ARTIFICIAL KNEE JOINT

• US 20150018960A1
• Filed: 03/27/2009
• Published: 01/15/2015
• Est. Priority Date: 03/27/2009
• Status: Active Grant

• Current Assignee: Smith & Nephew Orthopaedics Ag (Smith & Nephew PLC)
• Original Assignee: Smith & Nephew Orthopaedics Ag (Smith & Nephew PLC)
• Inventors: El Zoghbi, Gaser Nmi, Reinbold, Ulrich Nmi
• Granted Patent: US 9,452,052 B2
• Time in Patent Office: Days
• US Class Current: 623/20.27
• CPC Class Codes: A61F 2/3836 Special connection between upper and lower leg, e.g. constrained
• CPC Class Codes: A61F 2/3859 Femoral components
• CPC Class Codes: A61F 2/3886 for stabilising knees against anterior or lateral dislocations
• CPC Class Codes: A61F 2/389 Tibial components A61F2/3868 takes precedence
• CPC Class Codes: A61F 2002/302 toroidal, e.g. rings
• CPC Class Codes: A61F 2230/0065 toroidal, e.g. ring-shaped, doughnut-shaped

Abstract

An artificial knee joint (1) is described and comprises a femoral component (10) and a tibial component (30), for attachment to the femur (2) and tibia (3) of a patient (4) respectively. The femoral component (10) comprises a lateral condyle (11) and a medial condyle (12) which extend from the posterior (13) to the anterior (14) of the femoral component (10). A femoral gap (15) is provided between the lateral (11) and medial (12) condyles extending from the posterior (13) toward the anterior (14) of the femoral component (10). The lateral (11) and medial (12) condyles are joined at the anterior (13) of the femoral component (10) to form a patella tracking path or bearing surface (16) which is located at and forms the anterior end of the gap (17). A femoral cam (18) is provided bridging the posterior ends of both the lateral (11) and medial (12) condyles, and forms a posterior end of the gap (19), wherein the femoral cam (18) is structured to have the shape of a section of a ring (20). The tibial component (30) is provided with two approximately symmetric articulation bearing surfaces (31, 32) either side of a central post (33), wherein the articulation bearing surfaces (31, 32) are for receiving the lateral (11) and medial (12) condyles of the femoral component (10), and the post (33) is shaped such that it will fit within the femoral gap (15).

Claims

1. An artificial knee joint comprising a femoral component and a tibial component, for attachment to the femur and tibia of a patient respectively;

wherein

the femoral component having a lateral condyle and a medial condyle extending from the posterior to the anterior of the femoral component and wherein a femoral gap is provided between the lateral and medial condyles extending from the posterior toward the anterior of the femoral component, wherein further the lateral and medial condyles are joined at the anterior of the femoral component to form a patella tracking path or bearing surface which is located at and forms the anterior end of the gap;

a femoral cam bridging the posterior ends of both the lateral and medial condyles and forming a posterior end of the femoral gap, wherein the femoral cam is structured to have the shape of a section of a ring;

wherein further

the tibial component is provided with two approximately symmetric articulation bearing surfaces either side of a central post, wherein the articulation bearing surfaces are for receiving the lateral and medial condyles of the femoral component, and the post is shaped such that it will fit within the femoral gap.

2. The artificial knee joint of claim 1, wherein a high flexion articulation surface, situated on the tibial component, is provided at the lower posterior end of the post and has an indented shape which is approximately the same as the external surface of the femoral cam.

3. The artificial knee joint of claim 1, wherein the outer surface of the lateral and medial condyles has a curved surface which has a first radius of curvature which is approximately constant from the patella tracking path or bearing surface to the posterior of the femoral component, and which has a second radius of curvature at the portion near the femoral cam, wherein the first radius of curvature is larger than the second radius of curvature.

4. The artificial knee joint of claim 3, wherein the articulation bearing surfaces have indented surfaces which have a radius of curvature larger than the first radius of curvature of the lateral and medial condyles.

5. The artificial knee joint of claim 3, wherein the femoral and tibial components are structured such that when they are in contact via the lateral and medial condyles, with the post positioned through the femoral gap, and the inner diameter of the ring of the femoral cam is in contact with the post but preferably not with the high flexion articulation surface, the curved surface of the lateral and medial condyles with the first radius of curvature is in contact with the articulation bearing surfaces.

6. The artificial knee joint of claim 5, wherein the femoral and tibial components are structured such that should the femoral component be rotated further, the contact between the femoral and tibial components will proceed via the surface with the second radius of curvature, thus acting to bring the femoral cam into contact with the high flexion articulation surface.

7. The artificial knee joint of claim 5, wherein if a zero rotation point is defined as being when the lateral and medial condyles are in contact with the articulation bearing surfaces and the femoral and tibial components are oriented such that the femur and tibia of a patient would be in approximately linear alignment such that the knee would be in full extension, the amount of rotation which the femoral component has undergone at the point as defined in claim 5, occurs between 55°

and 75°

.

