CA1141828A - Electrification attachment for an osteosynthesis implantate - Google Patents

Abstract

Abstract of the Disclosure It is known to manufacture an osteosynthesis implantate, such a bone nail or plate, in combination with a receiving coil and electrode connections to form an electro-implantate. The coil and electrodes provide a small electrical voltage across the implantate and surrounding tissue to stimulate the healing process. It is also known to convert osteosynthesis implantates into electro-implantate by the addition of belt-like or loose pick-up type coil elements. The present invention relates to an attachment element consisting of a body support formed to attach to an ordinary implant-ate and which includes at least one induction coil and two electrodes, one of which is connectable with a conductive portion of the implantate, the other being exposed to bone or soft tissue of the patient. The present invention may be applied to the implantate so that it can be converted into an electro-implantate during the progress of an operation with greater ease and less complexity then can either the belt-like or pick-up coil elements. Further, the result will be a fully equivalent and effective substitute for a pre-manufactured electro-implantate but at substantially less cost.

Description

1~41828 This is a divisional of copending Canadian patent application Serial No. 311,778 filed September 21, 1978 in the name of Werner 1~raus.
The present invention relates to a surgical prosthesis, and more particularly to an osteosynthesis implantate, which, after its manufacture, can be associated with an electrical pick-up element to provide a small electrical voltage across the implantate and surrounding tissue of the patient to stimulate healing processes.
The term "tissue" as used herein includes soft tissue as well as bone tissue, unless it clearly appears otherwise.
It has previously been proposed - see the referenced United States Patents 3,745,995 and 3,820,534 - to provide an inductive receiving coil, preferably having a ferromagnetic core, for association with osteosynthesis implantates. The receiving coil has two or more connecting terminals, connected to electrodes which are attached to an injured or danaged bone which is fixed in relative position by the osteosynthesis implantate. Such an implantate may, for example, be a bone nail, securing together the ends of a fractured bone by extending through the marrow duct. After the operation of introducing the bone nail, and of closing the wound, a low-frequency electrical current is induced in the coil which flows through the electrodes and the damaged bone region, and promotes healing and reformation of bone substance.
Such osteosynthesis implantates are known as electro-osteosynthesis implantates and are provided with the receiving coil and the electrode connec-tions, as delivered from the manufacturer. The manufacture of any one electro-osteosynthesis implantate requires individual, special manufacture in which the electrical winding elements and the osteosynthesis implantate are individually associated. Such implantates may, also, be in the form of flat or bendable plates. The winding section is individually and securel3r connected to the - 1 ' ~418:28 implantate by adhesion, clamping connection or welding; likewise, the electrodes or electrode connection are so adhered or connected. Surgical clinics, trauma stations in hospitals, and the like, require a large stock of different types of electro-osteosynthesis implantates, for example bone nails of many different lengths in many different diameters. Such electro-osteosynthesis implantates are expensive and stocking and storage of a large number of such items in many different sizes, the requirements for which are hardly predictable, is a substantial drain on limited financial resources of public and private health facilities. Frequently, therefore, the patient is subjected to multiple surgical procedures since electro-osteosynthesis implantates were frequently introduced into the patients only in a second operation, after the initial operation of fixation of the bone has taken place, the type and size of the required electro-synthesis implantate has been determined and the appropriate unit has been ordered and received from the manufacturer.
Developments in surgical devices have been undertaken to reduce the financial load on health facilities and to reduce the requirement for stocking of specific electro-implantates. United States Patent 3,820,534 describes a belt-like element which is furnished with electrodes and a connecting element on which a coil is secured. After implantation of a bone nail, for example, the belt-like element is placed around the bone, and the connecting coil can be connected to the bone nail with one terminal. It has also been proposed to provide a loose pick-up coil which is embedded in a biologically tissue-compatible plastic material and which can be connected to bone screws by means of snap-button type connections. The bone screws function as electrodes across which an electric current will flow ~see eerman Disclosure Document DE-OS
23 11 817). United States Patent 3,918,440 describes such a loose receiving coil in combination with bone screws, in which the head of the bone screws is ~ 2 -~141828 insulated so that it can be used for attachment of a bone plate. The screws, themselves, form the electrodes which are insulated with respect to the bone plate.
