US20130150976A1 - Posterior Stabilized Knee With Varus-Valgus Constraint - Google Patents
Posterior Stabilized Knee With Varus-Valgus Constraint Download PDFInfo
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- US20130150976A1 US20130150976A1 US13/763,305 US201313763305A US2013150976A1 US 20130150976 A1 US20130150976 A1 US 20130150976A1 US 201313763305 A US201313763305 A US 201313763305A US 2013150976 A1 US2013150976 A1 US 2013150976A1
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
- A61F2/02—Prostheses implantable into the body
- A61F2/30—Joints
- A61F2/38—Joints for elbows or knees
- A61F2/3836—Special connection between upper and lower leg, e.g. constrained
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
- A61F2/02—Prostheses implantable into the body
- A61F2/30—Joints
- A61F2/38—Joints for elbows or knees
- A61F2/3868—Joints for elbows or knees with sliding tibial bearing
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
- A61F2/02—Prostheses implantable into the body
- A61F2/30—Joints
- A61F2/38—Joints for elbows or knees
- A61F2/3886—Joints for elbows or knees for stabilising knees against anterior or lateral dislocations
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
- A61F2/02—Prostheses implantable into the body
- A61F2/30—Joints
- A61F2002/30001—Additional features of subject-matter classified in A61F2/28, A61F2/30 and subgroups thereof
- A61F2002/30316—The prosthesis having different structural features at different locations within the same prosthesis; Connections between prosthetic parts; Special structural features of bone or joint prostheses not otherwise provided for
- A61F2002/30329—Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements
- A61F2002/30331—Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements made by longitudinally pushing a protrusion into a complementarily-shaped recess, e.g. held by friction fit
- A61F2002/30332—Conically- or frustoconically-shaped protrusion and recess
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
- A61F2/02—Prostheses implantable into the body
- A61F2/30—Joints
- A61F2002/30001—Additional features of subject-matter classified in A61F2/28, A61F2/30 and subgroups thereof
- A61F2002/30316—The prosthesis having different structural features at different locations within the same prosthesis; Connections between prosthetic parts; Special structural features of bone or joint prostheses not otherwise provided for
- A61F2002/30329—Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements
- A61F2002/30331—Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements made by longitudinally pushing a protrusion into a complementarily-shaped recess, e.g. held by friction fit
- A61F2002/30362—Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements made by longitudinally pushing a protrusion into a complementarily-shaped recess, e.g. held by friction fit with possibility of relative movement between the protrusion and the recess
- A61F2002/30364—Rotation about the common longitudinal axis
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
- A61F2/02—Prostheses implantable into the body
- A61F2/30—Joints
- A61F2002/30001—Additional features of subject-matter classified in A61F2/28, A61F2/30 and subgroups thereof
- A61F2002/30316—The prosthesis having different structural features at different locations within the same prosthesis; Connections between prosthetic parts; Special structural features of bone or joint prostheses not otherwise provided for
- A61F2002/30329—Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements
- A61F2002/30383—Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements made by laterally inserting a protrusion, e.g. a rib into a complementarily-shaped groove
- A61F2002/3039—Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements made by laterally inserting a protrusion, e.g. a rib into a complementarily-shaped groove with possibility of relative movement of the rib within the groove
- A61F2002/30398—Sliding
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
- A61F2/02—Prostheses implantable into the body
- A61F2/30—Joints
- A61F2002/30001—Additional features of subject-matter classified in A61F2/28, A61F2/30 and subgroups thereof
- A61F2002/30316—The prosthesis having different structural features at different locations within the same prosthesis; Connections between prosthetic parts; Special structural features of bone or joint prostheses not otherwise provided for
- A61F2002/30535—Special structural features of bone or joint prostheses not otherwise provided for
- A61F2002/30604—Special structural features of bone or joint prostheses not otherwise provided for modular
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F2220/00—Fixations or connections for prostheses classified in groups A61F2/00 - A61F2/26 or A61F2/82 or A61F9/00 or A61F11/00 or subgroups thereof
- A61F2220/0025—Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F2220/00—Fixations or connections for prostheses classified in groups A61F2/00 - A61F2/26 or A61F2/82 or A61F9/00 or A61F11/00 or subgroups thereof
- A61F2220/0025—Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements
- A61F2220/0033—Connections or couplings between prosthetic parts, e.g. between modular parts; Connecting elements made by longitudinally pushing a protrusion into a complementary-shaped recess, e.g. held by friction fit
Definitions
- the present invention relates to a knee prosthesis and more particularly to a mobile bearing knee providing posterior stabilization of the anterior-posterior translation of the femoral component relative to the tibial component.
- Flexion and extension of the normal human knee involves complex movements of the femur, the tibia and the patella.
- flexion i.e., when the knee is bent
- the distal end of the femur and the proximal end of the tibia roll and glide relative to each other, with the center of rotation of the joint moving posteriorly over the condyles of the femur.
- This complex movement is typically referred to as rollback.
- extension i.e., when the leg is straightened
- the tibia and femur follow a reverse path. Simultaneous with the movements of the tibia and femur, the patella moves over the surface of the femoral condyles, while remaining a constant distance from the tubercle of the tibia.
- a mobile bearing knee simulates the condylar and bearing surfaces of the knee to emulate the natural movement of the knee during flexion and extension.
- the tibial component is configured to permit rotation about the axis of the tibia to accurately replicate the effects of differential rollback in the transverse plane.
- the tibial component includes an upward projecting spine that translates within an intercondylar notch formed in the femoral component,
- the spine can contact cam surfaces at the anterior and posterior ends of the notch to limit the relative anterior-posterior movement between the two bones.
- the spine also operates to provide varus-valgus stability of the joint and to resist dislocation or subluxation at high angles of flexion.
- knee systems While mobile bearing knees are thought to most accurately mimic the natural movement of the intact knee, the design of knee systems requires the introduction of features to maintain the stability of the artificial joint. Thus, modern knee systems provide additional stability to posterior stabilized devices to prevent hyperextension. The articulating and rotating components of the knee system must do so smoothly and accurately. At the same time, the natural knee permits a certain amount of movement and pivoting in the transverse and coronal planes that should be approximated in the prosthetic knee system. The development of knee systems has attempted to harmonize the need for preserving a full range of motion with the need for maintaining the strength of the joint.
- a knee prosthesis in one embodiment includes a femoral component configured to be attached to a distal end of a femur and having a notch defined between spaced apart medial and a lateral condyle surfaces, the notch defining an elongated cam housing having a posterior cam at one end of the cam housing, and a tibial component including (i) a platform configured for attachment to a proximal end of a tibia, (ii) a bearing supported on and rotatable in relation to the platform, the bearing defining medial and lateral bearing surfaces configured to articulate with the medial and lateral condyle surfaces, and (iii) a spine projecting superiorly from the bearing within the cam housing when the medial and lateral condyle surfaces are in articulating contact with the medial and lateral bearing surfaces, wherein the spine includes an anterior face and an opposite posterior face facing the posterior cam when the medial and lateral condyle surfaces are in articulating contact with the medial and lateral bearing surfaces
- the present invention contemplates an improved knee prosthesis comprising a femoral component configured to be attached to the distal end of a femur and having a medial and a lateral condyle surface spaced apart to define a notch therebetween.
