Patent Publication Number: US-2020298010-A1

Title: Implantable medical device with locking datum arrangement between df4/is4 assembly and header

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional application of U.S. application Ser. No. 15/796,054 filed Oct. 27, 2017, which application claims priority to U.S. provisional application No. 62/436,896 filed Dec. 20, 2016. The contents of the above-mentioned patent applications are hereby incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     Aspects of the present invention relate to medical apparatus and methods. More specifically, the present invention relates to pulse generators and systems and methods for assembling pulse generators. 
     BACKGROUND OF THE INVENTION 
     Implantable pulse generators (IPGs) such as pacemakers and implantable cardioverter defibrillators (ICDs), which are used in the treatment of cardiac conditions, and neuromodulators or neurostimulators, which are used in chronic pain management or the actuation and control of other body systems, commonly include a housing, feedthrus, and a connector assembly that is enclosed in a header. Electrical stimulation originating in the housing is led to the connector assembly through feedthrus. The connector assembly serves to transmit electrical signals out of the IPG and to a lead electrically connected to the connector assembly, the lead transmitting electrical signals between the IPG and patient tissue. 
     Current header casting manufacturing processes and the associated methods of assembling the header and its enclosed connector assembly onto the housing require multiple operations, are skill intensive, and unavoidably time consuming. For example, at least some current cast-on header designs with quad pole (DF4/IS4) connectors require DF4/IS4 components to be stacked onto an inner core in in an arbor press to form a DF4/IS4 assembly. Once the tip block is placed on the end of the inner core, the entire stack of components is compressed axially together along the inner core using the arbor press. With the stack of components so compressed, a set screw of the tip block is tightened down on the inner core to lock the stack of components in the compressed state, thereby forming the DF4/IS4 assembly. The DF4/IS4 assembly is then placed into a mold for casting headers and, once molded, the cast header is attached to the housing (e.g., can) of the pulse generator via additional skill intensive and time consuming processes. 
     Injection molded headers are considered to be a way of reducing manufacturing costs. In at least some versions of the injection molding of headers, the DF4/IS4 tip block must be overmolded into the header. Unfortunately, some of the DF4/IS4 components are not capable of withstanding the high pressures of injection molding (e.g., upwards of 20,000 psi), resulting in the components needing to be installed after the injection molded header is procured. Without the DF4/IS4 tip block, the stack of components can no longer be locked as a sub-assembly prior to installation into the header, thereby increasing manufacturing complexity, costs and time. 
     There is a need in the art for systems and methods that reduces the complexity, time, and costs associated with the manufacturing headers employing DF4/IS4 connectors. 
     BRIEF SUMMARY OF THE INVENTION 
     Disclosed herein is an implantable electronic device. In one embodiment, the device includes a housing and a header connector assembly coupled to the housing. The header connector assembly includes a DF4/IS4 assembly and a header including a bore. The DF4/IS4 assembly is locked within the bore via a locking datum arrangement that exists between the DF4/IS4 assembly and the header. 
     In one embodiment, the locking datum arrangement is a push and twist locking datum arrangement. Thus, the DF4/IS4 assembly is pushed into the bore and then twisted within the bore to lock the DF4/IS4 arrangement within the bore via the locking datum arrangement. 
     In one embodiment, the DF4/IS4 assembly includes a strain relief and the locking datum arrangement exists between the strain relief and the header. 
     In one embodiment, the locking datum arrangement includes a male portion on the DF4/IS4 assembly and a female portion on the header. The male portion is received in the female portion when the DF4/IS4 assembly is locked within the bore via the locking datum arrangement. 
     In one embodiment, the locking datum arrangement includes a female portion on the DF4/IS4 assembly and a male portion on the header. The male portion is received in the female portion when the DF4/IS4 assembly is locked within the bore via the locking datum arrangement. 
     In one embodiment, the locking datum arrangement includes a key and a datum notch. The key radially extends from the DF4/IS4 assembly and the datum notch radially extends from the bore into the header. The key is received in the datum notch when the DF4/IS4 assembly is locked within the bore via the locking datum arrangement. 
