Abstract:
A prosthesis in the form of a cage having opposed complimentary bearing surface assemblies. The bearing surface assemblies moveable towards and away from each other. The moving mechanism being part of the bearing surface assemblies. Each of the bearing surface assemblies having an outer bearing surface whereby movement of one bearing surface assembly in one direction will move the bearing surface assemblies away from each other and movement in the opposite direction will move the bearing surface assemblies towards each other.

Description:
This is a continuation of application Ser. No. 09/360,796, now U.S. Pat. No. 6,454,806, filed Jul. 26, 1999, which is hereby incorporated by reference. 
    
    
     FIELD OF INVENTION 
     The present invention relates to an improved spinal surgical prosthesis and more particularly to apparatus and methods for achieving stability of adjacent vertebrae and preserving the inter-disc space following disectomy by internal fixation or fusion. 
     BACKGROUND OF THE INVENTION 
     Fusion commonly performed for adjacent bone structures and those not adjacent provides for long term replacement as a result of degenerative or deteriorated disorders in bone. 
     An inter-vertebral disc is a ligamentous cushion disposed between vertebrae and as a result of injury, disease or other disorders may deteriorate in part or in whole, thereby leading to mechanical instability and painful disc translocations and often necessitating bed rest or hospitalization. If left untreated possible subsequent involvement of adjacent nerves and muscular involvement may occur. In such cases, if treatment is delayed, permanent damage to the nerves may result in muscular atrophy and severe dysfunction. 
     Procedures for disc surgery may involve partial or total excision of the injured disc portion and replacement with biocompatible devices of bone or bone-like material. 
     EARLY TECHNIQUES 
     Bone material was simply disposed between the adjacent vertebrae, typically at the posterior aspect of the vertebrae and the spinal column was stabilized by way of a plate or rod connecting the involved vertebrae. However, the use of bone may require undesired additional surgery and is of limited availability in its most useful form. In addition, the risk of infection and rejection is a significant consequence. In any event, bone is only marginally structural and with bone it is difficult to stabilize both the implant against dislodgment and stabilize the adjacent vertebrae. It becomes desirable to find solutions for stabilization of an excised disc space by fusing the vertebrae between their respective end plates without the need for anterior or posterior plating or rods. 
     PRIOR ART 
     A review of the prior art clearly reveals attempts to achieve such solutions in two distinct areas, namely: 
     I. Static inter-body fusion devices 
     II. Adjustable inter-body fusion devices that can restore and stabilize varying heights of the intra-discal space. 
     I. Static Inter-body Fusion Devices 
     An extensive number of static inter-body fusion devices commonly called “cages” have evolved for replacement of a damaged disc while still maintaining stability of the disc inter-space between the adjacent vertebrae. 
     However, existing static inter-body fusion devices encountered some problems. They require drilling, boring or tapping of the end plates which sometimes results in removal of an excessive amount of supporting bone with possible damage to adjacent structures. Moreover, threads of the implant or cage may inadvertently engage the prepared threads of the vertebrae in an improper manner so as to cause a misalignment of the vertebrae in an anterior-posterior direction as well as laterally. If a second cage is needed, it involves the drilling, boring or tapping of the vertebral end plates for both cages so that the threads direct the cages into their proper respective positions. Such preparation requires highly skilled precision that may not be afforded or attainable under normal working conditions. 
     When a second cage is inserted, due to the unevenness of the vertebral end plates concave engaging surfaces, an unwanted increase in the inter-vertebral space may result in the loosening and possible dislodgment of the initially placed implant cage. 
     The anatomical configurations of the vertebrae necessitates that the two cages be positioned at an angle in respect to each other so as to be totally within the confines of the lateral borders of the vertebrae involved. 
     Use of tapered cages that are dimensionally greater in height anteriorally than posteriorally so as to provide the proper lordosis when such cage implants are employed creates complications. When the posterior approach is utilized and drilling, boring or tapping is necessary for placing threads on the vertebral end plates, difficulties exist in creating threads that will have a pitch compatible with those exhibited by the threads of such cages. A further complication is present when utilizing tapered cages via the posterior approach in that the dimensionally higher anterior threaded portion of the tapered cage is initially inserted and advanced to its most anterior final resting position. These cages are self-tapping to some degree and may result in the unwanted excessive removal of bone from the posterior portion of the lumbar segments where the lordosis is greatest. 
