Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1999-07-23
2001-07-10
Philogene, Pedro (Department: 3732)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S020140, C623S020340, C623S020330
Reexamination Certificate
active
06258127
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a tibia part of a new joint endoprosthesis with a tibia platform or tibia plateau and with an anchoring element which is arranged on the distal side of the tibia platform and which may be screwed to the tibia platform.
BACKGROUND OF THE INVENTION
In a cement free knee joint replacement, additional stabilisation of a tibia platform by means of Spongiosa screws is the state of the art. In addition to the screws, often pegs, webs or ribs which are connected to the plateau, are common. The advantage of screws lies in the fact that, as a result of the initial stress produced thereby, a compression force is produced between the tibia platform and the bone during implantation. As a result, the primary stability is increased. Furthermore, bone is encouraged to grow into the distal or rear surface of the tibia platform. However, anchoring with screws has the disadvantage that the latter can be displaced backwards if osteonecroses or osteolyses occur under the tibia platform. Furthermore, the danger exists in the previously mentioned construction that detached polyethylene particles which originate from the polyethylene inlay mounted on the proximal side are displaced through the screw holes formed in the tibia platform into the bone. This then leads to local osteolyses.
In the relevant literature, there are described various cylindrical expansion anchors on the distal side of the tibia platform. These have the advantage that they make a pretension force possible. However, since they are based on the expansion principle there is no assurance that the anchor remains securely connected to the tibia platform. The possibility exists of being displaced and hence the formation of a gap between expansion anchor and tibia plateau. Polyethylene particles, coming from the mentioned inlay, may be displaced through this gap into the bone and lead to osteolyses. In addition, the point shaped support which is produced by anchors is disadvantageous for a long term osteointegration of the implant.
As an alternative to short anchors, a long intramedullar support can be used. This support can be completed by ribs by means of which a somewhat more widespread supporting of the tibia platform is obtained. A construction of this type is known e.g. from U.S. Pat. No. 4,938,769. The use of an intramedullar support has the disadvantage however that the load transference takes place in the distal region. The proximal bone beneath the tibia platform is in contrast only slightly stressed. This effect, so called “stress shielding” leads to bone resorption and in the long term to loosening of the implant.
SUMMARY OF THE INVENTION
It would therefore be of advantage if by means of an appropriate construction, on the one hand pre-tension could be produced during implantation and if simultaneously the tibia platform and the anchoring element formed a unit so that, in the first place, displacing of the anchoring element is impossible and secondly a hermetic seal occurs against the detached polyethylene particles.
An aspect of the invention involves a tibia part of a knee joint prosthesis. The tibia part comprises anchoring element and a tibia platform which has a distal side. The anchoring element is arranged on the distal side of the tibia platform and attached to the tibia platform. Correspondingly, the anchoring element according to the invention is formed by a shield in the form of a U-, C- or V- shape as seen from the front, the height of which is smaller than the width. It is therefore crucial that the anchoring shield in its implanted condition has a greater horizontal extension than vertical extension or rather height. As a result of the relatively small height of the anchoring shield the occurrence of distal load transference is prevented. At the same time, the large-surface support in the bone offers increased resistance to horizontal transverse loads and hence tilting of the tibia platform. In order to produce a pre-stressing force during implantation, the anchoring shield is firstly inserted into the proximal tibia bone and indeed so far that the upper edge of the anchoring shield is sunk to a slight extent beneath the bone surface. Next, the tibia platform is screwed into the anchoring shield which is sunk in the bone. As a consequence, a pre-stress force between the tibia platform and the bone is produced because of the friction between the anchoring shield and the bone. Since no expansion effect occurs, the shield can adjust in a proximal direction and hence be screwed to the tibia platform to be flush and free from play without the pre-stress force being noticeably lost.
The distal edge of the anchoring shield is arc-shaped, in particular formed to be convexly arc shaped, the arc line defining an arc of a circular section, elliptical section or a parabola. By means of this configuration, the anchoring shield can be inserted more easily into the proximal tibia bone. In addition, it should be pointed out that to avoid a loss of a pre-stress force the wall surfaces of the anchoring shield extend parallel to one another. In one embodiment, thickness or wall strength of the anchoring shield decreases step wise from proximal to distal.
In order to achieve an even better anchoring in the proximal tibia bone, the anchoring shield embraces, according to a further embodiment, a central web which is in the region of maximal height or at approximately half the width and which extends in the manner of a bisector of the lateral and medial portions of the anchoring shield. If required a further anchoring web can be arranged diametrally thereto. However, it has been shown that as a rule the previously mentioned central web is adequate for difficult anchoring cases. This central web extends preferably over the entire height of the anchoring shield. However, it is also conceivable to design the central web to be somewhat shorter than the corresponding height of the anchoring shield.
In order to secure the anchoring shield to the distal side of the tibia platform, the anchoring shield has at least two especially three proximally accessible threaded borings into which screws extending through corresponding borings in the tibia platform may be screwed for securing the tibia platform to the anchoring shield. The threaded borings are preferably arranged centrally and at the lateral and also medial end of the anchoring shield. For this purpose, the anchoring shield is designed peg-like at the assigned spots respectively.
For easier inserting of the anchoring shield into the tibia bone, the distal edge of the anchoring shield is designed as a cutting edge.
A further embodiment is distinguished in that on the distal side of the tibia platform a grooved shape recess is incorporated into which the anchoring shield may be fitted by its proximal front side securely.
In order to increase the pre-stress force of the anchoring shield in the tibia bone, the surface of same is preferably roughened, especially structured and indeed structured in a longitudinal direction. As a consequence, the pre-stress force is also not lost if the anchoring shield is displaced in a proximal direction when screwing down the tibia platform. The enlargement of the contact surface between the anchoring shield and the tibia bone is crucial.
REFERENCES:
patent: 4213209 (1980-07-01), Insall et al.
patent: 4822362 (1989-04-01), Walker et al.
patent: 4892547 (1990-01-01), Brown
patent: 4938769 (1990-07-01), Shaw
patent: 5137536 (1992-08-01), Koshino
patent: 5176711 (1993-01-01), Grimes
patent: 5192329 (1993-03-01), Christie et al.
patent: 5201768 (1993-04-01), Caspari et al.
patent: 5326368 (1994-07-01), Collazo
patent: 5413604 (1995-05-01), Hodge
patent: 5571198 (1996-11-01), Drucker et al.
patent: 28 02 655 (1978-08-01), None
patent: 32 05 526 (1983-09-01), None
patent: 42 11 347 (1993-10-01), None
patent: 42 301 18 (1994-03-01), None
patent: 43 37 936 (1995-05-01), None
patent: 0 303 006 (1989-02-01), None
patent: 384854 (1990-08-01), None
patent: 0 380 045 (1990-08-01), None
patent: 0 552 949 (1993-07-01), Non
Knobbe Martens Olson & Bear LLP
Philogene Pedro
Plus Endoprothetik AG
LandOfFree
Tibia part of a new joint endoprosthesis does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Tibia part of a new joint endoprosthesis, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Tibia part of a new joint endoprosthesis will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2520936