Abstract:
Disclosed is an expandable percutaneous sheath, for introduction into the body while in a first, low cross-sectional area configuration, and subsequent expansion to a second, enlarged cross-sectional configuration. The sheath is maintained in the first, low cross sectional configuration by a removable tubular restraint. In one application, the sheath is utilized to introduce a formed in place orthopedic fixation rod such as for use in spinal fixation procedures.

Description:
[0001]     This is a continuation of U.S. application Ser. No. 10/188,732, filed Jul. 2, 2002, which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to medical devices and, more particularly, to methods and devices for forming a percutaneous channel. In one application, the present invention relates to a minimally invasive procedure to insert an orthopedic fixation or stabilization implant into the body, such as a formed in situ spinal stabilization rod.  
         [0004]     2. Description of the Related Art  
         [0005]     The vertebrae and associated connective elements are subject to a variety of diseases and conditions which cause pain and disability. Among these diseases and conditions are spondylosis, spondylolisthesis, vertebral instability, spinal stenosis and degenerated, herniated, or degenerated and herniated intervertebral discs. Additionally, the vertebrae and associated connective elements are subject to injuries, including fractures and torn ligaments and surgical manipulations, including laminectomies.  
         [0006]     The pain and disability related to these diseases, conditions, injuries and manipulations often result from the displacement of all or part of a vertebra from the remainder of the vertebral column. A variety of methods have been developed to restore the displaced vertebrae or portions of displaced vertebrae to their normal position and to fix them within the vertebral column. For example, open reduction with screw fixation is one currently used method. The surgical procedure of attaching two or more parts of a bone with pins, screws, rods and plates requires an incision into the tissue surrounding the bone and the drilling of one or more holes through the bone parts to be joined. Due to the significant variation in bone size, configuration, and load requirements, a wide variety of bone fixation devices have been developed in the prior art. In general, the current standard of care relies upon a variety of metal wires, screws, rods, plates and clamps to stabilize the bone fragments during the healing or fusing process. These methods, however, are associated with a variety of disadvantages, such as morbidity, high costs, lengthy in-patient hospital stays and the pain associated with open procedures.  
         [0007]     Therefore, devices and methods are needed for repositioning and fixing displaced vertebrae or portions of displaced vertebrae which cause less pain and potential complications. Preferably, the devices are implantable through a minimally invasive procedure.  
         [0008]     In addition, a wide variety of diagnostic or therapeutic procedures involve the introduction of a device through a natural or artificially created access pathway. A general objective of access systems which have been developed for this purpose, is to minimize the cross-sectional area of the puncture, while maximizing the available space for the diagnostic or therapeutic instrument. These procedures include, among others, a wide variety of laproscopic diagnostic and therapeutic interventional procedures. Accordingly, a need remains for access technology which allows a device to be percutaneously passed through a small diameter tissue tract, while accommodating the introduction of relatively large diameter instruments.  
       SUMMARY OF THE INVENTION  
       [0009]     A percutaneous access sheath is provided according to an aspect of the present invention. In one application, the percutaneous access sheath is used to facilitate the insertion of an orthopedic fixation or stabilization implant that is formed in situ, such as a spinal stabilization rod.  
         [0010]     The percutaneous access sheath may be used in conjunction with a deployment catheter, which is provided with a balloon at its distal end. The percutaneous access sheath has a proximal section and a variable diameter distal section. The deployment catheter may be disposed within the percutaneous access sheath such that the balloon is positioned within the distal section of the percutaneous access sheath.  
         [0011]     The distal section of the percutaneous access sheath is restrained in a first, small diameter by a releasable restraint such as a perforated insertion sheath. The distal section of the percutaneous access sheath is creased, folded inwards and inserted into a distal section of the insertion sheath. This gives the percutaneous access sheath a smaller cross sectional profile, facilitating its insertion.  
         [0012]     The percutaneous access sheath is inserted as packaged above. Following insertion, the insertion sheath may be torn away along its perforations. To facilitate this the balloon may be partially inflated, expanding the distal section of the percutaneous access sheath sufficiently to tear the insertion sheath along its perforations. After the insertion sheath is removed, the balloon may be fully inflated to distend the distal section of the percutaneous access sheath to its full cross-sectional profile. Afterwards, the balloon may be deflated to allow the removal of the deployment catheter, leaving the percutaneous access sheath in place.  
