Abstract:
An expandable cannula and method for using the expandable cannula to perform minimally invasive, percutaneous surgeries to access the spine or other bone structures, organs, or locations of the body. The expandable cannula includes a tubular body movable between first and second size states and an actuating mechanism on the tubular body for moving the tubular body between the first and second size states.

Description:
TECHNICAL FIELD  
       [0001]     The invention relates generally to devices and methods for performing minimally invasive, percutaneous surgeries. More particularly, the invention is an expandable and retractable cannula.  
       BACKGROUND  
       [0002]     Traditional surgical procedures often require a long incision, extensive muscle stripping, and prolonged retraction of tissues to access the desired surgical site as well as denervation and devascularization of surrounding tissue. This is particularly the case with spinal applications because of the need for access to locations deep within the body. Such surgical procedures can cause significant trauma to intervening tissues and potential damage to good tissue due to the amount and duration of tissue retraction, resulting in increased recovery time, permanent scarring, and pain that can be more severe than the pain that prompted the original surgical procedure. This is further exacerbated by the need to make a large incision so that the surgeon can properly view the areas inside the body that require attention.  
         [0003]     Endoscopic, or minimally invasive, surgical techniques allow a surgical procedure to be performed on a patient&#39;s body through a smaller incision in the body and with less body tissue disruption. Endoscopic surgery typically utilizes a tubular structure known as a cannula (or portal) that is inserted into an incision in the body. A typical cannula is a fixed diameter tube, which a surgeon uses to hold the incision open and which serves as a conduit extending between the exterior of the body and the local area inside the body where the surgery is to be performed. Thus, cannulae can be used for visualization, instrument passage, and the like.  
         [0004]     The typical cannula, however, presents at least two disadvantages. First, insertion of the cannula typically requires an incision the full depth and diameter of the cannula. Although this incision is often relatively smaller than incisions made for surgical procedures performed without a cannula, there is still trauma to healthy tissue. Additionally, endoscopic surgical techniques may be limited by the size of the cannula because some surgical instruments, such as steerable surgical instruments used in posterior discectomies, are sometimes larger than the size of the opening defined by the cannula. Therefore, there is a need for a cannula that can be inserted with minimal incision of tissue yet still provide an entrance opening and conduit sized for sufficient instrument passage and operation.  
       SUMMARY  
       [0005]     The invention is generally directed to a device and method for performing minimally invasive, percutaneous surgeries to access the spine or other bone structures, organs, or locations of the body. In one embodiment, the invention is an expandable cannula having a tubular body that may be moved between a first, or expanded, size state and a second, or relatively reduced, size state. An actuating mechanism on the tubular body can be actuated to move the tubular body between the first and second size states. In one embodiment, the actuating mechanism is actuated to move the tubular body between the first and second size states, thereby increasing the size at a distal end of the tubular body. In an alternative embodiment, the size at the distal end of the tubular body is decreased by actuating the actuating mechanism to move the tubular body between the first and second size states.  
         [0006]     Another embodiment of the invention is a method for using the expandable and retractable cannula to access an internal body part. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:  
         [0008]      FIG. 1  is an illustration of an expandable cannula in accordance with one embodiment of the invention showing the device in an expanded diameter state.  
         [0009]      FIG. 2A  is an illustration of the expandable cannula shown in  FIG. 1  from the top.  
         [0010]      FIG. 2B  is an illustration of the expandable cannula shown in  FIG. 1  from the top according to another embodiment of the invention.  
         [0011]      FIG. 3  is an illustration of the expandable cannula shown in  FIG. 1  from the bottom.  
         [0012]      FIG. 4  is an illustration of an expandable cannula in accordance with one embodiment of the invention showing the device in a reduced size state without a skirt.  
         [0013]      FIG. 5  is an illustration of an elongated curvilinear rod-shaped rib for the frame in accordance with one embodiment of the invention.  
         [0014]      FIG. 6  is an illustration of an elongated curvilinear paddle-shaped rib for the frame in accordance with an alternative embodiment of the invention.  
         [0015]      FIG. 7  is a cross-sectional view of the device shown in  FIG. 1  without a skirt showing a plurality of ribs coupled to a rotating member.  
         [0016]      FIG. 8  is a detailed view of a gear ring, a gear, and a rib of the device of  FIG. 1  in which the rotating member  7  is removed for clarity.  
         [0017]      FIG. 9  is a detailed view of a portion of an actuating mechanism for an expandable cannula having individually actuatable ribs in accordance with another embodiment of the invention.  