     The bore may include a groove that extends proximally from a distal opening of the bore, the groove being sized and shaped to receive the key as the DF4/IS4 is inserted into the bore. The datum notch may extend from the groove such that the DF4/IS4 assembly can be rotated to cause the key to exit the groove and enter the datum notch. A distal face of the key may make abutting contact with a distal datum wall of the datum notch when the DF4/IS4 assembly is locked within the bore via the locking datum arrangement. 
     In one embodiment, the device further includes an implantable lead including a DF4/IS4 connector end receivable within a receptacle defined by at least a portion of the DF4/IS4 assembly. The device may be an implantable pulse generator. 
     Also disclosed herein is a method of manufacturing an implantable electronic device. In one embodiment the method includes: inserting a DF4/IS4 assembly into a bore of a header; and rotating the DF4/IS4 assembly within the bore to engage a locking datum arrangement that exists between the DF4/IS4 assembly and the header, the locking datum arrangement preventing the DF4/IS4 assembly from being withdrawn from the bore. 
     In one embodiment, the DF4/IS4 assembly is supported on a core pin when the DF4/IS4 assembly is inserted into the bore. 
     In one embodiment, the header includes a tip block embedded in the header. A free end of the core pin projects proximally from the DF4/IS4 assembly. The free end is received in the tip block before the DF4/IS4 assembly is rotated to engage the locking datum arrangement. 
     In one embodiment, the bore includes a groove that extends proximally from a distal opening of the bore. The DF4/IS4 assembly includes a key radially extending from the DF4/IS4 assembly. The key moves along the groove when the DF4/IS4 assembly is inserted into the bore. 
     In one embodiment, a datum notch extends from the bore into the header. Rotating the DF4/IS4 assembly causes the key to extend into the datum notch, thereby engaging the locking datum arrangement. 
     In one embodiment, engaging the locking datum arrangement compresses the DF4/IS4 assembly. 
     In one embodiment, the DF4/IS4 assembly and header, when locked together via the locking datum arrangement, form at least part of a header connector assembly. In such a situation, the method may further include welding the header connector assembly to a housing of the implantable electronic device. The method may continue with epoxy backfilling of the header connector assembly. 
     Depending on the embodiment, the method may result in an implantable electronic device that is an implantable pulse generator. 
     While multiple embodiments are disclosed, still other embodiments of the present disclosure will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the disclosure. As will be realized, the invention is capable of modifications in various aspects, all without departing from the spirit and scope of the present disclosure. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of a proximal end portion (i.e., lead connector end) of a DF4/IS4 lead. 
         FIG. 2  is an isometric view of a cardiac pacemaker/defibrillator unit (i.e., implantable pulse generator (IPG)) incorporating connector junctions or terminals for communication with one or more electrodes. 
         FIG. 3  is an exploded isometric view of a DF4/IS4 assembly and a core pin on which the DF4/IS4 assembly is assembled. 
         FIG. 4  is a series of isometric views illustrating the assembly of the header connector assembly from a header and a connector assembly that includes DF4/IS4 assemblies. 
         FIG. 5  is a flow chart outlining the process illustrated in  FIG. 4 . 
         FIG. 6  is an isometric view of a step in the process outlined in  FIGS. 4 and 5 , wherein the DF4/IS4 assembly is assembled on the core pin, the core pin occupies the resulting lead connector receiving bore or receptacle, and the DF4/IS4 assembly is being positioned for insertion into a predefined bore in the injection molded header that includes the rest of the connector assembly. 
         FIG. 7  is an enlarged isometric view of a distal end of the strain relief of the DF4/IS4 assembly of  FIG. 6 . 
         FIG. 8  is an enlarged isometric view of a distal end of the the predefined bore in the injection molded header of  FIG. 6 . 
         FIG. 9  is an enlarged isometric view of the DF4/IS4 assembly, and more specifically, the strain relief, being received in the predefined bore in the injection molded header. 
         FIG. 10  is an enlarged side view of the DF4/IS4 assembly fully received in the predefined bore in the injection molded header, the key occupying the datum notch and the distal face of the key abutting the distal datum wall in planar contact. 