- the notch defines an elongated cam housing having an anterior cam and a posterior cam at opposite ends of the cam housing.
- the prosthesis further includes a tibial component including a platform configured for attachment to the proximal end of a tibia and a bearing supported on the platform.
- the bearing defines medial and lateral bearing surfaces configured to articulate with the medial and lateral condyle surfaces, and a spine projecting superiorly from the bearing within the cam housing when the condyle surfaces are in articulating contact with the bearing surfaces.
- the spine defines an anterior face facing the anterior cam and a posterior face facing the posterior cam.
- the posterior face and the posterior cam defining complementary curved surfaces configured for cooperative engagement when the femoral component and the tibial component are rotated relative to each other to at least a predetermined flexion angle. In certain embodiments, that predetermined angle corresponds to about 50° of flexion of the knee joint.
- the complementary curved surfaces of the posterior cam and posterior face of the spine are preferably curved at a common radius, while the anterior cam and the anterior face of the spine are substantially flat.
- the cam housing defines a width sufficient to provide a predetermined clearance on either side of the spine, when the spine projects into the cam housing, to limit varus-valgus movement or pivoting of the joint.
- the widths of the spine and cam housing are sized to limit varus-valgus pivoting to 0.5°-1.5°.
- the cam housing can be configured so that a gap exists between the posterior cam and the spine when the knee is in its normally extended position.
- the spine does not contact the posterior cam until the knee is flexed to the predetermined angle.
- the complementary surfaces of the spine and posterior cam do not nest or coincide until the knee is flexed further to another predetermined angle.
- the posterior cam can include a blunt or rounded anterior end that contacts the spine first when the knee is flexed. The spine and posterior cam produce roll-back for the knee prosthesis.
- the spine has a greater height than prior spine designs.
- the spine height is calibrated to prevent subluxation of the joint at high flexion angles.
- the spine height is about 24.6 mm.
- the cam housing includes a roof that is sized relative to the condyle surfaces so that the spine cannot contact the roof when the condyle surfaces are supported on the bearing surfaces.
- the invention also contemplates a knee prosthesis comprising a femoral component configured to be attached to the distal end of a femur and having a medial and a lateral condyle surface spaced apart to define a notch therebetween, the notch defining an elongated cam housing having an anterior cam and a posterior cam at opposite ends of the cam housing.
- the prosthesis also comprises a tibial component including a platform configured for attachment to the proximal end of a tibia and a bearing supported on the platform, the bearing defining medial and lateral bearing surfaces configured to articulate with the medial and lateral condyle surfaces, and a spine projecting superiorly within the cam housing when the condyle surfaces are in articulating contact with the bearing surfaces, wherein the spine defines an anterior face facing the anterior cam and a posterior face facing the posterior cam and configured for cooperative engagement when the posterior cam.
- the spine further defines a bore therethrough that receives a pin configured to be disposed within the bore.
- the pin is formed of a material different from the material of the spine to add stiffness or bending strength to the spine.
- the pin can be configured to be press-fit into the bore.
- the spine is formed of a plastic and the pin is formed of a metal.
- a knee prosthesis comprises a femoral component configured to be attached to the distal end of a femur and having a medial and a lateral condyle surface spaced apart to define a notch therebetween, the notch defining an elongated cam housing having an anterior cam and a posterior cam at opposite ends of the cam housing.
- a tibial component includes a platform configured for attachment to the proximal end of a tibia and a bearing supported on the platform, the bearing defining medial and lateral bearing surfaces configured for rotating contact with the medial and lateral condyle surfaces.
- a spine projects superiorly from the bearing within the cam housing when the condyle surfaces are in articulating contact with the bearing surfaces, the spine defining an anterior face facing the anterior cam and a posterior face adapted for articulating contact with the posterior cam.
- the cam housing is configured to define an anterior-posterior distance between the anterior cam and the posterior face of the spine when the femoral component and the tibial component are in a normally extended position relative to each other.
- the posterior face of the spine is in articulating contact with the posterior cam only at a first predetermined flexion rotation angle between the femoral component and the tibial component.
- the first predetermined flexion angle is about 50°.
- the posterior cam and the posterior face define complementary curved surfaces, whereby the complementary surfaces articulate relative to each other at flexion angles between the femoral component and the tibial component greater than the first predetermined flexion angle.
- the posterior cam can include a rounded anterior end that is arranged to contact the posterior face first at the first predetermined flexion angle.
- the complementary curved surface of the posterior cam can further be arranged on the posterior cam so that complementary curved surface of the posterior cam is substantially nested within the complementary curved surface of the posterior face of the spine only after the femoral component and the tibial component rotate relative to each other to a second predetermined flexion angle greater than the first predetermined flexion angle.
- a more specific object is to accomplish these functions with a posterior stabilized knee that can create proper joint roll-back.
- FIG. 1 is an exploded side view of a mobile bearing knee system according to one embodiment of the present invention.
- FIG. 2 is an anterior view of the knee system shown in FIG. 1 .
- FIG. 3 is a lateral view of the knee system shown in FIGS. 1 and 2 .
- FIGS. 4 a - 4 c are cross-sectional view of the knee system shown in FIG. 2 , taken along line 4 - 4 , with the knee system shown in its hyper-extended, normally extended, and flexed configurations.
- FIG. 4 c includes a partial cut-away of the spine on the bearing.
- FIG. 5 is an enlarged diagram illustrating roll-back of the contact point between the femoral and tibial components of the mobile bearing knee system shown in FIG. 4 c.
- a knee system 10 that includes a femoral component 12 and a tibial component 14 .
- the tibial component includes a tibial platform 16 from which extends a tibial stem 18 that is configured for engagement within the prepared end of the tibia.
- a bearing 20 is rotatably mounted on the platform 16 by way of a bearing stem 22 that fits within a complementary socket 24 within the platform.
- the bearing 20 defines an upper bearing surface that supports the femoral component. More specifically, the bearing 20 includes a lateral bearing surface 26 and a medial bearing surface 28 . These bearing surfaces 26 , 28 are configured for articulating support of corresponding condyle bearings 30 , 32 of the femoral component 12 . This articulating or sliding support is best seen in FIGS. 2 and 3 .
- the femoral component 12 is configured to emulate the configuration of the femoral condyles.
- the component 12 includes an anterior portion 34 and a posterior portion 36 that are curved in the manner of the natural condyles.
- the anterior portion 34 defines a patellar groove 49 that is configured to orient a patellar implant (not shown) in a manner known in the art.
- the femoral component 12 utilizes a number of surfaces to fix the component to the prepared end of the femur.
- the inner surface 37 of the anterior and posterior portions 34 , 36 are configured to directly interface over the prepared end of the femur.
- a stem 38 can be provided that is fixed within the femur.
