Abstract:
The present invention is an expandable sleeve deployable in a surgical implant. The sleeve has a head, a tubular shaft defining an open interior, and a distal tip, with the shaft having a length dimension. The shaft is provided with a plurality of slots that divide the shaft into partitions, wherein each of the partitions has a length, and the length of the partitions are not all equal. For example, the slots may have a curved portion that extends at an angle between 0° and 90° to the length dimension of the shaft. The slots may also have a straight portion and a curved portion. Further, the invention in another embodiment includes an expander pin, and in yet another embodiment, includes an expander pin.

Description:
STATEMENT OF RELATED CASES  
       [0001]    The present application claims the benefit of U.S. provisional application 60/243,920 filed on Oct. 27, 2000. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention is directed to devices that are used to facilitate post-operative bone-to-bone fusion, tissue-to-bone fusion and particularly, bone fusion between two adjacent vertebrae.  
         BACKGROUND OF THE INVENTION  
         [0003]    Vertebral disc degeneration has been associated with back pain and motor function loss. Loss of disc space height, extrusion of disc material, and translation of the vertebrae can result in compression of the spinal cord and nerve roots. One prescriptive treatment is to stabilize the vertebral bodies through fusion of adjacent vertebrae within the spinal column.  
           [0004]    An operative technique of spinal column fusion employs inter-vertebral body cages. Available in different configurations from several manufacturers, the cage is inserted between two vertebral bodies in order to restore space between the discs. The device is filled with bone graft to promote fusion between the vertebrae. Access holes around the periphery of the cage provide intimate contact between the graft and host bone. The cages are typically inserted from the back (posterior) or front (anterior) aspects of the spinal column. The anterior approach involves laparoscopic methods.  
           [0005]    Stabilization of the fusion site is advantageous in the early post-operation period. Similar to fracture healing, new bone is overlayed between the vertebral bodies, using the graft material as a lattice. Using cages as stand alone devices has met with limited success for the reason that immediate stabilization is not always guaranteed. For this reason, supplemental fixation is becoming more commonplace.  
           [0006]    One current stabilization technique employs the placement of fixed translaminar screws into a hole drilled through adjacent vertebrae. FIGS. 1A and 1B show typical lumbar vertebrae in which translaminar screws are driven across the facet joint, effectively locking the two vertebrae in place while allowing for the four types of spine motion: forward flexion, backwards extension, axial torsion, and lateral flexion.  
           [0007]    There is an ongoing need to provide for a facet fixation device that can be delivered simply, accurately, and quickly, while providing performance that is superior or equal to that of screw fixation.  
         SUMMARY OF THE INVENTION  
         [0008]    In one aspect, the present invention is an expandable sleeve deployable in a surgical implant. The sleeve has a head, a tubular shaft defining an open interior, and a distal tip, with the shaft having a length dimension. The shaft is provided with a plurality of slots that divide the shaft into partitions, wherein each of the partitions has a length, and the length of the partitions are not all equal. For example, the slots may have a curved portion that extends at an angle between 0° and 90° to the length dimension of the shaft. The slots may also have a straight portion and a curved portion.  
           [0009]    In yet another embodiment, the expandable sleeve has an open interior that is provided with a first zone proximate the head which has a first cross sectional area and a second zone proximate the distal tip that has a second cross sectional area, wherein the first cross sectional area is greater than the second cross sectional area. In yet another embodiment, the expandable sleeve has a third zone positioned intermediate the first zone and second zone, the third zone having a varying cross sectional area that decreases incrementally moving from the first zone to the second zone.  
           [0010]    In yet another embodiment, the slots of the expandable sleeve extend from a midsection of the shaft to a terminal location on the shaft that is short of the distal tip. In another embodiment, the head extends outward from the shaft and is provided with teeth facing the distal tip. In yet another embodiment, the head of the expander pin extends outward from the shaft and has a convex distal tip.  
