Abstract:
Apparatus and method for compressing a shape memory material implant to be implanted in a patient. The apparatus in some embodiments includes opposing dies, an actuator, and a uniformity controller. The opposing dies are configured to grasp the shape memory material implant, when placed therebetween. The actuator actuates the opposing dies toward each other to compress the shape memory material implant. The uniformity controller of some embodiments provides uniform compression of a given type of shape memory material implant.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally relates to an apparatus for compressing shape memory implants and a method for compressing and implanting such implants. The apparatus and method are generally intended for use in repairing various defects in bone and tissue, such as ruptured or herniated intervertebral discs. More specifically, the present invention may relate to a method and apparatus for compressing shape memory alloy cages in a controllable and repeatable manner.  
       BACKGROUND OF THE INVENTION  
       [0002]     Implants with shape memory features can be efficacious in repairing bone and tissues defects/deficits. The implants can be used to secure, replace, and/or supplement damaged or missing tissue or bone. The shape memory aspect of the implant typically provides added securement by expanding into the space it is to occupy after an implantation.  
         [0003]     A common injury in which such treatment is useful is a ruptured or otherwise damages intervertebral disc. An intervertebral disc is formed of a nucleus of gelatinous collagen fibers and an outer annulus. The gelatinous nucleus provides support between adjacent vertebrae. The nucleus is contained by the annulus, which is formed of layers of collagen fibers which secure the nucleus in place. A common cause of back pain and injury is a rupture or tear in the annulus that allows the nucleus to herniate. A herniated nucleus can put pressure on neural and ligamentary structures associated with the spine, which can leads to pain in the patient&#39;s back and legs.  
         [0004]     There are numerous conventional treatments for dealing with ruptured or degenerated intervertebral discs. One possible treatment for a ruptured annulus involves repairing the tear in the annulus by inserting an implant into the tear to, essentially, plug the rupture. Thus, the implant may be secured to the annulus at the rupture to help contain the nucleus in its original position. Alternatively, the disc may be completely replaced, or supplemented with a supporting structure. In particular, one treatment for a degenerated disc is to place an implant between adjacent vertebrae to maintain an appropriate space while the vertebrae grow together or fuse.  
         [0005]     A favorable option for such procedures is to use a shape memory alloy (SMA) to form the implant. An SMA is an alloy that can be compressed, but will return to an uncompressed form when exposed to certain conditions. For instance, an SMA may be compressed when below a transition temperature, and will expand back to a non-compressed shape when heated above the transition temperature. In other embodiments, the transition may occur through the provision of electrical stimulation, for instance. In addition, similar shape memory materials, such as plastics with shape memory aspects may also be used. For exemplary purposes, however, this application will discuss the present invention with respect to SMAs. One of ordinary skill in the art would understand that alternative materials could be used in the examples discussed below.  
         [0006]     Preferably, however, the implant will be formed of an SMA such as nitinol. Nitinol is a mixture of about 50 percent nickel and about 50 percent titanium. By varying the ratio of nickel to titanium, usually only slightly, the transition temperature of the alloy can be adjusted. Also, the SMA will typically be formed in the shape of a cage defined by a lattice structure, an example of which is shown in  FIG. 7 . With an SMA forming a cage, compression and expansion of the cage is readily achievable. For instance, when below a transition temperature (in situations where the shape memory material is controlled based on temperature), the structure can be compressed to tighten the lattice structure, forming a compressed shape. When heated past the transition temperature, or subjected to such other predetermined condition, the cage will expand back to its original form, or a similar non-compressed form.  
         [0007]     An example of such an SMA cage is discussed in U.S. Patent Publication No. US2003/0074075 (Thomas, Jr. et al.). The cage described therein may be used to repair a disc herniation. Another implant is shown in  FIG. 7 . The implant shown in  FIG. 7  may be used as a spacer between adjacent vertebrae to restore intervertebral space lost due to injury or the like. Thus, for example, the implant may support the anterior column load of the spine. Optionally, an osteogenic material may then be packed around the implant.  