The loosely implanted pick-up coil, as well as the belt-like element, and the snap button or push-button type connections are an entirely satisfactory substitute for premanufactured electro-osteosynthesis implantates. Use of the belt-like element introduces additional complexity; the loose pick-up coil is difficult to secure.
It is an object to provide an attachment element for an ordinary osteosynthesis implantate, specifically a bone plate, which attachment can be applied to the plate so that it can be converted into an electro-implantate during the progress of an operation and which then will be a fully equivalent and effective substitute for a premanufactured electro-implantate.
Briefly, in accordance with the invention, there is provided an attachment for converting an osteosynthesis plate into an electrified osteo-synthesis plate, the attachment comprising at least one body of electrically insulating material, an induction pick-up coil located in the body and having at least two terminals, a plurality of members supported by and protruding from the body and adapted to secure mechanically the body to the plate, one of said at least two terminals being provided with a connecting device for electrical and mechanical connection to a bone screw insulated with respect to the plate, the bone screw serving as a tissue electrode for electrically connecting the one terminal to the tissue of a patient, and means for electrically connecting another of the at least two terminals also to the tissue of the patient.
The attachment permits the surgeon to fix the bone in standard manner by an osteosynthesis plate implantate in accordance with standard surgical procedure, and using the ordinarily available implantates. He can then deter-1~418Z8 mine whether it would be desirable to have an electrical implantate and, if so, the osteosynthesis plate can be supplied with the attachment in accordance with the present invention and the implantate will then function as an electro-implantate without requiring any further changes or modifications, or a subse-quent operation.
A standard osteosynthesis plate and the attachment in accordance with the present invention, together, are substantially simpler and further less expensive than the combined electro-osteosynthesis implantates.
The present invention together with that of copending application Serial No. 311,778 will now be described in greater detail with reference to the accompanying drawings, in which:
Figure 1 is a top view of a standard bone nail in accordance with German Industrial Standard DIN 55801, Porm B;
Figure 2 is a schematic simplified longitudinal section of an elec-trification attachment for the bone nail of ~igure l;
Figure 3 is a cross section in the plane of III-III of Figure 2;
Figure 4 is a top view of a bone nail of Figure 1, partly in phantom view;
Figure 5 is a cross section in plane V V of Figure 4;
Figure 6 is a side view of a modified embodiment of the attachment of Figure 2, in which the electrical circuit inherent in the element is separately shown in view B, and the structural arrangement is shown in view A;
Figures 7 and 8 are two schematic electrical diagrams suitable for use in the electrical attachment;
Figure 9 is a highly schematic perspective view of an osteosynthesis plate, shown in broken lines, to which the electrification attachment in accor-dance with the present invention has been added;

~ 4 -11418Z~3 Figure 10 is a schematic top view of another arrangement of an osteosynthesis plate; and Figure 11 is a top view of an elastic electrode connection holding arrangement, in which view A illustrates the holding arrangement in relaxed state, and view B the same arrangement in stretched, or stressed state.
The invention will best be understood when considering first an embodiment for attachment to a standard bone nail, as shown in Figure 1. The cross section of the bone nail of ~igure 1 is approximately clover leaf-shaped, or pear-shaped (Figure 5). The bone nail 10 has a longitudinal slot 12, a tapering, somewhat pointed tip 14 and an enlarged terminal end 16.
In accordance with the present invention, the known and conventional bone nail 10 is converted into an electro-bone nail by the attachment 20 -see Figures 2 and 3. Damaged or diseased or fractured bone tissue is electro-dynamically stimulated in the region of injury or disease to stimulate reformation of bone tissue and improve and accelerate the healing process.
The attachment 20, in accordance with the present invention, has a body 22 made of a biologically compatible, tissue-compatible plastic, such as polyethylene, or a carbon-fluoropolymer. A receiving coil 24, shaped like a solenoid, is embedded in the body 22. The receiving coil 24 is only schemati-cally shown in Pigures 2 and 3, and there illustrated as a single-layer coil;
of course, it may be a coil wound of a plurality of tightly arranged windings.
The circuit and the electrical terminals have been omitted from the illustra-tion of Figures 2 and 3 for simplicity, and will be explained below.
The coil 24 preferably is a cored coil, and has a magnetic core 26 made of a magnetically soft material, having soft-iron characteristics, such as a ferrite, or an iron-nickel alloy. lt may also be a permanent-magnet material which, then, preferably, is brought into a partially saturated con-_ 5 =