         [0018]      FIG. 10  is an exploded view of the device of  FIG. 1 . 
     
    
       [0019]     While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described herein. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.  
       DETAILED DESCRIPTION  
       [0020]     An expandable cannula  10  in accordance with one embodiment of the invention is shown in  FIGS. 1 and 4 . As shown, the expandable cannula  10  includes an actuating mechanism  5  on a tubular body  3 . The actuating mechanism  5  can be actuated to move the tubular body  3  between a first, or expanded, size state and a second, or relatively reduced, size state.  FIG. 1  illustrates the expandable cannula  10  in a first, or expanded, size state while  FIG. 4  illustrates the expandable cannula  10  in a second, or relatively reduced, size state. As is shown in  FIGS. 1 and 4 , in the first, or expanded, size state, the tubular body  3  has a greater cross-sectional area than in the second, or reduced, size state.  
         [0021]     The illustrated embodiment of the tubular body  3  is connected at a proximal end to the actuating mechanism  5  and includes a frame  21  formed by ribs  23  and a skirt  25  supported by the ribs  23 . Together with the frame  21  and the skirt  25 , the tubular body  3  defines a conduit  31  as shown in  FIGS. 1 and 3  through which the surgeon may view the area of interest or insert surgical instruments by providing a barrier against surrounding tissue, organs, bodily fluids, and the like.  
         [0022]     The illustrated embodiment of the actuating mechanism  5  includes a rotating member  7  having a textured or roughened perimeter surface  9  to better grip the rotating member  7 . The illustrated embodiment of the actuating mechanism  5  also includes a stationary member  29  connected to the rotating member  7 .  
         [0023]     As shown in  FIGS. 7 and 8 , the actuating mechanism  5  further includes a mechanical linkage  11  for coupling the rotating member  7  to the tubular body  3  and for moving the tubular body  3  between the first and second size states in response to rotation of the rotating member  7 .  
         [0024]     The ribs  23  of the frame  21  are elongated curvilinear members positioned about a circumference of the tubular body  3  in the embodiment shown in  FIG. 10 . Generally, the circumference of the tubular body is circular but other, non-circular configurations are also contemplated by the invention. These non-circular configurations may include shapes such as an oval, triangle, rectangle, as well as other, less structured, shapes desired to provide access to the surgical site.  
         [0025]     The quantity of ribs  23  used to form the frame  21  can be varied to best suit the intended application of the expandable cannula  10 . For example, in the illustrated embodiment, the frame  21  is formed by four ribs  23  (the fourth rib  23  is hidden by the skirt  25 ). In other embodiments (not shown), the frame  21  is formed by three ribs  23 , 5 ribs  23  or a greater number of ribs  23  as desired.  
         [0026]     The shape of the ribs  23  used to form the frame  21  can also be varied to best suit the intended application of the expandable cannula  10 . For instance,  FIG. 5  shows a rib  23  assuming the shape of an elongated curvilinear rod. Alternatively,  FIG. 6  shows a rib  23  assuming the shape of an elongated curvilinear paddle. Other shapes, such as a bell shape, that would be suitable to optimize the particular application of the expandable cannula  10  are also contemplated by the invention.  
         [0027]     The ribs  23  are generally bowed as shown in  FIGS. 5 and 6 . By actuating the actuating mechanism  5 , these ribs  23  are rotated such that the distal ends of the ribs  23  extend outwardly to increase the size or the cross-sectional area of the tubular body  3  at a distal end of the expandable cannula  10  while maintaining a constant size at a proximal end of the expandable cannula  10 . These ribs  23  can also be rotated such that the distal ends of the ribs  3  extend inwardly to decrease the size of the tubular body  3  at the distal end of the expandable cannula  10  while maintaining a constant size at a proximal end of the expandable cannula  10 . It is also contemplated that actuation of the actuating mechanism  5  can cause the ribs  23  to rotate such that at least one of the distal ends of the ribs  23  extends inwardly and at least one of the distal ends of the ribs  23  extends outwardly, thereby allowing for localized expansion from one side of the expandable cannula  10  and not the other, for example. It is further contemplated that actuation of the actuating mechanism  5  can cause the ribs  23  to rotate such that tubular body  3  has varying sizes or cross-sectional areas along the length of an intermediate region the tubular body  3  between the proximal and distal ends.  
