Torque limiting device

Description of equivalent WO 2007008669 A2

PATENT TORQUE LIMITING DEVICE AND METHODS

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-Part application of, and claims benefit of, U.S.

Patent App. No. 11/256,036, filed on October 21, 2005, which claims benefit of U.S.

Provisional Patent App. No. 60/698,288, filed on July 11, 2005, each of which is incorporated by reference herein in its entirety. FIELD OF THE INVENTION

The present invention relates to torque limiting devices, tools comprising torque limiting devices, kits comprising torque limiting devices, and methods for using torque limiting devices.

BACKGROUND 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. In order to avoid injury-inducing breakage, conventional tools have been designed to break in a predetermined position when torque forces are greater than the tool can withstand.

For example, a tool can include a groove at a particular location such that a predetermined torque causes the tool to break at the groove. The predetermined torque breaking point is less than the torque that would cause other portions of the tool to break. Conventional medical curettes may employ such a design.

Although such a conventional design may be effective for reducing injuries, it is costly because once the tool is broken, it may be un-repairable and thus require replacement.

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, or all, of the medical tool, and insert a new, unbroken tool.

Therefore, it is desirable to provide a device that avoids breaking from excess torque so as to minimize injuries related to such breaking and to allow the tool to remain functional for repeated use. SUMMARY OF THE INVENTION

The present invention provides a torque limiting device, tools, including medical tools, comprising a torque limiting device, kits comprising a torque limiting device, and methods for using a torque limiting device. A torque limiting device of the present invention allows a predetermined amount of torque to be applied to a tool and disengages the torque force from the tool after the predetermined amount of torque has been reached. Torque limiting devices are also referred to by other names, such as, for example, slip clutches, friction torque limiters, overload clutches, torque limiting clutches, and the like. In an embodiment, a torque limiting device of the present invention can comprise 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 frictional engagement of the surfaces. That is, the first and second surfaces are releasably engageable. At, or above, a predetermined torque limit, frictional engagement of the surfaces is overcome such that the first planar surface rotates independently of the second planar surface. In an embodiment, 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.

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.

In some embodiments of a torque limiting device of the present invention, the first planar surface includes a projection and the second planar surface adjacent the first planar surface includes a notch for receiving the projection. The projection can extend in a direction substantially perpendicular to the planar surfaces. The projection is matingly engageable with the receiving notch such that there is no separation between the two planar surfaces and rotation of the planar surfaces is facilitated. When the planar surfaces are rotated and a predetermined torque limit is reached, the projection disengages from the notch, causing the projection to be positioned between the two planar surfaces such that the planar surfaces are forced apart. As a result, the second planar surface no longer rotates upon further rotation of the first planar sunace. in an embodiment, the projection and notch may be realigned and reengaged to permit further rotation.

The projection may comprise a tooth or a peg and may be substantially cylindrical, rectangular, pyramidal, trapezoidal, or other three-dimensional geometrical shapes. The sides of the projection may be sloped. In an embodiment, the projection may be in one planar surface or an adjacent planar surface engageable with the one planar surface, and the receiving notch is in the planar surface opposite the planar surface from which the projection projects. Another embodiment may include more than one projection and matable receiving notch in adjacent planar surfaces. In some embodiments, one planar surface can include a projection for engaging with a notch in an adjacent planar surface and a notch for engaging a projection from the adjacent planar surface.

The receiving notch in a planar surface may comprise a void, a hole, a slot, a track, or other suitably configured depression for receiving a projection from an adjacent planar surface. Preferably, the notch is configured to receive a projection from an adjacent planar surface so as to engage the two planar surfaces.