- the femoral component 12 can include an intercondylar notch 40 formed by a pair of opposite side walls 44 and a roof 46 .
- the prosthetic knee 10 can assume a variety of known configurations.
- the femoral component 12 and tibial component 14 as described above can have the configuration of like components of the mobile bearing knee described in U.S. Pat. No. 6,443,991, the description of which is incorporated by reference.
- the knee 10 of the present invention includes a spine 60 that projects from the upper surface 25 of the bearing 20 .
- the spine 60 resides within a cam housing 42 ( FIG. 3 ) that is essentially formed by the walls of the intercondylar notch 40 .
- the spine 60 is sized relative to the cam housing 42 to provide a measured degree of varus-valgus constraint.
- the spine 60 has a width W 1 that is slightly less than the width W 2 of the cam housing 42 at the intercondylar notch 40 ( FIG. 1 ). These two widths are sized relative to each other to limit varus-valgus movement or pivoting to a range of about 0.5°-2.5°.
- the width W i is sized relative to the width W 2 to provide 0.13 mm clearance on each side of the spine.
- this clearance should be limited to from about 0.12 mm to about 0.50 mm per side to avoid excessive varus-valgus movement of the knee components 12 , 14 relative to each other.
- this clearance permits about 1.25° of varus-valgus pivoting.
- each of the components must be sized to the skeletal dimensions of the patient.
- the femoral component 12 and tibial component 14 can be provided in several sizes, and preferably in six sizes ranging from small to extra-large.
- the tibial spine 60 can have a width W 1 of about 17.5 mm.
- the cam housing 42 would have a width W 2 of 17.76 mm to provide the proper side-to-side clearance for the spine 60 .
- the dimensions of the spine and the cam housing can be appropriately proportioned for other sizes of knee components.
- the spine 60 interacts with the cam housing 42 to prevent subluxation of the knee 10 .
- the spine 60 defines a subluxation height from the bearing surface 25 that corresponds to the distance that the femoral component must be raised relative to the tibial component until the femoral component is clear of the top of the spine.
- Subluxation is generally not a problem when the knee is straightened (as shown in FIGS. 3 and 4 b ), but can be problematic when the knee is flexed (as shown in FIG. 4 c ).
- the subluxation height is measured at a certain degree of flexion, most typically at 120° of flexion. (For comparison, the knee in FIG.
- the spine has an effective height of between 16-24 mm, and most preferably 19.3 mm, when the prosthesis is at 90° flexion.
- the femoral component must rise off the tibial bearing 20 by at least 19.3 mm to cause a dislocation of the knee.
- the natural ligaments and surrounding soft tissues of the knee provide sufficient resistance to femoral lift-off greater than this subluxation height, especially at high flexion angles.
- the cam housing 42 defines an anterior cam 50 having a cam face 51 .
- This anterior cam 50 is adjacent the anterior portion 34 of the tibial component 12 .
- the cam face 51 is substantially flat.
- the spine 60 has an anterior face 62 that is also substantially flat. The cam face 51 and anterior face 62 are arranged to restrict extension of the knee in the anterior direction (as designated by the arrow A in FIG. 4 a ).
- the spine 60 can contact the anterior cam 50 to prevent further movement in the anterior direction.
- this contact can occur at about 5° hyperextension.
- tension in the ligaments supporting and surrounding the knee will prevent hyper-extension of the knee, and ideally will prevent contact between the spine and the anterior cam 50 .
- the cam housing further defines a posterior cam 55 at the opposite end of the intercondylar notch 40 from the anterior cam 50 , as shown in FIG. 3 .
- the posterior cam 55 defines a curved surface 56 that cooperates with a curved posterior face 64 of the spine, as best shown in FIG. 4 c .
- These cooperating surfaces are configured for optimum roll-back characteristics of the prosthetic knee 10 .
- the contact point between the tibial and femoral components, as well as the axis of rotation of the tibia relative to the femur to shift posteriorly (as designated by the direction arrow P in FIG. 4 a ). This posterior shift optimizes the moment arm and reduces the strain on the quadricep muscle responsible for flexing the knee.
- the cam housing 42 is elongated between the anterior and posterior cams so that the bearing 20 , and particularly the spine 60 , can articulate as the knee is initially flexed and the condyle bearings 30 , 32 rotate on the bearing surfaces 26 , 28 .
- the posterior face 64 of the spine 60 contacts the posterior cam 55 .
- This contact between spine and cam provides posterior stability to the knee 10 as the knee continues to flex.
- the mating surfaces are complementary curved, as best illustrated in FIGS. 4 a - 4 b.
- the posterior face 64 of the spine 60 is concave from the bearing surface 25 of the bearing 20 to the posterior peak 66 at the top of the spine.
- the posteriorly directed peak 66 provides additional posterior stability and resistance to subluxation at high flexion angles of 120° and beyond.
- the curvature or concavity of the posterior face 64 is selected to permit a predetermined amount of roll-back, while maintaining the posterior stability afforded by the spine-to-cam contact.
- This roll-back is depicted in FIG. 5 .
- the contact point designated C 1 corresponds to the initial contact between the spine and the posterior cam. When the knee is flexed further, the contact point shifts posteriorly to the contact point C 2 .
- the posterior face 64 is configured to permit roll-back of between 0.0 mm up to about 5.0 mm. Most preferably this roll-back is about 4.2 mm.
- the curved posterior face 64 of the spine 60 is concave at a radius of between 28-32 mm. Most preferably, the radius of the posterior face is about 30 mm.
- the curved posterior face 64 transitions into the posterior peak 66 , which is preferably rounded. In a preferred embodiment, this peak is formed at a radius of about 5 mm. Since the curved surface 55 of the posterior cam is complementary to the posterior face 64 , it too has a most preferred radius of 30 mm.
- At least the anterior end 57 of the posterior cam 55 is blunted or rounded to provide a smooth transition when the cam contacts the spine 60 .
- the opposite posterior end of the cam 55 can also be rounded, as shown in the figures. This rounded anterior end 57 is the first portion of the posterior cam to contact the spine as the knee is flexed to the predetermined flexion angle. Nominally, the anterior end 57 will initially contact the spine 60 below the rounded posterior peak 66 .
- the curved posterior face 64 of the spine is curved along substantially the entire height of the spine 60 .
- the posterior cam 55 or more particularly the curved surface 56 of the cam, has a length that is substantially equal to the length or height of the curved face of the spine.
- the curved surface of the posterior cam is completely nested within the concave posterior face of the spine.
- This complementary interface can then operate as a fulcrum or pivot point for further relative rotation between the tibial and femoral components. While the condyle bearings and bearing surfaces continue to articulate relative to each other, the greater share of the shear load can now be borne by the complementary interface between the posterior cam 55 and the posterior face 64 of the spine 60 .
- This interface can thus preserve the mechanical advantage of the quadricep muscle through high flexion angles.
- the kinematics of this spine/cam interface allows a patellar implant to easily follow the patellar track 49 without placing undue stress on the patellar tendons.
