Abstract:
For minimally-invasive therapy for spinal canal stenosis, a therapeutic device capable of stationing an interspinous process spacer without the need of large skin incision or ligamentous tissue incision and also without the need of detaching of the paraspinal muscle from the spine. The interspinous process spacer includes a conoid screw region ( 2 ) to be screwed into a processus spinosus interspace; a spacer region ( 3 ) in the longitudinal direction of the screw region ( 2 ); head region ( 4 ) capable of free interlocking with a tool arbitrarily; and through-hole ( 5 ) passing through the axial centers of screw region ( 2 ), spacer region ( 3 ) and head region ( 4 ). The processus spinosus interspace is enlarged by screwing of the screw region ( 2 ) into the processus spinosus interspace. The spacer region ( 3 ) is pinched upon passing of the screw region ( 2 ) through the processus spinosus interspace to attain enlarging and fixing of adjacent processus spinosus interspaces.

Description:
BACKGROUND 
     The present invention relates to a minimally-invasive implant for the purpose of opening and enlargement of a processus spinosus interspace, and particularly an interspinous process spacer for enlarging the spinal canal. 
     The spinal canal is a cylindrical space in a vertical direction located in the center of a backbone (corpus vertebrae), and a spinal cord and cauda equina (nerve) are housed therein and protected firmly. Spinal canal stenosis where this spinal canal is stenosed due to various causes such as deformation of a bone, a cartilage or a ligament to press the nerve therein has become a major social problem as the number of patients has increased in conjunction with an aging society. 
     In particular, lumbar spinal canal stenosis refers to a state where the deformation and thickening of lumbar vertebra and intervertebral joints as well as deformation and bulging of the intervertebral disc which is cartilage tissue, or hypertrophy of a ligament occurs and these make the spinal canal narrow to apply pressure or squeeze the nerves and blood vessels. This symptom is typified by a gait disorder such as neurogenic intermittent claudication, and this symptom is characterized in that a lower limb does not advance forward after walking for a few minutes and when taking a rest by crouching, subsequently the patient can walk again. In addition, sciatic neuralgia, lower limb symptoms such as palsy, a cold sensation and a feeling of lassitude, lumbar pain and urinary bladder and rectal disorders (disorders of urination and defecation) and the like are lumbar and lower limb symptoms of lumbar spinal canal stenosis. 
     It has been known that lumbar and lower limb symptoms due to lumbar spinal canal stenosis are anatomically reduced and improved by anteflexion of the lumbar vertebra, e.g., crouching or riding a bicycle. 
     As conservative therapeutic methods which improve symptoms in daily life, physical therapies such as drug therapy of administering a drug which is a vasodilator drug or increases blood flow to a nerve root or a periphery of the cauda equina, an epidural block method, a radicular block method, an orthosis therapy of wearing a lumbar vertebra bending position corset to keep the lumbar portion at rest at the bending position, and an ultrasonic therapy and a hot pack therapy for improving pain relief, muscular spasticity and blood circulation are available. 
     When conservative therapy is ineffective and severe neurological disorder and intermittent claudication sustain, a surgical therapy countering this conservative therapy is available, and neurological decompression procedures such as a laminectomy and expanded fenestration have been conventionally performed. In the laminectomy and expanded fenestration, surgical invasion is applied to the patient to restore the lumbar vertebra stenosis site, and thus it is necessary to give general anesthesia to the patient. In this procedure, the patient is likely to be exposed to the risk of hemorrhaging and serious complications, and hospitalization for several days to several weeks is required for a patient after the operation. Therefore, this procedure heavily burdens the patient, and particularly when the patient is elderly, the symptom is sometimes further worsened. 
     However, in recent years, it has been reported that by stationing an interspinous process spacer in a minor surgical method, the effect of local lumbar anteflexion is obtained and satisfactory results are obtained (See International Application No. 2005-517467 and Sekitsui Sekizui Shinkei Shujutsu Shugi 6(1):120-123, 2004, “Therapeutic experiences of lumbar spinal canal stenosis by interspinous process spacer (Sten-X™) performed under local anesthesia.”). 
     Also, as the interspinous process spacer, the spacer inserted in the processus spinosus interspace using a guide pin and an obturator is publicly known (See WO 2005/072301). 
     Such a minimally invasive procedure can be performed under a local anesthesia. Thus, a shorter period is needed for recovery, there is almost no hemorrhaging, the risk of serious complications is reduced and therapeutic cost required for the patient is less. Therefore, it has been desired that spinal canal stenosis can be treated using the minimally invasive procedure. 