8. The artificial knee joint of claim 5, wherein if a zero rotation point is defined as being when the lateral and medial condyles are in contact with the articulation bearing surfaces and the femoral and tibial components are oriented such that the femur and tibia of a patient would be in approximately linear alignment such that the knee would be in full extension, the amount of rotation which the femoral component has undergone at the point where the femoral cam is in contact with the high flexion articulation surface as defined in claim 6, occurs between 95°

and 115°

, preferably between 100° and

110°

, more preferably at 105°

.

9. The artificial knee joint of claim 8, wherein if a zero rotation point is defined as being when the lateral and medial condyles are in contact with the articulation bearing surfaces and the femoral and tibial components are oriented such that the femur and tibia of a patient would be in approximately linear alignment such that the knee would be in full extension, when the femoral component has undergone a rotation of greater than 90°

, the femoral component is so structured that the only point of contact with the tibial component is via the femoral cam and the high flexion articulation surface.

10. The artificial knee joint of claim 9, wherein as the femoral cam is structured as a section of a ring when the femoral and tibial components are contacted only via the femoral cam and the high flexion articulation surface, the femoral cam is able to wobble in the lateral and medial directions before the posterior ends of either the lateral or medial condyles is brought into contact with the respective articulation bearing surface.

11. The artificial knee joint of claim 10, wherein this amount of wobble is between about 1°

and 8°

, preferably between about 2° and

5° and

most preferably about 3°

.

12. The artificial knee joint of claim 10, wherein the femoral component is able to wobble with respect to the tibial component at high levels of rotation because the outer radial surfaced of the section of the ring making up the femoral cam has a different radius of curvature than the high flexion articulation surface.

13. The artificial knee joint claim 1, wherein the femoral cam has a radius in its thickness direction of a first larger value at its upper, outer diameter of the ring and posterior sections, and a second radius smaller than the first radius at its lower and inner diameter of the ring sections, wherein preferably the first radius is between 5 mm to 15 mm, the second radius is between 3 mm to 10 mm.

14. The artificial knee joint of claim 1, wherein the minimum thickness of both the articulation bearing surfaces and the high flexion articulation surface of the tibial component are approximately the same, and further this thickness lies between 4 mm and 25 mm.

15. The artificial knee joint of claim 1, wherein an imaginary ring can be drawn which completes the section of the ring forming the femoral cam, and this imaginary ring has an outer radius which lies between 20 mm and 50 mm;

and the imaginary ring is structured so that it extends downward from the posterior of the femoral gap so that it would be directly in line with tibia of a patient, if the 0°

reference line is defined as exactly in line with the tibia, the imaginary ring can lie at an angle which is in the range between ±

15°

from this reference line.

16. An artificial knee joint for attachment to the fervor and tibia of a patient, comprising

a femoral component having a lateral condyle and a medial condyle extending from the posterior to the anterior of the femoral component such that a femoral gap is provided between the lateral and medial condyles extending from the posterior toward the anterior of the femoral component, wherein the lateral and medial condyles are joined at the anterior of the femoral component to form a patella bearing surface which is located at and forms the anterior end of the gap;

a femoral cam bridging the posterior ends of both the lateral and medial condyles and forming a posterior end of the femoral gap, wherein the femoral cam is structured to have the shape of a section of a ring; and

a tibial component having two approximately symmetric articulation bearing surfaces either side of a central post, wherein the articulation bearing surfaces are for receiving the lateral and medial condyles of the femoral component, and the post is shaped such that it will fit within the femoral gap.

17. The artificial knee joint of claim 16, wherein the tibial component is further provided with a high flexion articulation surface at the lower posterior end of the post and further having an indented shape which is approximately the same as the external surface of the femoral cam.

18. The artificial knee joint of claim 17, wherein the outer surface of the lateral and medial condyles has a curved surface which has a first radius of curvature which is approximately constant from the patella bearing surface to the posterior of the femoral component, and which has a second radius of curvature at the portion near the femoral cam, wherein the first radius of curvature is larger than the second radius of curvature.

19. The artificial knee joint of claim 18, wherein the articulation bearing surfaces have indented surfaces which have a radius of curvature larger than, approximately equal to, or equal to, the first radius of curvature of the lateral and medial condyles.

20. The artificial knee joint of claim 19, wherein the femoral and tibial components are structured such that when they are in contact via the lateral and medial condyles, with the post positioned through the femoral gap, and the inner diameter of the ring of the femoral cam is in contact with the post but preferably not with the high flexion articulation surface, the curved surface of the lateral and medial condyles with the first radius of curvature is in contact with the articulation bearing surfaces.