BACKGROUND OF THE INVENTION

Field of Invention

This invention pertains to a clip for securing the electrode lead of a prosthetic device, such as a cochlear implant, inside an aural cavity, and to a method of securing the electrode lead to a bone of the astoid using said clip. Description of the Prior Art

Persons having somewhat restricted hearing due to a disfunction of the ear are frequently provided with hearing aids, which are essentially sound amplifiers. However, for persons having a profound impairment due to a sensorineural hearing loss problem, hearing aids are ineffective. Fortunately, it has been found that this more severe problem can be alleviated, in at least some people, by providing a cochlear implant-type prosthetic device. One such prosthetic device, known as the Mini System 22, is available from the Cochlear Corporation, 61 Inverness Drive East, Englewood, Colorado 80112, and is described in commonly owned U.S. Patent No. 4,532,930, incorporated herein by reference. This prosthetic device is used for directly stimulating the auditory nerve of a person, and includes an external component for picking up ambient sounds and transforming these sounds into corresponding electrical signals. The electrical signals are relayed to an internal component, which includes a receiver implanted behind a person's ear. The internal component also includes an electrode is inserted in the cochlear for stimulating the person's nerves, in response to said electrical signals, to produce sound-like sensations. An electrode lead connects the electrode to the receiver.

An important consideration for the reliable operation of the prosthetic device of the type described above is the manner in which the electrode lead is secured. If the electrode is secured inadequately, or if it is not secured at all, movement of the device during installation (i.e., while the surgical incision made to implant the internal component is closed up), growth (if

the person is a child) , and other post-operative effects may cause the electrode to be withdrawn from the cochlea and, as a result, the electrode may fail to stimulate the nerves in the cochlea effectively. One popular device securing method is shown in Figure 1.

In this Figure, portions 100 of the person's skin, disposed behind ear 102, have been cut, folded back and clamped by forceps 104 to expose the mastoid bone 30 and a mastoid cavity 40 leading to the person's middle ear. Figure 1 also shows the internal component of a prosthetic device, including a receiver section 22 mounted on the mastoid bone 30. The receiver section 22 has a permanent magnet 32 to align the external component and a receiving antenna 34. The section 22 is secured to the mastoid bone 30 by sutures 36 extending through holes 37 made in bone 30. An electrode lead 38 extends toward the middle ear through the mastoid cavity 40. Holes are drilled adjacent to the cavity 40, as at 42, and polyester mesh ties 44 are threaded through these holes 42 and used to secure the lead 38 to the mastoid bone 30. A disadvantage of this method of securing lead 38 is that it requires drilling through the mastoid several times, and hence it is tedious and time consuming. Moreover, because of the location of mesh ties, it is difficult to insure that the lead is secured properly, i.e., with the correct tension. If the ties are tied too loosely, the lead may have enough play to allow the electrode to be withdrawn as discussed above. If the ties are secured too tightly, the lead may be strained and damaged, causing open or short circuits. For these reasons, some surgeons elect not to secure the electrode lead at all.

Another method used to secure the electrode lead included the use of a soft, pliable platinum wire to tie the lead to a bony bar in the mastoid cavity, known as the incus bar. This was accomplished by first passing the wire about the bar and tying the wire to the bar in a first loop, leaving two free ends. The free ends of the wire were then tied around the lead to form a second loop. The problem with this technique was that it required practice and dexterity. Moreover, this method was time consuming and difficult because of the limited visibility of the

bone through the mastoid cavity 40. Furthermore, the lead could still be tied improperly, (i.e., too tight or too loose, with the undesirable results discussed above.

Yet another technique of securing the electrode lead was to use a bone cement to glue the lead to the mastoid bone. However, this method was found to be ineffective and, moreover, could cause serious problems if the bone cement was not biocompatible.

Moreover, this cement is not available in the United States.

OBJECTIVES AND SUMMARY OF THE INVENTION In view of the above-mentioned disadvantages of the prior art, it is an objective of the present invention to provide a means of firmly securing the electrode of a prosthetic device of the kind discussed above within the middle ear, as close to the inner ear as possible to prevent post-operative electrode migration or withdrawal.

A further objective is to provide a means of securing the electrode lead quickly and easily, without the use of labor intensive and time consuming techniques.

Yet another objective is to provide an electrode securing means which clamps the electrode lead with a known force selected to insure that the lead is not injured, while holding the lead securely to prevent the withdrawal of the electrode. Other objectives and advantages of the invention shall become apparent from the following description. Briefly, the above-recited advantages are achieved by providing a rigid clip having a U-shaped mounting member arranged and constructed to be readily mounted on the bone of the ear. Preferably the mounting member is shaped and sized to snap on the incus bar. The clip is also provided with lead securing means for securing the lead to the clip. Preferably the lead securing means includes two jaws which clamp the lead with a force selected to insure that the lead is firmly grasped without injury. The mounting member and the clamping member are formed as an integral preassembled unit. BRIEF DESCRIPTION OF THE DRAWING

Figure 1 shows a side-elevational view of a person's ear with a portion of the skin removed to show a prosthetic device,

and illustrates a prior art technique of securing the electrode lead of the prosthetic device;

Figure 2 shows a front elevational view of a prosthetic device having an electrode lead secured using the clip of the present invention;

Figure 3 shows a side elevational view of a person's head with details of the external components of the prosthetic device of Figure 2;

Figure 4 shows an orthogonal view of the electrode lead securing clip constructed in accordance with this invention; Figure 5 shows a plan view of the clip of figure 4; Figure 6 shows a side elevational, partial sectional view of the clip of Figure 5;

Figure 7 shows a plan view of the clip of Figures 4-6 engaging an electrode lead; and

Figure 8 shows a side elevational view of the incus bar with the clip of Figures 4-6 being mounted thereon.