         [0008]     An SMA cage may be implanted in its compressed form, and then expand to fill the annular defect, intervertebral spaces, or the like. Among other benefits, the implantation of a compressed implant provides for a less invasive procedure, with a smaller incision. Typically, the SMA cage is temperature activated, and the body temperature of the patient heats the SMA cage to above the transition temperature, causing it to expand to the non-compressed form. The transition temperature may be set (for example, by the specific material used to form the cage) at or above 90°, for example, so that the compressed form is stable at room temperature. However, it still can be difficult to keep the cage in the compressed form prior to insertion into a patient. If the product is shipped to the hospital during warmer summer months, the device will likely encounter temperatures during delivery that exceed the transition temperature. This can occur, for instance, in the heat of a delivery truck, exposed to the summer sun. Thus, it is likely that a surgeon, nurse, or technician would have to compress the cage prior to or during the implantation surgery.  
         [0009]     Compression of an SMA cage is an important step in a successful implant surgery. If compressed too much, cracking of the material or “cold working” can occur. The lattice is typically arranged in an orderly structure, in both expanded and compressed forms. Cold working occurs when the lattice structure is compressed to a point that crushes or structurally alters the orderly lattice structure. Cold working and cracking of the material can cause the compressed structure to become, at least partially, unrecoverable (“over yielding”), such that the cage does not return to the proper expanded form when heated above the transition temperature.  
         [0010]     Typically, about an 8% local material strain is acceptable for an SMA of nitinol. Above that, risks of cracking and cold working heighten. An 8% local material strain could correspond, for example, to a 30% structural deformation of the cage. This, of course, will vary given the specifics of the cage design, material, etc.  
         [0011]     Thus, there is a need to provide controllable and repeatable compression of an SMA cage. More specifically, it is beneficial to be able to provide a surgeon with instruments and methods to produce controlled compression of SMA cages, from patient to patient and surgery to surgery and among an array of different types and sizes of SMA cages to be implanted.  
       SUMMARY OF THE INVENTION  
       [0012]     In one embodiment, the present invention is directed to an apparatus for compressing a shape memory material implant to be implanted in a patient. The apparatus includes opposing dies, an actuator, and a uniformity controller. The opposing dies are configured to grasp the shape memory material implant, when placed therebetween. The actuator actuates the opposing dies toward each other, such that the opposing dies impart forces in substantially direct opposition to each other, against the shape memory material implant, when placed therebetween, so as to compress the shape memory material implant. The uniformity controller provides uniform compression of a given type of shape memory material implant.  
         [0013]     In another embodiment, the present invention is directed to a method of inserting a shape memory material implant into a patient. The method includes steps of providing the shape memory material implant, which is compressible and capable of expanding to an expanded form, from a compressed form, when exposed to a predetermined condition, and placing the shape memory material implant in a mechanical actuator with opposing dies, such that the shape memory material implant is grasped between the opposing dies. The mechanical actuator provides controlled, repeatable actuation of the dies. The method also involves actuating the opposing dies of the mechanical actuator toward each other when the shape memory material implant is positioned therebetween, to compress the shape memory material implant into the compressed form, and inserting the compressed shape memory material implant into the patient at a medically efficacious location. After insertion, the compressed shape memory material implant is exposed to the predetermined condition so as to cause the shape memory material implant to expand to the expanded form. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a side view of a compression device according to an embodiment of the present invention.  
         [0015]      FIG. 2  is a side view of an opposite side of the compression device shown in  FIG. 1 .  
         [0016]      FIG. 3  is a front view of the compression device shown in  FIG. 1 .  
         [0017]      FIG. 4  is a side cross section of a portion of the compression device shown in  FIG. 3 , taken along line  4 - 4 ′.  
