in the following detailed description , reference is made to the accompanying drawings , which form a part hereof , and in which is shown by way of illustration specific embodiments in which the invention may be practiced . in this regard , directional terminology , such as “ top ,” “ bottom ,” “ front ,” “ back ,” “ leading ,” “ trailing ,” etc ., is used with reference to the orientation of the figure ( s ) being described . because components of embodiments can be positioned in a number of different orientations , the directional terminology is used for purposes of illustration and is in no way limiting . it is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention . the following detailed description , therefore , is not to be taken in a limiting sense , and the scope of the present invention is defined by the appended claims . it is to be understood that the features of the various exemplary embodiments described herein may be combined with each other , unless specifically noted otherwise . the term “ proximal ” as employed in this application means that the referenced part is situated next to or near the point of attachment or origin or a central point : as located toward a center of the human body . the term “ distal ” as employed in this application means that the referenced part is situated away from the point of attachment or origin or the central point : as located away from the center of the human body . a distal end is the furthest endmost location of a distal portion of a thing being described , whereas a proximal end is the nearest endmost location of a proximal portion of the thing being described . for example , the glans penis is located distal , and of the crus of the penis is located proximal relative to the male body such that a distal end of a corpora cavernosum of the patient extends about midway into the glans penis . multiple different tools and instruments are employed in a typical penile prosthetic implantation procedure to form a recess sized to receive the implant . in general , the fewer tools employed during a body implant procedure , the better . embodiments provide an instrument configured to prepare a penis for implantation of a penile prosthetic , where the instrument includes a dilation head that is movable longitudinally along a shaft of the instrument . the dilation head is movable to a proximal end of the shaft such that the shaft has a substantially uniform diameter that is unobstructed and thus configured for measuring a length of the corpora cavernosum . the dilation head is configured to be reversibly movable along the length of the shaft to “ core out ” and / or dilate the corpora cavernosum . thus , a single one of the instruments as described herein provides improved dilation of the corpora with improved procedural efficiency by performing the tasks of the multiple different tools and instruments typically employed in a penile prosthetic implantation procedure . fig1 is an exploded perspective view of one embodiment of an instrument 20 that is configured to prepare a penis for implantation of a penile prosthetic . the instrument 20 includes a shaft 22 , a plunger 24 that couples with and moves relative to the shaft 22 , and a dilation head 26 that couples with the plunger 24 . in one embodiment , the plunger 24 is inserted within the shaft 22 and the dilation head 26 is attached to the plunger 24 around the shaft 22 . longitudinal movement of the plunger 24 relative to the shaft 22 moves the dilation head 26 longitudinally along the shaft 22 . during use , as describe below , the plunger 24 is retracted proximally to draw the dilation head 26 toward a proximal end of the shaft 22 , which configures the shaft 22 for unobstructed insertion into a corpora cavernosa of the penis to allow the shaft 22 to measure the length of the corpora cavemosa . after the length measurement is taken , and while the shaft 22 is inserted into the corpora cavemosa , the plunger 24 is pushed proximally into the shaft 22 to pass the dilation head 26 along the shaft 22 in the distal direction . the movement of the dilation head 26 along the shaft 22 dilates the tissue in the corpora cavernosa . the dilation head 26 is removable from the shaft 22 and the plunger to allow other differently sized dilation heads 26 to be attached to the plunger 24 for selective dilation of the corpora . fig2 a is a perspective view and fig2 b is a cross - sectional view of one embodiment of the shaft 22 . in one embodiment , the shaft 22 has an exterior surface 30 that extends between a distal end 32 and a proximal end 34 and includes