Abstract:
Torque limiting devices, tools comprising torque limiting devices and methods for using torque limiting devices are disclosed. In an embodiment, a torque limiting device comprises a first and a second surface disposed in substantially adjacent parallel planar relationship such that within a predetermined torque range the first and second surface rotate together such than a torque applied to the first surface is translated to the second surface. When the torque applied exceeds a certain critical torque, the first and second surfaces slip and therefore the excessive torque is not transferred.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to mechanical devices. Embodiments of the present invention include torque limiting devices, tools comprising torque limiting devices, methods for using torque limiting devices and medical kits comprising torque limiting devices.  
       BACKGROUND  
       [0002]     Tools, such as medical tools, may undergo relatively high torque forces. If the torque force is greater than the tool can withstand, the tool may break or fracture. Tool breakage can lead to serious injuries. For example, if a medical tool breaks while still inserted in a patient, the patient may suffer serious injuries. Therefore, it is desirable to design tools such that injury inducing breakage is minimized or eliminated.  
         [0003]     In order to avoid injury inducing breakage past tools have been designed to break in a predetermined position when torque forces are greater than the tool can withstand. For example, a groove can be cut such that a predetermined torque causes the tool to break at the groove as the predetermined torque is less than the torque that would cause other portions of the tool to break. Such a design has been used with a form of medical tool referred to as a curette.  
         [0004]     Although this prior design may be effective for reducing injuries, it is costly as once the tool is broken it may be useless and therefore replaced. Furthermore, this prior design is inconvenient because when the tool breaks, work must be stopped and restarted with a new tool. In the case of a medical tool, a surgeon must stop surgery, remove the broken portion of medical tool, and insert a new, unbroken tool.  
         [0005]     Therefore, it is desirable to provide a device that could minimize injuries from tool breakage resulting from excess torque while allowing the tool to remain functional for repeated use.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention provides torque limiting devices, tools, including medical tools, comprising a torque limiting device, methods for using torque limiting devices and medical kits comprising torque limiting devices.  
         [0007]     A torque limiting device of the present invention allows a predetermined amount of torque to be applied and then disengages after the predetermined amount of torque has been reached. Torque limiting devices are also referred to in the art by other names, such as, for example, slip clutches, friction torque limiters, overload clutches, torque limiting clutches and the like.  
         [0008]     In embodiments, a torque limiting device of the present invention comprises a plurality of substantially planar surfaces disposed in a substantially parallel relationship. At least a first and a second planar surface are resiliently biased against one another such that within a predetermined torque range, rotational movement of the first planar surface results in rotational movement of the second planar surface in the same direction through surface friction. At, or above, a predetermined torque, surface friction is overcome and the first planar surface rotates independently of the second planar surface. In embodiments the first planar surface and second planar surface are resiliently biased through the use of a spring. The spring may comprise a metal and/or a polymer. The spring may comprise a coil spring, a compression spring, an extension spring or a torsion spring.  
         [0009]     In some embodiments, the first and second planar surfaces may be disposed in the interior of a housing. The first planar surface may be resiliently biased against the second planar surface through the use of a spring disposed between an interior wall surface of the housing and a side of the first planar surface opposite the side facing the second planar surface.  
         [0010]     In some embodiments of a torque limiting device of the present invention, a first planar surface comprises a projection and a second planar surface adjacent to the first planar surface comprises a receptacle. The projection will generally extend in a substantially perpendicular direction from the planar surface. The projection engages the receptacle such that rotation of the first planar surface results in rotation of the second planar surface. When a predetermined torque limit is reached, the projection clears the notch thus forcing the planar surfaces apart. As a result, the second planar surface no longer rotates upon further rotation of the first planar surface. The projection and notch may be realigned and reengaged to permit further rotation.  
         [0011]     Projections may comprise a tooth or a peg and may be substantially cylindrical, rectangular, pyramidal, trapezoidal or make take other three dimensional geometrical shapes. The sides of the projection may be sloped. A planar surface may comprise a plurality of projections.  
         [0012]     A receptacle in a planar surface adjacent to the planar surface comprising the projection, may comprise a void, a hole, a notch, a track etc. In some embodiments, the receptacle is adapted to receive the projection from the adjacent planar surface.  
