Prosthetic Hip Joint

Abstract

A prosthetic device and more particularly a hip-joint prosthesis having a fully assembled composite structure of a femoral head, neck and shank to be positioned in and on the femur, a cup for positioning in the acetabulum for relative articulation therein to closely approximate the anatomical function of the natural femur head and acetabulum joint with the femoral head and cup being connected with each other to restrain their separation, but to permit their relative movement.

Description

BACKGROUND OF THE INVENTION

Since arthroplasty was first introduced in about 1827, many surgical procedures have been attempted to produce the ideal pseudarthosis. These encompassed attempts to create artificial joints which would closely meet the anatomical function of the pre-existing diseased part and still be relatively painless. Such recent attempts are exemplified by United States Letters Patent to Scales et al U.S. Pat. No. 3,584,318, Haboush U.S. Pat. No. 2,668,531 and U.S. Pat. No. 3,067,740.

Prior attempts at the creation of artificial joints have included the provision of artificial femur heads and acetabulum sockets replacing the originals. Unfortunately, erosion and arthritis that sometimes takes place between the artificial insert and the body causes a mal relationship that produces new and additional problems. To overcome such problems, attempts have been made to cover the acetabulum with protective cups or shields which have been fastened to the acetabulum by pins, glue or other securing means.

The surgical procedures are complicated, time consuming and often performed at different times and require approximately 2 to 3 hours to perform during which the mortality or morbidity rate is high. Oftentimes the functioning of the resultant joint still does not permit a smooth movement between the head and the secured acetabulum to any great extent especially after a reasonable period of time.

SUMMARY OF THE INVENTION

The present invention is directed to a prosthetic device and more particularly to a hip-joint prosthesis although not specifically limited thereto.

An object of the invention is to provide a prosthesis that may be substituted for and to take the place of the natural anatomic structure and perform the same functions in substantially the same manner as such replaced structures were intended to perform.

Another object of the invention is to provide a prosthesis which is a composite of essentially non-separable parts capable of substantially frictionless articulation. In carrying out the above, an object and feature of the invention resides in the composite arrangement of detailed structures which enable a smooth cup to be inserted into relative articulating contact with the acetabulum while a femur head is retained within the cup and permitted substantially frictionless articulation relative to the cup.

Still a further object is to provide a prosthesis of assembled details that may be installed and substituted for the related anatomy in a single surgical procedure, in a fraction of the time required for prior similar surgical procedures to thereby reduce the mortality an morbidity rate.

It is another object of the present invention to provide an improved hip-joint prosthesis overcoming the shortcomings of the prior art. Specifically, it is an object to provide an artificial hip-joint prosthetic device in which a cup is utilized for touching and articulating engagement with the acetabulum, thereby avoiding the pinning, gluing and other securing means that have been utilized and taught in the prior art. Further, the femur head is permitted relative substantially frictionless articulation within the cup while the head and the cup are restrained from relative separation, thereby permitting the surgical procedure to be accomplished all at one time and enabling alternate articulation between the head and the cup in the event the cup and the acetabulum should for some reason become restricted in their articulation.

The above description, as well as further objects, features and advantages of the present invention, will be more fully appreciated by reference to the following detailed description of a presently preferred, but nonetheless illustrative, embodiment in accordance with the present invention, when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a partial perspective view illustrating the prosthetic device as applied to the hip joint according to the teaching of the present invention;

FIG. 2 is an isolated front elevational view, on an enlarged scale, of the prosthetic device in its unassembled condition; and

FIG. 3 is a partial front elevational view, similar to FIG. 2, illustrating the prosthetic device in its assembled condition.

Referring to the drawing, the composite prosthetic device there shown is generally identified by the numeral 10. Throughout the description, reference will be made to the use of the prosthesis 10 in connection with a hip 12 and more particularly to the acetabulum socket 14. This description should not constitute a limitation upon the scope of the invention. The reference of the prosthetic device 10 for use in connection with the hip is merely to enable a simple and easy explanation of the invention. Obviously, the invention may be applied to other body parts and is equally applicable in veterinary uses.

The prosthetic device 10 comprises a femoral insert adapted to take the place of the damaged or diseased femur head. The insert is generally identified by the numeral 16 and comprises a stem 18 that is adapted to be forced into the femur after the natural head of the femur has been removed. The stem 18 is provided with an enlarged stop or positioning shoulder 20 that merges with a narrowed neck 22 that extends between the stem 18 and a substitute head 24. Because the narrowed neck 22 is intermediate the stem and the head 24, it joins the two parts together to form a single structure. The overall femur insert structure 16 may be made of any well known metallic material that is inert and that is commonly or conventionally utilized for these purposes. The specific nature or composition of such material forms no part of this invention, although Vitallium has been conventionally employed for such purposes.

