Surgical knife for controlled lengthening of an incision

A surgical knife has a blade portion including a sharp edge disposed in a first plane and a dull portion offset from the first plane by a selected amount substantially equal to the amount of desired lengthening. When the blade is inserted into a previously-formed incision in tissue and moved in the direction of desired lengthening, the sharp edge cuts the tissue to lengthen the incision until the dull portion abuts against a wall of the incision to prevent further travel of the blade. The dull portion thus acts as a "stop" which prevents further travel of the blade beyond a desired point, enabling controlled lengthening of the incision.

BACKGROUND OF THE INVENTION 
This invention relates generally to a surgical instrument for making 
surgical incisions, and, more particularly, relates to a surgical knife 
for extending in a controlled manner the length of a surgical incision. 
DESCRIPTION OF THE PRIOR ART 
Various forms of surgical knives exist. Examples of such devices are set 
forth in the following United States patents: 
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U.S. Pat. No. Inventor Date 
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2,649,860 Royer Aug. 25, 1953 
3,798,688 Wasson Mar. 26, 1974 
4,844,070 Dee Jul. 04, 1989 
5,201,747 Mastel Apr. 13, 1993 
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U.S. Pat. No. 2,649,860 to Royer discloses a surgical instrument having a 
concave cutting saddle 15 bounded by rounded surfaces 12 and 16. As stated 
at col. 2 of Royer, "the purposes of having rounded edges through the 
major portion of the knife is to avoid injury to important tissues in the 
hand." 
U.S. Pat. No. 3,798,688 to Wasson discloses a surgical scalpel construction 
having an outer blade end which is pointless to prevent accidental 
stabbing of the surgeon or assistant during transfer of the scalpel and 
which may be formed with a concave tip portion having sharp side edges for 
cutting. See, for example. FIGS. 1 and 4 of Wasson. 
U.S. Pat. No. 4,844,070 to Dee discloses a changeable scalpel blade and 
chuck assembly. 
U.S. Pat. No. 5,201,747 to Mastel discloses an ophthalmological surgical 
instrument having a triple edge tip. 
Surgical scalpels typical of the prior art, however, suffer from a number 
of deficiencies. Most notably, conventional scalpels and surgical knives 
do not provide for extremely precise extension of the length of a 
previously made surgical incision. It is common practice in surgery, and 
particularly in ocular surgery where there is a corneal incision, for the 
surgeon to make an incision of a predetermined length. Further, it is 
often necessary, at that time or at a later time, to enlarge the incision 
by a minuscule amount. This required lengthening of the original incision 
is typically for a quarter of a millimeter or less, and accuracy is 
essential. Unintended lengthening of an incision beyond the desired 
distance can be extremely harmful to the patient, particularly when 
forming an incision in the cornea. 
Because of the extremely short distances involved and the need for 
accuracy, the lengthening procedure can be very difficult, even for highly 
skilled surgeons. 
SUMMARY OF THE INVENTION 
It is accordingly an object of the present invention to provide a surgical 
knife that enables precise and controlled lengthening of a surgical 
incision. 
It is a further object of the present invention to provide such a knife 
having a blade configuration that facilitates the lengthening of a 
previously-formed incision by a predetermined amount. 
It is another object of the invention to provide an improved surgical knife 
that is easily used by a surgeon to extend the length of a previously 
formed incision by a minuscule amount, on the order of one-quarter of a 
millimeter or less. 
Other general and specific objects of the invention will in part be obvious 
and will in part appear hereinafter. 
The foregoing objects are attained by the present invention, which provides 
a surgical knife for controlled lengthening of a previously-formed 
surgical incision. 
In accordance with one aspect of the invention, the surgical knife has a 
blade portion including a sharp edge disposed in a first plane and a dull 
portion disposed offset from the first plane by a selected amount 
substantially equal to the amount of desired lengthening. When the blade 
is inserted into a previously-formed incision in tissue and moved in the 
direction of desired lengthening, the sharp edge cuts the tissue to 
lengthen the incision until the dull portion abuts against a wall of the 
incision to prevent further travel of the blade. The dull portion thus 
acts as a "stop" which prevents further travel of the blade beyond a 
desired point. 
The invention will next be described in connection with certain illustrated 
embodiments; however, it should be clear to those skilled in the art that 
various modifications, additions and subtractions can be made without 
departing from the spirit or scope of the claims.

