Patent Publication Number: US-2010121381-A1

Title: Surgical method and apparatus for treating spinal stenosis and stabilization of vertebrae

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims priority to provisional applications 61/131,427 filed on Jun. 9, 2008; 61/132,978 filed on Jun. 23, 2008; 61/135,161 filed on Jul. 17, 2008; and 61/201,657 filed on Dec. 15, 2008. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to spinal prosthetic devices and more specifically to apparatus and approaches for interlaminar process, interspinous process, and spinolaminar junction distraction and stabilization for treatment of spinal stenosis. 
     2. Description of the Related Art 
     The spine and its components can become damaged through disease, injury, or natural degeneration. In such cases, the vertebrae no longer articulate or properly align with each other. This can result in deviation from the normal spinal structure, loss of mobility, and pain or discomfort. For example, degenerative phenomena such as spinal stenosis, spondylosis, spondylolisthesis, or osteoarthritis may cause back pain, such as lower back pain localized in the lumbosacral region. Such phenomena may be caused by a narrowing of the spinal canal by pre-existing congenital conditions or injuries such as ligamentum flavum hypertrophy, intervertebral disc bulging or herniation, and facet thickening with arthropathy of the capsule soft tissues that result in the pinching of the spinal cord and/or nerves in the spine. Indeed, lumbar spinal stenosis is a common reason for surgery of the spine in patients over the age of 65. The relevance in the geriatric population makes traditional surgical treatment of spinal stenosis particularly difficult because these patients are at a significantly increased surgical risk because of their pre-existing medical conditions or history. 
     The traditional treatment of spinal stenosis consists of an extensive resection of posterior spinal elements. Additionally, wide muscular dissection and retraction is usually employed to achieve adequate visualization during surgery. Various operative techniques have been used for decades with varying degrees of success. The surgical process and the attendant manipulation of the spine and the tissue surrounding it can also be associated with significant operative blood loss as well as prolonged post-operative pain and weakness at the surgery site. Further, iatrogenic injuries can lead to paraspinal muscle denervation and atrophy, which may correlate with an increased incidence of “failed back syndrome” and chronic pain. Because patients who have stenosis are usually elderly and medically frail, these injuries often cause one or more post-operation complications and a prolonged recovery time. 
     The current management of such spinal conditions may also include the use of prosthetic devices. In all such devices, it is essential to securely anchor the device to the vertebra while not damaging it. It is also desirable to minimize the requisite surgery to place the device in the patient. Furthermore, it is desirable for the device to contain minimal working or moving parts since a complex system could be prone to malfunction and may require more invasive surgery for insertion and calibration. Additionally, it is desirable for a prosthetic device to be able to distract both adjacent and nonadjacent vertebrae and to be able to be functional between the lumbar and the sacral portions of the spine. 
     Present spinal prosthetic devices do not address many of the desirable characteristics mentioned above. For example, many of the current prosthetic devices contain multiple moveable parts that could be prone to mechanical malfunction and may require complex insertion procedures and calibrations. U.S. Pat. No. 4,611,582 to Duff, for example, discloses a device consisting of moveable vertebral clamps that hinge on a ball-and-socket mechanism disposed on a moveable body. The device has to be correctly calibrated in order to control the spatial relationship between the clamps, and thereby between the vertebrae. The Duff device also contains multiple moveable sub-parts that have to be individually calibrated and secured by screws. This system is both complex and could be prone to malfunction. Similarly, U.S. Pat. No. 7,491,238 to Amin et al., discloses a large and complex apparatus comprising multiple moveable mechanical arms secured to multiple spinal structures by fasteners such as screws. The Arnin device is large and contains multiple adjustable parts which could result in complicated insertion surgery requiring extensive manipulation by the surgeon. Similarly, U.S. Pat. No. 7,011,658 to Young discloses a device with opposite first and second engagement ends and a screw-based mechanism for moving the opposite engagement ends in extension and refraction. The Young device additionally utilizes a complex locking and driving mechanism that contains multiple screws and pins that could also complicate the insertion surgery. Similarly, U.S. Pat. No. 5,007,909 to Rogozinski discloses multiple clamps and a rod that are affixed to the lamina of the vertebra, where each clamp is affixed to the vertebrae and the rod through a complex assembly. Given the fact that the Rogozinski device requires multiple clamps and that each clamp has to be calibrated to the vertebrae and the rod, it is likely that a complex insertion and calibration procedure is required. Also, U.S. Pat. No. 4,697,582 to Williams discloses a mechanical assembly with retaining clamps, where each clamp is screwed onto the vertebra and an elastic structure is attached to the retaining clamp fixed to each vertebra. Similar to the Rogozinski device, the Williams device also utilizes multiple clamps where each clamp has to be individually screwed into the vertebrae. 