Embodiments of a torque limiting device of the present invention are advantageous for use in tools designed to impart a rotational force. A curette is a medical tool in which a rotational force, or torque, is used to scrape, score, or otherwise form a cavity or create a void within an interior body region, such as in bone, a solid organ, or other tissue. A curette can include a tip that scrapes bone or other tissue. The tip may be made of any biocompatible material, for example, stainless steel, cobalt, chromium, titanium, and alloys or mixtures thereof suitable for scraping tissue. Because of the relatively small overall size and thinness of the tip, it is possible that the tip may break or deform when too great a torque is applied to the curette. A surgical tool, such as a curette, having a torque limiting device of the present invention, can limit the torque applied to the tip of the tool to reduce the possibility of damaging the tool. In addition, once a predetermined torque limit has been surpassed and rotationally engaged planar surfaces of the tool are disengaged and forced apart, a torque limiting device of the present invention allows the planar surfaces to be reengaged such that the tool may be used again immediately after disengagement and without the need to remove the tool or a portion of the tool from a surgical site.

In an illustrative embodiment, a surgical tool of the present invention may comprise a rod having a first end and a second end, a handle positioned near the first end of the rod, and a surgical implement attached to the second end of the rod. The surgical tool may further comprise a first surface attached to the handle and in factional engagement with a second surface attached to the rod. The first and second surfaces may comprise at least two plates, one of which includes a projection and the other of which includes a notch, or another configuration that will allow disengagement between the plates upon application of a preset amount of torque. When a surgeon applies a rotational force to the handle and the first surface attached to the handle, the engagement between the first surface and second surface causes the torque applied to the first surface to translate to the second surface and the attached surgical implement. If a torque greater than a predetermined, disengaging torque limit is applied to the handle, the force of engagement between the first and second surfaces due to friction between the surfaces and of the mated configuration between the projection and the notch will be overcome, and the first surface will become disengaged from the second surface. That is, the projection and the notch are releasably engageable. Disengagement of the first and second surfaces results in the torque applied to the handle not being translated to the rod. In this manner, a torque that exceeds a predetermined threshold can be prevented from damaging the surgical tool or injuring a patient on whom the tool is being used. In addition, after the first and second surfaces become disengaged, they may be readily reengaged so that the surgeon may immediately continue using the tool.

That is, if a surgeon applies too great a rotational torque force to the handle of the tool, the force-translating interface between the handle and the surgical implement will become disengaged, thus avoiding damage to the tool. Accordingly, an embodiment of the present invention can provide a surgical tool that limits torque applied to the surgical implement without deforming or damaging the tool.

An embodiment of the present invention can include a kit. Such a kit can include a surgical tool that includes a torque limiting device according to the present invention. The medical kit may further comprise additional surgical instruments.

A tool, such as a surgical tool, of the present invention may be used in a manner similar to conventional tools, while providing the benefit of being re-settable and reusable if a predetermined torque is exceeded. For example, a method of the present invention can include applying a torque to a tool comprising a torque limiting device according to the present invention. If a predetermined torque is exceeded, the first and second planar surfaces can become disengaged and rotate independently from each other. A rotational force can then be applied to the first planar surface in a direction opposite the direction of the excess torque to re-engage the first and second planar surfaces. When the first and second planar surfaces become re-engaged, a rotational force applied to the first planar surface can agam be translated to the second planar surface, causing the tool to rotate.

Features of a torque limiting device and method of the present invention may be accomplished singularly, or in combination, in one or more of the embodiments of the present invention. As will be realized by those of skill in the art, many different embodiments of a torque limiting device and method according to the present invention are possible. Additional uses, advantages, and features of the invention are set forth in the illustrative embodiments discussed in the detailed description herein and will become more apparent to those skilled in the art upon examination of the following. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a diagrammatic view of a surgical tool having engageable planar surfaces in an embodiment of the present invention.

Fig. 2 is a diagrammatic view of a portion of the surgical tool shown in Fig. 1 , showing disengagement of the planar surfaces. Fig. 3 is a cross-sectional view of a surgical tool in an embodiment of the present invention.

Fig. 4 is a view of the surgical tool shown in Fig. 3, showing engagement of the planar surfaces.

