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Tibial componentRelated Patent Categories: Prosthesis (i.e., Artificial Body Members), Parts Thereof, Or Aids And Accessories Therefor, Implantable Prosthesis, Bone, Joint Bone, Knee Joint Bone, Tibial Bone, Movable BearingTibial component description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060190087, Tibial component. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The invention relates in general to prosthetic knee joint devices, and in particular to bi-compartmental devices for use in the lateral and medial compartments of the tibia. [0002] Considerable development has taken place in recent decades with regard to knee joint replacement. However, continuous review of clinical experience with unicompartmental meniscal knee implants has shown that problems can occur, particularly in the case of replacement of the lateral compartment. Whilst great success has been achieved with medial compartmental replacement, dislocation of the meniscal bearing in the lateral compartment remains a problem. The success rate of such replacements has been limited, due to the fact that the lateral soft tissues (principally the lateral collateral ligament and the ilio-tibial band) offer less certain resistance to distraction of the joint. There is also evidence to suggest that the lateral compartment may lift off under certain circumstances, such as during single leg stance, resulting in unequal loading of the joint. The lateral collateral ligament is a much slimmer structure than the medial collateral ligament and there is evidence to suggest that it is slack in the unloaded joint, except at extension. It therefore offers much less resistance to bearing dislocation or lift-off than do the more inextensible medial structures. On the lateral side, the tendon of the popliteus muscle passes across the postero-lateral corner of the joint. When the joint is replaced, the tendon can act to propel the meniscal bearing towards the intercondylar region where dislocation can occur. [0003] The early total condylar prostheses designed in the 1970's sacrificed both cruciate ligaments as does their successor, the Insall-Burstein posterior stabilised prosthesis. Many of the prostheses designed in the 1980's sacrificed the anterior cruciate ligament (ACL) but allowed retention of the posterior cruciate ligament. Attempts to develop total joint prostheses where the ACL is also retained have generally been unsuccessful. The prosthetic components were either designed to constrain antero-posterior translational movements and inadequate steps were taken to prevent loosening, or the components were unconstrained relative to anterior/posterior translation and many wore out. [0004] It has been observed that during flexion and extension of the knee joint, the contact points between the femoral and tibial condyles move in an antero-posterior direction. The femoral component moves on the tibial plateau in a posterior direction during flexion and in an anterior direction during extension. One of the problems caused by absence of the ACL is increased antero-posterior movement of the femoral condyle relative to the tibial condyle, which is responsible for further loosening of the tibial component and often leads to dislocation. A conventional tibial component will generally have a large central pin for location in the prepared end of the tibia. The ACL may be present in a diseased knee but is usually removed to improve access to the joint area during surgery, which is necessary to provide sufficient clearance to insert the tibial component and provide a site for the central pin. [0005] Examination of records of the state of the ligaments at the time of knee-replacement surgery shows that in more than 50% of cases, both in osteoarthritis or in rheumatoid arthritis, all the ligaments, including the ACL, were found to be intact. Where present, these ligaments are generally sacrificed in the above surgical techniques. Although tibial components having a central cut-out slot of the type illustrated in FIG. 1, which can be inserted with the ACL in place, have been employed, there will still be a tendency for dislocation or lift-off in the lateral compartment. [0006] In those cases where the ligaments are already absent, they may be reconstructed. Since the attempts of the 1960's, the practice of ACL reconstruction in young athletes, using muscle tendons as grafts, has become widespread and there is a large body of surgeons for whom this operation forms a substantial part of their practice. Although such routine reconstructions have usually only been performed in young persons, following injury involving ligament damage, there is considerable scope for reconstruction in the elderly patients who are the usual candidates for knee replacement, in cases where the ACL is absent. [0007] From the foregoing it is apparent that a need exists for knee replacement prostheses which provide sufficient stability in the lateral compartment and which are suitable for joints with intact cruciate ligaments. [0008] The aim of the invention is to provide a tibial component that will cause the lateral ligament to be tightened relatively more than the medial. It is intended that such a component be suitable in surgical situations where the anterior cruciate ligament is retained, replaced or reconstructed. [0009] In accordance with the present invention, there is provided a prosthesis for implantation in the knee joint, said prosthesis comprising: a tibial component having a first, upper surface and a second, lower surface opposite said first surface for attachment to the tibia, said first surface including a lateral bearing region and a medial bearing region, wherein the respective angles of inclination of said lateral and said medial bearing regions of said first surface, with respect to said second surface, are dissimilar. [0010] Advantageously, the direction of inclination is between the anterior side and the posterior side, and the angle of inclination of the lateral bearing region is more positive than the angle of inclination of the medial bearing region. Preferably, the difference in angle of inclination is approximately 2 to 4 degrees. The