Abstract:
A spinal implant helps stabilize vertebrae for fusion. The implant includes first and second plates, a brace and a locking mechanism. When installed, the plates extend superiorly-inferiorly along respective lateral sides of the spinous processes. The plates are moved toward one another and relative to the brace by the locking mechanism to clamp the implant to the spinous processes.

Description:
BACKGROUND 
       [0001]    This invention relates generally to devices for the treatment of spinal conditions, and more particularly, to the treatment of various spinal conditions that cause back pain. Even more particularly, this invention relates to devices that may be placed between adjacent spinous processes to treat various spinal conditions. For example, spinal conditions that may be treated with these devices may include spinal stenosis, degenerative disc disease (DDD), disc herniations and spinal instability, among others. 
         [0002]    The clinical syndrome of neurogenic intermittent claudication due to lumbar spinal stenosis is a frequent source of pain in the lower back and extremities, leading to impaired walking, and causing other forms of disability in the elderly. Although the incidence and prevalence of symptomatic lumbar spinal stenosis have not been established, this condition is the most frequent indication of spinal surgery in patients older than 65 years of age. 
         [0003]    Lumbar spinal stenosis is a condition of the spine characterized by a narrowing of the lumbar spinal canal. With spinal stenosis, the spinal canal narrows and pinches the spinal cord and nerves, causing pain in the back and legs. It is estimated that approximately 5 in 10,000 people develop lumbar spinal stenosis each year. For patients who seek the aid of a physician for back pain, approximately 12%-15% are diagnosed as having lumbar spinal stenosis. 
         [0004]    Common treatments for lumbar spinal stenosis include physical therapy (including changes in posture), medication, and occasionally surgery. Changes in posture and physical therapy may be effective in flexing the spine to decompress and enlarge the space available to the spinal cord and nerves—thus relieving pressure on pinched nerves. Medications such as NSAIDS and other anti-inflammatory medications are often used to alleviate pain, although they are not typically effective at addressing spinal compression, which is the cause of the pain. 
         [0005]    Surgical treatments are more aggressive than medication or physical therapy, and in appropriate cases surgery may be the best way to achieve lessening of the symptoms of lumbar spinal stenosis and other spinal conditions. The principal goal of surgery to treat lumbar spinal stenosis is to decompress the central spinal canal and the neural foramina, creating more space and eliminating pressure on the spinal nerve roots. The most common surgery for treatment of lumbar spinal stenosis is direct decompression via a laminectomy and partial facetectomy. In this procedure, the patient is given a general anesthesia and an incision is made in the patient to access the spine. The lamina of one or more vertebrae may be partially or completely removed to create more space for the nerves. The success rate of decompressive laminectomy has been reported to be in excess of 65%. A significant reduction of the symptoms of lumbar spinal stenosis is also achieved in many of these cases. 
         [0006]    The failures associated with a decompressive laminectomy may be related to postoperative iatrogenic spinal instability. To limit the effect of iatrogenic instability, fixation and fusion may also be performed in association with the decompression. In such a case, the intervertebral disc may be removed, and the adjacent vertebrae may be fused. A discectomy may also be performed to treat DDD and disc herniations. In such a case, a spinal fusion would be required to treat the resulting vertebral instability. Spinal fusion is also traditionally accepted as the standard surgical treatment for lumbar instability. 
         [0007]    A wide variety of spinal fusion devices are used following partial or total discectomies for stabilization of the spine at that site. Many such devices are secured extradiscally, such as to the pedicles or spinous processes. For example, the spinous process fusion plate available from Medtronic, Spinal and Biologics of Memphis, Tennessee under the brand name CD Horizon Spire is typically secured to the spinous processes. See for example the devices and methods disclosed in U.S. Pat. Nos. 7,048,736 and 7,727,233, the entire contents of which are expressly incorporated herein by reference. These devices typically work for there intended purposes. However, with the demands of spinal surgery, the medical device industry is continually looking for ways to improve currently available devices. 
       SUMMARY 
       [0008]    The spinal implant described herein may include first and second plates, a brace extending between the plates and a locking mechanism that moves the two plates toward each other and locks them in an appropriate relative position. When installed in the patient&#39;s anatomy, the brace extends laterally through the interspinous space, and the plates extend superiorly-inferiorly along respective lateral sides of the spinous processes. 
