Abstract:
The present invention is an expandable and adjustable bone cage designed to be used in conjunction with a pedicle screw or plating fusion system. The expandable and adjustable bone cage provides structure for the placement of bone graft material between two adjacent vertebral bodies in order to stabilize or fuse the spine in a predetermined position. The expandable and adjustable bone cage is contoured for easy insertion between vertebral bodies and may be expanded after insertion to maintain, establish or increase lordosis, as well as help secure the bone cage.

Description:
FIELD OF INVENTION 
     The present invention relates to the field of implants and more particularly to an expandable and adjustable bone cage with a rotatable cam lift for spinal fusions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a left side view of an exemplary embodiment of an expandable and adjustable bone cage implanted and in a closed/first position. 
         FIG. 2  illustrates a left side view of an exemplary embodiment of an expandable and adjustable bone cage implanted and in an expanded position. 
         FIG. 3  illustrates a perspective view of the proximal end of an exemplary embodiment of an expandable and adjustable bone cage in a closed/first position. 
         FIG. 4  illustrates a perspective view of the distal end of an exemplary embodiment of an expandable and adjustable bone cage in a closed/first position. 
         FIG. 5   a  illustrates a perspective view of an exemplary embodiment of a cam lift for an expandable and adjustable bone cage. 
         FIG. 5   b  illustrates a proximal view of an exemplary embodiment of an expandable and adjustable bone cage in a closed/first position. 
         FIG. 6  illustrates an exploded view of the proximal end of an exemplary embodiment of an expandable and adjustable bone cage. 
         FIG. 7  illustrates a right side view of an exemplary embodiment of an expandable and adjustable bone cage in a closed/first position. 
         FIG. 8   a  illustrates a sectional view of an exemplary embodiment of an expandable and adjustable bone cage taken along line  8   a  of  FIG. 7 . 
         FIG. 8   b  illustrates a sectional view of an exemplary embodiment of an expandable and adjustable bone cage taken along line  8   b  of  FIG. 7 . 
         FIG. 8   c  illustrates a sectional view of an exemplary embodiment of an expandable and adjustable bone cage taken along line  8   c  of  FIG. 7 . 
         FIG. 9  illustrates a bottom view of an exemplary embodiment of an expandable and adjustable bone cage with a cam lift. 
         FIG. 10  illustrates a proximal view of an exemplary embodiment of an expandable and adjustable bone cage expanded to a second position. 
         FIG. 11  illustrates a right side view of an exemplary embodiment of an expandable and adjustable bone cage expanded to a second position. 
         FIG. 12  illustrates a sectional view of an exemplary embodiment of an expandable and adjustable bone cage expanded to a second position taken along line  12  of  FIG. 11 . 
         FIG. 13  illustrates a proximal view of an exemplary embodiment of an expandable and adjustable bone cage expanded to a third position. 
         FIG. 14  illustrates a right side view of an exemplary embodiment of an expandable and adjustable bone cage expanded to a third position. 
         FIG. 15  illustrates a sectional view of an exemplary embodiment of an expandable and adjustable bone cage expanded to a third position taken along line  15  in  FIG. 14 . 
         FIG. 16  illustrates a perspective view of the distal end of an exemplary embodiment of an expandable and adjustable bone cage expanded to a second position. 
         FIG. 17  illustrates a perspective view of the distal end of an exemplary embodiment of an expandable and adjustable bone cage expanded to a third position. 
         FIG. 18  illustrates a perspective view of the distal end of an exemplary embodiment of an expandable and adjustable bone cage with upper and lower bodies of varying sizes. 
         FIG. 19  illustrates a perspective view of the left side of an exemplary embodiment of an expandable and adjustable bone cage with upper and lower bodies of varying sizes. 
         FIG. 20  illustrates a proximal view of an exemplary embodiment of an expandable and adjustable bone cage with upper and lower bodies of varying sizes. 
     
    
    
     GLOSSARY 
     As used herein, the term “bone cage” refers to an implant that is inserted into the space between vertebrae bodies replacing a damaged vertebra disc and restoring the spacing between the vertebrae. 
     As used herein, the term “bone graft material” refers to the substance placed in a bone cage that facilitates the growth of new bone tissue. Bone graft material may be artificial (e.g., created from ceramics), synthetic (e.g., made from hydroxylapatite or calcium carbonate), or a natural substance (e.g., bone harvested from another bone in the patient&#39;s body (autograft), bone taken from a donor (allograft), or bone morphogenetic proteins (BMPs). 
     As used herein, the term “cam lift” refers to a component with a rotational driving surface used to expand a bone cage. A cam lift may further serve a safety and control function. For example, a cam lift may be structurally designed to allow only a certain amount of expansion (e.g., 1 mm to 2 mm) to prevent over rotation. 
     As used herein, the term “cam lift shaft” refers to the circular portion of a cam lift that is placed between the bearing surfaces of the upper and lower bodies of a bone cage. 
     As used herein, the term “driver” refers to an instrument used to rotate a cam lift. 
     As used herein, the term “flat spring groove” refers to a channel cut into the side of lower and upper body members that forms a spring tab and allows it to flex. 
     As used herein, the term “end plug” refers to a component that prevents leakage of bone graft material. 
     As used herein, the term “lordosis” means inward curvature of the spine. 
     As used herein, the term “pivotally attached” means two or more components connected at a pivot point. 
     As used herein, the term “pivot mechanism” refers to an assembly of two or more moving parts that turn or rotate upon each other. 
