Abstract: An implantable cardiac stimulator delivers a first electrical shock via implantable stimulating electrodes at a time when there is substantially no flow of blood. At least one of the stimulating electrodes is disposed in a blood flow path of the cardiovascular system. The first shock is of insufficient energy level to cause defibrillation. An electrical potential is measured as a function of time between the blood-contacting electrode and a reference electrode following delivery of the first shock to obtain a first potential equilibration function under no-flow conditions. A second therapeutic electrical shock, of sufficient energy level to effect defibrillation, is delivered via the stimulating electrodes. A second potential equilibration function is measured following delivery of the second shock. The first and second potential equilibration functions are compared, and if the two functions are sufficiently different in morphology, it is determined that blood is flowing.

Abstract: A patellar prosthesis includes an articulation component having a prosthetic articulation surface and a base component for fixation to resected patellar bone. Each of the articulation and base components include planar bearing surfaces in sliding engagement. The base component includes a fixed pin extending perpendicularly from its respective planar bearing surface. The articulation component includes an elongate groove in its respective planar bearing surface. The pin and groove have complementary wall profiles that provide for an elastic snap-retention of the pin within the groove. The articulation component is free to rotate about the axis of the pin received within the groove, and is free to translate parallel to the planar bearing surfaces, limited by the length of the groove. The articulation component enjoys only one rotational degree of freedom, and only two translational degrees of freedom.

Abstract: A method for making a lead body for use in a conductive insulated lead for a cardiac stimulator. Alternating layers of conductive and insulative thermosetting polymers are extruded through successively arranged heated nozzles of increasing outlet diameter. As the inner layer emerges from its nozzle in a thermoset state, it is passed through a following nozzle while surrounded by another thermosetting polymer that is extruded through that following nozzle. The second polymer becomes thermoset and bonded to the already thermoset inner layer. Successive nozzles can be provided to form successive layers of alternating conductive and insulative polymers, where the conductive layers serve as the electrical conductors of the lead.

Abstract: An instrument for holding an acetabular cup. An elongate hollow tubular member has a proximal end and a distal end and a generally transverse end face at the distal end. A pair of pins extend axially outwardly from the transverse end face. An elongate rod is mounted within the elongate hollow tubular member for axial movement relative thereto. A ball is attached to one end of the elongate rod proximate the transverse end face and is moveable together with the elongate rod. The ball has a spherical surface for engaging a portion of the inner bearing surface of an acetabular cup that extends radially inwardly relative to the polar axis of the acetabular cup. Retraction of the ball toward the end face of the tubular member draws the cup toward the end face. Corresponding holes in the rim of the cup receive the pins to prevent lateral movement of the cup on the end face of the instrument.

Abstract: An angled orthopedic surfacer and guide which is particularly useful in connection with revision surgeries for femoral hip prostheses. The surfacer comprises a drive shaft connected to a milling head through a U-joint. A housing for the U-joint supports an adjustable spacer which can be moved to selected positions to control the depth of cut. A pivoting guide connects the surfacer to a rasp used to ream out a cavity for a prosthesis. The surfacer can be pivoted around a proximal and medial side of the rasp to cut away bone.

Abstract: The present invention relates to prosthetic knee devices providing for an expanded range of translational movement without substantially reducing the risk of inadvertent dislocation of the knee when implanted. The devices of the invention achieve the expanded range of motion without requiring a substantial posterioral shifting of the points of contact between the femoral and tibial components. The prostheses of the invention also reduce the risk of breakdown of the plastic components of the prosthesis and the underlying resectioned proximal tibia surface by providing an expanded, winged fixation post.

Abstract: A transvenous implantable defibrillation lead includes a conductor and inner and outer coaxial cylindrical electrodes. The inner electrode is connected to the conductor, and the outer electrode is connected to a sheath overlying the conductor in rotatable relationship thereto. The sheath is fixed to the outer cylindrical electrode so that rotation of the sheath relative to the conductor results in rotation of the inner and outer cylindrical electrodes relative to each other. The inner electrode has a plurality of hooks extending generally transversely and tangentially thereto, with the hooks being biased such that the terminal ends of the hooks tend to spring outwardly from the inner electrode. The hooks are constrained against the inner cylindrical electrode by the outer cylindrical electrode, except that a window in the outer electrode permits the hooks to spring outwardly therethrough upon rotation of the outer electrode relative to the inner electrode.

