HK1178419B - Interlocking reverse hip and revision prosthesis - Google Patents

Description

Interlocking reverse hip and revision prosthesis

Technical Field

The present invention relates generally to hip prostheses and more particularly to interlocking reverse hip prostheses that allow for increased range of motion and increased stability during excessive ranges of motion.

Background

It is to be appreciated that several hip implants have been used in the past years. Typically, conventional hip implants include a femoral component having an articulating femoral ball attached to a stem. After preparation and reaming by the surgeon using a suitable reamer, the femoral stem is inserted into the medullary canal of the femur. The stem may be securely fixed using bone cement or a press fit. After preparation and proper reaming, a cup-shaped acetabular component is inserted into the acetabular socket and secured through holes in the cup with cancellous bone screws. It may also be fixed with bone cement or press fit or a combination thereof.

The acetabular cup is metallic and it is internally lined with high density polyethylene or ceramic. The liner is secured within the acetabular cup by a press-fit mechanism.

The main problem with conventional hip implants is instability of the prosthesis at excessive ranges of motion, thereby causing dislocation and dislocation/dislocation of the articular femoral ball. The prior art teaches one or more constrained and pre-assembled ball and cup devices in which the ball and cup members are implanted separately, whereupon the ball element is forced into a resilient opening in the cup and then held in place by the resilient material. Other constrained acetabular cups may include locking rings such as those described by albertori et al in U.S. patent 6,527,808. In the case of a cup element with a retaining ring, the ball member is forcibly inserted into the cup after both elements have been implanted. This constitutes a weak link, in which the force exerted on the prosthesis by the walking motion (ambularmototion) may exceed the force used to assemble the implant, thereby causing the ball to separate from the cup.

While these devices may be suitable for the particular purpose to which they address, they do not provide an interlocking mechanism as in the reverse hip implant design of the present invention. The nature of the applicant's design allows for increased range of motion, and increased stability at extreme ranges of motion, thereby reducing the risk of dislocation.

In these respects, the interlocking reverse hip prosthesis according to the invention substantially departs from the conventional concepts and designs of the prior art because the prior art articular femoral ball is replaced by an articular femoral cup and the acetabular cup is provided with an acetabular ball. Thus, a device is provided which was developed primarily for the purpose of reducing the risk of hip implant dislocation in the case of extreme ranges of motion.

Furthermore, since the articular surface of the femoral cup of the present invention is in full contact with the surface of the acetabular ball 100% of the time, it is clear that this will improve friction, since the load-bearing distribution is improved on the articular surface, thus reducing wear of the contacted surfaces and reducing the risk of release of wear particles in the joint. Wear particles are very harmful to the normal function of the joint.

Disclosure of Invention

The present invention provides a new interlocking reverse hip prosthesis configuration in which the acetabular ball is firmly and concentrically attached to the central protrusion or stem of the acetabular cup via morsetape (Morsetaper). In a preferred embodiment a metal acetabular cup is used. The femoral cup (also referred to herein as a hemispherical femoral cup or an articular femoral cup) is preferably firmly attached to the femoral implant by virtue of a morse taper. Other attachment means known to those skilled in the art may also be used. And whenever reference is made herein to a morse taper, it is intended to describe a preferred embodiment. The morse taper can be replaced by other suitable attachment mechanisms, as will be apparent to those skilled in the art.

The acetabular cup is implanted in an acetabular socket created in the pelvis by a surgeon and is securely fixed to the pelvis with one or more fasteners through one or more openings in the acetabular cup. The fasteners may be a variable number of reticulated bone screws or biocompatible resorbable studs. The femoral implant is then inserted and compacted into the femoral medullary canal, which has been prepared and hollowed out by the surgeon using a suitable reamer. During walking, the articular femoral cup rim or lip will slide comfortably and concentrically into the space between the acetabular ball and the acetabular cup. As will be apparent to those skilled in the art, the geometry of applicants' invention makes it difficult for the femoral cup to misalign as the range of motion increases because it becomes constrained within the space between the acetabular cup and the acetabular ball.