- the spine 60 has an anterior-posterior dimension that is significantly less than the distance between the anterior and posterior cams 50 , 55 in the cam housing 42 . From the limit of extension, shown in FIG. 4 a , to the normal straight leg position of FIG. 4 b the spine does not contact the cam housing and therefore does not either bear any knee loads or dictate any knee motion.
- the cam housing 42 is elongated with a distance between anterior and posterior cams that is significantly greater than the anterior-posterior (a-p) dimension of the spine.
- the distance between cams is about 1.5 times the a-p dimension of the spine.
- the a-p dimension of the spine is about 10.0 mm at the posterior peak 66 , and the distance between the anterior cam face 51 and the anterior end of the posterior cam 55 is about 15.0 mm.
- the knee load is carried solely by the articulating interface between the condyle bearings 30 , 32 and the bearing surfaces 26 , 28 .
- the quadricep muscles enjoy their greatest moment arm and mechanical advantage.
- the femoral component 12 moves posteriorly relative to the tibial component 14 so the quadricep mechanical advantage gradually decreases.
- the present invention contemplates that the posterior face 64 of the spine will contact the posterior cam 55 after a pre-determined amount of flexion. In a preferred embodiment, this pre-determined amount of flexion of about 50°.
- the spine and posterior cam cooperate to provide an additional articulating bearing interface to not only share in the shear loads, but also to provide a fulcrum or reaction surface working against the quadricep muscle to preserve the flexion moment arm and mechanical advantage.
- the posterior cam 55 becomes fully seated within the concave posterior face 64 of the spine to maximize the bearing contact between these two components.
- the stem 22 of the bearing 20 defines a central bore 70 at least partially therethrough, as shown in FIG. 4 b .
- a stiffening pin 72 can be pressed into the bore 70 , as shown in FIG. 4 c .
- the pin 72 can be formed of a stiff metal, such as a cobalt chrome alloy.
- the prosthetic components designed to engage the natural bone are formed of a biocompatible metal, such as cobalt chrome alloy.
- the bone engaging surfaces of these components can be textured to facilitate cementing the component to the bone, or can be porous coated to promote bone ingrowth for permanent fixation.
- the bearing 20 is most preferably formed of a material that allows for smooth articulation and rotation between the bearing and the other components. The material is selected to meet several criteria, such as producing as little friction as possible between the articulating/rotating surfaces, providing as much wear resistance as possible, and remaining as strong as possible.
- ultra-high molecular weight polyethylene UHMWPe
- UHMWPe ultra-high molecular weight polyethylene
- the spine 60 can be provided as a separate component that mates with the remainder of the bearing 20 .
- the spine can be formed of a high strength metal, such as the cobalt alloy mentioned above. This approach adds to the complexity of the knee construct and adds the problem of interfacing the spine to the remainder of the bearing.
- the spine 60 be integrally formed with the bearing 20 , which means that the spine will be formed of the same material. Where this material is UHMWPe, transverse or shear strength, and even bending stiffness, becomes a design consideration, particularly for active patients.
- the stiffening pin 72 can extend through the axis of the spine 60 to add bending stiffness and shear resistance to the spine.
- the pin 72 can be provided in different lengths depending upon the desired effect.
- the pin can be sized for insertion from the top of the spine 60 and to only extend for the height of the spine.
- the pin can be introduced from the bottom of the bearing stem 22 and can include a stepped diameter to be press-fit into a comparable stepped diameter bore 70 of the stem 22 .
- the preferred embodiment contemplates one form of mobile bearing knee in which the tibial bearing rotates relative to the tibial platform.
- Other mobile bearing knees are contemplated, including knee prostheses in which the bearing slides on the platform.
- the inventive concepts can also be implemented in knee prosthesis in which the bearing does not move or is incorporated into the tibial platform.
- the illustrated embodiments contemplate that the spine projects from the bearing. The inventive concepts can be implemented where the spine is separate from the bearing, whether as a separate insert or integrated with the tibial platform.
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Abstract
A knee prosthesis in one embodiment includes a femoral component having a notch defined between spaced apart medial and a lateral condyle surfaces, the notch defining an elongated cam housing having a posterior cam at one end of the cam housing, and a tibial component including (i) a platform, (ii) a bearing supported on and rotatable in relation to the platform, the bearing defining medial and lateral bearing surfaces, and (iii) a spine projecting superiorly from the bearing within the cam housing, wherein the spine includes an anterior face and an opposite posterior face facing the posterior cam when the medial and lateral condyle surfaces are in articulating contact with the medial and lateral bearing surfaces, wherein the posterior face of the spine is concave along substantially the entire height of the spine, and wherein the spine terminates in a convex rounded posterior peak.
Description
- This is a divisional application of co-pending U.S. application Ser. No. 11/121,408, filed on May 4, 2005, which is a continuation of application Ser. No. 10/242,122, filed on Sep. 12, 2002, the disclosure of which are both incorporated by reference in their entirety.
- The present invention relates to a knee prosthesis and more particularly to a mobile bearing knee providing posterior stabilization of the anterior-posterior translation of the femoral component relative to the tibial component.
- Flexion and extension of the normal human knee involves complex movements of the femur, the tibia and the patella. During flexion (i.e., when the knee is bent), the distal end of the femur and the proximal end of the tibia roll and glide relative to each other, with the center of rotation of the joint moving posteriorly over the condyles of the femur. This complex movement is typically referred to as rollback. During extension (i.e., when the leg is straightened), the tibia and femur follow a reverse path. Simultaneous with the movements of the tibia and femur, the patella moves over the surface of the femoral condyles, while remaining a constant distance from the tubercle of the tibia.
- Damage or disease can deteriorate the bones, articular cartilage and ligaments of the knee, which can ultimately affect the ability of the natural knee to function properly. To address these conditions, prosthetic knees have been developed that are mounted to prepared ends of the femur and tibia. Among the many knee prostheses, a mobile bearing knee simulates the condylar and bearing surfaces of the knee to emulate the natural movement of the knee during flexion and extension. The tibial component is configured to permit rotation about the axis of the tibia to accurately replicate the effects of differential rollback in the transverse plane. In one type of mobile bearing knee, the tibial component includes an upward projecting spine that translates within an intercondylar notch formed in the femoral component, The spine can contact cam surfaces at the anterior and posterior ends of the notch to limit the relative anterior-posterior movement between the two bones. The spine also operates to provide varus-valgus stability of the joint and to resist dislocation or subluxation at high angles of flexion. An exemplary mobile bearing knee is disclosed in
- U.S. Pat. No. 6,443,991, the disclosure of which is incorporated herein by reference. Other exemplary mobile bearing knees are embodied in the LCS™ System and the PFC Sigma RP™ knee system marketed by Depuy Orthopaedics, Inc., of Warsaw, Ind.
