Patent Application
20160015520
The present disclosure relates to an acetabular shell liner, and particularly to a reinforcing structure for a shell liner.
This section provides background information related to the present disclosure which is not necessarily prior art.
Articulating regions of the anatomy can include areas where two bone sections move relative to one another. For example, an acetabulum can provide a region for articulation with a femoral head. The articulating region, however, can become injured, worn, or suffer from a condition such as arthritis, but it can be replaced with various prostheses. Such prostheses can replace the acetabulum, the femoral head, and various other portions of the femur, or other combinations thereof. The replacement of both the acetabulum and the femoral head is generally referred to as a total joint replacement. When the joint being replaced is a hip, the replacement is generally referred to as a total hip replacement.
Surgeons that perform total hip replacements often look to maximize hip joint stability. One way to achieve stability may be with a larger femoral head size. To maximize an acetabular size, however, one generally needs to minimize thickness of the components. This reduction in thickness may lead to deformation of the components during use, insertion, etc. If an acetabular shell liner deforms more than a determined amount of clearance between the head and liner, pinching may occur.
This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
An acetabular prosthesis liner for a hip replacement assembly includes a thin shell liner forming a portion of a sphere. The thin shell liner includes an outer surface, an inner surface, and a member that is or may be, according to various embodiments, formed as one piece integrated with the outer surface and inner surface. The member extends away from the thin shell liner outer surface for a distance and has a thickness which is generally smaller than the distance. The member may form a flange.
A hip replacement assembly may include an acetabular cup, a large femoral head, a small femoral head. The large femoral head may articulate within the acetabular cup, and the small femoral head is configured to articulatingly fit within the large femoral head. A shell liner forming a portion of a sphere may engage the acetabular cup. The shell liner includes an acetabular cup engaging surface, a large femoral head engaging surface, and a stiffening member integrated with the acetabular cup engaging surface and the large femoral head engaging surface. The stiffening member is further configured to minimize distortion of the shell liner from the portion of the sphere shape when force is applied to the liner. The large femoral head articulatingly engages the shell liner.
A method of manufacturing a thin shell acetabular liner includes forming an outer surface into at least a part of a sphere and forming an inner surface into at least part of a sphere. Furthermore, forming the inner surface and forming the outer surface forms the liner to have a liner thickness and a flange that extends a distance away from the outer surface. The flange is formed to have a thickness that is about equal to the liner thickness. The flange is formed to have the thickness that is smaller than the distance of the flange. Furthermore, forming a centering member on the outer surface at a near central position of the outer surface.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
Example embodiments will now be described more fully with reference to the accompanying drawings.
According to the present disclosure and as illustrated in
The shell liner 18, as shown in
The shell liner 18 may also be thin and have a thickness 25 measured between the inner surface 22 and the outer surface 20. The thickness 25 may be uniform from the apical portion 18a and the open portion 18b. For example, the thickness 25 may be about 2 millimeters (mm) to about 10 mm and further including about 5 mm. The thickness of the liner 18 is generally defined by the thickness 25 of the source material from which the liner 18 is formed. The thickness 25, however, may also vary between an apical portion thickness 25a, measured near the apical portion 18a, and an open portion thickness 25b, measured near the open portion 18b. Thus, the apical portion thickness 25a and the open portion thickness 25b may be unequal. According to various embodiments, the apical thickness may be about 5 mm to about 15 mm and the open portion thickness may be about 2 mm to about 5 mm. The thickness may vary gradually, or the wall of the liner 18 may be stepped.
The shell liner 18 is a thin member. For example, the inner surface 22 of the shell liner 18 may have an inner diameter 22a and the outer surface may have an outer diameter 20a. The shell liner 18 may be thin when the inner diameter 22a has a dimension that is close to the outer diameter 20a. For example, the inner diameter 22a may be about 70% to about 99% of the outer diameter 20a, further including about 85% to about 90%, and further including about 91% to about 97%. In various embodiments, the thickness of the liner near the rim may be about 0.5 millimeter (mm) to about 1.5 (mm), including about 1 mm to about 1.5 mm, and further including about 1 mm. The thickness may be the dimension between the inner diameter 22a and the outer diameter 20a.
As a further example, the shell liner 18 may be thin when the inner surface 22 is such that the large femoral head 14 may have a volume that is maximized for the shell liner 18. In various embodiments, the large femoral head 14 with maximum volume may increase a range of motion, reduces the risk of dislocation, and/or minimize point loading on the head 14 compared to the large femoral head 14 at a smaller volume.
