Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2002-02-06
2004-04-20
Brown, Michael A. (Department: 3764)
Surgery
Instruments
Orthopedic instrumentation
C606S082000
Reexamination Certificate
active
06723101
ABSTRACT:
STATEMENT REGARDING FEDERRALY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
REFERENCE TO A “MICROFICHE APPENDIX”
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
The following invention relates generally to instrumentalities for cutting bone during surgery. More particularly, the instant invention is directed to a saw blade adapted to be operatively coupled to an oscillatory (or sagittal) surgical power tool which reciprocates the cutting blade back and forth about a small arc.
2. Description of the Prior Art
One of the most vexing problems that surgeons face when using surgical bone saws is the tendency of the saw to “kick” i.e., become caught upon the bone being cut by the point of the saw tooth. Another form of kicking occurs where the kerf has the same contour as the blade which is due to the fact that the cutting surface (i.e., teeth) lies on the same radius as the radius of tool rotation. In this scenario, all teeth grab nearly at the same time. This causes the saw apparatus to rotate about that point, transmitting a rotational force back through the saw and to the surgeon. This kicking or grabbing that occurs causes a loss of accuracy in the cut from the sudden, unpredictable movements of the saw and induces increased fatigue of the surgeon because of the greater tension that the surgeon must maintain in his hands and arms in anticipation of receiving this kicking or grabbing motion.
Another problem noted in existing blades involves the tendency of the saw to initially wander rather than to form a kerf. One reason for this involves the nature of oscillatory cutter blades. The handle portion of the saw remains stable because it is in the surgeon's control and remote from the cutting. However a blade (having a proximal end mounted into the oscillatory power tool) moves at a distal end that scribes an arc of a circle. Most surgical cutting saw blades have teeth on the distal extremity which are also oriented in an arc of constant radius. Especially when that arc has a geometrical center which coincides with the center of oscillatory motion, the bone to be penetrated is normally initially addressed by only one active cutting tooth in the series of teeth that resides on the arc, and as the blade completes its outward motion many teeth come into contact simultaneously. With several teeth contacting the bone, there is a greater tendency of the saw blade to kick and wander. The effect is even more pronounced when the blade teeth's center of arc is between the oscillatory center of the power tool and the blade's distal end.
Another problem involves the non-aggressive nature of prior art blades. Even when more than one tooth contacts the bone, it is primarily due to the manipulation of the blade by the surgeon. The effect is that adjacent teeth do not effect progressive cutting and therefore make binding and kick back more likely.
Moreover, once the kerf has formed, several other problems attend the cutting process. For one thing, substantially all the saw's teeth traverse along the entire extent, of the kerf. This decreases the aggressiveness of the cutting action as the cutting action is an abrading one rather than chipping. The teeth reside within the kerf for a longer period of time and tend to naturally generate more heat than had they been allowed outside the kerf. In addition, not having the teeth exit the working surface periodically tends to leave the chips of bone that have been abraded by the teeth to remain between the teeth. Lack of efficient chip removal is recognized as one cause of excessive heat generation. In surgical situations, such unwanted heat generation is undesirable because of thermal necrosis which damages bone structure adjacent to the cut.
The following documents reflect the state of the art of which applicants are aware and are tendered herewith to discharge the applicants' acknowledged duty to disclose relevant prior art of which they are aware. However, it is respectfully stipulated that none of these prior art teachings anticipate when considered singly or render obvious when considered in any conceivable combination the nexus of the instant invention as particularly detailed hereinafter.
INVENTOR
PATENT NO.
ISSUE DATE
Carroll
2,455,655
1948
Tuke
3,905,105
1975
Winter
3,905,374
1975
Bent
3,943,934
1976
Mongeon
4,386,609
1983
Arnegger
4,513,742
1985
Arnegger
4,584,999
1986
CATALOG
TITLE
Micro-Aire ™ Catalog
“Accessories-Orthopedic Power
Instrument System”
Stryker* Surgical Catalog
“Cutting Accessories Guide”
Hall Surgical Catalog
“Hall Quality Saw Blades for
Stryker and 3M”
None of the prior art explicitly recognizes the value in having the teeth on an oscillatory cutter placed substantially on a tangent which is perpendicular to a radial line extending from the center of the power tools cutting axis that bisects the arc of travel within which the blade travels.
BRIEF SUMMARY OF THE INVENTION
The instant invention is distinguished over the known prior art in a multiplicity of ways.
In its essence, the blade of the instant invention takes into consideration the natural tendencies at play when a surgeon is cutting a bone with an oscillatory saw. In general, the natural tendency is to make a plunge type cut, i.e., move the tool and blade in a single direction, plunging the saw in the bone for cutting. The direction of force imposed by the surgeon is intuitively coaxial with the long axis of the saw and blade. When viewed in this light, it should be clear that prior art cutting blades having curved cutting heads will cause the tip of the tooth to either wander or kick. The instant invention, however, addresses the bone to be cut in a manner which reduces fatigue by the surgeon and vibration or impulses generated during the cutting process.
More specifically, when a tooth profile parallels tangents to the arc of travel of the oscillatory cutter, the bone to be cut sees approximately one tooth at a time when the surgeon is making a plunge into the bone. Actually, the contact starts at the center and moves outwards. In this way, there is less pulsed vibration, there is a lower tendency of the saw to kick by having one tooth engage the bone and rotating thereabout, and there is better bone chip evacuation which reduces the operating temperature of the saw adjacent the cut.
One attribute of the instant invention is that each working tooth progressively cuts more material than the previous working tooth so that collectively, all teeth contacting the bone to be cut make progressive contributions.
Three types of saw blades illustrative of these phenomena are disclosed in the instant application. One blade includes a series of cutting tips all oriented in a linear plane and the teeth which support these tips all have the general configuration of isosceles triangles.
A second form of cutting tool is disclosed in which the tips of all of the teeth are also substantially in a horizontal plane, but the teeth which support these tips have a different contour from the first version. A central-most tooth may be in the form of an isosceles triangle as in the first invention form, but the remaining teeth disposed outboard the central isosceles tooth are all substantially right triangles in which the vertical leg of the right triangle is oriented adjacent the central isosceles tooth and the hypotenuse portion is outboard from the central isosceles tooth. This provides a positive rake, and the most aggressive cut as the blade cuts progressively from the inside out.
A third form of cutting blade is shown in which the right triangles of the second version have been oriented 180° so that the hypotenuse of each cutting tooth faces the center of the cutting blade. In practice, the “right” triangles may be “near” right triangles with the included angle greater than 90° for an aggressive cut. The cutting occurs on the tip of the hypotenuse. Also, there is a central isosceles void provided where there had been the central tooth of the second invention form.
Accordingly, it is the primary object of the present invention to pr
Fisher Michael Gerard
Fletcher Henry Hasbrouck
Brown Michael A.
Meaney, Jr. Daniel J.
Synvasive Technology, Inc.
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