     Drilling and other types of preparation of the vertebral end plates may result in the removal of excessive amounts of supporting bone, and may cause the cage implants to rest upon the cancellous portion of the vertebrae. In such instances the cages may settle into said vertebrae resulting in a decreased inter-vertebral space other than that desired with subsequent complications of stabilization, pain and discomfort. 
     II. Adjustable Inter-body Fusion Devices 
     These are designed for restoring and maintaining the inter-vertebral space thereby providing for the normal contour of the fused spinal segments. Once the disc is removed, the normal lordotic or kyphotic curvature is eliminated and adjustable inter-body fusion implants are employed for re-establishing the proper curvature and stabilization of the spine. 
     Adjustable inter-body fusion devices have universal applicability and may eliminate the need for surgical preparation of the vertebral end plates such as contouring of bone and drilling, boring and tapping of said vertebral end plates. Such devices restore and preserve the inter-space and the integrity of the adjacent vertebrae thereby making the selection of the proper implant easier. They result in preservation of the highly specialized weight bearing cortical bone thereby preventing end plate perforation into the highly vascular cancellous bone marrow and unwanted subsequent bleeding may result in many complications due to excessive blood loss risks (e.g. hypoglycemic shock, transfusion, and possible diseases such as hepatitis and Acquired Immune Deficiency Syndrome, etc.),. Another advantage of such devices is the elimination of incorrect implant size selection as no significant amount of bone is removed and the correct size implants are easily fitted to restore the proper inter-space. In addition, the implant is self-stabilizing without the use of threads and may be further enhanced by surface treating of the implant for bone in-growth and osseous integration of the implant. 
     DESCRIPTION OF THE RELATED ART 
     The following patents disclose Static Inter-Body Fusion Devices: U.S. Pat. Nos. 5,785,710; 5,782,919; 5,766,253; 5,609,636; 5,425,772; 4,878,915; 4,501,269; 4,961,240 and 5,055,104. 
     The following patents disclose Adjustable Inter-Body Fusion devices: U.S. Pat. Nos. 5,782,832; 5,766,199; 5,702,455; 5,609,635; 5,336,223; 5,306,310. 
     ADVANTAGES OF INVENTION 
     The present invention overcomes the disadvantages represented by the prior art by not requiring drilling procedures for threaded engagement of adjacent vertebrae and subsequent end plate preservation. It restores and preserves the disc inter-vertebral space with the proper curvature of the spine. As taught by this invention, the methods and devices for insertion following disc removal requires no specialized surgical technique and allows for precise placement of the device and subsequent re-establishment of the proper inter-vertebral space and lordosis by either an anterior or posterior surgical approach. Further, this invention permits precise implant size to fit within the space allowed and not endanger or damage adjacent structures. Hence, incorrect implant size selection and the need for a variety of implant sizes is eliminated. An added advantage is, if removal is necessary it would not result in iatrogenic destruction of the adjacent vertebrae. Also, spinal stability is obtained without the use of threads since such threads may adversely affect the vertebrae themselves. 
     SUMMARY OF INVENTION 
     The present invention is an inter-space implant utilized to replace a damaged disc. The present invention is clearly an improvement over the prior art providing an implant prosthesis intrinsically participating in this fusion process, self-stabilizing to the spinal segments, consistent with conventional methods of disectomy and uniquely and novel consistent with the preservation of the integrity of the adjacent vertebrae. 
     The present invention comprises an artificial implant for the purpose of which is to aid in and directly cause bone fusion across an inter-vertebral space following the removal of a damaged disc. Said prostheses are biocompatible, structurally load bearing devices, stronger than bone, capable of withstanding the forces generated within the spinal inter-space. They have a plurality of openings of specific size which can be filled with fusion promoting material by inducing bone growth and osseous integration with the adjacent vertebrae forming a bony bond to the implants and each other. The implant bone-contacting surface may be textured, designed or otherwise treated by any known technologies to achieve bone in-growth and fusion to the implants to enhance stability of the implant and to expedite the fusion. The improved devices are configured and designed so as to promote their own stability within the vertebral inter-space to resist dislodgment and stabilize the adjacent vertebrae. 
