Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1997-05-01
1998-10-20
Jones, Mary Beth
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
A61F 238
Patent
active
058241051
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a medical prosthetic device and more particularly to an orthopedic medical prosthetic device. Even more particularly, the present invention relates to an improved asymmetric knee prosthesis and method of surgically implanting same wherein the prosthetic medial femoral condyles include a thinner medial posterior condyle and a thicker lateral posterior condyle, resulting in an elevation of the posterior medial femur joint line with the knee in flexion. The present invention also has a concave proximal anterior region.
Arthroplasty is the making of an artificial joint. In total knee arthroplasty there is a difficulty in reproducing the exact anatomy. The tibia is usually cut at ninety degrees (90.degree.) to its axis in the frontal plane but the tibial plateau is at about eighty seven degree (87.degree.). The disparity is due to the difficulty in accurately reproducing an eighty seven degrees (87.degree.) cut. Also, it has been documented that with an eighty seven degrees (87.degree.) or varus cut the tibial component has a tendency to loosen. (Proceedings of the Knee Society 1985-1986, Laskin, Varus Knee deformity). (Surgery of the Knee, Insall et al, 1993).
With a ninety degree (90.degree.) cut, more bone is removed on the lateral side than on the medial side of the tibia. Neutral is defined as, parallel to a line tangent to the intact (not worn) posterior femoral condyles. When neutral femoral cuts are performed, and implants with equal medial and lateral thicknesses are used, there is a laxity of the lateral collateral ligament at ninety degrees (90.degree.) of flexion. The lateral collateral ligament is lax in flexion because the resection of the tibia and the posterior resection of the femur are not parallel, but the prosthesis implanted has equal medial and lateral thicknesses on the tibial component and posterior condyles of the femoral component. This results in less space on the medial side and more space on the lateral side, which causes unbalanced ligaments.
The current solution to this problem is to rotate the cutting block so that more bone is removed from the posterior medial femoral condyle, this is referred to as external rotation. By externally rotating (clockwise rotation for a left knee when viewed from the distal end), the posterior femoral resection is parallel to the ninety degree (90.degree.) tibial cut. This results in the collateral ligaments being balanced in extension and flexion when the prosthesis is implanted. The current industry standard is three degrees (3.degree.) of external rotation which corresponds to the three degree (3.degree.) difference between the eighty seven degree (87.degree.) anatomical angle of the tibial plateau and the ninety degree (90.degree.) angle of the tibial resection.
The benefits of this surgical procedure have been mentioned but there are some drawbacks. The femoral component is no longer aligned with the tibial component in full extension. The femoral component is rotated about three degrees (3.degree.) with respect to the tibia when it is aligned parallel to the lateral plane. This malalignment potentially could cause increased wear of the tibial insert. A possible solution to this malalignment could be to externally rotate the tibial component, but this would result in reduced tibial coverage, which is not desired. Another possible solution may be to design the insert at an angle, but both turning the tibial tray externally or designing it into the insert have the problem of malalignment in flexion. With externally rotating the femoral component, there will be malalignment with the tibial insert either in flexion or extension whether the tibial tray or tibial insert is aligned straight or externally rotated.
A second problem with traditional external rotation is the chance of notching the lateral anterior femoral cortex. "Notching" occurs when more bone is removed anterolaterally than with the neutral resections resulting in a notch being created in the anterior cortex of the femur. Notching greatly increases the
REFERENCES:
patent: 4081866 (1978-04-01), Upshaw
patent: 4865606 (1989-09-01), Rehder
patent: 5047057 (1991-09-01), Lawes
patent: 5133758 (1992-07-01), Hollister
patent: 5133759 (1992-07-01), Turner
patent: 5192328 (1993-03-01), Winters
patent: 5203807 (1993-04-01), Evans et al.
patent: 5282870 (1994-02-01), Moser et al.
patent: 5314483 (1994-05-01), Wehrli et al.
patent: 5326361 (1994-07-01), Hollister
"Femoral Implant" (single sheet).
"The Technique of Total Knee Arthroplasty-Intraoperative Alignment and Instrumentation", pp. 130-133.
"Genesis Total Knee System", Smith & Nephew Richards Publication on Surgical Technique.
Ries Michael
Schumacher Brian
Jones Mary Beth
Smith & Nephew Inc.
LandOfFree
Asymmetric femoral prosthesis does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Asymmetric femoral prosthesis, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Asymmetric femoral prosthesis will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-240316