"Smyth Clothespin Strut," Richards Manufacturing Co. Catalog, Micro-Surgery Instruments and Implants, 1965, Richards Mfg. Co., Memphis Tenn., page 31. .
"Amstrong Modification of Schuknecht Gelfoam-Wire Prosthesis," Richards Manufacturing Co. Catalog, Micro-Surgery Instruments and Implants, 1965, Richards Mfg. Co., Memphis, Tenn., page 34..
BACKGROUND OF THE INVENTION
This invention pertains to surgical replacement of defective or missing bones of the middle ear by implanting a prosthetic device and is indexed by the Patent Office as Class 3-1.
Attention is called to the very high proportion of delayed failures of ossicle replacement implants. Most such failures are caused by the failure of a rigid prosthesis to yield to unidirectional movements of the tympanic membrane. In most cases movements are caused by air pressure changes. Some are caused by swelling of certain tissues, etc.
The tympanic membrane must respond to two unrelated kinds of movements. Its first and objective function is to transform airborne sound waves into corresponding mechanical oscillations which, via the ossicle chain, will move the oval window diaphragm inward and outward to correspond in time and magnitude with the said sound waves. These movements are of very small magnitude, even for loud sounds, and are of equal magnitude inwardly and outwardly resulting in zero mean movement of the tympanic membrane. These movements rarely, if ever, damage tissues or bones. The second kind of movement to which the tympanic membrane is subjected is usually caused by changes in air pressure which force the membrane unidirectionally inward or outward. The eustachian tube opens, occasionally, and allows air to enter or leave the tympanic cavity and thus equalize the pressure on the membrane, allowing it to return to its normal position, but the eustachian tube is closed most of the time and so does not protect the middle ear parts from injury from such movements. In the normal ear the joint connecting the malleus to the incus provides for such movements without injury to tissues or bones and without interruption of sound transmission.
It is believed that, prior to this invention, there was no device known for prosthetically connecting the central area of the tympanic membrane direct to the oval window which did, or was claimed to, allow the tympanic membrane to move freely inward or outward while continuously transmitting sound oscillations from said membrane to the oval window diaphragm.
DESCRIPTION OF PRIOR ART
Heretofore surgeons, when prosthetically replacing auditory ossicles, have connected the tympanic membrane to the oval window with a single strut, of metal, plastic or living bone. Such struts might take the form of wire, rod or tubing and were usually attached near the center of the tympanic membrane so as to obtain maximum sensitivity to sounds striking the membrane. The distal end of the prosthesis was implanted in the oval window diaphragm. This transmitted the sound oscillations to the inner ear. But when, post-surgically, the tympanic membrane was forced inward, the rigid strut pressed in upon the paralymph usually causing vertigo and sometimes rupture of the oval window membrane. This, in turn, caused loss of the fluid and/or cochlear fracture. If the tympanic membrane were forced outward the result was similar, usually requiring further surgery to restore hearing. Often permanent and irreparable damage resulted.
In trying to avoid these strains surgeons tried moving the point of attachment away from the center of the tympanic membrane. When a functional malleus long process was present the surgeon might attach the strut to the neck of the malleus long process. However, as the point of attachment was moved away from the tip of the malleus long process and toward the fulcrum of the malleus-incus complex, the availability of sound energy approached zero. Such attachments were less likely to fracture but were also less likely to restore a satisfactory level of hearing. Some surgeons tried making a firm attachment to the tympanic membrane and depended on contact with the oval window membrane or stapes footplate being sustained by pressure, by using a too long strut. This was found objectionable because:
1. Resulting pressure on the paralymph caused vertigo.
2. The healing process tends to relieve any sustained pressure on body tissues and it usually released the tight contact needed to transmit sound oscillations to the oval window.
3. Pressure tends to dampen oscillations.
4. Distorting the tympanic membrane, by stretching it over the overly long strut, reduced its ability to transform sound waves to mechanical oscillations. If the prosthesis was not attached to the oval window diaphragm but relied on pressure to transmit sound oscillations the results were intermittent and unreliable.
Bearing in mind that sound energy is here transmitted, not as sound waves travelling through the material of which the prosthesis is made, but rather by longitudinal oscillation of the entire prosthesis, it becomes evident that the prosthesis alternately pushes and pulls the oval window diaphragm. It is also clear that a pressure free contact would rattle and/or release the contact, interrupting the hearing.
DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
The accompanying drawings form a part of this specification in which like numerals are employed to designate like parts throughout same.
FIG. 1 Is a view of a section of an ear. The small circle shows the location in the ear of the implanted prosthesis replacing the three missing ossicles.
FIG. 1A Is an enlarged view of the structure enclosed in the small circle appearing in FIG. 1.
FIG. 2 Is a generally longitudinal section of the invention.
Section A--A Is a cross-sectional view of the invention taken at lines designated A--A on FIG. 2.
Numeral designations are explained hereinafter:
1. Strut, herein designated as distal strut, made of magnetic wire having a loop 10 for implanting in the oval window membrane. After removal of the stapes, absorbable gelatine foam is placed in the oval window and the loop 10 is placed in the foam near the center of the annulus. Tissue re-growth will include loop 10 in new diaphragm. Some surgeons may prefer to use autogenous vein or fat plugs instead of gelatine foam.
2. Strut, herein designated as proximal strut. It has an arm 9 bent at an angle of about 85° more or less to match the relaxed slant of the tympanic membrane radius where it is to be implanted in the tympanic membrane 13 by grafting a strip of autogenous fibrous tissue 6 over the arm in such a manner as to seal the arm securely to the tympanic membrane. The other end of this strut 2 is embedded securely in the non-magnetic sheath 4.