         [0009]    The first plate and the second plate may each have a generally linear longitudinal axis or may extend along curved longitudinal axes or may have a longitudinal axis that is off-set along its height. Each plate may also have an inner face configured to abut adjacent spinous processes with projections extending therefrom that engage or “bite into” the spinous processes. The brace may be fixed to the first plate and extend through an opening in the second plate. Alternatively, the first plate may include an opening through which the brace extends and the brace may include an enlarged proximal end that can be located on the proximal side of the first plate to prevent that plate from moving proximally with respect to the brace. The opening in the second plate allows the brace to be placed through the opening and allows the second plate to slide along the brace and thus vary the distance between the first and second plate. The axis of the brace is transverse to the longitudinal axes of the first and second plates. The brace may be a hollow tube defining a lumen extending therethrough. The plate to which the brace is affixed may also define an opening to allow a locking element to extend through the first and second plates and through the brace. 
         [0010]    The locking element may include an enlarged distal element connected along its proximal portion to a proximal rod. The diameter of the enlarged distal element is chosen so that its maximum diameter is greater than the diameter of the lumen of the brace. The locking element is located within the lumen of the brace so that the enlarged distal element extends distally beyond the distal end of the brace and the rod extends proximally beyond the proximal end of the brace. When the locking element is pulled proximally, the enlarged distal end deforms the distal portion of the brace so the diameter of the distal portion of the brace increases so as to be greater than the diameter of the opening in the second plate, thus preventing the second plate from being moved distally off of the brace. Continued proximal movement of the locking element moves the two plates together so that the projections of each plate engage and “bite into” the spinous processes and lock the implant to the spinous processes. The proximal portion of the rod of the locking element extending from the proximal end of the brace may then be broken or cut off from enlarged distal end or the remainder of the distal portion of the rod. 
         [0011]    A method of implanting the spinal implant may include the following steps. After access to the desired spinal motion segment is obtained, a first plate is located adjacent to the proximal lateral sides of adjacent superior and inferior spinous processes. Where the brace is fixed to the first plate, placement of the first plate should be made so that the brace extends in the interspinous space through the sagittal plane. Where the brace is not fixed to the first plate, the brace is inserted through an opening in the first plate so the brace extends in the interspinous space through the sagittal plane and moved distally until an enlarged proximal tab abuts the proximal face of the first plate. The second plate is located over the brace so that the second plate is placed adjacent to the distal lateral sides of the adjacent superior and inferior spinous processes. The locking mechanism is then placed through the brace such that the proximal rod is first inserted through the distal opening to the lumen of the brace and moved proximally until the enlarged distal element abuts the distal opening of the brace. The surgeon may then pull the proximal rod from the proximal side of the brace to enlarge the distal portion of the brace. Continued proximal movement of the locking mechanism forces the enlarged distal element into the distal portion of the brace, enlarging this portion of the brace and forcing the distal plate to move proximally into engagement with the distal lateral faces of the adjacent superior and inferior spinous processes. Once the surgeon is satisfied with the placement of the implant, the surgeon may then break or cut off the proximal rod of the locking element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a perspective view of a spinal motion segment with a spinal implant located therein; 
           [0013]      FIG. 2  is a perspective view of the opposite side of the spinal implant shown in  FIG. 1 ; 
           [0014]      FIG. 3A  is a front elevation view of a spinal implant; 
           [0015]      FIG. 3B  is a front elevation view of the spinal implant shown in  FIG. 3A  but with the locking mechanism moved proximally with respect to the spinal implant; 
           [0016]      FIG. 3C  is a front elevation view of the spinal implant shown in  FIG. 3B  but with the locking mechanism moved further proximally with respect to the spinal implant; 
           [0017]      FIG. 3D  is a front elevation view of the spinal implant shown in  FIG. 3C  but with the proximal end of the locking mechanism removed; 
           [0018]      FIG. 4  is a cross-sectional view of the spinal implant shown in  FIG. 3A ; 
           [0019]      FIG. 5  is a cross-sectional view of the spinal implant shown in  FIG. 3D ; and 
           [0020]      FIG. 6  is a cross-sectional view of another embodiment of a spinal implant. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    As used in this specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, the term “a member” is intended to mean a single member or a combination of members, and “a material” is intended to mean one or more materials, or a combination thereof. Furthermore, the words “proximal” and “distal” refer to directions closer to and away from, respectively, an operator (e.g., surgeon, physician, nurse, technician, etc.) who would insert the medical device into the patient, with the tip-end (i.e., distal end) of the device inserted inside a patient&#39;s body first. Thus, for example, the device end first inserted inside the patient&#39;s body would be the distal end of the device, while the device end last to enter the patient&#39;s body would be the proximal end of the device. 