Fig. 5 is a view of a portion the surgical tool of Figs. 3 and 4. Fig. 6 is a perspective view of the surgical tool shown in Figs. 3, 4, and 5.

Fig. 7 is a block diagram representation of a embodiment of a method of the present invention.

Fig. 8 is a diagrammatic view of a surgical tool in another embodiment of the present invention. Fig. 9 is a close-up view of the handle of the surgical tool shown in Fig. 8, with part of the handle housing removed to show the internal components of the handle.

Fig. 10 is a diagrammatic view of the shaft assembly shown in the embodiment in Figs. 8 and 9.

Fig. 11 is view of the proximal portion of the shaft assembly shown in Figs. 8-10. DETAILED DESCRIPTION

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 vaiy 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.

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, for example, 5.5 to 10. Additionally, any reference referred to as being "incorporated herein" is to be understood as being incorporated in its entirety.

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.

In an embodiment, 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. Torque is defined as a turning or twisting force, or the measure of a force's tendency to produce torsion and rotation about an axis. The present invention provides a torque limiting device that may be incorporated into any tool or system that experiences a torque.

In an embodiment, a surgical device of the present invention can comprise a rod attached on one end to a rotatable handle. The rod can be attached on the opposite end to a surgical implement. The surgical device can include a first torque limiting element connected to the handle, and a second torque limiting element operably connected to the rod and surgical implement. The second torque limiting element is releasably engageable with the first torque limiting element. Rotation of the handle when the first and second torqtxe limiting elements are engaged causes rotation of the rod and surgical implement. When a rotational force is applied to the handle that exceeds a predetermined torque limit, the first torque limiting element disengages from the second torque limiting element, so that the handle is rotatable without rotation of the rod and surgical implement. After becoming disengaged, the first torque limiting element is re-engageable with the second torque- limiting element so that further rotation of the handle causes rotation of the rod and surgical implement.

In one illustrative embodiment, a torque limiting 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 respective tip of the rod as well as a region of the rod near that tip. The device may further comprise a handle rotatably attached to the first end of the rod and a surgical implement fixedly attached near the second end of the rod. The device may further comprise a first surface attached to the handle and a second surface attached to the rod. The two surfaces may be disposed in factional contact with each other, for example via a projection and a notch. The two surfaces may be contained within a housing, which may be attached to the handle.

The device may further comprise a biasing mechanism, such as a spring, positioned between the housing and the first surface to force the projection into the notch when the projection and notch are aligned. The two surfaces are able to rotate independently, but when the projection and notch are engaged, the two surfaces rotate together. The projection and notch may be designed to disengage when a torque equal to or greater than a predetermined torque limit is applied to the device. The torque limit can be the torque that is required to cause the projection to overcome the static friction force between the surfaces and the spring force exerted by the spring on the first surface such that the projection disengages from the notch. When the projection 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. 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 incorporated herein by reference in its entirety. The disengagement of the projection 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 a patient. 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 re-engaged to resume use. After the projection disengages from the notch, the device may be re-engaged by rotating the first surface until the projection and notch re-align, at which point the spring forces the projection into the notch. When the projection and notch are engaged again, the use of the tool may resume. The ability to re-engage the device is a advantageous over conventional devices, which may suffer permanent damage when an excessive torque is applied. Therefore, conventional torque limiting devices are unable to be used after one instance of excessive torque, whereas a torque limiting device of the present invention may be reused after many instances of excessive torque.

The torque limiting device of the present invention may be used in medical tools, such as a curette, as described above. The torque limiting device may be used in other surgical tools for use in human and veterinary applications, including tools for grasping, scraping, bending, pushing, or otherwise manipulating tissue or an organ, including bone. The device may be used in other tools or machines in which a maximum torque should not be exceeded. For example, the torque limiting device of the present invention can be included in a screwdriver or wrench to prevent over-tightening of a screw or bolt. The torque limiting device may also be used on machines in which certain components could break when excessive torque is applied. Referring now to Figures 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 a tip of the rod 12 as well as a region of the rod 12 proximate each tip. A handle 20 may be positioned near the first end 14 of the rod 12, and the handle 20 may be manipulated by a user. A surgical implement 18 may be coupled or fixedly attached to the second end 16 of the rod 12. A torque limiting device 22 may be attached to the handle 20 and to the rod 12, so that rotation of the handle 20 causes rotation of the rod 12, and therefore, of the surgical implement 18.

