HIP STEM PROSTHESIS WITH A POROUS COLLAR TO ALLOW FOR BONE INGROWTH
A femoral hip implant includes a first end, a second end, and a collar with a porous surface, all fabricated from a single piece of material. The entire area of the collar is porous, and the collar elastically deflects under load to promote bone ingrowth.
This application claims the benefit of U.S. Provisional Application No. 61/697,177, which was filed on Sep. 5, 2012, and U.S. Provisional Application No. 61/790,528, which was filed on Mar. 15, 2013, both of which are incorporated herein by reference in their entirety.
FIELDThe present disclosure relates to embodiments of a femoral hip implant.
BACKGROUNDThere are two primary methods of fixation for femoral hip implants in total hip replacement. The first method utilizes bone cement to bond the femoral hip implant to the surrounding bone. The second method relies on a press fit between the femoral hip implant and the bone to promote long term stability. Such press fit implants are commonly tapered to resist post-operative subsidence into the bone canal, and can include porous surfaces to promote bone ingrowth. Many press fit implants also include a collar that rests on the calcar area of the femur, acting to restrain subsidence and allow load sharing between the bone and the implant.
SUMMARYIn some embodiments, a bone implant apparatus is provided. The apparatus comprises a first end having a substantially smooth surface to inhibit bone ingrowth, a second end extending from the first end in a non-coaxial fashion with a tapered shape and a surface, at least a portion of which comprises a porous surface to allow bone ingrowth, and a collar located between the first and second end. The collar further comprises a porous surface to allow bone ingrowth into the collar.
In some implementations, a femoral hip implant is provided comprising a first end, the first end having a substantially smooth surface to inhibit bone ingrowth, a second end having a substantially tapered shape and extending from the first end in a non-coaxial fashion, at least a portion of which comprises a porous surface to allow bone ingrowth, and a collar located between the first end and the second end, at least a portion of the collar having a porous surface to allow bone ingrowth. The second end of the femoral hip implant is inserted into a femur, and the femoral hip implant is positioned to subside into the femur until the collar contacts the femur so that the porous surfaces of the second end and the collar are aligned with bone to allow bone ingrowth.
The foregoing and other objects, features, and advantages of the invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.
For purposes of this description, certain aspects, advantages, and novel features of the embodiments of this disclosure are described herein. The disclosed methods, apparatuses, and systems should not be construed as limiting in any way. Instead, the present disclosure is directed toward all novel and nonobvious features and aspects of the various disclosed embodiments, alone and in various combinations and sub-combinations with one another. The methods, apparatus, and systems are not limited to any specific aspect or feature or combination thereof, nor do the disclosed embodiments require that any one or more specific advantages be present or problems be solved.
Although the operations of some of the disclosed methods are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed methods can be used in conjunction with other methods. Additionally, the description sometimes uses terms like “provide” or “achieve” to describe the disclosed methods. These terms are high-level abstractions of the actual operations that are performed. The actual operations that correspond to these terms may vary depending on the particular implementation and are readily discernible by one of ordinary skill in the art.
As used in this application and in the claims, the singular forms “a,” “an,” and “the” include the plural forms unless the context clearly dictates otherwise. Additionally, the term “includes” means “comprises.” Further, the terms “coupled” and “associated” generally mean electrically, electromagnetically, and/or physically (e.g., mechanically or chemically) coupled or linked and does not exclude the presence of intermediate elements between the coupled or associated items absent specific contrary language.
As used herein, the term “porous” means a structure having one or more openings, gaps, or other such surfaces that allow bone to grow into the structure and mechanically interlock with the structure. “Bone ingrowth” refers to the growing of bone into a porous structure in a manner that allows the bone to interlock with the structure.
As used herein, the term “smooth” means a structure lacking in openings, gaps, or other such surfaces that would allow bone to grow into the structure.
A collar with a porous surface acts to stabilize a femoral hip implant by promoting bone ingrowth. However, due to manufacturing limitations, the existing art implants often comprise a solid metal collar with only a textured undersurface. Such textured undersurfaces are ineffective at promoting bone ingrowth, and frequently cause bone resorption under the collar instead. Such bone resorption in turn can cause the femoral hip implant to loosen in some cases, and can result in undesirable revision surgery.
