Abstract:
The present invention relates generally to devices and methods for identifying landmarks on the anatomy of a human for reference in a surgical procedure. In certain embodiments of the present invention, a stylus body is provided with a spring member and stop with openings having different shaped portions so that when the stop is depressed it can free the stylus arm and allow rotation and/or translation and, when released, it can lock the stylus arm from rotating and/or translating.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application No. 60/649,059 filed Feb. 1, 2005, the contents of which are incorporated herein by reference. 

   TECHNICAL FIELD OF INVENTION 
   This invention relates to devices and methods for identifying landmarks on the anatomy of a patient for reference in a surgical procedure. 
   BACKGROUND OF THE INVENTION 
   Certain surgical procedures, such as orthopedic surgery, generally involve preparing a particular bone for attaching a sizing guide to the particular bone and resecting the particular bone in order to fit it with a prosthesis. An example of one such procedure is found in connection with the GENESIS II® Total Knee System by Smith &amp; Nephew. 
   In a procedure such as the GENESIS II® Total Knee System, the surgeon first flexes the knee to 70-90° and performs a longitudinal incision over the anterior aspect of the knee along the medial border of the patella. The surgeon then retracts the patella laterally. Using a drill, a hole is made into the distal femur for an intramedullary rod. A valgus alignment guide and anterior cutting guide are connected to the intramedullary rod and inserted into the distal femur. The surgeon resects the anterior femur using the anterior cutting guide and a conventional resecting stylus guide such as that illustrated in  FIG. 1 . A conventional stylus  10  generally includes a stylus body  12 , stylus shaft  14 , stylus arm  16 , an arm knob  18 , and a locking mechanism such as a screw  20 . 
   After removing the intramedullary rod, valgus alignment guide, and anterior cutting guide, the surgeon attaches a femoral sizing guide to the distal femur. The femoral sizing guide may also include a sizing guide stylus, similar to the conventional stylus  10 , for example, illustrated in  FIG. 1 , to assist in referencing a position. The surgeon utilizes the stylus to determine the size of the prosthetic component from indicia on the stylus shaft  14 . Once a reference point is found with the stylus arm  16 , the surgeon turns the locking mechanism  20 , which locks the stylus arm  16  into place. An appropriate reading of the stylus shaft  14  is taken, the stylus and sizing guide are removed and a prosthetic component is then attached. 
   As stated above, generally a stylus is utilized by the surgeon to resect a bone while referencing an unaffected area of the bone. In the particular case of knee surgery, for instance, this may include the tibial plateau or the femoral anterior. To reference an unaffected area, the surgeon manipulates the stylus height relative to the bone by moving the stylus body up or down. Furthermore, the surgeon manipulates the stylus arm by the arm knob in the rotational and translational direction to obtain an appropriate reference for resecting. Once an appropriate reference is determined, conventionally, the surgeon utilizes a screw or cam-lock means to prevent the stylus arm from rotating in the translational or rotational directions. Alternatively, a spring may be conventionally utilized to provide resistance to rotation but not prevent rotation. 
   Current surgical techniques attempt to reduce ancillary tissue damage performed during a surgical procedure. Such minimally invasive surgical techniques have resulted in less disturbance and potential trauma to soft tissue which would have been either removed or moved for greater access to the surgical area of the body in conventional surgery. Minimally invasive surgical techniques have, however, created issues with respect to navigating and maneuvering instruments in the presence of soft tissue. For example, in orthopedic surgery, the stylus arm must be manipulated against unaffected areas of the bone under soft tissue. 
   Conventional stylus locking structures generally involve either several steps to lock the stylus arm or do not completely prevent stylus arm rotation. For example, locking with a screw or cam-lock involves the surgeon applying the necessary torque to ensure that the screw or cam-lock does not loosen while a reference is made for resecting. There is a danger that the surgeon may not sufficiently tighten or lock the screw or cam-lock means and the stylus arm, unknown to the surgeon, rotates during the procedure. Additionally, even if the surgeon sufficiently tightens the screw or cam-lock, the stylus arm may still become disengaged if the screw or cam-lock is jarred, or otherwise, during the procedure. Furthermore, as stated previously, the conventional spring mechanism only provides resistance to the stylus arm rotating and does not entirely prevent rotation in either the rotational or translational directions. 
