Abstract:
The method and apparatus as shown in  FIGS. 8-10  in which a fluid expandable member ( 208 ) is positioned in concentric relation about a needle ( 202 ). The fluid expandable member ( 208 ) is expanded into the nucleus pulposus potential space bordered by the annulus fibrosus of an intervertebral disk. Then, thermoplastic material in a flowing state is injected by a needle ( 202 ) within the annulus fibrosus to collapse the fluid expandable member ( 208 ) and occupy the space formerly occupied by the fluid expandable member ( 208 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of pending application Ser. No. 09/456,375 filed Dec. 8, 1999; which is a continuation-in-part of application Ser. No. 09/274,217 filed Mar. 23, 1999; which is a continuation-in-part of application Ser. No. 09/255,372 filed Feb. 22, 1999. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to surgical methods generally, and is more specifically related to a method and apparatus for treating intervertebral disks of mammals. 
     BACKGROUND OF THE INVENTION 
     The intervertebral disk is a disk with fibrosus bands occupying the space between two vertebrae. The anatomy of the disk provides a cushion to allow motion, limit motion and provide space, distancing the vertebra off the nerves and compressible tissue. Part of the vertebrae are bony blocks, which, when stacked one upon the other, form the anterior portion of the spine. The fibrosus band includes an outer annulus fibrosus which surrounds an inner nucleus pulposus. Annulus fibrosus, as referred to herein, is the marginal or peripheral portion of an intervertebral disk. Intervertebral disks are prone to injury. Due to the low blood supply to this area, intervertebral disks are slow to heal, and may not materially heal. When the annulus fibrosus is torn, or punctured, the nucleus pulposus can leak or migrate from the annulus fibrosus. The nucleus pulposus is a substance of jelly like consistency found in the center of an intervertebral disk and flows from the associated annulus fibrosus when the annulus fibrosus is ruptured or prolapsed. 
     The effect of a ruptured or prolapsed annulus fibrosus may result in spasm, and neurological compromise, such as the compressed nerve and other compressible soft tissues, i.e. arteries, veins. Degeneration of the condition may increase over time, resulting in chronic and debilitating pain. The condition is usually disabling. 
     Suppressive measures include steroidal injection, removal of the nucleus pulposus, and fusion either by donor bone, coral or by metal bracing. If disk removal is performed, a healthy part of the disk is often taken, eradicating the function of the joint, and accelerating the degeneration of adjacent segments of the body, as the body attempts to stabilize. This approach frequently leaves the patient immunologically and structurally compromised if not permanently disabled. 
     Isolated treatment to only the damaged structures employing the most non-invasive procedure possible is preferred. This approach allows as much of the healthy tissue as possible to remain, and to retain normal neurological function. While the offending material can be removed, the material must be replaced with a material which will perform the function formerly performed by the material removed. A need exists for a process which limits the material removed from the intervertebral disk, and which replaces the material so removed with a composition that is physiologically acceptable to the human body, and which allows the intervertebral disk to retain motion and characteristics of normal joint function, including cushioning the joint as compression is introduced from the stacking of the vertebrae. The thermoplastic material must be pliable in its application, and non-flowing after replacement. 
     In addition, many patients suffer from scoliosis or lateral curvature of the spine. The most common remedy at the present time is the fusion normally by donor bone or metal bracing which oftentimes is not successful or only partially successful. Pain normally accompanies scoliosis and pain suppressants may result in an undesirable chemical dependency in some instances. A need exists to correct the abnormal curvature of the spine without utilizing fusion techniques applied to the spine. 
     SUMMARY OF THE INVENTION 
     The present invention is particularly directed to a process for treating the spine including the injection of a thermoplastic material heated to a predetermined temperature for injection into the nucleus pulposus in a flowing state where it cools and sets at body temperature into a non-flowing state. Inorganic materials have been shown to penetrate the endplates of the associated vertebrae. A thermoplastic or thermoplastic polymer material is any plastic or organic material that softens when heated and hardens when cooled. The thermoplastic material prior to injection is heated to a temperature sufficient for the material to flow under pressure into the nucleus pulposus and, after it sets into a non-flowing state at body temperature, the material retains sufficient resilience to provide desired cushioning of the spine. 