     As used herein, the term “pivot retention catch” refers to a component that protrudes from a first body member of a bone cage and latches into a corresponding pivot retention hole in a second body member of the bone cage. 
     As used herein, the term “pivot retention hole” refers to an aperture in a body member of a bone cage that is adapted to receive a pivot retention catch. 
     As used herein, the term “pivot surface” refers to the concave and convex portions of the first body member that fit against the convex and concave portions of the second body member of a bone cage. When the bone cage is expanded, the pivot surfaces of the first body member rotate along the pivot surfaces of the second body member. 
     As used herein, the term “positional flats” refers to a series of flattened segments that encircle a portion of a cam lift. When the cam lift is rotated, the positional flats press against the spring tab of the lower and upper body members of a bone cage. 
     As used herein, the term “spring tab” refers to a portion of the lower and upper body members of a bone cage that flexes during rotation of the cam lift and returns to position when the final position of the cam lift is reached. 
     As used herein, the term “surface engaging contour” refers to a portion of a lower or upper body member shaped to mate with the other body member. 
     As used herein, the term “vertebral engaging contour” refers to a portion of a lower or upper body member that is shaped to better conform to a part of a vertebral body endplate. 
     BACKGROUND 
     Spinal fusion surgery for degenerative disc disease involves removing the damaged disc and replacing it with bone grafted from another site on the patient&#39;s body, bone from a donor, or artificial or synthetic bone graft material that stimulates bone growth to fuse, or join, the two vertebrae together to stabilize the spine. In all spinal interbody fusion surgeries, disc material is removed. A spacer, referred to as a “cage” is then inserted into the disc space. 
     The fusion cages help separate the vertebral bodies, taking pressure off the spinal nerves, which travel from the spinal canal through openings, each called the neural foramen. The expansion pulls the ligaments inside the spinal canal taut so they don&#39;t buckle into the spinal canal and cause compression of the nerves. Surgeons monitor the position and correct placement of the cages using fluoroscopy and Electromyography (EMG) monitoring. 
     Fusion cages known in the art are most commonly made of metal, graphite, bone, or PEEK (polyether ether ketone). Many of these cages are shaped like cylinders. A few are rectangular in shape. The main purpose of the cage, regardless of the shape or material, is to hold the two vertebrae apart while the fusion becomes solid. 
     Generally, two cages are placed side by side within the disc space spreading the vertebrae apart. After implanting the cages, most surgeons attach metal hardware or screws to the vertebrae to rigidly lock them in place. This allows the bone graft to effectively fuse the vertebrae together. 
     The hollow center of the cage is packed with bone graft material, either in the form of natural bone taken from another site on the patient or from a donor or an artificial or synthetic bone substitute. 
     When bone is taken from another part of the patient&#39;s own body (i.e., autograft), there is a risk of pain, infection, or weakness in the area where the graft is taken. Synthetic bone growth alternatives offer an alternative to using the patient&#39;s own bone. Using gene therapy, scientists have produced bone graft substitutes (i.e., growth factors). These growth factors are natural proteins found in the human body. Genetic engineers have been able to clone proteins known as bone morphogenetic proteins (BMPs). These proteins are then made available as powder, small particles, or chips. Hormones that circulate in the bloodstream act on the BMP molecules, causing them to build new bone tissue. 
     The growth factor that is approved for lumbar fusion with titanium fusion cages is BMP-2. Substituting BMP-2 for an autograft eliminates complications and the recovery associated with harvesting autograft material from the patient&#39;s own body. One example of a commercially available bone growth material is Infuse® Bone Graft by Medtronic. 
     A risk associated with the use of bone growth material is that the nerves may be exposed to the material causing bone formations around or adjacent to the nerves, which can cause severe neurological injury or paralysis. 
     There are three different approaches for spinal fusion surgeries: anterior, posterior and lateral. Anterior interbody spinal fusion is performed via an incision in the patient&#39;s abdomen and the vertebral bodies are approached from the front. This approach is generally used when the surgeon needs to reach the front part of the spine. The abdominal muscles must be displaced resulting in considerable patient discomfort and increased recovery time. The use of bone formation material is currently approved by the FDA only for the anterior approach, because this approach reduces risk of exposing the lumbar nerves to the bone growth material. 
     Posterior interbody spinal fusion is performed from an incision made in the back. The posterior approach is necessary if a decompression procedure is performed in addition to a spinal fusion. The use of bone formation material poses considerable risk since the lumbar nerves are exposed during the procedure. Any displacement of the bone formation material can cause substantial nerve damage. 
     Lateral spinal fusion techniques have been gaining popularity. The procedure is performed through the patient&#39;s side, avoiding the major muscles of the abdomen and back. With recent advances in neurologic monitoring capabilities, surgeons are able to safely navigate around the lumbar nerves in order to enter the disc space laterally. However, synthetic bone growth material is not currently approved by the FDA for use in lateral spinal fusion procedures. 
     Each vertebra has a pair of transverse processes, one on each side of the spinal column. Spinal muscles attach to the transverse processes. The pedicle, a short projection of bone, lies between the back of the vertebral body and the transverse process and extends from the spinal column in the back to the vertebral body in front. 
     Pedicle screws can be used alone or in conjunction with bone cages. Using the “posterior approach,” pedicle screws are placed into the pedicles. Each patient&#39;s pedicles are of a different size, so the screws are available in different diameters and lengths. Two screws are placed into each vertebra (one in each of two pedicles). 