The stiffening member 24 is configured to minimize and/or eliminate distortion of the shell liner 18. In particular, the stiffening member 24 minimizes distortion of the shape or configuration of the liner 18 from the portion of the sphere shape when force, such as a compressive body force, is applied to the shell liner 18. For example, force I may be applied to the shell liner 18 by an insertion tool 27 when the hip replacement assembly 10 is placed in the patient, as shown in
In addition, force B may be applied to the outer surface 20 of the liner 18 by a body weight of the patient, for example, when the patient is standing. Therefore, the liner 18 also experiences reaction force F on the inner surface 22 of the liner because of the body weight of the patient. The stiffening member 24 minimizes and/or eliminates distortion of the shell liner 18, despite being thin, when a force is applied to the shell liner.
The stiffening member 24 may extend away from the outer surface 20 of shell liner 18. The stiffening member 24 may be formed as one piece that is integral with the outer surface 20 and the inner surface 22. Therefore, the stiffening member 24 may be a lip or flange. The stiffening member may be formed by machining or bending a solid portion of the liner 18. The stiffening member 24 may also be formed separately from the outer surface 20 and the inner surface 22 and attached to the liner 18. The stiffening member may be attached using commonly known joining methods, such as welding or brazing. The stiffening member 24 may, therefore, have surfaces that are continuous with the outer surface 20 and the inner surface 22.
As shown in
The stiffening member 24 may also have the thickness 24a similar to the liner thickness 25 or the open portion thickness 25b′ (shown in phantom). For example, the liner 18 may have the open portion thickness 25b′ near the stiffening member 24 that is similar to the stiffening member thickness 24a. Alternatively, the open portion thickness 25b may be substantially larger than stiffening member thickness 24a. It is understood, however, that the stiffening member 24 may have any appropriate thickness 24a that is generally larger in dimension than the extension 24b.
Again referring to
Referring to
The shell liner 18 may be manufactured or formed by forming the outer surface 20 and the inner surface 22, such as by machining the shell liner 18 from a solid member. One having ordinary skill in the art would understand that forming may also be other methods, such as casting, forging, welding, or 3D printing. Such methods may include investment casting of the liner 18.
In various embodiments, the inner surface 22 and outer surface 20 are each formed into a partial sphere. Forming the inner surface 22 and forming the outer surface 20 also forms the liner thickness 25 of the liner 18. For example, the liner thickness 25 may be formed to be much less than its diameter. As a further example, the liner thickness 25 may be formed to the dimensions as described above.
Furthermore, forming the centering member 26 on the outer surface 20 at a near central position of the outer surface 20. The centering member 26 may be formed as a protrusion that is formed to engage the acetabular cup 12 and center the shell liner 18 within the acetabular cup 12. For example, the centering member 26 may be formed on the outer surface 20 of the shell liner 18 and formed to frictionally engage and center the shell liner 18 within an acetabular cup 12. As a further example, the centering member 26 may be formed to fit within a depression 28 of the acetabular cup 12 such that movement and position of the shell liner 18 relative to the acetabular cup 12 is restricted.
In various embodiments, the stiffening member 24 is formed to extend away from the outer surface 20 to minimize distortion of the shell liner 18. In particular, the stiffening member 24 is formed to minimize distortion from the formed shape, such as the portion of the sphere or sphere-like shape, when pressure is applied to the shell liner 18. The stiffening member 24 may be formed with a thickness that is nearly equal to the liner thickness. For example, the lip may be formed to have dimensions as described above.
The flange, or stiffening member 24, may further be formed to have a thickness that is much smaller than a width of the flange. For example, the stiffening member 24 may be formed to have the dimensions as described above. Forming the stiffening member 24 includes forming the outer surface 20 to include a side of the stiffening member 24 and forming the inner surface 22 to include an opposing side of the stiffening member 24. For example, a cylinder of appropriate material may be machined to form the stiffening member 24 to extend away from the outer surface 20. Further, the liner 18 may be formed and the stiffening member 24 may be machined separately as an annular member and affixed to the liner 18 near the open end 18b.
The shell liner 18 according to various embodiments may provide for a shell acetabular prosthesis liner 18 that maximizes femoral head size for increased hip H joint stability. To avoid deformation of the shell liner 18 bone when under a force, such as a compressive force or pressure, while being inserted in the acetabulum of the hip H, the shell liner 18 includes the stiffening member 24 that is configured to minimize distortion. Therefore, the acetabular shell liner 18 according to the present teachings increases range of motion and reduces the risk of dislocation of the hip replacement assembly 10.
The foregoing description of the acetabular shell liner has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.