         [0013]     In one embodiment where the percutaneous access sheath is used to facilitate the insertion of an orthopedic spinal stabilization implant that is formed in situ, a percutaneous access sheath may advantageously be first inserted through the portals of adjacent bone anchors, by the method described above. This provides a smooth channel to facilitate the passage of another deployment catheter carrying an inflatable orthopedic fixation device at its distal end.  
         [0014]     Other applications of the percutaneous access sheath include a variety of diagnostic or therapeutic clinical situations which require access to the inside of the body, through either an artificially created or natural body lumen. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  is a side elevational view of a percutaneous access sheath.  
         [0016]      FIG. 2  is a side elevational view of a insertion sheath.  
         [0017]      FIG. 3  illustrates the percutaneous access sheath in a reduced cross-sectional configuration and inserted into the insertion sheath.  
         [0018]      FIG. 4  is a side elevational view of an access sheath expansion catheter.  
         [0019]      FIG. 5  is an enlarged view of the distal end of the expansion catheter.  
         [0020]      FIG. 6  is an enlarged view of the proximal end of the expansion catheter.  
         [0021]      FIG. 7  illustrates the percutaneous access sheath assembly, with the expansion catheter inserted into the structure illustrated in  FIG. 3 .  
         [0022]      FIG. 8  is a side elevational view of a bone anchor.  
         [0023]      FIG. 9  is a side elevational view of the bone anchor of  FIG. 8 , rotated 900 about its longitudinal axis.  
         [0024]      FIG. 10  is a longitudinal cross-sectional view of the bone anchor of  FIG. 9 .  
         [0025]      FIG. 11  is a side elevational view of an alternative embodiment of a bone anchor.  
         [0026]      FIG. 12-15  illustrate one embodiment of a method of threading a guide wire through the portals of bone anchors that have been implanted into adjacent vertebrae in a vertebral column. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]      FIG. 1  is an overview of the percutaneous access sheath  100 . It generally comprises an elongate tubular body with an axial lumen, and is designed to provide percutaneous access to a diagnostic or treatment site in the body. The elongate tubular body has a proximal section and a distal section  110 . The length of these two sections can be varied according to clinical need, as will be understood by those skilled in the art with reference to this disclosure. The distal section  110  is expandable from a first, smaller cross-sectional profile to a second, larger cross-sectional profile. The first, smaller cross profile of the distal section  110  eases its insertion into the percutaneous treatment site. After insertion, the distal section  110  is expanded to a second, larger cross-sectional profile to provide a larger passageway for surgical instruments to reach the percutaneous treatment site.  
         [0028]     In the illustrated embodiment, the percutaneous access sheath  100  is made of a double-layered co-extruded tubing  102 , with an inner layer  104  and an outer layer  106 . The inner layer  104  defines a lumen  108 . The inner layer  104  extends further distally than the outer layer  106 , such that the distal section  110  of the tubing  102  is of a single layer, the inner layer  104 . The inner layer  104  may be made of PTFE and the outer layer  106  may be made of HDPE. Other suitable materials, such as nylon, PEBAX or PEEK, may be used for either layer.  
         [0029]     In this embodiment, the distal section  110  is creased, folded inwards, and collapsed from a larger to a smaller cross-sectional profile to ease its insertion. As discussed below, in one application of the invention, the distal section  110  is inserted through adjacent bone screws or anchors. Its length is thus determined by the distance between such adjacent bone screws, and is generally in the range of 4-12 cm. The proximal end  112  of the tubing  102  is flared and fitted onto a handle  114 . A distal cap  116  may be threaded onto the handle  114  to secure the proximal end  112  of the tubing  102 . Additionally a proximal cap  118  may be threaded onto the handle  114 . The overall length of the tubing  102  depends on the distance between the insertion and treatment locations, and is generally in the range of 15-60 cm for orthopedic fixation surgery of the vertebrae. In the illustrated embodiment the length of the tubing is approximately 20 cm, with the distal section  110  accounting for approximately half of that length.  