         [0013]     Torque limiting devices of the present invention are advantageous for use in tools designed to impart a rotational force. A curette is a medical tool used to scrape, score, or otherwise form a cavity or create a void within one of the body&#39;s solid organs. A curette comprises a tip that scrapes the bone, or other organ. The tip may be made of any suitable biocompatible material, for example, stainless steel, cobalt chromium, titanium, and alloys or mixtures thereof. Because of the relatively small size of the tip and thin material wall thickness, it is possible that the tip may break or deform when too high a torque is applied to the handle of the curette.  
         [0014]     A surgical tool, such as a curette, with a torque limiting device of the present invention, limits the torque applied to the tip of the tool to reduce the possibility of damaging the tool. In addition, the torque limiting device of the present invention may be reengaged so that the tool may be used again immediately after disengagement.  
         [0015]     In some embodiments, a surgical tool of the present invention may comprise a rod having a first and a second end, a surgical implement attached to the first end of the rod, and a handle positioned near the second end of the rod. The surgical tool may further comprise a first surface attached to the rod and a second surface attached to the handle, the first surface in frictional contact with the second surface. The first and second surfaces may comprise plates, a notch and a tooth, or any other configuration that will allow disengageable torque translation. When a surgeon applies a torque to the handle, the friction between the first surface and second surface causes the torque to translate to the rod, and consequently, to the surgical implement. If a torque greater than a certain critical torque is applied to the handle, the friction force between the first and second surfaces will be overcome, and the second surface will slip with respect to the first surface, which causes the torque applied to the handle not to be translated to the rod. In addition, after the first and second surfaces slip, they may be reengaged so that the surgeon may immediately continue using the tool.  
         [0016]     Accordingly, in some embodiments, the present invention provides a surgical tool that limits torque applied to the surgical implement without permanently deforming or damaging the tool. Therefore, if a surgeon applies too high a torque to the handle of the tool, the tool will disengage without permanently damaging the tool. In addition, the tool may be reengaged so that the surgeon may continue the surgery without delay.  
         [0017]     The present invention also provides medical kits. In some embodiments, a medical kit of the present invention comprises a surgical tool of the present invention. The medical kit of the present invention may further comprise additional surgical tools.  
         [0018]     A tool, and/or a surgical tool, of the present invention may be used in a manner similar to prior tools and provide the added benefit of being re-settable and thus reusable if a predetermined torque is exceeded. Thus, in some embodiments, a method of the present invention comprises applying a torque to a tool comprising a torque limiting device of the present invention wherein if a predetermined torque is exceeded by an excess torque causing the first and second planar surfaces to rotate independently from each other, the method comprises applying a rotational force to the first planar surface in a direction substantially opposite the direction of the excess torque to re-engage the first and second planar surfaces and cause a rotational force applied to the first planar surface to be transmitted to the second planar surface.  
         [0019]     Further details and advantages of the present invention are set forth in the following detailed description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is a perspective and partially exploded view of a surgical tool according to certain embodiments of the present invention.  
         [0021]      FIG. 2  is a perspective and partially exploded view of a portion of the surgical tool of  FIG. 1 .  
         [0022]      FIG. 3  is a section view of a surgical tool according to certain embodiments of the present invention.  
         [0023]      FIG. 4  is a perspective view of the surgical tool of  FIG. 3 .  
         [0024]      FIG. 5  is a perspective view of a portion the surgical tool of  FIGS. 3 and 4 .  
         [0025]      FIG. 6  is a perspective view of the surgical tool of  FIGS. 3, 4 , and  5 .  
         [0026]      FIG. 7  is a block diagram representation of a method according to certain embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0027]     For the purposes of this specification, unless otherwise indicated, all numbers expressing quantities, conditions, and so forth used in the specification are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification are approximations that can vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.  
         [0028]     Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a stated range of “1 to 10” should be considered to include any and all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more, e.g. 1 to 6.1, and ending with a maximum value of 10 or less, e.g., 5.5 to 10. Additionally, any reference referred to as being “incorporated herein” is to be understood as being incorporated in its entirety.  
         [0029]     It is further noted that, as used in this specification, the singular forms “a,” “an,” and “the” include plural referents unless expressly and unequivocally limited to one referent.  
