Patent Publication Number: US-7585313-B2

Title: Rotatable interspinous spacer

Description:
BACKGROUND OF THE INVENTION 
     The leading cause of lower back pain arises from rupture or degeneration of lumbar intervertebral discs. Pain in the lower extremities is caused by the compression of spinal nerve roots by a bulging disc, while lower back pain is caused by collapse of the disc and by the adverse effects of articulation weight through a damaged, unstable vertebral joint. 
     In some cases, when a patient having a collapsed disc moves in extension (e.g., leans backward), the posterior portion of the annulus fibrosis or folding of the ligamentum flavum may further compress and extend into the spinal canal. This condition, called “spinal stenosis”, narrows the spinal canal and causes impingement of tissue upon the spinal cord, thereby producing pain. 
     There have been numerous attempts to provide relief for these afflictions by providing a spacer that inserts between adjacent spinous processes present in the posterior portion of the spinal column. This spacer essentially lifts the upper spinous process off of the lower spinous process, thereby relieving stenosis. In general, these interspinous implants are adapted to allow flexion movement in the patient, but resist or limit extension. 
     U.S. Pat. No. 6,068,630 (“Zuchermann”) discloses a spinal distraction implant that alleviates pain associated with spinal stenosis by expanding the volume in the spinal canal or neural foramen. Zucherman discloses a plurality of implants having a body portion and lateral wings. The body portion is adapted to seat between the adjacent spinous processes, while the wings are adapted to prevent lateral movement of the body portion, thereby holding it in place between the adjacent spinous processes. The designs disclosed in FIGS. 15, 80 and 84 of Zuchermann comprise central body having an integral wing. 
     Although the Zuchermann device achieves spinal distraction, it nonetheless possesses some limitations. First, since the Zuchermann central bodies have at least one integral wing, the clinician may encounter difficulty in sizing the central body independently of delivering the lateral wings. Second, the expansive geometry of the disclosed devices may not lend itself to minimally invasive surgical techniques seeking to conserve muscle mass and soft tissue in the regions adjacent the spinous processes. 
     U.S. Pat. No. 5,645,599 (“Samani”) attempts to relieve spinal stenosis by essentially inserting a flexible horseshoe-shaped device between the adjacent spinous processes. Although the Samani device desirably provides a self-limiting flexibility, it nonetheless suffers from some inadequacies. For example, the Samani device does not provide for natural physiologic rotational movement, nor for post-operative adjustment. In addition, the Samani device discloses the insertion of a bearing cushion, and the adhesive bonding of the bearing cushion to the horseshoe element. However, it is believed that mere adhesive bonding of these elements would cause the cushion to be prone to migration. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an expandable interspinous spacer that can be laterally inserted between adjacent spinous processes in an initial state, and then one portion of the device is pivotally rotated relative to a second portion of the device to provide firm securement to the adjacent spinous processes. 
     In a preferred embodiment, the spacer comprises two S-shaped members that can pivot about a pair of central elements. Because the S-shaped members are oriented in opposite directions, the spacer has a narrow distal portion in its initial state that allows for its minimally invasive insertion between the adjacent spinous processes. Once this distal portion is positioned substantially on the distal side of the interspinous space, the S-shaped members are rotated past each other in opposite directions about the central element to a final state. As the S-shaped members rotate, the spacer pulls itself into the interspinous space, thereby positioning the central element within the interspinous space. Once in this final position, the two bodies are locked together. 
     Therefore, in accordance with the present invention, there is provided an interspinous implant for insertion between adjacent spinous processes, the implant comprising:
         a) a first S-shaped member having a central element, an upper arm attached to the central element and adapted to bear against the upper spinous process, and a lower arm attached to the central element and adapted to bear against the lower spinous process, and   b) a second S-shaped member having a central element, an upper arm attached to the central element and adapted to bear against the upper spinous process, and a lower arm attached to the central element and adapted to bear against the lower spinous process,
 
wherein the central elements of the first and second members are pivotally connected.
       