     The present implant is made of a biocompatible material and has means if desired for increasing osseous integration, controlling hemostasis and preventing infection. It establishes proper spinal curvature or lordosis and kyphosis and capable of reducing a vertebral listness (a forward or backward translation of one vertebrae upon another as well as lateral misalignment of said vertebrae). It gives increased safety and precision which provides complete and easy visualization of the structures involved and adjacent vital structures (e.g. organs, neural structures and blood vessels and related bony surfaces). It also eliminates the need for a second surgical procedure to harvest bone. It also provides the method and material that is resorbable for additional means of stabilization to be used in conjunction with the implant prosthesis for certain conditions that require additional stabilization for osseous integration. It may be used in distraction osteogenesis procedures in order to increase bone length and/or for inducing bone growth and osseous integration of the implant, and for controlling hemostasis and pain and preventing infection during and following the surgical procedure allowing for an increased opportunity of success. 
     Procedure for Implant 
     A conventional disectomy is performed and the vertebral end plates are roughened in preparation for use of the implant prosthesis of the present invention. 
     In an anterior cervical device implantation a short transverse incision is made across the front of the neck and off-center, preferably to the right of the midline and directly over the diseased or otherwise disc being replaced. The platysma muscle is dissected and split and the sternocleido-mastoid muscle with the carotid sheath is protected and retracted laterally. The esophagus, trachea and associated midline structures are protected and retracted medially, thus exposing the anterior aspect of the cervical spine. The disc involved is identified and removed by known, acceptable and conventional surgical methods. The adjacent vertebral end plates are gently scraped free of any remaining cartilage until diffuse fine punctuate decortication is achieved. The dimensions of the inter-space are then measured in mild distraction and compared with the stereo-tactic pre-surgical x-ray diagnostic procedures and video imaging devices which helps to determine the exact intra-discal space to be restored relative to the vertebrae involved and the undamaged disc space that exists inferiorly and superiorly to the vertebrae involved. The appropriate device or devices are selected for insertion with a specially designed device that establish the necessary space for insertion behind the anterior lips of the vertebrae. The device is activated for establishing the desired inter-vertebral space and said device is locked at the desired height. Alternatively, the prosthesis may be a single, double or multiple activated device so as to properly provide stability and the proper curvature or lordosis of the spine. Harvested bone or bone fill material commonly employed is packed into and around the implant. Alternatively a new bone fill material is provided that is a polymer capable of being polymerized into a desired shape and size via being a resorbable biocompatible photo-initiated polymer and cured via visible light. In certain situations of trauma and disease additional stabilization is required and a resorbable biocompatible photo-initiated polymer rod or plate and screws may be utilized and to be attached to the vertebrae involved as well as healthy vertebrae above and below the damaged site. Guide plates are provided for drilling holes to affix the plate and or rod to the vertebrae with the necessary screws. In extreme cases the additional stabilization may employ currently available rigid devices for such purposes. All areas are inspected and the wound is then closed in the routine manner. A further biocompatible resorbable photo-initiated polymer is provided to control hemostasis as well as controlling post-operative pain or infection. The devices may also be used in other areas of the spine, such as the thoracic and lumbar regions, utilizing both the anterior or posterior surgical approaches as selected by the surgeon. 
     Objects of the Invention 
     It is the object of the present invention to provide for a means of achieving fusion of the inter-vertebral space and stabilization as a single procedure by a means consistent with the conventional method of disectomy and re-establishing the ideal and normal pre-existing disc inter-space. 
     It is another object of the present invention to provide for a means of achieving an inter-space fusion and stabilization that is easier, quicker, safer and entails less blood loss than other known means. 
     It is another object of the present invention to provide for a means of achieving a one stage inter-space fusion and stabilization with minimal damage and less removal of bone from the surface of the adjacent vertebrae than other known means. 
     It is another object of the present invention to provide for a method and device for inter-vertebral arthrodesis and stabilization and establishing the normal and pre-exiting inter-vertebral space in an easy, quick, safe and precise manner and in addition the entire procedure is performed under direct vision and may be further guided by optical imaging computerized devices. 
     It is another object of the present invention to provide for a method and device of inter-vertebral arthrodesis and stabilization that allows for the inter-vertebral space to be adjusted and of variable sizes unlike any other known means and with greater simplicity and accuracy than any other known means. 
     It is another object of the present invention to provide for a modular prosthesis having similar and multiple attachments that allows for insertion through a small opening and then to reconstitute an inter-space occupying device much larger than would be normally inserted. 
