Patent Application
20110218637
1. Field of the Invention
The present invention relates generally to hip prostheses and more specifically to an interlocking reversed hip prosthesis allowing increased range of motion and stability during excessive range of motion.
2. Description of the Prior Art
It can be appreciated that several hip implants have been in use for years. Typically, conventional hip implant comprising a femoral component having an articular ball attached to a stem, which is inserted into the medullary canal of the femur after preparation and reaming using appropriate reamers by the operating surgeon. Said stem can be secured with bone cement or press fit. The acetabular component or socket having the shape of a cup is inserted into the acetabular cavity after preparation and appropriate reaming and secured with cancellous screws through holes in the implant, bone cement or press fit or combination of thereof.
The acetabular cup will then receive a lining made of high-density polyethylene or ceramic. Said lining will be secured into the acetabular shell by a press fit mechanism. The main problem with conventional hip implants is the instability of the prosthesis at the extreme range of motion thereby allowing the femoral head to dislodge and dislocate. Prior art teaches constrained and preassembled ball and socket devices or a device wherein the ball and socket members are implanted separately whereupon the ball element is forced into a resilient opening in the socket and thereafter held in place by the resilient material. Other constrained acetabular sockets include a locking ring such as the one described by Albertorio et al. U.S. Pat. No. 6,527,808. In the case of socket elements having retaining ring, the ball member is forcefully inserted into the socket after the two elements are implanted, This constitutes a weak link where forces exerted on the prosthesis by ambulatory motion may exceed the forces used to assemble the implant thereby causing the ball to be separated from the socket.
While these devices may be suitable for the particular purpose to which they address, they are not suitable for providing an interlocking mechanism as in reverse hip implant design of the present invention, which by the very nature of its design allows increased range of motion and increased stability at extreme range of motion thereby reducing the risk of dislocation.
In these respects, the interlocking reverse hip prosthesis according to the present invention substantially departs from the conventional concept and design of the prior art, and in so doing provides an apparatus primarily developed for the purpose of reducing the risk of dislocation of hip implants at extreme range of motion. Furthermore, since the articular surface of the two components are fully in contact 100% at all time, it is clear that this will improve the weight distribution and decrease the wear of the surfaces in contact and reduce the number of wear particles released in the joint. The later, being very detrimental to the proper function of the joint.
Various other objects, features and advantages of the present invention will become fully appreciated as the same becomes better understood when considered in conjunction with the current accompanying drawings, in which like reference characters designate the same or similar report throughout the several viewers, and wherein:
The present invention provides a new interlocking reversed hip implant construction wherein the articular ball member of the acetabular component is solidly and concentrically attached to the central protrusion or stem of the acetabular cup via Morse taper. The hemispherical femoral cup member is solidly attached to the femoral stem via Morse taper. Said acetabular cup or socket is implanted in an acetabular opening or cavity constructed by the surgeon into the pelvic bone to which it is firmly secured by one or more screws through one or more openings in the acetabular shell. In another embodiment of this invention the screws can be replaced by biocompatible resorbable studs of variable number. The femoral stem is then inserted and impacted into the femoral medullary canal which has been prepared and hollowed by the surgeon using appropriate reamers. The femoral hemispherical articular cup is then firmly attached to the proximal end of the femoral stem via Morse Taper. Subsequently, the hip is reduced and the femoral and acetabular components are put in contact whereby the femoral hemispherical cup will concentrically glide over the acetabular articular head. During ambulation, the femoral cup edge or lip will glide conformably into a hemispherical space located between the acetabular articular ball and acetabular shell. Furthermore, by its very geometrical configuration, it becomes very difficult for the femoral cup to dislocate when range of motion increases since it becomes constrained in the hemispherical locking space between the acetabular shell and the acetabular ball.
