Abstract:
An embodiment of a handle assembly for an elongate medical device that may reduce the weight and/or expense of traditional handle may include an exterior adjusting knob extending along a longitudinal axis and configured to rotate about the axis, an insert, and a dowel pin. The insert may be configured to engage the adjusting knob and to rotate about the axis responsive to rotation of the adjusting knob. The insert may comprise an annular groove configured to engage a dowel pin, the annular groove comprising a sidewall comprising a chamfer. The dowel pin may be configured to engage the annular groove to resist rotation of the insert. In an embodiment, the insert may comprise plastic or polymer.

Description:
BACKGROUND 
     a. Technical Field 
     The instant disclosure relates to handle assemblies for elongate medical devices, including interior components of a handle assembly for resisting deflection of the shaft of the medical device. 
     b. Background Art 
     Catheters are used for an ever-growing number of procedures. For example, catheters are used for diagnostic, therapeutic, and ablative procedures, to name just a few examples. Typically, the catheter is manipulated through the patient&#39;s vasculature and to the intended site, for example, a site within the patient&#39;s heart. The catheter typically carries one or more electrodes, which may be used for ablation, diagnosis, or the like. Often, another medical device, called an introducer or sheath, is used to position a catheter within the heart. 
     To increase the ability to move and navigate an introducer or catheter within a patient&#39;s body, steerable introducers and catheters have been designed. Such steerable devices often have a steering mechanism near the distal end of the device. This steering mechanism typically includes a pull ring and one or more pull wires (or deflection wires) attached thereto and extending proximally towards an actuator that can place the wire or wires in tension. Placing a pull wire in tension may cause the distal end of the device to deflect in at least one plane. In this fashion, the introducer and/or catheter can be navigated through the tortuous path of a patient&#39;s vasculature to a target site. 
     The foregoing discussion is intended only to illustrate the present field and should not be taken as a disavowal of claim scope. 
     BRIEF SUMMARY 
     An embodiment of a handle assembly for a catheter that may reduce the weight and/or expense of a traditional catheter handle may include an exterior adjusting knob extending along a longitudinal axis and configured to rotate about the axis, an insert, and a dowel pin. The insert may be configured to engage the adjusting knob and to rotate about the axis responsive to rotation of the adjusting knob. The insert may comprise an annular groove configured to engage a dowel pin, the annular groove comprising a sidewall comprising a chamfer. The dowel pin may be configured to engage the annular groove to resist rotation of the insert. In an embodiment, the insert may comprise plastic or polymer. 
     Another embodiment of a handle assembly may include an exterior adjusting knob extending along a longitudinal axis and configured to rotate about the axis, a polymer or plastic insert, and a dowel pin. The insert may be configured to engage the adjusting knob and to rotate about the axis responsive to rotation of the adjusting knob. The insert may comprise an annular groove configured to engage a dowel pin. The dowel pin may be configured to engage the annular groove to resist rotation of the insert when no external force is applied to the adjusting knob, wherein the insert is configured to rotate relative to the dowel pin when an external force is applied to the adjusting knob. 
     An embodiment of an elongate medical device may comprise a shaft and a handle assembly. The shaft may comprise a distal end portion, a proximal end portion, a longitudinal axis extending through the distal and proximal end portions, and a pull wire coupled to the distal end portion configured to deflect the distal end portion. The handle assembly may be coupled to the proximal end portion of the shaft and may comprise an exterior adjusting knob extending along the axis and configured to rotate about the axis, an insert, and a dowel pin. The insert may be configured to engage the adjusting knob and to rotate about the axis responsive to rotation of the adjusting knob. The insert may comprise an annular groove configured to engage a dowel pin. The annular groove may comprise a sidewall, wherein rotation of the insert applies a tensile force to the pull wire to deflect the shaft distal end portion. The dowel pin may be configured to engage the annular groove to resist rotation of the insert. The shaft and handle assembly may be configured to allow another medical device to be passed therethrough. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic view of an embodiment of an elongate medical device disposed in the body of a patient. 