a first channel 36 and a second channel 38 that are formed in the exterior surface 30 . the exterior surface 30 defines an outside diameter of the shaft 22 , and in one embodiment the shaft 22 has a constant outside diameter that is suited for insertion into and measurement of a length of each corpora cavernosum . in one embodiment , the channels 36 , 38 are open channels formed from a circular arc of greater than 180 degrees , where the first channel 36 is spaced a first distance h 1 apart from the second channel 38 . in one embodiment , the shaft 22 is formed as a single monolithic shaft molded as a unit between the distal end 32 and the proximal end 34 , and a handle 40 is attached to the proximal end 34 of the shaft 22 . in one embodiment , at least a portion of the exterior surface 30 of the shaft 22 is provided with indicia 42 placed at selected intervals , for example a series of markings spaced 1 cm apart , although other spacing is also acceptable . in one embodiment , the shaft 22 is fabricated from a circular rod to include the channels 36 , 38 and a flat surface on which the indicia 42 are marked . in one embodiment , the indicia 42 are marked on the flat surface of the shaft 22 and over the exterior surface 30 . marking the indicia 42 on the flat surface minimizes the deleterious effects of glare , which can occur in the typically brightly - lighted operating rooms . fig3 a is a perspective view and fig3 b and 3c are cross - sectional views of one embodiment of the plunger 24 . in one embodiment , the plunger 24 extends between a distal end 52 and a proximal end 54 and includes a first rod 56 and a second rod 58 spaced apart from the first rod 56 , where the rods 56 , 58 extend from a handle 60 . the rods 56 , 58 are sized to slide within the channels 36 , 38 ( fig2 b ). for example , the rods 56 , 58 are formed to have a diameter that is similar to or slightly less than the diameter of the channels 36 , 38 ( in order to allow for clearance between the rods 56 , 58 and the channels 36 , 38 ). in one embodiment , the first channel 36 and the second channel 38 are open channels such that at least a portion of the first rod 56 and the second rod 58 is visibly exposed through the exterior surface 30 of the shaft 22 ( fig2 b ) when the instrument 20 is assembled . in one embodiment , the rods 56 , 58 are flexible and pre - flexed or stressed such that the distal ends 52 deflect inwardly toward each other as illustrated by the distance h 2 in fig3 c showing the distal ends 52 are more narrowly spaced apart than the distance h 1 between the rods 56 , 58 near the handle 60 ( fig3 b ). in particular , in one embodiment the rods 56 , 58 are spaced by the first distance h 1 apart near the handle 60 as illustrated in the cross - sectional view of the proximal end portion of fig3 b and the distal ends 52 of the rods 56 , 58 are tensioned ( e . g ., bent ) to flex together such they are spaced apart by a distance h 2 that is less than the distance h 1 as illustrated in the cross - sectional view of the distal end portion of fig3 c . in this manner , when the rods 56 , 58 are engaged with the channels 36 , 38 ( fig2 b ) the shaft 22 maintains the rods 56 , 58 apart , one from the other , by the distance h 1 . alternatively , when the distal ends 52 of the rods 56 , 58 extend beyond the distal end 32 of the shaft 22 ( fig2 a ) the ends 52 are unconstrained and thus flex and pinch together a distance h 2 apart . in one embodiment , the rods 56 , 58 are formed to be substantially parallel with each other , for example as illustrated by the rods of plunger 134 in fig9 . fig4 a is a side view , fig4 b is an end view , and fig4 c is a cross - sectional view of the dilation head 26 . in one embodiment , the dilation head 26 includes an exterior surface 70 having an outside diameter of d 1 and an inside surface 72 that is formed to provide a recess 74 . the dilation head 26 is attachable to the distal ends 52 of the rods 56 , 58 and its annular conformation is configured to be disposed over the shaft 22 . in one embodiment , the recess 74 is provided as an annular groove formed around the inside surface 72 of the dilation head 26 . in one embodiment , the diameter d 1 is larger than the diameter of the shaft 22 ( fig2 b ) and the inside surface 72 of the dilation head 26 includes clearance notches 76 sized to move over the rods 56 , 58 ( fig3 b ) of the assembled instrument 20 . in one embodiment , the dilation head 26 is removably attachable and re - attachable to the plunger 24 ( fig3 a ). suitable examples of mechanisms that allow the dilation head