     Furthermore, many of the current devices are large or their insertion surgical techniques could result in higher risk of post-operative complications. For example, U.S. Pat. No. 7,052,497 to Sherman et al. discloses a loading device that requires two different surgeries for proper insertion and calibration. The multiple surgeries required by the Sherman device could result in increase in recovery time and post-operation complications and also increase the medical cost associated with each surgery. Similarly, U.S. Pat. No. 5,540,688 to Navas discloses a device in the form of a damper attached to two anchor implants that are screwed into two adjacent vertebrae. The need for screwing both ends of the Navas device into the vertebrae complicates the surgical procedure and is likely to cause greater damage to the surrounding tissues. 
     Also, many of the current devices are impractical to function between non-adjacent vertebrae. For example, U.S. Pat. No. 5,415,661 to Holmes discloses a flexible implantable device that is fitted in between, and screwed on to adjacent vertebrae. Given that the device needs to be fitted between two adjacent vertebrae, it is unlikely to function successfully on non-adjacent vertebrae. 
     In addition to the abovementioned limitations, it is impractical for many of the current spinal prosthetic devices to perform distraction on the lumbosacral level. For example, U.S. Pat. No. 5,645,599 to Samani discloses a device comprising a U-shaped body and two pairs of brackets that are fixed to spinous process of adjacent vertebrae. U.S. Pat. No. 6,074,390 to Zucherman et al. discloses a spine distraction implant that alleviates pain associated with spinal stenosis by inserting the device between affected adjacent vertebrae by means of telescoping fork ends, where the fork ends brace the spinous process. Both the Zucherman device and the Samani device are specifically structured to receive the spinous process. However, it is less desirable for either of the devices to be used at the sacral level since the sacrum lacks a significant spinous process to allow for proper docking and distraction. 
     Given the limitations of traditional surgical treatments and current prosthetic devices, there is a need for a novel prosthetic device that embodies the above desirable qualities. Such a device should contain minimal working parts. It should also be insertable with minimally invasive procedure and should be easy to manufacture. It should achieve decompression and alleviation of pain on the lumbosacral junction and be structured to function on adjacent and non-adjacent vertebrae. At least some of these objectives will be addressed by the present invention. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a prosthetic device for distracting and stabilizing spinal column segments in the lumbar and the lumbar-sacral regions by engaging the spinal column segments. Engagement occurs with two engagement arms that are configured to distract the targeted spinal segments to relieve pain and discomfort associated with spinal stenosis or other spinal disorders. 
     In one embodiment, the prosthetic device comprises a first engagement arm and a second engagement arm wherein each of the engagement arms terminates in a lamina receiving configuration that comprises at least two tines that are configured to receive a lamina portion of the spinal column segment. The engagement arms may further comprise a secondary branch or an opening to receive an attachment screw configured to attach to a vertebra. Additionally, the preferred embodiment may be further secured to a lamina portion by a safety band or a screw. 
     The device further comprises a coupling mechanism disposed between the first and the second engagement arms. The coupling mechanism is configured to allow the device to transition from an unextended configuration to an extended configuration in order to distract the spinal column segment. The coupling mechanism of the preferred embodiment may be a joint such as a pivot joint, a revolute joint, a pin joint, or a hinge joint. The coupling mechanism may also be a telescoping mechanism, a spring, a rotation mechanism or a slidable mechanism. 
     Also, the device comprises a locking mechanism that is configured to maintain the extended configuration of the device. The locking mechanism of the preferred embodiment may be a self-locking joint, a fastening screw and an opening configured to receive the fastening screw or a sleeve configured to be placed over the coupling mechanism. 
     Additionally, multiple devices may be used. For example, the devices may be used as part of aa bilateral system comprising two devices working together to distract two or more spinal column segments. Such a bilateral system may further comprise a connecting mechanism such as a U-hook, a process pin or a safety band. 
     Other aspects of the invention include methods corresponding to the devices and systems described above. Such methods include the steps of positioning and securing the prosthetic device by fitting lamina portions of the first and the second spinal portions between the tines of the engagement arms. The preferred embodiment further includes the step of operating the coupling mechanism to extend the first and second engagement arms such that the engagement arms engage with the lamina portions of the first and the second spinal portions to distract the spinal column segment. Furthermore, the preferred embodiment includes the step of operating the locking mechanism by engaging a self-locking joint, inserting a fastener screw into a receiving hole or placing a sleeve over the coupling mechanism in order to maintain the distraction. Additionally and optionally, the method includes the pre-insertion step of separating the ligamentum flavum from the spinal column segments, preparing the lamina portions of the spinal column segments to receive the device and sizing the spinal column segments to determine the desired degree of distraction. Additionally and optionally, the method further includes the step of using the device as a fusion adjunct to supplement posterolateral fusion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a posterior view of the device engaging at L 4  superiorly and S inferiorly on the right and at L 5  superiorly and S inferiorly on the left. 