         FIG. 2  is an isometric view of an embodiment of an elongate medical device. 
         FIG. 3  is an exploded isometric view of an embodiment of the handle assembly of the elongate medical device of  FIG. 2 . 
         FIG. 4  is an enlarged isometric view of an embodiment of a clip subassembly of the handle assembly of  FIG. 3 . 
         FIG. 5  is a side view of the clip subassembly of  FIG. 4 . 
         FIG. 6  is an exploded isometric view of an embodiment of the interior assembly of the handle assembly of  FIG. 3 . 
         FIG. 7  is a cross-sectional view of the interior assembly illustrated in  FIG. 6 . 
         FIG. 8  is an enlarged side view of an embodiment of a dowel pin of the interior assembly of  FIG. 6 . 
         FIG. 9  is a cross-sectional view of the interior assembly illustrated in  FIG. 6 . 
         FIG. 10  is an enlarged view of a portion of  FIG. 9 . 
         FIG. 11  is an end view of an embodiment of the bushing and adjustment knob insert of the interior assembly of  FIG. 6 . 
         FIG. 12  is an enlarged isometric view of the bushing of  FIGS. 6 ,  7 ,  9 , and  10 . 
         FIG. 13  is a cross-sectional view of the bushing of  FIGS. 6 ,  7 ,  9 , and  10 . 
         FIGS. 14A and 14B  are side views of a first embodiment of an adjustment knob insert that may be a part of the interior assembly of  FIGS. 3 ,  6 ,  7 ,  9 , and  10 . 
         FIGS. 15A and 15B  are side views of a second embodiment of an adjustment knob insert that may be a part of the interior assembly of  FIGS. 3 ,  6 ,  7 ,  9 , and  10 . 
         FIG. 16  is an isometric view of an embodiment of slider blocks that may be a part of the interior assembly of  FIGS. 3 ,  6 ,  7 ,  9 , and  10 . 
         FIG. 17A  is a plot illustrating the load capacity of an exemplary interior assembly including the first adjustment knob insert embodiment shown in  FIGS. 14A and 14B . 
         FIG. 17B  is a plot illustrating the load capacity of an exemplary interior assembly including the second adjustment knob insert embodiment shown in  FIGS. 15A and 15B . 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments are described herein to various apparatuses, systems, and/or methods. Numerous specific details are set forth to provide a thorough understanding of the overall structure, function, manufacture, and use of the embodiments as described in the specification and illustrated in the accompanying drawings. It will be understood by those skilled in the art, however, that the embodiments may be practiced without such specific details. In other instances, well-known operations, components, and elements have not been described in detail so as not to obscure the embodiments described in the specification. Those of ordinary skill in the art will understand that the embodiments described and illustrated herein are non-limiting examples, and thus it can be appreciated that the specific structural and functional details disclosed herein may be representative and do not necessarily limit the scope of the embodiments, the scope of which is defined solely by the appended claims. 
     Reference throughout the specification to “various embodiments,” “some embodiments,” “one embodiment,” or “an embodiment”, or the like, means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in various embodiments,” “in some embodiments,” “in one embodiment,” or “in an embodiment”, or the like, in places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Thus, the particular features, structures, or characteristics illustrated or described in connection with one embodiment may be combined, in whole or in part, with the features structures, or characteristics of one or more other embodiments without limitation given that such combination is not illogical or non-functional. 
     It will be appreciated that the terms “proximal” and “distal” may be used throughout the specification with reference to a clinician manipulating one end of an instrument used to treat a patient. The term “proximal” refers to the portion of the instrument closest to the clinician and the term “distal” refers to the portion located furthest from the clinician. It will be further appreciated that for conciseness and clarity, spatial terms such as “vertical,” “horizontal,” “up,” and “down” may be used herein with respect to the illustrated embodiments. However, surgical instruments may be used in many orientations and positions, and these terms are not intended to be limiting and absolute. 