         [0028]     The overall length of the ribs  23  can be set to suit the particular application and the anatomy of the surgical site. Accordingly, various lengths are contemplated by the invention. In one embodiment, the overall length of the ribs  23  is about 5 inches. In another embodiment, the overall length of the ribs  23  is about 7 inches. In yet another embodiment, the overall length of the ribs  23  is about 9 inches.  
         [0029]     The ribs  23  can generally be constructed of biocompatible materials that are sufficiently strong and resilient to withstand pressure exerted by the surrounding tissue and body parts. Examples of suitable materials include metals, such as a surgical stainless steel, and shape memory alloys, such as nitinol, as well as plastics, such as polycarbonate and Delrin®, or other sufficiently strong polymers. In some applications, the ribs  23  are constructed of reusable, durable, sterilizable materials. Alternatively, the ribs  23  are constructed of disposable materials or more lightweight materials.  
         [0030]     In one embodiment, the ribs  23  are detachable from the actuating mechanism  5 . Thus, the ribs  23  may be more easily sanitized for later use or replaced with new ribs  23  so that the expandable cannula  10  can be used with a subsequent patient or repaired in the event damage occurs to one of the ribs  23 .  
         [0031]     In the illustrated embodiment, the skirt  25  is supported by the frame  21  such that actuation of the actuating mechanism  5  causes the skirt  25  to move with the frame  21  between the first and second size states. The skirt  25  is generally wrapped around the perimeter of the frame  21  formed by the ribs  23 . In the illustrated embodiment, the skirt  25  has compartments  27 , or pockets, for engaging the ribs  23  as shown in  FIG. 10 . In this embodiment, the ribs  23  are inserted into the compartments  27  along their full length.  
         [0032]     The skirt  25  can be secured to the frame  21  at the proximal end of the frame  21  to prevent the skirt  25  from sliding off of the frame  21  during insertion and removal of the expandable cannula  10 . For example, the proximal end of the skirt  25  may be adhesively secured to the proximal end of the frame  21 . In one embodiment (not shown), the pockets  27  are closed and/or reinforced at a distal end so that the skirt  25  resists being pushed along the ribs  23  toward the proximal end of the frame  21  during insertion of the expandable cannula  10 , which would expose portions of the ribs  23  and potentially compromise the conduit  31 . Although it is intended that the skirt  25  remain in place during insertion and removal of the expandable cannula  10 , the skirt  25  should also be detachable such the skirt  25  is disposable. Alternately, the skirt  25  may be formed of a material that allows it to be sterilized for later, repeated use.  
         [0033]     The skirt  25  is preferably constructed of a biocompatible, elastic material that retains a substantially smooth surface when the skirt  25  moves with the frame  21  between the first and second size states. In one embodiment, the skirt  25  is constructed of a material that returns to its original, unstretched form in the absence of mechanical force without wrinkling. In another embodiment, the skirt  25  is provided with pre-stressed or fold lines, for example, pleats, along which the skirt  25  tends to bend when moving between size states. The skirt  25  preferably also resists stretching against forces typically exerted by retracted tissues, body parts, and bodily fluids yet stretches enough against the mechanical force of the frame  21  as it moves between the first and second size states. The skirt  25  can also be constructed of a material that has minimal tendency to grip the surrounding tissue or body parts, which may cause damage to the tissue or body parts. Suitable materials of construction for the skirt  25  include materials such as silicone, latex or of C-Flex®, a general purpose, thermoplastic elastomer sold by Linvatec Corporation, Clearwater, Fla. Other suitable materials include shape memory materials or nitinol. The skirt  25  can also be constructed of an elastic, biodegradable material that may be left in the body to be reabsorbed by the body without damaging tissues in the body. In one embodiment, the biodegradable skirt  25  can further include a coating that has therapeutic benefits, promotes tissue growth, prevents infection, etc. It is also contemplated that the skirt  25  can be constructed of a transparent material for increased visibility.  
         [0034]     The actuating mechanism  5  can be actuated by rotating the rotating member  7  in either a clockwise or counterclockwise direction, resulting in movement of the tubular body  3  between the first and second size states. In one embodiment, the rotating member  7  is operated manually but it is also contemplated that other tools and methods can be employed to rotate the rotating member, such as in situations where access to the rotating member is limited or additional leverage is required. The stationary member  29  can also be used for leverage or as a counter force when rotating the rotating member  7  so that actuation of the actuating mechanism  5  does not simply cause the expandable cannula  10  to be shifted from its position within the body. In one embodiment as illustrated by  FIG. 10 , the rotating member  7  is secured to the stationary member  29  for rotation by a cylindrical lip  33  on the rotating member  7  that extends into a hole  35  in the stationary member  29 . A snap-fit or other mechanism can be used to engage the lip  33  with the stationary member  29 .  