to be removed from the plunger 24 include tension latches , threads , snap fits , friction fits , and quarter - turn quick attachment mechanisms ( e . g ., post - and - slot arrangements ). in one embodiment , the instrument 20 is configured to be reusable and is fabricated from a suitable material such as a polymer . suitable polymers include polysulfone , polyetherimide , or polyester , or blends or derivatives of polysulfone , polyetherimide , or polyester . in one example , the shaft 22 , the plunger 24 , and the dilation head 26 are each fabricated from polysulfone and thus configured for disposable single surgical use . fig5 a is a cross - sectional view of the dilation head 26 disengaged from the plunger 24 . in one embodiment , the plunger 24 is longer than the shaft 22 such that the distal ends 52 of the rods 56 , 58 extend beyond the distal end 32 of the shaft 22 when the handle 60 of the plunger 24 is in contact with a handle 40 of the shaft 22 . in one embodiment , the distal ends 52 of the rods 56 , 58 combine to provide a tension latch 80 . the tension latch 80 is flexible and compresses to release from the dilation head 26 ( fig5 a ) and expands to engage with the dilation at 26 ( fig5 b ). for example , in one embodiment the tension latch 80 includes a boss 82 that extends from an exterior surface of the each of the rods 56 , 58 . the tension latch 80 is characterized in that the distal ends 52 of the rods 56 , 58 deflect inwardly together when the ends 52 of the plunger 24 extend beyond the shaft 22 , which provides clearance for the bosses 82 to pass inside the interior surface 72 of the dilation at 26 for attachment / removal of head 26 from plunger 24 . for example , and with additional reference to fig3 c , the distal ends 52 of the rods 56 , 58 deflect inwardly to a spacing of approximately h 2 , which provides clearance for the bosses 82 to enter inside the interior surface 72 of the dilation head 26 . that is to say , the inside diameter of the inside surface 72 is about equal to the distance h 1 plus twice the diameter of one of the proximal portion of the rods 56 , 58 . fig5 b is a cross - sectional view of the dilation head 26 attached to and engaged with the plunger 24 . when the dilation head 26 is placed over the compressed distal ends 52 of the rods 56 , 58 ( fig5 a ) and the plunger 24 is retracted such that the ends 52 no longer extend beyond the shaft 22 , then the bosses 82 of the tension latch 80 are forced outward to engage with the recess 74 of the dilation head 26 . in this manner , a removable dilation head 26 is provided for the instrument 20 , which allows the surgeon to select differently sized dilation heads 26 to selectively dilate the corpora of the penis to a desired diameter , as described below . the plunger 24 is movable longitudinally relative to the shaft 22 . movement of the plunger 24 back and forth relative to the shaft 22 moves the dilation head 26 longitudinally back and forth along the shaft 22 . in one embodiment , the handle 40 attached to the shaft 22 is separated from the handle 60 attached to the plunger 24 when the distal ends 52 of the plunger 24 are located between the distal end 32 and a proximal end 30 of the shaft 22 . fig6 is an end view of the instrument 20 . the plunger 24 is engaged with the shaft and 22 such that the rods 56 , 58 are engaged with the channels 36 , 38 formed in the shaft 22 . the dilation head 26 is attached to the rods 56 , 58 of the plunger 24 such that the dilation head 26 is disposed around the shaft 22 . fig7 a is a schematic view of one embodiment of a penis p prepared for implantation of a penile prosthetic showing the instrument 20 a in a corpora measurement configuration and fig7 b is a cross - sectional view of the corpora c 1 and c 2 of the penis p . while the penile prosthetic is not shown , it would typically include a pair of inflatable cylinders , a reservoir , and a pump employed to transfer fluid to / from the reservoir , where the instrument 20 is employed to dilate the corpora for insertion of the cylinders . the penis p is reclined against the torso such that the urethra u , surrounded by corpus spongiosum tissue , is oriented upward . the penis p has been incised to expose the corpora cavernosa ( c 1 and c 2 ) and the instrument 20 a has the dilation head 26 fully retracted proximally to allow the shaft 22 to measure the length of each of the corpora cavernosum ( c 1 or c 2 ). in the corpora measurement configuration , the entire distal portion of the shaft 22 is unobstructed from the dilation head 26 . the groin area 100 of the