   During minimally invasive surgical techniques, especially, soft tissue may cause pressure to be placed on the stylus arm and cause the stylus arm to change position. The soft tissue may also cause pressure to be placed on the stylus locking mechanism and cause the locking mechanism to become unlocked, thereby possibly allowing the stylus arm to change position and, possibly, without the surgeon&#39;s knowledge. The consequences of a stylus arm unintentionally or unknowingly rotating may impair the integrity of the particular orthopedic procedure or even the health and welfare of the patient. The surgeon, for instance, may be unable to make a correct resection due to the stylus arm rotating while the surgeon is determining a reference for the resection. Furthermore, a stylus arm that unknowingly rotates may cause the surgeon to choose an incorrectly sized prosthesis and prolong the surgical procedure or adversely affect the results of the procedure. 
   Therefore, there is a need for a stylus that will allow a surgeon to rotate the stylus arm in the rotational and translational direction and lock the stylus arm to a particular position, when desired, while preventing the stylus arm from becoming unintentionally or accidentally unlocked. Additionally, there is a need for a stylus in which a surgeon can easily and quickly lock the stylus arm and one that provides the surgeon with an indication that the stylus arm is indeed locked. Such devices can be particularly useful in minimally invasive surgery. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention includes new devices and methods for identifying landmarks on the anatomy of a human for reference in a surgical procedure. In some embodiments of the present invention, a stylus body is provided with openings, opposite one another, in the sides of the top of the stylus body. The stylus body may also contain a cavity or opening extending from the top of the stylus body and into the stylus body. A spring may be provided and located inside the cavity and a stop may also be provided with two openings, opposite each other on the sides of the stop. The stop openings may preferably include a first portion with a first shape and a second portion with a second shape. Additionally, the stop may be received in the cavity and partially extending out of the top of the stylus body. A stylus arm may also be provided with a portion that has a flat, and is partially received in the openings in the stylus body and the stop. The second portion of the stop opening may be configured to prevent the stylus arm from rotating when the stylus arm penetrates the second portion. The first portion of the stop opening may allow the stylus arm to rotate when the stylus arm penetrates the second portion. The stylus arm may include one end that may be used to contact an unaffected portion for referencing and another end that may include a detachable arm knob. 
   The stop may be depressed, compressing the spring and aligning the first portion of the stop opening with the openings in the stylus body. The stylus arm may then be rotated in the rotational and translational direction, as necessary, to maneuver the stylus arm under the soft tissue and obtain an appropriate reference point on the bone. When an appropriate reference point is determined, a first end of the stylus arm is generally pointed downward, the stop may be released and the spring causes the stop to move upward. The stylus arm then penetrates the second portion of the stop opening as the spring pushes the stop upward. The stylus arm will be preferably prevented from rotating by the particular configuration of the second portion of the stop opening and part of the stylus arm, which cooperates with each other in shape or otherwise and also, if desired, using some or all of the force imparted by the spring to stop or reduce rotation or translation. 
   After completing the necessary surgical procedural steps that utilize a stylus, the stop may be depressed, thereby allowing the stylus arm to penetrate the first portion of the stop opening, so that it can rotate and translate and be removed as desired. 
   A surgeon may utilize a stylus according to various embodiments of the present invention to perform a variety of surgical procedures, such as minimally invasive orthopedic surgical procedures, with confidence that the stylus arm will be locked into place. A stop, according to certain aspects of the present invention, may, when desired, prevent the stylus arm from rotating and/or translating even when the stylus arm is under pressure from soft tissue or other sources. 
   An advantage of certain aspects and embodiments of the present invention is to provide a stylus with a device to and quickly lock a stylus arm in place easily during a surgical procedure. 
   A further advantage of certain aspects and embodiments of the present invention is to decrease the likelihood that a stylus arm will be unintentionally or unknowingly rotated during a surgical procedure. 
   A still further advantage of certain aspects and embodiments of the present invention is the ability to allow rotation of the stylus arm when it is desired but lock the stylus arm in a certain position after the desired rotation is completed. 
   A still further advantage of certain aspects and embodiments of the present invention is the ability to prevent rotation even when soft tissue applies pressure to the stylus arm. 
   A still further advantage of certain aspects and embodiments of the present invention is that it allows rotation or locks the stylus into place without requiring several steps. 