~18Z8 dition and permits modification of the wave shape of the voltage applied to the electrodes and hence of the currents being supplied to the body tissue.
Embodiment of Figures 2 and 3: The body 22 has three leaf-likeJ
spring electrodes 28 secured thereto, for example by being set into a groove of the body ~see Figure 2) which are bowed outwardly. The electrodes 28 are connected together and to one end terminal or end point of the winding 24 and provide electrical connection of the attachment to the metal bone nail 10, by bearing against the inside wall, as illustrated in Figure 5. The dimensions of the body 22 and the outward bulge of the electrodes 28 are preferably so select-ed that the same attachment 20 can be used for bone nails of a wide range of diameters, preferably the entire range of diameters of bone nails which are used in surgical procedures. ~t most, however, two such bodies 20 need be pro-vided, one for a thinner group of bone nails and another for a group of bone nails having a wider diameter. The spring electrodes 28 permit deflection, and hence reliable electrical contact, as well as reliable seating within the bone nail.
The body 22 is formed with an extension 30 which, in cross section, is essentially T-shaped ~Figure 3~ and which fits through the slot 12 of the bone nail 10. The upper cross portion 34 of the T-extension 30 (Figure 5) is bent downwardly so that it fits at least approximately around the curvature of the bone nail 12. Since the body 20, with the integral extension 30, is made of a soft plastic, the pre-bowing of the cross portion 34 can be such that it fits the thinnest nail, since it will then expand, or resiliently bow outwardly to fit over nails of larger diameter. ~n longitudinal extent, the cross portion 34 can be flat (Figures 4, S) or can be slightly bowed (Figure 2). An electrode 36 is applied to the outside of the bowed cross extension 34, connected to another point on the winding 24 of the attachment. The electrode 36 is the - 6 ~

