Abstract:
A releasable interlock assembly having axial and rotational engagement, and suitable for use in catheter introducers and other medical devices, has a tapered female member which receives a tapered male member. The female member has protrusions which engage corresponding grooves on the male member. The grooves have a generally axially aligned portion and a generally circumferentially aligned portion, terminating in a pocket to receive the corresponding protrusion on the female member. The depth of the each groove decreases from the open axially aligned end to a point just before the pocket, causing a dimensional interference which prevents the protrusion from disengaging the pocket axially, unless deliberately rotated by an operator.

Description:
BACKGROUND 
     The present invention relates to releasable interlock assemblies, particularly to those used in medical devices such as catheter introducer assemblies, catheter introducer-to-accessory assemblies, and catheters which generally comprise two or more portions, each of which must releasably engage with the other. The present invention relates particularly to elective engagements where the axial engagement between the portions must withstand forces urging the portions to separate from one another. 
     Catheter introducers provide a reusable conduit for the passage of guide wires, catheters, pacemaker leads, or other medical devices, e.g. biopsy instruments, through the skin, flesh, and vessel walls to gain access into blood vessels or other body passageways and cavities. Many types of accessories are used in conjunction with catheter introducers, such as hemostasis valves, Tuohy-Borst adapters, and aseptic catheter shields These accessories must by necessity couple to the catheter introducer or each other, or both, in some combination. This invention is directed to providing a simple and secure means of releasably coupling any combination of these and other devices to one another. 
     In typical use, say for introducing a catheter into a blood vessel, a physician inserts a needle through the body flesh and into a blood vessel, and then inserts a guide wire in to the blood vessel through the center passage of the needle. The needle is then removed leaving the guide wire in place. The introducer assembly is then inserted over the guide ire such that the tapered distal portion of the dilator acts to gradually expand the puncture opening to ease the pas sage of the introducer sheath into the blood vessel. After the introducer sheath has been inserted to a desired depth within the blood vessel, the dilator portion is removed from within the introducer portion. In this disclosure, “proximal” refers to the portions of an introducer nearest to the physician or health care worker performing the insertion procedure, and “distal” refers to the portions of the introducer nearest to, or inside of, the human or animal patient receiving the catheter. 
     During the initial insertion of the introducer assembly, the body&#39;s resistance to the expansion of the puncture opening exerts forces on the distal portion of the dilator tending to push the dilator distal end rearwardly in the proximal direction into the introducer sheath. In order to ensure that the tapered distal portion of the dilator remains extended beyond the blunt distal end of the introducer sheath during the initial insertion the introducer assembly, the dilator hub should be connected to the introducer hub to prevent relative axial movement of the two portions. It is important that the dilator hub and the introducer hub not disengage during the insertion procedure, but be capable of being disengaged when desired. 
     Catheter introducers of various forms exist in the prior art. Such devices generally consist of: (1) a dilator comprised of an elongated flexible tube with a hub permanently affixed to the proximal end. The distal end of the tube is fashioned into a generally conical tapered tip. (2) an introducer comprised of an elongated flexible tube or sheath with a hub permanently affixed to the proximal end and a distal tip which is fashioned in such a way as to minimize the resistance to insertion and trauma to the body tissue. The introducer interior diameter is sized to slidably accommodate the exterior of the dilator tube, since the two are inserted into the body as a set. 
     As a set, the dilator resides within the introducer, and while assembled, the distal tip of the introducer resides axially proximal to the proximal end of the tapered end of the dilator. As the name would suggest, the purpose of the dilator is to dilate or enlarge a hole in the body tissues so as to allow entry of the tubular portion of the introducer. This dilation is accomplished by means of the conical tip of the dilator which, as it is progressively inserted into the body, stretches the tissue radially outward to allow entry of the distal portion of the introducer. Once the insertion is achieved, the dilator is removed and the introducer remains as a transcutaneous conduit whereby other instruments are afforded ready access into the passageway. 
     During the insertion process, the body tissues resist stretching, and the resistance force vector in the axial direction would cause the dilator to move axially relative to the introducer if there were no means present to prevent such relative movement. Accidental movement of the dilator relative to the introducer during the insertion process is undesirable, for if the distal tip of the introducer is allowed to extend beyond the proximal end of the dilator tip, significant trauma to the vessel and surrounding tissues would result. 
     Numerous means for releasably connecting the introducer to the dilator, or to connect accessories to the introducer, or to one another, are known in the prior art. Prior art means for releasably connecting the dilator hub and the introducer hub have utilized rotatably engaging studs and complimentary slots, tapered fits, exterior clips, and ring and collar mechanisms. Many of these devices either require a significant effort to engage the locking mechanism, or do not prevent the portions from accidentally disengaging, or leave exposed protrusions on one or more members which can snag and tear a surgical glove. 