     A thermoplastic material which has been found to be highly satisfactory is gutta percha which is normally combined with other elements or ingredients in a suitable gutta percha compound. Gutta percha is a linear crystalline polymer which melts at a predetermined temperature a random but distinct change in structure results. Normal body temperature is 37 C and a suitable thermoplastic material hardens into a non-flowing state at a temperature range between about 35 C and 42 C (the degree symbol for temperature is omitted in all references herein to a specific temperature). A crystalline phase appears in two forms; an alpha phase and a beta phase. The alpha form is the material that comes from the natural tree product. The processed form is the beta form. When heated, gutta percha undergoes phase transitions. When there is a temperature increase, there is a transition from beta phase to alpha phase at about 46 C. The gutta percha changes to an amorphous phase about 54 C to 60 C. When cooled very slowly, about 1 C per hour, the gutta percha crystallizes to the alpha phase. Normal cooling returns the gutta percha to the beta phase. Gutta percha softens at a temperature above about 64 C. A suitable gutta percha compound is dental gutta percha which contains by weight only about 20% gutta percha with zinc oxide comprising about 60% to 75% of the material. The remaining 5% to 10% consists of various resins, waxes, and metal sulfates. The percentages listed are directed to an optimum gutta percha compound. The preferred percentage of gutta percha is in the range of 15% to 40%. Zinc oxide and metals in the gutta percha compound are desirable for imaging such as X-rays while resins and waxes are desirable for obtaining an adequate flow of the thermoplastic material. Gutta percha provides the desired resiliency at body temperature and is at least about 15% of the compound. Zinc oxide also provides an anti-inflammatory property. In some instances, a mineral trioxide aggregate may be added to the gutta percha compound. 
     An injection device, such as an injection gun, is utilized for heating and injecting the thermoplastic material under a predetermined pressure within the spine. The injection device may utilize a silver needle, encased in ceramics, of about 20 to 30 centimeters in length with a diameter as high as 1 centimeter. The size of the needle may depend on such factors as the amount of thermoplastic material to be injected, the temperature of the thermoplastic being injected, and the axial pressure applied by the injection device, such as a piston or plunger, to the thermoplastic material to force the heated material from the end of the needle into the spine. The thermoplastic material is physiologically acceptable to the human body. 
     When the thermoplastic material is utilized to treat a ruptured annulus fibrosus, the nucleus pulposus is removed and the material removed is replaced by the heated thermoplastic material which sets at body temperature and provides sufficient resilience after setting to permit adequate motion and cushioning of the vertebrae. The cushioning effect of the gutta percha compound provides a semimobile disk as a buffer to a fusion to reduce the possibility of sequential iatrogenic disk degeneration. The thermoplastic material is injected within the potential nucleus pulposus space bordered by the annulus fibrosus to replace the removed nucleus pulposus by a needle of the injection device. 
     When the thermoplastic material is injected within the spine to reduce a scoliosis, the material is sequentially injected by a needle of the injection device into the annulus fibrosus or interannular at the apex and adjacent joints of the concavity of the scoliosis. Such an injection tends to straighten the curvature of the spine is a wedge-like action. 
     An embodiment illustrated in  FIGS. 8-10  includes an injection system in which an expandable member is first expanded into the annulus fibrosus of a disk and then a thermoplastic material is injected into the annulus fibrosus to collapse the expandable member and occupy the space formerly occupied by the expandable member. The expandable member is mounted in concentric relation about the needle. 
     It is an object of the present invention to provide a method of injecting a thermoplastic material into the annulus fibrosus of a spine. 
     A further object of the present invention is to provide such a method in which the thermoplastic material is heated to a predetermined temperature for flow into the annulus fibrosus and hardens when it cools from body temperature into a non-flowing state to form a resilient support for cushioning between vertebrae. 
     Another object of the invention is to provide a method to treat a ruptured annulus fibrosus of a spine by removal of the nucleus pulposus and injection of a thermoplastic material into the annulus fibrosus to replace the nucleus pulposus. 
     An additional object is to provide an apparatus to treat an annulus fibrosus of a spine in which an injection device heats the thermoplastic material for flow into the annulus fibrosus and another injection member is effective for expanding an expandable member in the annulus fibrosus. 