         [0030]      FIG. 2  is an overview of the insertion sheath  200 . It is preferably made of a thin, smooth and flexible material. The insertion sheath  200  has a proximal section and a distal, restraint section  210 . The restraint section  210  has a smaller cross-sectional profile than the proximal section of the insertion sheath  200 . The restraint section  210  is adapted to restrain the distal section  110  of the percutaneous access sheath  100  in its smaller cross-sectional profile. This is achieved by inserting the percutaneous access sheath  100  into the insertion sheath  200  such that the distal section  110  of the percutaneous access sheath  100  lies within the restraint section  210  of the insertion sheath  200 .  
         [0031]     In the illustrated embodiment, the insertion sheath  200  may be made of PTFE. The proximal end  202  of the insertion sheath  200  terminates at a pull tab  204 , which may be formed by a threaded luer lock. The insertion sheath  200  is provided with a slit  206  near its proximal end  202 . The insertion sheath  200  tapers at a first tapering point  208  into a restraint section  210 , which tapers again into the distal tip  212 . As discussed above, the restraint section  210  restrains the distal section  110  of the percutaneous access sheath  100  in its smaller cross-sectional profile. Thus the length of the restraint section  210  is approximately the same as or slightly longer than the distal section  110 , and generally falls in the range of 4-13 cm.  
         [0032]     The diameter of the restraint section  210  is preferably smaller than the diameter of the eye of the bone screw used, as discussed below. The insertion sheath  200  may be perforated or otherwise provided with a tear line distally from the first tapering point  208  to its distal tip  212 . The distance between the slit  206  and the distal tip  212  is generally approximately equal to or slightly shorter than the length of the tubing  102 , and thus is generally in the range of 12-57 cm. In the illustrated embodiment this distance is approximately 15 cm, and the overall length of the insertion sheath  200  is approximately 24 cm.  
         [0033]      FIG. 3  illustrates the percutaneous access sheath  100  inserted into the insertion sheath  200  via the slit  206  provided near its proximal end  202 . The diameter of the restraint section  210  of the insertion sheath  200  is smaller than the diameter of the distal section  110  of the tubing  102 . The distal section  110  is creased and folded inwards to decrease its effective diameter, and inserted into the restraint section  210 . As discussed above, the restraint section  210  restrains the distal section  110  of the percutaneous access sheath  100  in its smaller cross-sectional profile The restraint section  210  is approximately the same length as or just longer than the distal section  110 . Thus inserted, the distal section  110  extends to a point just proximal of the distal tip  212  of the insertion sheath  200 .  
         [0034]     In certain embodiments an insertion sheath  200  may not be necessary if the distal section  110  of the percutaneous access sheath  100  is made of a stretchable material that may be stretched from a first, smaller cross-sectional profile to a second, larger cross-sectional profile. In these embodiments the outer surface of the distal section  110  is preferably made of a smooth material to facilitate the insertion of the percutaneous access sheath  100  into a treatment site.  
         [0035]      FIG. 4  is an overview of the deployment catheter  300 . It is provided with an expansion element such as balloon  310  at its distal end. The deployment catheter  300  is inserted into the lumen  108  of the percutaneous access sheath  100  such that the balloon  310  is arranged within the distal section  110 . The balloon  310  may be inflated to expand the distal section  110  from its first, smaller cross-sectional profile to its second, larger cross-sectional profile following the insertion of the percutaneous access sheath  100  into a treatment site.  
         [0036]     An inner tube  302  extends the entire length of the deployment catheter  300 . A guide wire lumen  304  is defined by the interior of the inner tube  302 . The deployment catheter  300  can travel along a guide wire extending through the guide wire lumen  304 . The inner tube  302  carries coaxially on its exterior an outer tube  306 . The outer tube  306  terminates proximally into the distal end of a handle  308 , and distally into the proximal end of a balloon  310 . The balloon  310  may be made of PET. The handle  308  may be provided with an optional support tube  312  extending from its distal end and over a proximal section of the outer tube  306 , to increase the rigidity of the deployment catheter  300  during insertion. This support tube  312  may be made of aluminum.  