     It is another object of the present invention to provide for a method and device that precisely fits the contours of any inter-space without the need to sacrifice any vertebral bone to accommodate the prosthesis and can be inserted from an anterior or posterior surgical approach if desired. 
     It is another object of the present invention to provide for an implant that has means for osseous integration with the adjacent vertebrae and said device having additional means to act as a shock absorber when extremely heavy forces are exerted upon said device. 
     It is another object of the present invention to provide for a method and device that reestablishes the normal lordosis of the spine in a simple and precise manner. 
     It is another object of the present invention to provide a method and biocompatible material for inducing bone growth that is easier to use than any other known materials for this purpose and can readily be shaped into a desired form and resist dislodgment. This material may also act over a prolonged period of time by being time released for this purpose. 
     It is another object of the present invention to provide a biocompatible material and method for use in controlling hemostasis thereby enhancing the opportunity of success for osseous integration in individuals with abnormal clotting times. The hemostatic agent may also act over a prolonged period of time to further control post- operative bleeding, especially in individuals with poor clotting times, by being time released for this purpose. 
     It is another object of the present invention to provide a material and method for controlling post-operative pain following the surgical procedure, and said material may be time released locally over a period of time for this purpose. 
     It is another object of the present invention to provide a material and method for preventing and controlling infection following the surgical procedure and said material may be time released locally and/or in combination with systemic drugs for this purpose. 
     It is another object of the present invention to provide a material and method for use of time released anti-tumor drugs or radiation seeds that may control or eradicate tumors related to the area of uses of said invention. 
     It is another object of the present invention to provide a method and device for use in distraction osteogenesis procedures unlike any other known devices and method currently employed. 
    
    
     These and other objects of the present invention will be apparent from review of the following documentation and accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Although the invention has been described with regard to the preferred embodiments, it is recognized that other embodiments of the present invention may be devised which would not depart from the scope of the present invention. 
     FIG. 1 is an exploded perspective view showing a prosthesis made in accordance with the present invention. 
     FIG. 2 is a cross-sectional view of the prosthesis, with a spring biasing the top and bottom sections. 
     FIG. 3 is a highly simplified side view showing the prosthesis in place between vertebrae. 
     FIG. 4 is a rear view of the prosthesis as shown in FIG.  3 . 
     FIG. 5 is an exploded perspective view showing a modification of the prosthesis of the present invention. 
     FIG. 6 is an exploded perspective view showing another modification of the present invention for vertebrae replacement. 
     FIG. 7 shows another modification of the present invention for aligning the vertebrae. 
     FIG. 8A is a perspective view of a part of the prosthesis shown in FIG.  7  and FIG. 8B is an extremely magnified detail of a portion thereof. 
     FIG. 9 is a perspective view showing another modification of the present invention for multi-directional leveling of the vertebrae. 
     FIGS. 10A through 10C are several views of another embodiment of the present invention as a flexible prosthesis partially made of a bio-resorbable material. 
     FIGS. 11A through 11D are several views of another embodiment of the present invention for two level stabilization of the vertebrae. 
     FIGS. 12A through 12I are several views of another modification of the present invention. 
     FIGS. 13A through 13D are several views of another modification of the present invention. 
     FIGS. 14A through 14C are several views showing another modification of the present invention. 
     FIG. 15A through 15C are several views showing another modification of the present invention. 
     FIG. 16 shows another modification of the present invention. 
     FIGS. 17A through 17C are several views showing another modification of the present invention. 
     FIGS. 18A through 18F are several views showing another modification of the present invention. 
     FIG. 19 shows still another modification of the present invention. 
     FIGS. 20A through 20F are several views showing still another modification of the present invention. 
    
    
     DESCRIPTION 
     In general the present invention provides two identical interlocking disc shaped parts that have an elevated, spiraling steps-like surface around the perimeter and inner walls that provide an axis and bearing surface for rotation/interlocking. When these discs are rotated toward or away from each other the discs will increase or decrease the distance between them at 10 degrees rotation by a predetermined amount. In effect, this changes the rotational motion of the discs with a linear motion. 