         FIG. 11  is an enlarged distal end view of the DF4/IS4 assembly in the situation depicted in  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
     Implementations of the present disclosure involve an implantable electronic device such as an implantable cardiac device (ICD) or an implantable pulse generator (IPG). The IPG administers electrotherapy or other neurostimulation via an implantable lead having a lead connector end on a proximal end of the implantable lead. The IPG includes a housing or can and a connector assembly enclosed in a header to form a header connector assembly that is coupled to the housing or can. The header connector assembly has at least one DF4/IS4 assembly that defines at least one lead connector receiving bore or receptacle. The DF4/IS4 assembly includes electrical contacts of the connector assembly that make electrical contact with corresponding electrical terminals on the lead connector end on the proximal end of the implantable lead when the lead connector end is plugged into or otherwise received in the lead connector receiving bore or receptacle. 
     Via the electrical connection between the corresponding electrical terminals of the lead connector end and the electrical contacts of the lead connector receiving bore, electrical signals can be administered from the IPG and through the lead to patient tissue. Similarly, but in reverse, electrical signals originating in patient tissue can travel via the lead to the IPG to be sensed at the IPG. 
     The implantable electronic device configurations and methods of assembly disclosed herein are advantageous for at least the reason that they simplify the process of manufacturing the header connector assembly of an IPG, wherein the connector assembly employs DF4/IS4 assemblies. Specifically, a twist and lock interface between a strain relief of the DF4/IS4 assembly and a bore of an injection molded header is provided in the form of a keyed locking datum arrangement, which allows the DF4/IS4 assembly to be aligned, inserted, rotated, compressed, and locked together within the bore without the use of additional tooling. The keyed locking datum arrangement provides the axial compression required within the DF4/IS4 assembly to prevent epoxy from leaking into the components and spaces of the DF4/IS4 assembly when the DF4/IS4 assembly is being encapsulated in epoxy during the backfill process, and this benefit is provided without the use of any additional tooling or set screws. Additionally, there is no risk of damaging the pre-molded headers in tooling, no set screw is required to lock, and the keyed locking datum arrangement removes the variability in axial compression caused by manufacturing via an arbor press. 
     Before beginning a detailed discussion of the assembly of the header and the connector assembly employing DF4/IS4 assemblies to form the header connector assembly, a general discussion is first given regarding features of a DF4/IS4 lead connector end at the proximal end of an implantable medical lead followed by a general discussion of the features of an IPG. 
     A. Overview of a DF4/IF4 Connector End and an IPG. 
       FIG. 1  shows a proximal end portion  10  of a conventional DF4/IS4 lead, but is generally representative of any type of implantable lead whether in the cardiac, pain management or other medical treatment space. The diameter of such a lead may be made a sufficiently small diameter to facilitate the lead&#39;s implantation into small veins such as those found in the coronary sinus region of the heart and to allow implantation of a plurality of leads into a single vessel for multi-site or multi-chamber pacing. 
     As is well known in the art, DF4/IS4 leads typically consists of a tubular housing of a biocompatible, biostable insulating material containing an inner multifilar conductor coil that is surrounded by an inner insulating tube. The inner conductor coil is connected to a tip electrode on the distal end of the lead. 
     In one embodiment and moving radially outwardly from the inner insulating tube is a series of surrounding concentric alternating layers of multifilar conductor coils and insulating tubes. Specifically, there may be two intermediate multifilar conductor coils and an outer multifilar conductor coil, each of the concentric coils being isolated from the other via an intervening concentric insulating tube. The entirety of these concentric coil layers and intervening concentric insulating tubes are enclosed within the outer tubular housing. 
     The two intermediate conductor coils and the outer conductor coil are individually connected to respective anodal ring electrodes and, in some cases, a defibrillation coil, all of which are located near the distal region of the lead. The layers of inner insulation tubes are intended to electrically isolate the conductor coils from each other, thereby preventing any internal electrical short circuit, while the housing protects the entire lead from the intrusion of body fluids. These insulating materials are typically either silicone rubber, polyurethane or a combination thereof. 
     In some embodiments, any one or more of the conductor coils may be replaced with a corresponding multifilar cable conductor. Such cable conductors may extend through respective wall lumens within a multilumen housing in order to reduce even further the overall diameter of the lead. 