As indicated above, the articular surface of the femoral cup always completely contacts the articular surface of the acetabular ball, which improves weight distribution, reduces wear of the contacted surfaces, and reduces the risk of wear particles being released in the joint.

In an optional embodiment of the invention, applicants have addressed the less likely occurrence that soft tissue may become lodged/embedded in the implant, in the space between the acetabular cup and the acetabular ball. Protective sleeves may be used to avoid this possibility. As discussed in more detail below, the sleeve is disposed in the space between the acetabular cup and the acetabular ball and is allowed to freely glide therein.

There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. The novel feature of the present invention is that the positions of the articular surfaces of the hip joint (i.e., ball and socket) are reversed. This results in a new opposite hip implant which is not anticipated, rendered obvious, suggested or even suggested by any previous hip prosthesis when considered alone or in any combination.

In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components 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 that will be apparent to those skilled in the art from the description herein. Also, it is to be understood that the terminology used herein is for the purpose of description and should not be regarded as limiting.

To the accomplishment of the foregoing and related ends, the invention may be embodied in the form illustrated in the drawings. However, the drawings are merely guide and changes may be made to any specific configuration shown without departing from the principles of the present invention.

Drawings

Various other objects, features and advantages of the present invention will become more fully understood as the same becomes better understood when considered in connection with the accompanying drawings, in which like reference characters designate the same or similar elements throughout the several views, and wherein:

figure 1 is a perspective view of an interlocking reverse hip prosthesis of the present invention.

Figure 2 is a cross-sectional view of an interlocking reverse hip prosthesis.

Figure 3 is a cross-sectional view of the interlocking reverse hip prosthesis in extension and external rotation.

Figure 4 is a cross-sectional view of the interlocking reverse hip prosthesis in extension and rotation.

FIG. 5 is a perspective view of a prosthesis of the present invention showing an optional soft tissue protective sheath.

Figure 5A is a perspective view of the protective sheath itself.

Fig. 6 is a cross section of the embodiment of fig. 5.

Fig. 7 is a cross-sectional view showing a femoral cup having a recess instead of a stem for connection to a femoral implant.

Fig. 8 is a sectional view of the embodiment of fig. 7 hinged to an extreme position.

Detailed Description

Turning now to the drawings, wherein like reference numerals designate identical or similar elements throughout the several views, fig. 1-4 illustrate an interlocking reverse hip prosthesis comprising an acetabular cup (11), the acetabular cup (11) having a smooth concave surface and a convex non-articular surface. The convex non-articulating surface abuts a socket in the pelvic bone when the acetabular cup is implanted in a patient and provides a porous surface having a plurality of microprotrusions (asperities) and microporosities to allow bone ingrowth. Furthermore, the acetabular cup {11} provides one or more holes (12) in different locations for the purpose of using one or more fasteners (14). The fasteners (14) may be screws of different diameters and lengths or resorbable non-metallic and biocompatible studs. The studs, which may be referred to as bone (orthopedics) resorbable studs, will secure the acetabular cup (11) in the initial stages of bone ingrowth and will resorb within a year, be replaced by newly growing bone and become part of the host pelvic bone. During this period, the acetabular cup (11) becomes firmly attached to the acetabular socket in the pelvic bone (4) by bone ingrowth. The acetabular cup (11) has a concave hemispherical surface in which a larger acetabular cup stem (9) is seated. The acetabular cup stem (9) has a male morse taper for assembly to an acetabular ball (8) by means of an acetabular ball recess (10) having a female morse taper. Referring to fig. 2-4 and 6, the femoral cup (6) has a femoral cup stem (7) with a convex morse taper, while the femoral implant (1) has a cooperating femoral implant recess (5) with a concave morse taper located in the neck (3). Fig. 7 and 8 show a femoral cup (20), the femoral cup (20) having a neck (22), and a femoral cup recess (21) with a concave morse taper. This works in conjunction with a femoral implant stem having a convex morse taper (not shown). In a preferred embodiment, a modular system is used in the kit according to the invention, wherein the femoral cup stem (7) or neck (22) may have different lengths to suit the size needs of the patient. Thus, in the kit of the present invention, two or more femoral cups are provided having different stem lengths. In a less preferred embodiment, the length of the neck (3) or femoral implant stem (not shown) of the femoral implant (1) may also be of various lengths to suit the size needs of the patient, and in a kit including this embodiment, two or more neck or stem members of different lengths will be included. Other variations of the design to meet different size requirements will be apparent to those skilled in the art.