     The present invention solves the problems associated with prior art devices by generally providing an axial coupling means with an improved rotatably engaging releasable interlock between the dilator and introducer portions of an introducer assembly. It reduces the risk of inadvertent disengagement while minimizing the effort required for proper deployment and eliminates externally protruding portions. Additionally, all protrusions, grooves, and parts of the locking mechanism are internal when the releasable interlock is engaged, thus eliminating the risk that such parts could snag and tear a surgical glove. 
     SUMMARY 
     The present invention describes an improvement of a rotatably engaging axial coupling connection between at least two constituents of a medical device, such as between a dilator hub and an introducer hub of a catheter introducer, although the scope of application of this invention is not limited to the example. 
     The releasable interlock assembly with axial and rotational engagement has a first portion having a generally cylindrical or conical male member at the engaging end with one or more radially disposed grooves which engage a second portion. The second portion has a generally cylindrical or conical female member at the engaging end dimensioned so as to receive the male member of the first portion. The female portion has one or more protrusions which extend from the interior wall of the tapered female member, or socket, radially inward towards the common longitudinal axis of the two portions and which engage and cooperate with the grooves of the first portion. Upon axial engagement of the two portions, male member into female member, one portion is rotated relative to the other portion causing the protrusions in the second portion to enter engagement with the grooves of the first portion. Upon continued rotation, the protrusions of the second portion encounter a dimensional interference with the grooves of the first portion. Upon continued rotation, and with a greater amount of applied torque required, one or both of the portions elastically deform into a stressed condition so as to overcome the dimensional interference thus allowing continued relative rotational motion between the two portions. 
     With continued applied torque, this relative rotational motion is sustained, with one or both portions in a stressed condition, until the inwardly radially directed protrusions of the second portion come to a blind end of the grooves of the first portion at which point the dimensional interference between the two portions is significantly reduced. This represents the releasably locked state of engagement between the two portions. The sudden reduction of dimensional interference and subsequent stress relaxation provides a tactile sensation thus signaling the user that the releasably locked state has been achieved. Only by reversing the amount and direction of applied torque and retracing the original path of the protrusions within the grooves can the interference fit be defeated and disengagement of the two members achieved. 
     The preferred embodiment of this invention achieves the engagement and disengagement within a ninety-degree range of rotation. The preferred embodiment of this invention would be comprised of portions with generally elastic, but resilient, materials which will elastically deform at the strain represented by the interference fit overcome, but would possess a relatively high stiffness and natural frequency of vibration so as to spring back into their unstressed state with a minimum of damping. Some of the suitable materials would be polypropylene or acrylonitril butadine styrene (ABS), or metals having these characteristics. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of the preferred embodiment of the improved catheter introducer which depicts the two major portions axially disengaged from their locked state. 
     FIG. 2 is an side view of dilator portion of the introducer assembly showing the portion of the locking mechanism associated with the dilator hub. 
     FIG. 3 is a sectional view of the dilator portion depicted in FIG.  2 . 
     FIG. 4 is an enlarged sectional view of the dilator and introducer portions of the preferred embodiment showing the two portions engaged. 
     FIG. 5 is sectional side view of the introducer portion of the preferred embodiment. 
     FIG. 6 is an end view of the introducer portion of the preferred embodiment. 
     FIG. 7 is a side view of the dilator hub of the preferred embodiment, showing the groove and pocket which cooperate with the protrusions of the introducer hub. 
     FIG. 8 is an end view of the dilator hub. 
     FIGS. 9,  10 ,  11 , and  12  show, respectively, a hemostasis valve, a Tuohy-Borst adapter, an aseptic shield assembly, and an obturator, each connecting to the female portion of an introducer by means of the preferred embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description will disclose an embodiment of the invention in the context of a catheter introducer. However, this is intended to be illustrative only. The invention is not limited to applications in catheter introducers, and is applicable to other medical devices, as the reader will see. 
     Referring to FIG. 1, the catheter introducer assembly comprises a dilator portion  100  and an introducer portion  110 . The dilator portion  100  comprises a dilator hub  120  and a dilator tube  160  with a conical tapered distal tip  170 . The introducer portion is comprises an introducer hub  180  and an introducer tube  150  with a tip  190  fashioned onto the distal end. The introducer portion and the dilator portion are shown partly disengaged and unlocked in FIG.  1 . FIG. 1 also shows the common longitudinal axis  330  of the dilator portion  100  and the introducer portion  110 . 