     A problem known in the art is that when a disc is removed and pedicle screws are inserted, there is a loss of support due to the displacement of the disc material that is normally in contact with the endplates. Displacement of disc material leaves a void and pressure formerly absorbed by the disc material is partially redistributed to a component held in place with pedicle screws. It is desirable to minimize the amount of force placed on the pedicle screws to avoid breakage of the pedicle screw system. It is further desirable to fill the void left by the removal of disc material in a manner that maximizes contact of the device (e.g., a bone cage known in the art) with the endplates. It is critical that any device placed in the space formerly occupied by the disc has effective contact with the endplates in order for the surgery to promote the fusion of the vertebrae and to avoid fracture of the endplates. This fusion process is the objective of the surgery, and the success of the surgery depends on how effectively fusion occurs. 
     A bone cage(s) is placed in the disc space while the pedicle screws are in the two pedicles. With the bone cage in place, the pedicle screws are compressed along the rods which will shorten the posterior column, and the bone cage will maintain the anterior column height by keeping the disc space distracted, thereby restoring lordosis of the lumbar spine. The rods are then tightened to the screws to hold the spine in its new position until the bone graft fuses. The bone cage and pedicle screws have stability (the implant in front, and the two screws in back) forming a triangle. 
     Prior to fusion, and prior to inserting the bone cage, pedicle screws absorb the stress of supporting the spine. In older patients, bone is weaker and the pressure of the pedicle screws can cause osteoporotic complications. Thus, it is desirable, when possible, to effectively balance the pressure placed on the pedicle screws and on the bone cages. This requires that the bone cage make effective contact with the endplate of the two vertebrae bodies during the fusion process. 
     There are many versions of bone cages known in the art, and many attempts have been made to solve the problem of stable placement of bone cages with the optimum and controlled contact with the vertebral endplates. However, devices known in the art are associated with problems due to incomplete or uncontrolled contact between the endplates of the vertebral bodies and the upper and lower surfaces of the cage. Many attempts have been made in the art to create bone cages which can be adjusted or positioned to account for physiological differences in patients and achieve pressure reduction. 
     Bone cages, such as the Continental™ and Colonial™ by Globus Medical, have a chamfered leading edge to facilitate insertion in multiple footprints, heights, and profiles allowing the surgeon to match various patient anatomies. However, these devices cannot be adjusted for a particular patient nor can they be expanded to provide physiologic lordosis (i.e., normal curvature of the lumbar spine where the disc space is wider anteriorly). 
     The Sustain® O by Globus Medical has a tapered leading edge for easier insertion and rounded corners, which allow for rotation (positioning) during insertion, and thus also attempt to give the physician greater control. The Continental™, Colonial™ and Sustain® O, however, are not desirable because they are not ideally contoured to the shape of the vertebral endplates resulting in a minimal area of contact between the cage and the vertebral endplates. In addition, each bone cage has a fixed height, which cannot be adjusted after insertion. 
     Bone cages contoured to mimic the shape of vertebral endplates are also available. Globus Medical also has bone cages with varying shapes designed to mimic the shape of vertebral endplates. The Sustain® Small has a convex sagittal profile to mimic the shape of vertebral endplates, Sustain® Large has a trapezoidal footprint to mimic the shape of vertebral endplates, and Sustain® Medium has a teardrop footprint to mimic the shape of vertebral endplates, The LT-Cage® Lumbar Tapered Fusion Device by Medtronic is tapered to more closely match the shape of the disc space. 
     The AVS TL PEEK and AVS PL PEEK Spacer Implants by Stryker are also available in a shape that more closely mimics the shape of the vertebral endplates. Each is available in rectangular or parallel (0 degree) and wedge (4 degree) as well as in varying heights and two different lengths/widths. The Ogival Interbody Cage implant by Stryker is a bullet shaped cage to facilitate intracanal navigation and is available in 4 degree and 8 degree lordotic versions to provide better coverage. In addition, the AVS TL PEEK, AVS PL PEEK, and Ogival Interbody Cage implants include serrations on the top and bottom weight bearing surfaces to provide stability and prevent migration. Each of these bone cages is uniquely shaped and designed to mimic the contours of the vertebral endplates, however, the correct bone cage and the correct size/height must be chosen in order to match each patient&#39;s particular anatomy. None of these bone cages are capable of being adjusted to conform to a particular patient&#39;s vertebral endplates. 
     Other types of expandable bone cages, such as the VBoss Implant by Stryker are also expandable, The VBoss Implant has an expandable column with modular end caps that are available in 5 diameters with 0, 5, or 10 degree angles to enhance restoration of lordsis. The XPand® by Globus Medical is an expandable cage that comes in a variety of footprints, heights, and lordotic angles. Both of these devices can be expanded vertically; however, these cages are indicated in cases to replace the whole vertebra body after the entire vertebral bone is removed. 
     U.S. Pat. No. 6,852,129 (Gerbec &#39;129) teaches a wedge-shaped bone fusion implant with expandable sidewalls that allows the height of the implant to be adjusted when a component is inserted for expansion. This design requires that the physician manually control expansion and determine the position of the plates of the device without mechanical guidance or physical precision. In addition, the flattened and rectangular plates of the device do not accomplish effective contact with the endplates, and this leaves a gap between the surfaces of the device and the endplates. 