The torque limiting device 22 may comprise a first plate 24 having a projection 30 and a second plate 28 having a notch 26. The notch 26 and projection 30 can be interchangeable, that is, the first plate 24 can have the notch 26 and the second plate 28 can have the projection 30. The projection 30 and notch 26 may be substantially the same shape and size so that they can fit together. The projection 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 projection 30 and the surface of the second plate 28. The projection 30 and the notch 26 may be radially aligned such that the projection 30 fits into the notch 26 when they are rotationally aligned.

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 biasing mechanism, such as compression spring 35, may be disposed between the cap 34 and the first plate 24. The first plate 24 may include 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 first plate 24 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 first plate 24 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 first plate 24 to slide longitudinally along the at least one guide pin 40 and prevent the first plate 24 from rotating with respect to the housing 32. The first plate 24 will then rotate only when the housing 32 rotates.

Conversely, the second plate 28 may be disposed in the housing 32 such that rotational movement of the second plate 28 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 second plate 28, or by other suitable means. Accordingly, the second plate 28 is permitted to rotate about the support 44 but is not permitted to move longitudinally along the rod 12.

The rod 12 may be integrally formed with the second plate 28 or may be fixedly attached to the second plate 28, such as by welding. Therefore, rotation of the second plate 28 is directly translated to the rod 12, and consequently to the surgical implement 18. In an embodiment, the housing 32 may be attached to the handle 20. As such, rotation of the handle 20 can be directly translated to the housing 32, and consequently, via the at least one guide pin 40, to the first plate 24. Rotation of the first plate 24 is translated to the second plate 28 by the frictional interface between the projection 30 and the notch 26. When the projection 30 and notch 26 are engaged, that is, when the projection 30 and notch 26 are rotationally aligned and the projection 30 is positioned within the notch 26, rotation of the handle 20 causes rotation of the surgical implement 18. The frictional engagement interface between the first plate 24 and the second plate 28 that provides for translation of the torque applied to the first plate 24 to rotate the second plate 28 can be referred to as a torque translation interface.

However, if a torque above a predetermined torque limit is applied to the handle 20, the engaging friction force between the projection 30 and notch 26 and the spring force of the compression spring 36 against the first plate 24 may be overcome. When these forces are overcome, and the projection 30 may disengage from the notch 26, such that the projection 30 releases from the notch 26 and the projection-30 and the notch 26 are no longer rotationally aligned. When the projection 30 is disengaged from the notch 26, a rotation of the handle 20 does not cause a rotation of the implement 18. The projection 30 and notch 26 may be engaged again by rotating the handle 20 until the projection 30 and notch 26 are rotationally aligned, at which point the compression spring 36 will push the projection 30 into the notch 26 again.

The predetermined torque limit may be determined by varying any one or more of the following or combination of the following: the spring rate of the compression spring 36; the relative slopes of the projection 30 and notch 26; the length and depth of the notch 26; the height of the projection 30; the radial distance of the projection 30 and notch 26 from the center of the first and second plates 24, 28, respectively; and the materials used for the plates 24, 28. Spring rate is a measure of the compressive force potential of a compression spring. Spring rate is expressed as the spring constant "k" for a compression spring that exerts a force "F" when an applied load defoπns the spring from a free length to particular deformed length. The spring rate constant is calculated as k = F / L_{f1 ee} - Ldet-