The head 24 is substantially spherical in shape narrowing toward the neck 22, beyond its diametral line 26. The overall femur insert 16 may be made as a unitary, nonseparable structure which may be cast, machined or forged if desired, the method of construction being immaterial for the purposes of the present invention.

Cooperating with the femur insert 16 is a universally movable acetabulum insert cup generally identified by the numeral 28. The acetabulum cup 28 is formed as a unitary structure and comprises an outer cup member or liner 30 and an inner cup or liner 32. The elements 30 and 32 are joined together either by lamination, gluing or any other convenient securing means to form the unitary overall acetabulum insert cup structure 28. The outer cup or liner 30 is made of a highly polished, inert metal, such as Vitallium. Its outer surface, being highly polished, free of radial projections and interruptions is essentially and substantially spherical in shape to enable the same to be moved substantially universally within a corresponding opening or socket that may be subsequently provided at the acetabulum socket 14. The inner liner 32 is bonded or adhered throughout its surface adjacent to and in engagement with the outer liner 30 so that they form a unitary structure incapable of relative separation or movement. The means for accommodating or enabling such relative securement between the liners 30 and 32 forms no part of the present invention.

The inner liner 32 is composed of a material having low frictional resistance and apparent high lubricating characteristics. Such materials as silicone, polyethylene and polyfluroethylene are inert, resilient plastics that may be machined, molded and shaped congruent to that of the interior surface of the outer cup or liner 30. The interior of the inner cup or liner 32 thus presents a very smooth essentially spherical surface 34 of high lubricity and, therefore, low substantially frictionless engagement with the highly polished surface of the femur head 24 when the femur head 24 is inserted into the acetabulum insert cup structure 28 as seen in FIG. 3. Thus, the interface established between the head 24 and the lubricating liner 32 provides a universal joint having very low, substantially frictionless characteristics.

Both cup or liner members 30 and 32 extend beyond a diametral line 36 defining the substantially and essentially spherical shape of the interior of the cup structure 28. The extension of the overall cup structure 28 beyond the diametral line 36 includes both the outer cup 30 as at 38 and the inner cup 32 as at 40. The inner cup 32 is narrowed at the extension 40 such as is shown by the wall 42 to form a constricted opening 44 which defines an entranceway into the interior of the acetabulum insert cup structure 28. The bounding outer wall 38 prevents the inner wall from resiliently expanding but does not inhibit the wall 42 from yielding to enable the insertion of the head 24 into and out of the cup 32.

In practice, the cup structure 28 is formed independently of the femur insert 16. However, before use, the femur insert head 24 is positioned within the cup structure 28 so that both elements are connected together against relative separation for use as a unitary or composite prosthetic device 10. In this connection although the opening 44 of the acetabulum insert cup structure 28 is narrower in diameter than the widest diameter extending across the diametral line 26 of the head 24, the nature of the silicone liner wall 42 is such that the same yields slightly under pressure, restricted by the wall 38, and thus upon the application of lengthwise pressure, the cup and the head 24 may be joined together by forcing the head 24 through the opening 44 bordered by the wall 42 and then into the confines of the socket defined by the surface 34. The head is retained within the socket of the inner cup liner 32 because of the constricted size of the opening 44 and the insert 16 and the cup structure 28 are restrained and normally prevented from relative accidental subsequent separation. Obviously, a surgeon may separate the two structures 16 and 28 should he find the same necessary, but in normal use the composite of the inserts 16 and 28 form a unitary prosthetic device 10.

The connection of the two inserts 16 and 28 is illustrated in FIG. 3. It should be obvious to those skilled in the art that the connection formed between the highly polished, smooth metallic head 24 and that of the surface 34 of the acetabulum insert cup structure 28 permits substantially frictionless universal movement between the femur stem and the acetabulum if and when the outer surface of the outer cup or liner 30 is positioned within the acetabulum socket 14 and restricted or restrained from movement relative thereto. Such relative movement between the head 24 and the surface 34 is enhanced and facilitated in a substantially frictionless manner because the inner liner 32 is formed of a very smooth, high lubricity material.

In practice, the femur stem 18 is inserted by being pressed into the femur 46 as seen in FIG. 1 after the natural femur head has been removed. The stem is inserted as deep as the shoulder 20 will permit. Thereafter, the acetabulum socket 14 is reamed or shaped by the surgeon to conform it substantially congruent to that of the outer highly polished surface of the outer liner or cup 30, which is then placed within such shaped socket. All of this is performed in single operation without the need to pin, glue, bolt or otherwise secure the cup 30 to the acetabulum. The operation is quite simple and can be performed in a single procedure reducing mortality and morbidity to a very low rate.