         [0022]    As used in this specification and the appended claims, the terms “up”, “upper”, “top”, “down”, “lower”, “bottom”, “front”, “back”, “rear”, “left”, “right”, “side”, “inner”, “middle” and “center”, and similar terms, refer to portions of or positions in or on the implant when the implant is oriented in its implanted position, such as shown in  FIG. 1 . 
         [0023]    As used in this specification and the appended claims, the term “axial plane” when used in connection with particular relationships between various parts of the implant means a plane that divides the implant into upper and lower parts. As used in this specification and the appended claims, the term “coronal plane” when used in connection with particular relationships between various parts of the implant means a plane that divides the implant into front and back parts. As used in this specification and the appended claims, the term “sagittal plane” when used in connection with particular relationships between various parts of the implant means a plane that divides the implant into left and right parts. 
         [0024]    As used in this specification and the appended claims, the term “body” when used in connection with the location where the device of this invention is to be placed, or to teach or practice implantation methods for the device, means a mammalian body. For example, a body can be a patient&#39;s body, or a cadaver, or a portion of a patient&#39;s body or a portion of a cadaver. A “body” may also refer to a model of a mammalian body for teaching or training purposes. 
         [0025]    As used in this specification and the appended claims, the term “parallel” describes a relationship, given normal manufacturing or measurement or similar tolerances, between two geometric constructions (e.g., two lines, two planes, a line and a plane, two curved surfaces, a line and a curved surface or the like) in which the two geometric constructions are substantially non-intersecting as they extend substantially to infinity. For example, as used herein, a line is said to be parallel to a curved surface when the line and the curved surface do not intersect as they extend to infinity. Similarly, when a planar surface (i.e., a two-dimensional surface) is said to be parallel to a line, every point along the line is spaced apart from the nearest portion of the surface by a substantially equal distance. Thus, two geometric constructions are described herein as being “parallel” or “substantially parallel” to each other when they are nominally parallel to each other, such as for example, when they are parallel to each other within a tolerance. Such tolerances can include, for example, manufacturing tolerances, measurement tolerances or the like. 
         [0026]    As used in this specification and the appended claims, the terms “normal”, “perpendicular” and “orthogonal” describe a relationship between two geometric constructions (e.g., two lines, two planes, a line and a plane, two curved surfaces, a line and a curved surface or the like) in which the two geometric constructions intersect at an angle of approximately 90 degrees within at least one plane. For example, as used herein, a line is said to be normal, perpendicular or orthogonal to a curved surface when the line and the curved surface intersect at an angle of approximately 90 degrees within a plane. Thus two geometric constructions are described herein as being “normal”, “perpendicular”, “orthogonal” or “substantially normal”, “substantially perpendicular”, “substantially orthogonal” to each other when they are nominally 90 degrees to each other, such as for example, when they are 90 degrees to each other within a tolerance. Such tolerances can include, for example, manufacturing tolerances, measurement tolerances or the like. 
         [0027]    A spinal implant  100  for spinal fusion that attaches to adjacent spinous processes to fixate the corresponding vertebrae relative to the other is described herein. Implant  100  may include two fixation plates  10 ,  20 , a brace  30  and a locking element  40 . Plates  10 ,  20  are adapted to be disposed on respective lateral sides of the adjacent superior and inferior spinous processes. Projections  15  may extend from the inner surfaces of plates  10 ,  20  and are adapted to engage or “bite into” the surfaces of the spinous processes to fix plates  10 ,  20  with respect to the spinous processes. Brace  30  may be fixed to plate  10  and is adapted to extend through at least plate  20  with distal plate  20  adapted to be moveable proximally with respect to brace  30 . Brace  30  may be hollow and may define a lumen  31  extending therethrough that defines a first diameter. Locking element  40  is adapted to be disposed within lumen  31 . 