         [0037]      FIG. 5  is an enlarged view of the distal end of the deployment catheter  300 . Both the inner tube  302  and the guide wire lumen  304  extend through the distal end  314  of the balloon  310 . The inner tube  302  carries coaxially on its exterior a marker ring  316  near the distal end  314  of the balloon  310 . Alternatively the marker ring  316  maybe carried by the distal end  314  of the balloon  310 . The marker ring  316  is preferably made of gold, tantalum, or another radio-opaque material. Additional marker rings may be provided in the balloon  310  to aid in visualizing its location. A balloon inflation lumen  318 , defined in the space between the inner tube  302  and the outer tube  306 , communicates with the interior of the balloon  310 . As discussed above, the balloon  310  may be inflated to expand the distal section  110  of the percutaneous access sheath  100  from its first, smaller cross-sectional profile to its second, larger cross profile. Thus the length of the balloon  310  is approximately equal to or slightly longer than the length of the distal section lift In the illustrated embodiment the length of the balloon  310  is approximately 10 cm.  
         [0038]      FIG. 6  is an enlarged view of the proximal end of the deployment catheter  300 . Both the inner tube  302  and the guide wire lumen  304  extend through the proximal end of the handle  308 . The balloon inflation lumen  318 , defined in the space between the inner tube  302  and the outer tube  306 , opens into a port  320  in the handle  308 . A stopper  322  supports the inner tube  302  within the handle  308  and prevents the balloon inflation lumen  318  from communicating with the space  324  in the main branch of the handle  308 . Thus only the port  320  communicates via the balloon inflation lumen  318  with the interior of the balloon. A pump may be connected to the port  320  to inflate or deflate the balloon. To enable visualization of the state of the balloon, it may be inflated with contrast media.  
         [0039]      FIG. 7  illustrates the percutaneous access sheath assembly  150 . The percutaneous access sheath assembly  150  comprises the percutaneous access sheath  100 , the insertion sheath  200  and the deployment catheter  300 . It is assembled by inserting the deployment catheter  300  into the percutaneous access sheath  100  and inserting the percutaneous access sheath  100  into the insertion sheath  200  such as via the slit  206  or other proximal opening provided near its proximal end  202 . The balloon  310  of the deployment catheter  300  is deflated, folded and inserted into the distal section  110  of the access sheath  100 . The distal section  110 , as discussed above, is creased and folded inwards to decrease its effective diameter, and inserted into the restraint section  210  of the insertion sheath  200 . As discussed, the balloon  310  is approximately the same length as or just longer than the distal section  110  and the restraint section  210 .  
         [0040]      FIGS. 8-11  illustrate one embodiment of a bone anchor  410  as mentioned above. It is provided with at least one connector  422  at or near its proximal end (or top end, as illustrated). This connector  422  is used to engage an orthopedic spinal stabilization implant that is formed in situ, as discussed below. The connector  422  is preferably an aperture  422 , to achieve a more secure engagement in one embodiment the percutaneous access sheath  100  extends through the apertures  422  of two or more bone anchors  410  to establish a passageway to facilitate the insertion of a formed in situ orthopedic spinal stabilization implant.  
         [0041]     An embodiment with two bone anchors is now described. The percutaneous access sheath  100  is extended through the aperture  422  of a first bone anchor  410 , then through the aperture  422  of a second bone anchor  410 . The first bone anchor  410  is preferably implanted within a first bone. The second bone anchor  410  may be implanted within the second bone. The bones may be adjacent vertebral bodies or vertebrae, or first and second vertebrae spaced apart by one or more intermediate vertebrae. The clinical procedure is described in further detail below.  
         [0042]     The bone anchors  410  of  FIGS. 8-11  are made of a biocompatible material such as titanium or stainless steel. Alternatively, the bone anchors  410  may be made of a composite material. The bone anchors  410  may also be made of a suitable medical grade polymer. In one embodiment, the bone anchors  410  have a length between about 40 mm and 60 mm, preferably about 50 mm. However, the actual length is dependent on the location of the fracture, size of patient, etc.  