Furthermore, since the articular surface of the two components are fully in contact 100% at all time, it is clear that this will improve the weight distribution and decrease the wear of the surfaces in contact and reduce the number of wear particles released in the joint.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description may be better understood, and in order that the present contribution to the art may be better appreciated. The novel feature of this invention, whereby the location of the articular surfaces of the hip joint namely the ball and socket is reversed, resulting in a new restrained reversed hip implant which is not anticipated, rendered obvious, suggested or even implied by any of the prior conventional hip prosthesis, either alone or in any combination thereof.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not committed in its application to the details of construction and it arrangements of the component set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the terminology employed herein are for the purpose of the description and should not be regarded as limiting
To the accomplishment of the above and related objects, this invention may be embodied in the form illustrated in the accompanying drawings. Attention being called to the fact, however, that the drawings are elicited only, and that change may be made into any specific construction illustrated.
Turning now descriptively to the drawings, in which similar reference characters denote similar elements throughout the several views, the attached figures illustrate an interlocking reversed hip prosthesis, which comprises a hemispherical acetabular shell (11) having a smooth concave surface and convex non-articular. surface. The convex non-articular surface provides a porous surface with multiple asperities and micro-voids to allow bone ingrowth. Furthermore, the acetabular shell provides one or more holes (12) at different locations for the purpose of using one or more screws (14). In another embodiment, the screws can be replaced with resorbable nonmetallic and biocompatible studs of different diameter and length. These orthobiologic resorbable studs will secure the acetabular shell during the initial phase of bone ingrowth and will resorb within one year, being replaced by newly generated bone and become part of the host bone. During that period, the acetabular shell is by then solidly attached to the acetabular bone by bone ingrowth. The concave hemispherical surface of the acetabular shell provides a large interior cylindrical protrusion (9), which has a male Morse taper for assembly to the female Morse taper (10) of the acetabular articular head (8). The femoral hemispherical articular cup (6) has a central cylindrical protrusion (7) on its convex surface, which has a male Morse taper for assembly to a recess (5) with female Morse taper located at the shoulder (3) of the femoral stem (1). The central protrusion of the femoral cup (7) comes in different length thereby allowing use of several neck length in a modular fashion.
In another embodiment of the invention, the femoral articular cup will have a female Morse taper while the femoral stem (1) would have a male Morse taper.
An important advantage of the present invention is that the greater the interdigitation the more stability of the implant as opposed to the conventional ball and socket hip implants, where increased range of motion is usually associated with increased risk of dislocation.
During the implantation of the prosthesis of the present invention, the operating surgeon will initially prepare the proximal femoral bone (2) by using conventional reamers in the usual fashion. The acetabular cavity in the pelvic bone (4) is reamed to the appropriate size to accept the acetabular shell (11), which is impacted for press fit at the right angle of inclination and orientation. Fixation screws or biocompatible resorbable studs are then inserted in place to secure the cup. The femoral stem (1) is then inserted into the femoral canal and can be cemented or press fit. The acetabular ball (8) is then inserted onto the central protrusion of the acetabular cup (9). Subsequently, the femoral articular cup (6) is inserted onto the proximal femoral stem via Morse taper (5). Once the insertion of the components is complete, the implant is assembled together.
In one embodiment, the articular surface of the femoral cup contains a high molecular polyethylene lining of varying thickness, but no less than 4 mm. In a different embodiment the lining could be porcelain or other metallic alloy.
Another embodiment is directed to prosthesis for a shoulder joint. The first component includes an anchoring glenoid plate attached to the concave surface of the glenoid fossa having a glenoid ball. The second component being a hemispherical humeral cup having a stem like protrusion, which is attached via Morse taper to humeral stem to be inserted into the proximal humerus.
It is therefore the object of the present invention to provide a new and improved interlocking and restrained reversed hip prosthesis system, where to conventional articular surfaces of the hip joint are reversed and interlocked. The system described in the present invention, which has all the advantages of the prior art of known design and configuration and none of the disadvantages.
With respect to the above description then, it is to be realized that the optimum dimensional relationships for the parts of the invention, to include variations in size, material, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention. Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/339,680 filed on Mar. 8, 2010 and entitled “INTERLOCKING REVERSE HIP PROSTHESIS,” the entirety of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61339680 | Mar 2010 | US |
