Dual modulus hip stem
View Patent ↗An orthopaedic prosthesis for use in a hip replacement surgery. The orthopaedic prosthesis includes a metallic foam shell and a metallic core. The metallic core includes a neck configured to receive a femoral head component and a stem extending through the metallic foam shell.
1. An orthopaedic prosthesis, comprising:
a metallic foam shell including a sheath, and
a metallic core including (i) a neck positioned proximal of the sheath, the neck being configured to receive a femoral head component, (ii) a first core segment positioned in the sheath, and (iii) a second core segment positioned distal of the sheath,
wherein the metallic foam shell further includes a cover layer extending distally from the sheath, the cover layer engaging only a lateral surface of the second core segment,
wherein when the orthopaedic prosthesis is viewed in a transverse plane extending through the cover layer of the metallic foam shell, (i) the cover layer defines a first cross-sectional area, (ii) the cover layer and the second core segment define a second cross-sectional area, and (iii) a ratio of the first cross-sectional area to the second cross-sectional area is greater than 0.30.
2. The orthopaedic prosthesis of claim 1 , wherein the ratio of the first cross-sectional area to the second cross-sectional area is between 0.35 and 0.47.
3. The orthopaedic prosthesis of claim 1 , wherein the ratio of the first cross-sectional area to the second cross-sectional area is less than 0.56.
4. The orthopaedic prosthesis of claim 1 , wherein when the orthopaedic prosthesis is viewed in a second transverse plane extending through the sheath of the metallic foam shell,
the sheath defines a third cross-sectional area,
the sheath and the first core segment define a fourth cross-sectional area, and
a ratio of the third cross-sectional area to the fourth cross-sectional area is greater than 0.38.
5. The orthopaedic prosthesis of claim 4 , wherein the ratio of the third cross-sectional area to the fourth cross-sectional area is between 0.46 and 0.54.
6. The orthopaedic prosthesis of claim 4 , wherein the ratio of the third cross-sectional area to the fourth cross-sectional area is less than 0.70.
7. The orthopaedic prosthesis of claim 4 , wherein the ratio of the third cross-sectional area to the fourth cross-sectional area is greater than the ratio of the first cross-sectional area to the second cross-sectional area.
8. The orthopaedic prosthesis of claim 4 , wherein:
the first core segment of the metallic core has a medial surface and a lateral surface positioned opposite the medial surface of the first core segment,
the sheath has a medial surface and a lateral surface positioned opposite the medial surface of the sheath, and
when the orthopaedic prosthesis is viewed in the second transverse plane, a first thickness is defined between a lateral-most point of the lateral surface of the sheath and a lateral-most point of the lateral surface of the first core segment, (ii) a second thickness is defined between a medial-most point of the medial surface of the sheath and a medial-most point of the medial surface of the first core segment, and (iii) a ratio of the second thickness to the first thickness is greater than 0.14.
9. The orthopaedic prosthesis of claim 1 , wherein:
the cover layer of the metallic foam shell extends distally from a proximal end attached to the sheath, and
the transverse plane extends through the proximal end of the cover layer, and when the orthopaedic prosthesis is viewed in the transverse plane: (i) the cover layer has a first thickness, (ii) the second core segment has a second thickness, and (iii) a ratio of the first thickness to the second thickness is greater than 0.46.
10. The orthopaedic prosthesis of claim 9 , wherein the first thickness is greater than three millimeters.
11. The orthopaedic prosthesis of claim 4 , wherein when the orthopaedic prosthesis is viewed in the second transverse plane, a medial surface of the first core segment is convex and a lateral surface of the first core segment is convex.
12. The orthopaedic prosthesis of claim 10 , wherein when the orthopaedic prosthesis is viewed in the second transverse plane, the medial surface of the first core segment is defined by a first radius, and the lateral surface of the first core segment is defined by a second radius that is greater than the first radius.
13. The orthopaedic prosthesis of claim 1 , wherein the sheath and the cover layer of the metallic foam shell have a first elastic modulus and the first core segment and the second core segment of the metallic core have a second elastic modulus, the first elastic modulus being approximately one-twentieth of the second elastic modulus.
14. An orthopaedic prosthesis, comprising:
an elongated femoral stem component having a longitudinal axis, the stem component comprising:
a metallic foam shell including a sheath, and
a metallic core including (i) a neck positioned proximal of the sheath, the neck being configured to receive a femoral head component, (ii) a first core segment positioned in the sheath, and (iii) a second core segment positioned distal of the sheath,
wherein (i) the metallic foam shell further includes a cover layer extending distally from the sheath, the cover layer engaging only a lateral surface of the second core segment and defining a first cross-sectional area at a first point on the longitudinal axis, (ii) the cover layer and the second core segment define a second cross-sectional area at the first point, and (iii) a ratio of the first cross-sectional area to the second cross-sectional area is greater than 0.30.
15. The orthopaedic prosthesis of claim 14 , wherein (i) the sheath defines a third cross-sectional area at a second point on the longitudinal axis, (ii) the sheath and the first core segment defines a fourth cross-sectional area at the second point, and (iii) a ratio of the third cross-sectional area to the fourth cross-sectional area is greater than 0.38.
16. An orthopaedic prosthesis for a patient, comprising:
an elongated femoral stem component having a longitudinal axis, the stem component comprising:
a metallic foam shell having a first elastic modulus, and
a metallic core including a neck positioned proximal of the shell and a body that extends through the shell, the core having a second elastic modulus greater than the first elastic modulus,
wherein (i) the metallic foam shell defines a first cross-sectional area at a first point on the longitudinal axis, (ii) the stem component defines a second cross-sectional area at the first point, and (iii) a ratio of the first cross-sectional area to the second cross-sectional area is greater than 0.38,
wherein (i) the metallic foam shell defines a third cross-sectional area at a second point on the longitudinal axis, the second point being distal of the first point, (ii) the stem component defines a fourth cross-sectional area at the second point, and (iii) a ratio of the third cross-sectional area to the fourth cross-sectional area is greater than the ratio of the first cross-sectional area to the second cross-sectional area,
wherein (i) the metallic foam shell defines a fifth cross-sectional area at a third point on the longitudinal axis, the third point being distal of the second point, (ii) the stem component defines a sixth cross-sectional area at the third point, and (iii) a ratio of the fifth cross-sectional area to the sixth cross-sectional area is less than the ratio of the third cross-sectional area to the fourth cross-sectional area,
wherein the metallic foam shell includes a cover layer attached to only a lateral surface of the metallic core at the third point on the longitudinal axis.
17. The orthopaedic prosthesis of claim 16 , wherein the ratio of the fifth cross-sectional area to the sixth cross-sectional area is between 0.30 and 0.56.
18. The orthopaedic prosthesis of claim 16 , wherein the ratio of the third cross-sectional area to the fourth cross-sectional area is less than 0.70.