- While mobile bearing knees are thought to most accurately mimic the natural movement of the intact knee, the design of knee systems requires the introduction of features to maintain the stability of the artificial joint. Thus, modern knee systems provide additional stability to posterior stabilized devices to prevent hyperextension. The articulating and rotating components of the knee system must do so smoothly and accurately. At the same time, the natural knee permits a certain amount of movement and pivoting in the transverse and coronal planes that should be approximated in the prosthetic knee system. The development of knee systems has attempted to harmonize the need for preserving a full range of motion with the need for maintaining the strength of the joint.
- A knee prosthesis in one embodiment includes a femoral component configured to be attached to a distal end of a femur and having a notch defined between spaced apart medial and a lateral condyle surfaces, the notch defining an elongated cam housing having a posterior cam at one end of the cam housing, and a tibial component including (i) a platform configured for attachment to a proximal end of a tibia, (ii) a bearing supported on and rotatable in relation to the platform, the bearing defining medial and lateral bearing surfaces configured to articulate with the medial and lateral condyle surfaces, and (iii) a spine projecting superiorly from the bearing within the cam housing when the medial and lateral condyle surfaces are in articulating contact with the medial and lateral bearing surfaces, wherein the spine includes an anterior face and an opposite posterior face facing the posterior cam when the medial and lateral condyle surfaces are in articulating contact with the medial and lateral bearing surfaces, wherein the posterior face of the spine is concave along substantially the entire height of the spine, and wherein the spine terminates in a convex rounded posterior peak.
- The present invention contemplates an improved knee prosthesis comprising a femoral component configured to be attached to the distal end of a femur and having a medial and a lateral condyle surface spaced apart to define a notch therebetween. The notch defines an elongated cam housing having an anterior cam and a posterior cam at opposite ends of the cam housing.
- The prosthesis further includes a tibial component including a platform configured for attachment to the proximal end of a tibia and a bearing supported on the platform. The bearing defines medial and lateral bearing surfaces configured to articulate with the medial and lateral condyle surfaces, and a spine projecting superiorly from the bearing within the cam housing when the condyle surfaces are in articulating contact with the bearing surfaces.
- The spine defines an anterior face facing the anterior cam and a posterior face facing the posterior cam. In one feature of the invention, the posterior face and the posterior cam defining complementary curved surfaces configured for cooperative engagement when the femoral component and the tibial component are rotated relative to each other to at least a predetermined flexion angle. In certain embodiments, that predetermined angle corresponds to about 50° of flexion of the knee joint.
- The complementary curved surfaces of the posterior cam and posterior face of the spine are preferably curved at a common radius, while the anterior cam and the anterior face of the spine are substantially flat.
- In one aspect of the knee prosthesis the cam housing defines a width sufficient to provide a predetermined clearance on either side of the spine, when the spine projects into the cam housing, to limit varus-valgus movement or pivoting of the joint. In a preferred embodiment, the widths of the spine and cam housing are sized to limit varus-valgus pivoting to 0.5°-1.5°.
- In addition, the cam housing can be configured so that a gap exists between the posterior cam and the spine when the knee is in its normally extended position. The spine does not contact the posterior cam until the knee is flexed to the predetermined angle. In another aspect, the complementary surfaces of the spine and posterior cam do not nest or coincide until the knee is flexed further to another predetermined angle. The posterior cam can include a blunt or rounded anterior end that contacts the spine first when the knee is flexed. The spine and posterior cam produce roll-back for the knee prosthesis.
- In yet another aspect of the invention, the spine has a greater height than prior spine designs. The spine height is calibrated to prevent subluxation of the joint at high flexion angles. In a preferred embodiment, the spine height is about 24.6 mm. The cam housing includes a roof that is sized relative to the condyle surfaces so that the spine cannot contact the roof when the condyle surfaces are supported on the bearing surfaces.
- The invention also contemplates a knee prosthesis comprising a femoral component configured to be attached to the distal end of a femur and having a medial and a lateral condyle surface spaced apart to define a notch therebetween, the notch defining an elongated cam housing having an anterior cam and a posterior cam at opposite ends of the cam housing. The prosthesis also comprises a tibial component including a platform configured for attachment to the proximal end of a tibia and a bearing supported on the platform, the bearing defining medial and lateral bearing surfaces configured to articulate with the medial and lateral condyle surfaces, and a spine projecting superiorly within the cam housing when the condyle surfaces are in articulating contact with the bearing surfaces, wherein the spine defines an anterior face facing the anterior cam and a posterior face facing the posterior cam and configured for cooperative engagement when the posterior cam.
- In this embodiment, the spine further defines a bore therethrough that receives a pin configured to be disposed within the bore. The pin is formed of a material different from the material of the spine to add stiffness or bending strength to the spine. The pin can be configured to be press-fit into the bore. In certain embodiments, the spine is formed of a plastic and the pin is formed of a metal.
- In still another aspect of the invention, a knee prosthesis comprises a femoral component configured to be attached to the distal end of a femur and having a medial and a lateral condyle surface spaced apart to define a notch therebetween, the notch defining an elongated cam housing having an anterior cam and a posterior cam at opposite ends of the cam housing. A tibial component includes a platform configured for attachment to the proximal end of a tibia and a bearing supported on the platform, the bearing defining medial and lateral bearing surfaces configured for rotating contact with the medial and lateral condyle surfaces. A spine projects superiorly from the bearing within the cam housing when the condyle surfaces are in articulating contact with the bearing surfaces, the spine defining an anterior face facing the anterior cam and a posterior face adapted for articulating contact with the posterior cam.
- With this embodiment, the cam housing is configured to define an anterior-posterior distance between the anterior cam and the posterior face of the spine when the femoral component and the tibial component are in a normally extended position relative to each other. With this configuration, the posterior face of the spine is in articulating contact with the posterior cam only at a first predetermined flexion rotation angle between the femoral component and the tibial component. In a specific embodiment, the first predetermined flexion angle is about 50°.
- This embodiment further contemplates that the posterior cam and the posterior face define complementary curved surfaces, whereby the complementary surfaces articulate relative to each other at flexion angles between the femoral component and the tibial component greater than the first predetermined flexion angle. The posterior cam can include a rounded anterior end that is arranged to contact the posterior face first at the first predetermined flexion angle. The complementary curved surface of the posterior cam can further be arranged on the posterior cam so that complementary curved surface of the posterior cam is substantially nested within the complementary curved surface of the posterior face of the spine only after the femoral component and the tibial component rotate relative to each other to a second predetermined flexion angle greater than the first predetermined flexion angle.
- It is one object of the present invention to provide a prosthetic knee that accurately and efficiently emulates the kinematics and function of a normal, health knee.
- A more specific object is to accomplish these functions with a posterior stabilized knee that can create proper joint roll-back.
- Another object is accomplished by features of the invention that restrict varus-valgus movement or pivoting, as well as provide resistance to subluxation. Other objects and certain benefits of the invention can be appreciated from the following written description together with the accompanying figures.