         [0028]    Both proximal plate  10  and distal plate  20  may have a generally curved configuration that extends along a curving longitudinal axis. It is to be understood however that plates  10 ,  20  may be generally rectangular with a straight longitudinal axis or may have an offset configuration where the upper and lower portions of the longitudinal axis are offset from each other. Projections, or teeth,  15  extend inwardly away from the longitudinal axis of the plate on which they are located and toward the spinous process. As mentioned above, projections  15  are adapted to engage or “bite into” the surfaces of the spinous processes to fix plates  10 ,  20  with respect to the spinous processes. Each plate  10 ,  20  defines an opening  11 ,  21 , respectively, therein along a medial portion. Opening  21  in distal plate  20  should have a diameter large enough to allow distal plate  20  to slide proximally along brace  30 . Opening  11  in proximal plate  10  should have a diameter large enough to allow the proximal rod  42  of locking element  40  to slide proximally past proximal plate  10 . As shown in  FIG. 6 , plates  10 ,  20  may be substantially mirror images of each other. 
         [0029]    Brace  30  may have a generally tubular configuration defining lumen  31  therein. Brace  30  may be fixed to either plate  10 ,  20 . As shown in  FIGS. 1-5 , brace  30  may be fixed along its proximal end to proximal plate  10  using any suitable means such as welding, brazing, adhesive or mechanical engagement. Distal plate  20  may define an opening  21  to allow brace  30  to extend through plate  20  and thus slide along brace  30  and vary the distance between proximal plate  10  and distal plate  20 . The axis of brace  30  is generally transverse to the longitudinal axes of plates  10 ,  20 . Proximal plate  10  may also define an opening  11  to allow proximal rod  42  to extend proximally through plate  10 . As shown, in  FIG. 6 , brace  30 ′ need not be fixed to plate  10 ′. Instead, plate  10 ′ may define an opening  11 ′ having a diameter to allow brace  30 ′ to extend through plate  10 ′. A proximal flange  35  may be located at the proximal end of brace  30 ′ to prevent plate  10  from moving proximally off of brace  30 ′. As mention above, the diameter of the proximal portion of brace  30 ′ and the diameter of opening  11 ′ may be matched to provide an interference fit therebetween. 
         [0030]    Locking element  40  includes an enlarged distal knob  41  and a proximal rod  42  attached to distal knob  41 . The maximum diameter of enlarged distal knob  41  is chosen so that it is greater than the diameter of lumen  31 . Although knob  41  is shown in the FIGS. as having a generally circular cross-section, it is to be understood that other configurations could be used for knob  41 . However, it is desireable that the proximal portion of knob  41  have a tapered proximal configuration that increases in diameter in the distal direction. This taper facilitates proximal movement of locking element  40  with respect to brace  30 . Locking element  40  is disposed within lumen  31  of brace  30  so that knob  41  is initially located beyond the distal end of brace  30  and the proximal end of rod  42  extends proximally beyond the proximal end of brace  30  and plate  10 . See, e.g.  FIG. 4 . When locking element  40  is pulled proximally, the tapered portion of knob  41  engages the distal end of brace  30  and forces the distal portion of brace  30  to deform so it increases in diameter such that the enlarged diameter is greater than the diameter of opening  21  in distal plate  20 . This increase in diameter for the distal portion of brace  30  prevents plate  20  from being moved distally off of brace  30  and thus locks plate  20  to brace  30  and plate  10 . In addition, since the increased diameter of the distal portion of brace  30  caused by knob  41  is larger than the diameter of opening  21 , proximal movement of knob  41  forces plate  20  to move proximally. Continued proximal movement of locking element  40  moves plates  10 ,  20  together so that projections  15  of each plate  10 ,  20  engage and “bite into” the spinous processes and lock implant  100  to the spinous processes. 