     Referring now to the Figures, in which like reference numerals refer to the same or similar features in the various views,  FIG. 1  is a diagrammatic view of an elongate medical device  10  disposed within a patient  12 . More specifically, the elongate medical device  10  is disposed in the vasculature  14  of the patient  12 , with a distal end portion  16  of a shaft  18  of the elongate medical device  10  disposed in a chamber  20  of the heart  22  of the patient  12 . The elongate medical device  10  may also include a handle assembly  24  with an adjustment knob  26  for guiding the shaft  18  and deflecting the distal end portion  16  of the shaft  18 . 
     The elongate medical device  10  may comprise, for example, a diagnostic and/or therapy delivery catheter, an introducer or sheath, or other like devices. For purposes of illustration and clarity, the description below will be with respect to an embodiment wherein the elongate medical device  10  comprises an introducer (i.e., introducer  10 ). It will be appreciated, however, that embodiments wherein the elongate medical device comprises devices other than an introducer remain within the spirit and scope of the present disclosure. 
     Referring to  FIGS. 1 and 2 , in an exemplary embodiment, the introducer  10  may be configured to be inserted into the body of the patient  12 , and more particularly, into the heart  22 . The introducer  10  may include a shaft  18  having a proximal end portion  28  and a distal end portion  16 , a handle assembly  24  including an adjustment knob  26  and a grip portion  30 , a hemostasis valve  32 , and an exterior fluid lumen  34  terminating in a stopcock  36 , which may also include a luer lock connector  38  for connection to an irrigation system (not shown). The introducer  10  may further include other conventional components such as, for example and without limitation, one or more position sensors, a temperature sensor, additional sensors or electrodes, ablation elements (e.g., ablation tip electrodes for delivering RF ablative energy, high intensity focused ultrasound ablation elements, etc.), and corresponding conductors or leads. Additionally, the shaft may include one or more fluid lumens extending from the distal end portion  16  to the proximal end portion  28  (and, in an embodiment, into and though the handle assembly  24  for fluid coupling with the exterior fluid lumen  34 ) for the delivery and/or removal of one or more fluids such as, for example only, irrigation fluids, bodily fluids, and cryogenic ablation fluids. 
     The shaft  18  may also include one or more pull wires for deflecting a portion of the shaft such as, for example only and not by limitation, the distal end portion  16 . Each pull wire may extend through the shaft  18  and be coupled with a pull ring within the shaft  18  or may otherwise be directly or indirectly attached to a portion of the shaft  18  where deflection is desired. Each pull wire may extend through the shaft  18  to the handle assembly  24 . 
     The handle assembly  24  is provided to enable a clinician to guide the distal end portion  16  of the shaft  18  to a target site, such as a location within the chamber  20 , to allow another medical device to be passed through the introducer  10  to perform a particular diagnostic and/or therapeutic function. Accordingly, the handle assembly  24  may be coupled with the proximal end portion  28  of the shaft  18  and may comprise an adjustment knob  26  and a grip portion  30 . The grip portion  30  may be configured in size, shape, and materials to be comfortably and securely gripped by a clinician guiding the introducer  10 . The adjustment knob  26  may be provided as an exterior mechanism through which a clinician can deflect the shaft  18  such as, for example, the distal end portion  16  of the shaft  18 . The adjustment knob  26  may thus be coupled, directly or indirectly, with one or more pull wires  46 A,  46 B that extend through the shaft  18  as shown in  FIG. 3 . 
     Although embodiments of the handle assembly  24  are described herein with reference to a single adjustment knob  26  for deflecting the shaft  18 , it should be understood that this disclosure is not so limited. Rather, alternative and/or additional known exterior mechanisms for applying a force to a pull wire or other control element are within the spirit and scope of this disclosure. For example, a single or multiple adjustment knobs may be provided, substantially as described in U.S. patent application publication no. 2011/0282176A1, which is hereby incorporated by reference in its entirety as though fully set forth herein. 