     Other objects, features, and advantages of the invention will be apparent from the following specification and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic view of a ruptured/prolapsed annulus fibrosus and the resulting migrated nucleus pulposus of an intervertebral disk; 
         FIG. 2  is a sectional view of the ruptured annulus fibrosus showing leakage of the nucleus pulposus; 
         FIG. 3  is a diagrammatic view illustrating injection of a thermoplastic material by an injecting device into the annulus fibrosus for replacement of the nucleus pulposus; 
         FIG. 4  shows the intervertebral disk after setting of the thermoplastic material; 
         FIG. 5  illustrates the abnormal curvature of the lower spine for the injection of a thermoplastic material into the curved concave portion of the spine; 
         FIG. 6  is a perspective view of a modified injecting device for injecting a thermoplastic material within the spine; 
         FIG. 7  is a perspective view of a disk dilator; 
         FIG. 8  is a generally schematic view of a separate embodiment of the invention in which a disk dilator is intentionally provided to force adjacent disks apart and then a thermoplastic material is injected in the space occupied by the expandable dilator member; 
         FIG. 9  is a section taken generally along line  9 - 9  of  FIG. 8 ; and 
         FIG. 10  is a sectional view of an annulus fibrosus showing the expandable member expanded and the injection of the thermoplastic material adjacent the expandable member. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings for a better understanding of the invention, and more particularly to the embodiment shown in  FIGS. 1-4 , a portion of a spine is shown generally pictorially in  FIG. 1  including an intervertebral disk  10  adjacent a vertebra  11 . Disk  10  has an annulus fibrosus  12  which has ruptured at  14  resulting in a leakage or migration of nucleus pulposus  16  from the annulus fibrosus  12 . In this example a sacral nerve is shown at  18  extending from the cauda eqina  19  and the migrating or flowing nucleus pulposus  16  may result in a compression of nerve  18  with recognition that the techniques will be adapted specific to facilitate delivery to different levels of the spine. 
     It is desired to remove nucleus pulposus  16  which flows at body temperature and replace it with a thermoplastic material which does not flow at body temperature (37 C).  FIGS. 1-4  illustrate the removal of the nucleus pulposus  16  and replacement with a thermoplastic material. For this purpose the rupture or prolapse of the annulus fibrosus  12  is first identified and isolated. This identification and isolation is by means such as X-ray, MRI or other diagnostic imaging procedures which are diagnostically acceptable. After the area of rupture or prolapse is identified and isolated the site is surgically accessed. Since it is a goal of the invention to minimize trauma associated with the procedure, it is preferred to access the site through an arthroscopic procedure, or technology that involves minimal invasion and offense to healthy areas of the annulus fibrosus  12 , while damaged parts of the intervertebral disk are removed. Current technology allows for surgical removal of nucleus pulposus  16  by irrigation and suction. 
     The nucleus pulposus  16  removed is replaced with a thermoplastic material which is physiologically acceptable to the human body and flows when injected but hardens at body temperature into a non-flowing resilient material. The thermoplastic material is first heated by a suitable injection device having an injection needle to a predetermined temperature for flow under pressure from the needle into the annulus fibrosus  12  wherein the nucleus pulposus  16  has been removed. A thermoplastic material which has been found to be highly satisfactory is gutta percha or a gutta percha compound. Gutta percha is a geometric isomer of natural rubber. A substance such as mineral trioxide aggregate and other anti-inflammatory elements may be added to the gutta percha to facilitate the binding properties and to facilitate healing of the affected area. Dental gutta percha which may be utilized contains approximately 20% gutta percha, with zinc oxide comprising 60% to 75% of the material. The remaining 5% to 10% consists of various resins, waxes, metal sulfates for radioopacity, and coloration. When cold, gutta percha is relatively inelastic, but as it warms it becomes moldable. At a high temperature gutta percha will flow under pressure to permit injection from an injection needle into the annulus fibrosus  12 . 