    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1  is a top view of a first embodiment of an interspinous spacer of the present invention in its initial state. 
         FIG. 2  is a posterior view of the interspinous spacer of  FIG. 1  being inserted laterally between adjacent spinous processes so that the distal elements are positioned substantially on the distal side of the interspinous space, while the central element is positioned on the proximal side of the interspinous space. 
         FIG. 3  is a posterior view of the interspinous spacer of  FIG. 2  wherein, after its lateral insertion into the interspinous space, the S-shaped members are rotated past each other in opposite directions about the central element to its final state. 
         FIG. 4  is a posterior view of the interspinous spacer in its final state and centrally positioned within the interspinous space. 
         FIGS. 5A-5B  disclose exploded and assembled side views of a second embodiments of the present invention in its initial state, wherein the concave arms traverse several planes. 
         FIGS. 6A-6B  disclose upper and side views of a second embodiment of the present invention in its final state. 
         FIG. 7A  is a posterior view of a second embodiment of the interspinous spacer of the present invention being inserted laterally in its initial state between adjacent spinous processes so that the distal elements are positioned partially on the distal (left) side of the interspinous space, while the central element is positioned on the proximal (right) side of the interspinous space. 
         FIG. 7B  is a posterior view of the interspinous spacer of  FIG. 7A  centrally positioned within the interspinous space in its final state. 
         FIG. 7C  is a side view of the interspinous spacer of  FIG. 7B  in its final state centrally positioned within the interspinous space. 
         FIGS. 8A-8B  disclose exploded and assembled views of an embodiment of the present invention having locking elements. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For the purposes of the present invention, the term “interspinous” refers to the volume located between two adjacent spinous processes of adjacent vertebrae. The terms “anterior” and “posterior” are used as they are normally used in spinal anatomy. Accordingly, the “anterior” portion of the interspinous device is that portion rests relatively close to the spinal cord, while the “posterior” portion of the interspinous device is that portion rests relatively close to the skin on the patient&#39;s back. Now referring to  FIG. 7C , there is provided an anatomic “functional spinal unit” or FSU comprising an upper vertebrae having an upper vertebral body VB U  and an upper spinous process SP u , a lower vertebra having a lower vertebral body VB L  having a lower spinous process SP L . The vertebral bodies lie in the anterior A portion of the FSU, while the spinous processes lie in the posterior portion P of the FSU. Disposed between the vertebral bodies is a disc space “disc”. Disposed between the spinous process is an “interspinous region”. 
     Now referring to  FIG. 1 , there is provided an interspinous implant for insertion between adjacent spinous processes. The implant in its initial state comprises:
         a) a first S-shaped member  11  having a central element  13  having a throughbore, a distal concave arm  17  having a proximal end  19  attached to the central element and a proximal concave arm  23  having a distal end  25  attached to the central element, wherein the concave arms face away from each other, and   b) a second S-shaped member  31  having a central element having a throughbore, a distal concave arm  37  having a proximal end  39  attached to the central element and a proximal concave arm  43  having a distal end  45  attached to the central element, wherein the concave arms face away from each other,
 
wherein the central elements of the first and second members are pivotally connected by a pivot pin  51  that extends through the throughbores of the central elements.
       

     Also as shown in  FIG. 1 , in the initial state, the proximal concave arm of the first S-shaped member opposes the proximal concave arm of the second S-shaped member, while similarly the distal concave arm the first S-shaped member opposes the distal concave arm of the second S-shaped member. 
     Now referring to  FIG. 2 , the distal arms of the spacer are inserted between adjacent spinous processes so that these arms will become positioned substantially on the distal (left) side of the interspinous space, while the central element is positioned on the proximal (right) side of the interspinous space. 
     Now referring to  FIG. 3 , once these distal arms are positioned substantially on the distal (left) side of the interspinous space, these arms are rotated past each other in opposite directions about the central elements to bring the spacer to its final state. 
     Now referring to  FIG. 4 , as the S-shaped members rotate, the bearing of the distal arms upon the adjacent spinous processes acts to pull the rest of the itself into the interspinous space, thereby positioning the central elements within the interspinous space. Once in this final position, the two S-shaped members are locked together. 
     Therefore, in accordance with the present invention, there is provided a method of inserting an interspinous implant comprising the steps of:
         a) providing an interspinous implant comprising:
           i) a first member having a central element, a distal concave arm having a proximal end attached to the central element and a distal end, and   ii) a second member having a central element, a distal concave arm having a proximal end attached to the central element and a distal end,
 
wherein the distal concave arms substantially oppose each other, and
 
wherein the central elements of the first and second members are pivotally connected,
   
           b) inserting the distal concave arms between adjacent spinous processes so that the distal concave arms are positioned substantially on the distal side of the interspinous space, and   c) pivoting the distal end of the first member about the central element so that the distal concave arms pass from each other.       

