Patent Publication Number: US-2013245632-A1

Title: Method and apparatus for insertion of an elongate pin into a surface

Description:
RELATED APPLICATION 
     This application claims priority from U.S. Provisional Application No. 61/534,152, filed 13 Sep. 2011, the subject matter of which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to an apparatus and method for use of an insertion tool and, more particularly, to an apparatus for dictating trajectory and location for insertion of an elongate pin into a surface. 
     BACKGROUND OF THE INVENTION 
     In the installation of a prosthetic hip joint into a patient&#39;s body, an acetabular component is implanted into the acetabulum of the patient&#39;s pelvis. An obverse surface of the acetabular component is configured for articulating contact with a femoral component carried by the patient&#39;s femur. A reverse surface of the acetabular component is secured to the bone surface of the acetabulum. 
     Because the hip prosthesis is normally provided to correct a congenital or acquired defect of the native hip joint, the acetabulum often exhibits a pathologic, nonstandard anatomic configuration. A surgeon must compensate for such pathologic acetabular anatomy when implanting the acetabular component in striving to achieve a solid anchoring of the acetabular component into the acetabulum. Detailed preoperative planning, using two- or three-dimensional internal images of the hip joint, often assists the surgeon in compensating for the patient&#39;s anatomical limitations. During the surgery, an elongated pin may be inserted into the surface of the patient&#39;s bone, at a trajectory and location that are either predetermined or arbitrarily chosen, to act as a passive landmark or active guiding structure in carrying out the preoperatively planned implantation. This “guide pin” may remain as a portion of the implanted prosthetic joint or may be removed before the surgery is concluded. This type of pin-guided installation is common in any joint replacement procedure—indeed, in any type of surgical procedure in which a surgeon-placed fixed landmark is desirable. 
     In addition, and again in any type of surgical procedure, modern minimally invasive surgical techniques may dictate that only a small portion of the bone or other tissue surface being operated upon is visible to the surgeon. Depending upon the patient&#39;s particular anatomy, the surgeon may not be able to precisely determine the location of the exposed area relative to the remaining, obscured portions of the bone through mere visual observation. Again, a guide pin may be temporarily or permanently placed into the exposed bone surface to help orient the surgeon and thereby enhance the accuracy and efficiency of the surgical procedure. 
     A carefully placed guide pin, regardless of the reason provided, will reduce the need for intraoperative imaging in most surgical procedures and should result in decreased operative time and increased positional accuracy, all of which are desirable in striving toward a positive patient outcome. 
     SUMMARY OF THE INVENTION 
     In an embodiment of the present invention, an apparatus for dictating an insertion trajectory and an insertion location for insertion of an elongate pin into a surface is described. A primary leg has longitudinally spaced proximal and distal primary leg ends. The distal primary leg end is configured for direct contact with the surface. At least one subordinate leg has longitudinally spaced proximal and distal subordinate leg ends. The proximal subordinate leg end is movably attached to the primary leg by a coupling mechanism allowing at least two degrees of freedom of motion of the subordinate leg relative to the primary leg. The distal subordinate leg end is configured for contact with the surface concurrently with contact of the distal primary leg end with the surface, to support the apparatus in a predetermined guiding relationship with the surface during use of the apparatus. The subordinate leg is adjusted relative to the primary leg to impart the dictated insertion trajectory and insertion location to the apparatus. The primary leg guides longitudinal translational movement of the elongate pin to insertion into the surface at the dictated insertion trajectory and insertion location when the apparatus is being supported in the predetermined guiding relationship with the surface. 