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counter electrode or soft-tissue electrode of the attachment.
Embodiment of Pigure 4: A plurality of separate counter electrodes 36a, 36b can be provided, each one connected to different points on the winding of the coil 24. In all other respects, the structure is similar to that of the embodiment of Figures 2 and 3.
The body 22 is preferably formed at its end with recesses, notches or grooves 38 to permit attachment of an insertion or removal tool, and to facilitate insertion or removal of the attachment 20 into or from the nail 10.
In a preferred form, the surgeon ls provided, together with the attachment 20, with an additional filler strip which, for example, may be formed similar to an I-beam, that is, have a double T-profile in cross section~ and so dimensioned that it cannot pass through the narrow end 14 of the bone nail.
The filler strip is then trimmed to the desired length by the surgeon during the operation and introduced into the nail 14 together with the attachment 20 in order to ensure proper spacing of the attachment 20 from the end 14 of the nail, or in order to ensure spacing between a plurality of attachment elements 20 which can be se~uentially, axially introduced into the nail 10. The filler strip is preferably made of the same material as that of thé body 20, and soft enough so that it can be cut by surgical scissors to the desired length, being supplied, for example, in coil or rod form.
The body 22 with the T-pro~ection 30 and the electrode 36, or the electrodes 36a, 36b, are so dimensioned that they fit within the diameter of the surgical drill with which the opening for the bone nail 10 is drilled.
The entire length of the attachment 20 preferably is between about 3 to 5 cm. The material is somewhat resilient and the dimensions are preferably so arranged that, coupled with the elasticity of the material of the body 22, it is possible to introduce the attachment simply and effortlessly even over ~ 7 114~8Z8 a bent-over end formed at the upper end of a bent bone nail and from there into the there widened slot 12. The outer diameter of the attachment is larger than the lower opening of the end 14 of the conically tapering bone nail, so that the attachment device cannot slip upon introduction, or when pulling the nail.
The bone nail 10 is galvanically connected over the electrodes 28 with the coil 24 and forms one of the electrodes, engaging the bone. The other electrode 36, or the electrodes 36a, 36b, may have galvanic, semiconductive or capacitive connection with the adjacent tissue of the patient. If semi-conductive orcapacitative contact is desired, the electrodes 36 are suitably coated at the outside with either a thin coating of semiconductor material or with a thin coating of an insulator. A galvanic contact is desirable in tissue poorly supplied with blood, or having few blood vessels. In tissue having better blood supply, a semiconductive contact is desirable. This can be obtain-ed by coating the electrode with a thin layer of aluminum oxide (A1203), biological carbon, calcium phosphate, or the like. Tf the tissue to be contact-ed has high blood supply, a capacitative contact may be desirable since rise of current beyond the physiologically compatible value of about 100,u amperes is prevented. Galvanic contact, due to the high conductivity of tissue well supplied with blood might result in an excessive current flow.
Embodiment of Figure 6: The attachment has four tissue electrodes 36a, 36b, 36c, 36d. The projection 30 which carries these electrodes is sub-divided into four parts 30a, 30b, 30c, 30d (see view A). The body 22 is con-stricted between the respective pro~ections, as seen at 40a, 40b, 40c. As seen in the electrical connection of Pigure 6, view B, one end of the coil 24 is connected to the electrode 28 which is used to connect the entire unit to the bone nail 10. The electrodes 28 are identical to those described in connection ~418Z8 with Figures 2 and 3. The soft-tissue electrodes 36 to 36d are connected to winding terminals of the coil 24 which have increasingly longer distances from the end of the coil 24 connected to the electrodes 28.
The attachment in accordance with Pigure 6 can be fitted to bone nails of any length by cutting or trimming the body 22' at any one of the con-strictions 40a, 40b, 40c, which function as break point, so that the extent of contact of the tissue electrodes can be matched to the extent of the region of the fracture which is to be subjected to an electrical current. The soft-tissue electrodes 36b to 36d are connected to the coil 24 by connecting lines 42, for example in the form of thin foils, which can be readily severed.
Circuit arrangements, with reference to Figures 7 and 8: The circuit of Figure 7 permits application to the electrodes of a-c with a superimposed d-c.
As seen, coil 24 is connected in series with a semiconductor rectifier 50 and two voltage divider resistors 52, 54. The tap point 56 of the voltage divider thus has a d-c potential appear thereat. The magnitude will depend on the a-c induced in the coil 24 and the dimension of the voltage divider resistors 52, 54. The tap 56 is additionally connected by a capacitor 58 to the junction of the diode rectifier 50 and the coil 24 50 that the d-c voltage appearing at the tap 56 is superimposed on the a-c supplied by the coil 24. The tap 56 and the terminal 60 of the coil 24 are connected, respectively, to the electrodes 36, 28 (Figures 2, 3; 4-6~ so that the bone nail is negative with respect to the soft-tissue electrode. The diode 50 preferabl~ is a miniature semiconductor diode with low threshold voltage, for example of 50 mV. The circuit is suit-ably so dimensioned that the d-c component is about 20% of the peak amplitude of the a-c voltage; in a preferred form, the d-c component is approximately 10 of the peak amplitude of the a-c voltage which may be about i V or possibly e~en higher.