     FIG. 2 shows the dilator of the preferred embodiment, comprising a hub  120  and a tube  160 . The dilator hub  120  includes a conically tapered male member  210  disposed on the distal end of the hub. In the preferred embodiment, the male member  210  is an integral part of the dilator hub  120 , is symmetric about the longitudinal axis of the hub, and is dimensioned to establish a slip fit relationship when fully engaged with the female member  220  of the introducer hub  180  (See FIG.  5 ). In the preferred embodiment, two grooves  260  are disposed on the male member  210 , with each of the grooves  260  having an open end  270  and a blind end  280 . In the preferred embodiment, the two grooves  260  are identical in geometry and axial location and positioned  180  degrees apart in radial orientation. The grooves  260  are oriented to require a clockwise rotation of the dilator hub  120  within the introducer hub  180  when viewed from the proximal end, so as to cause a locking engagement between the introducer hub  180  and the dilator hub  120 . The open end  270  of each groove  260  is distally disposed and broadened at the open end to readily receive the complementary protrusions  240  on the introducer hub  180  (see FIGS. 4 and 5) upon insertion of the dilator hub  120  into the introducer hub  180 . 
     FIGS. 4 and 5 more clearly show the protrusions  240  on the interior wall of the introducer hub engaged with the pockets  250  in the dilator hub. The two portions are depicted in the mechanically interlocked state in FIG.  4 . 
     Tracing the groove  260  from its broad distal opening  275  proximally, the width of the groove  260  decreases until it enters the distal opening of the groove knee  290  where the groove transitions from being generally axially aligned to generally circumferentially aligned. That is, the groove  260  has a generally axially aligned portion  295  and a generally circumferentially aligned portion  300 . At the distal opening of the knee  290 , the width is slightly greater than the greatest width of the introducer hub protrusion  240 . Similarly, as the width of the groove  260  diminishes, the radial distance to the bottom of the grooves as measured from the longitudinal axis  330  of the dilator hub  120  increases until the radial distance from the bottom of one groove  260  to the bottom of the other groove  260  is slightly less than the minimum radial distance from one introducer hub protrusion  240  to the other. Continuing to trace the groove  260  along the knee  290  in a proximal and increasingly radial direction, the distance from the bottom of the groove  260  to the longitudinal axis  330  of the dilator hub  120  (which is also the axis of rotation of the dilator hub  120 ) increases until the distance from the bottom of one groove  260  to the bottom of the other groove  260  is greater than the minimum radial distance from one introducer hub protrusion  240  to the other. 
     It would be possible to implement the invention with only one groove  260  and one complementary protrusion  240 , although the best mode for practicing the invention requires the use of at least two, or more, complementary grooves  260  and protrusions  240 . In the case of one groove  260 , and one protrusion  240 , it may be explained that the distance from the bottom of the groove  260  from the longitudinal axis  330  of the introducer hub (which is also the axis of rotation of the introducer hub) is greater than the radial distance from the longitudinal axis  330  of the dilator hub to the protrusion, at a point before the pocket  250 . And, the radial distance of the bottom of the pocket  250  from the longitudinal axis  330  of the introducer hub  180  is equal to or less than the radial distance from the longitudinal axis  330  of the introducer hub  180  to the protrusion  240 , so that the introducer hub  180  and the dilator hub  120  are again inhibited from axial and rotational disengagement. 
     Continuing to trace the groove  260  around its now generally circumferential portion  300  about the male member  210 , the radial spacing between grooves  260  continues until the blind end  280  of the groove  260  is approached. A pocket  250  is disposed at the blind end  280  of the groove  260 . In the preferred embodiment, the radial distance between the bottom of each pocket  250  in each of the two grooves  260  is equal to or less than the minimum radial distance from one introducer hub protrusion  240  to the other. The pocket  250  is otherwise designed geometrically to receive the complementary protrusion  240  on the introducer hub  180 . The axial distance separating the pocket  250  from the proximal end of the male member  210  of the dilator hub  120  is sufficient to allow for a fall locking engagement of the dilator hub  120  into the introducer hub  180  without causing dimensional interference between the two hubs  120  and  180  in the axial direction. In the preferred embodiment, the dilator hub  120  includes fins  130  to facilitate a greater degree of fingertip control by the user when locking or unlocking the dilator hub  120  with the introducer hub  180 . 