     In an embodiment of the present invention, a method for inserting an elongate pin into a bone surface is described. A primary leg having longitudinally spaced proximal and distal primary leg ends is provided. At least one subordinate leg is provided. Each subordinate leg has longitudinally spaced proximal and distal subordinate leg ends. The proximal subordinate leg end is movably attached to the primary leg by a coupling mechanism allowing at least two degrees of freedom of motion of the subordinate leg relative to the primary leg. The subordinate leg is adjusted in at least two degrees of freedom relative to the primary leg to impart the dictated insertion trajectory and insertion location to the primary leg. The bone surface is contacted with the distal primary leg end. The bone surface is contacted with the distal subordinate leg end concurrently with contact of the distal primary leg end with the bone surface. The apparatus is supported in a predetermined guiding relationship with the bone surface during use of the apparatus via contact between the distal primary and subordinate leg ends with the bone surface. At least one of an insertion location and an insertion trajectory of the elongate pin relative to the bone surface is dictated by maintaining the primary leg in a predetermined position relative to the bone surface. With the primary leg, longitudinal translational movement of the elongate pin to insertion into the surface is guided at the dictated insertion trajectory and insertion location when the apparatus is being supported in the predetermined guiding relationship with the surface. The bone surface is contacted with a distal end of the elongate pin at the insertion location. The distal end of the elongate pin is inserted into the bone surface along the insertion trajectory. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the invention, reference may be made to the accompanying drawings, in which: 
         FIG. 1  is a side view of one embodiment of the present invention; 
         FIG. 2  is a front view of the embodiment of  FIG. 1 ; 
         FIG. 3  is a rear view of the embodiment of  FIG. 1 ; 
         FIG. 4  is a top view of the embodiment of  FIG. 1 ; 
         FIG. 5  is a bottom view of the embodiment of  FIG. 1 ; 
         FIG. 6  is a perspective bottom view of the embodiment of  FIG. 1 ; 
         FIG. 7  is a side view of the embodiment of  FIG. 1  having an optional configuration; 
         FIG. 8  is a side view of the embodiment of  FIG. 1  having other optional configurations; and 
         FIG. 9  is a schematic side view of the embodiment of  FIG. 1  in an example use environment. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     In accordance with the present invention,  FIG. 1  depicts an apparatus  100  for dictating an insertion trajectory  102  and an insertion location for insertion of an elongate pin (not shown) into a surface. The surface is shown and described herein at least as a patient tissue (here, an acetabulum), but the patient tissue could be any desired type such as, but not limited to, hip joints, shoulder joints, knee joints, ankle joints, phalangeal joints, metatarsal joints, spinal structures, long bones (e.g., fracture sites), other bones or soft tissues, or any other suitable body tissue of a patient for the present invention. The apparatus  100 , or portions thereof, may be sterilizable or otherwise reusable for multiple patients. 
     A primary leg  104  has longitudinally spaced (i.e., longitudinal with respect to the primary leg) proximal and distal primary leg ends  106  and  108 , respectively. The distal primary leg end  108  is configured for direct contact with the surface, such as during insertion of the elongate pin into the surface. In the apparatus  100  shown in the Figures, the primary leg  104  has a principal body  110  and a stabilizing limb  112  branching outward at an angle from the principal body of the primary leg. The elongate pin may be guided to the dictated insertion trajectory and insertion location by the principal body  110  of the primary leg  104 , as described below. 
     In the apparatus  100  depicted in the Figures, the stabilizing limb  112  includes the distal primary leg end  108  (i.e., the portion of the primary leg  104  which contacts the surface) at a location spaced apart from the principal body  110  of the primary leg, though it is also contemplated that the distal primary leg end may instead be a portion of the principal body. The stabilizing limb  112 , when present, may be attached to the principal body  110  in a fixed relationship or, as shown in the Figures, may be movably attached to the principal body via a mechanism such as the coupling mechanism  114  shown. This coupling mechanism  114  has a collar  116  which can be slid up and down (i.e., substantially longitudinally with respect to the primary leg  104 ) on the principal body  110  and/or rotated around the principal body. The coupling mechanism  114  also has a turnscrew  118  that can be tightened to hold the collar  116 , and thus the attached stabilizing limb  112 , in a predetermined relationship with the principal body  110 . In this way, the stabilizing limb  112  can be adjusted in at least two degrees of freedom with respect to the principal body  110 . The six degrees of freedom available to an untethered structure are translational movement along each of the X, Y, and Z axes, as well as rotation about each of those axes—i.e., roll movement about the X-axis, pitch movement about the Y-axis, and yaw movement about the Z-axis. 
     At least one subordinate leg  120  (two shown in the Figures) may be provided to the apparatus  100 . As can be seen in  FIG. 2 , each subordinate leg  120  has longitudinally spaced (i.e., longitudinal with respect to the subordinate leg) proximal and distal subordinate leg ends  222  and  224 , respectively. Each proximal subordinate leg end  222  may be movably attached to the primary leg  104  by a coupling mechanism  114  (similar to that used with the stabilizing limb  112 ) which allows at least two degrees of freedom of motion of the subordinate leg  120  relative to the primary leg. Here, the coupling mechanisms  114  allow translational movement of the subordinate legs  120  along the primary leg  104 , as well as allowing rotational movement of the subordinate legs about the primary leg. Optionally, a subordinate leg  120  may be connected to the coupling mechanism  114  for pivoting movement of the subordinate leg with respect to the primary leg  104 . This pivoting movement, when present, may be facilitated by a ball-and-socket joint (not shown) or other mechanism allowing the subordinate leg  120  to trace a conical range of motion with an apex of the cone at or near the primary leg  104 . Another pivoting movement which may be facilitated by an appropriately-designed coupling mechanism  114  could be rotation of the subordinate leg  120  about its own longitudinal axis. 