         FIG. 2A  shows a lateral view of the device. 
         FIG. 2B  shows a lateral view of the device comprising a joint mechanism in partially collapsed and expanded configurations. 
         FIG. 2C  shows the device with at least one dynamic portion. 
         FIG. 2D  shows an embodiment of the device comprising a slidable mechanism. 
         FIG. 2E  shows an embodiment of the device comprising a telescoping mechanism. 
         FIG. 2F  shows an embodiment of the device comprising a spring. 
         FIG. 3A  shows a locking mechanism which uses a screw-type fastener to lock the joint. 
         FIG. 3B  shows a sleeve which can slide onto the hinge portion of the device to lock the hinge. 
         FIG. 4A  shows the inferior and superior engagement arms of the device from a lateral view engaging on L 4  and S. 
         FIG. 4B  shows the device in operation. The device starts out in a contracted configuration, wherein the inferior and superior engagement arms of the device engage and distract L 5  and S 1  spinal column segments. 
         FIG. 4C  shows two devices operating together to distract two spinal column segments. 
         FIG. 5  shows safety bands used to secure the device to the spinal column segment to inhibit movement of the device once implanted. 
         FIG. 6A  shows different configurations of the engagement arms. 
         FIG. 6B  shows one embodiment of the device comprising engagement arms with multiple tines at various orientations. 
         FIG. 6C  shows an alternative embodiment of the device comprising one engagement arm with four tines and a second engagement arm with a fan shaped tine. 
         FIG. 6D  shows the lateral view of an alternative embodiment of the device where one engagement arm with four tines engages L 5  and the other engagement arm with two tines engages S 1 . 
         FIG. 7  shows different possible curvatures of the device. 
         FIG. 8  depicts an alternative embodiment for locking the device in place once implanted. 
         FIG. 9  depicts an alternative embodiment for locking the device in place once implanted. 
         FIG. 10  shows an alternative embodiment that comprises a screw attachment and a multi-branched tine arrangement. 
         FIG. 11  shows one embodiment in which one engagement arm comprises a pin assembly while the other engagement arm comprises two moveable tines connected by a pivot point. 
         FIG. 12  shows one embodiment in which one engagement arm comprises a pin assembly while the other engagement arm comprises two fixed tines. 
         FIG. 13  shows one embodiment in which both engagement arms comprise pin assemblies. 
         FIG. 14A  shows one embodiment in which both engagement arms comprise clamp-like configurations. 
         FIG. 14B  shows one embodiment in which one engagement arm comprises a clamp-like configuration while a second engagement arm comprises a tine configuration. 
         FIG. 15  shows one embodiment in which the device is single bodied with no moveable parts. 
         FIG. 16A  shows an embodiment of the device comprising flared ends. 
         FIG. 16B  shows an embodiment of the device comprising non-flared ends. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Although the detailed description contains many specifics, these should not be construed as limiting the scope of the invention but merely as illustrating different examples and aspects of the invention. It should be appreciated that the scope of the invention includes other embodiments not discussed in detail above. Various other modifications, changes and variations which will be apparent to those skilled in the art may be made in the arrangement, operation and details of the methods and systems of the present invention disclosed herein without departing from the spirit and scope of the invention as described. 
     The present invention is a prosthetic device for distracting spinal column segments in the lumbar and the lumbar-sacral regions by engaging the spinal column segments. Engagement occurs with two engagement arms that are configured to distract the targeted spinal segments to relieve pain and discomfort associated with spinal stenosis or other spinal disorders. Although the device is used for distraction and stabilization, it is contemplated that the device may also be used for inhibition of spinal flexion through attachment around the spinous process and the laminar process. 
     The device may be inserted through a minimally invasive incision and extended after engaging a portion, for example the lamina, of the spinal column segment. The act of extending the device will serve as an internal distraction mechanism for alleviating spinal stenosis by opening the neural foramina in between the segments of interest. This device can also be customized to a patient&#39;s degree of stenosis using a variable adjusting portion. 