           [0011]    In yet another embodiment, the head of the expandable sleeve is provided with a recess for receiving a bushing. The recess may be provided with a tapered profile that varies in cross sectional area over a length dimension.  
           [0012]    In yet another embodiment, the slots divide the shaft into a first slot half and a second slot half, with the length dimension of the first half being greater than the length dimension of the second half. In yet another embodiment, the shaft of the expandable sleeve is provided with additional slots that divide the shaft into four quarters, wherein the length dimension of two quarters is greater than the length dimension of the two other quarters.  
           [0013]    In yet another embodiment, the shaft of the expandable sleeve is provided with fenestrations on an exterior side. The fenestrations may vary in their length as measured in a radial dimension of the sleeve.  
           [0014]    In yet another embodiment the present invention is a surgical implant having an expandable sleeve having any of the features as aforedescribed, and an expander pin comprised of a head and a shaft positioned within the open interior of the sleeve. The cross sectional area of the expander pin is larger than cross sectional area of at least a portion of the cross sectional area of the open interior, so that when the expandable pin is moved through the open interior, the expandable sleeve expands at the slots.  
           [0015]    The expander pin has a distal tip and an end opposite the head, wherein the shaft is provided with a first zone proximate the head having a first cross sectional area and a second zone proximate the distal tip having a second cross sectional area, wherein the second cross sectional area is greater than the first cross sectional area.  
           [0016]    In a further embodiment, the surgical implant is further provided with a bushing that resides in a cavity positioned within the open interior of the sleeve, located proximate the opening of the sleeve. The bushing has a shaped portion and a flange portion extending outward of the shaped portion, the bushing further provided with a through-channel dimensioned to receive the pin, and a discontinuation in the bushing, the channel being sized the same as or substantially the same as the pin, wherein the cavity is provided with dimensions complimentary to the dimensions of the shaped portion to retain the shaped portion within the sleeve. The shaped portion may have a tapered shape. The pin may be positioned within the sleeve by passing it through the bushing, which expands the bushing.  
           [0017]    For simplicity&#39;s sake, as used herein the words “tube” or “tubular” are used with the intention of encompassing a hollow structure of any shape, whether cylindrical or not.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIGS. 1A, 1B shows a posterior and lateral view, respectively of prior art fixation devices.  
         [0019]    FIGS.  2 A- 2 C show an earlier embodiment of the applicant surgical implant made subject of the aforedescribed provisional application.  
         [0020]    FIGS.  3 A- 3 D show side plan and cross sectional views of the FIGS.  2 A- 2 C surgical implant.  
         [0021]    FIGS.  4 A- 4 B show alternatives to the FIGS.  2 A- 2 C embodiments.  
         [0022]    [0022]FIG. 5 shows a perspective view of another embodiment of the present invention in an unexpanded position.  
         [0023]    [0023]FIG. 6 shows a perspective view of the embodiment of FIG. 5 of the present invention, this time in an expanded position.  
         [0024]    [0024]FIG. 7 shows an embodiment of an expander pin.  
         [0025]    [0025]FIG. 8 is a cross sectional view of the embodiment of FIG. 5 of the present invention in which the sleeve is in an unexpanded state.  
         [0026]    [0026]FIG. 9 is a cross sectional view of the embodiment of FIG. 5 of the present invention in which the sleeve is in an expanded state.  
         [0027]    [0027]FIG. 10 is a side view of an embodiment of a bushing of the present invention.  
         [0028]    [0028]FIG. 11 is a side elevational view of the sleeve of the present invention.  
         [0029]    [0029]FIG. 12 is a side elevational view of a half of the distal tip of the sleeve of the present invention.  
         [0030]    [0030]FIG. 13 is a side elevational view of a half of the distal tip of the sleeve of the present invention.  
         [0031]    [0031]FIG. 14 is a perspective view of another embodiment of the present invention.  
         [0032]    [0032]FIG. 15 is a side elevational view of another embodiment of the present invention.  