         [0030]     According to certain embodiments, the present invention provides a torque limiting device which may be used with medical devices or other mechanical devices to which a torque is applied. The present invention provides a torque limiting device that may be incorporated into any tool or system that experiences a torque. A device according to the present invention may comprise a rod having a first end and second end. The first and second ends may include the tips of the rod as well as a region of the rod near each tip. The device may further comprise a surgical implement attached to the first end of the rod and a handle positioned near the second end of the rod. The device may further comprise a first surface attached to the rod and a second surface attached to the handle. The two surfaces may be disposed in frictional contact with each other, for example via a tooth and notch. The two surfaces may be contained within a housing, which may be attached to the handle.  
         [0031]     The device may further comprise a spring disposed between the housing to force the tooth into the notch when the tooth and notch are aligned. The two surfaces are able to rotate independently, but when the tooth and notch are engaged, the two surfaces rotate together. The tooth and notch may be designed to disengage when a torque equal to or greater than a predetermined maximum torque is applied to the device. The maximum torque is the torque that is required to cause the tooth to rise out of the notch, overcoming the static friction force between the surfaces and the spring force exerted by the spring on the tooth. When the tooth disengages from the notch, the two surfaces rotate independently, and consequently the excessive torque applied to the first surface is not translated to the second surface. The two surfaces may be made of a polymer, stainless steel, aluminum, or any other material or combination of materials suitable for creating friction between the two surfaces.  
         [0032]     This torque limiting device may be used, for example, on a curette. A curette may comprise the elements disclosed in PCT Patent Application WO 2005/023085, which is herein incorporated by reference. The disengagement of the tooth from the notch protects the curette tip, for example, from an application of torque that may be sufficient to break the tip while still inserted in the patient.  
         [0033]     In addition to limiting the amount of torque that can be applied to the functional implement of the tool, the device of the present invention may be engaged again to resume use. After the tooth disengages from the notch, the device may be reengaged by rotating the first surface until the tooth and notch align, at which point the spring forces the tooth into the notch. When the tooth and notch are engaged again, the use of the tool may resume. The ability to reengage the device is a significant advantage over previous devices, which suffer permanent damage when an excessive torque is applied. Therefore, previous torque limiting devices are useless after one instance of excessive torque, whereas the device of the present invention may be reused after many instances of excessive torque.  
         [0034]     The torque limiting device of the present invention may be used on medical tools, such as a curette, as described above. The torque limiting device may also be used on other surgical tools for use in human and veterinary contexts, including tools for grasping, scraping, bending, pushing, or otherwise manipulating an organ of the body, including bone. The device may also be used on other tools or machines in which a maximum torque should not be exceeded. For example, the torque limiting device of the present invention could be included in a screwdriver or wrench to prevent over-tightening of the screw or bolt. The torque limiting device may also be used on machines in which certain components could break when excessive torque is applied.  
         [0035]     Referring now to  FIGS. 1-2 , in one embodiment of the present invention, a surgical tool  10  may comprise a rod  12  having a first end  14  and a second end  16 . The first end  14  and second end  16  may each comprise the tip of the rod  12  as well as a region of the rod  12  proximate each tip. A surgical implement  18  may be coupled or fixedly attached to the first end  14  of the rod  12 . A handle  20  may be positioned near the second end  16  of the rod  12 , and the handle  20  may be manipulated by a user. A torque limiting device  22  may be attached to the handle  20  and to the rod  12 , so that a rotation of the handle  20  causes a rotation of the rod  12 , and therefore, of the implement  18 .  
         [0036]     The torque limiting device  22  may comprise a first plate  24  having a notch  26  and a second plate  28  having a tooth  30 . The notch and tooth can be interchangeable, i.e. the first plate can have the tooth and the second plate can have a notch. The tooth  30  and notch  26  may be substantially the same shape and size so that they may fit together. The tooth  30  may be V-shaped, V-shaped with a flat bottom, U-shaped, semi-circular, or any other shape that provides a non-perpendicular angle between the tooth  30  and the surface of the second plate  28 . The tooth  30  and the notch  26  may be radially aligned such that the tooth  30  fits into the notch  26  when they are rotationally aligned.  