3. Permanent magnet molded in the non-magnetic sheath.
4. Sheath, made of non-magnetic material, containing the permanent magnet 3, attached to the proximal strut 2 and having a guide hole 5 for the body of the distal strut 1.
5. Guide hole in sheath to keep the distal strut 1 parallel with the proximal strut and within the magnetic field of the permanent magnet 3.
6. Tissue graft used to secure arm 9 to the tympanic membrane.
7. Oval window membrane, re-grown.
9. Arm of proximal strut, for attaching to tympanic membrane.
10. Distal strut loop, to be implanted in oval window membrane 7.
11. Oval window niche.
12. Annulus of oval window.
13. Tympanic membrane.
14. External ear canal.
The proximal strut 2, the permanent magnet 3 and sheath 4 of FIG. 2 are herein referred to as the proximal assembly.
FIG. 3 Is a generally longitudinal view of a variation of the invention made entirely of wire, herein designated as variant. The permanent magnet forms part of one strut, the other strut is magnetically attracted to it. Its functions, actions and attachments essentially correspond with basic invention FIG. 2.
15. Interlocking loops, on variant, to hold the bodies of the struts parallel and in proximity to each other.
16. Distal strut of variant, to attach to oval window membrane.
17. Distal loop of variant, implanted same as loop 10.
18. Proximal strut of variant.
19. Proximal arm of variant, to be attached to tympanic membrane same as arm 9.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIGS. 1 and 2 of the drawing, the self-adjusting ossicle replacement prosthesis is seen to consist of two struts, herein designated by reference numerals 1 and 2, and made of biochemically inert wire. The distal strut 1 must be composed of material magnetically responsive to the permanent magnet 3, embedded in the sheath 4. The distal strut has a loop 10 to be implanted in the oval window membrane 7 as shown in FIG. 1. The sheath 4 is composed of non-magnetic material whose purpose is to hold the distal strut 1 loosely in close proximity to the permanent magnet 3 and parallel to the proximal strut 2. The guide hole 5 in the sheath 4 must be large enough to allow distal strut 1 to slide FREELY yet small enough to keep said strut generally parallel with proximal strut 2. Proximal strut 2 is securely embedded in sheath 4 and has an arm 9 bent at an angle 85° more or less to generally match the radius of the relaxed tympanic membrane.
When all three ossicles are missing or defective and a functional (original or reconstructed) tympanic membrane is present, the surgeon should measure the distance from the tympanic membrane to the annulus of the oval window and select the correct size prosthesis. Next remove all vestiges of the stapes footplate and place absorbable gelatine foam, (or autogenous fibrous tissue such as vein or fat) in the oval window. The loop 10 of the distal strut 1 is placed in the center of the annulus 12 of the oval window. The proximal strut 2 is securely attached near the center of the tympanic membrane with its arm 9 lying preferrably across the center along a radius extending toward the edge of the membrane, so as to utilize that portion of the tympanic membrane having the greatest sensitivity to sound waves. The arm 9 is secured to the tympanic membrane by placing a small bit of autogenous fibrous tissue over the arm so as to seal the arm to the membrane with minimal stiffening of the tympanic membrane beyond the arm.
When the proximal assembly is set in motion by sound waves striking the tympanic membrane 13 the magnetic lines of force surrounding the permanent magnet are distorted by the magnetic reluctance of the stationary distal strut 1. Resistance to this distortion causes the distal strut to be moved to correspond with the movements of the proximal assembly. The magnetic couple offers no significant resistance to the relatively slow unidirectional movements of the proximal assembly in relation to the distal strut which are caused by unidirectional movements of the tympanic membrane, but it does resist the rapid alternations caused by sound waves striking the tympanic membrane and oscillating the proximal assembly longitudinally. This resistance causes the distal strut 1 to move the oval window diaphragm correspondingly in time and magnitude with the sound waves.
In a telephone receiver the central portion of its diaphragm is set in motion by an alternating magnetic field acting against the resilient suspension of its center. In this invention the magnetic field is set in motion by the sound waves acting upon the tympanic membrane and oscillating the magnet itself.
It should be noted that the magnetic couple in this invention is not for the purpose of holding the struts so tightly together that sound oscillations might be transmitted by frictionally sustained rigidity between the moveable parts of the prosthesis. Such rigidity would not yield to protect delicate tissues. It is demonstrable that sound oscillations will be transmitted across such a magnetic couple as contained in this invention if one strut completely surrounds the body of the other strut, as in a solenoid, with zero friction between the surfaces of the parts. (It appears desirable to have some minimal friction to prevent rattling of the struts striking together.)
By reshaping the arm 9 into a loop it can be connected to an existing and functional malleus, as in the report by J. L. Sheehy in LARYNGOSCOPE (76:1165-80, July, 1966). A similar shape of loop enables it to be attached to the long process of a functional incus, replacing only the stapes. It may be thus useful as protecting the implant in the oval window, of an incus replacement, form strain during the healing process, and so reducing the incidence of fistula.
By setting the distal loop 10 on an existing functional stapes footplate and securing an attachment to the footplate by grafting autogenous fibrous tissue over the loop, or some other method of securing a firm attachment, it may be used as a replacement for the incus, with or without using the malleus and without removing the stapes.
The variant (FIG. 3) embodies the permanent magnet as part of one strut. The entire strut may be a permanent magnet. The other strut must be magnetically attractive to it. It is made entirely of wire.
It is to be understood that the forms and materials of this invention, herein shown and described, are to be taken as preferred examples of same, and that various changes may be made in the materials and the size, shape and arrangements of parts thereof, without departing from the spirit of the invention or the scope of the subjoined claim.