires positioning of the prosthesis from the abdomen side in order to allow access to the vertebral column from the front. The disc to be replaced is cleared out, whereby the vertebrae are drawn apart with the aid of tension pliers. 
     After using instruments for shaping grooves in the surfaces of vertebrae for the cooperation with possible projecting protrusions for the purpose of achieving a correct position for the disc prosthesis, the latter is now to be positioned. 
     According to today&#39;s methods, this is achieved by placing the prosthesis on a holder and hammering it in with great force between the vertebrae, guided by the prepared grooves. This step in the operation is very problematic, since the vertebrae tend to be drawn against each other and then it is often difficult to implant the prosthesis between the vertebrae. For this reason, implantation by hammering is risky. 
     When the prosthesis is finally positioned, which is verified with X-ray radioscopy, tension pliers are used in order to again span apart the vertebrae, and thereby the disc plates of the prosthesis, in order to be able to position a joint detail between these plates. Also this step is troublesome and sometimes laborious. 
     When using prostheses that are completely assembled which include the joint detail, this second step is not necessary. Such prostheses are, however, thicker and thus, more troublesome to position between the vertebrae. Sometimes, unfortunately, damage to the vertebrae can occur during the positioning of the prosthesis. Such damage can be serious and have serious consequences. For that reason, the surgical operation puts great demands on the skill and experience of the surgeon. 
     When, finally, everything is place, the operation is terminated and a final X-ray is made. Sometimes, it is discovered that the disc prosthesis is positioned in such a way that it is not placed exactly on the middle line or is not in a proper position. The possibilities of adjusting the position are at this stage almost none. 
     Since the disc prosthesis rests on the brittle covering plate of the vertebra, the prosthesis must have maximal size in order to support on a relatively strong peripheral rim of the vertebra. Exact positioning is therefore very essential. Patient having osteoporosis are therefore often disqualified for this type of surgical operation depending on lack of congruence between the parts of the disc prosthesis and the vertebra. 
     Incorrect positioning results in risk of uncontrolled separation and repositioning of the vertebrae. 
     OBJECTS AND IMPORTANT FEATURES OF THE INVENTION 
     It is an aim of the present invention to provide a positioning device of the kind mentioned initially and a system which makes it possible to eliminate or at least reduce the problems of the background art. 
     These aims and advantage of the present invention can be achieved in a positioning device according to features disclosed herein. 
     Hereby it is achieved that when two vertebrae of the vertebrae in a spinal column are push apart, a prosthesis device, such as for example a disc prosthesis or a vertebral prosthesis, can be correctly positioned with respect to at least one vertebra when the vertebrae are spanned, e.g., pushed, apart, so that, when the separation is ended, the prosthesis is indeed in the right position. X-ray radioscopy can be used in connection with adjusting holding means of the disclosed embodiments in order to assist the surgeon during the positioning. The invention is, however, not limited to this method, but also other corresponding methods for this are possible to use, such as for example translucence with NMR-camera, magnet camera. Also, other fluoroscopy and positioning indication methods can be used. 
     When the pushed apart vertebrae are released against the prosthesis device, through X-ray radioscopy or the like, the final position of the prosthesis device can be verified that it is in the desired position. In the event this is not the case, there is a real possibility of repositioning the prosthesis device after a renewed pushing apart of the vertebrae, although this would not be necessary if the positioning is made accurately from the beginning. 
     After a verified correct positioning, the holding device is released from the prosthesis device, whereafter the used device can be removed permanently. Altogether, the positioning device according to the invention allows essentially more secure and further, more easily handled equipment, which also can be used in a patient-friendly manner with minimized risks of injuries to the patient when it is used. 
     By providing two fixing elements for different engagement positions and which are mutually lockable, satisfactory stability is obtained and positioning security after possibility of adjustment. 
     By providing a universal joint, which is lockable/releasable through locking means, great positioning freedom is provided. 
     In particular, it is preferred that the positioning device according to the invention includes distance means having connection portions which carry engagement means that are constructed for engagement with two vertebrae at a distance from each other. Hereby the prosthesis device is positioned with respect to these vertebrae, which are preferably located on either side of the operation point. 