     U.S. Pat. No. 6,962,606 (Michelson &#39;606) teaches an adjustable “push in” implant by which the “front, back or both” of the implants are raised by “the same or various amounts.” The implant taught by Michelson &#39;606 is expandable; however, Michelson &#39;606 is not enabling and does not teach one of ordinary skill in the art how to make or use a bone cage. 
     Several problems are associated with this device. Michelson &#39;606 does not enable a device which effectively makes contact with the endplates of the vertebral bodies because the device is comprised of two flattened (or uniformly curved) panels that do not conform to the contours of the vertebral bodies and thus the objective of the device of reducing pressure on the pedicle screws and equalizing the pressure over the surface of the device is not effectively achieved despite the capability of the device to be expanded in place. More significantly, placement of the Michelson &#39;606 device requires a rectangular “blocker” component to keep the ends apart and the expansion is not effectively controlled. In addition, this device has only two positions: open or closed. 
     Michelson teaches expanding the implant with an unspecified tool “such as a spreader or distracter [or] scissor type” device. No method for expanding the device is disclosed or claimed, and a “scissor type” device cannot provide adequate control, which is critical during placement of the cage. Michelson &#39;606 does not allow for controlled expansion of the device, which can result in substantial risk to a patient because the bone cage may pack or break through the bone of the vertebral bodies. 
     The device disclosed in Michelson may potentially be dislodged because it does not have secure points of contact. In addition, the lack of secure points of contact results n an unpredictable reduction of pressure over the pedicle screws. 
     It is desirable to have a bone cage that allows for maximum control and predictability of expansion, and which protects the endplates from fracture by distributing the forces along a greater surface area. 
     It is desirable to have a bone cage that is in secure contact with the endplates of the vertebral bodies. 
     It is desirable to have a modular system that allows the surgeon to size the implant to accommodate patients with varying size disc spaces and/or disc heights. 
     It is desirable to have a reliable means for expanding a bone cage device. 
     It is desirable to have a bone cage which reduces pressure on pedicle screws during the fusion process by maximizing contact between the bone cage and the vertebral endplates through the use of anthropometric contours. 
     It is desirable to have a bone cage which is shaped to conform to the contours of the vertebral endplates and which is capable of expanding at an angle optimum for controlled support and to prevent the device from being displaced while restoring lordosis to the spinal column. 
     It is further desirable to have a bone cage which is adapted for insertion of bone graft material after the device is stably in place, minimizing the risk that the bone graft material will be displaced or come in contact with the nerves during implantation. 
     SUMMARY OF THE INVENTION 
     The present invention is an expandable and adjustable bone cage designed to be used in conjunction with a pedicle screw or plating fusion system. The expandable and adjustable bone cage provides structure for the placement of bone graft material between two adjacent vertebral bodies in order to stabilize or fuse the spine in a predetermined position. The expandable and adjustable bone cage is contoured for easy insertion between vertebral bodies and may be expanded after insertion to maintain, establish or increase lordosis, as well as help secure the bone cage. 
     The expandable and adjustable bone cage is shaped to the normal concave elliptical endplates of the vertebral bodies, and includes modular components for accommodating differences in disc space size. The bone cage is also designed to expand in steps so that the proper amount of distraction and lordosis can be customized to the individual patient. 
     DETAILED DESCRIPTION OF INVENTION 
     For the purpose of promoting an understanding of the present invention, references are made in the text to exemplary embodiments of an expandable and adjustable bone cage, only some of which are described herein. It should be understood that no limitations on the scope of the invention are intended by describing these exemplary embodiments. One of ordinary skill in the art will readily appreciate that alternate but functionally equivalent materials, dimensions and designs may be used. The inclusion of additional elements may be deemed readily apparent and obvious to one of ordinary skill in the art. Specific elements disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one of ordinary skill in the art to employ the present invention. 
     It should be understood that the drawings are not necessarily to scale; instead, emphasis has been placed upon illustrating the principles of the invention. In addition, in the embodiments depicted herein, like reference numerals in the various drawings refer to identical or near identical structural elements. 
     Moreover, the terms “substantially” or “approximately” as used herein may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. 
       FIG. 1  illustrates a left side view of an exemplary embodiment expandable and adjustable bone cage  100  implanted and in a closed/first position. Shown in  FIG. 1  are two vertebra comprised of vertebral bodies  110   a,    110   b,  pedicles  120   a,    120   b , lamina  130   a,    130   b,  spinous processes  140   a,    140   b,  transverse processes  150   a,    150   b,  superior articular facets  160   a,    160   b,  inferior articular facets  170   a,    170   b , and spinal canal  180 . Also visible is pedicle screw fusion system  190 . 
     Vertebral bodies  110   a,    110   b  are the main portion of vertebra and bear about 80% of the body&#39;s weight while standing. Between vertebral bodies  110   a    110   b  is disc space  98 , where an intervertebral disc (not shown) is normally located. Each vertebral body  110   a,    110   b  has top endplate  114   a,    114   b  and bottom endplate  116   a ,  116   b,  which provide an attachment for the intervertebral disc. 
     Pedicles  120   a,    120   b  are cylinder-shaped projections of hard bone that stick out from the back part of vertebral bodies  110   a,    110   b.  Pedicles  120   a,    120   b  serve as pillars, joining the front and back parts of the vertebra, and provide side protection for the spinal cord and nerves. 