     Now referring to  FIGS. 5A and 5B , there is provided an interspinous implant  50  for insertion between adjacent spinous processes. The implant is in its initial state and comprises:
         a) a first S-shaped member  51  having:
           i) a central region  53  having a throughbore  54 ,   ii) a distal concave arm  57  having a proximal end  59  lying in a first plane and attached to the central element, an intermediate curved region  60  and a distal end  61  lying in a second plane, and   iii) a proximal concave arm  63  lying in the first plane and having a distal end  65  attached to the central element, wherein the concave arms of the first S-shape member face away from each other, and   
           b) a second S-shaped member  71  having:
           i) a central element  73  located in the first plane,   ii) a distal concave arm  77  having a proximal end  79  lying in a third plane and attached to the central element, an intermediate curved region  81  and a distal end  83  lying in the first plane,   iii) a proximal concave arm  85  lying in the second plane and having a distal end  87  attached to the central element, wherein the concave arms of the second S-shape member face away from each other, and
 
wherein the first and second S-shaped members are pivotally connected by the central element  73  that extends through the throughbore  54  of the central region.
   
               

     In an alternative embodiment, the central element  73  of the second S-shaped member is an independent component, and the distal and proximal arms of the second S-shaped member have throughbores that accommodate the central element. 
     Now referring to  FIGS. 6A and 6B , there is provided an interspinous implant  50  for insertion between adjacent spinous processes. The implant is in its final state and comprises:
         c) a first S-shaped member  251  having:
           i) a central region  253  having a throughbore  254 ,   ii) a distal concave arm  257  having a proximal end  259  lying in a first plane and attached to the central element, an intermediate curved region  260  and a distal end  261  lying in a second plane, and   iii) a proximal concave arm  263  lying in the first plane and having a distal end  265  attached to the central element, wherein the concave arms of the first s-shape member face away from each other, and   
           d) a second S-shaped member  271  having;
           i) a central element  273  located in the first plane,   ii) a distal concave arm  277  lying in the second plane and having a proximal end  278  attached to the central element,   iii) a proximal concave arm  285  having a distal end lying in the third plane and attached to the central element, an intermediate curved region  287 , and a proximal end  289  lying in the first plane, wherein the concave arms of the second s-shape member face away from each other, and
 
wherein the first and second S-shaped members are pivotally connected by the central element  273  that extends through the throughbore  254  of the central region.
   
               

     The advantage of the design of  FIGS. 6A and 6B  is that, in its final state, the upper arms lie in the same plane and the lower arms lie in the same plane. That is, the distal concave arm of the first S-shaped member lies in a first plane and the proximal concave arm of the second S-shaped member lies in the first plane. Also, the proximal concave arm of the first S-shaped member lies in a second plane and the distal concave arm of the second S-shaped member lies in the second plane. 
     Now referring to  FIGS. 7A-C , there is provided a posterior view of an interspinous implant  101  being inserted between adjacent spinous processes. Referring to  FIG. 7B , the implant comprises:
         a) a first S-shaped member  111  having a central element  113 , a distal concave arm  117  having a proximal end  119  attached to the central element and a proximal concave arm  123  having a distal end  125  attached to the central element, wherein the concave arms face away from each other, and   b) a second S-shaped member  131  having a central element  133 , a distal concave arm  137  having a proximal end  139  attached to the central element and a proximal concave arm  143  having a distal end  145  attached to the central element, wherein the concave arms face away from each other,
 
wherein the central elements of the first and second members are pivotally connected by a pivot pin  151 .
       