In an embodiment, the surgical tool 10 of the present invention may be designed to begin to disengage the torque translation interface at, for example, about 10 ± 1 in.-lbs. torque and to completely disengage at, for example, about 13 ± 1 in.-lbs. torque. Thus, if a torque of 13 in.-lb., for example, is required to completely disengage the torque translation interface

(such as the coupling of the first and second plates 24, 28, respectively, between the handle 20 and the surgical implement 18), the projection 30 and notch 26 may be designed to begin to disengage when a torque of approximately 10 in.-lb, for example, is applied to the handle 20, and to completely disengage when 13 in.-lb. torque is applied to handle 20. As a result, a torque greater than the predetermined torque limit, for example, a torque of 15 in.-lb., cannot be translated to the rod 12 because the projection 30 will disengage from the notch 26 at a torque of 13 in.-lb. It has been found that the mean torque required to scrape normal bone with a curette is approximately 2.0 in.-lb. Therefore, a torque limiting device adapted 22 that causes disengagement to begin at 10 in.-lb and to complete at 13 in.-lb. can allow a torque that is required for normal bone scraping to be translated to the surgical implement.

Referring now to Figures 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 a tip of the rod 112 as well as a region of the rod 112 proximate each tip. A handle 120 may be positioned near the first end 114 of the rod 112, and the handle ^'1^'2^'O may be manipulated by a user. A surgical implement 1 IS may be coupled or fixedly attached to the second end 116 of the rod 112. 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 surgical implement 118. 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 can 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

(not shown), as will be apparent to those of skill in the art of surgical instrument design. 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 130 and a biasing mechanism, such as a spring, that tends to push the ball 130 longitudinally in the cylinder. The ball plunger 128 may also have other configurations that allow for longitudinal movement of the ball 130.

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. In such an embodiment, rotation of the housing 132 results in a rotation of the ball plunger 128.

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.

The rod 112 may be integrally formed with the plate 124 or may be fixedly attached to the plate 124, such as by welding. As such, rotation of the plate 124 can be directly translated to the rod 112, and consequently to the surgical implement 118.

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, rotational movement of the handle 120 can be translated through the flange 136 to the housing 132, and in turn to the ball plunger 128.

Rotation of the ball plunger 128 is translated to the plate 124 by the frictional engagement interface between the ball 130 and the depression 126. When the ball 130 and depression 12 δ are eήgageHj tliat ^"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 surgical implement 118. The factional engagement interface between the ball 130 and the depression 126 that provides for translation of the torque applied to the plate 124 to rotate the surgical implement 118 can be referred to as a torque translation interface.

However, when the torque applied to the handle 120 exceeds^' a certain predetermined torque limit, the ball plunger 128 may be compressed and the ball 130 of the ball plunger 128 rises out of engagement with the depression 126 to a disengaged position. When the ball 130 and depression 126 are disengaged, rotation of the handle 120 no longer causes a rotation of the surgical 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, at which point the ball plunger 128 can extend so that the ball 130 again rests in engagement within the depression 126. The maximum torque limit may be determined by varying any one or more of the following or combination of the following: the spring rate of the compression spring in the ball plunger 128; the shape and size of the ball 130 and depression 126; the radial distance of the ball 130 and depression 126 from the center of the plate 124; and the materials used for the ball 130 and the plate 124. Figs. 8-11 illustrate another embodiment of the present invention. In such an embodiment, a surgical tool 10 may comprise a shaft assembly 150 having a proximal end 151 and a distal end 152. The proximal end 151 and the distal end 152 of the shaft assembly 150 may each comprise a tip of the shaft assembly 150 as well as a region of the shaft assembly 150 proximate each tip. The shaft assembly 150 can include a hollow shaft 153 having a ball engaging receptacle, for example, the ball detent collar 154, fixed to the outer surface of the proximal end 151 of the shaft 153. A rod 155 having a length greater than the length of the shaft 153 can be inserted into the shaft 153. The rod 155 can include a ball joint 156, as shown best in Figs. 10 and 11, attached at the proximal end 151 of the rod 155.