     Lamina  130   a,    130   b  serve as the roof of spinal canal  180  providing support and protection for the backside of the spinal cord. Spinous processes  140   a,    140   b  are bony projections that arise at a right angle to the midline of lamina  130   a,    130   b.  Each spinous process  140   a,    140   b  is attached to the spinous process above and below it by ligaments (i.e., spinous process  140   a  is attached to spinous process  140   b ). 
     Transverse processes  150   a,    150   b  are located at right angles to the junction of pedicles  120   a,    120   b  and lamina  130   a,    130   b.  Transverse processes  150   a,    150   b  provide a place for the back muscles to attach to the spine. 
     Spinal canal  180  is a bony tunnel surrounding the spinal cord. Spinal canal  180  is made up of the front of vertebral body  110   a,    110   b,  pedicles  120   a,    120   b  on the sides of vertebral body  110   a,    110   b,  and lamina  130   a,    130   b  in the back. In the lower back, spinal canal  180  also contains the nerve roots of the lower spine. 
     Mating superior articular facets  160   a,    160   b  and inferior articular facets  170   a,    170   b  connect each vertebra to the vertebrae above and below it. 
     In the embodiment shown, the intervertebral disc has been removed and bone cage  100  has been implanted into disc space  98  between vertebral body  110   a  and vertebral body  110   b.  Bone cage  100  is inserted posteriorly. The shape of bone cage  100  allows it to be inserted flat into disc space  98  without the need to distract vertebral bodies  110   a,    110   b,  minimizing retraction of the nerve root and the resulting injury and scarring. 
     In the embodiment shown, bone cage  100  is in the closed/first position and outer surface  31  of lower body  10  of bone cage  100  rests against top endplate  114   b  of vertebral body  110   b.    
       FIG. 2  illustrates a left side view of an exemplary embodiment of expandable and adjustable bone cage  100  implanted and in an expanded position. After bone cage  100  has been implanted, it can be pivotally expanded by rotating cam lift  60  to provide for maximum surface contact between expandable and adjustable bone cage  100  and vertebral bodies  110   a,    110   b.  In the embodiment shown, cam lift  60  is accessible through the distal end of bone cage  100  between lower body  10  and upper body  40 . 
     Outer surfaces  31 ,  34  of bone cage  100  are convexly-shaped to conform to the concave shape of endplates  114   b,    116   a  of vertebral bodies  110   a,    110   b.  In the embodiment shown, bone cage  100  is expanded until outer surface  34  of upper body  40  rests against bottom endplate  116   a  of vertebral body  110   a.    
     Expanding bone cage  100  increases the amount of contact between outer surface  34  of upper body  40  and bottom endplate  116   a  of vertebral body  110   a , promoting healing and fusion by distributing the weight and pressure of vertebral bodies  110   a,    110   b  more evenly over the length of bone cage  100  allowing restoration of lordosis with compression of the pedicle screw fusion system  190 . In addition, distributing the weight of vertebral bodies  110   a,    110   b  onto bone cage  100  decreases the amount of stress placed on pedicle screw fusion system  190  and the likelihood that screws will loosen, further delaying healing. 
       FIG. 3  illustrates a perspective view of the proximal end of an exemplary embodiment of expandable and adjustable bone cage  100  in a closed/first position. In the embodiment shown, bone cage  100  is comprised of lower body  10 , upper body  40 , cam lift  60 . Bone cage  100  may be expanded by rotating cam lift  60 . 
     In an exemplary embodiment, lower body  10  and upper body  40  are identical, reducing the cost and time of manufacturing. In various embodiments, lower body  10  and upper body  40  are available in varying heights. In the embodiment shown, bone cage  100  is assembled using lower body  10  and upper body  40  of identical heights (e.g., 4 millimeters); however, in other embodiments, bone cage  100  may be assembled using lower body  10  and upper body  40  having varying heights (e.g., 4 millimeter lower body and 5 millimeter upper body) to accommodate differences in the distance between vertebral bodies in patients. Inner surface  33  of lower body  10  mates with inner surface  36  of upper body  40 . Mating inner surfaces  33  and  36  allow lower body  10  and upper body  40  to fit together even when a lower body and upper body of different heights are used. 
     Lower body  10  and upper body  40  are selected based on the desired height. Once selected, cam lift  60  is placed between lower body  10  and upper body  40  and lower body  10  and upper body  40  are snapped together. 
     In the embodiment shown, bone cage  100  has a length of approximately 25 to 30 millimeters, a height of approximately 6 to 7 millimeters in the closed/first position. In the embodiment shown, bone cage  100  is capable of expanding 2 to 3 millimeters; however, in other embodiments, may be capable of expanding more than 3 millimeters. 
     In the embodiment shown, bone cage  100  is comprised of titanium; however in other embodiments, may be comprised of another material including, but not limited to PEEK, tricalcium phosphate, ceramics, metallic alloys, or any other implantable material. 
       FIG. 4  illustrates a perspective view of the distal end of an exemplary embodiment of expandable and adjustable bone cage  100  in a closed/first position. In the embodiment shown, bone cage  100  is comprised of lower body  10 , upper body  40 , and cam lift  60 . 
