Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2001-06-14
2002-11-19
Philogene, Pedro (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C606S080000, C606S08600R, C606S088000, C623S020210
Reexamination Certificate
active
06482209
ABSTRACT:
BACKGROUND OF THE INVENTION
A joint generally consists of two relatively rigid bony structures that maintain a relationship with each other. Soft tissue structures spanning the bony structures hold the bony structures together and aid in defining the motion of one bony structure to the other. In the knee, for example, the bony structures are the tibia and the femur. Soft tissue such as ligaments, tendons, menisci, and capsule provide support to the tibia and femur. A smooth and resilient surface consisting of articular cartilage covers the bony structures. The articular surfaces of the bony structures work in concert with the soft tissue structures to form a mechanism that defines the envelop of motion between the structures. Within a typical envelop of motion, the bony structures move in a predetermined pattern with respect to one another. When fully articulated, the motion defines a total envelop of motion between the bony structures. The soft tissue structures spanning the knee joint tend to stabilize the knee in a transverse plane. This transverse stability enables the bony structures to slide and rotate on one another in an orderly fashion.
The articular surfaces are subject to a variety of diseases, accidents and the like that cause the surfaces to be damaged. A common disorder of joints is degenerative arthritis. Degenerative arthritis causes progressive pain, swelling, and stiffness of the joints. As the arthritic process develops, the joint surfaces wear away, resulting in contractures of the surrounding soft tissues that provide stability to the joint. Changes in the articular surfaces resulting from arthritis decrease stability and increase the translation of the joint.
Treatment of the afflicted articular bone surfaces depends, among other things, upon the severity of the damage to the articular surface and the age and general physical robustness of the patient. The end result commonly necessitates joint replacement surgery wherein the articulating elements of the joint are replaced with artificial elements commonly consisting of a part made of metal articulating with a part made of ultra high molecular weight polyethylene (UHMWPE).
A relatively young patient with moderate to severe degeneration of the knee joint is often treated with drug therapies. While drug therapies may temporarily provide relief of pain, progression of the disease, with resulting deformity and reduced function, ultimately necessitates surgery. Alternative treatments such as nonsteroidal anti-inflammatory drugs, cortisone injections, and arthroscopic debridement similarly provide only temporary relief of symptoms.
In severe situations, the entire articular surface of a bone may be replaced with an artificial surface, as, for example, when condyles at the distal end of the femur are largely replaced with a prosthetic device having polished metal condyles and the tibial plateau is replaced with a plastic bearing that may be supported by a metal component. Joint replacement surgery has become a proven and efficacious method of alleviating pain and restoring function of the joint.
Current methods of preparing the intraarticular rigid elements of a joint to receive components as in joint replacement surgery involve an extensive surgical exposure. The exposure must be sufficient to permit the introduction of guides that are placed on, in, or attach to the joint, along with cutting blocks to guide the use of saws, burrs and other milling devices, and other instruments for cutting or removing cartilage and bone that subsequently is replaced with artificial surfaces. The distal end of the femur may be sculpted to have flat anterior and posterior surfaces generally parallel to the length of the femur, a flat end surface normal to the anterior and posterior surfaces, and angled flat surfaces joining the above mentioned surfaces, all for the purpose of receiving a prosthetic device.
A full joint replacement, using the example of the knee joint, also requires the proximal end of the tibia to be sculpted to receive a prosthesis having a generally upwardly facing bearing surface mimicking the normal tibial bearing surface and designed to articulate with the condylar surfaces of the femoral prosthesis. Typically, this surgery is performed with instruments or guides to orient cutting blocks, such that the preparation of the bone is in concordance with the correct alignment of the limb and the parts are correctly oriented in both coronal and sagittal positions. The guides are placed on exposed bones and generally reference anatomical points on that bone to establish a resection plane. For instance, with total knee replacement, arthroplasty guides are used by referencing, for example, the intramedullary cavity and the epicondylar and posterior condylar axes.
Knee joint prosthesis of the type referred to above are well known, and are described, for example, in Caspari et. al., U.S. Pat. Nos. 5,171,244, 5,171,276 and 5,336,266, Brown, U.S. Pat. No. 4,892,547, Burstein et al., U.S. Pat. No. 4,298,992, and Insall et. al., U.S. Pat. 6,068,658.
Substantial effort has been made to provide appropriate degrees of curvature to the condyles. For example, the earlier mentioned U.S. Pat. Nos. 5,171,276, 4,298,992 and 6,068,658 show that the radius of curvature in the anterior-posterior direction of the condyle of a femoral prosthesis may be somewhat greater near the anterior portion of the condyle than near the posterior portion. Kester et al., U.S. Pat. No. 5,824,100 teaches that a portion of this curvature of the condyle may be formed about a constant radius having its origin along a line between the lateral and medial collateral ligament attachment points on the femur.
Historically, a variety of modular prosthetic joint implants have been developed. The following descriptions of modular implants relate specifically to the knee. Early designs for knee implants, called polycentric knee implants, were developed with separate components for the medial and lateral compartments. Additionally, modular fixed-bearing knee implants having a polyethylene insert that is held relatively rigidly in place have been developed. Alternately, there are mobile bearing knee implants wherein the polyethylene bearing is designed to slide or move with minimal or no constraint on a tibial baseplate. Furthermore, both meniscal bearing and fixed bearing knee implants have been developed including either separate polyethylene bearings or a single polyethylene bearing that resides on a metallic tibial baseplate. While implant systems have been developed with fixed bearing elements or mobile bearing elements on the medial and lateral sides of the tibiofemoral joint, systems have not been developed having a combination of a fixed bearing on one side and a mobile bearing on the other side of the tibiofemoral joint.
Mobile bearing tibial implants may be configured to be more congruent with the femoral side of a knee arthroplasty, yielding lower contact stress. The resultant lower contact stress reduces the. possibility of damage sometimes encountered with some fixed bearing designs wherein the yield strength of the bearing material is exceeded. In general, fixed bearing implant designs are. less difficult to properly align and balance than mobile bearing designs. Mobile bearing designs are frequently desirable to reduce contact stress and the resulting wear of the bearing surface. However, with mobile bearing designs, there is the possibility of the bearing becoming dislodged from the implant. Additionally, mobile bearing knee designs are more surgically demanding to implant then fixed bearing designs.
The combination of a fixed bearing insert for the medial compartment and a mobile bearing insert for the lateral compartment is particularly attractive because the lateral femoral condyle rolls backward on the lateral tibial plateau as much as 10 to 20 mm whereas the medial condyle moves only a few millimeters. A mobile bearing insert is able to accommodate the rollback of the lateral condyle but would not be necessary for the medial condyle.
Two primary
Engh Gerard A.
Johnson Wesley D.
Fredrikson & Byron , P.A.
Philogene Pedro
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