Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
1999-02-10
2001-10-30
Reip, David O. (Department: 3731)
Surgery
Instruments
Orthopedic instrumentation
Reexamination Certificate
active
06309393
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a bone fixation device, and in particular to a bone plate.
BACKGROUND OF THE INVENTION
Bone plates have been used for many years in the field of orthopaedics. There have been many attempts to develop improved bone plates. For example, European Patent No. B 0355 035 teaches a bone plate with conical plate holes which provide a rigid connection between the plate and the fixation screws even after bone resorption has occurred. The plate disclosed in this European Patent has a concave bone-contacting surface which reduces the surface area of bone contact in order to improve the healing process. Published European Patent Application A 0 684 017 discloses a bone plate having widened plate holes on the upper side. Despite these and other advancements, all known bone plates have drawbacks. For example, common concerns related to the use of bone plates include strength of the implant, stability of fixation on the bone, and biological incorporation.
Thus, there exists a need for an improved bone plate.
SUMMARY OF THE INVENTION
One object of the present invention is to create a bone plate that, in addition to optimum incorporation characteristics, has the lowest possible volume (and therefore weight) while still having a high degree of strength.
Compared to the prior art, the bone plate according to the present invention has the following advantages:
Optimum utilization of material characteristics through optimum distribution of tension when bending the bone plate, inserting the bone screws, and transferring the load in the implanted state;
Optimum bearing surface on the bone;
Optimum bearing force of the bone plate on the bone, which guarantees minimal disruption of blood supply;
Blocking of the conical screw heads in the conical screw hole, which means that the transfer of force in the bone/plate bond is no longer based on friction, but instead forms a positive-locking system.
The bone plate according to the present invention has an upper side, a lower side with a plurality of projections between first and second recesses configured and dimensioned to produce a plurality of bearing surfaces for contact with bone, at least two sides arranged about a longitudinal axis of the plate, and at least one plate hole extending from the upper side to the lower side of the plate for receiving a fastener. The upper side includes a region adjacent each plate hole with an insular recess.
In order to promote load transfer, the plate holes may taper conically from the upper side to the lower side with a cone angle from about 5° to 7°. Preferably, the fastener is a bone screw having a conical head. At least part of the bone screw surface may be anodized to prevent the screw head from sticking in the plate hole.
In one embodiment, the first recesses include a first cylindrical recess having a longitudinal axis oriented parallel to the longitudinal axis of the bone plate. Each second recess may include a second cylindrical recess with the longitudinal axis running between plate holes and either perpendicular or oblique to the longitudinal axis of the bone plate. The radius of the first cylindrical recess is preferably from about 3.2 mm to 3.8 mm and the radius of the second cylindrical recess is preferably from about 9 mm to 15 mm.
Although the dimensions of the bone plate will vary with application, the width is preferably from about 8 mm to 11 mm and the thickness is preferably from about 1.9 mm to 2.8 mm. Furthermore, the longitudinal sides of the plate may converge toward the lower side to minimize the degree of bone coverage by the plate.
With respect to the insular recess, the bone plate preferably has insular recesses with a volume of at least 20 mm
3
but less than 50 mm
3
and a surface area from about 38 mm
2
to 47 mm
2
. The surface area of each insular recess may be from about 2.5 times to 4.2 times larger than the surface area of each plate hole. The insular recess may have a butterfly-like shape with swallowtails. Preferably, the swallowtails are parallel to the longitudinal axis of the bone plate.
REFERENCES:
patent: 5053036 (1991-10-01), Perren et al.
patent: 5549612 (1996-08-01), Yapp et al.
patent: 5733287 (1998-03-01), Tepic et al.
patent: 5807396 (1998-09-01), Raveh
patent: 0 355 035 B1 (1990-02-01), None
patent: 0 530 585 A2 (1993-03-01), None
patent: 0 684 017 A1 (1995-11-01), None
Bresina Stephen J.
Perren Stephen
Tepic Slobodan
Pennie & Edmonds LLP
Reip David O.
Synthes (U.S.A.)
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