-
FIG. 1 is an exploded side view of a mobile bearing knee system according to one embodiment of the present invention. -
FIG. 2 is an anterior view of the knee system shown inFIG. 1 . -
FIG. 3 is a lateral view of the knee system shown inFIGS. 1 and 2 . -
FIGS. 4 a-4 c are cross-sectional view of the knee system shown inFIG. 2 , taken along line 4-4, with the knee system shown in its hyper-extended, normally extended, and flexed configurations.FIG. 4 c includes a partial cut-away of the spine on the bearing. -
FIG. 5 is an enlarged diagram illustrating roll-back of the contact point between the femoral and tibial components of the mobile bearing knee system shown inFIG. 4 c. - For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains.
- Referring to
FIG. 1 , aknee system 10 is depicted that includes afemoral component 12 and atibial component 14. The tibial component includes atibial platform 16 from which extends atibial stem 18 that is configured for engagement within the prepared end of the tibia. Abearing 20 is rotatably mounted on theplatform 16 by way of a bearingstem 22 that fits within acomplementary socket 24 within the platform. - The
bearing 20 defines an upper bearing surface that supports the femoral component. More specifically, thebearing 20 includes alateral bearing surface 26 and amedial bearing surface 28. These bearing surfaces 26, 28 are configured for articulating support of correspondingcondyle bearings femoral component 12. This articulating or sliding support is best seen inFIGS. 2 and 3 . - The
femoral component 12 is configured to emulate the configuration of the femoral condyles. Thus, thecomponent 12 includes ananterior portion 34 and aposterior portion 36 that are curved in the manner of the natural condyles. Theanterior portion 34 defines apatellar groove 49 that is configured to orient a patellar implant (not shown) in a manner known in the art. - The
femoral component 12 utilizes a number of surfaces to fix the component to the prepared end of the femur. Theinner surface 37 of the anterior andposterior portions stem 38 can be provided that is fixed within the femur. In addition, thefemoral component 12 can include anintercondylar notch 40 formed by a pair ofopposite side walls 44 and aroof 46. - As thus far described, the
prosthetic knee 10 can assume a variety of known configurations. For instance, thefemoral component 12 andtibial component 14 as described above can have the configuration of like components of the mobile bearing knee described in U.S. Pat. No. 6,443,991, the description of which is incorporated by reference. - As with the prior mobile bearing knee of the '991 Patent, the
knee 10 of the present invention includes aspine 60 that projects from theupper surface 25 of thebearing 20. Thespine 60 resides within a cam housing 42 (FIG. 3 ) that is essentially formed by the walls of theintercondylar notch 40. In one aspect of the present invention, thespine 60 is sized relative to thecam housing 42 to provide a measured degree of varus-valgus constraint. Thespine 60 has a width W1 that is slightly less than the width W2 of thecam housing 42 at the intercondylar notch 40 (FIG. 1 ). These two widths are sized relative to each other to limit varus-valgus movement or pivoting to a range of about 0.5°-2.5°. In a specific preferred embodiment of the invention, the width Wi is sized relative to the width W2 to provide 0.13 mm clearance on each side of the spine. - Preferably, this clearance should be limited to from about 0.12 mm to about 0.50 mm per side to avoid excessive varus-valgus movement of the
knee components - As with other known prosthetic knees, each of the components must be sized to the skeletal dimensions of the patient. Thus, it is contemplated that the
femoral component 12 andtibial component 14 can be provided in several sizes, and preferably in six sizes ranging from small to extra-large. For a medium sized knee, thetibial spine 60 can have a width W1 of about 17.5 mm. In accordance with the specific embodiment discussed above (i.e., with a 0.13 mm clearance on each side), thecam housing 42 would have a width W2 of 17.76 mm to provide the proper side-to-side clearance for thespine 60. The dimensions of the spine and the cam housing can be appropriately proportioned for other sizes of knee components. - In addition to providing a measured degree of varus-valgus constraint, the
spine 60 interacts with thecam housing 42 to prevent subluxation of theknee 10. In particular, thespine 60 defines a subluxation height from the bearingsurface 25 that corresponds to the distance that the femoral component must be raised relative to the tibial component until the femoral component is clear of the top of the spine. Subluxation is generally not a problem when the knee is straightened (as shown inFIGS. 3 and 4 b), but can be problematic when the knee is flexed (as shown inFIG. 4 c). Thus, the subluxation height is measured at a certain degree of flexion, most typically at 120° of flexion. (For comparison, the knee inFIG. 4 c is shown at approximately 80° of flexion). In accordance with the preferred embodiment of the present invention, the spine has an effective height of between 16-24 mm, and most preferably 19.3 mm, when the prosthesis is at 90° flexion. Thus, the femoral component must rise off thetibial bearing 20 by at least 19.3 mm to cause a dislocation of the knee. The natural ligaments and surrounding soft tissues of the knee provide sufficient resistance to femoral lift-off greater than this subluxation height, especially at high flexion angles. - Referring now to
FIGS. 3 and 4 a-c, a further feature of the present invention is depicted. In particular, thecam housing 42 defines ananterior cam 50 having acam face 51. Thisanterior cam 50 is adjacent theanterior portion 34 of thetibial component 12. As seen inFIGS. 3 and 4 a, thecam face 51 is substantially flat. Similarly, thespine 60 has ananterior face 62 that is also substantially flat. Thecam face 51 andanterior face 62 are arranged to restrict extension of the knee in the anterior direction (as designated by the arrow A inFIG. 4 a). Thus, as the tibia, and hence thetibial component 14, moves anteriorly relative to the femur andfemoral component 12, thespine 60 can contact theanterior cam 50 to prevent further movement in the anterior direction. In the illustrated embodiment, this contact can occur at about 5° hyperextension. However, tension in the ligaments supporting and surrounding the knee will prevent hyper-extension of the knee, and ideally will prevent contact between the spine and theanterior cam 50. - The cam housing further defines a
posterior cam 55 at the opposite end of theintercondylar notch 40 from theanterior cam 50, as shown inFIG. 3 . Theposterior cam 55 defines acurved surface 56 that cooperates with acurved posterior face 64 of the spine, as best shown inFIG. 4 c. These cooperating surfaces are configured for optimum roll-back characteristics of theprosthetic knee 10. As the knee is flexed from the neutral position depicted inFIG. 4 b to the position shown inFIG. 4 c, it is desirable for the contact point between the tibial and femoral components, as well as the axis of rotation of the tibia relative to the femur, to shift posteriorly (as designated by the direction arrow P inFIG. 4 a). This posterior shift optimizes the moment arm and reduces the strain on the quadricep muscle responsible for flexing the knee. - As shown in
FIG. 4 b, thecam housing 42 is elongated between the anterior and posterior cams so that thebearing 20, and particularly thespine 60, can articulate as the knee is initially flexed and thecondyle bearings posterior face 64 of thespine 60 contacts theposterior cam 55. This contact between spine and cam provides posterior stability to theknee 10 as the knee continues to flex. In order to accommodate continued femoral roll-back, the mating surfaces are complementary curved, as best illustrated inFIGS. 4 a-4 b. Specifically, theposterior face 64 of thespine 60 is concave from the bearingsurface 25 of thebearing 20 to theposterior peak 66 at the top of the spine. The posteriorly directedpeak 66 provides additional posterior stability and resistance to subluxation at high flexion angles of 120° and beyond. - The curvature or concavity of the
