Patent Publication Number: US-2005131457-A1

Title: Variable stiffness shaft

Description:
BACKGROUND OF THE INVENTION  
      1. Field of Invention  
      The present invention relates to the field of variable stiffness devices and surgical instrumentation. More specifically, it relates to a variable stiffness shaft having means to stiffen the shaft and means to activate a surgical tool carried at a distal end of the shaft independently from one another.  
      2. Description of Related Art  
      Variable stiffness devices are used in primarily two situations during a surgical procedures. The first involves the accurate positioning of a surgical device, such as a retractor or stabilizer. A flexible shaft overcomes the difficulty of manipulating a rigid shaft. Once the device is in place, the shaft may be made more rigid, in order to allow the position of the device to be accurately held.  
      A second situation involves the positioning of multiple surgical devices at the surgical site, thereby congesting the working view or area for the surgeon. This problem is particularly acute when using less invasive and minimally invasive surgical techniques, which are becoming more frequently used for their benefits to the patient. Using a variable stiffness shaft in this circumstance, the surgeon can place or manipulate the device while the shaft is rigid, then transition the shaft to a flexible state, and move the shaft out of the working view or area, thereby improving access and/or visualization.  
      There are a number of known devices utilizing variable stiffness shafts. Known methods for accomplishing a variable stiffness shaft include cable tension, mechanically telescoping sheaths, and one-dimensional flexibility. These devices are sub-optimal in part because of the large diameter needed to obtain the required stiffness.  
      Mechanical telescoping devices have a generally flexible shaft that is made stiff by a rigid telescoping sheath extended over it. Once in place, the sheath is retracted, and the flexible shaft may be moved away from the surgical field. At least one drawback of these devices is that the sheath is difficult to retract in vivo.  
      Cable tension devices suffer from the problem that they will typically manipulate the operation of the surgical tool carried at the distal end of the flexible shaft in the process of stiffening the shaft.  
     BRIEF SUMMARY OF THE INVENTION  
      Therefore, in order to overcome these and other deficiencies in the prior art, provided is a flexible malleable shaft comprising a plurality of generally prismatic shaft elements adjacent one another, each having a first longitudinal axis, and a plurality of axial through holes. A recess is formed in a proximal end of the shaft element, the recess defined along a second axis transverse to the first longitudinal axis and a protrusion is formed in a distal end of the shaft element, the protrusion defined along a third axis transverse to the longitudinal axis. The second and third axes are oriented relative to one another such that the respective axial through holes of adjacent like shaft elements are aligned with one another when a protrusion of one shaft element is aligned with a recess in an adjacent like shaft element. A tension element secured to a distal end of the malleable shaft is in communication with a proximal end of the malleable shaft via an axial through hole.  
      In another embodiment, a variable stiffness malleable shaft comprises a plurality of tension elements connected to a distal end of the malleable shaft, an actuator for applying force to the plurality of tension elements, a compensation element mounted to articulate about a point in space, and a connector linking the plate to the actuator.  
      Alternately, a variable stiffness malleable shaft has a first pair of tension elements, each connected between a distal end of the malleable shaft and the other tension element of the pair. A fulcrum has a distal side and a proximal side, with the joined proximal ends of the tension element passing over a proximal side of the fulcrum. An actuator is linked via a connector to the fulcrum, and applies force to the plurality of tension elements. The fulcrum may be a ball, and may have one or more channels to accommodate one or more pairs of tension elements over its proximal side. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The foregoing features, benefits, and advantages of the present invention will be made apparent with reference to the following descriptions and figures, wherein like reference numerals refer to like elements across the several views.  
       FIG. 1  illustrates a surgical instrument according to a first embodiment of the present invention;  
       FIG. 2A  illustrates a shaft element according to the first embodiment;  
       FIG. 2B  illustrates an alternate embodiment of a shaft element according to the present invention;  
       FIG. 3  illustrates a portion of the assembled malleable shaft section according to the first embodiment;  
       FIG. 4  illustrates a portion of the assembled malleable shaft according to a second embodiment;  
       FIG. 5  illustrates an embodiment of the present invention including a malleable shaft section that changes diameter along its length; and  
       FIG. 6  illustrates a transitional shaft element according to the embodiment of  FIG. 5 .  