         [0018]      FIG. 5  is a perspective view of a modular die to be used with the compression device shown in  FIG. 1 .  
         [0019]      FIG. 6  is a front view of the modular die shown in  FIG. 5 .  
         [0020]      FIG. 7  is a perspective view of one example of an SMA cage.  
         [0021]      FIG. 8  is a perspective view of the SMA cage from  FIG. 7  positioned on an insertion device.  
         [0022]      FIG. 9  is a side view of a compression device according to another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]      FIGS. 1-3  show one embodiment of the present invention embodied in a hand-held compression device  100 . Of course, a number of other arrangements are possible while keeping within the scope of the intended scope of the present invention, as defined by the claims provided below. For instance, the compression device need not be hand held, and can work with alternate mechanics as those described below. For instance, the device may be a table-top device. Also, the mechanics may be automatically controlled through electrical components or pneumatics, such that the device is not actuated manually. Thus, the following description should be taken as exemplary.  
         [0024]     As shown in  FIG. 1 , a compression device  100  is provided. The compression device  100  includes opposing heads  102   a  and  102   b.  The opposing heads  102   a  and  102   b  include stops  108   a  and  108   b  and cavities  106   a  and  106   b.  As shown in  FIG. 4 , in addition to opening towards each other, the cavities  106   a  and  106   b  open at distal ends to form window  124 . The stops  108   a  and  108   b  come into contact when the heads  102   a  and  102   b  are actuated toward each other, so as to prevent further actuation after abutment of the stops  108   a  and  108   b.    
         [0025]     The cavities  106   a  and  106   b  each securably receive a die  130  (dies  130   a  and  130   b,  are shown in  FIGS. 3 and 4 ). In the depicted embodiment, male and female coupling is provided between the cavities  106   a  and  106   b  and the dies  130   a  and  130   b,  respectively. In the present embodiment, a male projection  136  of die  130 , shown in  FIGS. 5 and 6 , extends into the depth of the female part of a cavity, such as the cavities  106   a  and  106   b.  In this embodiment, a tight fit between the projection  136  and such a cavity secures, for example, the die  130   a  to the head  102   a.  However, any one of a number of mechanisms may be used to secure dies  130   a  and  130   b  in their respective cavities while keeping within the intended scope of the present invention.  
         [0026]     In addition to the projection  136 , a die  130  includes die stops  132  and a cradling face  134 . In some embodiments of the present invention, the die stops  132  will act to stop further compression of an SMA cage placed between opposing dies  130 . In this embodiment, the die stops  132  are flat surfaces of top portions of the die  130  shown in  FIGS. 5 and 6 . In other embodiments, however, the die  130  may be provided with projections formed integrally with, or secured to, die  130  to act as a die stop. In fact, die stops may be any mechanism that serves to limit the amount of compression applied to a given implant, such as an SMA cage  140  shown in  FIG. 3 . In the embodiment shown in  FIGS. 1-3 , die stops  132  will not be used as a stopping mechanism inasmuch as the stops  108   a  and  108   b  are provided on the compression device  100 , to act as a stopping mechanism to prevent compression of an SMA cage past a given point. It should be appreciated, however, when the stops  108   a  and  108   b  are not provided, opposing die stops  132  may project up from the cavities  106   a  and  106   b  to abut each other to inhibit further compression.  