_ ~ ~

1~418Z8 The embodiment of F~gure 8 is a modlfication of the circuit for an insert in accordance with Pigure 4J in which the a-c is applied to the junction 56 from a tap 62 of the coil 24. The capacitor then need not be used. a-c can be applied to the terminal 56 also over a separate winding, for example formed on another layer of winding 24, and connected between terminals 60 and 56.
The rectifier diode 50 is connected to the winding 24 over a conduc-tor loop which, physically, extends into a projecting portion 66 of the body 22, or 22', respectively, as schematically indicated in broken lines in Figure 8. If the surgeon decides that no d-c should be applied, he can cut the pro-1~ jection 66 during the surgical procedure, thus interrupting connection between coil 24 and the rectifier diode 50, so that the applied electric current will be only a-c, without a d-c component.
Embodiment of ~lgure 9- The attachment can be used not only with a bone nail, but also with an osteosynthesis plate 70, shown in broken lines in Figure 9. The attachment 72 has a body 74 ~ade of biologically tissue-compatible material, similar to body 22, in which a receiving coil is located. The re-ceiving coil has been omitted from ~igure 9 for clarity. The body 74 preferably has an approximately rectangular cross section which has a thickness not sub-stantially in excess of that of the plate 70. One or more pairs of knife contact electrodes 76 project from one side of the body 74. Preferably, these contacts 76 are made of springy metal which simultaneously provide electrical connection to the plate 70 as well as ensuring attachment of the body 74 on the plate 70. The electrodes 76, similar to the electrodes 28 of Figures 1-6, form electrical contact between the coil in the body 74 and the plate 70. An additional spring electrode 28' may be provided which, similar to the electrodes 28 of the embodiment of Figures 2 and 3 is bowed or bulged outwardly and set in at an edge of the body 74, to bear against the edge of plate 70 when the ~ 10 -1~418ZB

attachment 72 is associated with the plate 70. The body 74 has additional strip-like springy projections 78, made of plastic, and for example molded integrally on the body 74. The pro~ections 78 carry connection arrangements 80, connected over the projections 78 by electrical leads embedded therein with the coil 24 in body 74, similar to the electrodes 36a to 36d, Figure 6. The connection arrangements 80 permit connection of the coil 74 to bone screws, not shown. The bone screws are insulated with respect to the plate 70 and, simultaneously, form electrodes and attach the plate 70 to the bone. These screws may be constructed as described in the aforementioned United States Patent 3,918,440. Projections 78 which are not needed can be trimmed. The projections may have different lengths, as shown, and be so constructed that the location of the connection arrangements 80 corresponds to the position or dis-tribution of the holes in a standard osteosynthesis plate.
Embodiment of Figure lO: Two bodies 74a, 74b, each one similar to body 74 (Figure 9) and each one having a coil 24a, 24b, are located at opposite sides of a plate 70 ~not shown, and omitted for clarity). The lower ends of the receiving coils have electrodes 76 and, if desired, electrodes 28 attached thereto, similar to the illustration of Pigure 9, and also omitted from Figure 10. The sense of winding or connection of the coils 24a, 24b may be the same, or opposite, so that the terminals 80 of facing projections 78 will either carry the same, or different voltage levels. The two bodies 74a, 74b are connected at their ends - only one is shown - by a spring 82 made of plastic material so that the attachment arrangement can be used for plates of different widths.
Embodiment of Figure ll: The projections 78', which carry the connection arrangement 80, are preferabl~ so constructed that they are made of two elastic, oppositely howed strips, made of plastic. In quiescent state, - 11 =

