referring initially to fig2 , 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 fig2 , 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 fig4 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 fig4 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 a 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 118 to rotate or translate relative to the stylus body 100 . according to the specific embodiment illustrated in fig2 , 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 fig4 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 fig3 , illustrated is a side - view of one embodiment of a stop 200 of the present invention . the stop 200 specifically illustrated in fig3 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 fig4 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 fig4 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 fig4 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 fig4 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 fig4 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 . fig4 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 fig4 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 fig5 , 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 fig5 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 fig4 a and 4 b . preferred embodiments of the stop 411 include two openings 204 and 205 of fig3 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 fig4 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 fig4 a , is not compressed . the stop 411 , however , may be depressed into a second position , where the spring 307 b , as shown in fig4 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 fig4 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 410 may also be of any shape to communicate with one of the stop openings to prevent rotation . referring now to fig6 , 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 fig6 , 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 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 fig6 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 fig6 , 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 .
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 .