     Referring particularly to  FIG. 3 , injection of thermoplastic material  20  within the annulus fibrosus  12  by an injection device or gun illustrated schematically at  22  is shown. Injection gun  22  has a body  24  with a removable plunger  26  adapted to receive a cylindrical plug of the thermoplastic material  20 . A heater  28  is provided to heat the thermoplastic material  20  and a heater control unit  30  having an adjustable temperature control knob  32  is provided with a temperature readout at  34 . Electrical leads  36  extend to heater  28 . An injection needle  38  preferably formed of silver extends from body  24  and has a ceramic sheath  40  about a portion of needle  38 . A hand operated trigger  42  may be activated for forcing thermoplastic material  20  from the end of needle  38  upon heating of the thermoplastic material  20  to a predetermined temperature. To assist trigger  42  in exerting an axial force against the plug of thermoplastic material  20  in gun  22 , a foot operated hydraulic pump may be provided at  44  to supply fluid through lines  46 ,  48  to a hydraulic cylinder  45 . A pressure readout is provided at  49 . A suitable piston  51  may exert an axial force against the thermoplastic material  20 . A hydraulic system is effective in providing an axial injection force that may be easily regulated and controlled by personnel performing the procedure. A suitable injection device designated as a Obtura II Heated Gutta Percha System may be purchased from Obtura of Fenton, Mo. 
     Needle  38  preferably formed of silver may be of various diameters but will not exceed a diameter of about 1 centimeter. Needle  38  may have a length of between 20 centimeters and 30 centimeters. A plug or stick of the thermoplastic material  20  may have a total volume of about 21 cubic centimeters with a diameter of about 16 millimeters and a length of about 10½ centimeters. The thermoplastic material  20  is required to be heated prior to injection to permit flow of the thermoplastic material. The higher the temperature of the thermoplastic material, the lower the viscosity and the faster flow. A lower temperature heating increases the viscosity and retards the flow rate. The degree to which the thermoplastic material  20  is heated may vary substantially dependent primarily on the diameter of needle  38  and the axial force applied to the heated thermoplastic material for injection. Generally the lowest temperature to which the thermoplastic material is heated while utilizing a large diameter needle such as 1 centimeter in diameter with a relatively high axial force may be 50 C while the highest temperature will be less than about 250 C. 
     The optimum temperature is about 185 C within an optimum range between about 150 C and 200 C. 
     It is desirable for the thermoplastic material to have a viscosity and temperature suitable for injection and flow into the space previously occupied by the annulus fibrosus  12 . After injection of the thermoplastic material  20  into the annulus fibrosus  12 , the material flows to fill the entire void area of the annulus fibrosus possibly including the ruptured area  14 . The thermoplastic material  20  cools relatively rapidly and, for example, reaches body temperature about its outer surface very quickly if injected at a temperature of about 185 C and then cools internally to body temperature in several minutes depending primarily on the thickness and surface area of the thermoplastic material. The thermoplastic material  20  tends to set at about 42 C and is not in a flowing state lower than about 42 C. Upon reaching the body temperature of 37 C, the thermoplastic material is set. At normal human body temperature the thermoplastic material is no longer moldable and is not flowing or migrating. Thus, the thermoplastic material  20  remains within the annulus fibrosus  16  and repairs the rupture  14  of the annulus fibrosus. It is, however, necessary that the thermoplastic material retain sufficient resilience in order to provide in a satisfactory manner the functions of allowing motion and adequately cushioning of the joint between associated vertebrae. If necessary, the thermoplastic material  20  may be subsequently removed from the annulus fibrosus  12  by surgical, physical, enzymatic, and/or chemical means. 
     Referring now to  FIG. 5 , a spinal column is shown generally at  50  having vertebrae  52  with intervertebral disks  54  positioned therebetween.  FIG. 5  shows spine  50  with scoliosis or abnormal curvature of the spine. The abnormal curvature of spine  50  provides a concave curvature as shown in  FIG. 5  at which disks  34  are positioned. To correct or remedy the abnormal curvature of spine  50 , a thermoplastic material  20  may be injected at intervertebral disks  54  progressively to reduce the concavity for flow into the associated annulus fibrosus as in the procedure set forth in  FIGS. 1-4 . The amount of the injected material will vary with the greatest amount of injected material at the greatest deflection and the least amount at the disks closest to the terminal ends of the abnormal curvature. However, the nucleus pulposus is not removed from the spine  50 . The injected material provides a force acting as a wedge to reduce the concavity of the scoliosis. Gutta percha as set forth in the embodiment of  FIGS. 1-4  is the preferred material for the thermoplastic material to be injected due to the characteristics that allow gutta percha to be used in other joints of the body. 
