Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1998-02-02
1999-03-30
Milano, Michael J.
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
A61F 244
Patent
active
058882278
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to an intervertebral implant having a frame-like cage, perforated cover and base faces, two lateral surfaces and front and rear walls, where at least one of the cover or base face has a plurality of perforations.
BACKGROUND ART
Intervertebral implants are used for the fusion of two vertebral bodies, especially in the area of the lumbar spine. One or two implants are used for each intervertebral space.
Various types of such intervertebral implants are already known from the prior art. However, all of these have the disadvantage that they harbor the risk of the implant sinking into the end plates of the affected vertebrae. For example, an intervertebral implant in the form of a ring or double ring open on top and bottom is known from the U.S. Pat. No. 5,192,327 BRANTIGAN. Since only the edge of the ring implant and at most also the narrow connection web in the case of a double ring design can act as bone contact surface, there is considerable risk that the end plates of the thereby spaced-apart vertebral bodies will sink in.
SUMMARY OF THE INVENTION
The invention is intended to remedy this. It is an object of the invention to create an intervertebral implant which can be inserted into the intervertebral space in a controlled manner, which has an optimal bone contact surface, and, due to a number of perforations in the bone contact surface, nevertheless promotes good ingrowth behavior on the part of the bone.
This object is achieved by the use of an intervertebral implant having a frame-like cage which is essentially wedge shaped, encloses a cavity and has perforated cover and base faces as bone contacting surfaces, along with two lateral surfaces, and front and rear walls. The cover and base faces diverge toward the front wall, and at least one of those faces includes a plurality of perforations whose total area makes up 40 to 55% of the total area of that face. The individual area of an individual perforation is at most 20% of the area. Also, the ratio of cavity volume to cage volume is preferably in the range of 0.11 to 0.42.
This achieves the advantage that, due to the large bone contact surface of the cover and base faces, the implant is prevented from sinking into the end plates of the vertebral bodies.
However, at the same time a number of perforations in the cover and/or base face allow the bone to grow in. The perforations in the cover and/or base face are extremely important for the bone to grow in, which causes the adjoining vertebral bodies to fuse. Surprisingly, it has appeared that the geometrical relationships of these perforations have decisive significance for clinical success. If the total area of these perforations is too small, the bone cannot grow in to the required extent so that fusion does not occur. On the other hand, if the total area of these perforations is too large, the remaining contact surface of the cover and base faces of the implants relative to the end plates of the adjoining vertebral bodies is too small, which results in excessive contact forces between the implant and the end plates, which again increases the risk that the implant will sink into the end plates.
It has appeared that the total area of the perforations in the cover and/or base face must lie in the range of 40-55% of the total area of the cover and/or base face, in order to achieve good clinical results. The total area of the perforations in the cover and/or base face preferably should be 43-51%, typically 45-49% of the total area of the cover and/or base face.
The dimensions of the individual perforations in the cover and/or base face have also proven to be very important for the degree of clinical success. If the area of the individual perforations is too small, it becomes more difficult for the bone to grow in, even though the total perforation area may be considerable. On the other hand, perforations in the cover and/or base face with too great an average area also have a negative effect, because they impair the uniform support of the end plate, thus creating
REFERENCES:
patent: 5147402 (1992-09-01), Bohler
patent: 5192327 (1993-03-01), Brantigan
patent: 5294391 (1994-03-01), McMillin
patent: 5425772 (1995-06-01), Brantigan
patent: 5522899 (1996-06-01), Michelson
patent: 5658337 (1997-08-01), Kohrs
patent: 5683463 (1997-11-01), Godefroy
patent: 5749916 (1998-05-01), Richelsoph
patent: 5766252 (1998-06-01), Henry
patent: 5776199 (1998-07-01), Michelson
patent: 5782919 (1998-07-01), Zdeblick
Milano Michael J.
Synthes (U.S.A.)
LandOfFree
Inter-vertebral implant does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Inter-vertebral implant, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Inter-vertebral implant will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1209882