     As described above, it has been reported that by stationing the interspinous process spacer, the effect of local lumbar anteflexion is obtained and satisfactory results are obtained. A prior and existing spacer device used for this is described with reference to  FIGS. 1A-1D .  FIGS. 1A-1D  show an entire schematic view and a use example of the prior and existing spacer device.  FIG. 1A  shows a completed view of an assembly of the spacer device,  FIG. 1B  shows an appearance where one wing region has been removed in the spacer device,  FIGS. 1C and 1D  show the appearances before and after attaching the spacer device. In the prior and existing spacer device  30 , as shown in  FIG. 1A , the wing regions  32  are constituted by pinching the spacer region  31 , and as shown in  FIG. 1B , one wing region is detachable. 
     Such a spacer device is disposed in the stenosed processus spinosus interspace as shown in  FIG. 1D  to enable enlarging and fixing the processus spinosus interspace. 
     In such a spacer device  30 , as shown in  FIGS. 2A-2D , a part of a back of a patient is cut open by means of surgical operation, the paraspinal muscle is detached, the processus spinosus and interspinous ligament are exposed ( FIG. 2A ), first a specialized device is inserted in the processus spinosus interspace to provide a hole in the processus spinosus interspace ( FIG. 2B ), subsequently the spacer device is inserted in the processus spinosus and screwed into the processus spinosus interspace ( FIG. 2C ), and finally the wing region is placed from above and fixed with a screw ( FIG. 2D ). Thus, in the operation using this device, a minimal skin incision of about 3 cm or more is required, and it is necessary to detach the paraspinal muscle from the spine. 
     Such a procedure may be possible under local anesthesia but is difficult. Further surgical invasiveness is never minor. 
     In the interspinous process spacer disclosed in WO 2005/072301, in order to insert the spacer in the processus spinosus interspace, it is required to first insert the guide pin from the skin incision site, subsequently the obturator is inserted which covers it to enlarge the processus spinosus interspace and finally insert the spacer. This obturator has a large diameter, thereby functioning to construct a path from the skin incision site to the processus spinosus interspace for inserting the spacer. However, in insertion of such an obturator, if the processus spinosus interspace is enlarged smoothly, it is required to insert the obturator by sequentially changing the diameter from small to large. Thus, the patient is heavily burdened and simultaneously the operator is burdened because of multiple procedures. 
     SUMMARY 
     Based on the above problems, the present invention aims at realizing a more minimally invasive therapeutic method for spinal canal stenosis, and aims at providing a therapeutic device capable of simply stationing the interspinous process spacer without the need for a large skin incision and also without the need for detaching the paraspinal muscle from the spine. 
     The present inventor is a doctor specializing in organ treatment, has invented the interspinous process spacer according to the present invention through a wide range of clinical experience against spinal canal stenosis, and completed the present invention by producing and improving various prototype products. In order to achieve the above object, the interspinous process spacer according to the present invention including a conoid screw region to be screwed into the processus spinosus interspace; a spacer region formed in a longitudinal direction of the screw region; and a head region capable of freely interlocking with a tool arbitrarily or freely attaching a coupling member arbitrarily; and has a through-hole in an axial center of the screw region, the spacer region and the head region. 
     According to the above constitution, the processus spinosus interspace is enlarged smoothly by utilizing an opening and enlarging force generated when the screw region is screwed and inserted in the processus spinosus interspace, and the spacer region is pinched by passing the screw region through the processus spinosus interspace. Thus, finally the adjacent processus spinosus interspaces can be enlarged and fixed (the predetermined distance can be maintained in neutral or extension position). In addition, the head region capable of freely interlocking with the tool arbitrarily or freely attaching the coupling member arbitrarily means including, for example, a hole for a hexagon driver tool. Using the driver tool, it is possible to push the interspinous process spacer of the present invention by rotating from the small incision site toward the internal processus spinosus interspace. By forming the through-hole in the axial center of the screw region and the spacer region, it becomes possible to couple with the guide member such as a guide wire through the through-hole. By the guide member, the interspinous process spacer of the present invention is guided to the processus spinosus interspace from the small incision site toward the internal processus spinosus interspace. 
     Here, it is preferable that the screw region of the interspinous process spacer according to the present invention has a substantially radial outer contour or a cone shape having a round tip end part. More preferably, the screw region of the interspinous process spacer according to the present invention is formed into not a simple screw shape but an interference screw shape. The interspinous process spacer of the present invention proceeds in the dorsal skin and muscle of the patient by screw-rotating like a drill. By an obtuse angle and round cone-shape rather than an acute angle tip end part the screw region can reduce risk such as wrong insertion into the spinal canal. 