         [0027]     Cradle faces  134  are used to receive and cradle an SMA cage. Specifically, when the dies  130   a  and  130   b  are positioned in the heads  102   a  and  102   b,  respectively, the cradling faces  134  of the different dies oppose each other so as to receive and cradle an SMA cage therebetween, as shown with respect to the cylindrical SMA cage  140  in  FIG. 3 . During compression, which occurs by actuating the opposing dies  130   a  and  130   b  toward each other in parallel movement to compress an SMA cage positioned therebetween, the cradle faces  134  spread the compression forces across opposite sides of the SMA cage to provide more uniform compression, and to avoid concentrating of a compression force on, for instance, one point of the SMA cage, risking cracking or cold working. In this embodiment, the cradling surfaces  134  are semicylindrical in shape. This shape allows the surfaces of cradling faces  134  to disperse the force of the moving heads  102   a  and  102   b  over more of the surface area of the cage. However, the shape of cradling faces  134  may be varied as needed to receive different types of cages. For instance, a less cylindrical SMA cage  142  is shown in  FIGS. 7 and 8 . Alternative cradling faces may be formed to cradle such a cage. For instance, SMA cage  142  includes support surfaces  144   a  and  144   b,  which, when implanted, may contact opposing surfaces of adjacent vertebrae. In the expanded form, shown in  FIG. 7 , SMA cage  142  acts as a spacer to restore intervertebral space and to bear the anterior column load. Thus, separate cradling faces may be formed to mate with the support surfaces  144   a  and  144   b,  so as to compress the SMA cage  142  to move surfaces  144   a  and  144   b  closer to each other, prior to implantation. Also, crutches  146  may be manually bent inward before compression of the SMA cage  142 , so as not to interfere with or prevent proper compression. Crutches  146  may provide additional strength to the structure when in the expanded form, by moving back into the position shown in  FIG. 7 . In that position, the crutches  146  may inhibit compression of the cage  142  by acting as a brace between the top and bottom portion of the cage  142 , defined by surfaces  144   a  and  144   b,  respectively.  
         [0028]     However, any one of a number of SMA cages or other compressable devices may be used with the present invention, and SMA cages  140  and  142  are shown only for exemplary purposes.  
         [0029]     As discussed earlier, the dies  130   a  and  130   b  are removably secured in the heads  102   a  and  102   b.  This allows multiple dies  130  to be interchanged in a given compression device  100  so that the compression device  100  can be used with a variety of different types and sizes of SMA cages. In some embodiments, compression device  100  will be provided with a set of interchangeable dies  130 , which correspond with SMA cages of different sizes and styles. In other embodiments, a die  130  may be provided with a particular SMA cage to be implanted, so as to account for design changes over time. Thus, the dies  130  may be made specific to the SMA cages with which they are to be provided.  
         [0030]     The dies  130  can be made of any one of a number of different types of materials. For example, plastics such as acetyl copolymer or polyethylene may be used. Plastics are beneficial because they are not as hard as metal, and thus are less likely to damage the implants. Of course any one of a number of types of materials may be used, including metals.  
         [0000]     Actuation Control  
         [0031]     When moving the heads  102   a  and  102   b  together to provide compression, as discussed above, dies  130   a  and  130   b  may move in parallel such that the dies  130   a  and  130   b  provide substantially opposing forces against an SMA cage positioned therebetween. For instance, if a cage is shaped as a cylinder, opposing dies  130   a  and  130   b  may provide forces in substantially opposing radial directions. By providing substantially opposing forces, it is possible to help prevent shearing forces that could crack or otherwise damage the SMA cage. In addition, this helps prevent uneven compression of the lattice structure of a given SMA cage, particularly in connection with the shape of the cradling surface. Thus, the substantially opposing forces may be applied in opposition to each other substantially along (i.e., with respect to) a single axis of the implant to be compressed, or a common axis of the opposing dies. The axis can be any straight line (i) passing through the implant positioned in the compression device  100 , or (ii) passing through both opposing dies. When the implant is substantially rectangular in shape, the forces may be described as being applied to opposite transverse or opposite lateral surfaces of the implant.  
         [0032]     Any mechanism may be used to provide such even compression to avoid shearing forces and the like. Such mechanisms may include gears or levers that operate to move the dies  130  to provide such opposing forces. In addition, it is possible that only one die  130  moves, while an opposing die is kept stationary (either completely, or partially to incorporate a rotational aspect such as with a gimble support or the like) such that the opposing die provides a resistance force during compression. For example, the mechanics of a conventional die press machine may be incorporated into the present invention to provide the actuation.  
