Abstract:
Disclosed is a surgical extractor ( 20 ) for surgically removing intervertebral prostheses that are provided with two support plates ( 3, 4 ) with one respective joint part ( 5, 6 ). The inventive extractor ( 20 ) comprises two legs ( 21, 21 ′) which are interconnected in a prong-shaped manner, can be inserted into an intermediate space between the two support plates ( 3, 4 ), and each support at least one locking element ( 22, 22 ′) at the free end thereof. Said at least one locking element ( 22, 22 ) allows for insertion into the intermediate space between the two support plates ( 3,4 ) in a first position while protruding from the intermediate space in a vertical direction in a second, locked position. The two legs ( 21, 21 ′) are connected to a common extraction means ( 24, 25, 26 ) for transmitting a tractive power to the legs ( 21, 21 ′) in the longitudinal direction thereof.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a surgical extractor for surgical removal of intervertebral disc prostheses, which comprise two endplates with in each case one joint part. 
       BACKGROUND OF THE INVENTION 
       [0002]    Intervertebral disc prostheses are known from use which comprise two sub-elements with in each case one endplate. Each endplate has on its outward-facing side a bearing face with which the endplate is supported against a vertebra adjoining the intervertebral disc space. On the inside of each endplate there is disposed a joint part, which in the case of the one endplate takes the form of a dome-shaped joint socket and in the case of the other endplate takes the form of a corresponding dome-shaped is joint head. When inserted, joint socket and joint head together form a ball-and-socket joint, such that the two endplates may be tilted in any spatial direction relative to one another. 
         [0003]    Since such ball-and-socket joints are exposed to heavy wear due to the forces acting on them, it may be necessary to renew the entire intervertebral disc prosthesis. Replacement may also be necessary if the adjoining vertebrae become pathologically deformed, such that the intervertebral disc prosthesis is no longer optimally conformed to the physiological conditions. 
         [0004]    The object of the invention is to provide a surgical extractor for surgical removal of intervertebral disc prostheses of the above-mentioned type. 
       SUMMARY OF THE INVENTION 
       [0005]    This object is achieved by a surgical extractor which comprises two legs connected together in the manner of a fork, which may be introduced into an interspace between the two endplates of an intervertebral disc prosthesis to be extracted and which each bear at least one locking element at their free ends, which locking element, in a first position, allows introduction into the interspace between the two endplates of the intervertebral disc prosthesis and, in a second, locked position, projects vertically beyond the interspace. The two legs are connected to a common extraction means for transmitting a tensile force to the legs in the longitudinal direction thereof. 
         [0006]    For the purpose of extraction, the legs are introduced through the interspace between the endplates of an intervertebral disc prosthesis and then locked in place. The intervertebral disc prosthesis may then be driven out of the intervertebral disc space using the extraction means. 
         [0007]    If the legs are connected detachably to the extraction means, the legs may be introduced separately on in each case one side of the ball-and-socket joint of the intervertebral disc prosthesis and only connected to one another and to the common extraction means for the purpose of extraction once in the introduced state. This simplifies introduction of the legs. 
         [0008]    The locking elements may be constructed in such a way that they are wider in a first transverse direction than in a second transverse direction. Thus, the two legs may in each case be introduced in one orientation, in which the locking element fits in its narrower transverse direction through the interspace between the endplates, then turned 90° into the locked position and connected together. 
         [0009]    Preferably, the legs have a substantially round profile over their introducible length and the locking elements are in each case constructed as rigid extensions formed in T-shaped manner on the ends of the legs. 
         [0010]    The locking elements should conveniently be so shaped that no force component tending to spread the endplates apart can be transmitted by said locking elements in the locked position, which would make it more difficult to drive the intervertebral disc prosthesis out of the intervertebral disc space. 
         [0011]    The extraction means may advantageously comprise a shank with a limit stop and a percussive weight movable along the shank as far as the limit stop. The intervertebral disc prosthesis may then be carefully driven out in small steps in that the percussive weight is moved by the surgeon jerkily against the limit stop. The surgeon thus has good control of the force impulses which he is exerting on the intervertebral disc prosthesis. 