         [0037]     The first plate  24  and the second plate  28  may be disposed within a housing  32 . The housing  32  may be generally in the shape of a hollow cylinder having an inner diameter equal to or larger than the diameter of the larger of the first plate  24  and the second plate  28 . The housing  32  may comprise a cap  34 , and a compression spring  36  may be disposed between the cap  34  and the second plate  28 . The second plate  28  may comprise a collar  38  over which the spring  36  fits so that lateral movement of the spring  36  is substantially prevented. The torque limiting device  22  may further comprise at least one guide pin  40 , and the second plate  28  may comprise at least one slot  42 . The at least one guide pin  40  may be integrally formed with the cap  34  or with the housing  32 , or the at least one guide pin  40  may be fixedly attached to the cap  34  or to the housing  32 . The second plate  28  may be positioned in the housing  32  such that the at least one guide pin  40  fits into the at least one slot  42 . The at least one slot  42  allows the second plate  28  to slide longitudinally along the at least one guide pin  40  but thereby prevents the second plate  28  from rotating with respect to the housing  32 . The second plate  28  will then rotate only when the housing  32  rotates.  
         [0038]     Conversely, the first plate  24  may be disposed in the housing  32  such that rotational movement of the first plate  24  with respect to the housing  32  is allowed but longitudinal movement with respect to the housing  32  is prevented. This may be accomplished by providing the housing  32  with a support  44 , such as a ledge, that contacts the bottom surface of the first plate  24 , or by other suitable means. Accordingly, the first plate  24  is permitted to rotate along the support  44  but is not permitted to move longitudinally.  
         [0039]     The rod  12  may be integrally formed with the first plate  24  or may be fixedly attached to the first plate  24 , such as by welding. Therefore, a rotation of the first plate  24  is directly translated to the rod  12 , and consequently to the surgical implement  18 .  
         [0040]     The housing  32  may be attached to the handle  20 . Therefore, a rotation of the handle  20  is directly translated to the housing  32 , and consequently, via the at least one guide pin  40 , to the second plate  28 .  
         [0041]     The rotation of the second plate  28  is translated to the first plate  24  by the frictional interface between the tooth  30  and the notch  26 . When the tooth  30  and notch  26  are engaged, that is when the tooth  30  and notch  26  are rotationally aligned and the tooth  30  is positioned within the notch  26 , rotation of the handle  20  causes rotation of the implement  18 .  
         [0042]     However, if a torque above a maximum torque is applied to the handle  20 , the friction force between the tooth  30  and notch  26  and the spring force of the compression spring  36  may be overcome, and the tooth  30  may disengage from the notch  26 , that is the tooth  30  may rise out of the notch  26  and become no longer rotationally aligned. When the tooth  30  is disengaged from the notch  26 , a rotation of the handle  20  does not cause a rotation of the implement  18 . The tooth  30  and notch  26  may be engaged again by rotating the handle  20  until the tooth  30  and notch  26  are rotationally aligned, and at that point the compression spring  36  will push the tooth  30  into the notch  26  again.  
         [0043]     The maximum torque may be determined by varying any of the following: the spring rate of the compression spring; the slope of the tooth and notch; the length and height of the notch; the radial distance of the tooth and notch from the center of the plate and pedestal, respectively; and the materials used for the plate and pedestal. In an embodiment, a surgical tool of the present invention may be designed to slip at about 10±1 in.-lbs. torque and to break at about 13±1 in.-lbs. torque. Thus, if a torque of 13 in.-lb., for example, is required to break the coupling between the rod  12  and the surgical implement  18 , the tooth and notch may be designed to slip and begin to disengage when a torque of approximately 10 in.-lb, for example, is applied to the handle  20 , and then completely disengage when 13 in.-lb. is applied to handle  20  As a result, a torque of 15 in.-lb. would never be transmitted to the rod  12  because the tooth  30  would disengage from the notch  26  at a torque of 13 in.-lb. Furthermore, it has been found that the mean torque required to scrape normal bone is approximately 2.0 in.-lb. Therefore, a configuration that caused disengagement to begin at 10 in.-lb and complete at 13 in.-lb. would allow a torque that is required for normal scraping to be translated to the surgical implement.  
         [0044]     Referring now to  FIGS. 3-6 , in another embodiment of the present invention, a surgical tool  110  may comprise a rod  112  having a first end  114  and a second end  116 . The first end  114  and second end  116  may each comprise the tip of the rod  112  as well as a region of the rod  112  proximate each tip. A surgical implement  118  may be coupled or fixedly attached to the first end  114  of the rod  112 . A handle  120  may be positioned near the second end  116  of the rod  112 , and the handle  120  may be manipulated by a user. A torque limiting device  122  may be attached to the handle  120  and to the rod  112 , so that a rotation of the handle  120  causes a rotation of the rod  112 , and therefore, of the implement  118 .  