       FIG. 5   a  illustrates a perspective view of an exemplary embodiment of cam lift  60 . Cam lift  60  includes a plurality of nesting surfaces  62   a,    62   b,    63   a,    63   b,    64   a ,  64   b  and cam lift lobes  65   a,    65   b,    66   a,    66   b,    67   a,    67   b,  When cam lift  60  is in a closed/first position, nesting surfaces  62   a,    62   b  mate with cam lift followers  45 ,  15  (not shown) of upper body  40  and lower body  10  (not shown, see  FIG. 8   c ). To expand expandable and adjustable bone cage  100  to a first expanded position, cam lift  60  is rotated one step so that nesting surfaces  63   a,    63   b  mate with cam lift followers  45 ,  15  of upper body  40  and lower body  10  (see  FIG. 12 ). Nesting surfaces  64   a,    64   b  mate with cam lift followers  45 ,  15  (see  FIG. 15 ) when cam lift  60  is rotated to a second expanded position. In other embodiments, cam lift  60  may have more or fewer cam lift lobes and/or nesting surfaces. 
     Also visible is cam shaft  69  which rests between bearing surfaces  48  of upper body  40  (not shown) and bearing surface  18  (not shown) of lower body  10  (not shown) (see  FIG. 6 ). 
     In the embodiment shown, cam lift  60  further includes a plurality of positional flats, e.g.,  70 ,  71 ,  72 ,  73 ,  74 , around the proximal end. The function of the positional flats is to prevent accidental rotation of the cam lift giving the surgeon added control when placing and expanding bone cage  100 . Positional flats are designed to engage spring tab  49  of upper body  40  (not shown) and spring tab  19  of lower body  10  (not shown) (see  FIG. 6 ). 
       FIG. 5   b  illustrates a proximal view of an exemplary embodiment of expandable and adjustable bone cage  100 . Cam lift  60  and cam lift rotational driving surface  61  are accessible through the proximal end of bone cage  100  between lower body  10  and upper body  40 . 
     In the embodiment shown, cam lift rotational driving surface  61  has a hexalobe design with six driving slots that correspond to and are adapted to receive a hexalobe driver. However, in other embodiments, cam lift rotational driving surface  61  can be any polygon or another shape and may have any number or style of driving slots to correspond to a particular style of driver. 
     In the embodiment shown, the plane represented by line az is fixed on the vertical center of cam lift  60  when it is in the first position, that is, when bone cage  100  is closed. 
       FIG. 6  illustrates an exploded view of the proximal end of exemplary embodiment of an expandable and adjustable bone cage  100  showing lower body  10 , upper body  40 , cam lift  60 , and optional end plug  80 . 
     Prior to assembly, lower body  10  and upper body  40  are selected based on height and cam lift  60  is placed in its first position, that is, so that nesting surfaces  62   a,    62   b  rest against cam lift followers  15 ,  45  (not visible). Cam lift shaft  69  is placed between cam lift bearing surface  48  of upper body  40  and cam lift bearing surface  18  of lower body  10 . 
     In the embodiment shown, cam lift  60  further includes a plurality of positional flats, e.g.,  70 ,  71 ,  72 ,  73 ,  74 , around the proximal end. Positional flats of cam lift  60 , e.g.,  70 ,  71 ,  72 ,  73 ,  74 , mate with spring tab  49  of upper body  40  and spring tab  19  of lower body  10 . Spring tabs  19 ,  49  are made by adding flat spring grooves  20  (lower body  10 ),  50  (upper body  60 ) around the intended spring area. The combination of positional flats and spring tabs help retain cam lift  60  while expandable and adjustable bone cage  100  is in the closed/first, second, and third positions. When cam lift  60  is rotated between first positional flat  73  and second positional flat  74 , first positional flat  73  pushes on spring tabs  19 ,  49  which flex, then return when the final position is reached. 
     Also shown are pivot surfaces  13 ,  14 , pivot retention catch  11 , and pivot retention hole  12  of lower body  10 , and pivot surfaces  43 ,  44  (not visible), pivot retention catch  41 , and pivot retention hole  42  of upper body  40 . Pivot retention catches  11 ,  41  are designed to be flexible by pivot retention catch spring grooves  16 ,  46  and when cam lift  60  is placed in its first position, upper body  40  is snapped into position. 
     To keep the retention features from sliding apart, tab  21  of lower body  10  mates into recess  52  of upper body  40  and tab  51  (not visible, see  FIG. 7   a ) of upper body  40  mates into recess  22  of lower body  10 . 
     To ensure that spring tabs  19 ,  49  keep pressure against positional flats  70 ,  71 , and  72  of cam lift  60 , outer backing surface  23  of lower body  10  contacts inner backing surface  54  (not visible, see  FIG. 7   b ) of upper body  40  and inner backing surface  24  of lower body  10  contacts outer backing surface  53  (not visible, see  FIG. 7   b ) of upper body  40 . 
     Pivot rotation stops  17 ,  47  at the proximal end of lower body  10  and upper body  40  limit the amount of pivot and prevent lower body  10  and upper body  40  from pivoting open too far and allowing cam lift  60  to fall out. Cam lift  60  also has distal flange surface  75  ( FIG. 5   a ) and proximal flange surface  76  ( FIG. 5   a ) which prevent cam lift  60  from dislocating. 
     Also shown in  FIG. 17  is optional end plug  80 . Bone graft material is inserted into bone cage  100  after bone cage  100  is inserted. Optional end plug  80  prevents bone graft material from leaking out of bone cage  100 . 
     In the embodiment shown, optional end plug  80  has a conical nose, radial distal spring slots and radial proximal slots that will allow it to compress when pushed into the proximal end of the upper and lower bodies and expand into graft plug retention grooves  25 ,  55  of lower body  10  and upper body  40 . The tooth configuration that expands while positioned in graft plug retention grooves  25 ,  55  has perpendicular plug retention shoulder  84  which mates with perpendicular body shoulders (not visible) of lower body  10  and upper body  40  preventing optional end plug  80  from backing out once inserted. 