         [0033]     For exemplary purposes, we show a hand-held compression device  100 . One of ordinary skill in the art would recognize that the design thereof can be varied as discussed above or in other manners to provide the forces necessary for compression. In the present compression device  100 , handles  150   a  and  150   b  are operated by a user to provide force to actuate the heads  102   a  and  102   b.  As shown in  FIG. 1 , the compression device  100  may also be provided with springs  170   a  and  170   b  which provide a biasing force to keep the handles  150   a  and  150   b  in an open position when not in use. While these springs are shown, other biasing mechanisms may be used while keeping within the scope of the present invention. In addition, the springs  170   a  and  170   b  are provided only for ease of use and are not necessary for operation.  
         [0034]     Also, with respect to the compression device  100 , to keep the heads  102   a  and  102   b  moving in parallel, a four-bar linkage  104  is used in this embodiment. The four-bar linkage  104  includes parallel bars  110   a  and  110   b  and crossing bars  112   a  and  112   b.  The heads  102   a  and  102   b  are secured to the parallel bars  110   a  and  110   b,  respectively. The crossing bars  112   a  and  112   b  have a common pivot point defined by a post  120 . The crossing bar  112   a  is pivotably connected to the parallel bar  110   a  at a common pivot point defined by a post  118   a.  The crossing bar  112   a  is also pivotably connected to the parallel bar  110   b  by a post  114   b.  The crossing bar  112   b  is pivotably connected to the parallel bar  110   a  by a post  114   a.  The crossing bar  112   b  is also pivotably connected to the parallel bar  110   b  by a post  118   b.    
         [0035]     In addition, the posts  114   a  and  114   b,  secured to the crossing bars  112   a  and  112   b,  respectively, slide relative to the parallel bars  110   a  and  110   b,  respectively, within slots  116   a  and  116   b,  which are formed in the parallel bars  110   a  and  110   b.    
         [0036]     The handle  150   b  crosses, and is pivotably secured to, the handle  150   a  by a post  122 . The handle  150   b  is pivotably connected to the parallel bar  110   a  at post  118   a.  Handle  150   a  is similarly connected to the parallel bar  110   b  at post  118   b.    
         [0037]     Thus, as the handles  150   a  and  150   b  are moved from an open position, at which they are spaced apart from each other, to a closed position (i.e., toward each other), parallel bars  110   a  and  110   b  are also biased toward each other. As the parallel bars  110   a  and  110   b  are biased toward each other, they pivot with respect to handles  150   b  and  150   a,  respectively, about posts  118   a  and  118   b,  respectively. In addition, as the parallel bars  110   a  and  110   b  are biased toward each other, the crossing bars  112   a  and  112   b  pivot about posts  118   a,    120 , and  114   b,  and  114   a,    120  and  118   b,  respectively, so as to move from a position defined by a substantial “X” shape (shown in  FIG. 2 ) made by those two bars, to a position in which the “X” flattens as the crossing bars  112   a  and  112   b  rotate toward more parallel positions.  
         [0038]     As the crossing bars  112   a  and  112   b  pivot with respect to each other and the parallel bars  110   a  and  110   b,  posts  114   b  and  114   a,  secured thereto, respectively, slide within slots  116   a  and  116   b.  In this regard, we note that the length of the slots  116   a  and  116   b  can be varied in accordance with design choices. When made shorter, slots  116   a  and  116   b  can form stops that inhibit further actuation of the compression device  100 , and specifically, actuation of opposing dies  130   a  and  130   b  toward each other.  