     Referring to the drawings, and particularly to the embodiment of the invention shown in FIGS. 1 and 4, the prosthesis or implant of the present invention comprises a cage  1  having a pair of upper and lower sections  2  and  3  which are identical to and complimentary to each other and are adapted to interfit and rotate relative to each other. The upper section  2  has a top bearing surface  4  and the lower section  3  has a bottom bearing surface  5  which is substantially identical to the top bearing surface  4 . The bearing surfaces  4  and  5  are shown as being circular and have circular side-walls  6  and  7 , respectively, extending at right angles from each. The top and bottom bearing surfaces  4  and  5  have a central opening  8  and  9 , respectively, and the side walls  6  and  7  have a plurality of openings  10  therein. Circular ridges  11  are provided on the top and bottom bearing surfaces  4  and  5 , each of which are concentrically located with respect to the central openings  8  and  9 . Radiating outwardly from each central opening  8  and  9  are channels  12 . A plurality of openings  13  are preferably provided in the top and bottom bearing surfaces  4  and  5 . Bearing surfaces  4  and  5  are not limited to being circular in shape as shown and can be oval or having the shape of the vertebrae endplates or other shapes. Similarly, ridges  11  are not limited to being concentrically circular as shown and other shapes or non-uniformly aligned ridges may be used. 
     Spaced inwardly from the side walls  6  of each of the two sections  2  and  3  are a pair of opposed curved outer guide partitions  20  and  21 , each of which is substantially equally spaced from the central openings  8  and  9  and equally spaced from their respective side walls  6  and  7 . Each of the top and bottom sections  2  and  3  have an inner curved guide partition  22  inwardly spaced from one of the outer partitions  20  and  21 . The top and bottom sections  2  and  3  are adapted to be assembled together so that the partition  21  of one section will fit between the partitions  20  and  22  of the other section, as more clearly shown in FIG.  2 . This will permit the two sections  2  and  3  to rotate relative to each other while remaining in axial alignment with each other. Furthermore, the partitions  20 ,  21  and  22  limit the degree of rotation when partitions  20 ,  21  or  22  of the top section  2  is rotated until it comes in contact with the corresponding partitions  20 ,  22  or  21 , respectively, of bottom section  3 . A spring  41  is inserted in and extends between the openings  8  and  9  in order to hold the two section  2  and  3  together and biased towards each other. Other means of biasing, for example, elastic string or post can be used. 
     The side walls  6  and  7  of each section  2  and  3  are arranged in a plurality of inclined cam surfaces  25  which extend substantially from the bearing surfaces  4  and  5  of each and incline away from the bearing surfaces  4  and  5 . In the embodiment shown in FIGS. 1 through 4, three identical cam surfaces  25  are shown on each section  2  and  3 . However, it will be understood that the number of cam surfaces  25  may be increased or decreased if desired. The cam surfaces  25  of each section  2  and  3  are complimentary to each other. In the drawings, the edge of each cam surface  25  has a plurality of teeth  26 . The teeth  26  and the cam surfaces  25  of each top and bottom section  2  and  3  are the same so that the teeth  26  of each will interfit with each other when the two sections  2  and  3  are assembled together. Preferably, the apexes of the teeth  26  are rounded with a radius of 0.005 inch as shown in FIG.  8 B. However, different radii can be used. The sections  2  and  3  are adjusted to the desired height by rotating one section relative to the other. The cam surfaces  25  will move the sections  2  and  3  away from each other or toward each other and the teeth  26  in both sections will interfit with each other to prevent rotary displacement and to hold the sections  2  and  3  at the desired height. The openings  10  on the side walls  6  and  7  may be used to rotate one section relative to the other section by inserting a tool (not shown) therein and rotating one section relative to the other section. The sections  2  and  3  are adjusted to the desired height by rotating one section relative to the other. The cam surfaces  25  will move the sections  2  and  3  away from each other or toward each other and the teeth  26  in both sections will interfit with each other to prevent rotary displacement and to hold the sections  2  and  3  at the desired height. The openings  10  on the side walls  6  and  7  may be used to rotate one section relative to the other section by inserting a tool (not shown) therein and rotating one section relative to the other section. 
     The two sections  2  and  3  of the cage  1  are assembled together and inserted between vertebrae  30 ,  31  as shown in FIGS. 3 and 4. Prior to insertion between vertebrae  30  and  31 , various substance or agents  27  to promote osseous integration (e.g. De-Mineralized Bone Matrix available from Grafton Inc., which is putty-like in an uncured state for ease of placement and becomes not pliable upon curing), control post-operative bleeding, pain, infection or control or eradicate tumors may be placed between the two sections  2  and  3  and/or between cage  1  and vertebrae  30  and  31 . These substance or agents  27  may be incorporated in a bio-compatible or bio-resorbable material. The bio-compatible or bio-resorbable material containing the various substance or agents  27  may be photocurable polymers, by either ultraviolet light in the range of 350-385 nanometers in wavelength or visible light in the range of 385-550 nanometers in wavelength. Furthermore, the bio-compatible or bio-resorbable material may also be colored in the uncured state and turn clear upon curing to aid in assuring visually that the polymer has been completely cured, such as photo-initiator HU-470 available from Spectra Inc. 