A handle 160 may be operably connected to the proximal ends 151 of the rod 155 and the shaft assembly 150, and the handle 160 may be manipulated by a user. Fig. 8 shows the handle 160 as assembled with the shaft assembly 150. Fig. 9 shows the handle 160 with one side of the handle housing 161 removed to illustrate the internal configuration and operation of the handle 160 and associated components of the surgical tool 10. The surgical tool 10 can include a lever 162 hingedly attached on one end to the grip portion 163 of the handle 160 and pivotably attached on the^" opposite end to the head 164 of the handle 160 within the handle housing 161. As shown in Fig. 9, the lever 162 can be configured on the end attached to the head 164 of the handle 160 to include a ball joint receptacle 165, or socket, for receiving the ball joint 156 at the proximal end 151 of the rod 155 and thereby operably connect the lever 162 to the rod 155.

A surgical implement 166 may be attached to the distal end 152 of the rod 155, as shown in Figs. 8 and 10. In this embodiment, the surgical implement 166 is a curette. However, the surgical implement 166 can be any surgical implement adaptable for use at the end of a rod 155 as described. As shown in Fig. 8, the curette can be aligned with the longitudinal axis of the rod 155 and shaft 153, which may be a preferred position for the curette as the surgical tool 10 is being inserted into a patient's interior body region. When the tool 10 is in a desired position in the patient's body, the curette can be articulated about a joint 167 in the rod 155 that extends beyond the distal 152 tip of the shaft 153 such that the curette can be moved into a different position. For example, the curette may be moved to a desired position with a range of positions from alignment with the longitudinal axis of the rod 155 to a position about 135 degrees from the aligned position (that is, forming an angle of about 45 degrees with the rod). One preferred position for use of the curette is substantially perpendicular with the longitudinal axis of the rod 155. Such articulation of the curette about the joint 167 can be achieved by movement of the lever 162 toward or away from the grip portion 163 of the handle 160. As the lever 162 is moved toward the grip portion 163 of the handle 160, the pivotable end of the lever 162 pivots in the distal direction, causing the ball joint 156 and the attached rod 155 to move in the distal direction. As the rod 155 moves in the distal direction, the curette articulates about the joint 167 and moves out of alignment with the rod 155 and into an angled position relative to the rod 155. As the lever 162 is moved away from the grip portion 163 of the handle 160, the pivotable end of the lever 162 pivots in the proximal direction, causing the ball joint 156 and the attached rod 155 to move in the proximal direction. As the rod 155 moves in the proximal direction, the curette articulates about the joint 167 and moves toward alignment with the rod 155. In this manner, the curette can be moved into various desired positions for scraping tissue in an interior body region.

In the embodiment shown in Figs. 8-11, a torque limiting device 170 may be attached to the handle 160 and to the shaft assembly 150, so that rotation of the handle 160 causes rotation of the shaft assembly 150 and rod, and, in turn, rotation of the surgical implement 166. The torque limiting device 170 can include a first torque limiting element releasably engageable with a second fόfquelimiting element. The torque limiting device 170 can comprise a ball plunger (not shown) having a ball, or engaging end, and the ball engaging receptacle, or ball detent collar, 154 having a detent 172, in its outer surface. The ball plunger and engaging ball may be similar to the ball plunger 128 and ball 130 shown in Fig. 3. The ball detent collar 154 is fixed to the proximal end 151 of the shaft 153. The detent 172 in the ball detent collar 154 can be a notch, depression, or other void configured to receive and engage the ball of the ball plunger. The engaging ball may be rounded, semicircular, U-shaped, V-shaped, V-shaped with a flat bottom, or any other suitable shape that allows for engagement and disengagement with the ball detent 172. The ball plunger and attached engaging ball can be housed in a ball plunger housing