patient is shaved , cleaned and suitably prepped with a surgical solution prior to draping with a sterile drape as directed by the healthcare provider &# 39 ; s procedures . a retraction device , such as a retractor 102 sold under the trademark lone star and available from lone star medical products of stafford , tex ., is placed around the penis p if so desired by the surgeon to establish a surgically clean field . a catheter 103 is inserted into the urethra u from the distal end 104 of the penis p . thereafter , the surgeon forms an incision to access the corpora cavernosa c 1 and c 2 of the penis . suitable examples of incisions include either an infrapubic incision or a transverse scrotal incision . the infrapubic incision is initiated between the umbilicus and the penis ( i . e ., above the penis ), whereas the transverse scrotal incision is made across an upper portion of the patient &# 39 ; s scrotum sc . as an example of the transverse scrotal approach , with reference to fig7 b , the surgeon forms a 2 - 3 cm transverse incision through the subcutaneous tissue of the median raphe of the upper scrotum sc and dissects down through the darto &# 39 ; s fascia df and buck &# 39 ; s fascia bf to expose the tunicae albuginea ta of the penis p . thereafter , each corpora cavernosum c 1 and c 2 is exposed in a corporotomy where a small ( approximately 1 . 5 cm ) incision is formed to allow the surgeon to access and subsequently dilate the corpora cavernosa c 1 and c 2 . with reference to both fig7 a and 7b , the surgeon typically will insert a blunt - ended scissors or other elongated tool to separate a portion of the spongiosum material to open a pathway for the instrument 20 a . the surgeon inserts the shaft 22 ( instrument 20 a ) into the corpora cavernosa c 1 and c 2 to measure the proximal and distal length of each corpora cavernosum c 1 and c 2 . for example , the shaft 22 is inserted into one of the corpora cavernosa c 1 or c 2 forward in the distal penis toward the glans penis , the distal measurement is recorded by reading the indicia 42 , and the shaft 22 is inserted into the same corpora cavernosa c 1 or c 2 rearward in the proximal penis toward the crus of the penis to record the proximal length of the corpora by reading the indicia 42 . the distal and proximal measurements would typically be made in reference to a “ stay stitch ” temporarily placed in the incision . the sum of the distal and the proximal measurements represent the length of the corpora into which the implant is placed . this procedure is repeated for the other of the corpora cavernosa c 1 or c 2 to measure the length of the companion corpora . thereafter , each corpora cavernosum c 1 and c 2 is dilated distally and proximally with the instrument 20 . fig8 a and 8b illustrate the instrument 20 in the dilation configurations with the dilation head 26 moved midway along the shaft 22 ( fig8 a ) and the dilation head 26 moved to the distal end of the shaft ( fig8 b ). in one exemplary approach , the surgeon begins dilation of the distal and proximal corpora cavernosum c 1 and c 2 by introducing a dilation head 26 having an 8 mm outside diameter ( d 1 in fig4 a ) into the spongy tissue of one of the corpora c 1 or c 2 . the plunger 24 is moved into the shaft 22 to move the dilation head 26 from a proximal location ( instrument 20 a in fig7 a ) to a distal location ( instrument 20 c ) to open the spongy tissue of the corpora along the length of the penis p . the plunger 24 is withdrawn proximally with the shaft 22 remaining in the penis p , and if the surgeon determines it to be desirable , once again advances the dilation head 26 distally and longitudinally along the shaft 22 to fully dilate the tissue of the corpora . thereafter , the surgeon may optionally remove the instrument 20 from the penis p , remove the 8 mm dilation head , for example , and attach a larger diameter dilation head 26 to the plunger 24 , and insert the newly configured tool 20 into the penis p to sequentially dilate the corpora cavernosum c 1 and c 2 to a width that accommodates the selected cylinder diameter of the implant . in another exemplary approach , the surgeon may choose to dilate the distal and proximal corpora by a single introduction of a dilation head having a 14 mm outside diameter . alternatively , the surgeon may choose to sequentially dilate the corpora with a series of dilation heads 26 having an outside diameter ranging from 8 mm to 10 mm to 12 mm and outward to 14 mm in diameter , in the manner described above . other dilation heads 26 wider than 14 mm are also within the