     Referring to the figures,  FIG. 1  shows one embodiment of the device oriented within the spinal column. The device  100  can be inserted between adjacent spinal column segments such as the lumbar vertebra five L 5 , and the sacral vertebra one S 1 . Alternatively the device  100 ′ can be inserted between non-adjacent spinal column segments such as the lumbar vertebra four L 4  and the sacral vertebra one S 1 . In this embodiment the device engages with at least one lamina portion of the spinal column segment without disturbing the spinous process SP. For purposes of this description, the term lamina portion is used interchangeably with the terms lamina, and laminar process. Further, for the purposes of this description, all spinal vertebrae, including the sacrum, include a lamina portion that is. Although the device is used for lumbar spinal column segments as well as the lumbosacral junction, it is anticipated that the device may also be used in any spinal column segments, including the cervical and thoracic spinal column segments as well as at the occipital cervical junction. 
       FIG. 2A  shows one embodiment of the device comprising a first engagement arm  110 , a second engagement arm  120 , and a coupling mechanism  130  disposed between the first engagement arm  110  and the second engagement arm  120 . The first engagement arm  110  terminates in a lamina receiving configuration that comprises at least one projection such as a tine. For example as shown in  FIG. 2A , the device comprises a first tine  111  and a second tine  112  (which together form a clevis with an intermediate region shaped to receive the lamina). The tines may be of various shapes, sizes, or lengths. As shown in  FIG. 2A , for example, the first tine  111  is longer than the second tine  112 . Similar to the first engagement arm, the second engagement arm  120  terminates in a lamina receiving configuration that comprises at least one projection such as a tine. As shown, the second engagement arm comprises tines  121  and  122 . These tines too may be of various shapes, sizes, and lengths. As shown in  FIG. 2A , for example, the first tine  121  may be longer than the second tine  122 . Furthermore, the size, shape, or length of the tines  111  and  112  are independent of the size, shape, or length of tines  121  and  122 . In certain specific embodiments, however, the devices of the present invention will generally be symmetrical on each side being formed as mirror images with the structure joining the tines being straight or slightly arched or alternatively, being resilients joined as illustrated in later embodiments. 
       FIG. 2B  shows one embodiment of the device where the first engagement arm  110  and the second engagement arm  120  are connected by a coupling mechanism  130 . In this embodiment, the coupling mechanism  130  comprises a joint  131 . The joint allows the first engagement arm  110  and the second engagement arm  120  to transition to an extended configuration as indicated by arrow I by unfolding away from each other in the direction indicated by the arrows II and III while maintaining the structural integrity of the device. In  FIG. 2B , a hinge joint is shown. However, the joint may be a pivot joint, a revolute joint, a pin joint, or any other joint configured to foldably connect the engagement arms  110  and  120 . 
     As shown in  FIG. 2C , the device optionally further comprises at least one dynamic portion  140  that is capable of contracting or expanding upon the application of biomechanical force within the body, thereby providing flexibility while maintaining distraction of spinal column segments. The dynamic portion may damp, absorb, or otherwise reduce the impulse created by the biomechanical force The dynamic portion may comprise a defined area of either one or both of the two engagement arms, or the dynamic portion may comprise the entirety of either one or both of the two engagement arms. The dynamic portion may also be incorporated onto a surface of either one or both of the two engagement arms. The dynamic portion may comprise any or a combination of a variety of biocompatible dynamic materials, such as polyetheretherketone (PEEK). In addition, a variety of growth factors, such as bone morphogenetic protein (BMP), may be incorporated into the device as a fusion adjunct to stimulate bone deposition and growth. Optionally, the device may also be made of a bioresorbable material such as polylactic acid (PLA). Furthermore, the entirety or a portion of one or more engagement arms may be made of or be coated by a material to provide better docking or interfacing between the device and the vertebrae. This material may be compliant, and formed from such materials as rubber or plastic. 
       FIG. 2D  shows another embodiment of the device where the first engagement arm  110  and the second engagement arm  120  are connected by a coupling mechanism comprising a slidable mechanism  132 . The slidable mechanism  132  comprises a first sliding end  133  and a second sliding end  134  configured to slide relative to each other to extend the device. As shown in  FIG. 2D , the first end  133  is a male end and the second end  134  is a female end joined in a telescoping manner. Alternatively the first and second sliding ends may comprise a side-by-side sliding mechanism, for example using tracks or brackets to join the arms together. As shown in  FIG. 2D  the device starts out in an axially contracted configuration. During or after insertion between the spinal column segments, the engagement arms are pulled axially apart in the direction of the arrows II and III so that the two engagement arms  110  and  120  slide and extend away from each other, thereby transitioning the device to an extended configuration as indicated by arrow I. At the extended configuration, the slidable mechanism  132  optionally snaps into position using a detent or other locking mechanism to maintain the extended configuration. Optionally, in this embodiment, the device may include springs or other resilient mechanism to provide dynamic characteristics wherein the sliding ends may be able to slide within a range after insertion without bending the device. 