         [0012]    In another advantageous exemplary embodiment, the legs have different lengths. This makes it possible to extract the intervertebral disc prosthesis from the intervertebral disc space by way of lateral access. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Further features and advantages of the invention are revealed by the following description of an exemplary embodiment made with reference to the drawings, in which: 
           [0014]      FIG. 1  is a side view of an intervertebral disc prosthesis inserted between two vertebrae; 
           [0015]      FIG. 2  is a plan view of an extractor according to the invention with an endplate of the intervertebral disc prosthesis disposed therebelow; 
           [0016]      FIG. 3  is a side view of an individual leg of the extractor of  FIG. 2 ; 
           [0017]      FIG. 4  shows the intervertebral disc prosthesis of  FIG. 1  with an extractor introduced from the hidden side; and 
           [0018]      FIG. 5  is an exploded representation of the extractor shown in  FIGS. 2 to 4 ; 
           [0019]      FIG. 6  is a plan view based on  FIG. 2  of an extractor according to another exemplary embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]      FIG. 1  shows an intervertebral disc prosthesis  10 , which has been inserted into an intervertebral disc space between an upper vertebra  1  and a lower vertebra  2 . The intervertebral disc prosthesis comprises an upper endplate  3  and a lower endplate  4 . 
         [0021]    On the inside of each endplate  3 ,  4  there is disposed a protrusion with a joint part, which in the case of the lower endplate takes the form of a dome-shaped joint socket  5  and in the case of the upper endplate  3  takes the form of a corresponding dome-shaped joint head  6 . Joint socket  5  and joint head  6  together form a ball-and-socket joint, such that the two endplates  3 ,  4  of the intervertebral disc prosthesis  10  may be tilted in any spatial direction relative to one another. 
         [0022]    If such an intervertebral disc prosthesis  10  needs to be removed surgically for replacement, a surgical instrument known as an extractor is required. An extractor  20  according to the invention is shown schematically in plan view above the lower endplate  4  of the intervertebral disc prosthesis  10  in  FIG. 2  and in exploded representation in  FIG. 5 . 
         [0023]    The extractor  20  has two legs  21 ,  21 ′ of identical construction, which in each case bear at one end a rigidly formed-on, T-shaped extension  22 ,  22 ′ and at their other end in each case a laterally offset fastening lug  23 ,  23 ′. In  FIG. 3  the leg  21  is shown from the side. The leg  21  and the T-shaped extension  22  have round profiles. A hole  28  in the fastening lug  23  for accommodating a pin  27  is indicated by broken lines. The T-shaped extension  22  is mounted orthogonally relative to the fastening lug  23 , such that it is perpendicular to the plane generated by the legs  21 ,  21 ′ when the extractor  20  is in the assembled state. 
         [0024]    The two legs  22 ,  22 ′ may be connected detachably by means of the pin  27  to a common shank  24 , on which a movable percussive weight  25  is guided, which may be moved against a limit stop  26 . It goes without saying that a screw, a pin or a similar fastening means may be selected instead of a pin  27 . 
         [0025]    When connected together the two legs  22 ,  22 ′ form a fork, which grips around the ball-and-socket joint of the intervertebral disc prosthesis  10  formed by the joint parts  5 ,  6 . As a result of the curved portions between the fastening lugs  23 ,  23 ′ and the legs  21 ,  21 ′, the latter are arranged in one plane when they are connected together by means of the pin  27 . 
         [0026]    The dismantleable nature of the extractor  20  allows introduction of the legs  21 ,  21 ′ into the interspace between the endplates  3 ,  4  of an intervertebral disc prosthesis  7  to be removed. In addition, all the parts of the extractor  20  may in this way be individually cleaned and sterilised. 
         [0027]    Preferably, the extractor  20  consists of surgical stainless steel (316L). Alternatively, other, sufficiently inert, break-resistant materials such as for example titanium or titanium alloys may of course be used. 