         [0033]    [0033]FIG. 16 is a perspective view of another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0034]    FIGS.  2 A- 2 C shows a two piece fixation device  700  utilizing a pin  702  and a sleeve  704 . The pin  702  (FIG. 2A) is comprised of a head  706  and a tip  708  which are connected by a cylindrical shaft  710 . The head may be provided with flat sides  712 . Due to the size of head  706 , which is greater than the size of the opening in the sleeve into which the pin is inserted, the head eventually provides a positive stop when the pin  702  is driven into the sleeve  704 .  
         [0035]    Tip  708  is provided with a rounded end  714  (FIGS. 3C, 3D) which facilitates the entry the expander pin  702  into the sleeve  704  and provides a smooth surface to reduce or avoid tissue irritation. Behind the spherical tip, in the direction of the shaft  710  is at least one recess  716 . A plurality of recesses  716  are shown in FIG. 2A. The recesses are less thick when compared to the thickness of the shaft  710 . Behind the recesses, also in the direction of the shaft  710 , is an undercut  718 , which also is a region of reduced thickness.  
         [0036]    Sleeve  704  (FIG. 2B) is comprised of a head  720 , a hollow tubular mid-shaft  722 , and a distal tip  724 . Head  720  has a slot  721  which receives the head  706  of the expander pin  702 . Behind this is an undercut that captures an inserter instrument. One wall of the undercut is graduated to ease disengagement of the Inserter. The mid-shaft  722  has a series of fenestrations  726  intended to provide an interference fit with the walls of the hole prepared in the bone or tissue. The distal tip  728  has a series of slots  730  which allow the sleeve to expand.  
         [0037]    The interior of sleeve  704  is open so that the pin  702  can be received therein. The inner wall of the sleeve  704  near the distal tip  728  is provided with tabs  732  that project into the open space. As the pin is driven the Tabs engage the undercut on the pin. The exterior of the distal tip has fenestrations  715  that in the deployed condition create an interference fit with the walls of the prepared hole. The distal tip may also be smooth. The fenestrations of the preferred embodiment resemble a cortical screw thread. They could however be of any configuration (grooves, splines, etc.) which would provide a “bite”.  
         [0038]    [0038]FIG. 2C shows a tapered portion  717  as an alternate to the fenestrations  715 . Rather than cutting into bone, the taper would engage a conic shape prepared in the bone, providing a measure of resistance to pull out of the Implant.  
         [0039]    [0039]FIGS. 3A, 3B,  3 C, and  3 D illustrate the transformation of the implant from the non-deployed, pre-expanded state to the deployed, expanded state. The sleeve and pin arrangement is inserted into the prepared drill hole in the initial, non-deployed state. In the initial, non-deployed state, in which the head  706  of the pin is situated outside of the slotted head  720  of the sleeve, the tab  732  on the inner wall of the sleeve resides within the slot  730  provided on the pin  702 . In this arrangement the sleeve is in an unexpanded state. The pin  702  is then moved forward in the sleeve  704  so that the head  706  of the pin  702  is situated in the slot  721  of the head  720  on the sleeve  704 . Forward movement of the pin moves the recess out from under tab, and the tab rides up on the shaft  710 . Since the shaft is thicker than the recess, the abutment of the tab against the shaft expands the sleeve at the recessed region. To maintain the tab in position on the sleeve, the shaft is provided with an undercut, which is a grooved region on the shaft having a modest reduction in thickness, i.e., a thickness intermediate that of the recess  716  and shaft  710 . The undercut  718  is situated where the tab will reside when the pin is fully inserted in the sleeve and the device is in the deployed state. The walls of the groove retain the tab within the undercut, insuring that the tab will remain within the groove. See, e.g., FIG. 25D.  
         [0040]    [0040]FIGS. 4A and 4B show alternate head configurations. In these embodiments, the slotted head of the sleeve  704  is omitted and the head of the pin is replaced by a hex head (FIG. 4A), or alternatively by a smooth head (FIG. 4B).  