Abstract: A method of verifying whether an atrium of the heart has been captured by an atrial cardiac stimulation pulse. An atrial signal is sensed via an electrode located in the atrium during a period of time from before delivery of the stimulation pulse to after delivery of the stimulation pulse. The sensed signal is analyzed by detecting whether a P-wave occurred prior to delivery of the cardiac stimulation pulse such that stimulation pulse would have been delivered within a refractory period. If a P-wave did not occur, the slope of the sensed waveform signal is determined within a selected interval of time beginning at a selected time after the time of delivery of the stimulation pulse. A capture status signal is generated that indicates non-capture, if a P-wave was detected, or capture, if a P-wave component was not detected and the determined slope of the sensed waveform signal surpasses a pre-selected slope threshold demarcating capture from non-capture.

Abstract: An intercondylar notch cutter using a plunge milling bit and bit guide which engages parallel tracks in a trial prosthesis. The intercondylar notch cutter comprises a cutting bit and a guide sleeve. The cutting bit can be thrust into the femur and then translated through the femur cutting a notch without removing the trial prosthesis. The bit is supported by a guide or housing with a guide platform which extends medially and laterally from the guide. Two condyle articulating surfaces on the platform slidingly engage a condyle surface on a trial prosthesis. Along the condyle surfaces on the trial prosthesis are two parallel grooves. Posts on the notch cutter are slidingly received within the grooves. A surgeon first places the trial implant on the femur without cutting an intercondylar notch. The surgeon can proceed immediately to cut an intercondyle notch without removing the femoral trial prosthesis.

Abstract: A connector terminal in a cardiac stimulator for receiving a connector pin of an associated lead includes a hollow box member having opposite end walls defining a first bore for receipt of the connector pin. A ring member movably disposed within the box member defines a second bore generally aligned with the first bore for also receiving the connector pin. A threaded neck connected to the ring member extends perpendicular to the second bore and is received within a through bore of the box member that is disposed perpendicular to the first bore. An internally threaded cap threadedly engages the threaded neck and bears in a thrust bearing relationship on the box portion. As the cap is rotated, the ring portion is drawn upwardly as the cap presses downwardly on the box portion, causing the second bore to be moved transversely out of alignment with the first bore. A connector pin received through both first and second bores is clamped therebetween and retained against axial withdrawal from the connector terminal.

Abstract: A method of communicating data between an external device and an implantable medical device wherein a first pulse is transmitted as electromagnetic energy from one device to the other, is received and stored as electrostatic energy in the second device and, after a delay period representing data to be communicated, the stored energy is released and transmitted as electromagnetic energy back to the first device. A communications circuit in the implantable device for accomplishing the method includes an antenna coil, a non-linear electronic component in circuit communication with the antenna coil, a storage capacitor in circuit communication with the antenna coil and non-linear electronic component for storing energy received by the antenna coil, and a switch for selectively connecting the charged storage capacitor and the antenna coil to discharge the charge stored in the capacitor into the antenna coil.

Abstract: A lead insertion tool for use with an implantable cardiac stimulator having a connector receptacle and for use with an associated lead having a connector pin for insertion within the connector receptacle. The tool includes spring biased jaws for gripping the lead at a location set back from the terminus of the connector pin. An insertion stop is connected to the jaw for engaging the cardiac stimulator to limit the depth of insertion of the connector pin within the connector receptacle. An integral depth gauge extends from the gripping jaws toward the terminus of the connector pin for gauging the location of the insertion stop relative to the terminus of the connector pin. Full insertion of the connector pin within the connector receptacle is assured when the insertion stop engages the cardiac stimulator. The depth gauge is hinged to the gripping jaws and can move out of the way as the connector pin is inserted into the connector receptacle.

Abstract: A dental implant assembly includes an implant for osseointegration in alveolar bone, an abutment removably attached to the implant for supporting a tooth prosthesis, and a screw received through an axial bore in the abutment and engaging a threaded bore in the implant. The implant includes an annular shoulder and a plurality of splines spaced from one another to define slots therebetween and disposed circumferentially about the opening of the threaded bore. The abutment includes an annular end face in engagement with the annular shoulder of the implant. A cylindrical recess is disposed radially inwardly of the annular end face and receives the splines of the implant therewithin. The cylindrical recess communicates with the axial bore. A plurality of circumferentially spaced axially extending splines defining slots therebetween are disposed within the cylindrical recess and are interleaved with the splines of the implant.