     Also as shown in  FIG. 7A , in this initial state, the proximal concave arm of the first S-shaped member opposes the proximal concave arm of the second S-shaped member, while similarly the distal concave arm the first S-shaped member opposes the distal concave arm of the second S-shaped member. In this  FIG. 7A , the distal arms of the spacer are partially inserted between adjacent spinous processes so that these arms are positioned partially on the distal (left) side of the interspinous space, while the central element is positioned on the proximal (right) side of the interspinous space. 
     Now referring to  FIG. 7B , once these distal arms are positioned substantially on the distal side of the interspinous space, the S-shaped members are rotated past each other in opposite directions about the central element to bring the spacer to its final state. The bearing of the distal arms upon the adjacent spinous processes acts to pull the rest of the itself into the interspinous space, thereby positioning the central element within the interspinous space. Once in this final position, the two S-shaped members are locked together. 
     Now referring to  FIG. 7B , central element  113  contains concave bearing surfaces  153  and  155  for securing the implant to the upper and lower spinous processes. As seen in  FIG. 7C , the extension of the concave arm in the anterior-posterior direction provides a holding feature  123  that allows for better securement of the device to the spinous process against which it bears. 
     In some embodiments, the central elements of the implant are joined together by a pin and groove arrangement. Now referring to  FIGS. 8A-8B , in some embodiments, a first S-shaped member  324  has a projection  325  extending from an inner face  341  of the central element  326  thereof and a second S-shaped member  329  has a corresponding groove  327  extending into the inner face  343  of the central element  328  thereof. Preferably, the projection fits into the groove and may articulate in the groove to allow relative pivoting movement of the arms. 
     In some embodiments, the implant has a locking element. Preferably, the locking element comprises a pin having a leaf spring. 
     Now referring to  FIGS. 8A-8B , in some embodiments, the device has a pair of locking elements. Each locking element  301  comprises a pin  303  having a leaf spring  305  extending therefrom. This locking element is received in the corresponding cavities  307  in each of the central elements. Central element  326  also has cavities  351  corresponding to the pins. 
     In use, when the device is in its initial position, the pins  303  with leaf springs initially sit completely in cavities  307  in central element  328 . When the two S-shaped members are aligned in their final position, the cavities of the two central elements become aligned and the pin seated in the cavity  307  pops up to become partially seated in the opposing cavity on central element  326 . This locks the implants in its final position. In some embodiments (such a during revision surgery), the leaf spring pins can be released by inserting a two-pronged key (not shown) in holes  353  on the outside face  331  of the first S-shaped member  324 , and holding down the internal leaf spring pins while turning the key. 
     In some embodiments, the concave arms of the present invention are substantially U-shaped. In some embodiments, the concave arms of the present invention are substantially V-shaped. 
     In some embodiments (not shown), the central portion of the device is angled so that its anterior portion has a thickness that is greater than its posterior portion. This provides a desired angulation to the device. Preferably, each central element has an anterior portion having a thickness and a posterior portion having a thickness, and the thickness of each anterior portion is greater than the thickness of each posterior portion. 
     In preferred embodiments, the implant of the present invention is used posteriorly in conjunction with a motion disc inserted within the disc space of the anterior portion of the spinal column. For example, in some embodiments, the implant of the present invention is used in conjunction with a motion disc having a large range of motion (“ROM”). Various motion discs are described by Stefee et al. in U.S. Pat. No. 5,071,437; Gill et al. in U.S. Pat. No. 6,113,637; Bryan et al. in U.S. Pat. No. 6,001,130; Hedman et al. in U.S. Pat. No. 4,759,769; Ray in U.S. Pat. No. 5,527,312; Ray et al. in U.S. Pat. No. 5,824,093; Buttner-Janz in U.S. Pat. No. 5,401,269; and Serhan et al. in U.S. Pat. No. 5,824,094; all which documents are hereby incorporated herein by reference in their entireties. The flexibility of the flexible body provides resistance to extreme extension, thereby restricting the motion disc to a more narrow and more physiologically desirable range of motion. 
     Therefore, in accordance with the present invention, there is provided a kit for providing therapy to a functional spinal unit comprising an upper vertebrae having an upper spinous process, a lower vertebrae having a lower spinous process, and a disc space therebetween, the kit comprising:
         a) an implant of the present invention, and   b) an artificial intervertebral disc.       

     The implants disclosed herein may be suitably manufactured from any suitable biomaterial, including metals such as titanium alloys, chromium-cobalt alloys and stainless steel), ceramics (such as alumina and zirconia, and mixtures thereof) and polymers (such as PEEK, carbon fiber-polymer composites and UHMWPE). In preferred embodiments, the s-shaped members are made of titanium, titanium alloy, or PEEK.