         [0028]    To remove an intervertebral disc prosthesis  10 , the two legs  21 ,  21 ′ are inserted individually into the gap-like interspace between the two endplates  3 ,  4  preferably via a ventral or lateral access canal. To this end, the legs  21 ,  21 ′ are turned in such a way that the T-shaped extension  22 ,  22 ′ is positioned in the gap direction. Once the two legs  21 ,  21 ′ have been introduced so far into the joint interspace of the intervertebral disc prosthesis  10  that the T-shaped extensions  22 ,  22 ′ project into the spinal canal on the opposite side, the legs  21 ,  21 ′ are turned by 90°, fitted together with the shank  23  and connected together by means of the pin  27 . 
         [0029]    The two extensions  22 ,  22 ′ are now positioned, as shown in  FIG. 4 , perpendicularly to the gap direction of the interspace between the endplates  3 ,  4  and grip around these from the back. The surgeon then begins to drive the intervertebral disc prosthesis  10  out of the intervertebral disc space by striking with the percussive weight  25  against the limit stop  26 . 
         [0030]    The T-shaped extensions  22 ,  22 ′ are designed such that they rest substantially flat against the end faces of the two endplates  3 ,  4 , such that no orthogonally acting force component tending to spread the endplates  3 ,  4  apart is transmitted. 
         [0031]    Alternatively, the end faces of the endplates  3 ,  4  may also be slightly bevelled towards the outsides thereof. If the extensions  22 ,  22 ′ are then configured in such a way that they in each case form an angle with the legs  21 ,  21 ′ which is somewhat smaller than 90°, upon driving out of the intervertebral disc prosthesis  10  a force component is transmitted which pushes the endplates  3 ,  4  together on the side facing the spinal canal and spreads them apart on the opposing, ventral side. A slightly wedge-shaped arrangement of the endplates thus arises, such that the intervertebral disc prosthesis  10  can slip more readily out of the intervertebral disc space. 
         [0032]    It should be pointed out that the extractor illustrated is merely a non-limiting exemplary embodiment. An informed reader will obviously know that numerous modifications and additions to the above-described extractor are possible. 
         [0033]    For instance, instead of a percussive mechanism any other type of extraction means may be used which is suitable for transmitting a tensile force in the longitudinal direction of the legs  21 ,  21 ′. For example, a lateral projection may be provided on the shank  24  instead of a limit stop  26  for a percussive weight  25 , by means of which the surgeon may drive out the intervertebral disc prosthesis  10  using a hammer. Alternatively, a screw mechanism may also be provided, which rests against the adjoining vertebrae, in order to push the intervertebral disc prosthesis  10  out of the intervertebral disc space by screwing in one or more extraction spindles against the vertebrae. 
         [0034]    As an alternative to the T-shaped extensions  22 ,  22 ′ with which the legs  21 ,  22 ′ are locked in place, it is also possible, for example, to provide erectable barbs or locking members mounted rotatably at the ends of the legs, which may be actuated by means of a suitable mechanism at the front end of the legs after introduction of the legs. It is also not essential for the legs  21 ,  21 ′ to be inserted over the entire width of the intervertebral disc prosthesis  10  as far as into the spinal canal. Alternatively, for example, recesses may be provided in the endplates, into which suitable locking members may engage at the ends of the extractor legs. 
         [0035]      FIG. 6  is a plan view based on  FIG. 2  of an extractor according to another exemplary embodiment of the invention and designated overall as  20 . The extractor  120  differs from the above-described extractor  20  solely in that the legs  121 ,  121 ′ are of different lengths. In addition, the outwardly directed short legs of the T-shaped extensions  122 ,  122 ′ have a semicircular profile and the endplates  3 ,  4  have at their dorsal ends semicircular recesses  130 ,  130 ′, which are of complementary construction to the profile of the extensions  122 ,  122 ′. 
         [0036]    The legs  122 ,  122 ′ of different lengths and the form-fitting engagement of the extensions  122 ,  122 ′ in the recesses  130 ,  130 ′ make it possible to pull the endplates  3 ,  4  out of the intervertebral disc space by way of laterally acting forces without the extensions  122 ,  122 ′ slipping against the endplates  3 ,  4 . The semicircular shape additionally ensures that the extensions  122 ,  122 ′ do not project beyond the dorsal end of the endplates  3 ,  4  and in this way injure the adjoining sensitive tissue during the extraction process