   A still further advantage of certain aspects and embodiments of the present invention is the ability to provide an accurate reference point to a surgeon during a surgical procedure. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a conventional stylus with a screw locking mechanism. 
       FIG. 2  is an exploded perspective view of a lockable stylus according to one embodiment of the invention. 
       FIG. 3  is a side view of a stylus stop according to one embodiment of the invention. 
       FIG. 4   a  is a cross-sectional view of a stylus stop and a stylus arm in the rotating position according to one embodiment of the invention. 
       FIG. 4   b  is a cross-sectional view of the stylus stop and stylus arm of  FIG. 4   a  in the non-rotating position. 
       FIG. 5  is a perspective view of an assembled stylus according to one embodiment of the invention. 
       FIG. 6  shows, in perspective, a stylus referencing a reference portion during a surgical procedure according to one embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring initially to  FIG. 2 , illustrated are parts of a stylus according to one embodiment of the present invention. Included in this particular embodiment is a stylus body  100  that includes a stylus shaft  102  and an upper member  104 , stylus arm  106 , an arm knob  108 , a spring member  110 , and a stop  112 . In the particular embodiment illustrated in  FIG. 2 , the stylus body upper member  104  has two openings  113 ,  114  in two sides opposite one another for receiving a stylus arm  106 . The openings  113 ,  114  are preferably circular in shape but may be any shape to allow rotation by the stylus arm  106 . The stylus body upper portion  104  preferably also includes a cavity  308  of  FIGS. 4   a  and  4   b  extending from the top of the upper member  104  to the stylus shaft  102  or as far as otherwise desired. The stylus shaft  102  is essentially an elongated member that extends from the stylus body upper member  104 . The stylus shaft  102  preferably includes a cavity  308  of  FIGS. 4   a  and  4   b  extending from stylus body upper member  104 , which can communicate with the cavity and upper member  104 , such as for receiving a spring member  110  or other component. 
   The stylus arm  106  is preferably a metallic member with a first end  116  that is curved downward for referencing a reference bone portion and a second end  117  that preferably includes a threaded portion for receiving and holding an arm knob  108 . Alternatively, the second end  117  may include any configuration that is adapted to receive and hold the arm knob  108 . The stylus arm  106  also preferably includes at least one essentially flat portion  118  (“flat”) that extends, preferably, between the first end  116  and second end  117 . As will be more clearly understood below, the flat portion  118  cooperates with the stop  112  to prevent or allow the stylus arm  106  to rotate or translate relative to the stylus body  100 . 
   According to the specific embodiment illustrated in  FIG. 2 , the spring  110  may preferably be located within the cavity  308  and  309  of the stylus body upper member  104  and stylus shaft  102 . While in the cavity  308  and  309 , the spring  110  may preferably cooperate with the stop  112  to control the rotation of the stylus arm  106 . The stop  112  may therefore be located in the cavity  308  of the stylus body upper member  104  for manipulation into a first position to allow rotation of the stylus arm  106  and to be locked into a second position to prevent rotation and/or translation of the stylus arm  106 . The stop  112  preferably includes two openings  120 ,  121  opposite one another and located on the sides of the stop  112 . In certain preferred embodiments of the present invention, the openings  120 ,  121  may include a first portion and second portion that are of different shapes. As will be more apparent below, the first portion preferably allows the stylus arm  106  to rotate while the second portion preferably prevents the stylus arm  106  from rotating. 
   As stated previously, the spring  110  is inserted into the cavity  308  and  309  of  FIGS. 4   a  and  4   b  of the stylus shaft  102  and stylus body upper member  104 . The stop  112  is preferably inserted into, at least, the cavity  308  of the stylus body upper member  104 . Alternatively, the stop  112  may be inserted into the cavity  308  and  309  of the stylus body upper member  104  and at least a portion of the stylus shaft  102 . The stop  112  is initially in a first position but may be depressed and held into a second position thereby compressing the spring. 