The collar 16 can comprise a substantially semicircular projection from second end 14 generally normal to the second end 14, as shown in
Collar 16 can comprise a top surface 24 and a bottom surface 26, as shown in
In some embodiments, the collar 16 can be fully porous, with the entire surface area of the collar 16 exhibiting porosity as shown in
In some embodiments, the top surface 24 of the collar 16 can comprise a solid (i.e., non-porous) metal surface or skin. The solid metal surface can be from about 0.005 inches to about 0.025 inches thick, and can further strengthen the collar 16. In other embodiments, the thickness of the metal at top surface 24 (the surface facing away from the femur 22) can vary between between 0.005 inches to 0.08 inches thick, or more preferably between 0.01 to 0.06 inches thick. An embodiment with the top surface 24 being formed with a metal surface (e.g., a thin metal “skin”) is shown in
In some embodiments, the length L1 of the collar 16 can be related to a cross-sectional dimension D of the second end 14, as shown in
The femoral hip implant 10 described herein can be formed of various biocompatible materials. In some embodiments, the femoral hip implant 10 can be formed of titanium alloys, such as ASTM F-136 (Ti6Al4V ELI Titanium Alloy). In other embodiments, the implants can be formed using other biocompatible materials, such as cobalt chromium, stainless steel, and various composite materials or plastics.
Existing art implants require that the implant comprise multiple parts joined together to achieve a porous surface on both the collar and tapered body of the implant. However, using additive machining techniques such as electron beam melting (EBM) or laser sintering, the femoral hip implant 10 can be made from a single piece of material. In the case of the EBM technique, the implant can be produced by building the implant layer-by-layer from metal powder (e.g., a titanium alloy powder) using a powerful electron beam. In the case of the laser sintering technique, a high-powered laser is used to fuse beads of material to form the desired three-dimensional structure. These techniques can be used to produce an implant with the desired porous surfaces, allowing the porous surface of the femoral hip implant 10 to extend from the porous region 28 of the second end 14 to cover the entire surface area of the collar 16, as shown in
The porosity of the femoral hip implant 10 is generally of a diamond cubic unit cell geometry, as shown in
An additional feature of the collar 16 is its greater ability to elastically deflect under load compared to existing art solid collars with porous or textured surface treatments. The porosity of the collar 16 increases the elastic deflection of the collar 16 when subjected to loading by reducing the ultimate strength of the collar 16. Existing art collars fabricated from ASTM F-136 (Ti6Al4V ELI Titanium Alloy) with cross-sections of 0.310 inches by 0.120 inches exhibit an ultimate material stress of approximately 138,000 pounds per square inch with a fracture force of approximately 466 pounds. Such existing art solid collars generally are too stiff to deflect under normal loading conditions induced in femoral implants, leading to stress disuse bone resorption in the calcar area and destabilization of the implant. However, in some embodiments of the femoral hip implant 10, the collar 16 exhibits an ultimate material stress of approximately 48,000 pounds per square inch and a fracture load of approximately 163 pounds with a cross-section of 0.310 inches by 0.120 inches, as shown in
Referring now to
In some embodiments, the top surface 124 of the collar 116 can comprise a solid (i.e., non-porous) metal surface similar to the solid metal surface discussed above with respect to the embodiment of
In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims. I therefore claim as my invention all that comes within the scope and spirit of these claims.
Claims
1. A bone implant apparatus comprising:
- a first end having a substantially smooth surface to inhibit bone ingrowth;
- a second end extending from the first end in a non-coaxial fashion, the second end having a tapered shape and a surface, at least a portion of which comprises a porous surface to allow bone ingrowth; and
- a collar located between the first end and the second end, the collar comprising a surface at least a portion of which comprises a porous surface to allow bone ingrowth into the collar.
2. The bone implant apparatus of claim 1, wherein the first end, the second end, and the collar comprise a single piece of material.
3. The bone implant apparatus of claim 1, wherein the entire surface area of the collar is porous.
4. The bone implant apparatus of claim 1, wherein the collar further comprises a top surface and a bottom surface, both of which are porous.
5. The bone implant apparatus of claim 4, wherein the top surface and the bottom surface of the collar are generally parallel.
6. The bone implant apparatus of claim 4, wherein the portion of the surface of the second end comprising a porous surface extends along the top surface and the bottom surface of the collar.
7. The bone implant apparatus of claim 4, wherein the bottom surface of the collar forms an angle with a longitudinal axis of the bone implant apparatus of from about 45 degrees to about 130 degrees.
8. The bone implant apparatus of claim 7, wherein the bottom surface of the collar forms an angle with the longitudinal axis of the bone implant apparatus of about 110 degrees.