         [0035]     In the illustrated embodiment, the mechanical linkage  11  is a gear system having a plurality of gears  15 , each mounted to one of the ribs  23 , and a gear ring  13  on the rotating member  7 .  FIG. 8  is a detailed illustration of a gear ring  13 , a gear  15 , and a rib  23  of the illustrated embodiment. As shown in  FIG. 8 , the gear ring  13  is located around an inner perimeter of the rotating member  7 . Consistent with the general operation of a gear system, movement of the rotating member  7  in either a clockwise or counterclockwise direction will result in rotation of the gear ring  13  in the same direction, causing the gears  15  to move in the opposite rotational direction. Because the rib  23  is connected to the gear  15 , it will move in the same rotational direction as the gear  15 , ultimately causing the rib  23  to rotate and the distal end of the rib  23  to move between the first and second size states. In one embodiment, the rib  23  is connected to the center of the gear  15 . Alternatively, the rib  23  can be connected to the gear  15  such that the axis of the rib  23  is offset compared to the axis of the gear  15  to facilitate operation of the actuating mechanism  5  as a cam system and generally increase the amount of overall expansion and contraction of the expandable cannula  10 . In addition, the opening through which the rib  23  extends may be kidney-shaped such that the rib  23  travels along the opening when operating as a cam system.  
         [0036]      FIG. 9  shows an expandable cannula  400  according to another embodiment of the invention. Cannula  400  involves an actuating mechanism  405  on a tubular body  403 . In the present embodiment, the tubular body  403  includes a frame  421  formed by ribs  423  and a skirt  425 . In the present embodiment, the ribs  423  are each individually actuatable via a grip  415 . In this manner, individual ribs  423  may be rotated to change the size of the tubular body  403  asymmetrically or to move the tubular body  403  between size states one rib  423  at a time.  
         [0037]     Although spur gears are illustrated, other gear systems such as bevel gears, gear and belt systems, and cam systems are contemplated by the invention. It is further contemplated that the gears  15  can be of varying diameters to allow for localized expansion from one side of the expandable cannula  10  and not the other, for example. Additionally, the gear ring  13  can be located around an exterior perimeter such that the gears  15  rotate around the outside of the gear ring  13  instead of the inside of the gear ring  13  as shown in  FIG. 8  for increased visibility and access to the desired tissue site through the conduit  31 .  
         [0038]     Suitable materials of construction for the actuating mechanism  5 , including the rotating member  7 , mechanical linkage  11 , gear ring  13 , and gears  15 , include materials of sufficient strength to be able to withstand the pressure of the tissues being retracted by the expandable cannula  10 , such as stainless steel. The actuating mechanism  5  is preferably constructed of materials that can withstand autoclave temperatures, such that they can be sterilized for subsequent use. The actuating mechanism  5  can also be constructed of biocompatible materials such as surgical stainless steel. Other suitable materials of construction can be used in this invention and one of skill in the art could readily select the appropriate materials based upon the intended application. For example, other materials can be used if the actuating mechanism  5  or other parts of the cannula  10  are integrated for single use applications.  
         [0039]     As illustrated in  FIGS. 2A and 2B , the actuating mechanism  5  can include indices  17  for monitoring the expansion or contraction of the tubular body  3  as it moves between the first and second size states in response to actuation of the actuating mechanism  5 . As seen in  FIG. 2A , the indices  17  can be visual markings such as an indexing mark on the stationary member  29  combined with marks on the rotating member  7  that correspond to the first and second size states (i.e., “open” and “close”). Alternately, as shown in  FIG. 2B , the indices  17  can correspond to multiple intermediate size states (i.e., 1-4), in which “1” represents the smallest size state and “4” represents the largest size state. Alternatively, the indices  17  can be an audible tone such as a clicking sound that can be heard when the actuating mechanism  5  is actuated. It is contemplated that the audible tone can correspond to whether the tubular body  3  is moving between the first and second size states or has reached the first or second size state. The indices  17  can also be used to monitor the extent of the expansion of the expandable cannula  10  to better prevent tissue damage by over expansion. The indices  17 , therefore, can provide particular advantage to the surgeon during the process of “dialing in” to the appropriate size state, making it easier for the surgeon to adapt the expandable cannula  10  to the particular application.  