       FIG. 2E  shows another embodiment of the device comprising a first engagement arm  110 , a second engagement arm  120 , and a coupling mechanism comprising a telescoping mechanism  190 . The telescoping mechanism  190  may comprise a bolt and screw expanding assembly wherein by turning the bolt, the assembly expands the body of the device. Alternatively, the telescoping mechanism may be any assembly that is able to elongate the body of the device such as a rotation mechanism that is effected by turning or rotating the engagement arm(s). 
       FIG. 2F  shows another alternative embodiment of the device comprising a first engagement arm  110 , a second engagement arm  120 , and a coupling mechanism comprising a spring  195 . The spring  195  comprises a spring  196 . The device is first compressed into the compressed state as shown by arrows VI and VII to load the potential energy in the spring. Compression may be achieved by using one of various compression tools known by those skilled in the art. Alternatively, the spring is pre-compressed during manufacturing. During insertion, the spring is released to transform the device into the extended state as shown by arrow I by pushing the two engagement arms  110  and  120  away from each other in the directions shown by arrows II and III. Additionally and optionally, the spring  195  may comprise a spring  196  housed within a sleeve  197 . The sleeve  197  may be a sliding tube, sheath or other configuration made of compressible material. 
     Additionally and optionally, to further enhance device stability and retention, the first and the second engagement arms may be secured to the spinal column segments by using screws  151  that are received by holes  113 , which are located on the engagement arms. 
     Although the coupling mechanisms described above are described with respect to one embodiment of the device, it should be noted that any coupling mechanism may be used in conjunction with any embodiment described herein. 
     Additionally, as shown in  FIG. 3A  the device comprises a locking mechanism  150 . In one example embodiment, the locking mechanism  150  is a self-locking joint comprising a self-locking assembly. In such an embodiment, when the foldable arms engage with and distract the spinal column segments, the self-locking joint assembly locks automatically upon fully unfolding the arms. Additionally and optionally the locking mechanism may comprise a fastener screw  151  received by a hole in the device (hole not shown). Furthermore, the locking mechanism may comprise a fastener screw independent of the self-locking joint. The fastener screw may be of any shape, size, or design as long as the screw is configured to be inserted into the device without disturbing the interspinous ligament. The fastener screw may be made of titanium or any other biocompatible material. 
     Alternatively, as shown in  FIG. 3B , the device comprises a locking mechanism  150  and a moveable sleeve  152 . The moveable sleeve can be placed or slid over the point of extension such as the joint or the contact position of the sleeve. Additionally and optionally, the sleeve may be further secured by a fastener screw  151 . The sleeve may be of any shape, size, length, or design as long as the sleeve covers the coupling mechanism in a manner that inhibits the coupling mechanism from moving. The sleeve may be made of titanium or any other biocompatible material. 
     Although the locking mechanisms described above are described with respect to one embodiment of the device, it should be noted that any locking mechanism may be used in conjunction with any embodiment described herein. For example, locking mechanisms such as one or more turn-key mechanisms, a clamp or a clasp, may be used to maintain the expanded configuration of the device. 
     Prior to insertion of the device, a separating device (not shown) may be used to separate the ligamentum flavum from the lamina portion of the spinal column segment. Furthermore, a sizing device (not shown) may be used to determine the desired degree of distraction. Optionally, the lamina portion of the spinal column segment may be prepared to receive the device by creating an indentation at the engagement site on the lamina portion by using a rongeur. Also, the desired degree of distraction may be first achieved by using tools and methods known in the art before the device is inserted. 
       FIG. 4A  shows the device being inserted into the spinal column as exemplified by arrow I. During insertion, as shown by arrow II and arrow III, the first engagement arm  110  and the second engagement arm  120  transitions from the unextended position to the extended position. For example, in the embodiment shown, the coupling mechanism comprises a joint wherein the unextended position is the folded position and the extended position is the unfolded position. Alternatively, if the coupling mechanism comprises a slide, the unextended position may be the shortened position and the extended position may be the expanded position. The device may be inserted manually or may be inserted by using a holder implement (not shown). The holder implement may be used to hold the device in the unextended configuration and positions the device for insertion. Once the device is inserted, the holder implement may be used to engage the device with the spinal column segments and transform the device to the extended position. The holder implement may comprise a handle of any appropriate size or shape. Optionally, the holder may further comprise magnetic prongs to hold the device during insertion. 