posterior face 64 is selected to permit a predetermined amount of roll-back, while maintaining the posterior stability afforded by the spine-to-cam contact. This roll-back is depicted inFIG. 5 . The contact point designated C1 corresponds to the initial contact between the spine and the posterior cam. When the knee is flexed further, the contact point shifts posteriorly to the contact point C2. In a preferred embodiment, theposterior face 64 is configured to permit roll-back of between 0.0 mm up to about 5.0 mm. Most preferably this roll-back is about 4.2 mm. - Thus, as the knee continues to flex from the 50° point of contact between spine and posterior cam, the
curved surface 56 of the cam nestles into thecurved posterior face 64. At the same time, the contact point between thefemoral component 12 and thetibial component 14 shifts posteriorly. Continued flexing causes thecurved cam surface 56 to articulate within theconcave posterior face 64 of the spine, which further shifts the contact point in the posterior direction. - In a preferred embodiment, the
curved posterior face 64 of thespine 60 is concave at a radius of between 28-32 mm. Most preferably, the radius of the posterior face is about 30 mm. Thecurved posterior face 64 transitions into theposterior peak 66, which is preferably rounded. In a preferred embodiment, this peak is formed at a radius of about 5 mm. Since thecurved surface 55 of the posterior cam is complementary to theposterior face 64, it too has a most preferred radius of 30 mm. - At least the
anterior end 57 of theposterior cam 55 is blunted or rounded to provide a smooth transition when the cam contacts thespine 60. The opposite posterior end of thecam 55 can also be rounded, as shown in the figures. This roundedanterior end 57 is the first portion of the posterior cam to contact the spine as the knee is flexed to the predetermined flexion angle. Nominally, theanterior end 57 will initially contact thespine 60 below the roundedposterior peak 66. - The
curved posterior face 64 of the spine is curved along substantially the entire height of thespine 60. Moreover, theposterior cam 55, or more particularly thecurved surface 56 of the cam, has a length that is substantially equal to the length or height of the curved face of the spine. At about 120° of flexion, the curved surface of the posterior cam is completely nested within the concave posterior face of the spine. This complementary interface can then operate as a fulcrum or pivot point for further relative rotation between the tibial and femoral components. While the condyle bearings and bearing surfaces continue to articulate relative to each other, the greater share of the shear load can now be borne by the complementary interface between theposterior cam 55 and theposterior face 64 of thespine 60. This interface can thus preserve the mechanical advantage of the quadricep muscle through high flexion angles. In addition, the kinematics of this spine/cam interface allows a patellar implant to easily follow thepatellar track 49 without placing undue stress on the patellar tendons. - Referring to
FIG. 4 b, it can be seen that thespine 60 has an anterior-posterior dimension that is significantly less than the distance between the anterior andposterior cams cam housing 42. From the limit of extension, shown inFIG. 4 a, to the normal straight leg position ofFIG. 4 b the spine does not contact the cam housing and therefore does not either bear any knee loads or dictate any knee motion. In one feature of the invention, thecam housing 42 is elongated with a distance between anterior and posterior cams that is significantly greater than the anterior-posterior (a-p) dimension of the spine. In a preferred embodiment, the distance between cams is about 1.5 times the a-p dimension of the spine. In one specific embodiment, the a-p dimension of the spine is about 10.0 mm at theposterior peak 66, and the distance between theanterior cam face 51 and the anterior end of theposterior cam 55 is about 15.0 mm. - With this configuration, the knee load is carried solely by the articulating interface between the
condyle bearings FIG. 4 b the quadricep muscles enjoy their greatest moment arm and mechanical advantage. As the knee continues to flex, thefemoral component 12 moves posteriorly relative to thetibial component 14 so the quadricep mechanical advantage gradually decreases. - In order to preserve the quadricep mechanical advantage, the present invention contemplates that the
posterior face 64 of the spine will contact theposterior cam 55 after a pre-determined amount of flexion. In a preferred embodiment, this pre-determined amount of flexion of about 50°. At this point, the spine and posterior cam cooperate to provide an additional articulating bearing interface to not only share in the shear loads, but also to provide a fulcrum or reaction surface working against the quadricep muscle to preserve the flexion moment arm and mechanical advantage. As the flexion continues, theposterior cam 55 becomes fully seated within theconcave posterior face 64 of the spine to maximize the bearing contact between these two components. - In another aspect of the invention, the
stem 22 of thebearing 20 defines acentral bore 70 at least partially therethrough, as shown inFIG. 4 b. A stiffeningpin 72 can be pressed into thebore 70, as shown inFIG. 4 c. Thepin 72 can be formed of a stiff metal, such as a cobalt chrome alloy. - In accordance with accepted practice, the prosthetic components designed to engage the natural bone, such as the
femoral component 12 and thetibial platform 16, are formed of a biocompatible metal, such as cobalt chrome alloy. The bone engaging surfaces of these components can be textured to facilitate cementing the component to the bone, or can be porous coated to promote bone ingrowth for permanent fixation. However, thebearing 20 is most preferably formed of a material that allows for smooth articulation and rotation between the bearing and the other components. The material is selected to meet several criteria, such as producing as little friction as possible between the articulating/rotating surfaces, providing as much wear resistance as possible, and remaining as strong as possible. One preferred material is ultra-high molecular weight polyethylene (UHMWPe) because it optimizes these three and other criteria. One concern posed by the material used for thespine 60 is that the spine must bear significant loads in the transverse and coronal planes—i.e., lateral to the spine axis. In one approach, thespine 60 can be provided as a separate component that mates with the remainder of thebearing 20. With this approach, the spine can be formed of a high strength metal, such as the cobalt alloy mentioned above. This approach adds to the complexity of the knee construct and adds the problem of interfacing the spine to the remainder of the bearing. - It is preferred that the
spine 60 be integrally formed with thebearing 20, which means that the spine will be formed of the same material. Where this material is UHMWPe, transverse or shear strength, and even bending stiffness, becomes a design consideration, particularly for active patients. To address this concern, the stiffeningpin 72 can extend through the axis of thespine 60 to add bending stiffness and shear resistance to the spine. Thepin 72 can be provided in different lengths depending upon the desired effect. For instance, the pin can be sized for insertion from the top of thespine 60 and to only extend for the height of the spine. Alternatively, as shown inFIG. 4 c, the pin can be introduced from the bottom of the bearingstem 22 and can include a stepped diameter to be press-fit into a comparable stepped diameter bore 70 of thestem 22. - While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected.
- For instance, the preferred embodiment contemplates one form of mobile bearing knee in which the tibial bearing rotates relative to the tibial platform. Other mobile bearing knees are contemplated, including knee prostheses in which the bearing slides on the platform. Of course, the inventive concepts can also be implemented in knee prosthesis in which the bearing does not move or is incorporated into the tibial platform. In addition, the illustrated embodiments contemplate that the spine projects from the bearing. The inventive concepts can be implemented where the spine is separate from the bearing, whether as a separate insert or integrated with the tibial platform.