     Embodiment of  FIG. 6   
     Referring to  FIG. 6 , a modified injection device is shown generally at  60  including an injection needle  62 , a heater  64  receiving an inner end portion of needle  62 , and an electrical heater control element  66  having leads  68  extending to heater  64 . A suitable control knob  70  controls the temperature and a readout panel indicates the temperature which, for example, may be about 185 C. 
     A generally cylindrical chamber or housing  72  adjacent heater  64  is provided to receive a cylindrical plug  74  of the thermoplastic material. Housing  72  has open ends to receive removable threaded end plugs  73  for maintaining plug  74  in a sealed relation. One plug  73  is shown removed from housing  72  in  FIG. 6 . Plug  74  may also be covered with a suitable cover which may be manually removed for use, either in combination with or without end plugs  73 . Housing  72  upon removal of plugs  73  may be connected to heater  64  at one end and connected to a fluid pressure chamber  76  at an opposed end. A suitable fluid from a reservoir  78  having a foot operated pedal  80  and a vent  82  is supplied through line  84  to pressure chamber  76 . Concentric pistons  86  and  88  responsive to pressurized fluid in chamber  76  are provided to engage the end of thermoplastic plug  74  to urge plug  74  into heater  64  for injection from needle  62  under a predetermined pressure. A pressure gauge  90  is provided to indicate the fluid pressure applied against thermoplastic plug  74 . In some instances, housing  72  may be disposable with heater  64  being of an increased length to receive the entire length of plug  74 . 
     Needle  62  is preferably about 6 mm in diameter, and between about 20 cm and 30 cm in length for maneuverability. The volume of thermoplastic material to purge needle  62  may be between about 5.65 cc and 8.48 cc dependent on the size of the needle. Approximately 15 cc of thermoplastic material may be utilized for injection within the spine. Cylindrical plug  74  may have a total volume of 21 cc with a diameter of 16 mm and a length of 10.45 cm to provide a compact unit. 
     It may be desirable in some instances to provide a heater tape  63  in needle  62  for heating of the projecting needle  62 . Needle  62  may be formed of a ceramic material and preferably includes an inner silver liner for receiving heater tape  63  which may be formed of a suitable material to provide an electrical resistance, for example. Needle  62 , heater  64  and housing  72  may comprise separate injection subassemblies removably connected to pressure chamber  76  by a suitable threaded connection thereby to provide disposable units if desired with leads  68  detached from heater  64 . The fluid for the hydraulic system for fluid cylinder  76  may be water or another innocuous fluid. 
     Embodiment of  FIG. 7   
     Also shown in  FIG. 7  as an attachment is a disk dilator assembly generally indicated at  100  having a cylindrical chamber  102  with an inert fluid such as saline therein and a piston  108  for pressurizing the fluid. Disk dilator assembly  100  is designed for detachable connection to pressure chamber  76  of the injector device of  FIG. 6  for the supply of hydraulic fluid for acting against piston  108 . A detachable balloon dilator sleeve  106  extends about the extending end of needle  104  having lateral openings  107 . Piston  108  is effective to pressurize the fluid for flow through openings  107  for expansion of sleeve  106  as shown in broken lines in  FIG. 7 . Dilator sleeve  106  upon injection of needle  104  in a disk of the spine is expanded for exerting an expanding force against the disk. 
     Embodiment of  FIGS. 8-10   
     Referring now to  FIGS. 8-10  which are partially schematic, a further modification of an injection device and injection system is illustrated utilizing certain features shown in the embodiments of  FIGS. 6 and 7 . The injection system shown generally in  FIG. 8  includes an injection device generally indicated at  200  having an inner needle  202  and an outer concentric sheath or housing  204  forming an annulus  206  therebetween. An outer dilator sleeve  208  is mounted about sheath  204 . Openings  210  in the wall of sheath  204  permit fluid flow from annulus  206  through openings  210  for expansion of dilator sleeve  208 . Dilator sleeve  208  may be formed of an inert elastomeric material. 