     In particular, it is preferred that the distance means are arranged such that they are capable of changing the degree of separation of the vertebrae when the engagement means are in engagement therewith. Hereby, in the positioning device, the means for spanning apart the vertebrae are integrated which is a considerable advantage since the arrangement for spanning apart can be constructed optimally to function as a mechanism for spanning apart, and further, as the base for the fixing means. Greater freedom when removing the old, damaged disc is also achieved. With previously known technology, the tooling for holding apart the vertebrae comprises an obstacle making it difficult to evacuate the old, damaged disc. This process is time consuming and positioning of a disc implant is more difficult. The integrated aspect of this invention essentially simplifies clearing out of the damaged disc, whereby the entire operation is facilitated and speeded up, resulting in a safer operation. The possibility of spanning apart, which is provided according to this aspect of the invention, makes it possible to freely remove the old disc. 
     The positioning of the holding means will thereby be very stable and no further engagement points, besides the ones belonging to the mechanism for spanning apart, the distance means, are necessary. The number of operation points in the patient in the form of holes for screws or the like can thereby be limited to a minimum. 
     The distance means preferably includes two distance means arranged in parallel each carrying the engagement means. The adjustment and handling of the holding means and the prosthesis carried thereon takes place between the parallel arranged distance means. The fixing means are suitably comprised of elongate elements, that are arranged on the distance means and are fixable thereon, which in a common crossing point are lockable, which results in a very stable fixation. The crossing point between these elements is preferably also the starting point for locking means, which, in its locked position, fixes the holding means. Preferably the locking means in the locked position also locks the fixing elements in said crossing point. 
     By providing the fixing elements with one slotted portion in their free regions, in the free state, sideways adjustment of the crossing point is allowed with respect to the operation point, which can be desirable for providing an accurate positioning of the prosthesis device in its rotational direction. 
     It is previously known to use so called retractors in the kind of surgical operation of the present type in order to hold the soft parts in the abdomen from the operation point. A system according to the invention includes and preferably carries support devices for that purpose. By fastening them to the distance means, they contribute in an optimal manner to hold the abdomen wall pressed down and the operation field free. The clearing out of the old disc is also simplified with these means. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention will now be described by way of embodiments and with reference to the annexed drawings, wherein: 
         FIG. 1  shows a positioning device according to the invention during the process of introducing an implant in a spinal column, partly in section, 
         FIG. 2  shows the positioning device in  FIG. 1  in a perspective view, 
         FIG. 3  shows the positioning device in  FIGS. 1 and 2  in a separate perspective view, 
         FIG. 4  shows the positioning device according to the invention with some details removed for the sake of clarity, and 
         FIGS. 5   a  and  b  show in different views a holding device for the use with a device according to the invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  shows a positioning device  1  in the process of positioning a disc implant  2  between two vertebrae  3  and  3 ′ in a spinal column of a living human being. Reference numeral  5  are two healthy discs, whereas between the vertebrae  3  and  3 ′ is cleared out all material from a damaged disc to be replaced by the disc implant  2 . 
     The disc implant  2  is held by a holding device  6  including a fork-shaped head  10 , which releasably grips around the disc implant  2  and a rod shaped manipulating element  11  which can be manipulated by hand by a surgeon. In the embodiment shown in  FIG. 1 , the manipulating element  11  is controlled by a fixing means  7 , which in turn is connected to the distance device  8  (only one shown on  FIG. 1 ), which in turn includes engagement means in the form of screws, (indicated with dash dotted lines, and with numerals  4  and  4 ′), for engagement with two vertebrae  3 ,  3 ′. 
     The fixing means  7  includes fixing elements  12  (only one shown in  FIG. 1 ) together with a universal joint  9 ′ which is lockable by means of locking means  9 , wherein the universal joint  9 ′, in a first, free state, allows adjustable movement including rotations and displacements of the holding means  6  and thereby for the disc implant  2 . In a second, locked position, the locking means  9  locks the universal joint  9 ′, and thereby the holding device  6  and the disc implant  2 , in a chosen position. 