angle of the lateral bearing region may be inclined positively to the second surface and the medial bearing region substantially parallel to the second surface. Alternatively, with appropriate changes made to the angles of saw cut in the tibia, the lateral bearing region may be substantially parallel to the second surface, and the medial bearing region inclined at a negative angle to said second surface, or the lateral bearing region can be inclined at a greater positive angle to the second surface, and the medial bearing region inclined at a lesser positive angle to said second surface. The bearing regions may be formed as flat plane plateaux. For added stability, the bearing regions may be given a convex, part-spherical or part cylindrical form. They can also be formed with a convex lateral bearing region and a concave medial bearing region, similar to the physiological knee, or alternatively with either the lateral region convex and the medial region flat, or the lateral region flat and the medial region concave. In practical terms, the angles of inclination of said lateral and said medial bearing regions may be chosen such that, when attached to the tibia, the lateral bearing region is inclined downwards at a lesser angle to the horizontal than the medial bearing region, in an anterior to posterior direction. [0011] There is further provided a method of implanting a prosthesis comprising sawing the medial and lateral compartments of the tibial bone condyles and attaching the prosthesis to the prepared surface of the tibial bone, wherein the angle of the saw cut is chosen such that the posterior side of the lateral bearing region sits higher on the tibia than the posterior side of the medial bearing region. [0012] In an alternative aspect of the invention there is provided a prosthesis for implantation in the knee, said prosthesis comprising: a tibial component for attachment to the tibia, having a first, upper surface and a second, lower surface opposite said first surface for attachment to the tibia, said first surface including a lateral bearing region and a medial bearing region, arranged such that the respective angles of inclination in sagittal planes of said lateral and said medial bearing regions of the component in situ are different. [0013] Preferably the lateral and medial bearing regions are inclined downward, the angle of downward inclination of said lateral bearing region to the horizontal being less than the angle of inclination of said medial bearing region, such that the posterior of the lateral bearing region is higher than the posterior of the medial bearing region. [0014] In a further aspect, the invention provides a prosthesis comprising a tibial component having lateral and medial portions of differing height, wherein the difference in height of the lateral and medial portions increases posteriorly, such as to progressively tighten the lateral ligament more than the medial ligament as the joint moves from extension to flexion. [0015] The complete prosthesis may further comprise intermediate meniscal bearing components and a femoral component for attachment to the femur. [0016] According to another aspect of the invention, there is provided a tibial component having lateral and medial bearing portions and dimensioned such that a difference in the respective thicknesses of the lateral bearing portion and the medial bearing portion increases in an anterior to posterior direction. [0017] A further aspect of the invention provides a tibial component having lateral and medial bearing portions, wherein the thickness of at least one bearing portion changes progressively from the anterior side to the posterior side. [0018] Preferably the cross-sectional area of the lateral bearing portion in a sagittal plane that bisects the lateral bearing portion is greater than the cross-sectional area of the medial bearing portion in a corresponding sagittal plane. The change in thickness of the lateral and medial bearing portions in the anterior to posterior direction is advantageously described by the following expression: t.sub.lat(p)-t.sub.lat(a)>t.sub.med(p)-t.sub.med(a) [0019] Where t.sub.lat(p) is the thickness of the lateral bearing portion to the posterior side, tlat(a) is the thickness of the lateral bearing portion to the anterior side, t.sub.med(p) is the thickness of the medial bearing portion to the posterior side and t.sub.med(a) is the thickness of the medial bearing portion to the anterior side. A further aspect of the invention provides a tibial component having a lateral and a medial bearing portion comprising means for tensioning the lateral ligaments progressively more than the medial ligament. [0020] To better illustrate the invention, it will now be described, by way of example, with reference to the accompanying drawings. [0021] FIG. 1 illustrates a prior art tibial tray component in plan (1a), side (1b) and posterior (1c) views. [0022] FIG. 2 depicts plan, side and posterior views of a tibial component according to a first embodiment of the invention, for incorporation in a right-hand joint. [0023] FIG. 3 depicts plan, side and posterior views of a tibial component according to a first embodiment of the invention, for incorporation in a left-hand joint. [0024] FIG. 4 depicts plan, side and posterior views of a tibial component according to a second embodiment of the invention, for incorporation in a right-hand joint. Continue reading about Tibial component... Full patent description for Tibial component Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Tibial component patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Tibial component or other areas of interest. ### Previous Patent Application: Knee implant Next Patent Application: Prosthesis for correction of flatfoot deformity Industry Class: Prosthesis (i.e., artificial body members), parts thereof, or aids and accessories therefor ### FreshPatents.com Support Thank you for viewing the Tibial component patent info. IP-related news and info Results in 0.1762 seconds Other interesting Feshpatents.com categories: Accenture , Agouron Pharmaceuticals , Amgen , AT&T , Bausch & Lomb , Callaway Golf 174 |
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