       FIG. 7  illustrates a further aspect of the present invention for accommodating differential lengths due to the orientation of the malleable shaft.  
       FIG. 8  illustrates an alternate embodiment for accommodating differential lengths due to the orientation of the malleable shaft. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring now to  FIG. 1 , shown is a surgical instrument, generally  10 , according to a first embodiment of the present invention. The surgical instrument comprises a proximal base section  12 , and a malleable shaft section  14 . The base section  12  is adapted for the surgeon to manipulate by hand. It includes actuating levers  16  for actuating a remote apparatus  18  carried on a distal end  20  of the malleable shaft section  14 . In this case, the remote apparatus is a clamp. Other remote apparatus contemplated include, but are not limited to, surgical retractors or stabilizers, which may or may not include remote actuation, ligation, ablation, and endoscopy tools. Neither is the present invention limited to only one remote apparatus.  
      In alternate embodiments, the proximal base section may be additionally or alternately adapted for securement to additional surgical hardware, including, but not limited to, a surgical retractor or other apparatus. Base section  12  will also include an actuator  22  to transition the malleable shaft portion between flexible and rigid states. A lead screw, among other means, is known in the art to transition a malleable shaft between flexible and rigid states. A preferred embodiment of a malleable shaft actuator is disclosed in U.S. patent application Ser. No. 10/609,726, filed 30 Jun. 2003, which is hereby incorporated by reference in its entirety for all purposes.  
      Malleable shaft section  14  may be integrally formed with the base section  12 , or may be adapted to be removable from and/or interchangeable with one or more embodiments of base section  12 . Malleable shaft section  14  includes a shaft  16 , comprised of a plurality of shaft elements  24 .  
      Referring now to  FIG. 2A , a shaft element  24  according to a first embodiment of the present invention is shown. Shaft element  24  is generally prismatic in shape, in this case generally cylindrical. A generally prismatic shape will be understood to be that substantially encompassed by a volume extending between two substantially parallel geometric faces. Shaft element  24  has a central through hole  26  generally aligned with a first longitudinal axis  28  of the shaft element  24 . Preferably, through hole  26  is substantially parallel with the first longitudinal axis  28 , and even more preferably centered on it. A plurality of distributed axial through holes  30 , in this embodiment four (4), are distributed about the longitudinal axis  28 .  
      The shaft element  24  has a proximal end  32  having a recess  34  formed therein. Recess  32  is defined along a second transverse axis  36 . A protrusion  38  is formed at a distal end  40  of the shaft element  24 . Protrusion  38  is defined along a third transverse axis  42 , which extends out of the plane of  FIG. 2A . Second transverse axis  36  and third transverse axis  42  are oriented relative to one another such that the central axial through hole  26  and distributed axial through holes  30  of a first shaft element  24  are aligned with the central axial through hole  26  and distributed axial through holes  30  of an adjacent shaft element  24  when the transverse axis  42  defining the protrusion  38  of the first shaft element  24  is aligned with the transverse axis  36  defining the recess of the adjacent shaft element  24 . With respect to the relationship of adjacent through holes, aligned will be taken to mean that a distal or proximal opening of one axial through hole, whether distributed  30  or central  26 , is positioned to coincide with the proximal or distal opening, respectively, of the corresponding through holes in the adjacent shaft element  24 , thereby forming an open passage through both shaft elements.  
      In the exemplary embodiment, transverse axes  36  and  42  are oriented at 90 degrees to one another, and four (4) distributed axial through holes  30  are spaced at or about 90 degree intervals. In an alternate embodiment, shown in  FIG. 2B , a shaft element  24   a  has three (3) distributed axial through holes  30   a , and transverse axes  36   a  and  42   a  are oriented at or about 120 degrees to one another. Other possible combinations of transverse axis orientation and distributed axial through hole placement will therefore be apparent to those skilled in the art in light of the foregoing disclosure.  
      Referring again to  FIG. 2A , either or both of protrusion  38  and recess  34  may additionally be formed with a friction-enhancing geometry, for example micro-teeth  39  and  35 , respectively, or other random or pseudo-random generalized surface roughness. Alternately or additionally, the surfaces may be formed with at least a coating of a high-friction material such as a polyurethane or silastic.  