     In addition, the cross section of the spacer region of the interspinous process spacer according to the present invention can be circular, elliptical, substantially triangular, substantially rectangular or polygonal. As described above, by passing the screw region through the processus spinosus interspace, the spacer region is pinched to enlarge and fix the adjacent processus spinosus interspaces. 
     If the cross section of this spacer region is circular or elliptical, even when the screw region is passed through the processus spinosus interspace in any condition, it is possible to easily pinch the spacer region in the processus spinosus interspace. In addition, if the cross section of the spacer region is substantially triangular or substantially rectangular, the range joined to the adjacent processus spinosus is increased compared with the circular and elliptical cases. Thus, it is possible to stably pinch the spacer region in the processus spinosus interspace. 
     It is preferable that an outer shape of the entire interspinous process spacer according to the present invention is elliptical. From anatomical morphology, a wholly elliptical shape of the interspinous process spacer is easily housed between vertebral arches. 
     It is preferable that the diameter of the spacer region is larger than the diameters of the screw region and the head region in the diameter of the through-hole in the interspinous process spacer according to the present invention and the cross section of this through-hole in the longitudinal direction is substantially a spindle. 
     By making the hole for the guide wire of the interspinous process spacer spindle, i.e., making a middle thick, there is an advantage that the interspinous process spacer can be smoothly inserted even under the condition where the guide wire is not straight but bent. 
     It is also preferable that the screw region and the spacer region of the interspinous process spacer according to the present invention are composed of a ceramic material selected from alumina, zirconium, hydroxyapatite and calcium phosphate, a calcium phosphate based glass material having bioactivity, a resin material, a plastic material or a metal material selected from stainless steel, titanium and titanium alloy. 
     In addition, in the interspinous process spacer according to the present invention, the through-hole formed in the axial center of the screw region and the spacer region is used as an insertion hole of the guide member. By coupling with the guide member introduced in the processus spinosus interspace via the dorsal skin in the patient, the interspinous process spacer can be easily guided to the processus spinosus interspace. 
     The method of percutaneously enlarging the processus spinosus interspace using the interspinous process spacer of the present invention is achieved by the following procedures. The processus spinosus interspace is enlarged by first identifying the location of spinal canal stenosis by radioscopic techniques such as an X-ray, and including (1) a stage of introducing the guide member from a posterolateral side via the dorsal skin in the patient to the above location; (2) a stage of inserting the guide member in the through-hole in the interspinous process spacer of the present invention; (3) a stage of inserting the screw region of the interspinous process spacer by rotating using a tool such as a driver; (4) a stage of enlarging the processus spinosus interspace by insertion of the screw region by rotating, subsequently passing the screw region through and pinching the spacer region in the processus spinosus interspace to fix the processus spinosus interspace; and (5) a stage of removing the guide member and the tool. 
     In particular, it is preferable that the interspinous process spacer of the present invention is embedded in the processus spinosus interspace of the adjacent thoracic vertebra and/or lumbar vertebra by the method of percutaneously enlarging the processus spinosus interspace described above. 
     In the interspinous process spacer of the present invention, by compositing the screw region and the spacer region, enlargement of the processus spinosus interspace and the insertion of the spacer can be achieved in one step. Further it becomes possible to insert and station the interspinous process spacer percutaneously even under local anesthesia. Thus, there is the effect that a minimally invasive operation simple in procedure can be performed. In particular, the spacer of the present invention far exceeds the prior and existing spacer device in that the interspinous process spacer can be stationed without the need for large skin incision or ligamentous tissue incision and also without the need for detaching the paraspinal muscle from the spine. 
     In addition, an early effect after operation can be anticipated, an outpatient operation is thought to be possible, and it is possible to further reduce temporal, physical and financial burdens on the patient. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1D  are perspective views of the prior and existing spacer device, and  FIGS. 1B and 1C  are cross-sectional views showing the prior and existing spacer device in use. 
         FIGS. 2A-2D  show a surgical operation using the prior and existing spacer device. 
         FIGS. 3A-C  show an example of the interspinous process spacer according to the present invention where  FIG. 3A  is a front view,  FIG. 3B  is a side view and  FIG. 3C  a rear view. 
         FIG. 4A  is a cross sectional view of spinal canal, and  FIG. 4B  is a diagrammatic view showing the interspinous process spacer of the present invention mounted in the spinal canal. 
         FIGS. 5A-5D  are diagrammatic views showing procedures of an operation using the interspinous process spacer of the present invention. 