     The proximal lead end portion  10  shown in  FIG. 1  includes a lead connector end  11  that conforms to the DF4/IS4 standard and includes a plurality of proximal terminals or contacts, namely, a straight pin tip contact  12 A, and three ring contacts  123 ,  12 C,  12 D, respectfully, as one advances in a distal direction. The pin tip contact  12 A is electrically coupled to the tip electrode on the distal end of the lead via the inner conductor coil, and the ring contacts  12 B,  12 C, and  12 D are electrically coupled to ring electrodes (and where applicable, a defibrillation coil) via the respective other intermediate and outer conductor coils or, alternatively, via conductor cables residing within lumens of the housing, Each of the plurality of contacts  12 A,  12 B,  12 C.  12 D is separated from its neighbor by a sealing surface  13 . The lead connector end  11  proximally extends from the proximal end of the tubular lead body  14 , which is enclosed by the above-described outer tubular housing  16 . 
     The tip and ring terminals or contacts of the lead connector end may each be engaged by a conductive garter spring contact or other resilient electrical contact element in a corresponding lead connector receiving bore of the DF4/IS4 assembly of the connector assembly of the header connector assembly, the resilient electrical contact element being carried by a DF4/IS4 assembly of the connector assembly enclosed in the header as described below. The sealing surfaces  13  on the lead connector end  11  interface with spaced-apart pairs of seal rings in the lead connector receiving bore of the header connector assembly, the seal rings abutting against in a fluid-sealing manner the outer circumferential surface of the sealing surfaces  13  of the lead connector end  11 , thereby preventing body fluids from reaching the electrical terminals and contacts when the lead connector end  11  is plugged into the corresponding lead connector receiving bore. 
     With the lead connector end  11  of the lead inserted in the lead connector receiving bore of the header connector assembly, the tip and ring terminals  12 A,  12 B,  12 C,  12 D are electrically coupled via the contacts of the DF4/IS4 assembly of the connector assembly and a feedthru to the electronic circuits within the hermetically sealed housing of the IPG (e.g., cardiac pacemaker, ICD, or other implantable tissue stimulation and/or sensing device such as those used in pain management, etc.). 
       FIG. 2  shows a multi-site or multi-chamber cardiac pacemaker/defibrillator unit that is generally representative of any type of IPG  20  incorporating a header connector assembly  22  coupled to a housing  24 . The header connector assembly  22  includes a header  40  enclosing a connector assembly  42 , both of which are depicted in the process of being assembled together in  FIG. 4  discussed below. The IPG  20  is of a conventional design, including a hermetically sealed housing  24 , which is also known as a can or casing. The housing  24  encloses the electronic components of the IPG  20  with the header connector assembly  22  mounted along a top surface  26  of the housing  24 . 
       FIG. 2  illustrates that, in some embodiments, the header connector assembly  22  may include four or more lead connector receiving bores or receptacles  30 ,  31 ,  32 ,  33  for receiving the lead connector ends of four implantable leads.  FIG. 2  also shows the proximal end portion  10  of a lead, wherein the lead connector end on the proximal end portion  10  of the lead is received in a corresponding receptacle  32 . In other embodiments, the header connector assembly  22  includes two receptacles comprising a single pair of receptacles (i.e., receptacles  30  and  33 ) for receiving the proximal ends of leads such as, for example, conventional bipolar leads and/or conventional cardioverting and/or defibrillating leads. 
       FIG. 3  is an exploded isometric view of a DF4/IS4 assembly  48  and a core pin  50  on which the DF4/IS4 assembly  48  is assembled. As shown in  FIG. 3 , the core pin  50  includes an O-ring  52  on a distal end of the core pin, and the DF4/IS4 assembly  48  includes a strain relief  54 , four seal assemblies  56 , and three contact assemblies  58 . The strain relief, seal assemblies and contact assemblies are annular or donut-shaped and each have a central opening  59 . When the strain relief, seal assemblies and contact assemblies are stacked together to form a DF4/IS4 assembly  48 , the openings  59  combine to form a lead connector receiving bore or receptacle  30  of the header  40  of the header connector assembly  22 . 