         [0031]    Once plates  10 ,  20  are fixed to the adjacent spinous processes, rod  42  may then be removed from knob  41  so that there is nothing that extends proximally beyond plate  10 . See  FIG. 5 . Rod  42  or a proximal portion of rod  42  can be removed from locking element  40  by any number of mechanisms. For example, the compressive force between plates  10 ,  20  that is necessary to ensure that plates  10 ,  20  can be compressed so that projections  15  “bite into” the spinous processes can be determined. Once this force is determined, the cross-sectional area of a segment of rod  42  can be locally decreased so that it fractures after the desired compressive force has been reached. This cross-sectional area can be computed based on the mechanical properties chosen for knob  41  and rod  42  of locking element  40 . Alternatively, a mechanical connection, such as a thread located along the distal end of rod  42  and a tapped hole formed in knob  41 , may be used. In such an embodiment, the user would be able to manually disengage rod  42  from knob  41  after plates  10 ,  20  have been fixed to the spinous processes. Also, a cutting device may be used to cut off a proximal portion of rod  42 . 
         [0032]    A method of implanting the spinal implant may include the following steps. After access to the desired spinal motion segment is obtained, proximal plate  10  is located adjacent to the proximal lateral sides of adjacent superior and inferior spinous processes. Where brace  30  is fixed to plate  20 , proper placement of plate  10  ensures that brace  30  extends in the interspinous space through the sagittal plane. Where brace  30 ′ is not fixed to plate  10 ′, the distal end of brace  30 ′ may be inserted through opening  11 ′ in plate  10 ′, after plate  10 ′ is properly located adjacent the proximal lateral sides of the adjacent spinous processes, and moved distally through the interspinous space until flange  35  abuts the proximal medial face of plate  10 ′ around opening  11 ′. With proximal plate  10  and brace  30  properly located with respect to the spinal segment, the distal end of brace  30  should extend past the distal lateral sides of the adjacent spinous processes. Distal plate  20  may then be placed over the distal end of brace  30  so that plate  20  is placed adjacent to the distal lateral sides of the adjacent superior and inferior spinous processes. Locking mechanism  40  may then be placed into lumen  31  through brace  30  such that the proximal end of rod  42  is first inserted into the distal end of brace  30  and moved proximally through brace  30  until knob  41  abuts the distal opening of brace  30 . Rod  42  may continue to be pulled from the proximal side of brace  30  so knob  41  enlarges the distal portion of brace  30  and locks plate  20  onto brace  30  and with respect to plate  10 . Continued proximal movement of locking mechanism  40  forces knob  41  further into the distal portion of brace  30 , enlarging this portion of brace  30  and forcing distal plate  20  to move proximally into engagement with the distal lateral faces of the adjacent superior and inferior spinous processes. Once the surgeon is satisfied with the placement of implant  100 , rod  42  may be cut or broken off of knob  41 . For example, knob  41  may be connected to rod  42  by a frangible connection that may be broken by specific manipulation of rod  42 . If desired, the distal portion of brace  30  extending beyond the distal face of distal plate  20  can be removed to minimize the space occupied by implant  100 . However, it is contemplated that only a minor length of the distal portion of brace  30  will extend beyond the distal face of distal plate  20  after plates  10 ,  20  have been compressed into engagement with the spinous processes. Thus it may be unnecessary to remove any portion of the distal portion of brace  30 . 
         [0033]    Implant  100  may be formed of suitable biocompatible materials. For example, plates  10 ,  20  may be formed from stainless steel, titanium and its alloys, polymers such as PEEK, carbon fiber and the like. A softer, more ductile material, such as  316  stainless steel, may be used for brace  30 . This material would allow brace  30  to deform without fracture and would not require an extremely high force to deform. A harder material, such as a cobalt chrome alloy, may be used for locking element  40 . The various materials used for the parts of implant  100  may be considered in combination with the geometry of the various parts to obtain a customized force/implantation profile to facilitate implantation by the surgeon and achieve an optimized function. 
         [0034]    While various embodiments of the spinous process fusion device are described herein, it should be understood that they have been presented by way of example only, and not limitation. Many modifications and variations will be apparent to the practitioner skilled in the art. The foregoing description of the spinous process fusion device is not intended to be exhaustive or to limit the scope of the invention. It is intended that the scope of the invention be defined by the following claims and their equivalents.