     The subordinate leg(s)  120  may have a variable length. As shown in  FIG. 2 , a release slot  226  or other appropriate structure may be provided to allow a particular subordinate leg  120  to be readily removed from the coupling mechanism  114  and a substitute subordinate leg (not shown), having a different length or another structural difference from the particular subordinate leg, can then be attached to the coupling mechanism as desired. Additionally or alternatively, the subordinate leg  120  itself may include a telescoping mechanism or other structure to allow the length (or any other dimension) of the subordinate leg to vary as desired. 
     Optionally, the coupling mechanism  114  may include at least one detent feature (not shown) configured to facilitate discrete manual adjustment of the attached subordinate leg  120  or stabilizing limb  112  relative to the primary leg  104  in at least one degree of freedom. For example, a ratcheting or keyed structure, frictional engagement, or any other suitable means may be provided to restrict rotation and/or translation of the coupling mechanism  114  with respect to the primary leg  104 . One of ordinary skill in the art can readily provide a suitable detent feature for a particular application of the present invention. A visual and/or tactile indicator, such as the rotation scale  128  shown in  FIG. 1 , could provide a discrete indication of a position of the coupling mechanism  114  with respect to the primary leg  104  or another structure of the apparatus  100 , in cooperation with or instead of any detent feature provided to the apparatus. 
     As shown in the Figures, the primary leg  104  may be substantially larger in at least two dimensions (here, in all three dimensions of width, length, and depth) than corresponding dimensions of at least one subordinate leg  120 . 
       FIGS. 4 and 5  are top and bottom views, respectively, of the apparatus  100 . As can be seen here, the primary leg  104  includes a guiding passageway  430  extending longitudinally at least partway therethrough—as depicted in the Figures, the guiding passageway is a bore extending longitudinally entirely through the primary leg and having a tubular configuration with a closed-circle cross-sectional shape. Other suitable guiding passageways  430  include, but are not limited to, a passageway having a non-circular closed cross-sectional shape; a passageway extending longitudinally down a trough or groove in the primary leg  104  (i.e., a bore having an open cross-sectional shape); a series of longitudinally spaced rings, hooks, or other discrete guiding structures (e.g., a fishing rod type guiding configuration); a rail configured to engage at least a portion of the elongate pin; or any other suitable arrangement functioning as described. The elongate pin passes through at least a portion of the guiding passageway  430  and is guided thereby to attain the dictated insertion trajectory and/or insertion location with respect to the surface, as described below. 
     As shown in  FIG. 6 , at least one of the distal primary leg end  108  and the distal subordinate leg end  224  may include at least one projection  632  which engages with the surface to help maintain position of the respective primary or subordinate leg  104  or  120  with respect to the surface. For example, the projection  632  may penetrate at least a short distance into the surface in a spike-like manner. As another option, the projection  632  may engage the surface--if an engagement beyond mere contact is desirable—in an adhesive, suction, frictional, or any other suitable manner. 
     A permanently attached or removable handle  734  may be provided, as shown in  FIG. 7 , to facilitate manipulation of the apparatus  100 . When the apparatus  100  is used in a surgical setting, for instance, the handle  734  may be useful in positioning and/or steadying the apparatus  100  in a desired position while avoiding having yet another person&#39;s hand and arm crowding the surgical field. It is contemplated that the handle  734  will usually be attached to the primary leg  104 , but one of ordinary skill in the art will be able to configure a handle as desired for a particular application of the present invention and may permanently or removably attach the handle to any desired portion of the apparatus  100 . 