     As illustrated in  FIG. 3 , the central opening  59  of each contact assembly  58  of the DF4/IS4 assembly  48  contains a conductive garter spring contact  60  that biases into contact with the respective ring terminal  12 B,  12 C,  12 D of the lead connector end  11  when the lead connector end is received in a lead connector receiving bore or receptacle  30  of the DF4/IS4 assembly  48 . 
     B. Assembly of Header Connector Assembly onto IPG Housing. 
       FIG. 4  is a series of isometric views illustrating the assembly of the header connector assembly  22 , and  FIG. 5  is a flow chart outlining the process illustrated in  FIG. 4 . As can be understood from  FIGS. 4 and 5 , DF4/IS4 tip blocks  64 , other connector blocks  66 , and conductors  68  are welded together as indicated at  400  in  FIG. 4  [block  500 ]. As shown at  410 , these components  64 ,  66 ,  68  are overmolded by a header  40  via an injection molding process [block  510 ], the header including predefined bores  62  leading to, and coaxial with, the open centers of the blocks  64 ,  66 . 
     As depicted at  420  of  FIG. 4 , and shown in more detail in  FIG. 6 , as part of the process of assembling the header connector assembly  22 , the DF4/IS4 assembly  48  has been assembled on the core pin  50 , the core pin occupies the resulting lead connector receiving bore or receptacle  30 , and the DF4/IS4 assembly  48  is positioned for insertion into the respective predefined bore  62  in the injection molded header  40  to become part of the overall connector assembly  42  [block  520 ]. 
     As shown in  FIG. 6 , the core pin  50  extends through the open centers  59  of the strain relief  54 , four seal assemblies  56 , and the three contact assemblies  58  such that the strain relief, four seal assemblies and three contact assemblies are stacked together with the strain relief on the extreme distal end of the core pin and the order of the other elements being seal assembly, contact assembly, seal assembly, contact assembly, seal assembly, contact assembly, and seal assembly, moving distal to proximal along the stacked components of the DF4/IS4 assembly  48 . 
     So far in the process as discussed above and as can be understood from  FIGS. 4-6 , the header  40  is first injection molded about the DF4/IS4 tip block  64  [block  510 ], which is located at the interior end (i.e., extreme proximal end) of the predefined bore  62  in the injection molded header  40 . As reflected at  430  of  FIG. 4 , the assembled DF4/IS4 assembly  48  is proximally inserted into the predefined bore  62  to become part of the connector assembly  42  such that the proximal free end of the core pin  50  leads into the bore  62  to be eventually fully received in a central opening of the tip block  64  when the DF4/IS4 assembly  48  is fully received in the bore  62  [block  530 ]. As indicated at  430  in  FIG. 4 , the ribbons  70  are welded to the conductors and the carriers  72  are removed [block  535 ], thereby completing the header connector assembly  22 . 
     As shown at  440  of  FIG. 4 , the header connector assembly  22  is welded to the can or housing  24  [block  540 ]. Specifically, the ribbons  70  are welded to the feedthru of the can or housing  24 . Per  450 , the header connector assembly  22  is epoxy backfilled at the location indicated by Arrow A [block  550 ]. Finally, as shown at  460 , septums  74  are installed to complete the IPG [block  560 ]. 
     C. Keyed Interface of Strain Relief and Predefined Bore of Injection Molded Header. 
     As can be understood from  FIGS. 3-6  and explained above, during the process of assembling the connector assembly  42  and the header connector assembly  22 , the DF4/IS4 tip block  64  is not initially part of the DF4/IS4 assembly  48 , but is instead part of the overmolded header  40 . As illustrated in  FIGS. 4 and 6 , the DF4/IS4 tip block  64  is molded into the header  40  and awaits to receive of the proximal free end of the core pin  50  when the DF4/IS4 assembly  48 , and its supporting core pin  50 , are inserted as a whole into the predefined bore  62  in the injection molded header  40  to become part of the overall connector assembly  42 . 
