Abstract:
A sacral reconstruction fixation device aids in stabilizing the pelvis and the lumbar spine after a sacrectomy in cooperation with a spinal rod and transiliac rod. A pair of the fixation devices may be secured to respective ilia and respective spinal rods. The transiliac rod may be secured to both of the fixation devices. The fixation devices include first and second parts that are initially relatively rotatable about a common axis to aid in connecting the fixation devices to the spinal rod and transiliac rod. The body part is intended to be mated to the spinal rod, while the second part is intended to be mated to the transiliac rod. The fixation device&#39;s parts are subsequently locked against rotation and against longitudinal translation, advantageously both relative to each other and the rods.

Description:
BACKGROUND  
       [0001]    The invention relates to a fixation device to aid in the stabilization of the pelvis and the lumbar spine after a sacrectomy. 
         [0002]    Removal of the sacrum, while undesirable, is sometimes necessary. For example, a malignant or benign tumor may be found in the sacrum, and removal of the sacrum may be the best treatment option. However, the sacrum performs two structural functions: vertically supporting the spine and securing the ilia of the pelvis against relative lateral displacement. Thus, during a sacrectomy surgical procedure, a surgeon may find it desirable to install an artificial construct for performing these structural functions. Typically, such a construct is custom made and involves the use of rods anchored to the ilia via the Galveston technique and joined to other rods anchored to the vertebrae of the spine. Installing such a construct increases the complexity and time required for the surgical procedure. 
         [0003]    While the above approach may be appropriate for some situations, there remains a need for alternative surgical methods and devices for stabilization of the pelvis and the lumbar spine after a sacrectomy, advantageously ones that are compact and easy to use. 
       SUMMARY  
       [0004]    In one illustrative embodiment, a sacral reconstruction fixation device is provided for stabilization of the pelvis and the lumbar spine after a sacrectomy in cooperation with a spinal rod and transiliac rod. A pair of the fixation devices may be secured to respective ilia and respective spinal rods. The transiliac rod may be secured to both of the fixation devices. The fixation devices include first and second body parts that are initially relatively rotatable about a common axis to aid in connecting the fixation devices to the spinal rod and transiliac rod. The first body part is intended to be mated to the spinal rod, while the second body part is intended to be mated to the transiliac rod. The fixation device&#39;s body parts are subsequently locked against rotation and against longitudinal translation, advantageously both relative to each other and the rods. Additional embodiments and related methods are also disclosed. For example, a convexly curvate body having a central bore therethrough of variable size may be disposed in the second body to aid in joining to the transiliac rod; the fixation device may also accept a second transiliac rod; and/or the first body may be allowed to have selectively lockable polyaxial motion relative to the iliac screw anchoring the first body to the ilia. The various disclosed aspects and embodiments may be used alone or in any combination. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0005]      FIG. 1   FIG. 1  shows a human pelvic girdle and partial spinal column. 
           [0006]      FIG. 2  shows a posterior view of one embodiment of a sacral reconstruction fixation construct. 
           [0007]      FIG. 3  shows one spinal rod embodiment suitable for use in the sacral reconstruction fixation construct of  FIG. 2 . 
           [0008]      FIG. 4  shows one embodiment of a fixation device suitable for use in the sacral reconstruction fixation construct of  FIG. 2 . 
           [0009]      FIG. 5  shows a cross-section of the fixation device of  FIG. 4  in the adjustable configuration. 
           [0010]      FIG. 6  shows a cross-section of the fixation device of  FIG. 5  in the locked configuration. 
           [0011]      FIG. 7  shows a surgical tool applying a compressive force between the end of spinal rod and the superior face of the fixation device. 
           [0012]      FIG. 8  shows a cross-section of another embodiment of a fixation device with a compressible insert for clamping the transiliac rod in the corresponding connector body. 
           [0013]      FIG. 9  shows a cross-section of another embodiment of a fixation device suitable for mating to multiple transiliac rods. 
       
    
    
     DETAILED DESCRIPTION  
       [0014]    The sacrum  16  is an inferior portion of the spinal column  10  that helps join the spinal column  10  to the pelvic girdle  20 . The sacrum  16 , in a healthy spine, provides a base that vertically supports the remainder of the spinal column  10  and typically directly supports the vertebra  12  in the lumbar region know as the L 5  vertebra. In addition, the sacrum  16  helps maintain the pelvic girdle  20  against collapse. In particular, the sacrum  16  is disposed in the gap  26  between the right and left ilia  22 , 24 , and helps keep the posterior portions of the ilia  22 , 24  spaced from one another. As indicated above, it is sometimes necessary or desirable to remove the sacrum  16  for a variety of reasons. Illustrative embodiments of the present invention provide stabilization of the pelvis and the lumbar spine after a sacrectomy. 