     As is indicated by arrows P 1 -P 6 , essentially total freedom of movement is achieved with the shown embodiment with three linear degrees of freedom P 1 -P 3  and three rotational degrees of freedom P 4 -P 6  for the holding device  6 . It should be noted that freedom of movement in the length direction of the distance device  8  is obtained by displacement of the fixing element  12  relative thereto. Locking of the locking means  9  can suitably be arranged by means of a smaller rotation of the fixing element  12  with respect of the distance device  8  and thereby friction locking of these elements with respect of each other. 
     The function of the spanning device of the arrangement is such that the distance device  8  is extendable in the length direction by displacement in such a way that the engagement elements, which thus have been brought to engagement with two vertebrae because of the extension, will cause a change of the degree of separation between these vertebrae  3  and  3 ′ with respect to each other. 
     This way the vertebrae can be separated and the space between them be cleared out so that the disc implant  2 , without resistance, can be inserted between the vertebrae  3  and  3 ′ and accurately positioned by the surgeon supported by simultaneous X-ray radioscopy until an optimal positioning of the disc implant  2  has been reached. Thereafter the holding device  6  is locked and thereby the prosthesis device in positioned in the chosen position with the aid of the fixing means  7 , whereafter the distance device  8  is manipulated in such a way that the distance between its outer ends is reduced and the vertebrae  3  and  3 ′ move closer to each other until they come into contact against the outer plates of the disc implant  2 . Thereafter, a final control is made, by means of X-ray radioscopy or the like, that the disc implant  2  is indeed accurately positioned. 
     If that should not be the case, the degree of separation is again increased between the vertebrae  3  and  3 ′ and the disc implant  2  is repositioned. When accurate positioning has been reached, the holding device  6  is removed from the disc implant  2 , whereafter the distance device  8  and its engagement means  4  and  4 ′ can be removed from the engagement with the vertebrae. 
     In  FIG. 2 , the positioning device  1  is represented in a perspective view in about the same position as is shown in  FIG. 1 . Here, it is shown that the spanning device belonging to the positioning device  1  includes two sideways separated distance means  8  and  8 ′, which are positioned such that between them is a sufficient space for introducing a disc implant (not shown in  FIG. 2 ), which is carried by a fork head  10  of a holding device  6 . 
     From each one of the distance means  8  and  8 ′, extend fixing elements  12  and  12 ′, which are longitudinally displaceable on the respectively means  8  and  8 ′ through sleeve portions  19 . The fixing elements  12  and  12 ′ are united at a crossing point, where locking device  9  engages. The locking device  9  also activates and deactivates a universal joint  9 ′, which carries the manipulating element  11  of the holding device  6 . 
     Fixing means  12  and  12 ′ are arranged longitudinal through slots  20  and  20 ′, in which a bolt belonging to the locking means  9  can run. This way, in a free state of the locking means, it is possible to displace the locking device and the universal joint  9 ′ in height as well as sideways by side displacement of the locking device and the universal joint with respect to the operation point between the vertebrae  3  and  3 ′. 
     Further, the distance devices  8  and  8 ′ are telescopic and thus axially displaceable in order to allow an increased separation of those vertebrae, with which they are in engagement. In the shown example, distance means  8  and  8 ′ are not in engagement with two adjacent vertebrae, but with a first vertebra  3 ′ and a second vertebra  3 ″, whereas a third vertebra  3  is between these vertebrae. This arrangement allows better space at the place of operation. 
     Spanning apart the distance devices are made with a pliers device  18 , which forces apart two telescopic parts  15 ′ and  14 ′ belonging to the distance device  8 ′. For fixing of an obtained separation position, a locking ring  16 ′ is used, which locks against the smaller one of the telescopic parts  15 ′ by means of a locking screw  17 . In practice, the spanning apart of the vertebrae are made through step-wise manipulation of the pliers device  18  by first, the one on the distance devices a smaller step, locking thereof, thereafter spanning apart of the second distance device a smaller distance, locking thereof etc. etc. 
