Abstract:
This document discusses, among other things, a medical device including an implantable medical device casing including an opening having an inner surface, a screw, and a non-conductive sleeve configured to fit within the opening, the non-conductive sleeve having an outer surface and an inner surface. An example screw includes a top portion including a driver interface, and a threaded bottom portion, at least one of the top portion and the bottom portion being non-conductive. The sleeve and implantable medical device casing are adapted to sealingly engage with the screw when assembled. In another example, a screw includes a compressible rib that forms a seal with a medical device. In an example method, a screw is pressed against a compressible component such as a sleeve or rib to form a seal against a medical device.

Description:
TECHNICAL FIELD  
       [0001]     This patent document pertains generally to sealed connections for medical devices and more particularly, but not by way of limitation, to radially sealing set screws for electrical insulation from body fluids.  
       BACKGROUND  
       [0002]     Implantable medical devices such as pacers and defibrillators commonly include one or more screws. For example, leads are typically coupled to a pacer or defibrillator using one or more set screws.  
         [0003]     Penetration of body fluids around a lead connection can lead to corrosion or other problems. It is also desirable to avoid current leakage through electrical pathways created by body fluids. In some instances, set screws are accessible from the outside of a medical device. This allows leads to be connected or disconnected to a device.  
         [0004]     In one prior art seal configuration, a screw is assembled into a device under a seal plug that includes a slit, which allows for passage of a wrench through the plug to tighten the set screw. The plug is configured so that the slit closes after the wrench is removed, thereby sealing the set screw below the plug from body fluids above the plug. An example of such a seal plug is described in U.S. Pat. No. 4,479,489. Another example of a seal is described in U.S. Pat. No. 3,908,668. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]     In the drawings, which are not necessarily drawn to scale, like numerals describe substantially similar components throughout the several views. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.  
         [0006]      FIG. 1  is a cross-sectional view of a medical device including a screw and a sleeve.  
         [0007]      FIG. 2  is an enlarged view of the medical device of  FIG. 2 .  
         [0008]      FIG. 3  is a side view of a screw that has ribs extending around an outer surface.  
         [0009]      FIG. 4  is a perspective view of the screw of  FIG. 3 .  
         [0010]      FIG. 5  is a top view of the screw of  FIG. 3 .  
         [0011]      FIG. 6  is a cross-sectional view the screw of  FIG. 3 .  
         [0012]      FIG. 7  is a partially cut-away perspective view of the screw of  FIG. 3 .  
         [0013]      FIG. 8  is a partial cross-sectional view of an alternative screw inserted in an opening in a medical device.  
         [0014]      FIG. 9  is a perspective view of another example screw.  
         [0015]      FIG. 10  is a cross-sectional view of a screw, a medical device casing, and a conductor.  
         [0016]      FIG. 11  is a cross-sectional view of a screw configured in a sleeve that has an inwardly-extending rib configured to seal against the screw.  
         [0017]      FIG. 12  is a cross-sectional view of a screw configured in a sleeve.  
         [0018]      FIG. 13  is a cross-sectional view of a device and another example screw having an external drive interface.  
         [0019]      FIG. 14  is a cross-sectional view of a device, a sleeve, and another example screw having an external drive interface.  
         [0020]      FIG. 15  is a flow chart that illustrates an example method. 
     
    
     DETAILED DESCRIPTION  
       [0021]     The following detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are also referred to herein as “examples.” 
         [0022]     An example screw includes a non-conductive portion, such as a non-conductive head or a non-conductive shaft. In an example, the screw is a set screw that coupled a conductor to an object, such as a medical device casing. In an example shown in  FIGS. 1-6 , the screw includes one or more protruding features, such as a rib, that presses against a non-conductive sleeve in an opening in a medical device. In an example, an insulative head is insert-molded over a shaft. An example screw that can be formed by insert-molding is shown in cross-section in  FIG. 2 .  FIG. 7  shows a shaft that includes a structure that facilitates torque transfer between a molded head and the shaft.  FIG. 8  shows another example screw that can be formed by insert-molding a non-conductive head over a shaft.  FIGS. 9 and 10  show a screw having a compressible rib that is sealable against an opening in a medical device casing, for example.  FIG. 11  shows another example configuration in which a sleeve has an inwardly-extending rib.  FIG. 12  shows another example in which a screw fits with a press-fit or interference fit in a sleeve.  FIGS. 13 and 14  show example screws that have external drives that interface with a socket wrench.  FIG. 15  is a flow chart that illustrates a method.  