scope of this disclosure . in any regard , the dilation head 26 is introduced and pushed distally toward the glans penis and proximally toward the crus of the penis to dilate each of the corpora cavernosum c 1 and c 2 along its length . after dilation of the corpora cavernosum c 1 and c 2 , the surgeon selects a proper length of implant and proceeds with placement of cylinders of the implant within the fully dilated corpora . fig9 is a cross - sectional view of an instrument system 120 including a set 122 of dilation heads 26 , each removably attachable to the tension latch 80 of the plunger 24 . in one embodiment , the set 122 of dilation heads includes multiple dilation heads 26 a , 26 b , 26 c each having a different diameter , where each dilation head 26 a , 26 b , 26 c is configured to couple to the distal ends 52 of the plunger 24 . in one embodiment , the instrument 20 ( fig1 ) and the set 122 of dilation heads are provided as a kit of parts . in one embodiment , dilation head 26 a is provided with an outside diameter d 1 , dilation head 26 b is provided with an outside diameter d 2 , and dilation head 26 c is provided with an outside diameter d 3 , where d 3 is greater than d 2 , and d 2 is greater than d 1 . as an example , in one embodiment the diameter d 1 is about 8 mm , the diameter d 2 is about 10 mm , and a diameter d 3 is about 12 mm . it is to be understood that the set 122 of dilation heads 26 could be provided with diameters ranging from 6 mm to 18 mm or more , in increments of about 2 mm , for example , depending upon the patient size or surgeon preference . each of the dilation heads 26 a , 26 b , 26 c is provided with a recess 74 that is configured to couple with the bosses 82 of the tension latch 80 . during use , the surgeon would initially measure the length of the corpora cavernosa c 1 and c 2 with the shaft 22 , dilate the distal and proximal corpora cavernosa c 1 and c 2 ( fig7 b ) in the range of d 1 with the dilation head 26 a , remove the dilation head 26 a and attach the larger diameter d 2 of the dilation head 26 b to the plunger 24 , dilate the distal and proximal corpora cavernosa c 1 and c 2 in the range of d 2 , and remove the dilation head 26 b and attach the even larger diameter of the dilation head 26 c to the plunger 24 to sequentially and fully dilate the distal and proximal corpora cavernosa c 1 and c 2 of the penis p in the range of d 3 . fig1 is a cross - sectional view of one embodiment of an instrument 130 that is configured to prepare a penis for implantation of a penile prosthetic and including a dilation head 136 threaded onto a distal end of a plunger 134 . the instrument 130 includes a shaft 132 that supports the plunger 134 in a manner similar to that described above for instrument 20 . in one embodiment , the distal end of the plunger 134 is threaded to receive threads formed on an inside surface of the dilation head 136 . in this manner , the dilation head 136 is removable from the distal end of the plunger 134 in a twist - on and twist - off approach . as described above in fig8 , one embodiment of instrument 130 includes a set of dilation heads , where each dilation head is removably attachable to the plunger 134 to allow the surgeon to sequentially dilate the corpora cavernosa to an increasingly larger diameter . embodiments provide an instrument that is configured to prepare a penis for implantation of a penile prosthetic , where the instrument includes a shaft suited for measuring a length of the corpora cavernosum and a dilation head that is movable longitudinally along the shaft of the instrument to dilate the corpora cavernosum . thus , a single instrument is provided that has improved cost effectiveness and procedural efficiency over the prior tools , and is suited to measure and dilate the corpora cavernosum of the penis . although specific embodiments have been illustrated and described herein , it will be appreciated by those of ordinary skill in the art that a variety of alternate and / or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention . this application is intended to cover any adaptations or variations of medical devices as discussed herein . therefore , it is intended that this invention be limited only by the claims and the equivalents thereof .
a method of preparing an opening formed in a penis for reception of a penile prosthetic includes measuring a length of the opening formed in the penis with a shaft of an instrument , and moving a dilation head longitudinally along the shaft of the instrument and dilating a diameter of the opening formed in the penis .