DETAILED DESCRIPTION OF THE INVENTION A prosthetic device, such as the device described in the above-mentioned U.S. Patent No. 4,532,930, has two basic components, an external component 10 and an internal component 12 including the receiver 22 and the electrode lead 38.

The external component 10, illustrated in Figure 2 and 3, is worn by the person, and can be taken off and put on at will like a hearing aid. The external component 10 includes an electronic housing 14, an ear piece 16, a transmitter 18, and an interconnecting cable 20. The housing 14 contains a battery (not shown) for powering the component 10, and signal processing cir¬ cuitry (not shown) . The ear piece 16 includes a directional microphone (not shown) . Sounds picked up by the microphone in the ear piece 16 are converted into electrical signals, which are filtered, and otherwise processed in housing 14. The processed signals are sent via cable 20 to the transmitter 18 for transmission to the internal component. The transmitter 18 includes a plate made of a magnetizable material (not shown) .

The internal component 12 includes the receiver section 22 having a magnet 32 and a receiver antenna 34, and an electrode

lead 38 as discussed above. Lead 38 extends through the mastoid cavity 40 via a facial recess 51 into the middle ear defined by an aural cavity 50. The lead 38 is terminated with an electrode 52 disposed in the cochlea 54. Disposed in mastoid cavity 40 is the incus bar 41 disposed between the incus 58 and the facial recess 51. In accordance with this invention, a lead securing clip 62 is mounted on this bar 41.

Once the lead 38 is installed and secured as shown in Figure 2, the incision made to install the component 12 can be closed. Several weeks later, after the person has recovered, the prosthetic device is set up for normal operation. During this normal operation, the housing 14 is worn in a pocket or in another, preferably non-intrusive, manner. The ear piece 16 is positioned over the ear and the transmitter 18 is held over the receiver section 22 by the permanent magnet 32. As previously explained, ambient sounds are transformed by the microphone in the ear piece 16 into the electrical signals and sent to the transmitter 18. The transmitter 18 transmits the electrical signals to the receiver 34 which then sends them on to the electrode 52 through the lead 38 to allow the person to 'hear' the sounds as described in detail in U.S. Patent No. 4,532,930.

Details of the clip 62 are now described with reference to

Figures 4-7. The clip 62 is formed of two members: a mounting member in the form of a staple 64 and a lead engaging member in the form of a hook 66. The staple 64 is generally U-shaped and is formed of a relatively stiff wire made of a biologically neutral material. The wire used to make the staple 64 may have a diameter of about 0.25 mm. The staple 64 is preferably formed with two staple arms 68, 70 which have been flattened slightly to form opposing gripping surfaces as shown at 72, 74 respectively. The two arms 68 and 70 are not parallel but extend inwardly towards a longitudinal axis X-X of staple 64, as shown in Figure 5. In between arms 68, 70, the staple 64 is provided with a connecting portion 76. The distance between the ends of arms 68,70 is thus smaller than the distance between the arms adjacent to portion 76, as shown.

As best seen in Figures 4 - 6, the hook 66 is also U shaped and is disposed substantially perpendicularly to the plane of staple 64. The hook 66 is also made of a relatively rigid wire and is formed with two hook arms 78, 80, connected by an intermediate section 82. The end 84 of arm 80 is bent into a ring to engage the portion 76 of staple 64 as shown. Importantly, the two arms 78, 80 are bent slightly toward each other so that the minimum distance M between these arms, as shown in Figure 6, is smaller than the diameter D of lead 38. In this manner, when the lead 38 is pushed between arms 78, 80, the two arms cooperate to form clamping jaws to clamp and form an interface with the lead 38.

Preferably, the clip 62 is made of titanium or other similar material which is relatively rigid, but is slightly elastic so that it can form the interference fits with the bar 41 the electrode lead 38 as described above.

The clip 64 is preferably constructed and arranged so that its staple 64 can be shaped around the incus bar 41 as shown in

Figure 7. The electrode lead 38 can then be mounted on hook 66. Figure 8 shows a more detailed view of the electrode lead

38 being installed and then secured, using the clip 62. More particularly, in this Figure the electrode 52 terminating lead

38 is first pushed with a tool 92 through the round window 90, into the cochlea 54, disposed behind the window 90. Before the electrode 52 is properly positioned in the cochlea 54, the staple

64 of clip 62 is mounted on the incus bar 41. The spacing of the arms 68, 70 is selected so that the staple 64 snaps readily and easily around the incus bar 41 to form an interference fit therewith, as shown in Figure 7. Preferably the hook 66 is permanently secured to the staple 64 for example by welding or other similar techniques, thereby completing the clip 62.

Once the clip 62 is mounted on the incus bar 41, the lead 38 is secured to the clip 62 by pushing a portion of the lead 38 between the hook arms 78, 80 with tool 92, to the position shown in Figures 6 and 7. In this manner, the lead 38 is firmly attached to the incus bar 41 by the clip 62 and remains permanently secured to insure that the electrode 52 is not

withdrawn. Moreover, the hook 64 is preformed with its arms 78, 80 spaced to insure that the lead is firmly grasped between the arms 78, 80, without damaging the lead.

In the embodiment discussed above, the clip 62 is described as supporting a single lead. Obviously the clip can be arranged and constructed to support two or more leads as well.

Although the invention has been described with reference to a preferred embodiment, it is to be understood that this embodiment is merely illustrative of the application of the principles of the invention. Accordingly, the embodiment described in particular should be considered exemplary, not limiting, with respect to the following claims.