       FIG. 8  depicts several options for guiding an elongate pin at the dictated insertion trajectory  102  and/or insertion location. A guiding block  836  is provided to the primary leg  104 , optionally through the use of a coupling mechanism  114  as shown. The guiding block  836  includes a plurality of guiding passageways  430  extending longitudinally at least partially therethrough (here, the guiding passageways extend entirely through the guiding block). At least a portion of the elongate pin passes through at least a portion of a chosen one of the plurality of guiding passageways  430  to attain the dictated insertion trajectory ( 102 , only one shown for clarity) and insertion location with respect to the surface. The choice of the chosen one of the plurality of guiding passageways bears a direct positional relationship with the dictated insertion location. The function of the guiding block  836  as a portion of the apparatus  100  may bear similarities to the function of the location block of co-pending U.S. patent application Ser. No. 12/854,362, filed Aug. 11, 2010 and titled “Method and Apparatus for Insertion of an Elongate Pin Into a Surface”, and incorporated herein by reference in its entirety. As another, nondepicted option, the guiding passageways  430  of the guiding block  836  may be integrated into the principal body  110  of the primary leg  104  such that the principal body has a plurality of guiding passageways extending at least partially therethrough and the user can choose one of the plurality of guiding passageways to impart at least one of a desired insertion trajectory  102  and desired insertion location to the elongate pin. 
     Also depicted in  FIG. 8  is an offset guiding extension  838 , again provided to the primary leg  104  through the use of a coupling mechanism  114 . The offset guiding extension  838  has longitudinally spaced (i.e., longitudinal with respect to the offset guiding extension) proximal and distal extension ends  840  and  842 , respectively. The proximal extension end  840  may be movably attached to the primary leg  104  by a coupling mechanism  114  (similar to that used with the stabilizing limb  112  and/or the subordinate leg  120 ) which allows at least two degrees of freedom of motion of the offset guiding extension  838  relative to the primary leg. A guiding passageway  430  is located at the distal extension end  842  and is configured to guide the elongate pin to the dictated insertion trajectory and insertion location, as described below, instead of or in addition to the guiding of an elongate pin by a guiding passageway  430  formed in or by another portion of the primary leg  104 . 
     The apparatus  100  may include a depth control feature, such as the indication scale  844  shown in  FIG. 8 . The depth control feature may indicate and/or limit a depth to which the elongate pin is inserted into the surface. For example, the indication scale  844  can be configured to indicate a starting position, when the elongate pin is resting lightly on the surface, and an insertion position, when the elongate pin has been pushed into the surface. The distance between the starting position and the insertion position on the indication scale  844  will reflect the insertion depth of the elongate pin. One of ordinary skill in the art can readily provide another type of depth indicator or depth stop for a particular application of the present invention. 
       FIG. 9  schematically depicts the apparatus  100  in a first example use environment, the acetabulum  946  of a pelvis  948  of a patient. An acetabular rim  948  surrounds the acetabulum in a known manner. Before the apparatus  100  is placed into the depicted relationship with the acetabulum  946 , the distal primary leg end  108  and each of the distal subordinate leg ends  224  (only one visible in the view of  FIG. 9 ) should be adjusted to support the apparatus in a predetermined guiding relationship with the surface (here, the surface of the acetabulum  946 ) during use of the apparatus. In some embodiments of the apparatus  100 , the distal primary leg end  108  will be substantially nonadjustable, and in those embodiments, the distal subordinate leg end(s)  224  will be adjusted to help the apparatus achieve the predetermined guiding relationship with the surface. When there are two subordinate legs  120 , those two legs and the primary leg  104  will cooperatively create a tripod support of the apparatus  100  in the predetermined guiding relationship with the surface during use of the apparatus. 
     The predetermined guiding relationship that the apparatus  100  is configured to achieve with the surface may be predetermined in any suitable manner. It is contemplated, however, that the predetermined guiding relationship will include both contact of the surface with the apparatus  100  and placement of the primary leg  104  to guide an elongate pin ( 952  in  FIG. 9 ) to insertion into the surface at a dictated insertion trajectory and insertion location when the apparatus is being supported in the predetermined guiding relationship with the surface. To place the primary leg  104  appropriately for this result, each subordinate leg  120  may be adjusted relative to the primary leg  104  to impart the dictated insertion trajectory  102  and insertion location to the apparatus  100 . 