     Without the DF4/IS4 tip block being part of the DF4/IS4 assembly  48 , the stack of components  54 ,  56 ,  58  of the DF4/IS4 assembly  48  (see  FIG. 3 ) can not be locked as a sub-assembly prior to installation into the predefined bore  62  in the injection molded header  40 . Thus, the components  54 ,  56 ,  58  of the DF4/IS4 assembly  48  are placed onto the inner core pin  50  and immediately installed into the predefined bore  62  in the injection molded header  40 , as reflected in  FIGS. 3, 4 and 6 . To avoid the need to fixture and locate the pre-molded header  40 , the strain relief  54  and predefined bore  62  in the injection molded header  40  have been keyed to accept a locking feature, as discussed below with respect to  FIGS. 7 and 8 . This keyed interface between the strain relief  54  and the bore  62  allows the user to simply insert and rotate the strain relief  54  using tweezers or a spanner bit to “Twist and Lock” the DF4/IS4 assembly  48  into place within the bore  62 , as shown in  FIGS. 9-11  and discussed below. 
     As indicated in  FIG. 7 , which is an enlarged isometric view of a distal end of the strain relief  54  of the DF4/IS4 assembly  48  of  FIG. 6 , the strain relief includes a cylindrical outer circumferential surface  80 . Defined on or in the outer circumferential surface  80  of the strain relief may be a number of features, including, for example, a number of longitudinally extending radially protruding ribs  82  extending proximal-distal on the strain relief, a circumferentially extending and radially recessed groove  84  near the distal end of the strain relief, and a pair of opposed notches  86  extending proximally from the distal end of the strain relief and spaced 180 degrees from each other about the outer circumferential surface of the strain relief  50 . These notches  86  taper as they proximally extend from the distal end of the strain relief and can be used as assembly tool engagement features to be engaged by a tool (e.g., tweezers, spanners, etc.) to cause the DF4/IS4 assembly  48  to rotate about the longitudinal axis of the core pin  50  when the DF4/IS4 assembly  48  and its supporting core pin  50  are being installed into the predefined bore  62  in the injection molded header  40 , as reflected in  FIGS. 3, 4 and 6 . 
     As illustrated in  FIG. 7 , the key  88  radially projects from the outer circumferential surface  80  of the strain relief  54  and is located proximal of the groove  84 . In one embodiment, the key  88  includes an arcuate lateral or side surface  90  that extends distal-proximal between a proximal face  91  and a distal face  92  that is opposite the proximal face, both faces being perpendicular to the side surface  90 . As a result of such a configuration, the key  88  can be said to have a half-disc shape or semi-circular shape, as can be understood from  FIG. 7 . The faces  91 ,  92  are perpendicular to a longitudinal center axis of the DF4/IS4 assembly  48 . 
     In one embodiment, arcuate lateral surface  90  has a radius of approximately 0.025″. In other embodiments, the radius can be smaller or larger. 
     As depicted in  FIG. 8 , which is an enlarged isometric view of a distal end of the the predefined bore  62  in the injection molded header  40  of  FIG. 6 , the bore  62  includes a cylindrical inner circumferential surface  100 . This inner circumferential surface  100  is of a complementary or corresponding shape and size relative to the outer circumferential surface  80  of the strain relief  54  of  FIG. 7  such that the bore  62  can receive the DF4/IS4 assembly  48 , and more specifically, the strain relief  54  in mating fashion, as can be understood from  FIG. 4 . 
     As illustrated in  FIG. 8 , the longitudinally extending groove  102  extends distal-proximal in the inner circumferential surface  100  from the distal opening of the bore  62 . The groove  102  is of a shape and size that is complementary and corresponding to the shape of the key  88  such that the groove  102  can receive the key  88  as the strain relief  54  proximally moves within the bore  62  as the DF4/IS4 assembly  48  is inserted into the bore  62 , as can be understood from  FIG. 4 . 
     In one embodiment, the groove  102  has a diameter of approximately 0.053″. In other embodiments, the diameter can be smaller or larger. 
     As reflected in  FIG. 8 , a datum notch  104  extends perpendicularly from the groove  102  and the inner circumferential surface  100  of the bore  62 . The datum notch  104  includes a distal datum wall  106  that is perpendicular to a longitudinal center axis of the bore  62  and the inner circumferential surface  100  of the bore  62 . 
     In one embodiment, the datum notch has a distal-proximal width between its distal datum wall  106  and its proximal datum wall of approximately 0.055″. In other embodiments, the width can be smaller or larger. 