     Optional end plug  80  further includes cylindrical plug removal groove  86 , which requires a special instrument to compress optional end plug  80  for removal, and an outer cylindrical diameter  85  that mates in the inner cylindrical diameter  26  of lower body  10  and inner cylindrical diameter  56  (not visible) of upper body  40 . 
     In various embodiments, a second cam lift may be used in place of optional end plug  80 . After bone cage  100  has been expanded and bone graft material has been inserted, a second cam lift may be inserted into the proximal end of bone cage  100 . The second cam lift would allow bone cage  100  to be uniformly expanded. 
       FIG. 7  illustrates a right side view of an exemplary embodiment of expandable and adjustable bone cage  100  in a first/closed position. In the embodiment shown, lower body  10  has pivot surface  14  and pivot retention catch  11 , which protrudes from lower body  10 , and upper body  40  has pivot surface  43  and pivot retention hole  42 . 
     The left side of bone cage  100  has features identical to that of the right side shown. On the left side of bone cage  100 , lower body  10  has pivot retention hole  12  ( FIG. 6 ) and pivot surface  13  ( FIG. 6 ) and upper body  40  has pivot retention catch  41  ( FIG. 6 ) and pivot surface  44  (not visible). 
     Pivot retention catches  11 ,  41  secure upper body  40  to lower body  10  and allows pivot surfaces  43 ,  44  of upper body  40  to pivot into an expanded position along pivot surfaces  13 ,  14  of lower body  10 . 
     In the embodiment shown, pivot surface  14  of lower body  10  and pivot surface  44  of upper body  40  are concave, and pivot surface  13  of lower body  10  and pivot surface  43  of upper body  40  are convex (see  FIG. 6 ). Pivot surface  14  of lower body  10  fits against pivot surface  43  of upper body  40  and pivot surface  13  of lower body  10  fits against pivot surface  44  of upper body  40  when lower body  10  and upper body  40  are assembled. When bone cage  100  is expanded, upper body pivot surfaces  43 ,  44  rotate along lower body pivot surfaces  13 ,  14  and provide a large contact area between lower body  10  and upper body  40  when bone cage  100  is expanded. 
     Lower body pivot surfaces  13 ,  14  and upper body pivot surfaces  43 ,  44  support the load of the vertebral bodies. The weight of the vertebral bodies is not placed on pivot retention catches  11 ,  41  and pivot retentions holes  12 ,  42 . 
     In the embodiment shown, the proximal end of lower body  10  and upper body  40  are rounded with a constant slope forming a semicircle when lower body  10  and upper body  40  are connected. The distal end of lower body  10  and upper body  40  are tapered for easy insertion in the disc space. The rounded shape of the proximal end of bone cage  100  strengthens expandable and adjustable bone cage  100  during insertion. 
     In the embodiment shown, outer surface  31  of lower body  10  and outer surface  34  of upper body  40  further includes surface engaging contours  29 ,  69  which contact the endplates of the vertebral bodies and prevent migration of bone cage  100  when positioned. Surface engaging contours  29 ,  59  produce friction between the vertebral endplates and bone cage  100  to keep bone cage  100  from moving. 
       FIG. 8   a  illustrates a sectional view of an exemplary embodiment of expandable and adjustable bone cage  100  taken along line  8   a  of  FIG. 7 . In the embodiment shown, lower body  10  has tab  21  and tab recess  22  which correspond to tab recess  52  and tab  51  of upper body  40 , respectively. The pairing of tab  21  and recess  52  and tab  51  and recess  22  keep upper body  40  and lower body  10  from separating. In other embodiments, lower body  10  and upper body  40  may have contours, protrusions, or any other corresponding structural configuration which allow lower body  10  and upper body  40  to fit together. 
       FIG. 8   b  illustrates a sectional view of an exemplary embodiment of expandable and adjustable bone cage  100  taken along line  8   b  of  FIG. 7 . In the embodiment shown, lower body  10  has inner backing surface  24  and outer backing surface  23  which correspond to outer backing surface  53  and inner backing surface  54  of upper body  40 , respectively. 
       FIG. 8   c  illustrates a sectional view an exemplary embodiment of expandable and adjustable bone cage  100  taken along line  8   c  of  FIG. 7 . In the embodiment shown, cam lift  60  is in the closed position and nesting surface  62   a  (surface between cam lift lobe  65   a  and cam lift lobe  66   a ) mates with cam lift follower  45  and nesting surface  62   b  (surface between cam lift lobe  65   b  and cam lift lobe  66   b ) mates with cam lift follower  15 . 
     In the embodiment shown, the plane represented by line az is fixed on the vertical center of cam lift  60  when it is in the first position, that is, bone cage  100  is closed. 
       FIG. 9  illustrates a bottom view of an exemplary embodiment of expandable and adjustable bone cage  100  showing cam lift  60  and bone graft openings  28  (lower body  10 ),  58  (upper body  40 ) (see  FIG. 6 ). 
       FIG. 10  illustrates a proximal view of an exemplary embodiment of expandable and adjustable bone cage  100  expanded to a second position. In the embodiment shown, cam lift  60  has been rotated clockwise to a second position raising the distal end of upper body  40 . In other embodiments, the lobes on cam lift  60  may be reversed so that the distal end of upper body  40  is raised by rotating cam lift  60  counterclockwise. 