When the surgical procedure is completed, the acetabulum insert cup structure 28 is permitted relative universal movement with respect to the acetabulum socket 14 which has been shaped thereto. It is recognized that the body tends to reject the prostethic device 10 in some instances, in other instances disease and erosion as well as the accumulation of cartilage and other body accumulations may restrict the continued free movements of the femur 46 relative to the hip 12 at the interface between the outer surface of the outer cup 30 and the socket 14. In such instances, a secondary or alternate movement is permitted at the interface between the head 24 and the highly lubricated surface 34. Hence, in spite of the fact that the acetabulum insert cup structure 38 may subsequently become locked, or restricted and perhaps even totally immovable relative to the acetabulum socket 14 at the interface therebetween, continued, unrestricted, substantially universal movement of the femur 46 is permitted between the head 24 and the lubricating liner 32.

The interface movement between the head 24 or femur 46 and the liner 32 or hip 12 is of such nature as to last substantially indefinitely. With the prosthesis 10 surgically positioned as described, forces of motion of the hip 12 are divided over large surface areas. When the stress is greater than that able to be absorbed by the interface between the head 24 and liner 32, such forces are further distributed by motion afforded by the interface between the outer smooth surface of the cup 30 and the acetabulum socket 14.

What has been provided is a unique prosthetic device that may be applied in a single surgical procedure, within a relatively short time and which will permit its continued use without securing the same to the acetabulum. And even long after the body may erode or produce constrictions to movement that might normally occur at the interface between the acetabulum 14 and the acetabulum insert cup structure 28, movement is enabled at the interface of the cup 28 with the head 24.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended thereto.

Claims

What is claimed is:

1. A hip-joint prosthesis comprising a replacement member having a substantially spherical head for placement in articulating relation to an acetabulum opening,

an inner cup fabricated of material of low frictional resistance having a substantially spherical wall bounding a chamber of a corresponding substantially spherical shape and size in relation to that of said head and disposed in covering relation thereover so as to permit initial articulating traverses of comparatively large extent between said head and said inner cup substantially duplicating the movements of the femur head relative to the acetabulum,

and an outer cup fabricated of a metal alloy which is inert when disposed in live body tissue, said outer cup being disposed in covering fixed relation over said inner cup and having an unbroken, continuously smooth outer spherical cup surface free of radial projections and interruptions for allowing substantially universal articulating traverses within the acetabulum opening.

2. A hip-joint prosthesis as defined in claim 1 wherein said outer and inner cups have an annular wall section bounding the opening into said chamber thereof which is adpated to holdingly engage said spherical head against withdrawing movement therefrom.

3. A hip-joint prosthesis as defined in claim 2 wherein said fabrication material of said inner cup is a resilient plastic, such that the assembly of said metal outer cup and said inner plastic cup is adapted to snap in place over said spherical head.

4. A hip-joint prosthesis as defined in claim 3 wherein said inner cup is a polyethylene.

5. In a prosthesis for replacing at least part of a body joint comprising, in combination,

a substantially spherical head member for placement in articulating relation in a joint opening,

a socket for said head,

said socket having a continuously smooth unbroken outer substantially spherical surface, free of radial projections and interruptions for allowing substantially universal articulating traverses within the joint opening,

said socket and head including cooperating means connecting said socket to and about said head for relative movement but to prevent relative separation thereof,

and a low friction liner between said head and socket to permit relative movement between said head and socket and including means to connect the same to said head to prevent the relative separation thereof.

6. In a prosthesis as defined in claim 5 wherein said liner is fabricated of a material having a low friction surface.

7. In a prosthesis as defined in claim 6 wherein said cooperating means connecting said socket, liner and head comprises interfitting substantially spherical shapes permitting the insertion of said liner within said socket and said head within said liner.

8. In a prosthesis as defined in claim 7 wherein said fabrication material of said liner is a resilient plastic such that the assembly of said socket and said liner is adapted to snap in place over said head.

9. In a prosthesis as defined in claim 8 wherein said liner is polyethylene.

10. A hip-joint prosthesis comprising a femur stem, a femur configured head, and a neck narrower than said stem and head intermediate the same to connect said head and stem together,

a cup having an unbroken, continuously smooth outer surface free of projections and interruptions for insertion into and for allowing substantially universal traverses within an acetabulum opening,

a liner of inert low-friction material retained in said cup against removal therefrom,

said liner having a socket defined therein,

said head being movable within and relative to said socket,

said socket having a smooth surface shaped to correspond with that of said head and said socket terminating in narrowed opening engageable with and about said head adjacent said narrower neck to restrain the withdrawal of said head from said socket through said opening.