         [0015]    One embodiment of a sacral reconstruction fixation construct is shown in  FIG. 2 , and generally indicated at  28 . The construct of  FIG. 2  includes a fixation device  50  that is simultaneously anchored to an ilium  22  or  24 , fixed to a spinal rod  30 , and fixed to a transiliac rod  40 . The spinal rod  30  and fixation device  50  jointly vertically act to support the spinal column  10  from the ilium  22  or  24 . The transiliac rod  40  and the fixation device  50  jointly act to stabilize the pelvic girdle  20  by holding the ilia  22 , 24  in fixed relative positions. Advantageously, the transiliac rod  40  is secured on each end by a fixation device  50 , with each fixation device  50  anchored to a respective ilium  22  or  24  and to a respective a spinal rod  30 . Thus, the fixation construct shown in  FIG. 2  includes a transiliac rod  40 , a right fixation device  50  anchored to a right ilium  22  and secured to a right spinal rod  30 , and a left fixation device  50  anchored to a left ilium  24  and secured to a left spinal rod  30 . 
         [0016]    The spinal rods  30  are advantageously substantially similar. As such, only the right spinal rod  30  will be discussed; it being understood that the left spinal rod  30  is substantially similar. The spinal rod  30  may take the form of a L-shaped rod of generally constant outer diameter. The superior portion  32  of the spinal rod  30  is advantageously generally straight or slightly curved to follow the natural curve of the lower spine. The superior portion  32  joins to the inferior portion  34  proximate an approximately 90° bend  36 . The inferior portion  34  is likewise advantageously generally straight or slightly curved. The distal end  38  of the spinal rod  30  is advantageously enlarged, such as being formed as a Morse taper. The spinal rod  30  may be a single unitary member, or may be formed in sections that are joined end to end. The spinal rod  30  may be made of any suitable material, such as 5.5 mm or 6.35 mm diameter titanium rod stock. The superior portion  32  of the spinal rod  30  is secured to the spinal column by suitable means. For example, the spinal rod  30  may be secured to the L 4  and L 5  vertebrae by suitable polyaxial pedicle screws  31 . 
         [0017]    The transiliac rod  40  may advantageously take the form of a straight, constant diameter rod of length suitable to extend from the left fixation device  50  to the right fixation device  50 . The transiliac rod  40  may be made of any suitable material, such as 5.5 mm or 6.35 mm diameter titanium rod stock. 
         [0018]    One embodiment of a fixation device  50  is shown in  FIGS. 2 and 4 . The fixation device  50  generally includes a superior connector body  60 , an inferior connector body  80 , and an iliac screw  100 . The superior connector body  60  may take the form of generally hollow cylindrical body. A rod-receiving passage  66  extends through the superior connector body  60  from the superior face  62  to the inferior face  64 . This passage  66  is advantageously generally straight along axis  68 , and is intended to receive the corresponding spinal rod  30 . The superior connector body  60  may include an annular cavity  70  that opens to the inferior face  64 , for reasons discussed further below. If desired, the inferior face  64  of the superior connector body  60  may include suitable surface texturing (e.g., small radial ridges/ribs, roughened texture, etc.) to aid in engaging the superior face of the inferior connector body  80 , as discussed further below. The superior connector body  60  further includes locking elements  72 , 74  disposed on either side of axis  68  that are moveable relative to the remainder of the superior connector body  60 . Locking element  72  typically takes the form of a set screw that may be driven toward axis when appropriate. Thus, locking element  72  is moveable between an initial position relatively farther from axis  68  and a locking position relatively closer to axis  68 . Locking element  74  may take the form of an annular body with a generally spherically shaped side disposed toward iliac screw  100 . Locking element  74  is moveable between an initial position relatively closer to axis  68  and a locking position relatively farther from axis  68 . This locking element  74  is intended to be compressed between the spinal rod  30  and the head  102  of iliac screw  100  so as to fix the relative angle β between iliac screw  100  and axis  68 , and thus the angular relationship between the iliac screw  100  and superior connector body  60 . This locking element  74  functions similar to what is sometimes referred to as a “crown” in a polyaxial pedicle screw. 