         [0023]     Referring now to  FIGS. 1 and 2 , a screw  100  and sleeve  105  are insertable into an opening  115  in a casing  120  for a medical device  125 . In an example, the medical device  125  is an implantable device such as a pacer or defibrillator. In an example, the screw  100  is a set screw that secures a conductor in a header portion  130  of the casing  120 . Advancing the screw on threads in the casing  120  causes the screw to engage a conductor, such as a lead connector inserted through a second opening  116  in the casing. A shaft portion  101  of the screw  100  presses the conductor against an electrical contact  135  in the device  125  and fixes the conductor in the device. In an example, the shaft  101  extends through the electrical contact. In another example, the medical device includes a second electrical contact that touches the shaft. While the head portion  102  of the screw is shown having a larger cross-section than the shaft, in alternative examples the head has the same cross-section (e.g. same diameter) as the shaft, or is smaller than the shaft. In an example, the shaft is conductive. In implantable devices, it is desirable to avoid electrical conduction through the opening  115  in the casing  120 , for example through the screw  100  or through fluid in or around the opening. It is also desirable to avoid fluid contact with the electrical contact  135  or the conductor to avoid corrosion or other problems.  
         [0024]     Referring now to  FIG. 2 , in an example, the sleeve  105  includes an opening  200  in a top surface  205 , through which a wrench can be inserted and engaged with a driver interface  210  on the screw  100 . The screw  100  presses against an inner surface  215  of the sleeve  105  and sealably engages the sleeve. In an example, the screw  100  includes an outer surface  220  that has at least one wide portion  225  that has a larger outer dimension (e.g. diameter) than the inner surface  215  of the sleeve. In an example, the screw includes a raised rib  226  that includes the wide portion  225 . In the example shown in  FIG. 2 , the screw includes two raised ribs  226 ,  227 .  
         [0025]     In an example, the inner surface  215  of the sleeve is cylindrical. In an example, both raised ribs  226 ,  227  have the same outer dimension, e.g. the same outer diameter. In another example, one or more ribs has an outer dimension that is larger than the outer dimension of at least one other rib. The raised rib  226  (or other wide portion of the screw) presses against the sleeve  105  and sealably engages the sleeve.  
         [0026]     In an example, the sleeve  105  is compressible, and a rib  226  locally compresses the sleeve  105  to form a seal between the rib and the sleeve. In an example, the sleeve  105  includes silicone. The rib  226  locally increases the pressure on the sleeve  105  while still allowing the screw  100  to move past the sleeve as the screw advances on the threads. In an example, the screw includes only one rib. In other example, the screw includes multiple ribs, such as 2, 3, or 4 ribs, for example. In an alternative example, a rib is thicker (along the screw axis) or thinner than the rib shown in  FIGS. 1-2 . In another example, the screw rib is taller (radially relative to the outer surface of the screw) or shorter than the rib shown in the figures. The amount of interference with the sleeve can be controlled by varying the thickness of the ribs and the diameter (or height) of the ribs. Sealing and assembly characteristics can be controlled by varying the amount of interference between the screw and the sleeve.  
         [0027]     In an example, the sleeve includes a lip  230  that extends inwardly over the top surface  235  of the screw  100 . The lip  230  prevents the screw from falling out of the device  125  if the screw is disengaged with the threads. In an example, the lip defines the opening  200  in the sleeve  105 . In an example, the opening is circular and has a diameter that is smaller than an outer diameter of the top surface  235  of the screw  100 . In another example, the opening is slit shaped or oblong.  
         [0028]     Referring now to  FIG. 3 , a front view of the example screw  100  is shown.  
         [0029]     The shaft  101  includes external threads  305  which are engageable on internal threads in the medical device. In an example, the head  102  includes ribs  226 ,  227  near a bottom end  310  of the head. In an example, placing the ribs low on the head allows the ribs to seal throughout its range of travel. In other examples, the ribs are located elsewhere on the screw, including for example a middle portion or upper portion of the screw. In an example, the shaft  101  is conductive to allow electrical conduction through the screw between an electrical connector and an electrical contact  135  in the medical device shown in  FIG. 1 .  
         [0030]     Referring now to  FIGS. 4 and 5 , a perspective view of the screw is shown in  FIG. 4 , and a top view of the screw is shown in  FIG. 5 .  FIGS. 4 and 5  show the drive interface, which is an internal drive. In an example, the drive is a six lobed drive. In an alternative example, the drive is cross-shaped, as shown in  FIG. 9 . In another example, the drive is an external drive that interfaces with a socket wrench, as shown in  FIGS. 13 and 14 .  
         [0031]     Referring now to the cross-section shown in  FIG. 6 , in an example, the screw is formed from separate shaft and head components. In an example, an insulative head piece  600  is molded over a shaft member  605 , which is optionally conductive. In an example, the head  600  is insert-molded onto the shaft member  605 . In another example, the head is assembled, adhered, press fit, heat staked, sonically welded, or otherwise coupled to the shaft. In an example, the head  600  is formed from Polyetheretherketone (PEEK), polycarbonate, or a ceramic. In an example, the shaft is formed from titanium or stainless steel. In an example, the shaft member  605  includes features  610 ,  615  that transmit torque from the head  600  to the shaft member  605 .  