   Referring now to  FIG. 3 , illustrated is a side-view of one embodiment of a stop  200  of the present invention. The stop  200  specifically illustrated in  FIG. 3  includes a button portion  201  and a stop body  202  extending from the button portion  201 . The button portion  201  is preferably any rigid structure that is capable of receiving pressure, directed on top of the button portion  201 . The opening  203  of the stop  200  includes a first portion  204  and a second portion  205 . In certain preferred embodiments of the present invention, the first portion  204  may be essentially circular in shape while the second portion may be essentially D-shaped. In particular preferred embodiments of the present invention, the first portion  204  allows the stylus arm  106  to rotate and/or translate when the stylus arm  106  is received in or penetrates the first portion  204 . The second portion  205  preferably prevents the stylus arm  106  from rotating and/or translating when the stylus arm  106  is received in the second portion  204 . 
   Referring now the  FIGS. 4   a  and  4   b , illustrated are cross-sectional views of a stylus stop  300  and a stylus arm  304  in the non-rotating position according to one preferred embodiment of the present invention. The stylus stop  300  in  FIGS. 4   a  and  4   b  includes a button portion  301  with a stop body  302  extending from the button portion  301 . The stylus stop  300  in  FIG. 4   a  is being depressed and is located in the cavity  308  of the stylus body  303  and, if desired, cavity  309  of the stylus shaft  310 . In this position, the stylus stop  300  is preferably compressing a spring  307   a.    
   The stylus stop  300  also preferably includes openings with a first portion  305  that is essentially circular in shape and a second portion  306  that is essentially D-shaped, or any other desired shape. A cross-section of a stylus arm  304  is illustrated in  FIG. 4   a  and has a shape that cooperates with the shape of the second portion  306  of the stylus stop openings to control rotation and/or translation of the stylus arm  304 . In  FIG. 4   a , the stylus stop  300  is being depressed and the stylus arm  304  penetrates the first portion  305  of the stylus stop opening. Since the first portion  305  is larger than the cross-sectional portion of the stylus arm  304 , the stylus arm  304  may be rotated and/or translated. 
     FIG. 4   b  illustrates a stylus stop  300  that is released from the depressed position. The spring  307   b  is extended and pushes the stylus stop  300  upwards when the force pushing downward on the button portion  301 , as in  FIG. 4   a , is released and the stylus arm  304  is rotated into a position in which it will fit in the second portion  306  of the stylus stop  300  opening. The upward force exerted by the spring  307   b  on the stylus in this embodiment positions the stop  300  so that the stop  300  preferably locks the stylus arm  304  into position to prevent rotation and/or translation by the cooperation of shapes of the arm  304  and second portion  306 . 
   Referring now to  FIG. 5 , a preferred embodiment of the stylus of the present invention is shown. The stylus  400  includes a stylus body  401  with a stylus body upper portion  402  and a stylus shaft  403 . The stylus body upper portion  402  has two openings  404 ,  405  opposite one another and on the sides of the stylus body upper portion  402 , where a stylus arm  406  penetrates the two openings  404 ,  405 . The stylus arm  406  of the particular embodiment illustrated in  FIG. 5  includes a curved first end  407  for referencing an unaffected area of a bone and a second end  408  with an attached stylus knob  409 . The stylus arm  406  preferably also includes a flat  410  that extends from the first end  407  to a second end  408 . The flat portion  410  communicates with a stop  411  to prevent the stylus arm  406  from rotating and/or translating or allow the stylus arm  406  to rotate, depending on the location of the stop  411  and the forces exerted either from the button top  411  or from the spring  307   a    307   b , as shown in  FIGS. 4   a  and  4   b.    
   Preferred embodiments of the stop  411  include two openings  204  and  205  of  FIG. 3  on opposing sides of the stop  411 . The stop openings  204  and  205  preferably include a first portion that is essentially circular in shape and a second portion that is essentially D-shaped. The shapes of the first and second portions of the stop openings, however, may be of any shape or configuration. The stop  411  is installed in the cavity  308  of the stylus body upper portion  402  and is in communication with a spring  307   a  and  307   b  of  FIGS. 4   a  and  4   b . At least one portion of the two openings of the stop  411  are generally aligned with the two openings  404 ,  405  in the stylus body upper portion  402 . The stop  411  may be initially in a first position, where the spring  307   a , as shown in  FIG. 4   a , is not compressed. The stop  411 , however, may be depressed into a second position, where the spring  307   b , as shown in  FIG. 4   b , is depressed. The stop  411  stays in the second position until the force depressing the stop  411  is released. 