       FIG. 4B  shows the device distracting the targeted spinal column segment where the first engagement arm  110  engages with the lamina portion of a spinal column segment such as L 5 . The second engagement arm  120  engages with a lamina portion of a different spinal column such as S 1 . The lamina portions engaged by the first and the second engagement arms  110  and  120  can be lamina portions of any sacral vertebrae, lumbar vertebrae, thoracic vertebrae, or cervical vertebrae. The coupling mechanism  130  disposed in between the first and second engagement arms is adjusted, for example, by pushing on the hinge joint to unfold the engagement arms  110  and  120 . This alters the spatial relationship between the two spinal column segments by expanding the distance between the two spinal column segments. Alternatively, if a slidable or telescoping mechanism is used, the two engagement arms  110  or  120  are extended apart. Thus, the device is able to achieve distraction of the spinal column segments in the direction shown by arrows IV and V. The locking mechanism, if a self-locking mechanism is used, will automatically lock when the arms achieve their intended unfolded configuration. Additionally or alternatively, if a non-self locking mechanism such as a screw sleeve, or any other suitable locking mechanism, is used, it is then engaged to maintain the extended position of the engagement arms. Additionally, the device may achieve distraction to multiple levels of spinal column segments. For example, the engagement arms of the device may engage with L 4  and S 1  spinal column segments which results in distraction to both L 4 -L 5  and L 5 -S 1  junctions. 
       FIG. 4C  shows two devices working together as a bilateral distraction system to provide additional distraction or support. The first engagement arms  110  of both devices are attached to one spinal column segment while the second engagement arms  120  of both devices are attached to the second spinal column segment. Two devices may be connected by a connecting mechanism  180  to provide additional support and stabilization. The connecting mechanism may be a U-hook, an interspinous process pin, a safety band or any other suitable connecting mechanism. 
     Additionally and optionally, to further enhance device stability and retention other approaches could be used for securing the device to the vertebrae. For example, the device may be secured by a safety band  170  as shown in  FIG. 5 . The safety band  170  is placed across a tine on the dorsal portion of the lamina, and the ends of the safety band  170  are secured to the vertebra. The band  170  may be of any shape, size, length, or design suitable to aid in securing the engagement arms to the spinal column segments. The safety band may be made of any biocompatible material. Additionally and alternatively, the engagement arms of the device can be configured to receive a screw, and the device may be screwed onto some portion of a vertebra. 
     The number, size, shape, length, or orientation of the projections configured to receive a lamina may be specifically adapted or customized to best fit the targeted spinal column segment. For example,  FIG. 6A  shows three different configurations. The configurations shown comprises tines, however any projections may be used. In one configuration  200 , an engagement arm terminates in a lamina receiving configuration that comprises three tines, a first tine  201 , a second tine  202  and a third tine  203 . The tines are configured such that the first and the second tines  201  and  202  are oriented dorsal to the spinal column segment (e.g., the lamina) when engaged while the third tine  203  is oriented ventral to the spinal column segment. In another configuration  300 , an engagement arm terminates in a lamina receiving configuration that comprises four tines, a first tine  301 , a second tine  302 , a third tine  303  and a forth tine  304 . The tines are oriented such that the first tine  301  and the second tine  302  are oriented dorsal to the spinal column segment (e.g., the lamina), whereas the third tine  303  and the forth tine  304  are oriented ventral to the spinal column segment. In another configuration  400 , an engagement arm terminates in a lamina receiving configuration that comprises three tines, a first tine  401 , a second tine  402  and a third tine  403 . In this embodiment, the third tine  403  is configured to be broader than tines  401  and  402 . The tines are configured such that the first tine  401  and the second tine  402  are oriented dorsal to the spinal column segment (e.g., the lamina), and the third tine  403  is oriented ventral to the spinal column segment. 
     One embodiment of the device comprises additional projections such as tines at various orientations as shown in  FIG. 6B . The device comprises a first engagement arm  510  and a second engagement arm  520 . The first engagement arm comprises a first tine  511  and a second tine  512 , wherein the first and second tines  511  and  512  are configured to engage with a spinal column segment such as the spinous process. The second engagement arm comprises a first tine  521 , a second tine  522 , and a third tine  523 . The tines are configured such that the first and the second tines  521  and  522  engage the dorsal portion of the spinal column segment (e.g., the lamina) while the third tine  523  engages the ventral portion of the spinal column segment. 