9. The bone implant apparatus of claim 1, wherein the collar comprises a substantially semicircular projection from the second end of the bone implant apparatus in a direction substantially normal to the second end.
10. The bone implant apparatus of claim 1, wherein at least a portion of the surface of the bone implant apparatus comprises a substantially smooth surface that restricts bone ingrowth.
11. The bone implant apparatus of claim 1, wherein the collar elastically deflects under load to stimulate bone growth.
12. The bone implant apparatus of claim 11, wherein the elastic deflection of the collar is between 0.004 inches and 0.02 inches when subjected to a load of 188 pounds.
13. The bone implant apparatus of claim 11, wherein the elastic deflection of the collar is greater than 0.004 inches when subjected to a load of 188 pounds.
14. The bone implant apparatus of claim 1, wherein the porous surfaces of the second end and the collar comprise a diamond cubic unit cell geometry.
15. The bone implant apparatus of claim 1, wherein the bone implant apparatus is fabricated from a biocompatible material.
16. The bone implant apparatus of claim 1, wherein the collar comprises a non-porous metal surface with a thickness of from about 0.005 inches to about 0.025 inches.
17. The bone implant apparatus of claim 1, wherein the collar has a length of from about 12% to about 26% of a cross-sectional dimension of the second end of the implant.
18. A method for total hip replacement, comprising:
- providing a femoral hip implant comprising a first end, the first end having a substantially smooth surface to inhibit bone ingrowth, a second end having a substantially tapered shape and extending from the first end in a non-coaxial fashion, at least a portion of which comprises a porous surface to allow bone ingrowth, and a collar located between the first end and the second end, at least a portion of the collar having a porous surface to allow bone ingrowth;
- inserting the second end of the femoral hip implant into a femur; and
- positioning the femoral hip implant to subside into the femur until the collar contacts the femur so that the porous surfaces of the second end and the collar are aligned with bone to allow bone ingrowth.
19. The method of claim 18, wherein the collar of the femoral hip implant elastically deflects upon loading and unloading of the femoral hip implant.
20. The method of claim 19, wherein the elastic deflection of the collar is between 0.004 inches and 0.02 inches when subjected to a load of 188 pounds.
21. The method of claim 19, wherein the elastic deflection of the collar is greater than 0.004 inches when subjected to a load of 188 pounds.
22. The method of claim 18, wherein the inserting of the femoral hip implant into the femur comprises press-fitting the femoral hip implant into the femur.
23. The method of claim 18, wherein the first end, the second end, and the collar of the femoral hip implant comprise a single piece of material.
24. The method of claim 18, wherein the collar comprises a substantially semicircular projection from the second end of the femoral hip implant in a direction generally normal to the second end of the femoral hip implant.
25. The method of claim 18, wherein the entire surface area of the collar comprises a porous surface.
26. The method of claim 18, wherein the porous surfaces of the second end and the collar comprise a diamond cubic unit cell geometry.
27. The method of claim 18, wherein the bone implant apparatus is fabricated from a biocompatible material.
28. A bone implant comprising:
- a proximal portion adapted for receiving a femoral head, the proximal portion being fabricated from a biocompatible material;
- a distal portion having a generally tapered shape and extending distally from the proximal portion in a non-coaxial fashion, the distal portion comprising a femoral stem configured for press-fit insertion into a femur without the use of bone cement, the distal portion comprising a surface at least a portion of which is porous, the porosity of the porous surface of the distal portion comprising a diamond cubic unit cell geometry to allow bone ingrowth, the distal portion and the proximal portion comprising a single piece of material, the distal portion being fabricated from a biocompatible material;
- a collar, the entire surface area of which is porous, the collar being generally disposed between the proximal portion and the distal portion, the collar being generally disposed about a proximal end of the distal portion, the collar comprising a generally semicircular projection, the collar comprising a top surface and a bottom surface, both of which are porous, the top surface and bottom surface being generally parallel, the porous surface of the collar integrally extending onto the surface of the distal portion, the porosity of the collar comprising a diamond cubic unit cell geometry to allow bone ingrowth, the collar elastically deflecting more than 0.004 inches under a load of 188 pounds, the collar, the proximal portion, and distal portion comprising a single piece of material, and the collar being fabricated from a biocompatible material.
Type: Application
Filed: Sep 5, 2013
Publication Date: Mar 6, 2014
Inventor: Christopher G. Sidebotham (Mendham, NJ)
Application Number: 14/019,374
International Classification: A61F 2/36 (20060101);