         [0032]      FIG. 7  shows a perspective view of an example shaft member  605  that includes four protruding member  705 ,  710 ,  715 ,  720 . In an example, the protruding members have surfaces  725 ,  730 ,  735 ,  740 ,  745 ,  750 ,  755 ,  760  that are approximately parallel with the shaft axis  701 . The surfaces are arranged to transmit torque from an overmolded head to the shaft member. The surfaces define an opening which is filled with polymer when the shaft is molded into the head. In an example, the surfaces are approximately perpendicular to each other.  
         [0033]      FIG. 8  shows a top-view of a medical device  801  including another example screw  800 . In the illustrated example, the screw  800  is insertable into the back  802  of the device. In an example, the screw  800  includes a head  805  molded over a shaft  810 . In an example, the head  805  is non-conductive. The shaft  810  is optionally conductive. In an example, the shaft  810  engages a connector  815  that includes an electrical conductor  812 . In an example, the connector  815  includes an opening  820 , into which the shaft is inserted to hold the connector in place in the device and in connection with an electrical contact  825  in the device.  
         [0034]     In an example, the head  805  is insert-molded over the shaft  810 . In an example, the head includes a shoulder  830  which engages an opposed surface  835  on a sleeve. The head  805  optionally includes one or more raised ribs  840  which press against the sleeve to form a seal that prevents body fluid from flowing into contact with the conductor  812  or electrical contact  825 .  
         [0035]     Another example screw is shown in  FIGS. 9 and 10 . The screw  900  has at least one compressible rib  905  extending around a head portion  910  of the screw. The illustrated example has three compressible ribs extending around the head  910 . In an example, a shaft  920  is insert-molded or otherwise coupled to the head. In an example, the head has a cylindrical outer surface  925 . In an example, the screw includes a cross-shaped drive interface  930 .  
         [0036]     Referring now to  FIG. 10 , the screw  900  is shown in an opening  1005  in a medical device casing  1010 . In an example, the screw  900  includes a groove  1015  and an O-ring  1020  in the groove. The O-ring  1020  forms the compressible rib  905  ( FIG. 9 ). A shaft portion  1025  of the screw engages threads in the casing  1010 . An end portion  1035  of the shaft engages a conductor  1030 .  
         [0037]      FIG. 11  shows a cross-section of another example screw and sleeve system  1100 . A sleeve  1105  includes an inwardly-extending rib  1115  that contacts an outer surface  1120  of a screw  1110 . The rib  1115  creates a seal between the sleeve  1105  and the screw  1110 . The sleeve includes an opening  1125  through which a wrench can be inserted to engage a drive interface  1130  in the screw.  
         [0038]      FIG. 12  shows a cross-section of another example screw and sleeve system. A screw  1205  and sleeve  1210  are sized so that there is an interference fit between an outer surface  1215  of the screw and an inner surface  1220  of the sleeve. When the sleeve  1210  and screw  1205  are inserted in an opening in a device, such as an opening in a medical device casing, pressure between the sleeve and screw creates a seal between the screw and the sleeve, and between the sleeve and an inner surface of the opening in the device.  
         [0039]      FIG. 13  shows another example screw. The screw  1300  includes an external drive interface  1305  and compressible ribs  1310  that press against in inner surface  1315  of an opening in a medical device casing  1320  or other component or device to create a seal between the screw and the device. In an example, the external drive allows for application of additional torque compared to internal-drive screws of similar size. The external drive also facilitates location of the screw and engagement of a wrench  1325  on the screw.  
         [0040]      FIG. 14  shows another example screw  1400  assembled with a sleeve  1405  in a medical device casing  1410 . The screw  1400  includes an external drive interface  1415  and a rib  1420  that presses against the sleeve.  
         [0041]      FIG. 15  is a flow chart that illustrates a method. At  1505 , a screw is inserted into an opening of an implantable device casing or other device. At  1510 , a compressible member is inserted into the opening. In an example, a sleeve is inserted into the opening with the screw, and the sleeve is the compressible member. In another example, the screw includes a compressible member such as a compressible O-ring situated in a groove. At  1515 , the compressible member is pressed against an inner surface of the opening with the screw. In an example, pressing the compressible member (the sleeve or O-ring, for example) creates and/or maintains a seal between the screw, the compressible member, and an inner surface of the opening. Optionally, at  1520 , the screw is engaged with a lip on the sleeve. The lip prevents the screw from slipping out of the opening if the screw is not engaged with threads. In another example, friction between the screw, the compressible member, and the inner surface of the opening in the device holds the screw in place. At  1525 , the screw is engaged on threads in the opening in the implantable device. In an example, the screw is advanced on the threads to engage a conductor and connect the conductor the device. At  1530 , engagement of the screw is verified by tactilely detecting whether the screw is protruding from the opening. In an example, an operator such as a surgeon feels the screw with a finger to verify that it is engaged. In an example, the screw sticks out slightly when the screw is fully engaged, and the operator can confirm that the screw is in place by feeling for the screw. In another example, the screw is flush when fully engaged, and the operator can confirm that the screw is fully engaged by feeling for the screw and confirming that it is not protruding from the device.  
         [0042]     The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.