         [0041]    [0041]FIGS. 5 and 6 show a two piece fixation device  100  utilizing a pin  102  and a sleeve  104 . As best seen in FIG. 7 the pin  102  has a head  106  and a cylindrical shaft  110  having a tip  108 . As shown in FIG. 7, the shaft is provided with a midsection  111  and distal end  113 . Distal end  113  is sized greater than the midsection  111 . The increase in size may take place stepwise at step  115 . The head  106  may be provided with a rounded perimeter  112 . Due to the size of the head  106 , which is greater than the size of the opening  121  in the sleeve into which the pin is inserted, the head provides a positive stop when the pin  102  is driven into the sleeve  104 . See FIGS. 6 and 9.  
         [0042]    Tip  108  is provided with a rounded surface  114  at distal end  113  which facilitates entry of the pin  102  into the sleeve  104  and provides a smooth surface to reduce or avoid tissue irritation distal end  113 . See FIGS. 7, 8,  9 .  
         [0043]    Sleeve  104  (FIG. 5) is provided with a head  120  having an opening  121 . A shaft  122  extends from the head  120 . The shaft  122  defines an open interior which can be accessed through the opening in the head  120 . The pin  102  can be inserted through the opening and is received in the open interior. The shaft  122  is also provided with slots  130  that extend from the mid-section of the shaft  122  to the distal tip  124 . The sleeve  102  is also provided with a flange  125  to resist forces that would pull the device through the bone. The flange  125  may be provided with a plurality of teeth  129  directed distally, for additional fixation. The flange  125  is provided with a convex shape to better engage the bone. In an alternative embodiment illustrated in FIGS. 15 and 16, the flange  125 ′ is provided with a smooth, curved distal facing side that extends radially outward from the sleeve  102 . This arrangement may better conform to the host bone. The flange may be hemispherical in shape.  
         [0044]    The outer side of the shaft  122  has a series of fenestrations  126  intended to provide an interference fit with the walls of the hole prepared in the bone or tissue. As best seen in FIGS.  11 - 13 , the fenestrations  126  have a variable root diameter, which is the outer shaft diameter minus the diameter of the grooves of the fenestrations. See FIG. 12. Root diameter decreases as the tip  108  is approached. This places the largest and deepest fenestrations near the distal end  113 , which is the location of the greatest sleeve expansion. This arrangement may maximize interference with the bone. The fenestrations  126  with a shallow depth are located near the midsection, a location where sleeve wall thickness is maximized for strength. In one embodiment, the fenestrations  126  can be a series of circumferential grooves. In another embodiment the fenestrations take the form of a single lead thread, of varying pitch and minor diameter. Thread pitch decreases as the distal tip  108  is approached. Minor diameter decreases as the distal tip  108  is approached.  
         [0045]    The profile of a Fenestration  131  consists of a crest width  131   a , a clearance flank  131   b , and a pressure flank  131   c . These are based on standards set forth in ASTM F 543-98:  Standard Specification for Metallic Metal Bone Screws.  In FIG. 12, the angles X and Z are given in the standard. To match these in the deployed state, the entire profile is tilted Y degrees, yielding an angle from horizontal of X+Y degrees to the pressure flank. This will mimic the interference pattern of the standard.  
         [0046]    The slot  130  in the sleeve  104  runs from the midsection of the shaft  122  to near the distal tip  108 . The slot  130  extends through the sidewalls of the sleeve  104 , from the exterior of the sleeve to the open interior defined by the sleeve. The slots divide the sleeve  104  into partitions. In FIGS. 8, 9, and  12 , two slots are shown, dividing the sleeve into halves. The path of the slot is substantially aligned with the axis of the sleeve from the opening  121 , through the midsection. Moving towards the distal tip, the path of the slot  130  curves medially and then laterally, with the slot terminating at a point near, but short of, the distal tip of the sleeve. Over all, the slot has a linear portion  130   a  and a curved portion  130   b . In effect, the partitions do not all have the same length, with at least one partition being longer than at least one partition. For instance as shown in FIG. 8, the upper half of the sleeve is longer than the lower half.  