     In the acetabulum  946  example shown in  FIG. 9 , the distal primary leg end  108  is placed into contact with a fovia  954  of the acetabulum. Each distal subordinate leg end  224  is configured to contact a known point on the pelvis  948  (here, the acetabular rim  950 ) to support the apparatus in the predetermined guiding relationship with the surface of the acetabulum. Since the subordinate leg(s)  120  are adjustable, however, the user may manually adjust the subordinate leg(s)  120  relative to the primary leg  104  to dictate at least one of the insertion trajectory  102  and the insertion location  956  for the elongate pin  952 . For example, the longitudinal distance between the proximal and distal subordinate leg ends  222  and  224 --that is, the length of the subordinate leg  120 --may be adjustable to help dictate at least one of the insertion trajectory  102  and the insertion location  956  for the elongate pin  952 . As another example, substitute subordinate legs (not shown), having different lengths, sizes, shapes, or any other physical property can be provided to the apparatus  100  in lieu of one or more of the original subordinate legs  120  to help dictate at least one of the insertion trajectory  102  and the insertion location  956  for the elongate pin  952 . As a further example, the respective coupling mechanisms  114  could be loosened to allow translation and/or rotation of the coupling mechanisms with respect to the primary leg  104  to reposition the subordinate legs  120  as desired. One of ordinary skill in the art could provide other ways for the subordinate legs  120  to be adjusted. The manner in which the primary and/or subordinate legs  104  and  120  are adjusted is not essential to the functioning of the apparatus  100 . 
     Because the insertion trajectory  102  and insertion location  956  generally carry some significance for later use of the elongate pin  952  as a surgical landmark, it is contemplated that the user will generally plan the insertion trajectory and insertion location in advance of the surgery and transfer that pre-planned information to the apparatus  100  in any suitable manner. One way that the insertion trajectory  102  and/or the insertion location  956  may be predetermined by the user is through the use of an external dictator, such as, but not limited to, a preoperative planning system such as that disclosed in co-pending U.S. Provisional Patent Application No. 61/408,392, filed Oct. 29, 2010 and titled “System of Preoperative Planning and Provision of Patient-Specific Surgical Aids”, incorporated herein by reference in its entirety. A preoperative planning system may provide the user with predetermined settings for the adjustable portions of the apparatus  100 . In this instance, scales, detents, or other markings or structures may be provided to the apparatus  100  as adjustment aid tools to assist the user with placing the movable structures of the apparatus into the appropriate predetermined positions. As an example, the rotation scale  128  previously discussed could carry a variety of numerical values, and a marking on the coupling mechanism  114  could be lined up with a particular value dictated by the preoperative planning system. 
     Another way that a predetermined desired elongate pin  952  inserted position could be transferred from a preoperative planning system (such as through use of a bone model or predetermined apparatus  100  settings) to the apparatus is through use of a “setting stand” device for transferring predetermined spatial positioning information to the apparatus. A suitable device is disclosed in co-pending U.S. Patent Application Number [to be determined, attorney docket number CCF-020176] claiming priority to U.S. Provisional Patent Application No. 61/534,142, filed 13 Sep. 2011 and titled “Apparatus and Method for Transferring Predetermined Spatial Positioning Information to an Adjustable Tool”, incorporated herein by reference in its entirety. 
     Regardless of the manner in which the predetermined guiding relationship is provided, the user can preset the positions, lengths, orientations, and other physical characteristics of the apparatus  100  to assist in setting the elongate pin  952  into a desired landmarking relationship with the surface. In order to do so, the coupling mechanisms  114  can be manipulated to position the subordinate leg(s)  120  as desired in at least two degrees of freedom relative to the primary leg  104 . When an adjustable stabilizing limb  112  is provided, it, too, may be adjusted as desired. 
     Once the desired adjustments have been made to the apparatus  100 , the distal primary and subordinate leg ends  108  and  224  are concurrently brought into contact with the acetabular  946  surface to support the apparatus in the predetermined guiding relationship with the bone surface. This arrangement is shown in  FIG. 9 . As can be seen in this Figure, the guiding passageway  430  (shown partially in dotted line) extends through a substantial portion of the primary leg  104 . Since the guiding passageway  430  helps to impart the insertion trajectory  102  to the elongate pin  952 , the angle of a substantial portion of the primary leg  104  relative to the surface directly corresponds to the insertion trajectory in the depicted apparatus  100  and others similarly configured. 
     It is contemplated that the distal primary leg end  108  may contact an area of the surface directly adjacent the insertion location  956 , as shown in  FIG. 9 , when the apparatus  100  is being supported in the predetermined guiding relationship with the surface. Regardless of the adjacency between the distal primary leg end  108  and the insertion location  956 , it is also contemplated that the distal primary leg end may contact an area of the surface that is closer to the insertion location than the areas of the surface contacted by any subordinate leg  120  when the apparatus  100  is being supported in the predetermined guiding relationship with the surface. For example, as shown in  FIG. 9 , the distal primary leg end  108  could contact the fovia, which is directly adjacent the insertion location  956 , while the distal subordinate leg ends  224  contact the acetabular rim  950 , which is spaced apart from the insertion location. 