     Referring to FIGS. 5 and 6, the introducer portion  110  of the preferred embodiment comprises a hub  180  and an introducer tube  150 . The introducer tube  150  is sized to allow for easy passage over the dilator tubing  160 . Proximally disposed in the introducer hub  180  is a conically tapered female member  220  dimensioned to establish a slip fit relationship when fully engaged with the conical male member  210  of the dilator hub  120 . Two protrusions  240  are disposed in the proximal end of the female member  220 . Each protrusion  240  is directed inwardly toward the long axis of the hub, and faces the other protrusion. The protrusions  240  may be an integral part of the introducer hub  180  or may be included as inserts  320  which are permanently attached to the introducer hub  180 , depending on the actual manufacturing method and materials chosen. In FIGS. 5 and 6, they are shown incorporated into inserts  320 , which are permanently affixed within the introducer hub  180 . Each protrusion  240  is positioned within the introducer hub  180  in the same location axially and at the same distance from the longitudinal axis  330  of the hub  180  thus forming a symmetrical relationship. The distance separating the protrusions  240  from the proximal end of the hub  180  is sufficient to allow for a full locking engagement of the dilator hub  120  into the introducer hub  180  without causing dimensional interference between the two hubs  120  and  180  in the axial direction. 
     The dilator hub  120  and the introducer hub  180  are mechanically interlocked by first introducing the distal end of the dilator tube  160  into the proximal end of the introducer hub  180  and engaging the two axially until the distal end of the male member  210  of the dilator hub enters the female member  220  of the introducer hub  180 . Next, the user orientates the open ends of the dilator hub grooves  260  radially until they align with the protrusions  240  in the introducer hub  180 , to make possible further axial engagement. Upon further axial engagement, the grooves  260  engage and slidably cooperate with the introducer protrusions  240  until the protrusions  240  approach the knee  290  of the grooves  260 , at which point a combination of axial and radial relative motion is necessary to continue engagement. At the radially disposed point of the knee  290 , the relative movement between the two hubs  120  and  180  is generally radial and the protrusions  240  ramp into a state of dimensional interference. Further rotation causes compression in the outward radial direction of the introducer hub  180  via the protrusions  240 , and to a lesser extent a deflection in the inward radial direction of the dilator hub  120 . This deflection allows the further passage of the protrusions  240  along and within the grooves  260 , although the hubs  120  and  180  are now in a state of compressive stress and require a greater amount of torque to defeat the increased friction between the sliding surfaces and allow continued rotation. Once the protrusions  240  reach the blind end  280  of the grooves  260 , the dimensional interference between the two hubs  120  and  180  is substantially and rapidly reduced, and the stressed condition between the hubs  120  and  180  is relieved as the protrusions  240  fall into the pockets  250  and thus engage in the locked position. This rapid decompression caused by the protrusions  240  falling into engagement with the pockets  240  creates a tactile sensation to the user and provides a signal to the user that the locked condition has been achieved. The hubs  120  and  180  will remain in the locked position until the user reverses the engagement process. In the preferred embodiment of the invention, as shown in FIG. 7, the circumferential portion  300  of the grooves  260  is disposed at an angle, α,  340  greater than 90 degrees with the generally axial portion of the grooves  260 , which tends to urge the tapered male member  210  of the dilator hub  160  firmly into the tapered female member  220  of the introducer hub  180 . In the preferred embodiment this angle  340  is 92 degrees, or 2 degrees from the centerline of the circumferential portion  300  of each groove  260 . 
     As shown in FIG. 6, the introducer hub  180  preferably has a handle  140 . Removal of the introducer tube  150  may be accomplished by conventional means, such as the splitting away of the introducer tube  150 , which may have been pre-scored to allow this action. In this case, the handle  140  is constructed so as to allow the operator to grasp its two arms and break it in two along intentionally weakened areas  200 , thus beginning splits which remove the introducer tube  150  from the catheter or other medical device inserted into the body. In the preferred embodiment the dilator hub  120  has a conventional connection to other medical equipment. A Luer thread  225  and Luer taper  227  are shown in FIGS. 4 and 7. 
     The reader should understand that the invention is not limited to the catheter introducer described above. As shown in FIGS. 9-12, the hub  120  previously shown connected to a dilator portion  100  can be connected to other medical devices. Examples are the hub  120  containing the tapered male member  210  having the grooves  260  and pockets  250  previously described connected to a hemostasis valve  400 , a Tuohy-Borst adapter  410 , an aseptic catheter shield  420 , and an obturator  430 . Once the introducer portion  110  is in place within the desired blood vessel or body cavity, one of these instruments may be interchangeably connected to it. 
     The need for a mechanically simple yet secure introducer assembly capable of being releasably locked and disengaged has been attained by the present invention, as described above. Since certain changes could be made in the embodiment of the invention described above without departing from the spirit and scope of the invention, I intend that all matter contained in the foregoing description and drawings shall be interpreted as illustrative and not in a limiting sense. The reader should understand that the following claims are intended to cover all of the generic and specific features of the invention described in this application, and all statements of the scope of the invention which might be interpreted to fall between these features.