     Alternatively, as shown in  FIG. 6C , the device comprises a first engagement arm  610 , a second engagement arm  620 , and a coupling mechanism  630 . The first engagement arm  610  comprises projections such as a first tine  611 , a second tine  612 , a third tine  613  and a forth tine  614 . The second engagement arm  620  comprises a first tine, not shown, and a second tine  622 . The tines may vary in shapes, sizes, lengths or design. For example, the second tine  622  is shown comprising a broader configuration than the first tine (not shown). As shown in  FIG. 6D , the first tine  611  and the forth tine  614  are oriented to ventrally engage a spinal column segment (e.g., the spinous process) wherein the second and the third tines  612  and  613  are oriented to dorsally engage the spinal column segment (e.g., the spinous process). The tines of the second engagement arm  620  are configured such that one of the tines is configured to fit dorsal to the spinal column segment (e.g., the sacral lamina) whereas the other tine is configured to fit ventral to said spinal column segment. 
       FIG. 7  shows another embodiment of the device comprising a first engagement arm  710 , a second engagement arm  720 , and a curved body  730  therebetween. The curved body may comprise double curves as shown, but may also comprise a single curve or multiple curves. The curved body can have various degrees of curvature to best fit the contour of the patient&#39;s body or to provide dynamic load-bearing support. It is further contemplated that any of the embodiments described herein may comprise a curved body. 
       FIG. 8  shows yet another embodiment of the device comprising a first engagement arm  810  and a second engagement arm  820 . The first engagement arm further comprises projections such as a first tine  811  and a second tine  812 . Both the first tine  811  and the second tine  812  are configured to receive the lamina portion of a spinal column segment. The second engagement arm comprises a first tine  821  and a second tine  822 . The first tine  821  has a fixed position, and the second tine  822  is configured to revolve around a self-locking pivot point  823 . During insertion of the device into a patient&#39;s body, the first engagement arm  810  engages the lamina portion of a spinal column segment. The first tine  821  of the second engagement arm initiates the engagement of the lamina portion of a second spinal column segment by coming into contact with the lamina. Then, the second tine  822  of the second engagement arm revolves around the self-locking pivot point from a neutral position to an engagement position by coming into contact with the lamina. The self-locking pivot point then locks the second tine  822  in the engagement position and thus completes the engagement of the lamina portion of the second spinal column segment. 
       FIG. 9  shows another embodiment of the device comprising a first engagement arm  910  and a second engagement arm  920 . The first engagement arm comprises projections such as a first tine  911  and a second tine  912 . The tines  911  and  912  are configured to receive a lamina portion of a spinal column segment. The second engagement arm comprises a first tine  921  and a second tine  922 . The first tine  921  has a fixed position, and the second tine  922  is a separate body insertable into the main body of the device  900 , for example by using a pin  923  that is received by one of one or more outlets  930 . During insertion, the first engagement arm  910  engages the lamina portion of a spinal column segment. The first tine  921  of the second engagement arm also engages a lamina portion of a second spinal column segment by contacting the lamina. Then, the second tine  922  of the second engagement arm  923  is inserted into the appropriate outlet  930 , thus contacting a lamina portion. The pin  923  and outlet  930  then lock the second tine  922  and thus engage the lamina portion of the second spinal column segment. 
       FIG. 10  shows another embodiment of the device comprising a first engagement arm  1010  and a second engagement arm  1020 . The first engagement arm further comprises a fixation pin  1011  and a pin receiving opening  1012 . The second engagement arm comprises a first tine  1021 , a second tine  1022 , and at least one additional branch  1030  comprising at least two tines, for example, a third tine  1031  and a forth tine  1032 . During insertion of the device into a patient&#39;s body, the first engagement arm  1010  is fixed onto a spinal column segment by inserting the pin  1011  through the opening  1012  and securing the pin  1011  onto the spinal column segment. The second engagement arm  1020  engages the sacrum by receiving the lamina portion of the sacrum between tines  1021 ,  1022 ,  1031  and  1032 . 
     In an alternative embodiment, as shown in  FIG. 11 , the device comprises a first engagement arm  1110  and a second engagement arm  1120 , a coupling mechanism  1130 , and a dynamic portion  1140 . The first engagement arm comprises a fixation pin  1111  and a receiving opening (not shown) that is configured to receive the fixation pin  1111 . The second engagement arm comprises projections such as a moveable first tine  1122  and a moveable second tine  1123  connected by a pivot  1121  enabling the tines to move from an unfolded position to a folded position. During insertion of the device into a patient&#39;s body, the first engagement arm  1110  is configured to attach to the first spinal column segment by inserting the pin  1111  through the receiving opening and into the spinal column segment. The second engagement arm  1120  is configured to receive the second spinal column segment (e.g., sacral lamina) by moving the first and second tines  1122  and  1123  from an unfolded position to a folded position, as illustrated by the arrows in  FIG. 8D . The coupling mechanism  1130  may comprise an expanding mechanism that may be adjusted to alter the spatial relationship between the two spinal column segments in order to achieve the desired degree of distraction. The dynamic portion  1140  is capable of contracting or expanding upon the application of biomechanical force within the body, thereby providing flexibility while maintaining proper spinal distraction. 