         [0019]    The inferior connector body  80  may take the form of a laterally oriented U-shaped element, with a superior end section  82 , an inferior end section  84 , and an intermediate lateral bridging section  88 . The superior end section  82  may advantageously be relatively elongate and flat, with an aperture  86 a therethrough about axis  68 . A plurality of retention prongs  83  extend superiorly from the superior end section  82  into the annular cavity  70  of superior connector body  60 . These retention prongs  83  may include suitable flanges/barbs to ensure that the inferior connector body  80  remains mated to the superior connector body  60 . Further, the superior face of the inferior connector body  80  may include suitable surface texturing for engaging with the inferior face of the superior connector body  60  when the two are pressed together, as discussed further below. The inferior end section  84  is likewise advantageously relatively elongate and flat, with an aperture  86   b  therethrough about axis  68 . This aperture  86   b  may be in the form of a tapered hole, as shown in the Figures. The combination of aperture  86   a  and aperture  86   b  together form a passage  86  that is disposed about axis  68 . The intermediate lateral section  88  may advantageously take the form of a curvate section that forms a generally round passage  90  disposed transverse to axis  68 . This passage  90  is intended to receive the transiliac rod  40 . The passage  90  is variably sized such that it is relatively larger when the superior end section  82  and inferior end section  84  are spaced apart, and relatively smaller when superior end section  82  and inferior end section are pressed together  84 . 
         [0020]    The iliac screw  100  includes a head portion  102  and a shank portion  104  that extends from the head portion  102  along screw axis  108 . The head portion  102  is advantageously generally spherical with a faceted central drive recess  103  disposed away from shank  104 . The head portion  102  is configured to cooperate with a corresponding receiving chamber in superior connector body  60 , and may be inserted into the chamber in a direction toward axis  68 , and held mated to the superior connector body  60  by a suitable retaining ring  76  that forms an external boundary of the chamber. The shank portion  104  advantageously includes a threaded portion  105  disposed toward head portion  102 , and an unthreaded portion  106  disposed distal from head portion  102 . For additional information about this shank arrangement for an iliac screw, attention is directed to U.S. Pat. No. 5,643,264 to Sherman et al., which is incorporated herein by reference. The iliac screw  100  may advantageously be mated to the superior connector body  60  in a lockable polyaxial fashion, similar to a polyaxial pedicle screw. Thus, the shank portion  104  of iliac screw  100  may be disposed a wide variety of angular relationships with respect to axis  68  of superior connector body  60  until the polyaxial motion is locked down. 
         [0021]    The fixation device  50  may assume at least two different configurations. In a first configuration, referred to as the adjustable configuration, the superior connector body  60  and the inferior connector body  80  may be rotated relative to each other about axis  68 . Further, the superior face of inferior connector body  80  is advantageously slightly spaced from the inferior face  64  of superior connector body  60  so as to form a gap X therebetween, and passage  90  of inferior connector body  80  is relatively larger in size. In order to allow gap X to be present, annular chamber  70  in superior connector body  60  may be suitably oversized relative to prongs  83  so as to allow some longitudinal displacement of inferior connector body  80  away from superior connector body  60  generally parallel to axis  68 . In the second configuration, referred to herein as the locked configuration, the superior connector body  60  and inferior connector body  80  are prevented from rotating or being displaced relative to each other. Further, the superior end portion  82  and inferior end portion  84  of inferior connector body  80  are displaced toward each other, and advantageously touching, so that passage  90  is reduced in size from its size in the adjustable configuration. Also, the iliac screw  100  is angularly fixed relative to superior connector body  60  in the locked configuration. 