     The vertebrae  30  and  31  and the space between them have been prepared (by cleaning and otherwise) to receive the cage  1  as described hereinabove. After the cage  1  is inserted between the two vertebrae  30  and  31 , the two sections  2  and  3  are rotated relative to each other until their bearing surfaces  4  and  5  make the proper contact with the opposed bearing surfaces of the vertebrae  30  and  31  in order to support the vertebrae. The ridges  11  on the bearing surfaces  4  and  5  permit the two sections to be easily rotated on the vertebrae and permit positive contact with the vertebrae. The channels  12  act as a reservoir for cartilage and other bone material to enter as the bearing surfaces  4  and  5  grasp and become enmeshed with the two sections  2  and  3  thereby fusing the cage  1  between adjacent vertebrae  30  and  31 . Channels  12  may also be coated with a bone initiating or stimulating material to further promote osseous integration. 
     Referring now to the embodiment shown FIG. 5, the two sections  2 A and  3 A of the cage  1 A are similar to the sections  2  and  3  of cage  1  described in the embodiment of FIGS. 1 through 4. However, in this instance, four cam surfaces  25 A are shown. 
     In the embodiment shown in FIG. 6, the top and bottom sections  2 B and  3 B of cage  1 B are similar to the sections  2  and  3  discussed above. However, an elongated connecting tube  44  is interposed between them. The top and bottom end edges of the connecting tube  44  has cam surfaces  46 , teeth  47 , partitions  48  and  49  and openings  45  and are similar to the cam surfaces  25 , teeth  26 , partitions  20  and  22  and openings  10  in the sections  2  and  3  of the FIGS. 1 through 4 embodiment. Hence, the sections  2 B and  3 B are complimentary to the end edges of the tube  44 . With this structure, if the space between the vertebrae is very large, the connecting tube  44  is used in order to span the distance between the two sections  2 B and  3 B to fill the space between the vertebrae. Alternatively, the structure shown in FIG. 6 may be used to replace a vertebrae. 
     Referring to the embodiment shown in FIGS. 7 through 8B the prosthesis shown comprises double cages  50  and  51  which has top sections  2 C similar to the top section  2  of the FIGS. 1 through 4 embodiment. The bottom sections  3 C are also the same but are connected together by a web  52 . The top sections  2 C are rotated relative to the bottom sections  3 C. The cages  50  and  51  can be adjusted to different heights depending on the spinal curvature that is desired. Adjusting the cages to different heights will cause the cages to act as a leveling device. 
     The embodiment shown in FIG. 9 shows a prosthesis that is similar to the embodiment shown in FIGS. 7 through 8B. However, in this embodiment, three cages  60 ,  61  and  62  are used with the top sections 2D of each (only one is shown) being the same as the top section  2  of the FIGS. 1 through 4 embodiment and the bottom sections 3D being connected together by a web  63 . Again, the cages  60 ,  61  and  62  can be individually adjusted to different heights to act as a leveling device that allows multi-directional flexibility without sacrificing stability and restores natural mobility of the vertebrae. 
     FIGS. 10A through 10C show another embodiment of the present invention. A cage  53  is similar to the cage described in connection to FIG.  1 . However, the outer edge  54  of the cam surfaces  25  and the teeth  26  are made of a bio-resorbable material. A titanium bellows  55  surrounds the cage  53 . The bio-resorbable material between the upper and lower sections of cage  53  will degrade eventually and leaving the bellows  55  to give the cage multi-directional flexibility without causing associated instability. 