         [0043]     The bone anchor  410  comprises a proximal portion  412  having a proximal end  414  and a distal portion  416  having a distal end  418 . The proximal portion  412  typically comprises a head  420  and a portal  422 . In a preferred embodiment, the head  420  comprises a proximal portion  424  configured to mate with the tip of a screwdriver. The head  420  may comprise a standard or Phillips slot for mating with the screwdriver. A variety of slot configurations are also suitable, such as hexagonal, Torx, rectangular, triangular, curved, or any other suitable shape. The bone anchor of  FIG. 11  has a raised platform  434  having a plurality of substantially flat sides, such as a hexagonal platform, configured to mate with a corresponding depression in the distal end of a screwdriver, Platform  434  may come in a variety of shapes suitable mating with a screwdriver.  
         [0044]     The portal  422  of the bone anchor  410  may extend through the head  420  and is generally between about 4 mm and 8 mm in diameter, preferably about 6 mm to about 8 mm in diameter. The portal  422  may be of any suitable shape; however, the portal  422  is preferably round to facilitate the insertion of the percutaneous tube  100  as well as the in Situ forming orthopedic spinal stabilization implant.  
         [0045]     The distal portion  416  of the bone anchor  410  typically comprises threads  426  and a sharp tip  428 . The bone anchor  410  also preferably comprises a central lumen  430  extending coaxially through the length of the bone anchor  410  from its proximal end  414  to its distal end  418  and configured to receive a guidewire. The bone anchor  410  may also include one or more perforations  432 , as shown in  FIG. 11 . These perforations  432  are in communication with the central lumen  430  of the bone anchor  410 . The perforations  432  may be aligned axially, as illustrated, or may be staggered axially. The perforations  432  permit bone to grow into bone anchor  410 , stabilizing bone anchor  410  within the bone. Additionally, bone matrix material such as a hydroxyapatite preparation can be injected into the central lumen  430  and through the perforations  432  to promote bone in-growth.  
         [0046]     The method of using the percutaneous access sheath  100  to facilitate the insertion of an orthopedic spinal stabilization implant formed in situ according to one aspect of the present invention is described in the following figures. In this embodiment a smooth channel is first established between two or more adjacent bone anchors to facilitate the passage of another deployment catheter carrying an inflatable orthopedic fixation device at its distal end. While the method is disclosed and depicted with reference to only two vertebrae, one of which is either unstable, separated or displaced and the other of which is neither unstable, separated or displaced, the method can also be applied to three or more vertebrae simultaneously. Further, the method can be used to stabilize the L5 vertebrae, using the cranial-ward portion of the sacrum as the “vertebrae” with which L5 is anchored. Although the method is disclosed and depicted as applied on the left side of the vertebral column, the method can also be applied on the right side of the vertebral column or, preferably, on both sides of the vertebral column, as will be understood by those skilled in the art with reference to this disclosure. Other applications include the stabilization of other bones and skeletal elements of the body.  
         [0047]      FIG. 12  illustrates bone anchors  410  that have been inserted through the periosteal surface and into the anterior vertebral body or another suitable portion of the vertebrae  500  and  502 . As discussed above, bone matrix material such as a hydroxyapatite preparation can be injected into the central lumen  430  of a bone anchors  410  and through its perforations (not visible in this figure) to promote bone in-growth. The bone anchors  410  are arranged such that their portals  422  are substantially coaxial in relation to each other.  
         [0048]     A hollow needle  436  is inserted percutaneously and advanced into the portal  422  of one of the bone anchors  410 , with the aid of fluoroscopy. The hollow needle  436  may be 16 or 18 gauge. While the hollow needle  436  is shown engaging the bone screw  410  in the cranial-ward vertebrae  502 , it can alternatively first engage the bone screw  410  in the caudal-ward vertebrae  500 , as will be understood by those skilled in the art with reference to the disclosure.  FIG. 13  is an enlarged view of the distal end of the hollow needle  436 . A semi-rigid guide wire  438  is introduced through the lumen of the hollow need  436  and the portal  422  of the bone anchor  410  in the cranial-ward vertebrae  502 . The hollow needle  436  preferably has a Tuohy needle tip which causes the guide wire  438  to exit the hollow needle  436  perpendicularly to the central lumen  430  of the bone anchor  410 , or coaxially with the axis of the portal  422  of the bone anchor  410 . Alternatively, the bending of the guide wire  438  through the portal  422  of the bone anchor  410  may be accomplished by an angled-tip modified Ross needle or another suitable structure as will be understood by those skilled in the art with reference to the disclosure.  