         [0047]    In another embodiment, shown in FIG. 11, the sleeve  104  is provided with four slots  130 . The slots divide the sleeve  104  into partitions. The slots have a linear portion and a curved portion. In effect, the partitions do not all have the same length, with some of the partitions being longer than some of the other partitions.  
         [0048]    When the pin  102  is driven to its final position, the sleeve  104  is expanded (Compare FIGS. 5, 8 to FIGS. 6, 9). As shown in FIG. 9, the curved portion of the sleeve  122  that lies between the contact points  127  is supported by the pin  102  at contact points  127 . In the embodiment shown, the end  108  of the distal tip  113  is associated with this partition. This may maximize the support for the tip, thereby avoid the flexing and its potential fracture from the sleeve.  
         [0049]    In one embodiment, the shaft  122  defines an open interior that is provided with a first zone  140  proximate the head. See FIG. 8. The first zone  140  has a first cross sectional area A-A. The open interior of the shaft is also provided with a second portion  142  proximate the distal tip that has a second cross sectional area C-C and D-D. The first cross sectional area  140  is greater than the second cross sectional area  142 . In another embodiment, there is a third zone  144  positioned intermediate the first zone and second zone  140 ,  142 , with the third zone being tapered. That is, the third zone has a varying cross sectional area that decreases incrementally over its traversal from the first zone to the second zone.  
         [0050]    Near the distal end of the slot, there is a tapered section  144  that interfaces with the pin during expansion. As the pin is advanced, the pin enters the tapered section  144 . Further advancement drives the pin through the tapered section. The cross sectional area of the pin is greater than the cross sectional area of the tapered section, thereby expanding the sleeve at section B-B. Still further advancement brings the pin in contact with the region between the taper and the distal tip  142 , which also has a cross sectional area less than the cross sectional area of the pin. As the pin moves through the region between the taper and the distal tip, it encounters the curved segment of the slot. As it moves through this region  142 , the partitions rest on the pin. Note that the upper partition  145  of FIG. 9 possesses an arcuate portion  146  of the curved segment. This partition  145  contacts the pin at the ends of this segment, and the distal tip itself rests on the pin. The lower partition  147  has a surface that rests on the pin.  
       The Bushing  
       [0051]    In another embodiment of the present invention, shown in FIGS. 8, 9, and  10 , a bushing  150  is employed. When deployed, the bushing resides in a cavity  152  that is located adjacent the opening  121 . The cavity  152  is in communication with the opening  121  and the open interior. At its proximal end  154  the bushing is provided with flange  156  that extends outward from a tapered section  158 . Tapered section  158  increases its size in a dimension as the distal end  160  is approached. A slot  162  extending in the longitudinal direction allows for compression and expansion of the bushing  150 . A channel  164  extends through the bushing. The size or diameter of the channel  164  closely matches the size or diameter of the midsection  111  of the pin.  
         [0052]    The bushing  150  is first snapped into the sleeve  104 , followed by the pin  102 . As the pin is pushed in, its distal end  113  expands the bushing  150  into the cavity  152 . The pin  102  is further advanced until the midsection  111  passes though. The bushing  150  then reduces to its original size and shape. The bushing  164  prevents the pin  102  from falling out of the sleeve should the device be inverted during handling. If inverted, the pin  102  will drop onto the bushing  150  and be stopped by the step  115  located between its midsection  111  and distal end  113 . The bushing is maintained in the cavity by the mating tapered surface within the cavity  152 . In one embodiment, the bushing, sleeve, and pin come pre-assembled for the ease of the surgeon who will deploy the device within a vertebrae.