173. In the embodiment shown in Figs. 8-11, the ball plunger housing 173 is seated in a depression in the handle housing 161 and is aligned perpendicularly with the ball detent collar 154 such that the engaging ball is engageable with the detent 172 in the ball detent collar 154. The ball plunger housing 173 may comprise a hollow cylinder, within which the ball plunger and engaging ball can slide at least partially along the longitudinal axis of the ball plunger housing 173. A biasing mechanism (not shown), for example, a compression spring, can be positioned between the outer end 174 of the ball plunger housing 173 and the ball plunger so as to bias the ball plunger longitudinally in the ball plunger housing 173 toward the ball detent 172 in the ball detent collar 154. The ball plunger housing 173, biasing mechanism, ball plunger, and engaging ball may include other components (not shown) and/or have other configurations that allow for longitudinal movement of the ball plunger into and out of engagement with the ball detent 172.

The engaging ball and the detent 172 in the ball detent collar 154 may be matingly configured such that the ball can engage the detent 172 so that the ball detent collar 154 and attached shaft 153 can be rotated when the handle 160 is rotated. Rotational force applied to handle 160 and the ball plunger is translated to the shaft 153 by the fπctional engagement interface between the engaging ball and the ball detent 172. When the ball and ball detent 172 are engaged, that is, when the ball and ball detent 172 are rotationally aligned and the ball is positioned within the detent 172, rotation of the handle 160 causes rotation of the surgical implement 166. The frictional engagement interface between the engaging ball and the ball detent 172 that provides for translation of the torque applied to the handle 160 to rotate the surgical implement 166 can be referred to as a torque translation interface.

When a user applies pressure to rotate the handle 160 beyond a predetermined torque limit, the ball plunger may be compressed and the engaging ball rises out of engagement with me ball detent I Il to a disengaged position. JL hat is, the engaging ball and the ball detent 1 /2 are releasably engageable. When the ball and ball detent 172 are disengaged, rotation of the handle 160 no longer causes a rotation of the surgical implement 166. When the handle 160 is rotated while the engaging ball is disengaged from the ball detent 172, the handle 160 rotates about the rod 153 by means of the ball joint receptacle 165 in the lever 162 rotating about the ball joint 156 of the rod 153. As such, the handle 160 is disengaged from the shaft assembly 150, and breaking of the surgical tool 10 from too great a torque is avoided. The configurations of the engaging ball and the ball detent 172 also provide for disengagement of the ball from the detent 172 when a predetermined torque limit caused by rotation of the handle 160 is surpassed. When the engaging ball becomes disengaged from the ball detent 172 on the shaft 153, the handle 160 can be freely rotated to reposition the ball plunger, and engaging ball, back into the ball detent 172 to re-engage the handle 160 with the shaft assembly 150. In addition to avoiding breaking of the surgical tool 10, use of the tool can be readily resumed without removing the tool 10 to repair or reset it for further use. These features may avoid injury to a patient and decrease surgical time related to broken surgical tools.

As shown in Fig. 8, the ball detent collar 154 may be in rotatable contact with a thrust bearing 175 adjacent the proximal surface, or top, of the collar 154 and with another thrust bearing 175 adjacent the distal surface, or bottom, of the collar 154. In this embodiment, each of the thrust bearings 175 is embedded, or fixed, in a mating cavity 176 in the handle housing 161. Ball bearings (not shown) are located at the interface between the thrust bearings 175 and the ball detent collar 154. The thrust bearings 175 help reduce friction between the ball detent collar 154 and the handle 160 when the ball plunger is disengaged from the ball detent 172 and the handle 160 is rotated freely about the shaft assembly 150 after a predetermined torque limit is surpassed.