     FIGS. 11A through 11D show another embodiment of the present invention. In this embodiment, an upper vertebrae,  30 , a lower vertebrae  31 , and an intermediate vertebrae  32 , are to be linked together. A cage  34  similar to the cage described in connection with FIG. 1, is inserted between the upper vertebrae  30  and the intermediate vertebrae  32 , and another similar cage  34  is inserted between the lower vertebrae  31  and the intermediate vertebrae  30 . A connecting and stabilizing assembly  35  is provided to connect the two cages  34  and to connect and stabilize all the vertebrae  30 ,  31  and  32 . The connecting assembly  35  comprises a clamping plate  36  having a plurality of threaded openings  37  therein. The clamping plate  36  is to be screwed or otherwise mounted to the central vertebrae  32  by a screw or some other suitable means  40 . Connecting rods  38  are threadably inserted through the openings  37  in the clamping plate  36 . The outer ends of the connecting rods  38  have holding knobs  39  which bear against the outer surfaces of each cage  34  on each side thereof as shown in FIG.  11 B. With this structure the clamping plate  31  is affixed to the intermediate vertebrae  32  and the holding knobs  39  of each connecting rod  38  extends along both sides of each of the cages  34  and stabilizes the cages and the vertebrae  30 ,  31  and  32 . 
     Referring now to the embodiment in FIGS. 12A to  12 I, a gear type expansion cage  70  is shown. The expansion cage  70  comprises a pair of curved elongated outer bearing surfaces  71  each of which have a geared threaded opening  72  therein. A gear wheel  73  has threaded extensions  74  on each side thereof which are inserted in the threaded openings  72  in each of the curved bearing surfaces  71 . A pair of such gears  73  with threaded extensions  74  is mounted on each end of the bearing surfaces  71  and the two gears  73  are connected together by a central gear  75 . When one of the gears  73  is rotated, that end of the bearing surface  71  will expand or contract depending on the direction that the gear  73  is turned and at the same time, the central gear wheel  75  will also rotate the second gear  73  in order to expand that side of the curved bearing surface  71 . In this manner, the curved bearing surfaces  71  will move away or toward each other to fill the gap between the vertebrae. The outer surfaces of the bearing surfaces  71  have grooves  76  to permit and enhance fusing the prosthesis with bone. 
     Referring now to the embodiment shown in FIGS. 13A through 13D, a jack-type cage  80  is shown. A pair of opposed bearing surfaces  81  (shown elongated and flat—but which may be curved) are connected together by a plurality of cross arms  82  through the intermediation of a jack screw  83 . The ends of the arms  82  are connected to each end of the two bearing surfaces  81  and to each end of the jack screw  83 . Rotating the jack-screw  83  in one direction or the other extends or contracts the arms  82  in either one direction or the other to either move the bearing surfaces  81  away from each other or to move them toward each other. In this manner, the bearing surfaces  81  will fill the gap between vertebrae. 
     In the embodiment shown in FIGS. 14A through 14C, a wedge type cage  90  is described. The curved elongated outer bearing surfaces  91  have a pair of wedges  92  therebetween which are controlled and connected together by a screw  93 . The wedges  92  are adapted to move in grooves  94  in the inner channels  95  in the bearing surfaces  91 . The wedges  92  having opposed inclined surfaces  96 . By rotating the screw  93  in one direction or the other the wedges  92  are moved closer or further apart from each other and since the surfaces  96  are angled in opposite directions, the two bearing surfaces  91  are moved towards or away from each other. In this manner, the space between the vertebrae may be filled by merely adjusting the height of the two bearing surfaces  91 , as described above. 
     FIGS. 15A through 15C show a cam type expandable cage. In this embodiment, the opposed curved elongated bearing surfaces  110  have a rod  111  interposed between them with cams  112  in each end. The rod  111  has an opening  113  at its edges which permit the rod  111  and the cams  112  to be rotated. When the rod  111  is rotated, the cams  112  will rotate and strike the interior of the two bearing surfaces  110  to move the two bearing surfaces  110  towards or away from each other. A pair of elongated guides  114  extend from the interior of one of the bearing surfaces  110 , which correspond to a pair of grooves  115  on the interior of the opposite bearing surface  110 , to prevent lateral movement and dislodgment of the opposed bearing surfaces  110  from each other. 
     Referring to the embodiment of FIG. 16, a flexible spinal fusion prosthesis is shown in which upper and lower plate members  100  and  101  are provided with an intermediate convex flexible disc  102  interposed therebetween. The disk  102  may be made of titanium or some other known material which is biocompatible and compressible. A rigid collar  103  of resorbable material surrounds the disc  102  to make the flexible disc  102  rigid in order to allow integration of the upper and lower plate members  100  and  101  with the bones of the vertebrae. The collar  103  will be resorbed and thereafter the flexible disc  102  will function in a flexible manner between the vertebrae. 