      Referring now to  FIG. 3 , a portion of the assembled malleable shaft  16  is shown in greater detail. A plurality of shaft elements  24  are arranged adjacent one another and oriented such that the protrusion  38  of one shaft element  24  is aligned with the recess  36  of another shaft element  24 . Accordingly, the central through holes  26  of adjacent shaft elements  24  form an open central passage  44 . Similarly, the distributed axial through holes  30  of adjacent shaft elements  24  form open distributed passages  46 . At least one of the distributed passages  46 , and more preferably each distributed passage  46 , provides clearance for tension elements  48  to run through the plurality of shaft elements  24 . The central passage  44  provides clearance for a device actuation cable  50  to run through the plurality of shaft elements  24 , where the malleable shaft section  14  is provided with a distal apparatus  18  whose utility is enhanced by remote actuation, as in the case of the clamp jaws shown in the embodiment of  FIG. 1 .  
      In operation, each tension element  48  that is provided will be secured to a distal end  20  of the malleable shaft section  14 . Each will pass through the length of the shaft section  14 , via one of distributed passages  46 . Further, each will be operatively connected to an actuator  22  in the proximal base section  12 . Actuator  22  is operative to apply force to each tension element  48 , and thereby transition the malleable shaft section  14  from a flexible to a rigid state.  
      Referring now to  FIG. 4 , a portion of the assembled shaft  116  according to a second embodiment of the present invention is shown in greater detail. The similarities between the first and second embodiments will be apparent. Malleable shaft section  114  comprises a plurality of shaft elements  124 . Shaft elements  124  are shorter in the longitudinal dimension than their counterparts of the first embodiment. Additionally, the size of the recess  134  in a proximal end  132  of shaft element  124  and the size of the protrusion  138  in a distal end  140  of each shaft element  124  will be seen as significantly smaller in both height and width. This has the effect of limiting the angular freedom of each shaft element  124 . However, this is compensated for by the fact that the shaft elements are significantly shorter in the longitudinal dimension. The result is that, overall, the flexibility of the shaft in its flexible state is not compromised.  
      Additionally, the smaller angular displacements impose correspondingly smaller side loads than larger angular displacements, and a shaft under smaller side loads is generally more rigid for a given diameter. Those skilled in the art will appreciate that the choice of shaft element length and maximum angular displacement can be customized to individual applications without departing from the scope of the present invention. Further, the recess  134  and/or the protrusion  138  can be provided with one or more type of friction-enhancing treatment including, but not limited too, micro teeth, random or pseudo-random generalized surface roughness, or a coating layer or more of high-friction material.  
      It is desirable that the diameter of the malleable shaft section  14  be as thin as possible to improve visualization and access at the surgical site. However, a minimum diameter is approached where the shaft can no longer hold its position while under the loads applied along its length or specifically at the distal end  20 . Additionally, the shaft must accommodate within it the distributed passages  46  for tension elements  48 , and optionally a central passage  44 . It is further apparent that these loads are greater at a proximal portion of the malleable shaft section  14 . However, rather than dimension the entire length of the shaft to a diameter necessary to accommodate the loads at the proximal end, it is contemplated that the diameter may change in some manner over the length of the shaft.  
      Referring now to  FIG. 5 , another embodiment  200  of the present invention including a malleable shaft section  214  that changes diameter along its length is shown. In this embodiment, the shaft is comprised of a proximal first plurality of first shaft elements  224   a , and a distal second plurality of second shaft elements  224   b . These first shaft elements  224   a  and second shaft elements  224   b  may be generally similar to each other, but for their size. Further, a transitional shaft element  224   c  is provided at the interface between the first shaft elements  224   a  and second shaft elements  224   b . Transitional shaft element  224   c , shown in greater detail in  FIG. 6 , will have a proximal end  232   c  which is generally similar to a proximal end of a first shaft element  224   a , and a distal end  240   c  which is generally similar to a distal end of a second shaft element  224   b . Distributed axial through holes  230   c  will adjust position accordingly with the change in size, shape, and/or diameter to effect the transition.  