         [0049]      FIG. 14  illustrates an optional guide wire directing device  440 , according to one aspect of the present invention, inserted percutaneously between the bone anchors  410 . The guide wire directing device  440  may have a forked end used to direct the guide wire  438  through the portal  422  of the bone anchor  410  in the caudal-ward vertebrae  500 . In another embodiment a guide wire capture device  442 , such as a snare or forceps, may be inserted percutaneously caudal to the portal  422  of the bone anchor  410  in the caudal-ward vertebrae  500 . The guide wire capture device  442  engages the distal end of the guide wire  438  after the guide wire  438  has passed through portal  422  of the bone anchor  410  in the caudal-ward vertebrae  500 , and pulls it through the skin dorsally, so that both ends of the guide wire  438  are secured.  
         [0050]      FIG. 15  illustrates the guide wire  438  in place after the procedure described above in  FIGS. 12-14 .  
         [0051]     The guide wire  438  may be inserted into the guide wire lumen  304  of the deployment catheter  300  of the percutaneous access sheath assembly  150 . The entire assembly  150  may travel over the guide wire  438  until its distal tapered portion is inserted through the portals  422  of the bone anchors  410 . The insertion sheath  200 , which is on the exterior of the percutaneous access sheath assembly  150 , facilitates the insertion because of its smooth, low profile exterior. As discussed above, it may be made of PTFE.  
         [0052]     Following the insertion of the percutaneous access sheath assembly  150 , the insertion sheath  200  is removed. This may be accomplished by pulling on the pull tab  204  and tearing the insertion sheath  200  along the perforations, crease line, or other structure for facilitating tearing provided along its restraint section  210 . This may be facilitated by first partially inflating the balloon  310  of the deployment catheter  300 . As discussed above, the balloon  310  is arranged within the distal section  110  of the percutaneous access sheath  100 , which is itself arranged within the restraint section  210  of the insertion sheath  200 . Thus, inflating the balloon  310  causes the distal section  110  of the percutaneous access sheath  100  to expand, tearing the restraint section  210  of the insertion sheath  200  along its perforations.  
         [0053]     After the removal of the insertion sheath  200 , the balloon  310  may be fully inflated to expand the distal section  110  of the percutaneous access sheath to its full cross sectional profile. Afterwards the balloon  310  may be deflated to ease the removal of the deployment catheter  300 . As discussed above, the inflation and deflation of the balloon  310  may be done via a pump connected to the port  320  of the deployment catheter  300 , and preferably with contrast media being pumped, to better convey the state of the balloon.  
         [0054]     Thus the percutaneous access sheath  100  is inserted through the portals  422  of the bone anchors  410 . The establishment of this smooth channel through the portals  422  of the bone anchors  410  facilitates the passage of another deployment catheter carrying an inflatable orthopedic fixation device at its distal end. An example of such a deployment catheter with an inflatable orthopedic fixation device at its distal end as well as the associated anchors and methods are disclosed in U.S. patent application Ser. No. 10,1161,554 filed on May 31, 2002, the disclosure of which is hereby incorporated by reference in its entirety.  
         [0055]     Although the present invention has been described in terms of certain preferred embodiments, other embodiments of the invention including variations in dimensions, configuration and materials will be apparent to those of skill in the art in view of the disclosure herein. In addition, all features discussed in connection with any one embodiment herein can be readily adapted for use in other embodiments herein. The use of different terms or reference numerals for similar features in different embodiments does not imply differences other than those which may be expressly set forth. Accordingly, the present invention is intended to be described solely by reference to the appended claims, and not limited to the preferred embodiments disclosed herein.