     In  FIG. 3 , the device of  FIG. 2  is shown in a different perspective and freed from a spinal column. The distance devices  8  and  8 ′ have at their ends known joint devices for cooperation with the engagement means  4 ,  4 ′, which are comprised of known skeleton screws. By the engagement means being articulately fastened to the distance devices, excess breaking forces onto the vertebra are avoided in connection with spanning-apart the spinal column. The positioning of the screws  4 ,  4 ′ in the vertebrae, which are least porous, and thereby best resist the forces for spanning apart. 
     On  FIG. 3  also illustrates two supporting elements  21  and  21 ′, preferably lockable and slightly curved, which are arranged for cooperation with (not shown) supporting plates for free holding the operation point from body organs in connection with the surgical operation. 
     In  FIG. 4  illustrates the positioning of essential parts, according to the invention, with some details removed. 
     A holding device  6  is shown in  FIG. 5   a  and  b . The holding device  6  includes a fork-shaped head  10  with fork shanks  10 ′ and 10″, which form an engagement position, where, with the aid of the engagement means  24 , engage a disc implant. Accordingly, holding device  6  can be brought to a position where the disc implant is released. This is achieved when the normally curved element  23  between the fork shanks  24 , by means of an actuating means  22  in the form of an element inside the rod shape maneuvering element  11 , is brought to a straightened state, where it presses apart the fork shanks  24 . See interrupted arrows in  FIG. 5   b . The actuating means  22  can be manipulated by hand by a surgeon through a press button outermost on the means  22 . The head  10  is preferably made of a plastic material in one piece in such a way that in an unloaded condition, it is in a position for engagement and with a bent element  23 . 
     It should be noted that the invention can be modified within the scope of the claims. The shown embodiment with the positioning device directly cooperating with a spanning device in the form of distance means is preferred. However, it is not excluded that the positioning device is separate from the spanning device, and in that case, it is arranged such that the fixing means are fastened otherwise to one or a plurality of vertebrae. This is, however, not desired, since it means that further operations with holes etc. in the spinal column have to be made. It, however, makes it possible to use another type of spanning device for separating the vertebrae than the one that is described and shown here. 
     In order to arrange that a greater space is provided between two distance devices, the attachments of the engagement means can be positioned sideways outwardly, so that the distance devices can be positioned sideways with respect of the axes of the engagement means. 
     A modification of the spanning device can have one single distance device, which provides spanning apart instead of two that are shown in the Figures. At the ends, this single distance device can have sideward angled portions for cooperation at different positions after their lengths, with each two engagement means engaged with the vertebrae so that the spanning device includes a shallow U-shaped construction with the distance device as a web and the sideward angled portions as the shanks of the U. In this case positioning, as an example, there may need to be arranged, on the one hand, on the only distance device, and on the other hand, on a fixed point on a vertebra. 
     The arrangement between the distance device (devices) and the engagements means can be different: For example, an arrangement with three independent joints for allowing movements: 1: in a plane parallel with the axis of the distance device, 2: in a plane at right angle to the axis of the distance device, 3: in a plane at right angle against the axis of the engagement means (screw). Independent locking of these joints results in possibility of changing the angles of the screws, also under load, which gives greater possibilities of influencing the positions and the parallelism of the vertebrae. 
     The fixing means can, such other cases, be constructed otherwise, thus including portions for cooperation directly with a vertebra. Also other kinds of arrangements for locking the holding means can be envisaged. For example, with a locking device arranged at the fastening point of the fixing means on the spanning device or on the vertebra itself. It is also possible to have other types of locking and a plurality of separate locks for movements in different directions instead of the integrated lock shown in the Figures. The distance devices can be manipulated otherwise, for example, by screwing, with a notched rod with possibly a spring loaded locking device, or with a leaver mechanism. 
     In a simply handled modification, the distance device is maneuvered with the aid of an adjustment cable, such as a “Bowden cable”, which can have its fastenings on engagement portions on mutually movable parts of a distance device in a manner which is obvious for the person skilled in the art. This way, spanning apart of two vertebrae is initiated from a distance from the area of spanning apart, which is an advantageous, since it enhances control and accessibility. Also, other arrangements, such as with a pawl and rack and corresponding actuating means with hydraulics or with pneumatics, can be used for spanning apart. 
     It shall be noted that it is not excluded that other prostheses are positioned with a device according to the invention, for example vertebra prostheses.