     In the embodiment shown, angle θ 1  represents the rotation of plane az and cam lift  60  and the vertical plan through lower body  10  and upper body  40 . When cam lift  60  is rotated to angle θ 1 , cam lift lobes/nesting surfaces open the distal end of expandable and adjustable bone cage  100 . 
       FIG. 11  illustrates a right side view of an exemplary embodiment of expandable and adjustable bone cage  100  expanded to a second position. When cam lift  60  is rotated to a second position, pivot surface  43  of upper body  40  rotates around pivot surface  14  of lower body  10  raising the proximal end of upper body  40 . 
       FIG. 12  illustrates a sectional view of an exemplary embodiment of expandable and adjustable bone cage  100  expanded to a second position taken along line  12  of  FIG. 11 . In the embodiment shown, cam lift  60  has been rotated to a second position so that nesting surface  63   a  (surface between cam lift lobe  66   a  and cam lift lobe  67   a ) mates with cam lift follower  45  and nesting surface  63   b  (surface between cam lift lobe  66   b  and cam lift lobe  67   b ) mates with cam lift follower  15 . Nesting surfaces  63   a,    63   b  are machined at angle θ 1  for a mating fit with cam lift followers  45 ,  15 . 
     When cam lift  60  is rotated clockwise to a second position, cam lift lobes  66   a,    66   b  follow cam lift followers  15  and  45  until nesting surfaces  63   a,    63   b , mate with cam lift followers  15 ,  45  securing cam lift  60  into position. 
       FIG. 13  illustrates a proximal view of an exemplary embodiment of expandable and adjustable bone cage  100  expanded to a third position. In the embodiment shown, cam lift  60  has been rotated clockwise to a third position raising the distal end of upper body  40 . In other embodiments, the lobes on cam lift  60  may be reversed so that the distal end of upper body  40  is raised by rotating cam lift  60  counterclockwise. 
     In the embodiment shown, angle θ 2  represents the rotation of plane az and cam lift  60  and the vertical plane through lower body  10  and upper body  40 . When cam lift  60  is rotated to angle θ 2 , cam lift lobes/nesting surfaces open the distal end of expandable and adjustable bone cage  100 . 
       FIG. 14  illustrates a right side view of an exemplary embodiment of expandable and adjustable bone cage  100  expanded to a third position. When cam lift  60  is rotated to a third position, pivot surface  43  of upper body  40  rotates around pivot surface  14  of lower body  10  raising the proximal end of upper body  40 . 
     Also visible are pivot rotation stops  17 ,  47 , which prevent further rotation, and surface engaging contours  29 ,  59  that contact the endplates of the vertebral bodies when implanted preventing migration of bone cage  100 . 
       FIG. 15  illustrates a sectional view of an exemplary embodiment of expandable and adjustable bone cage  100  expanded to a third position taken along line  14  in  FIG. 13 , In the embodiment shown, cam lift  60  has been rotated to a second third position so that nesting surface  64   a  (surface between cam lift lobe  67   a  and cam lift edge  68   a ) mates with cam lift follower  45  and nesting surface  64   b  (surface between cam lift lobe  67   b  and cam lift edge  68   b ) mates with cam lift follower  15 . Nesting surfaces  64   a,    64   b  are machined at angle θ 2  for a mating fit with cam lift followers  45 ,  15 . 
     When cam lift  60  is rotated clockwise to a third position, cam lift lobes  67   a ,  67   b  follow cam lift followers  15  and  45  until nesting surfaces  64   a,    64   b  rest against cam lift followers  15 ,  45  securing cam lift  60  into position. Cam lift edges  68   a,    68   b  are higher and sharper than cam lift lobes  65   a,    65   b,    66   a,    66   b,    67   a,    67   b  to help prevent over rotation of cam lift  60 . 
     In the embodiment shown, the shape of cam lift lobes  66   a,    66   b,    67   a,  and  67   b  provides for a smooth transition when cam lift  60  is rotated from a closed/first position to a second (expanded) position or from a second (expanded) position to a third (expanded) position. 
       FIG. 16  illustrates a perspective view of the distal end of an exemplary embodiment of expandable and adjustable bone cage  100  expanded to a second position. In the embodiment shown, expandable and adjustable bone cage  100  further includes optional end plug  80 . 
       FIG. 17  illustrates a perspective view of the distal end of an exemplary embodiment of expandable and adjustable bone cage  100  expanded to a third position. In the embodiment shown, expandable and adjustable bone cage  100  further includes optional end plug  80 . 
       FIG. 18  illustrates a perspective view of the distal end of an exemplary embodiment of expandable and adjustable bone cage  100 . In the embodiment shown, lower body  10  has a height that is greater than the height of upper body  40 . In various embodiments, lower body  10  and upper body  40  may be of the same height or lower body  10  may have a height that is smaller or greater than the height of upper body  40 . The height of lower body  10  and upper body  40  selected is determined by the height/size of the patient&#39;s disc space. 
       FIG. 19  illustrates a perspective view of the left side of an exemplary embodiment of expandable and adjustable bone cage  100  with lower body  10  having a height that is greater than the height of upper body  40 . 
       FIG. 20  illustrates a proximal view of an exemplary embodiment of expandable and adjustable bone cage  100  with lower body  10  having a height that is greater than the height of upper body  40 .