     Optionally, a coupling mechanism  114  having an associated subordinate leg  120  in the form of a locating fin  960  could be provided to the apparatus  100 . When present, the locating fin  960  may be adjusted to contact a particular native tissue feature  962  (optionally in a mating relationship) to help orient the apparatus  100  as desired. For example, a native acetabulum  946  may have a distinctive anatomical feature (natively present or artificially provided) which can serve as a native tissue feature  962  landmark for the locating fin  960 . It is anticipated that the native tissue feature  962  contacted by the locating fin  960  will be located on a portion of the acetabulum  946  which is spaced apart from the acetabular rim  950  or other locations contacted by the other subordinate legs  120 —this spacing may help the locating fin and subordinate legs positively located and help steady the primary leg  104  with respect to the dictated trajectory and location. The locating fin  960  could instead be substantially rigidly attached to the primary leg  104  without an associated coupling mechanism  114 . 
     Optionally, the primary leg  104  may guide longitudinal translational movement (e.g., through use of a guiding passageway  430 ) of a pilot drill (not shown) into the surface at the dictated trajectory and location when the apparatus  100  is being supported in the predetermined guiding relationship with the surface. In this manner, the pilot drill can drill a pilot hole at the dictated trajectory and insertion location in the surface to prepare the surface for insertion of the elongate pin  952 . 
     Whether or not a pilot hole is provided, the primary leg  104  may guide longitudinal translational movement of the elongate pin  952  to insertion into the surface at the dictated insertion trajectory  102  and insertion location  956  when the apparatus  100  is being supported in the predetermined guiding relationship with the surface. In other words, the elongate pin  952  is moved in the insertion direction  958 , which directly corresponds to the insertion trajectory  102 , along the guiding passageway  430  (when present) or another structure of the primary leg  104  until a distal pin end  964  contacts the surface to be penetrated (the surface of the acetabulum  946  in  FIG. 9 ). The distal pin end  964  is then inserted into the surface along the insertion trajectory  102  until the elongate pin  952  achieves a desired landmarking relationship with the surface. The apparatus  100  can then be removed from the surgical field and the surgical procedure can continue. 
     While aspects of the present invention have been particularly shown and described with reference to the preferred embodiment above, it will be understood by those of ordinary skill in the art that various additional embodiments may be contemplated without departing from the spirit and scope of the present invention. For example, the specific methods described above for using the described apparatus  100  are merely illustrative; one of ordinary skill in the art could readily determine any number of devices, sequences of steps, or other means/options for dictating the insertion trajectory and/or insertion location as described. Any of the described structures and components could be integrally formed as a single piece or made up of separate sub-components, with either of these formations involving any suitable stock or bespoke components and/or any suitable material or combinations of materials. It is contemplated that the apparatus  100  may be reusable (optionally sterilizable). Although an elongate pin  952  is used as an example of a structure to be inserted into a surface through guidance of the apparatus  100 , any other suitable structures could be guided into position upon, or engagement with, the surface, such as, but not limited to, a bovie cauterizer, an electrode, a drill (e.g., for drilling fastener holes), a marking pen, or any other suitable structure. Though certain components described herein are shown as having specific geometric shapes, all structures of the present invention may have any suitable shapes, sizes, configurations, relative relationships, cross-sectional areas, or any other physical characteristics as desirable for a particular application of the present invention. Any structures or features described with reference to one embodiment or configuration of the present invention could be provided, singly or in combination with other structures or features, to any other embodiment or configuration, as it would be impractical to describe each of the embodiments and configurations discussed herein as having all of the options discussed with respect to all of the other embodiments and configurations. The mating relationships formed between the described structures need not keep the entirety of each of the “mating” surfaces in direct contact with each other but could include spacers or holdaways for partial direct contact, a liner or other intermediate member for indirect contact, or could even be approximated with intervening space remaining therebetween and no contact. Various structures are described as being movably attached to the primary leg  104  via coupling mechanisms  114  allowing optional movement in at least two degrees of freedom, but these structures could instead be fixedly attached to the primary leg or movably attached via any suitable attachment means, and the structures need not all be attached to the primary leg using the same attachment means. A device or method incorporating any of these features should be understood to fall under the scope of the present invention as determined based upon the claims below and any equivalents thereof. 
     Other aspects, objects, and advantages of the present invention can be obtained from a study of the drawings, the disclosure, and the appended claims.