An important advantage of the present invention is that the greater the interdigitation, the more stable the implant, unlike conventional ball and socket hip implants, where increased range of motion is generally associated with increased risk of dislocation.

Referring to fig. 2, the proximal femur (2) is reamed in the usual manner to receive the femoral implant (1), the femoral implant (1) being capable of being cemented or press-fit into the medullary canal of the femur. The acetabular socket in the pelvis (4) is reamed to a size to receive an acetabular cup (11), the acetabular cup (11) being compressed for press-fit at the correct inclination and anteversion angles. Fasteners (14) in the form of set screws or biocompatible resorbable studs are then inserted into place to securely fix the acetabular cup (11). The acetabular ball (8) is then attached to the acetabular cup stem (9), the centerline (C-C) also being shown in fig. 2. In the position shown, the centerline (C-C) passes through the center of the acetabular cup (11), the longitudinal centerline of the acetabular cup stem (9), the center of the acetabular ball (8), the longitudinal centerline of the femoral cup stem (7) and the longitudinal centerline of the femoral implant recess (5). Obviously, when the femoral cup is articulated on the ball, the centerline associated with the femoral component will not be collinear with the centerline of the acetabular component. This line is simply shown in this way for convenience.

Referring to fig. 3, 4 and 8, when the femoral cup (6) or (20) articulates on the acetabular ball (8), the rim of the femoral cup (6) or (20) moves into and out of the hemispherical space (16) and the articular surface of the femoral cup (6) or (20) maintains the same area of contact with the acetabular ball (8) throughout the range of motion. In other words, 100% of the articular contact area of the femoral cup (6) or (20) is maintained throughout the range of motion. Fig. 3 shows the prosthesis of the invention in extension and external rotation, fig. 4 shows the prosthesis in flexion and internal rotation, and fig. 8 shows the extreme articulated position of the femoral cup (20) on the acetabular ball (8).

In one embodiment, the articular surface of the femoral cup (6) or (20) comprises high molecular weight polyethylene liners of varying thickness, but not as much as 4 mm. In various embodiments, the liner may be ceramic, or metal alloy.

An important feature of the invention is the ability to place the acetabular ball (8) in a position that minimizes or eliminates torque forces on the acetabular cup and acetabular stem. This is shown in fig. 3, where the acetabular ball (8) is attached to the acetabular cup stem (9) at a location where the equatorial plane (P-P) of the acetabular cup passes through the acetabular ball center (15).

The optional embodiment of the invention shown in figures 5 to 8 adds a soft tissue protective sheath (17) to the embodiments described above. The protective sleeve, itself also shown in perspective in fig. 5A, solves the rare occurrence of the following: soft tissue may become lodged in the space (16) due to articulation of the prosthetic joint of the invention.

Referring to fig. 6-8, the sleeve (17) extends beyond the circular outer edge of the acetabular cup (11) and has a retaining ring (18). The sleeve (17) is installed by placing the sleeve (17) in the acetabular cup (11) prior to installation of the acetabular ball (8). The sleeve (17) may have a solid surface as shown or it may be perforated with holes, slots or the like, which may be of the same or different shapes and sizes as desired.

As can be seen from fig. 6 to 8, the sleeve (17) is allowed to move freely within the space (16), limited only by the acetabular ball (8) and the acetabular cup stem (9). The sleeve (17) is also moved by bringing the positioning ring (18) into contact with the outer edge of the femoral cup (6) or (20). The retaining ring (18) will for example contact the outer edge of the femoral cup (6) or (20), particularly in the extreme articulation position of the prosthetic joint as shown in fig. 8.