Abstract: An implantable defibrillator having a charging circuit for charging a high-voltage energy storage capacitor from a low voltage battery. Current from the battery is switched on and off through the primary winding of a voltage step-up transformer to induce a fly-back current in the secondary winding. The fly-back current is rectified and applied across the energy storage capacitor. The frequency of switching of the primary current is varied in relationship to the voltage of the battery to maintain a substantially constant average charging current as battery voltage decreases. Current through the primary is monitored on a cycle-by-cycle basis and switched off if it exceeds a preset limit.

Abstract: A capture detection circuit for an implantable cardiac stimulator. A signal detected by an electrode in the heart following delivery of a stimulating pulse is amplified, bandpass and highpass filtered, rectified, integrated over a selected window of time starting at a selected delay after delivery of the stimulating pulse, and applied to two comparators having different reference values. If the integrated signal exceeds the first reference value, the first comparator output goes high. If the integrated signal exceeds the second reference value, the second comparator goes high. If both comparators remain low, non-capture is indicated. If the first comparator goes high and the second comparator remains low, capture is indicated. If the second comparator goes high, an intrinsic contraction is indicated. The window of integration can be extended to distinguish capture from intrinsic contraction.

Abstract: A method of verifying cardiac capture. A cardiac signal evoked in response to a cardiac stimulation pulse is sensed via an electrode. The sensed signal is lowpass filtered to remove noise and to pass frequencies characteristic of the evoked cardiac signal. The filtered signal is processed to render a waveform signal representing the second derivative of said filtered signal and the second derivative signal is further analyzed to detect a minimum and a maximum amplitude excursion during a selected window of time beginning at a selected time delay following delivery of the cardiac stimulation pulse. The amplitude difference between the minimum and the maximum is measured and compared to a first reference value. The amplitude of the second derivative is measured during a second selected window of time beginning at a selected time delay following delivery of said cardiac stimulation pulse, and compared to a second reference value.

Abstract: A method and apparatus for processing data to be communicated between an implantable medical device and an external medical device to improve detectability of communication errors. An encoded block of data including message data and redundant data is processed by converting alternating data values of either the message data or the redundant data to respective complement data values. The altered block of data is communicated using relative pulse position modulation. The combination of alternating original and complement data with relative pulse position modulation (RPPM) takes advantage of the opposing adjacent errors characteristic of RPPM to decrease the probability of communication errors occurring in combinations that are undetectable by the decoding of the block of data.

Abstract: An implantable prosthesis comprises a polyethylene prosthetic member that is substantially transparent to x-rays and a radiographic marker that is substantially opaque to x-rays. The radiographic marker is configured as a tension spring arranged as a continuous ring encircling the prosthetic member.

Abstract: An apparatus for disassembling a head and acetabular component of a bipolar orthopedic hip prosthesis. The head includes a female taper configured for engaging a corresponding male taper of a femoral component of a hip prosthesis. The acetabular component includes a cavity in which the head is elastically constrained. The apparatus includes a rod having a male taper at one end thereof sized and configured to be received in taper locking engagement in the female taper of the head of the bipolar prosthesis. The rod has external threads that engage internal threads of a sleeve surrounding the rod. The sleeve includes a thrust surface at one end that engages the acetabular component as the sleeve is rotated relative to the rod. The sleeve causes the acetabular component to be pressed off of the head while the head remains taper locked to the rod. Continued rotation of the sleeve causes the head to be pressed off of the taper of the rod.

Abstract: A method of communicating data between an external device and an implantable medical device wherein a first pulse is transmitted as electromagnetic energy from one device to the other, is received and stored as electrostatic energy in the second device and, after a delay period representing data to be communicated, the stored energy is released and transmitted as electromagnetic energy back to the first device. A communications circuit in the implantable device for accomplishing the method includes an antenna coil, a non-linear electronic component in circuit communication with the antenna coil, a storage capacitor in circuit communication with the antenna coil and non-linear electronic component for storing energy received by the antenna coil, and a switch for selectively connecting the charged storage capacitor and the antenna coil to discharge the charge stored in the capacitor into the antenna coil.