      Alternately, each shaft element may be formed to progressively decrease in size along the length of the malleable shaft and/or include some size variation along its own length. Such size variation along the length, for example a smooth or discontinuous taper, should remain construed within the scope of the generally prismatic description as applied to shaft elements.  
      Referring now to  FIG. 7 , as the shape of malleable shaft section  16  is manipulated, the lengths of each distributed passage  46  may differ slightly, because each axial through hole  30  is located off of the longitudinal axis  28  of each shaft element  24 . Therefore, location of the proximal ends of each tension element  48  will similarly differ slightly, presuming each tension element is of equal length, because the precise orientation of the shaft generally cannot be predetermined. However, when applying force to the tension elements, it is desirable to apply the force uniformly. Generally, force is applied to the tension elements  48  by displacing the proximal ends proximally. If these ends are fixed in or near the base section  12 , then the tension applied may not be uniform, due to the passage length variations. Therefore, it would be desirable to have a means for accommodating the differential lengths when applying force.  
       FIG. 7  illustrates a further aspect of the present invention. Each tension element  48  is secured to a compensation element, for example swash plate  52 . Swash plate  52  is attached to tension rod  54  at a ball joint  56 . Tension rod  54  need not be rigid, and a cable or filament may be substituted to connect swash plate  52  with actuator  22 . Through the ball joint  56 , with support (not shown) by either or both of base section  12  and malleable shaft section  14 , the center of the swash plate  52  is generally fixed in space relative to the shaft  16 , preferably along the longitudinal axis  28  of a first shaft element  24 . The swash plate  52  is free to articulate around any axis. Swash plate  52  may optionally include a clearance area within itself for passage of the actuation cable  50  or the like. In an alternate embodiment, the compensation element may not be a plate at all, but may be replaced by any structure having arms to connect with tension elements  48  around central ball joint  56 .  
      In this embodiment, to transition the malleable shaft  16  from a flexible state to rigid state, the tension rod  54  is displaced proximally under the influence of actuator  22 . The freedom of motion of the swash plate  52  allows each tension element to be displaced uniformly. Optionally, when the malleable shaft section  14  is separable from the base section  12 , the swash plate will be incorporated into the malleable shaft section  14 , with the tension rod  54  extending proximally to interface with the actuator  22  in the base section  12 .  
      Referring now to  FIG. 8 , an alternate means for accommodating the differential lengths of passages  46  is shown. In the embodiment of  FIG. 8 , diametrically opposed tension elements  48  are connected at their proximal ends. In this exemplary embodiment, a ball element  156  has one or more channels,  156   a ,  156   b , formed substantially aligned with an equator or great circle of the ball  156  on its proximal side. Preferably, one channel  156   b  is set deeper into the ball  156  than another channel  156   a . Each channel  156   a ,  156   b  is also aligned with the diameter connecting its respective pair of tension elements  48 .  
      The each pair of tension elements is then set into a respectively aligned channel  156   a ,  156   b . As the length of passages  44  change, the tension elements ride over the proximal side of the ball  156  in the channels  156   a ,  156   b , shifting length from one side to the other accordingly. Because the channels  156   a ,  156   b  are set to differing depths, crossing tension elements  48  do not interfere with one another. To transition the malleable shaft  16  between flexible to rigid states, ball  156  is displaced proximally via connecting rod  154 .  
      Though the exemplary embodiment in  FIG. 8  includes a ball  156 , suitable substitutes need not be a ball per se, but merely structure to provide a fulcrum or pivot around which the connected tension elements  48  may reverse direction relative to the opposing tension element  48 . The channels  156   a ,  156   b , are optional, and if provided need not overlap.  
      It is further contemplated that in place of the arrangements disclosed, other pre-tensioning means may be provided for each tension element  48 , including, but not limited to a spring in any form known in the art. Further, the transition of the malleable shaft  16  from flexible to rigid states would include transitioning the tension load from the pre-tensioning means through the action of the actuator  22 .  
      The present invention has been described herein with respect to certain preferred embodiments. These embodiments are meant to be illustrative, and not limiting, of the scope of the present invention, which is defined by the appended claims.