         FIG. 6A  is a diagrammatic side cross sectional view of spinal canal,  FIG. 6B  is a similar view showing the interspinous process spacer according to the present invention mounted in the spinal canal, and  FIG. 6C  is a diagrammatic cross sectional view taken along the plane A-A′. 
         FIG. 7  is a diagrammatic side view of the interspinous process spacer of Example 1. 
         FIG. 8  is a diagrammatic side view showing the interspinous process spacer made without a step. 
         FIG. 9A  is a perspective view of the interspinous process spacer in Example 1. 
         FIG. 9B  is a side view of the interspinous process spacer of  FIG. 9A . 
         FIG. 9C  is a right end view of the interspinous process spacer of  FIG. 9B . 
         FIG. 9D  is a left end view of the interspinous process spacer of  FIG. 9B . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described in detail below with reference to the drawings. 
       FIGS. 3A-C  show the shape of the interspinous process spacer according to the present invention. As is shown in  FIG. 3B , the interspinous process spacer of the present invention is constituted by including the conoid screw region  2 ; the spacer region  3  formed in the longitudinal direction of the screw region; the head region  4  including the hole  6  for the hexagon driver which can interlock with the hexagon driver and the insertion hole  5  for the guide wire penetrating in the axial center of the screw region  2 , the spacer region  3  and the head portion  4 . As shown in  FIG. 3B , it is preferable that the outer contour of the shape in the cross sectional view of the interspinous process spacer is substantially elliptical. From clinical experience, it was found to be easily housed in vertebral arches. 
     Here, the screw region  2  of the interspinous process spacer has a substantially radial outer contour. This is because when the screw region  2  passes through the processus spinosus interspace, the processus spinosus interspace can be enlarged by the radial outer contour and the spacer region  3  is easily fitted in the processus spinosus interspace. Further, the cross section of the spacer region  3  in the interspinous process spacer is formed into circular shape, and the spacer region is wholly cylindrical. This is because the spacer region  3  can be stably fitted in the processus spinosus interspace even when the screw region  2  passes through the processus spinosus interspace at any angle. 
     By including the hole  6  for the hexagon driver, the interspinous process spacer of the present invention can be pushed from the small incision site toward the internal processus spinosus interspace by rotating the interspinous process spacer of the present invention using a driver tool. By including the insertion hole  5  for the guide wire, the interspinous process spacer of the present invention can be coupled with the guide wire, and by inserting the guide wire from the small incision site toward the internal processus spinosus interspace, the spacer can be guided to the processus spinosus interspace along the guide wire. 
     In  FIG. 4A , a cross sectional view of the spinal canal is shown. In  FIG. 4A ,  10  represents processus spinosus,  11  represents vertebral body and  12  represents vertebral foramen. As shown in  FIG. 4B , finally the spacer region of the interspinous process spacer is pinched between adjacent processus spinosus  11 . 
     In  FIGS. 5A-5D , the procedure in the operation using the interspinous process spacer according to the present invention is shown. First, as shown in  FIG. 5A , the guide wire  7  is inserted from the dorsal small incision site in the patient to insert the guide wire  7  between the processus spinosus  10 . Subsequently as shown in  FIG. 5B , one end of the inserted guide wire  7  is passed through the insertion hole for the guide wire penetrating in the axial center of the interspinous process spacer according to the present invention. And, as shown in  FIG. 5C , the hexagon driver  8  is inserted in the hole for the hexagon driver provided in the head region of the interspinous process spacer  1 , and the interspinous process spacer  1  is screwed in the processus spinosus interspace using a hexagon driver  8 . At that time, the processus spinosus interspace can be smoothly enlarged by the radial outer contour of the screw region of the interspinous process spacer  1 . And, as shown in  FIG. 5D , when the screw region of the interspinous process spacer  1  is passed through the processus spinosus  10 , the spacer region of the interspinous process spacer  1  is pinched, and the processus spinosus interspace can be stably enlarged and fixed. 
       FIG. 6A  shows a side cross sectional view of the spinal canal, and  FIGS. 6B and 6C  show the appearances where the interspinous process spacer according to the present invention has been loaded in the spinal canal. In the figure,  20  represents a hypertrophic yellow ligament and  21  represents the bulging of intervertebral disc. 
     It can be seen that the spinal canal is stenosed in  FIG. 6A  and as shown in  FIG. 6B , the spinal canal has been enlarged by the interspinous process spacer according to the present invention. 