Claims (16)
1. A knee prosthesis comprising:
a femoral component configured to be attached to a distal end of a femur and having a notch defined between spaced apart medial and a lateral condyle surfaces, the notch defining an elongated cam housing having a posterior cam at one end of the cam housing; and
a tibial component including (i) a platform configured for attachment to a proximal end of a tibia, (ii) a bearing supported on and rotatable in relation to the platform, the bearing defining medial and lateral bearing surfaces configured to articulate with the medial and lateral condyle surfaces, and (iii) a spine projecting superiorly from the bearing within the cam housing when the medial and lateral condyle surfaces are in articulating contact with the medial and lateral bearing surfaces,
wherein the spine includes an anterior face and an opposite posterior face facing the posterior cam when the medial and lateral condyle surfaces are in articulating contact with the medial and lateral bearing surfaces,
wherein the posterior face of the spine is concave along substantially the entire height of the spine, and
wherein the spine terminates in a convex rounded posterior peak.
2. The knee prosthesis of claim 1 , wherein:
the cam housing is configured to define an anterior-posterior distance between the anterior cam and the posterior face of the spine when the femoral component and the tibial component are in a normally extended position relative to each other, whereby the posterior face of the spine is in articulating contact with the posterior cam only at a first predetermined flexion rotation angle between the femoral component and the tibial component.
3. The knee prosthesis of claim 2 , wherein the first predetermined flexion angle is about 50°.
4. The knee prosthesis of claim 3 , wherein a complementary curved surface of the posterior cam is arranged on the posterior cam so that the complementary curved surface is substantially nested within the concave posterior face of the spine only after the femoral component and the tibial component rotate relative to each other to a second predetermined flexion angle greater than the first predetermined flexion angle.
5. The knee prosthesis of claim 4 , wherein the complementary curved surface of the posterior cam is substantially completely nested within the concave posterior face of the spine at about 120° of flexion.
6. The knee prosthesis of claim 5 , wherein the complementary curved surface is curved at a first radius, and the concave surface of the posterior face of the spine is curved at substantially the first radius.
7. The knee prosthesis of claim 6 , wherein:
the cam housing defines a width sufficient to provide a clearance ranging between about 0.12 mm to about 0.50 mm on each side of the spine when the spine projects into the cam housing.
8. The knee prosthesis of claim 2 , wherein:
the cam housing defines an anterior cam at an opposite end thereof;
the anterior face of the spine facing the anterior cam is substantially flat; and
the anterior cam defines a substantially flat surface complementary to the anterior face of the spine.
9. The knee prosthesis of claim 2 , further comprising:
a bore extending through the spine, the spine formed of a first material; and
a pin configured to be disposed within the bore, the pin being formed of a second material which is different from the first material.
10. The knee prosthesis of claim 1 , wherein the spine has a height of about 16.0-24.0 mm and the cam housing includes a roof and is sized relative to the condyle surfaces so that the spine cannot contact the roof when the condyle surfaces are supported on the bearing surfaces.
11. The knee prosthesis of claim 1 , wherein the spine and the cam housing interact with each other to allow X degrees of pivoting between the femoral component and the bearing of said tibial component, and
0.5 degrees≦X≦2.5 degrees.
0.5 degrees≦X≦2.5 degrees.
12. The knee prosthesis of claim 11 , wherein the cam housing defines an anterior-posterior distance between the posterior cam of the cam housing and an opposite end of the cam housing that is substantially greater than the maximum anterior-posterior dimension of the spine.
13. The knee prosthesis of claim 12 , wherein the anterior-posterior distance defined by the cam housing is about 1.5 times greater than the maximum anterior-posterior dimension of the spine.
14. The knee prosthesis of claim 13 , wherein the cam housing defines a width sufficient to provide a clearance ranging between about 0.12 mm to about 0.50 mm on each side of the spine when the spine projects into the cam housing.
15. The knee prosthesis of claim 1 , wherein:
the cam housing defines an anterior cam at an opposite end thereof;
the anterior face of the spine facing the anterior cam is substantially flat; and
the anterior cam defines a substantially flat surface complementary to the anterior face of the spine.
16. The knee prosthesis of claim 1 , further comprising:
a bore extending through the spine, the spine formed of a first material; and
a pin configured to be disposed within the bore, the pin being formed of a second material which is different from the first material.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US13/763,305 US20130150976A1 (en) | 2002-09-12 | 2013-02-08 | Posterior Stabilized Knee With Varus-Valgus Constraint |
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Application Number | Priority Date | Filing Date | Title |
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US10/242,122 US20040054416A1 (en) | 2002-09-12 | 2002-09-12 | Posterior stabilized knee with varus-valgus constraint |
US11/121,408 US8382847B2 (en) | 2002-09-12 | 2005-05-04 | Posterior stabilized knee with varus-valgus constraint |
US13/763,305 US20130150976A1 (en) | 2002-09-12 | 2013-02-08 | Posterior Stabilized Knee With Varus-Valgus Constraint |
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US11/121,408 Division US8382847B2 (en) | 2002-09-12 | 2005-05-04 | Posterior stabilized knee with varus-valgus constraint |
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US13/763,305 Abandoned US20130150976A1 (en) | 2002-09-12 | 2013-02-08 | Posterior Stabilized Knee With Varus-Valgus Constraint |
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US10/242,122 Abandoned US20040054416A1 (en) | 2002-09-12 | 2002-09-12 | Posterior stabilized knee with varus-valgus constraint |
US11/121,408 Active 2029-02-19 US8382847B2 (en) | 2002-09-12 | 2005-05-04 | Posterior stabilized knee with varus-valgus constraint |
Country Status (7)
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US (3) | US20040054416A1 (en) |
EP (1) | EP1400220B1 (en) |
AT (1) | ATE325587T1 (en) |
AU (1) | AU2003244616B2 (en) |
DE (1) | DE60305115T2 (en) |
DK (1) | DK1400220T3 (en) |
ES (1) | ES2263923T3 (en) |
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CN110432961A (en) * | 2019-07-19 | 2019-11-12 | 温州医科大学附属第一医院 | A kind of minimally invasive restorer of tibial plateau collapsed fracture block |
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Also Published As
Publication number | Publication date |
---|---|
ES2263923T3 (en) | 2006-12-16 |
DE60305115T2 (en) | 2006-11-30 |
US8382847B2 (en) | 2013-02-26 |
AU2003244616B2 (en) | 2008-08-21 |
US20040054416A1 (en) | 2004-03-18 |
AU2003244616A1 (en) | 2004-04-01 |
DK1400220T3 (en) | 2006-08-28 |
EP1400220A1 (en) | 2004-03-24 |
US20050192672A1 (en) | 2005-09-01 |
DE60305115D1 (en) | 2006-06-14 |
ATE325587T1 (en) | 2006-06-15 |
EP1400220B1 (en) | 2006-05-10 |
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