     Alternatively,  FIG. 12  shows the device comprising a first engagement arm  1210 , a second engagement arm  1220 , a coupling mechanism  1230 , and a dynamic portion  1240 . The first engagement arm comprises a fixation pin  1211  and a receiving opening (not shown) that is configured to receive the fixation pin  1211 . The second engagement arm  1220  comprises projections such as at least two tines, for example, the first tine  1221  and the second tine  1222 . During insertion, the first engagement arm  1210  is configured to attach to the first spinal column segment by inserting the pin  1211  through the receiving opening and into the spinal column segment. The second engagement arm  1220  is configured to receive the second spinal column segment (e.g., sacral lamina) between the tines  1221  and  1222 . A further embodiment shown in  FIG. 13  comprises a first engagement arm  1310  and a second engagement arm  1320 . The first engagement arm  1310  may be attached to a spinal column segment such as the spinous process or the spinolaminar junction by inserting an attachment pin  1311  through a receiving opening (not shown) and into the spinal column segment. The attachment pin  1311  may then be locked in place by a locking cap  1312 . The second engagement arm  1320  may be attached to another spinal column segment by inserting an attachment pin  1321  through a receiving opening (not shown) and into the spinal column segment. The attachment pin  1321  may then be locked in place by a locking cap  1322 . 
     An alternative embodiment (not shown) similar to the one disclosed in  FIG. 13  comprises a first engagement arm and a second engagement arm wherein the first and the second engagement arms terminate in U-shaped brackets. The U-shaped brackets are each shaped to receive the spinous processes of a spinal column segment. The U-shaped brackets may engage either unilaterally or bilaterally around the spinous processes. 
     In another embodiment as shown in  FIG. 14A , the device comprises a first engagement arm  1410 , a second engagement arm  1420  and a coupling mechanism  1430 . The first and the second engagement arms comprise clamp-like configurations that are configured to receive spinous processes of adjacent or non-adjacent spinal column segments. The coupling mechanism  1430  may be made of dynamic material or may comprise a spring or other load sharing mechanism. Alternatively, as shown in  FIG. 14B , the second engagement arm  1420  may terminate in a sacrum receiving configuration, for example the second engagement arm  1420  comprises tines  1421  and  1422  configured to receive the sacrum. The second engagement arm  1420  in the embodiment shown in  FIG. 14B  may be secured for additional stability to the sacrum by using a screw  1440  received by a hole  1423  located on the second engagement arm  1420 . Additionally, the engagement arm configuration exemplified in  1430  may be adapted to receive a lamina portion of the spinal column segment in addition to the sacrum. 
     In another embodiment as shown in  FIG. 15 , the device comprises a first engagement arm  1510  and a second engagement arm  1520 . The first and the second engagement arms  1510  and  1520  are configured to engage with the lamina portions of the spinal column segment. The first and the second engagement arms  1510  and  1520  may be secured to the spinal column segment by using screws  1540  received by receiving holes  1511  and  1521  located on the engagement arms. The receiving hole may be slotted as shown in  1511  or the receiving hole may be fitted as shown in  1521 . The first engagement arm and the second engagement arms  1510  and  1520  are coupled together by a body  1530 . The body  1530  may be rigid. During insertion, proper degree of distraction is first achieved by using methods and tools known to those skilled in the art, then the device embodied in  FIG. 15  is inserted into the distraction site to maintain the distraction. 
     Additionally and optionally, as shown in  FIG. 16A , the engagement arms of the device may comprise flared ends. Alternatively, as shown in  FIG. 16B , the engagement arms of the device may comprise non-flared ends. Alternatively, one engagement arm may have a flared end while the other engagement arm may have a non-flared end (not shown). Arms  110  and  120  are exemplarily shown; however, any of the arms described here may have said flared or non-flared configurations. The flared and non-flared configurations are selected to produce a customized fit to a particular patient&#39;s vertebrae. The flared and non-flared configurations may also be altered and the width or angle customized to accommodate an individual patient&#39;s anatomy and pathology. 
     In another embodiment of the device, axial rotation of one or both ends of the device may be allowed to better accommodate the natural motion of the spine. This can be accomplished anywhere along the length of the device, either within an existing coupling mechanism or with a swiveling mechanism located at one or both ends of the device which allows the pronged ends of the device to rotate about the long axis of the device. 
     While the above is a complete description of the preferred embodiments of the invention, various alternatives, modifications, and equivalents may be used by those skilled in the art. Therefore, the above description should not be taken as limiting the scope of the invention which is defined by the appended claims.