li4182B

they are widely bent - see Figure 11J view A. The strips act like a spring so that the position of the connection arrangement 80 can be matched to different distances of the connection openings between the edge of the plate and the openings for the bone screws themselves, with which the contact elements 80 are to be connected.
Vse and application: When using the attachment in accordance with Figures 9 and 10, the bone plate 70 is first secured to the bone to be joined, or set. Insulated bone screws having heads which fit the connection arrange-ment 80 are used at those portions where electrodes are deemed desirable.
Thereafter, the attachment body 74, or 74a, 74b, is attached to the plate by sliding it on the longitudinal edge of the plate; the insulated bone screws are then connected with the connection 80 of the projections 78, or 78' (Figure 11).
Those connection elements which are not desired or used are cut off together with the respective projections 78, 78'.
The attachment permits the surgeon to decide during the operation whether healing of a fractured or otherwise injured bone will be promoted by introducing an electrical current to the region of fracture or disease, and if electrodynamic activation of osteosynthesis is desirable.
If the attachment is to be used for an osteosynthesis implantate made of a non-conductive material, such as ceramic then the electrode which is designed for contact with the implantate is, instead, contacted with a large-area electrode foil, or sheet electrode which, preferably, is in contact with the soft tissue of the patient, preferably with the soft tissue immediately adjacent to the bone which is to heal. When using the embodiment in accordance with Figure 4 or 5, one of the electrodes 36a, 36b .... can be used as the tissue counter electrode.
The body 22, or 72, respectivel~, may also be made of metal and, for 1~41828 example, may include a housing made of a tlssue-compatible material such as a cobalt-chrome alloy, chrome-nickelmanganese steel; titanium, or the like. The body can then be used directly as the electrode for connection to a metallic osteosynthesis implantate, or as a large-area, soft-tissue electrode. The other electrodes are then suitably insulated from this conductive body, for example by a thin coating of biologically compatible plastic.

~ 13 -

Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An attachment for converting an osteosynthesis plate into an elec-trified osteosynthesis plate, the attachment comprising at least one body of electrically insulating material, an induction pick-up coil located in the body and having at least two terminals, a plurality of members supported by and protruding from the body and adapted to secure mechanically the body to the plate, one of said at least two terminals being provided with a connecting device for electrical and mechanical connection to a bone screw insulated with respect to the plate, the bone screw serving as a tissue electrode for electri-cally connecting the one terminal to the tissue of a patient, and means for electrically connecting another of the at least two terminals also to the tissue of the patient.

2. An attachment according to claim 1 wherein the means for electrically connecting said another of the at least two terminals comprises a metal protrud-ing member adapted to make electrical contact with an electrically conductive surface of said plate which thereby serves as a second tissue electrode.

3. An attachment according to claim 1 wherein the means for electrically connecting said another of the at least two terminals comprises a second connecting device for electrical and mechanical connection to a second bone screw insulated against the first mentioned bone screw, said second bone screw thereby serving as a second tissue electrode.

4. An attachment according to claim 1 in which there are at least three terminals on the induction pick-up coil, one of the terminals being connected to metal protruding members adapted to make electrical contact with an elec-trically conductive surface of said plate which thereby serves as a tissue electrode and the remaining terminals being provided with respective connecting devices for electrical and mechanical connection to respective bone screws insulated with respect to the plate and each other, the bone screws serving as respective further tissue electrodes.

5. An attachment according to claim 4 in which the body is elongate with the protruding members provided at spaced locations along the body and in which the connecting devices for the bone screws are carried, respectively, on electrically insulating protruding members, the metal protruding members being aligned with each other and spaced substantially by the plate thickness from the insulating protruding members which are also aligned with each other whereby the metal protruding members can be pushed against one major surface of the plate and the connecting devices for the bone screws are adjacent the other major surface of the plate.

6. An attachment according to claim 5 in which the body is formed as two parallel portions interconnected mechanically by resilient connecting mem-bers and with the protruding members of each body portion being directed generally toward the protruding members of the other body portion, whereby the body portions can be mounted to opposite edges of the plate.

7. An attachment according to claim 5 or 6 wherein the protruding members which carry the connecting devices are resiliently stretchable.