before explaining at least one embodiment of the invention in detail , it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings . the invention is capable of other embodiments or of being practiced or carried out in various ways . also , it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting . reference is now made to fig1 , which illustrates a positioning adapter 10 attached to four pedicle screws 22 which are anchored into two adjacent vertebrae , for example , l4 24 and l5 26 . the screws 22 were initially placed into the pedicle of the vertebrae as is known to those skilled in the art . the pedicle screws 22 may be used , for example , to anchor a posterior spinal prosthesis to the pedicles . although four pedicle screws are shown here in this non - limiting example of the application of positioning adapter 10 , a minimum of three anchoring elements such as pedicle screws are sufficient for the successful implementation of positioning adapter 10 . the attachment points from two vertebrae define a plane and connect two adjacent vertebrae . positioning adapter 10 may include a pair of connecting devices 12 and 14 . each connecting device may be shaped as a planar flange with a pair of arms 28 that extend outwards corresponding to the spacing of the pedicle screws 22 . arms 28 are preferably sufficiently long to accommodate most any spacing of the screws 22 . alternatively , a set of positioning adapters 10 may be provided to span any range of spacing of the screws 22 . the arms 28 of positioning adapter 10 may be attached to the vertebrae by inserting the arms into the heads 30 of screws 22 . as the screws are positioned in their correct place , so positioning adapter 10 is now positioned in place for the next stage of the procedure which is the distraction of the two vertebrae . each vertebra has its own connecting device as illustrated in fig1 . the connecting devices 12 and 14 may be formed with reference structure 16 , such as but not limited to , points , pivots or apertures , for example , holes . in summary , positioning adapter 10 is configured to be connected to pedicle screws 22 and has reference structure 16 ( also referred to as reference positioning points 16 ) for proper placement and registration of an anterior disc prosthesis with respect to a posterior spine prosthesis , as is described hereinbelow . reference is now made to fig2 , which is a side view of a distraction device 32 in place attached to screws 22 . distraction devices are known in the art and are commercially available , such as the distraction forceps with hinged handle for pedicle screws , manufactured by synthes spine , 1302 wrights line east , west chester , pa . 19380 . the purpose of distraction is to temporarily expose the posterior disc space in order to ease discectomy and the delivery of the disc implant . fig2 illustrates distraction device 32 assembled on the pedicle screws 22 . it is noted that positioning adapter 10 does not interfere with the positioning or functionality of distraction device 32 . following discectomy and endplate preparation , the next function of positioning adapter 10 can be implemented . reference is now made to fig3 a - 3b , which illustrate a disc implant holder 46 which is used for inserting an artificial disc into the intervertebral disc space , while providing the surgeon with freedom of movement in the workspace of the spinal operation . the disc implant holder 46 may include a handle 50 from which extends a proximal shaft 51 . a distal shaft 55 may be pivotally attached to proximal shaft 51 at a pivot 52 . the pivot 52 may be , for example , a pinned connection that allows free movement of the proximal shaft 51 relative to distal shaft 55 . alternatively , pivot 52 may be , for example , a ratcheted connection that allows ratcheted movement of the proximal shaft 51 relative to distal shaft 55 . more than one pivoted connection may be provided to allow other degrees of movement of the shafts . the distal shaft 55 may include a pair of clamping jaws 53 . jaws 53 may be spring - baised to be normally closed and may be opened by pressing or squeezing them to spread them apart , or by means of some opening handle or cam , as is well known in the art of clamps , pliers and the like . jaws 53 may clamp tightly on an artificial disc prosthesis or implant 48 ( also referred to as anterior prosthesis 48 ). the anterior prosthesis 48 may be , without limitation , an articulating prosthesis . a suitable articulating anterior prosthesis is described in u . s . patent application ser . no . 10 / 898 , 229 ( corresponding to pct application wo 2005 / 084590 ) to arnin , et al ., the disclosure of which is incorporated herein by reference . pct application wo 2005 / 084590 describes an endoprosthesis including a first articulating member formed with a generally concave articulating surface , and a second articulating member formed with a generally convex articulating surface which articulates with the concave articulating surface , the first and second articulating members each having a generally planar attachment surface for attachment to spine structure . reference is now made to fig3 b - 3d , which illustrate the disc implant holder 46 in the spinal procedure workspace . the spinal disc prosthesis or implant 48 may be attached to one end of disc implant holder 46 and handle 50 may be used for placing , guiding and pushing the implant 48 into workspace . fig3 b illustrates the first step of the insertion of the artificial disc into the intervertebral disc space using for example a tlif ( transforaminal lumbar interbody fusion ) procedure known in the art . pivot 52 provides the surgeon the ability to swing proximal shaft about an angle 54 relative to distal shaft 55 to facilitate the initial placement of the implant 48 . handle 46 may be used by the surgeon to vary the angle 54 about pivot 52 ( fig3 b , 3 c and 3 d ). reference is now made to fig4 . after initial placement of the implant 48 , positioning adapter 10 may be connected to disc implant holder 46 with a connecting element 56 ( fig4 ). connecting element 56 fixes disc implant holder 46 to positioning adapter 10 . for example , without limitation , connecting element 56 may include a tubular portion 71 through which the proximal shaft of disc implant holder 46 passes and a flange portion 73 that is fixedly attached to positioning adapter 10 at the reference positioning points 16 ( fig1 ), such as by means of mechanical fasteners ( e . g ., pins , screws ). connecting element 56 defines the final positioning of implant 48 in relation to the pedicle screws 22 . reference positioning points 16 define the ideal relative positioning between implant 48 and screws 22 . a correct positioning of implant 48 in relation to screws 22 will provide a merging of the centers of rotation of implant 48 and spinal posterior implant that is to be attached to screws 22 . it may also provide a correct load sharing between the anterior and posterior inserts . this will facilitate a close to natural range of motion and load sharing of the functional spinal unit . fig5 illustrates the workspace of the operation once again with only l5 visible from a top view for a clarified depiction of the devices . distraction device 32 , positioning adapter 10 , and disc implant holder 46 are seen together with positioning adapter 10 and disc implant holder 46 being connected at connecting point 56 . reference is now made to fig6 . after installation of anterior prosthesis 48 , a posterior prosthesis 60 may be attached to the pedicle screws 22 . fig6 illustrates two adjacent vertebrae with an anterior prosthesis 48 and posterior prosthesis 60 each in their respective correct position in relation to each other according to the embodiments of the present invention . in essence , according to the embodiments of this invention , an artificial disc , will work more efficiently if it articulates around same center of rotation with a posterior implant ( e . g ., facet replacement ). a suitable posterior prosthesis is described in u . s . pat . no . 7 , 011 , 685 to arnin , et al ., the disclosure of which is incorporated herein by reference . u . s . pat . no . 7 , 011 , 685 describes a spinal prosthesis having a unitary body with at least three attachment points attachable to spinal structure , the unitary body including a flexure assembly positioned between first and second attachment members , wherein flexure of the flexure assembly permits movement of the first attachment member relative to the second attachment member . it is appreciated that various features of the invention which are , for clarity , described in the contexts of separate embodiments , may also be provided in combination in a single embodiment . conversely , various features of the invention which are , for brevity , described in the context of a single embodiment , may also be provided separately or in any suitable subcombination .