     With respect to the embodiment shown in FIGS. 17A to  17 C, a pair of expandable cages  120  and  121  similar to the cages of FIGS. 1 and 2 are mounted between vertebrae in a spaced relationship to each other. A titanium bellows-like assembly  122  is interposed between the spaced cages  120  and  121 . Resorbable rigid material  123  surrounds the bellows  122  and make the bellows  122  rigid until the resorbable rigid material  123  is absorbed, after which the bellows  122  will become flexible to act as a cushion between the two cages  120  and  121 . If desired the space between the bellows  122  may be filled with a polymer. 
     In the embodiment shown in FIGS. 18A to  18 G, a plurality of expandable cages  130  similar to the cage  1  of FIGS. 1 through 4, are interposed between a pair of curved elongated bearing surfaces  131  so that contact with the vertebrae is made by the curved bearing surfaces  131  rather than by the expansion cages  130  themselves. The internal expansion cages  130  can be adjusted to different heights to permit the bearing surfaces  131  to achieve different heights and angles. 
     In the embodiment shown in FIG. 19 the elongated curved bearing surfaces  140  have a pair of cages  142  similar to the cage shown in FIG.  1 . Each cage has an outer gear  141  extending from its outer surface. When the gears  141  are rotated in one direction, the bearing surfaces  140  are moved towards each other. 
     It will be noted that in FIG. 19 the two gears are the same size and ratio. However, it is within the purview of the present invention for the two gears to be of different ratios and sizes so that movement of one gear will expand its cage to a certain height, and the other cage, having a gear of a different ratio, will expand its cage to a different height. This may also be accomplished by a connecting gear between the two gears (not shown). It is also possible to accomplish the same purpose by having geared teeth of different heights so that the two geared cages may move to different expansions. 
     Referring to the embodiment shown in FIGS. 20A through 20F, a tapered expandable cage  150  is shown. An expansion screw  151  is mounted in the cage  150  having a circular solid front portion  152  and expandable curved rear bearing surfaces  153 . By rotating the screw  151 , the inner edge of the screw  151  will contact the expandable bearing surfaces  153  and expand them. In version A (FIG.  20 E), the expandable screw  151  has a point  154  which moves toward the expandable bearing surfaces  153  and spreads them apart. In version B (FIG.  20 F), the expansion screw  151  has a tapered blunt edge  155  which contacts the expandable bearing surfaces  153  and spreads them apart. 
     It will thus be seen that the present invention provides improved means for achieving fusion of the inter-vertebral space and stabilization as a single procedure in a manner consistent with the conventional methods of disectomy and re-establishing the ideal and normal pre-existing disc inter-space which is easier, quicker, safer, and entails less blood loss than other known means. The present invention also achieves one stage inter-space fusion and stabilization with minimal damage and less removal of bone from the surface of the adjacent vertebrae and establishes the normal and pre-existing inter-vertebral space in an easy, quick, safe and precise manner. In addition, the present invention provides a method and device of inter-vertebral arthrodesis and stabilization that allows for the inter-vertebral space to be adjustable and of variable sizes and with greater simplicity and accuracy than any other known means by the use of a modular prosthesis having similar and multiple attachments that allows for insertion through a small incision and to reconstitute the inter-space occupying device into a much larger spacing member so as to fit the contours of any inter-space without the need to sacrifice any vertebral bone. The prosthesis of the present invention provides for an implant that has means for osseous integration with the adjacent vertebrae which can also act as a shock absorber when extremely heavy forces are exerted upon it and which permits the reestablishment of normal lordosis of the spine in a simple and precise manner and provides a method and biocompatible material for inducing bone growth that can readily be shaped into a desired form. 
     The present invention also provides a biocompatible material and method for controlling hemostasis thereby enhancing osseous integration in individuals with abnormal clotting problems and may also act over a prolonged period of time to control post-operative bleeding. With this invention, post-operative pain and infection are controlled and application of anti-tumor drugs or radiation beads may be easily administered by being time released locally and/or in combination with systemic drugs for this purpose. 
     As many varied modifications of the subject matter of this invention will become apparent to those skilled in the art from the detailed description given hereinabove, it will be understood that the present invention is limited only as provided in the claims appended hereto.