     In one embodiment, the key and datum notch may be designed to be injection moldable without undercut. 
     As can be understood from  FIG. 4  and, more particularly,  FIG. 9 , which is an enlarged isometric view of the DF4/IS4 assembly  48 , and more specifically, the strain relief  50 , being received in the predefined bore  62  in the injection molded header  40 , the key  88  is aligned with, and slid into, the groove  102  to allow the strain relief, and by extension, the DF4/IS4 assembly, to fully enter the bore  62 . Arrow A indicates the proximal displacement of the DF4/IS4 assembly  48  relative to the injection molded header  40  as the key  88  is aligned with and enters the groove  102  while the DF4/IS4 assembly  48  is received in the bore  62 . 
       FIGS. 10 and 11  are, respectively, an enlarged side view and an enlarged distal end view of the DF4/IS4 assembly  48  fully received in the predefined bore  62  in the injection molded header  40 , the key  88  occupying the datum notch  104  and the distal face  92  of the key  88  abutting the distal datum wall  106  in planar contact. As can be understood from  FIGS. 9-11 , once the DF4/IS4 assembly  48  has been fully received in the bore  62  and the key  88  has become aligned with the datum notch  104 , the DF4/IS4 assembly can be rotated clockwise to cause the key  88  to move from the groove  102  and into the datum notch  104 . Arrows B and C in  FIGS. 10 and 11 , respectively, indicate the clockwise rotation of the DF4/IS4 assembly  48  within the bore  62  and relative to the injection molded header  40 , thereby causing the key  88  to leave the confines of the groove  102  and enter the confines of the datum notch  104 . The distal face  92  of the key  88  abuts against the distal datum wall  106  in planar contact, thereby locking the DFT/IS4 assembly  48  fully inserted in the predefined bore  62  and preventing the DF4/IS4 assembly  48  from distally withdrawing from the bore  62 . The manufacturing process then continues as outlined above in  FIG. 4  at  430 ,  440 ,  450  and  460  and also  FIG. 5  at  530 ,  535 ,  540 ,  550  and  560 . 
     The embodiments of the push and twist keyed locking datum arrangement described above are provided in the context of the key being located on the DF4/IS4 assembly and, more specifically, on the exterior of the strain relief, and the datum being a complementary recess in the header and, more specifically, a complementary recess radially extending from the bore of the header. In other words, the locking datum arrangement described above includes a male portion of the DF4/IS4 arrangement interfacing in a male/female locking arrangement with a female portion of the header. 
     In other embodiments, the push and twist keyed locking datum arrangement can be reversed such the key is located on the header and the datum is located on the DF4/IS4 assembly and, more specifically, on the strain relief. In other words, the locking datum arrangement may be configured to include a female portion of the DF4/IS4 arrangement interfacing in a male/female locking arrangement with a male portion of the header. 
     In summary, on account of the keyed locking datum arrangement between the strain relief of the DF4/IS4 assembly and the bore of the injection molded header, the DF4/IS4 assembly can be simply inserted and twisted or rotated using tweezers or a spanner bit. Thus, the twist and lock interface between the strain relief and the bore of the injection molded header is advantageous because the keyed locking datum arrangement allows the DF4/IS4 assembly to be aligned, inserted, rotated, compressed, and locked together within the bore without the use of additional tooling. The keyed locking datum arrangement provides the axial compression required within the DF4/IS4 assembly to prevent epoxy from leaking into the components and spaces of the DF4/IS4 assembly when the DF4/IS4 assembly is being encapsulated in epoxy during the backfill process, and this benefit is provided without the use of any additional tooling or set screws. Additionally, there is no risk of damaging the pre-molded headers in tooling, no set screw is required to lock, and the keyed locking datum arrangement removes the variability in axial compression caused by manufacturing via an arbor press. 
     The foregoing merely illustrates the principles of the invention. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous systems, arrangements and methods which, although not explicitly shown or described herein, embody the principles of the invention and are thus within the spirit and scope of the present invention. From the above description and drawings, it will be understood by those of ordinary skill in the art that the particular embodiments shown and described are for purposes of illustrations only and are not intended to limit the scope of the present invention. References to details of particular embodiments are not intended to limit the scope of the invention.