       FIG. 3  is an exploded isometric view of an embodiment of the handle assembly  24 . In addition to the exterior adjustment knob  26  and grip portion  30 , the handle assembly may comprise a number of interior components, such as an adjustment knob insert  40 , a mounting shaft  42 , and two slider blocks  44 A,  44 B. Each slider block  44 A,  44 B may be coupled, directly or indirectly, to a respective pull wire  46 A,  46 B. In an embodiment, each pull wire  46 A,  46 B may extend through a respective slider block  44 A,  44 B to a respective clip subassembly  48 A,  48 B disposed proximal of the slider block  44 A,  44 B. Each slider block  44 A,  44 B may be configured to move distally and proximally within the mounting shaft  42  to apply and release force to/from the respective clip subassembly  48 A,  48 B, which may correspondingly apply and release tensile forces to/from the pull wires  46 . The adjustment knob insert  40  may be provided for transferring force from the adjustment knob  26  to the slider blocks  44 A,  44 B, and thus to actuate the pull wires  46  and deflect the shaft  18  (see  FIGS. 1 and 2 ). Accordingly, the insert  40  may comprise a knob coupling portion  50  to secure the adjustment knob insert  40  to the adjustment knob  26  so that the two components rotate substantially in unison. 
       FIGS. 4 and 5  are, respectively, an enlarged isometric view and an enlarged side view of an embodiment of the clip subassembly  48 , which may be employed as one or both of the clip subassemblies  48 A and  48 B, referenced above. The clip subassembly  48  may include a body  50  and a spring  52  disposed about an axis B and a pin  54 . The body  50  may have a distal end surface  56  configured for contact with a slider block  44 A or  44 B (shown, e.g., in  FIGS. 3 and 14 ). A pull wire  46  (not shown in  FIGS. 4 and 5 ) may extend through the body  50  and spring  52  substantially along the axis B. The spring  52  may apply a distal force to the pin  54 , such that the pin  54  pinches the pull wire  46  against the interior of the body  50  to maintain a stable connection between the pull wire  46  and the clip subassembly  48 . Thus, as the clip subassembly  48  receives a proximal force from a slider block  44 , the clip subassembly.  48  directly transfers the force to a pull wire  46  to deflect the shaft  18 . 
       FIG. 6  is a exploded isometric view of an interior assembly  60  of an embodiment of the handle assembly  24  with the pull wires  46  and clip subassemblies  48 A,  48 B removed for clarity of illustration.  FIG. 7  is a cross-sectional view of the interior assembly  60 , also with the clip subassemblies  48 A,  48 B and the portion of the pull wires  46  that extend from the slider blocks  44 A,  44 B to the clip subassemblies  48 A,  48 B removed for clarity of illustration.  FIG. 8  is an enlarged side view of an embodiment of a dowel pin.  FIG. 9  is a cross-sectional view of the interior assembly  60 , also with the clip subassemblies  48 A,  48 B and the pull wires  46  removed for clarity of illustration.  FIG. 10  is an enlarged view of a portion of  FIG. 9 . 
     Referring to  FIGS. 6-10 , the interior assembly  60  may comprise a wire guide  62 , the adjustment knob insert  40 , a bushing  64 , a first O-ring  66 , a dowel pin  68 , the mounting shaft  42 , the slider blocks  44 A,  44 B, and a second O-ring  70 . The interior assembly  60  may be generally disposed about an axis A. In an embodiment, the axis A may also be the central axis of the shaft  18  (see  FIGS. 1 and 2 ). 
     With continued reference to  FIGS. 6-10 , the wire guide  62  may be disposed at the distal end of the interior assembly  60  and extend proximally through the insert  40 , the bushing  64 , and a portion of the mounting shaft  42 . The wire guide  62  may be configured to receive a shaft (i.e., the shaft  18  shown in  FIGS. 1-3 ) and may provide a passage for the pull wires  46  from the handle assembly  24  to the shaft  18 . The wire guide  62  may also provide a passage for other components between the handle assembly  24  and the shaft  18  such as, for example only, electrical leads or wires, and one or more lumens for passing fluid and/or other medical devices, such as a catheter and/or guidewire, therethrough. The wire guide  62  may also comprise a coupling mechanism  72  for attachment with another component, such as the adjustment knob insert  40 . The coupling mechanism  72  may be a snap-fit protrusion (as shown in  FIGS. 6 and 7 ) or any other appropriate coupling mechanism known in the art. 