The surgical tool 10 may include a mechanism for further securing the shaft assembly 150 to the handle 160. As shown in Fig. 8, one such mechanism includes a hub 177, or plate, having a threaded bore fixed to the handle housing 161. For example, the hub 177 can include a notch 178 that is configured to securely fit about a mated portion of the handle housing 161 so as to fix the hub 177 to the handle housing 161. A "through hole" bolt 180 can then be threaded through the threaded bore of the hub 177. In an alternative embodiment, the hub 177 is not used and the handle housing 161 below the distal, or lower, thrust bearing 175 can be threaded to receive the through hole bolt 180. The through hole bolt 180 has a hole through the center of the length of the bolt 180. The through hole bolt 180 can be slid over the distal end ^"152 of tn^'e^"sha^'ft"153 tlirough the center hole m the bolt 180 and threaded through the threaded bore of the hub 177. A thumb wheel 181 on one end of the through hole bolt 180 can be rotated to thread the bolt 180 through the hub 177. The through hole bolt 180 can include a set screw support collar 182 positioned about the outer circumference of the bolt 180. The bolt 180 can be threaded through the hub 177 such that the upper edge 183 of the set screw support collar 182 abuts the distal, or bottom, edge 185 of the handle housing 161. When the set screw support collar 182 is in position abutting the handle housing 161, a set screw 184 can be inserted through the set screw support collar 182 and into contact with the outer surface of the through hole bolt 180. In this manner, any clearance, or "slack," between the thrust bearings 175 and the shaft assembly 150, including the ball detent collar 154, is reduced or eliminated. As such, any radial or axial movement of the shaft assembly 150 relative to the handle 160 when the handle 160 is engaged with the shaft assembly 150 is prevented.

Rotation of the ball plunger in the handle 160 is translated to the shaft 153 by the frictional interface between the engaging ball and the ball detent 172. When the ball and ball detent 172 are engaged, that is, when the ball and ball detent 172 are rotationally aligned and the ball is positioned within the detent 172, rotation of the handle 160 causes rotation of the surgical implement 166. However, when the torque applied to the handle 160 exceeds a certain predetermined torque limit, the ball plunger may be compressed and the engaging ball rises out of engagement with the ball detent 172 to a disengaged position. When the ball is disengaged from the ball detent 172, rotation of the handle 160 no longer causes a rotation of the surgical implement 166. The ball and ball detent 172 may be engaged again by rotating the handle 160 until the ball and ball detent 172 are rotationally aligned, at which point the ball plunger can extend so that the engaging ball again rests in engagement within the ball detent 172.

The maximum torque limit in the embodiment of the torque limiting device 170 shown in Figs. 8-11 may be determined by varying any one or more of the following or combination of the following: the spring rate of the compression spring in the ball plunger; the shape and size of the engaging ball (not shown) of the ball plunger; the size and shape of the ball detent 172; the radial distance of the ball detent 172 from the shaft 153; and the materials used for the ball plunger ball and the ball detent 172.

The present invention may include embodiments of a method for using the torque limiting device 22, 122 as described herein. Referring now to Figure 7, the illustrated embodiment of the method 200 comprises inserting 210 a surgical tool into a body, the surgical tool having^' a handle ^'Having a torque translation interface with a rod, the rod being attached to a surgical implement. The surgical implement, such as the curette, can be positioned 220 at a desired location within the body. Torque can then be applied 230 to the handle to cause the rod and the surgical implement to rotate. The method further includes disengaging 240 the torque translation interface between the handle and the rod by applying a torque greater than a predetermined torque limit. The method may further include reengaging 250 the torque translation interface after an excessive torque has caused its disengagement. In an embodiment, the torque translation interface comprises a first surface of the surgical tool and a second surface of the surgical tool. One of the surfaces includes a projection 30 engageable with a notch 26 in the other surface. Re-engaging 240 the first surface with the second surface may comprise rotating the handle until the projection 30 and the notch 26 are re-aligned for re-engagement.

Although the present invention has been described with reference to particular embodiments, it should be recognized that these embodiments are merely illustrative of the principles of the present invention. Those of ordinary skill in the art will appreciate that a torque limiting device and methods of the present invention may be constructed and implemented in other ways and embodiments. Accordingly, the description herein should not be read as limiting the present invention, as other embodiments also fall within the scope of the present invention.