         [0039]     With such action, as the handles  150   a  and  150   b  actuate the parallel bars  110   b  and  110   a  together, parallel bars  110   b  and  110   a  remain substantially parallel with each other. Because the heads  102   a  and  102   b  are secured to the parallel bars  110   a  and  110   b,  heads  102   a  and  102   b  actuate in parallel while moving towards to each other, so as to compress an SMA cage positioned between the dies  130   a  and  130   b.  This parallel movement helps prevent shearing forces that could damage a cage during compression. Thus, the opposing dies  130   a  and  130   b  each have substantially opposing movement along an axis common to dies  130   a  and  130   b,  with the directions of movement of each being in substantially opposing radial directions of SMA cage  140  shown in  FIG. 3 , for example.  
         [0040]     Again, however, this is only one mechanism for providing actuation of dies  130   a  and  130   b.  Numerous other arrangements may be used to provide adequate opposing forces to a given SMA cage during compression.  
         [0041]     In the embodiments shown in  FIG. 9 , compression device  100  is provided with a graduated scale  160 . The graduated scale  160  includes a graduation plate  162  and a pointer  164 . The gradation plate  162  is secured to parallel bar  110   a,  and moves freely with respect to parallel bar  110   b.  The parallel bar  110   b  has provided thereon the pointer  164 , which points to the graduation plate  162 , to indicate a graduation mark thereon. As the parallel bars  110   a  and  110   b  are actuated, the pointer  164  and the graduation plate  162  move relative to each other. Thus, the pointer  164  can indicate a mark corresponding to a beginning point of compression and a mark corresponding to an ending point of compression, so as to aid in controlled and repeatable compression amounts.  
         [0042]     The manufacturer of a given type of SMA cage can indicate a preferred compression amount or compression range for a specific SMA cage, which a user of the compression device  100  can measure using the graduated scale  160 . In that manner, like mechanical stops, the graduated scale  160  acts as a mechanism for inhibiting compression past a given compression amount (in association with presumed user vigilance) to help prevent over compression of an SMA cage. Unlike a stop, inhibition of over-compression is provided by a user operating the device so as to provide a given compression amount as indicated by the graduated scale  160 . Of course, the compression level does not have to be specifically indicated by the manufacturer, and the graduated scale  160  can be used to keep track of a compression amount of an SMA cage dictated by a user of the compression device  100 .  
         [0000]     Example Implantation Method  
         [0043]     With a compression device according to the present invention, the implantation of an SMA cage, such as the SMA cage  140  or SMA cage  142 , can be controlled and repeatable, leading to improved implantation techniques. In connection with such a compression device or other compression devices, another embodiment of the present invention is a preferred method of implanting SMA cages, or similar shape memory implants.  
         [0044]     With respect temperature sensitive SMA cages, compression is more easily achieved at lower temperatures, i.e., temperatures further from the transition temperature of the SMA. Thus, one embodiment, an implant surgery for inserting or securing the SMA cage  140  (for example) in a patient will involve reducing the temperature of the SMA cage  140  prior to implantation. The method of doing this may involve submerging, completely or partially, the SMA cage  140  in an ice bath. The SMA cage  140  may be submerged by plunging it directly into the ice bath (if sterile), or plunging in a sterile packet containing the SMA cage  140 , to maintain a sterile field during surgery.  
         [0045]     Once the SMA cage  140  is sufficiently reduced in temperature, it can be removed from the ice bath. The amount of temperature reduction can be varied as needed, depending on the transition temperature of the SMA, compression amount necessary, etc., as would be understood by one of ordinary skill in the art.  