In another embodiment of the invention, as also shown in figures 6 to 8, the acetabular cup (11) is designed for use in revision surgery of the hip. Revision is a surgical procedure to remove an existing implant. This most often requires removal of the acetabular cup and is associated with a high level of morbidity. Removal of a previously implanted acetabular cup can be quite difficult surgically, particularly when the cup has metal beads for bone ingrowth. In these cases, removal is also associated with iatrogenic bone loss, resulting in difficulty in inserting another conventional acetabular cup.

There are the following cases: wherein the acetabular cup is not properly implanted, or wherein the liner of the existing implant becomes worn and needs replacement. Recurrent malposition of hip implants is often secondary to surgical malposition (misprolament) of the conventional acetabular cup. For example, if during the initial procedure, the cup is placed too upright or tilted backwards (i.e., backwards rather than forwards).

To treat the above complications, sometimes a surgeon simply cements a conventional revision cup into a previously implanted acetabular cup using conventional bone cement. However, problems can arise if the initial position of the previously implanted acetabular cup is too vertical or retroverted, preventing the conventional revision cup from being glued to the previously implanted acetabular cup. Thus, removal of the previously implanted acetabular cup becomes necessary because of the greater risk and possible morbidity posed to the patient, as described above.

Another important advantage of the present invention is that the inclination and the caster angle are not critical, as the interlocking mechanism of applicants' implant will compensate for misalignment of the previously implanted acetabular cup.

The acetabular cup (11) of applicants' interlocking reverse hip prosthesis can optionally be provided with a thin circumferential groove (19) located near the equatorial plane of the cup, as shown in fig. 6-8.

In revision surgery using the hip prosthesis of the applicant's invention, the plastic polyethylene insert of the previously implanted acetabular cup is removed. The circumferential groove (19) of the interlocking reverse hip prosthesis will bear against the locating "O-ring" of the revision previously implanted acetabular cup, thereby providing the applicant's firm fixation of the revision interlocking reverse hip prosthesis to the previously implanted acetabular cup.

The components of the reverse hip prosthesis of the present invention are made of biocompatible materials commonly used in the art, and suitable materials will be apparent to those skilled in the art based on the disclosure herein. Metals or metal alloys such as titanium or cobalt chromium are suitable. For some components, such as acetabular balls, metals or ceramics may be used. High density polyethylene is also suitable for certain components, for example, protective sleeves or optional liners for the recesses of the femoral cup. Other biocompatible materials or combinations thereof may be used for the various components, as will be apparent to those skilled in the art.

The dimensions of the various components of the reverse hip prosthesis of the present invention can be readily determined by one skilled in the art from the disclosure herein, and for a hemispherical acetabular cup, an outer diameter of about 35 millimeters (mm) to about 65mm will be suitable for most applications. The spherical acetabular ball should have a diameter of from about 28mm to about 45 mm. The diameter of the acetabular ball should be from about 7mm to about 12mm smaller than the inner diameter of the acetabular cup, thus creating a hemispherical space or gap having a width of from about 7mm to about 12mm to allow the femoral cup to articulate therein. Of course, the concave hemispherical articulating surface of the femoral cup will be sized to be compatible with the acetabular ball to allow smooth articulation. Highly polished cobalt chromium is an excellent material for the articular surface of the femoral cup, but other materials such as biocompatible metal alloys may also be used. The femoral cup may also contain a liner made of high density polyethylene, ceramic, or biocompatible metal alloy.

It is therefore an object of the present invention to provide a new and improved interlock and limited reverse hip prosthesis system wherein the two conventional articular surfaces of the hip joint are reversed and interlocked. In the present invention, the system is described which has all the advantages of the prior art designs without any disadvantages of the prior art and with many improvements over the prior art, in particular in terms of significantly increased range of motion and reduced risk of release of wear particles into the joint.