     The adjustment knob insert  40  and bushing  64  may be configured to transfer force (i.e., circumferential force) from an exterior mechanism (i.e., the adjustment knob  26 , see  FIGS. 1-3 ) to the slider blocks  44 . The insert  40  may comprise a knob coupling portion  58  including one or more features for securing the insert to the adjustment knob such as, for example only, barbs or a knurled surface. The insert  40  may further comprise an annular circumferential groove  74  in its exterior surface for interacting with the dowel pin  68  to create an automatic locking, or “autolock” feature, as further explained below, and a circumferential protrusion  78  configured to abut the mounting shaft  42 . 
     The dowel pin  68  may define a longitudinal axis C and include a chamfered surface  76  at one end and may have a circular cross-section, in an embodiment. In an embodiment, the angle θ 1  of the chamfer may be configured in design and manufacture to interact with a chamfered surface of the groove  74  of the insert  40 . The dowel pin  68  may additionally or alternatively include a rounded end surface, a flat end surface, a different cross-section, and/or another appropriate structural feature. 
     The bushing  64  may be disposed inside the insert  40 , and the bushing  64  and insert  40  may include complementary mechanical features so that the bushing  64  and insert  40  rotate in unison. For example, the insert  40  may have a longitudinal protrusion  98 , and the bushing may have a longitudinal groove  80 , as shown in greater detail in  FIGS. 11 and 12 , such that the insert  40  and the bushing  64  are fixed rotationally about the axis A. 
     Referring to  FIGS. 6 ,  7 ,  9 ,  11 - 13 , and  16 , the bushing  64  may also include interior threads  82  for engaging threads  90  on the slider blocks  44 . Because the insert  40  and the bushing  64  may rotate in unison, a rotation of the insert  40  may rotate the bushing  64 , which may move the slider blocks  44  proximally and distally via interaction of complementary threads  82 ,  90  to increase and decrease tension in one or more pull wires. In an embodiment, the bushing  64  may comprise one or more metals, such as aluminum. The bushing  64  may additionally or alternatively comprise one or more plastics or polymers such as, for example only, polycarbonate, such as that available under the trade name Makrolon™ from Bayer MaterialScience. The bushing  64  may also comprise nylon and/or another plastic or polymer such as acrylonitrile butadiene styrene (ABS) or polyether imide (PEI). In a plastic or polymer embodiment, the bushing  64  may be manufactured according to a process involving injection molding, machining, and/or other processes known in the art. In an alternate embodiment, the bushing  64  may be omitted, and the interior threads  82  may be provided on an interior surface of the insert  40 . 
     In an embodiment, the insert  40  may comprise one or more plastic materials. For example, the insert may comprise polycarbonate, such as that available under the trade name Makrolon™ from Bayer MaterialScience. The insert  40  may also comprise nylon and/or another plastic or polymer such as acrylonitrile butadiene styrene (ABS) or polyether imide (PEI). The insert  40  may be manufactured according to a process involving injection molding, machining, and/or other processes known in the art. 
     The mounting shaft  42  may house the slider blocks  44  and may receive the portion of the adjustment knob insert  40  that holds the bushing  64  and includes the circumferential groove  74 . At the same longitudinal position as the circumferential groove  74 , the mounting shaft  42  may include a pinhole  84  for receiving and securing the dowel pin  68 . As mentioned above, the dowel pin  68  may interact with the circumferential groove  66  to create an autolock feature. 