         [0045]     The torque limiting device  122  may comprise a plate  124  having a depression  126  and a ball plunger  128  having a ball  130 . The ball  130  and depression  126  may be substantially the same shape and size so that they may fit together. The ball  30  may be V-shaped, V-shaped with a flat bottom, U-shaped, semi-circular, or any other suitable shape. The ball  130  and the depression  126  may be radially aligned such that the ball  130  fits into the depression  126  when they are rotationally aligned. The ball plunger  128  may comprise other components, as is commonly known. For example, the ball plunger  128  may comprise a hollow cylinder, partially within which the ball slides longitudinally. The ball plunger  128  may also comprise a shaft that limits the movement of the ball and a spring that tends to push the ball longitudinally in the cylinder. The ball plunger  128  may also have other configurations that allow for longitudinal movement of the ball.  
         [0046]     The plate  124  and the ball plunger  128  may be disposed within a housing  132 . The housing  132  may be generally in the shape of a hollow cylinder having an inner diameter equal to or larger than the diameter of the plate  124 . The housing  132  may comprise a cap  134 , and the ball plunger  128  may be mounted or attached to the cap  134 . Therefore, a rotation of the housing  132  also results in a rotation of the ball plunger  128 .  
         [0047]     The plate  124  may be disposed within the housing  132  such that rotational movement of the plate  124  is allowed but longitudinal movement with respect to the housing  132  is prevented. This may be accomplished by providing the housing  132  with a support  144 , such as a ledge, that contacts the bottom surface of the plate  124 , or by other suitable means.  
         [0048]     The rod  112  may be integrally formed with the plate  124  or may be fixedly attached to the plate  124 , such as by welding. Therefore, a rotation of the plate  124  is directly translated to the rod  112 , and consequently to the surgical implement  118 .  
         [0049]     The housing  132  may further comprise a flange  136  attached to the cap  134 . The handle  120  may be attached to the housing  132  by fitting over the flange  136  in a relatively tight tolerance. Accordingly, a rotational movement of the handle  120  would be translated through the flange  136  to the housing  132 , and therefore to the ball plunger  128 .  
         [0050]     The rotation of the ball plunger  128  is translated to the plate  124  by the frictional interface between the ball  130  and the depression  126 . When the ball  130  and depression  126  are engaged, that is when the ball  130  and depression  126  are rotationally aligned and the ball  130  is positioned within the depression  126 , rotation of the handle  120  causes rotation of the implement  118 .  
         [0051]     However, when the torque applied to the handle  120  exceeds a certain predetermined amount, the ball plunger  128  may compress and the ball  130  of the ball plunger  128  may rise out of the depression  126  to a disengaged position. When the ball  130  and depression  126  are disengaged, a rotation of the handle  120  no longer causes a rotation of the implement  118 . The ball  130  and depression  126  may be engaged again by rotating the handle  120  until the ball  130  and depression  126  are rotationally aligned, and at that point the ball plunger  128  will expand so that the ball  130  again rests in the depression  126 .  
         [0052]     The maximum torque may be determined by varying any of the following, as described above: the spring rate of the compression spring in the ball plunger; the shape and size of the ball and depression; the radial distance of the ball and depression from the center of the plate; and the materials used for the ball and the plate.  
         [0053]     The present invention may also comprise a method for using the device as described above. Referring now to  FIG. 7 , the method  200  may comprise the steps of: inserting  210  a surgical tool into a body of a living being, the surgical tool having a rod, a surgical implement, and a handle; positioning  220  the surgical implement, such as the curette, at the desired location within the body; and applying  230  a torque to the handle. The method may further comprise reengaging  240  a first surface of the surgical tool with a second surface of the surgical tool after an excessive torque has caused them to disengage. Reengaging  240  the first surface with the second surface may comprise realigning them, for example by rotating the handle until the first and second surfaces are realigned.  
         [0054]     While the invention has been described with reference to certain embodiments, other features may be included without departing from the spirit and scope of the invention.