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, materials, 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. Accordingly, the foregoing description 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 illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

Claims (13)

1. An opposed hip prosthesis comprising:

an acetabular cup (11) having a convex surface for attachment to an acetabular socket in the pelvic bone (4) and a concave surface located opposite the convex surface, the concave surface having an acetabular cup stem (9) attached therein and projecting outwardly therefrom,

an acetabular ball (8) attached to the acetabular cup stem (9), the acetabular ball (8) having a surface,

the concave surface of the acetabular cup (11) and the surface of the acetabular ball (8) being spaced from one another, thereby defining a gap (16) therebetween,

a femoral implant (1) for implantation in the medullary canal of the proximal femur; and

a femoral cup (6; 20) attached to the proximal end of the femoral implant (1), the femoral cup (6; 20) being sized to articulate in a gap (16) such that the femoral cup (6; 20) has a concave surface sized to articulate on the surface of the acetabular ball, the gap (16) being sized and configured to allow the articulation to be achieved when the femoral cup (6; 20) is constrained within the gap (16).

2. The prosthesis according to claim 1, wherein the concave surface of the acetabular cup (11) is hemispherical, the acetabular ball (8) is spherical and the concave surface of the femoral cup (6; 20) is hemispherical.

3. Prosthesis according to claim 1 or 2, wherein the concave surface of the acetabular cup (11) has a centre and the acetabular cup stem (9) is attached to and into the centre.

4. The prosthesis according to claim 1 or 2, wherein the acetabular ball (8) has an acetabular ball recess (10) sized to receive the acetabular cup stem (9).

5. The prosthesis according to claim 1 or 2, wherein the femoral cup (6; 20) has a femoral cup stem (7) projecting outwardly therefrom in a direction opposite to its concave surface, and the femoral implant (1) has a recess (5) at its proximal end sized to receive the femoral cup stem (7).

6. The prosthesis according to claim 1 or 2, wherein the femoral implant (1) has a femoral implant stem extending proximally from the femoral implant (1) and the femoral cup (6; 20) has a recess (21) sized to receive the femoral implant stem.

7. The prosthesis according to claim 1 or 2, wherein the acetabular ball (8) has a center, the acetabular cup stem (9) has a longitudinal centerline, and the acetabular ball recess (10) has a longitudinal centerline, both longitudinal centerlines being collinear and passing through the center of the acetabular ball (8).

8. The prosthesis according to claim 5, wherein the acetabular cup (6; 20) has a concave hemispherical portion with a centerline, the femoral cup stem (7) has a longitudinal centerline, and the femoral implant recess (5) has a longitudinal centerline, wherein all centerlines are collinear.

9. The prosthesis according to claim 6, wherein the acetabular cup (6; 20) has a concave hemispherical portion with a centerline, the femoral implant stem has a longitudinal centerline, and the femoral cup recess (21) has a longitudinal centerline, wherein all centerlines are collinear.

10. Prosthesis according to claim 1 or 2, wherein the acetabular cup (11) further comprises a circumferential groove (19) in the convex surface, said circumferential groove (19) being located near a circumferential edge of the acetabular cup (11).

11. The prosthesis of claim 1 or 2, further comprising: a hemispherical protective shield (17) movably disposed in the gap (16), the protective shield (17) having a positioning ring (18) for engagement with a circumferential outer edge of the femoral cup (6; 20), whereby articulation of the femoral cup (6; 20) on the acetabular ball causes movement of the protective shield.

12. Kit comprising a prosthesis according to any of claims 5 to 11 and further comprising one or more additional femoral cups (6; 20), wherein the femoral cup stems (7) have different lengths.

13. Kit comprising a prosthesis according to claim 6 or 9, wherein the femoral cup recess (21) is arranged in a neck (22) protruding outwardly from the femoral cup (6; 20) in a direction opposite to the concave surface of the femoral cup, and one or more additional femoral cups (6; 20), wherein the femoral cup necks (22) have different lengths.