         [0046]     If the compression device being used includes modular dies, proper modular dies would be selected in view of manufacturer suggestions, dies provided with SMA cage  140 , or in accordance with the surgeon&#39;s own judgment. To insert a selected die, for instance, the compression device  100  could be opened to allow room for insertion of the dies  130   a  and  130   b.  The dies  130   a  and  103   b  should be inserted and secured. Once secured, SMA cage  140  may be inserted into the compression device  100  through the window  124 , so as to be positioned between opposing cradling surfaces  134 . (When an implant such as the SMA cage  142  is used, the implantation method may include a step of manually biasing free ends  148  of crutches  146  inward (or outward), to allow for proper compression. In re-expansion, crutches  146  will reposition automatically to add strength to the SMA cage  142 .) In this embodiment, the handles  150   a  and  150   b  are squeezed to actuate the dies  130   a  and  130   b  until the opposing surfaces  134  just contact SMA cage  140 , simultaneously. In other words, the handles may be moved to the closed position until the opposing dies  130   a  and  130   b  just grip SMA cage  140  therebetween so as to cradle the SMA cage  140  simultaneously with opposing cradling surfaces  134 .  
         [0047]     At this point, if the compression device  100  includes a graduated scale  160 , an initial reading of the graduated scale  160  may be taken to determine the starting point of compression. When compression is based on the manufacturer&#39;s provided compression amount, to be measured by a scale such as graduated scale  160 , a user squeezes the handles  150   a  and  150   b  to actuate the heads  102   a  and  102   b  to compress the SMA cage  140  until the indicated compression is achieved, as measured by the movement of pointer  164  with respect to the graduation plate  162 .  
         [0048]     In other embodiments, the handles  150   a  and  150   b  may be squeezed until further compression is inhibited by a stopping mechanism. For instance, further compression may be inhibited by abutment of the stops  108   a  and  108   b,  or the die stops  132 . Of course, other stopping mechanisms may be provided, as would be understood by one of ordinary skill in the art. Also, the compression may be stopped based on the user&#39;s judgement.  
         [0049]     Before compression is complete, an insertion device may be positioned so as to be secured to the SMA cage to be used. For instance, as shown in  FIG. 8 , when a tip of the insertion device  200  is placed inside the SMA cage  142 , as compression continues, the SMA cage  142  will be clamped onto the insertion device  200 . This allows for ease of (i) removal of the SMA cage  142  from compression device  100  and (ii) insertion into the patient.  
         [0050]     Once the desired compression of the SMA cage  140  is achieved, the handles  150   a  and  150   b  may be released. When the springs  170   a  and  170   b,  or other such springs, are provided with respect to handles  150   a  and  150   b,  release of the handles  150   a  and  150   b  will be followed by automatic biasing of the handles  150   a  and  150   b  to the open position. In the open position, the compressed SMA cage  140  can be removed through the window  124 .  
         [0051]     When the surgeon, nurse, or technician moves the SMA cage  140  from the compression device  100 , it can be achieved by using a user&#39;s hand(s) or by using a sterile insertion device, such as insertion device  200 .  
         [0052]     The compressed SMA cage  140  can be implanted directly into an area to be treated. This can be achieved by the surgeon directly implanting compressed SMA cage  140 , or by inserting the compressed SMA cage  140  into position using insertion device, such as the insertion device  200 .  
         [0053]     The body heat of the patient will heat the compressed SMA cage  140  above the transition temperature (in instances in which temperature activated SMAs are used), causing compressed SMA cage  140  to expand to its expanded form. At this point, the cage will release its grip on an insertion device being used (such as insertion device  200 ) and the insertion device can be removed. This expansion further secures the SMA cage  140  in the implantation area. Of course, the application of some other stimulus may be provided to the compressed SMA cage  140  or other shape memory material, when the material is not temperature activated. Once the compressed SMA cage  140  is fully or partially secured in position, the surgeon may close the patient.  
         [0054]     Thus, with the compression device  100 , a surgeon can achieve controlled and repeatable compression, providing uniformity from surgery to surgery and preventing the likelihood of cracking of the SMA cage or cold working, which could lead to a defective implant. Thus, implantation of SMA cages can be improved so as to be more reliable, and thus more effective over a wide array of instances.  
         [0055]     While the present invention has been described with respect to what is presently considered to be example embodiments, the present invention is not limited to the disclosed embodiments. Rather, the present invention covers various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the appended claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.