   The essentially circular stop opening is preferably aligned with the stylus body upper portion openings  404 ,  405  when the stop  411  is depressed and the stylus arm  406  is rotated and/or translated so that it will fit into the second preferably D-shaped portion of the stop  411  opening. When the preferably D-shaped stop opening is aligned with the stylus body upper portion openings  404 ,  405  the D-shaped stop opening preferably communicates with the stylus arm flat  410  to prevent the stylus arm  406  from rotating. 
   If the stop  411  is depressed, the spring  307   b , as shown in  FIG. 4   b , is compressed by the stop  411 . The stop  411  moves downward, preferably until the essentially circular shaped stop opening is aligned with the stylus body upper portion openings  404 ,  405 . When the circular shaped portion is aligned with the stylus body upper portion openings  404 ,  405 , the stylus arm  406  may be rotated and/or translated. 
   Although the previous descriptions of the illustrated embodiments have described the opening portions of the stop  411  as essentially “D-shaped” and “circular,” it should be clear to those with skill in the art that these openings may be of any shape such that one portion allows the stylus arm to rotate and/or translate while the other portion prevents stylus arm rotation and/or translation. Furthermore, the stylus arm flat portion  410  may also be of any shape to communicate with one of the stop openings to prevent rotation. 
   Referring now to  FIG. 6 , illustrated is an example of a stylus  500  according to one embodiment of the present invention being utilized during a surgical procedure on the knee. In the particular example illustrated in  FIG. 6 , the stylus  500  is connected with a femoral sizing guide  501  during a surgical procedure involving a knee  502 . The stylus  500  includes a stylus shaft  503  and a stylus body upper portion  504  with a stylus arm  505  penetrating two opposing openings  506 ,  507  in the stylus body upper portion  504 . The stylus arm  505  includes a slightly curved first end  508  to provide contact with the bone for reference and a second end  509  that includes an arm knob  510 . The stylus arm  505  further includes a portion with a flat portion  511 . 
   A stop  512  is illustrated without the stylus stop  512  being depressed. According to particular embodiments of the present invention, therefore, the stylus stop  512  is in a position to prevent the stylus arm  505  from rotating and/or translating. A spring  307   a  is located inside a cavity  309  of the stylus shaft  503  and pushes the stop  512  upward when the stop  512  is not depressed. When the stop  512  is depressed, the spring  307   b  is compressed and allows the stop  512  to move downward. If the stop  512  moves downward to where the circular portion of the stop  512  opening is aligned with the two opposing openings  506 ,  507  in the stylus body upper portion  504 , the stylus arm  505  may be rotated and/or translated. 
   An example of a particular embodiment of the present invention, as illustrated in  FIG. 6  will now be described in the particular context of a minimally invasive knee surgical procedure. After the knee  502  has been resected, a femoral sizing guide, such as, for example, the femoral sizing guide  501  in  FIG. 6 , is placed at the end of the resected femur. A stylus  500  is attached to the femoral sizing guide  501  by connecting the stylus shaft  503  to the top of the femoral sizing guide  501 . At this point, the surgeon may depress the stop  512  and rotate and/or translate the stylus arm  505 . 
   Specifically, the surgeon, using the arm knob  510 , moves the stylus arm  505  in the translational and/or rotational direction and under soft tissue (not shown) until an appropriate reference point on the bone is located. Once the surgeon locates a desired reference point, the stop  512  may be released, the spring pushes the stop  512  upward and the stylus arm  505  preferably fits in the second portion of the stop  512  openings that are aligned with two opposing openings  506 ,  507  in the stylus body upper portion  504 . The stylus arm  505  will then be locked into place. The surgeon may then determine the femoral prosthesis size based on the relative reference point obtained with the stylus  500 , confident that the stylus arm  505  will not change position. Once the appropriate size is determined, the surgeon may depress the stop  512  until the first portion of the stop opening is aligned with two opposing openings  506 ,  507  in the stylus body upper portion  504  and rotate and/or translate the stylus arm  505  to remove it from under soft tissue. 
   The foregoing description of the embodiments, including preferred embodiments, of the invention has been presented only for the purpose of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Numerous modifications and adaptations thereof will be apparent to those skilled in the art without departing from the spirit and scope of the this invention.