     Referring to  FIGS. 3 ,  6 , and  16 , the slider blocks  44  may be disposed inside of the mounting shaft  42  and may each comprise a pull wire hole  86 , an interior channel  88 , and exterior threads  90  configured to interact with the interior threads  82  of the bushing  64 . Each slider block  44  may abut a clip subassembly  48  (see  FIG. 3 ) such that movement of the slider block  44  directly applies or releases tension to/from a pull wire  46 . Each pull wire  46  may extend distally through a respective pull wire hole  86  and channel  88 , through the remainder of the handle assembly  24 , and through the shaft  18  as described above. The slider block channels  88  may also allow longitudinal passage of electrical wiring, fluid lumens, and/or a guidewire that may be connected or inserted at the proximal end of the handle assembly  24  (see  FIG. 2 ). 
     In an embodiment, the slider blocks  44 A,  44 B may have opposite threads (e.g., the first slider block  44 A may have left-handed threads  90 A, and the second slider block  44 B right-handed threads  90 B) so that the slider blocks  44 A,  44 B move in opposite directions when the bushing  64  rotates. Such opposite threading  90 A,  90 B may be provided for a device having opposing pull wires  46 A,  46 B where the first pull wire  46 A deflects the shaft  18  in a first direction and the second pull wire  46 B deflects the shaft  18  in a second direction that is different from the first. In an embodiment, the second direction may be about one hundred and eighty degrees (180°) offset from the first. Of course, in an embodiment, a different relative angle between the pull wires may be included. Furthermore, in an embodiment, only a single pull wire may be included, or more than two pull wires may be included. 
       FIG. 14A  is a side view of the adjustment knob insert  40  and  FIG. 14B  is an enlarged side view of a portion of the insert  40 . The insert  40  may include, in addition to the features mentioned above, an annular groove  74  having a depth d, a first sidewall  92 , a second sidewall  94 , an interior surface  96 , and may extend from a distal end portion  102  to a proximal end portion  104  along axis D about which the insert  40  may be configured to rotate. In an embodiment, the axis D may be coincident with or otherwise parallel to the axis of the interior assembly of which the insert  40  forms a part (i.e., axis A, see  FIG. 6 ). Both the first sidewall  92  and the second sidewall  94  may be substantially perpendicular to a line that is parallel to the axis D, as well as to an exterior surface  100 . The interior surface  96  may comprise a number of flat or curved segments forming a collectively concave interior surface, as shown, or may have another shape or configuration. The depth d may be chosen as appropriate based on the materials of the insert  40  and other factors. For example, if the insert  40  comprises plastic, polymer, or another deformable material, the depth d of the groove  74  may be relatively deeper (i.e., as compared to an insert made of or comprising a less deformable material, such as metal, such as aluminum). In an embodiment, the depth d of the groove  74  may be approximately 0.1 inches. 
     As noted above, the groove  74  is configured to interact with a dowel pin (i.e., dowel pin  68 , see FIGS.  6  and  8 - 10 ) to create autolock. The dowel pin  68  and insert  40  may be configured so that a tip of the dowel pin  68  is disposed within the groove  74  with the dowel pin  68  extending generally transverse to the interior surface  96  of the groove  74 , as shown in  FIG. 14B . Further, when assembled, the axis C of the dowel pin (see  FIG. 8 ) may be positioned within the groove  74 . As the insert  40  rotates about the axis A, there may be friction between the dowel pin  68  and one or more of the first sidewall  92 , the second sidewall  94 , and the interior surface  96 . With two perpendicular sidewalls  92 ,  94  as illustrated in  FIGS. 14A and 14B , and plastic, polymer, or other relatively deformable material comprising the insert, there may be relatively little friction between the dowel pin  68  and the interior surface  96  of the groove  74 . As a result, the majority of the force opposing rotation of the insert  40  may be imparted from the dowel pin  68  to a sidewall (i.e., the first sidewall  92 ) and may be substantially parallel to the axis of rotation D. Thus, the insert  40  shown in  FIGS. 14A and 14B  may be used to create a relatively weaker autolock as compared to the embodiment of  FIGS. 15A-15B , discussed below. 