     The present invention can be executed by a specific method other than the method described herein above without departing from the scope and the essential features of the present invention. In one embodiment, the interspinous process spacer according to the present invention and the method of percutaneously enlarging the processus spinosus interspace are used for enlarging and fixing the adjacent processus spinosus interspaces. However, the present invention may be applied to making a space in other tissue in the body (enlarging and fixing the distance between the bones). The present embodiment is to be considered in all respects without being limited, and all changes which occur within the meanings of claims and the equivalent scope are intended to be included therein. 
     Example 1 
     An outline drawing of the interspinous process spacer in Example 1 is shown in  FIG. 7 . In the interspinous process spacer in Example 1, the spacer region  3  has been made by removing the center of an elliptical sphere made from titanium and the screw region  2  has been made by threading one end section of the spacer. 
     The dimensions (length and diameter) of the spacer region  3  have some variation depending on the condition of the processus spinosus interspace in a diseased part, and  FIG. 7  consistently shows one example of the dimensions. 
     The tip end part of the screw region  2  has been formed into a hemisphere in  FIG. 7 , but this may be formed into a cone shape having a round tip. In addition, a joint of the screw region  2  and the spacer region  3  has produced a step in  FIG. 7 , but as shown by an arrow in  FIG. 8 , an end-to-side of the spacer region  3  may be extended to a coronal side of the screw region  2  to be made adjacent without the step. In addition, a screw pitch in the screw region  2  is about 1 to 2 mm, and the screw wing is protruded from the radial outer contour of the screw region  2 .  FIGS. 9A-9D  include a perspective view, a plane view, a right side view and a left side view of the interspinous process spacer in Example 1, respectively. 
     Next, an insertion procedure protocol of the interspinous process spacer of the present invention will be described. The targeted patient is a patient diagnosed with lumbar spinal canal stenosis who exhibits a so-called intermittent claudication, and whose symptoms are reduced by anteflexion of lumbar vertebra and whose arteriosclerotic obliteration has been denied. However, extreme lumbar kyphos, epiphysis and lateral curvature are to be excluded, and severe osteoporosis is also to be excluded. 
     As a measurement and plan before the operation, the size (diameter) of the spacer region of the interspinous process spacer is determined on an X-ray side image of a sitting position and a lumbar maximum anteflexion position (actual measurement). Subsequently, the full length of the interspinous process spacer is determined by measuring the distance between superior articular processes on a standing position X-ray image or CT image. Also, an entry point and an angle of the guide pin are measured on the CT image. 
     The protocol of the actual operation is shown by the following procedures (a) to (i). 
     (a) Radioscopy (image) is performed in a knee/chest position. 
     (b) The entry point of the guide pin is determined according to the measurement. A horizontal incision of about 1 cm is made on the skin at the determined position. 
     (c) The guide pin is inserted. It is confirmed by an radioscopy (image) that the guide pin has passed the portion as close as possible to the base of the targeted processus spinosus interspace and the tip end of the pin has passed over an opposed intervertebral facet joint. 
     (d) A small incision is given to fascias according to the skin incision, and the interspinous process spacer of the present invention is inserted along the guide pin. 
     (e) The interspinous process spacer is allowed to proceed using the driver. 
     (f) When the tip end part of the interspinous process spacer reaches the processus spinosus interspace, the spacer is inserted by adding a rotational force to the driver. The screw region proceeds by enlarging the processus spinosus interspace and the spacer region is pinched, thereby the interspinous process spacer is fixed. 
     (g) The driver is changed to a multi-axial type (the tip has a paper-covered lamp shape), the guide pin is removed and subsequently the position (slope) of the interspinous process spacer is adjusted. 
     (h) The position of the interspinous process spacer is confirmed again by radioscopy (image), and subsequently the driver is removed. 
     (i) The fascias and skin are sewn to finish the operation. 
     The interspinous process spacer according to the present invention is anticipated to be utilized as a medical device useful for surgical therapy of spinal canal stenosis. 
     DESCRIPTION OF REFERENCE CHARACTERS 
     
         
         
           
               1 . Interspinous process spacer according to the present invention 
               2 . screw region 
               3 . spacer region 
               4 . head region 
               5 . insertion hole for guide wire 
               6 . hole for hexagon driver 
               7 . guide wire 
               8 . hexagon driver 
               10 . processus spinosus 
               11 . vertebral body (lumbar vertebra) 
               12 . vertebral foramen 
               13 . nerve root 
               20 . hypertrophic yellow ligament 
               21 . bulging of intervertebral disc 
               22 . small incision site 
               30 . prior and existing spacer device (spacer device shown in the Sekitsui Sekizui Shinkei Shujutsu Shugi publication) 
               31 . spacer region 
               32 . wing region