         [0040]     As is shown in  FIGS. 1 and 2 , the actuating mechanism  5  can further include a locking device  19 . In one embodiment, the locking device  19  is connected to the proximal end of the tubular body  3  to restrict the tubular body  3  from moving between the first and second size states. Optionally, the locking device  19  is operable to restrict or to lock in position individual ribs  23  while permitting actuation of other ribs  23  (such as for use with the embodiment of the invention shown generally in  FIG. 9 ). A suitable locking device  19  is a pin that obstructs movement actuating mechanism  5  as well as the tubular body  3 . Suitable materials of construction for the locking device  19  include materials of sufficient strength to be able to withstand the pressure of the tissues being retracted by the expandable cannula  10 . The materials can also include biocompatible and/or sterilizable materials such as stainless steel.  
         [0041]     The invention is not limited to particular sizes for the conduit  31 , or the first and second size states, because the actual dimensions of the expandable cannula  10  will depend upon the anatomy of the surgical site and the type of surgery being performed. Accordingly, various sizes are provided by the invention. In one embodiment, the size of the first and second size states can vary between about 19 mm to 25 mm. In another embodiment, the size of the first and second size states can vary between about 19 mm to 40 mm. In the illustrated embodiment, the proximal end of the expandable cannula  10  will retain a constant size. In a particular embodiment, this size is about 19 mm. In other embodiments, the proximal end of the expandable cannula  10  has varying size states. It is further contemplated that the expandable cannula  10  can be continuously adjusted to allow the surgeon to “dial in” to the appropriate first or second size state. Thus, the surgeon may incrementally increase the size or cross-sectional area at the distal end of the expandable cannula  10 , permitting the surrounding body tissues to slowly stretch, adapt to the new position, and relax.  
         [0042]     The invention has many uses in the surgical field including the spinal surgical field, specifically percutaneous surgical procedures such as laminotomies, laminectomies, foramenotomies, facetectomies, or discectomies. It is also contemplated that the invention may be used for other surgical applications, particularly where minimally invasive surgical fields and still other applications are desired.  
         [0043]     The invention additionally provides a method of accessing an internal body part by using the expandable cannula  10  previously described. The method includes the step of forming an opening in the body, such as by an incision in the epidermis. The expandable cannula  10  is then inserted into the body through the opening in a contracted state. In some embodiments, the opening is formed through blunt dissection and the cannula  10  is guided into the opening with the surgeon&#39;s fingers. In this embodiment, the cannula  10  is its own dilator. In other embodiments, the opening is formed at more shallow angles and the cannula  10  is guided into the opening with a separate dilator, and possibly a guide wire. With the expandable cannula  10  in position, the conduit  31  forms a working channel. In some instances, it may also be desirable to hold the expandable cannula  10  in place by use of a fixation device such as a mounting bracket attached to a flexible support arm (not shown). This fixation device can be readily adjusted into a fixed position to support for the expandable cannula  10  and provide the surgeon with increased accessibility to the conduit  31 . The selection of the appropriate fixation device can be readily accomplished by one of skill in the arm.  
         [0044]     Following insertion of the contracted expandable cannula  10  into the body, the surgeon can further expose an internal body part by actuating the actuating mechanism  5  of the expandable cannula  10  to cause the tubular body  3  to move between first and second size states. The surgeon can gradually and incrementally actuate the actuating mechanism  5  until a desired size state is obtained. The surgeon can then lock the expandable cannula  10  by activating the locking device  19 .  
         [0045]     Once the desired size state has been reached, the surgeon can conduct the surgical procedure through the conduit  31  as necessary, including inserting necessary tools and instruments such as standard surgical implements and visualization scopes. Upon completion of the surgical procedure and removal of the tools and instruments, the surgeon can deactivate the locking device  19  and then gradually decrease the size or cross-sectional area at the distal end of the cannula until a desired size state is obtained by actuating the actuating mechanism  5  to cause the tubular body  3  to move between the first and second size states. If the expandable cannula  10  has been attached to a fixation device, the fixation device is removed, allowing the expandable cannula  10  to be removed from the body. The incision may then be closed using standard surgical procedures.  
         [0046]     Following use, the expandable cannula  10  can be sanitized for future use, such as by use of an autoclave or other chemical sanitation processes. In one embodiment, the skirt  25  and/or ribs  23  are also detached from the actuating mechanism  5  and either sanitized for future use or replaced with a new skirt  25  and/or ribs  23 .  
         [0047]     The particular embodiments disclosed above are intended to be illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above can be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.