       FIG. 15A  is a side view of a second embodiment of an adjustment knob insert  40 ′ and  FIG. 15B  is an enlarged side view of a portion of the insert  40 ′, which may be similar to insert  40  described above. For example, the insert  40 ′ may be identical to the insert  40  (see  FIGS. 14A and 14B ) except for the configuration of the groove  74 ′. In the second  40 ′, the groove  74 ′ includes a first sidewall  92 ′ that includes a chamfer or is beveled with respect to the exterior surface  100 ′, a second sidewall  94 ′ that includes a portion that is perpendicular to a line parallel to the axis D, and an interior surface  96 ′. 
     The chamfer of sidewall  92 ′ may extend at an angle θ 2  relative to a line parallel to the axis D. The appropriate angle θ 2  may be determined experimentally or through simulations for an appropriate amount of friction with a dowel pin (e.g., the dowel pin  68 ) to create an appropriate autolock strength. The appropriate angle θ 2  for the chamfer may depend on the coefficient of friction of the respective materials used for the insert  40 ′ and the dowel pin  68 , the shape of the dowel pin  68 , and the depth of the groove  74 ′, for example only. In an embodiment, θ 2  may be about forty-five (45) degrees. 
     The groove  74 ′ may have a depth d that may be chosen as appropriate based on the materials of the insert  40 ′ and other factors. For example, if the insert  40 ′ comprises plastic, polymer, or another deformable material, the depth d of the groove  74 ′ may be relatively deeper (i.e., as compared to an insert made of or comprising a less deformable material, such as metal, such as aluminum). In an embodiment, the depth d of the groove  74 ′ may be approximately 0.1 inches. 
     Because of the chamfer in the first sidewall  92 ′, force opposing rotation of the insert  40 ′ as a result of friction between the dowel pin  68  and the groove  74 ′ may include components that are both parallel to the axis D and perpendicular to the axis D. Additionally, the total force opposing rotation, i.e., the friction force components that are parallel to the axis D, may be greater than in the configuration of the first insert  40 ′. Accordingly, the second insert  40 ′ may be used when a relatively stronger autolock is desired (i.e., with more force required to rotate the adjustment knob  26  and deflect the shaft  18 , see  FIG. 2 ). 
       FIGS. 17A and 17B  are plots illustrating the relative amounts of autolock force that embodiments of the inserts  40 ,  40 ′ may enable, respectively. For example, an in embodiment, as noted above, the inserts  40 ,  40 ′ may comprise a plastic material. In such an embodiment, the insert  40  may enable autolock force as shown in  FIG. 17A . As shown in  FIG. 17A , a plastic embodiment of the insert  40  may enable up to about 12 lbf at an extension of a slider block  44 A,  44 B of about 0.02 inches. Further slider block extension, however, may cause the force between the dowel pin  68  and the groove  74  to become so great that the groove  74  may deform and the dowel pin slip from the groove  74 , disabling the autolock feature. 
     In contrast, and as shown in  FIG. 17B , the chamfer in the first sidewall  92 ′ allows the insert  40 ′ to enable up to about 26 lbf at an extension of a slider block  44 A,  44 B of about 0.04 inches. Thus, as demonstrated by  FIGS. 17A and 17B , the addition of a chamfer to the first sidewall  92 ′ improves both the total force of the autolock feature and the effective movement range of the autolock feature over a non-chamfered embodiment. 
     Both the first and second inserts  40 ,  40 ′ may comprise a plastic or polymer material, as noted above. As a result, the inserts  40 ,  40 ′ may be relatively less expensive to manufacture than a similar metal component and may additionally be lighter. Accordingly, plastic or polymer inserts of one of the configurations illustrated in  FIGS. 14A-15B  may be preferred over metal inserts. 
     Although a number of embodiments have been described above with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this disclosure. For example, all joinder references (e.g., attached, coupled, connected, and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the spirit of the appended claims. 
     Any patent, publication, or other disclosure material, in whole or in part, that is said to be incorporated by reference herein is incorporated herein only to the extent that the incorporated materials does not conflict with existing definitions, statements, or other disclosure material set forth in this disclosure. As such, and to the extent necessary, the disclosure as explicitly set forth herein supersedes any conflicting material incorporated herein by reference. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material set forth herein will only be incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material.