         [0022]    The sacral reconstruction fixation construct  28  of  FIG. 2  is installed during a surgical procedure sometimes known as a sacrectomy. For this procedure, the surgeon prepares the surgical site and removes the sacrum  16  in a conventional fashion, typically using a combined anterior-posterior approach. See the article entitled “Surgical Treatment Of Primary Sacral Tumors: Complications Associated With Sacrectomy” by Dr. Mehmet Zileli et al., Neurosurgical Focus, volume 15, November 2003, which is incorporated herein by reference. Pedicle screws  31  are then attached to the relevant vertebrae  12  on each lateral side of the spinous process and initial pilot holes drilled in the ilia  22 , 24 . A fixation device  50  is then anchored to each ilia  22 , 24  by driving the iliac screws  100  into the corresponding ilia  22 , 24 . This may be achieved by removing the set screw  72  from the superior connector body  60  of the fixation device  50 , and driving the iliac screw  100  via driving recess  103  in a fashion similar to seating a polyaxial pedicle screw. At this time, the fixation device  50  is in the adjustable configuration so that superior connector body  60  and inferior connector body  80  may be relatively rotated about axis  68 . The relevant spinal rod  30  is then fed through passage  66  and passage  86  and up toward pedicle screws  31 . The tapered end  38  of spinal rod  30  may engage the tapered aperture  86   b  in inferior connector body  80 , but is not tightly held thereagainst at this time. The same procedure is repeated for anchoring the other fixation device  50  to the other ilium  24 , 22  and loosely connecting the same to the corresponding spinal rod  30 . The transiliac rod  40  is then fed into the passages  66 , 86  of the respective fixation device  50 . It should be noted that the ability of the inferior connector bodies  80  to rotate relative to their axis  68  helps facilitate the insertion of the transiliac rod  40 . A surgical tool  120  is then used to press against the tapered end  38  of a given spinal rod  30  and the superior face  62  of superior connector body  60 . This causes superior connector body  60  and inferior connector body  80  to be pressed together, locking down further relative rotation. The set screw  72  is then driven against the spinal rod  30  to clamp the spinal rod  30  between the set screw  72  and crown  74 . This action also has the effect of locking down the polyaxial motion of iliac screw  100  relative to superior connector body  60  and therefore relative to spinal rod  30 . The fixation device  50  is now in the locked configuration, with the inferior connector body  80  and superior connector body  60  relatively locked, the fixation device  50  fixed to spinal rod  30  and transiliac rod  40 . The same procedure is then used on the other fixation device  50  to place it in the locked configuration. The surgical procedure then proceeds as appropriate, and the surgical site is closed. 
         [0023]    The presence of the sacral reconstruction fixation construct  28  provides vertical support to the spinal column  10 . In particular, the spinal column  10  is supported by the spinal rods  32  which are in turn supported by the ilia  22 , 24  via the fixation devices  50 . Thus, the spinal column  10  is vertically supported by the pelvic girdle  20  via the sacral reconstruction fixation construct  28 . In addition, the presence of the sacral reconstruction fixation construct  28  helps prevent the pelvic girdle  20  from collapsing. The transiliac rod  40  provides resistance against the two anchoring points (e.g., at iliac screws  100 ) moving toward or away from each other. Thus, the sacral reconstruction fixation construct  28  performs the dual functions of supporting the spinal column  10  and maintaining the pelvic girdle  20  against collapse. In addition, these two functions are provided by an easy-to-use device that is easily adaptable to various patient morphologies. As such, the surgical process is simplified. And, if the sacral reconstruction fixation construct is formed of radiolucent materials, such as PEEK or carbon fiber reinforced PEEK, the scatter artifacts typically seen with metallic implanted materials may be minimized in post-operative radiological studies. Thus, it may be advantageous to form the fixation device  50  out of radiolucent materials. 
         [0024]    The discussion above has assumed that the spinal rod  30  engages the inferior connector body  80  sufficiently to prevent relative rotation of the inferior connector body  80  and superior connector body  60  by employing a Morse taper at spinal rod end  38 . However, other approaches may be used for this purpose. For example, the enlarged distal tip  38  of the spinal rod  30  may include a plurality of splines (not shown) thereon, and aperture  86   b  in inferior connector body  80  may include corresponding splines. Further, the enlarged distal tip  38  of the spinal rod  30  may be formed as a separate section of the spinal rod  30 , and then joined end to end with the remainder of the spinal rod  30 , such as via a threaded connection or the like. 
         [0025]    The discussion above has also assumed that the transiliac rod  40  is directly clamped within passage  90 . However, some embodiments of the fixation device  50  may alternatively use a compressible insert  92  disposed between the transiliac rod  40  and the interior wall of passage  90 . For such embodiments, the compressible insert  92  may advantageously take the form of a convexly curved body  94  with a bore  96  therethrough. A slit  98  may be formed in the body  94  to allow the insert  90  to be compressed while maintaining its general shape. The interior wall of passage  90  may advantageously be correspondingly shaped, so that the compressible insert  92  may be rotated in multiple directions. With such an arrangement, urging inferior end portion  84  toward superior end portion  82  will tend to shrink passage  90 , thereby compressing the insert  92 , and thereby clamping the transiliac rod  40  in passage  90 . 
         [0026]    Further, some embodiments of the sacral reconstruction fixation construct  28  may employ multiple transiliac rods  40  disposed parallel to one another. For such embodiments, the inferior connector body  80  may be altered to provide an additional passage  99  of variable size that is oriented parallel to passage  90 . It is intended that both of these passages  90 , 99  will assume their smaller size when the fixation device  50  is in its locked configuration. Further, as can appreciated, while the passages  90 , 99  are shown disposed on the same side relative to rod  30  in  FIG. 9 , the passages  90 , 99  may be alternatively be disposed on opposing sides of rod  30 . 
         [0027]    The present invention may be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.