for further understanding of the invention , reference is made to the attached drawing wherein : fig1 is a side elevational view of the trocar of this invention ; fig3 is a cross - section taken along lines 3 -- 3 of fig1 . fig4 is a cross - section taken along lines 3 -- 3 of fig1 with the cannula in extended position . fig6 is a partial section along lines 3 -- 3 of fig1 with parts broken away illustrating the trocar with the stylet extended . fig7 is a partial cross - section diagrammatically illustrating how a syringe may be coupled to the cannula . referring now to the drawing , and in particular to fig1 it may be seen that the trocar comprises a housing 12 formed from two components , e . g ., housing halves , 14 and 16 , secured together . extending axially forward of housing 12 are the concentrically disposed cannula 18 and stylet 20 . as best may be seen in fig6 a specimen notch 22 adjacent the tip 21 of the stylet 20 is normally covered by the cannula 18 when stylet and cannula are locked together for tissue penetration purpose , but becomes exposed upon retraction of cannula 18 . when cannula and stylet are locked for penetration , the stylet tip 21 extends a modest distance forward of the cannula terminus , typically 3 or 4 mm , and appropriately the proximate end 23 of specimen notch 22 is correspondingly 4 or 5 mm distally of stylet tip 21 . exemplary lengths for the stylet ( forward from housing 12 ) are 31 / 2 &# 34 ;, 6 &# 34 ; and 8 &# 34 ;. the extended and retracted positions for cannula 18 are illustrated by fig3 and 4 respectively . inside housing 12 , the cannula 18 is secured centrally of housing 12 to a movable hub 24 , which member 24 constitutes a plunger riding the inside wall of housing half 14 impelled by movement of cap 26 . spring 28 resists forward movement by cap 26 and hub 24 and generates retraction movement , as is illustrated by fig3 and 4 . a spring biased detent 30 set in the periphery of hub 24 engages in a central aperture 31 of the circular groove 32 on the side wall of the front housing half 14 to lock hub 24 and cannula 18 in their forward rest position . then , movement of detent 30 radially inward releases the hub 24 allowing spring 28 to push the hub and cannula rearward to their retracted rest position , see fig3 . a driver cap 26 extending distally out from rear housing half 16 bears against the hub 24 . thumb pressure against cap 26 causes cap 26 and hub 24 , and cannula 18 , to move forward as a unitary whole . the spring force of spring 28 causes cannula and hub to retract . through the presence of detent 30 in aperture 31 , the cannula and stylet are locked together and move as a unit while the trocar is being inserted . then , when detent 31 is depressed sufficient to clear the aperture 31 spring 28 causes hub 24 and cannula 18 to retract . thus , no undesired added penetration of tissue takes place by virtue of any forward movement of the cannula . as may be seen in fig3 retraction of cannula 18 along stylus 20 has exposed the notch 22 in stylus 20 . some of the soft tissue which collapses around stylus 20 , enters notch 22 . a subsequent advance of cannula 18 along stylus 20 traps ( specimen ) tissue in notch 22 . the concentricity of cannula 18 and stylet 20 along with location of the above - described latching mechanism for cannula 18 peripherally of the cannula makes feasible the already described movement of the cannula 18 relative to the stylet . the stylet can be moved relative to the cannula as well . the cannula 18 slidably fits a central aperture 13 in the front face 15 of housing 14 , and is affixed at periphery to the wall of a central aperture 25 of hub 24 ( see fig6 ). also the spring 28 and the hub locking detents 30 are radially outward of the cannula . thus , cannula 18 is secured within housing half 14 when locked in its forward rest position , but is free to move axially between its forward and its retracted position . thus , stylet 20 occupies what otherwise would be an open axial space that extends from the proximate end of cannula 18 to the distal end thereof being clear of the cannula and the mechanism which advances and retracts the cannula . appropriately , cap 26 is made hollow so that when cap 26 is pushed , advancing cannula 18 relative to housing 12 , the distal end of the stationary stylet 20 is encompassed within the cap hollow , as may be seen in fig3 and 4 . the stylet 20 is , of course , longer than the cannula 18 . as may be seen in fig4 and 5 , the rear end of stylet 20 is mounted fixedly in a blind hole 41 of a stylet hub 42 and in turn stylet hub 42 is formed with a reduced diameter face 44 that interengages in a press and / or glued together fit with locking ring 46 . the locking ring 46 interengages with mounting ring 50 through a luer - locking mechanism ( not fully illustrated ). the mounting ring 50 is made integral with forward housing half 14 and serves to lock stylet 20 to the housing half 14 , e . g ., through the luer - lock arrangement . the slots 52 in mounting ring 50 allow part of the cap 26 to reciprocate therethrough and move the cannula hub 24 . the forward end of cap 26 is split into a multiplicity of lugs , e . g ., four , the lugs being sized to pass through the slots 52 against cannula hub 24 . fig6 illustrates the relationship of the lugs on cap 26 to slots 52 of mounting ring 50 . since cannula 18 and stylus 20 are both locked to housing 12 , they move as a unitary whole during penetration of the trocar into the body tissues . important to practice of this invention is capability to remove cap 26 and stylet hub 42 . the housing halves 14 and 16 are separably threaded together . they may be separated when cannula 18 is locked to housing half 14 by detect 30 in its advanced position ( covering specimen notch 22 ), as shown in fig4 when cannula hub 24 is then well within housing half 14 , or when cannula hub is in its retracted position , as shown in fig3 . as can be appreciated from the drawing , cap 26 is free to rotate relative to rear housing half 16 so that when housing half 16 is being unthreaded ( or threaded ) cap 26 remains rotationally fixed to housing half 14 . a retaining ring 54 holds cap 26 within housing half 16 so cap 26 and housing half 16 are withdrawn together . separating the housing halves 14 , 16 and removing housing half 16 axially to the rear leaves the stylet hub 42 and locking ring 46 exposed . stylet 20 can be withdrawn from cannula 18 by twisting and relasing the luer - lock . a like stylet 20 can quickly and easily be inserted into the cannula 18 locking ring 46 secured to mounting ring 50 on housing half 14 , after which cap 26 can be repositioned in the slots 52 of mounting ring 50 and the housing halves joined together . as has already been pointed out when housing half 16 is separated from housing half 14 , the cap 26 remains with housing half 16 . the retaining ring 54 provided to retain cap 26 in housing half 16 is recessed inside housing half 16 to provide a recess region wherein mounting ring 50 seats . the threaded connection between housing halves 14 and 16 illustrated herein could as well be the luer - lock found on many medical devices , notably syringes . the trocar of this invention is adapted for ease of use . housing 12 can be gripped by the fingers of one or both hands for insertion of the needle and cannula as deeply into the body as required for the biopsy . to secure a tissue specimen , the surgeon can steady the housing 12 with the fingers of one hand while pressing detent 30 with the thumb of the other hand . when detent 30 is clear from aperture 31 , the spring 28 causes retraction of cannula 18 to expose the stylet 20 , collecting then a tissue specimen in notch 22 . thereafter the cap 26 is pressed forward , under the physician &# 39 ; s control against spring 28 , advancing cannula 18 to its fullest extent and engaging detent 30 in aperture 31 . whenever more than one biopsy specimen is wanted from the site , housing half 14 may be steadied by one hand , and housing half 16 twisted by the other hand . then , housing half 16 is removed to expose the stylet for removal thereof . given a second like stylet assembly at hand , stylet replacement may be done quickly , allowing a repeat specimen to be obtained promptly without moving the trocar . a syringe can be coupled to housing half 14 should the physician desire to irrigate or medicate the tissues at the proximate end of cannula 18 . fig7 diagrammatically illustrates a syringe 75 coupled to housing half 14 . the luer - lock 80 on a standard syringe couples to locking ring 50 . it may be noted that cannula hub 24 is in retracted position so as to create a well defined channel from the syringe 75 into cannula 18 . then expulsion of the ( liquid ) contents of syringe 75 sends the solution directly into cannula 18 to irrigate the body tissues at the proximate end of cannula 18 . no discussion is offered about the materials from which the trocar of this invention is found . medical grade plastic materials ( e . g ., abs plastic ), capable of radiation sterilization are known in the art and the important metal components like the cannula and stylet are well known in the medical arts . advantageously this entire assembly can be made as a disposable unit .
a trocar type biopsy instrument characterized by : structure for locking the cannula and stylet of the instrument together so as to allow these components to penetrate soft body jointly as a unitary whole ; structure for retracting the cannula rearward along the stylet far enough to expose the specimen notch , and for returning the cannula along the stylet to its original advanced position covering the specimen notch ; removable stylet retaining structure so that the stylet may be removed while the cannula remains locked in its advanced position . the instrument of the present invention facilitates the manipulative efforts required for performing soft tissue biopsy procedures .