     As shown in  FIG. 10 , annulus fibrosus  12  has a rupture  14  therein. Fluid such as a saline solution is first injected through annulus  206  and openings  210  to expand sleeve  208  in the void area of the annulus fibrosus  12  for forcing adjacent vertebrae apart. After the vertebrae have been forced apart and expandable sleeve  208  fits tightly against the surface defining the void area, a gutta percha compound is injected through needle  202  to fill the area occupied by expandable sleeve  208 . The pressure at which the gutta percha is injected is greater than the pressure of the saline solution to force the saline solution from sleeve  208  to collapse sleeve  208 . If desired, the pressure of the saline solution may also be decreased. 
     After insertion of the gutta percha compound, injection device  200  may be withdrawn from the annulus fibrosus  12 . Gutta percha is injected at pressures generally between about 10 psi and 150 psi dependent primarily on the size of the patient, such as infants requiring a very low psi and a relatively large person requiring a relatively high psi. 
     The system for injection of the saline solution and gutta percha as shown in  FIG. 8  includes a branch connection  212  extending from sheath  204  and connected to a flexible hose  214 . A cylindrical chamber  216  for saline or other suitable sanitary liquid fills chamber  216 , hose  112 , and annulus  206 . A piston  218  is mounted in chamber  216 . Hydraulic fluid in reservoir  220  of tank  222  is dispensed by operation of suitable foot pedals  223  and other suitable controls. The hydraulic fluid through hose  224  acts against piston  218  for pressurizing chamber  216  and forcing saline through openings  210  for expanding sleeve  208  against the surface defining the void area in annulus fibrosus  12 . 
     Hollow needle  202  is connected to a flexible hose  228  extending to a gutta percha injection device  230  generally similar to injection device  60  shown in  FIG. 6 . Gutta percha device  230  includes a cylindrical chamber or housing  232  having a plug  234  of gutta percha therein. A heater  236  is controlled by electrical control panel  238  having suitable electrical controls thereon. A hydraulic cap  240  mounted within the end of cylinder  232  has a pair of telescoping pistons  242 ,  244  for engaging gutta percha plug  234  and forcing the heated gutta percha through the end of needle  202  into the annulus fibrosus  12  as shown in  FIG. 10  to force expanding sleeve  208  to a collapsed position with gutta percha filling the entire void area in the annulus fibrosus  12 . Hydraulic fluid line  246  extends to a fluid reservoir  248  in tank  222  and foot pedals  250  may be operated for pressurizing and venting hydraulic cap  240  and chamber  232 . Thus, expanding sleeve  208  is effective in defining the void area upon the expansion of sleeve  208 . Then, the gutta percha easily flows into the area formed by expanding sleeve  208 . Expanding sleeve  208  is also effective in forcing adjacent disks apart and the increased area or volume is also filled with gutta percha thereby making the gutta percha more effective in filling the void area of the annulus fibrosus  12 . 
     The injection system shown in  FIGS. 8-10  is generally a combination of the embodiments shown in  FIGS. 6 and 7 . The housing and expandable sleeve shown in  FIG. 7  may befitted about the hollow needle of  FIG. 6  and saline for expanding the sleeve may be provided through a “y” adapter to the annulus between the needle and the housing. Thus, the system shown in  FIGS. 8-10  comprises a combination of the features shown in the embodiment of  FIGS. 6 and 7 . 
     While gutta percha or a gutta percha compound including at least about 15% of the compound by weight is the preferred thermoplastic material, it is understood that other types of thermoplastic material may be suitable if in a non-flowing state at body temperature (37 C) and in a flowing state when heated over at least about 50 C for injection from a needle of an injection device. Various other ingredients or elements may be added to the gutta percha compound in various percentages. Further, while specific injection devices have been illustrated for injection of the thermoplastic material, other types of injection devices for heating the thermoplastic material and for applying an axial force against the thermoplastic material for injection may be provided. For example, various devices may be provided for heating the thermoplastic material prior to injection and for pressurizing the thermoplastic material for controlled flow of the thermoplastic material through an injection needle for injection. Thus, while preferred embodiments of the present invention have been illustrated in detail, it is apparent that modifications and adaptations of the preferred embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention as set forth in the following claims.