DESCRIPTION OF ILLUSTRATED EMBODIMENTS 
FIGS. 1A and 1B depict side and front views, respectively, of a scalpel 10 
typical of the prior art. The scalpel 10 includes a blade portion 12 
having sharp edges 14, 16 and 18 for cutting tissue in a known manner. A 
scalpel of this type is disclosed in U.S. Pat. No. 5,201,747 to Mastel, 
the teachings of which are incorporated by reference herein. 
While this conventional type of scalpel is useful in ophthalmological 
surgery, it does not provide for extremely precise extension of the length 
of a previously made surgical incision. As noted above, it is common 
practice in corneal surgery for the surgeon to make an incision of a 
predetermined length, and then, at a later time, to enlarge the incision 
by a minuscule amount. This required lengthening of the original incision 
is typically for a quarter of a millimeter or less, and accuracy is 
essential. Because of the extremely short distances involved and the need 
for accuracy, the lengthening procedure can be very difficult, even for 
highly skilled surgeons. 
Controlled lengthening of a previously made incision, however, is provided 
by a scalpel or knife constructed in accordance with the invention, 
embodiments of which are depicted in FIGS. 2-6. Referring now to FIGS. 
2-6, each of the embodiments of the knife 10 includes a blade portion 12 
having a tip portion 13 with a distal side and a proximal side. In the 
embodiment shown in FIG. 2, tip portion 13 includes at least one sharp 
distal edge portion 14 on the distal side, disposed along a cutting plane, 
and a "step" or "notch" section N including a dull edge 20 that is offset 
or set back by a selected distance S from the cutting plane defined by 
sharp edge 14. By providing a step or notch in the blade as depicted, an 
incision can be lengthened by a controlled amount equal to the length S of 
the step. The offset or set-back distance S of the blade determines the 
amount of controlled lengthening that can be provided by the knife. 
As will be seen below, by providing a sharp edge 14 disposed in a first 
plane and a dull edge 20 disposed in a second plane set back from the 
first plane by a selected amount S substantially equal to the amount of 
desired lengthening, when the blade 12 is inserted into a 
previously-formed incision in tissue and moved edgewise in the direction 
of desired lengthening, the sharp edge 14 cuts the tissue to lengthen the 
incision until the dull edge 20 abuts against a wall of the incision to 
prevent further travel of the blade. The dull edge 20 thus acts as a 
"stop" which prevents further travel of the blade beyond a desired point. 
In the embodiments depicted in FIGS. 2 and 6, the dull edge 20 forms the 
"floor" portion of a notched section N which is bounded on two sides by 
sharp edges 14. FIG. 2 shows a knife adapted for edgewise cutting in a 
right-to-left direction, while FIG. 6 depicts a configuration adapted for 
cutting in a left-to-right direction. Moreover, FIG. 2 shows sharp edges 
14 and notched section including dull edge 20 disposed on the longer or 
"point" edge of the blade, while FIG. 6 illustrates the sharp edges and 
notched section on the shorter edge of the blade. If desired, in FIG. 6 
edge 23 may be sharp. 
FIG. 3 illustrates an "undercut" blade portion in which the sharp edge 
portion 14 is terminated by the notch or step portion defined by wall 21. 
As will be seen below, this configuration is utilized to initially extend 
the lower portion of an incision. 
FIGS. 4 and 5 illustrate two blade configurations having sharp edges 14 and 
22 and a dull edge 20. These blades are utilized by moving the blade in a 
downward edgewise direction, thereby to lengthen an upper portion of an 
incision, as will be discussed hereinafter. 
An example of this controlled lengthening function is seen in FIGS. 7 and 
8. FIG. 7 depicts the use of the knife embodiment 10 of FIG. 4 to lengthen 
an incision 32 previously made in a cornea 30 by cutting an additional 
portion A of tissue by a desired amount. FIG. 8 depicts completion of the 
lengthening process of FIG. 7 using a conventional scalpel to cut 
remaining tissue in the lengthened incision region. 
More particularly, as seen in FIG. 7, the pre-existing incision 32 made in 
cornea 30 is characterized by a depth D and a distal wall W. In order to 
lengthen the incision 32 by a desired additional amount A, the surgeon 
first utilizes knife 10 having a dull tip edge portion 20 and a sharp edge 
portion 14 set forward from the tip by an amount A. The knife is inserted 
into the pre-existing incision such that the sharp edge portion 14 abuts 
against the pre-existing distal wall W of the pre-existing incision. The 
knife is pushed then forward, so that sharp edge 14 cuts tissue in the 
additional incision region A, until the dull tip portion of the knife 
contacts the "wall" W of the pre-existing incision. 
Because of the geometry of the knife, particularly the selected offset 
between sharp edge 14 and dull portion 20, only a selected width of 
additional tissue A can be cut in the cutting procedure depicted in FIG. 
7. This cutting procedure leaves an incision having a "step" region B of 
additional tissue to be cut. The lengthening process of FIG. 7 is 
completed by cutting remaining tissue in region B, as shown in FIG. 8, 
using a conventional scalpel. In particular, the conventional scalpel 
having sharp edge portion 14 is introduced into the incision and moved 
from right to left to cut the tissue in region B, thereby completing the 
lengthening process of FIG. 7. 
FIGS. 9 and 10 depict a similar incision-lengthening process, wherein the 
knife embodiment of FIG. 3 is used to lengthen an incision by cutting a 
lower layer of tissue by a desired amount, as shown in FIG. 9, and the 
lengthening process is completed by using a conventional scalpel to cut 
remaining tissue in the lengthened incision region (FIG. 10). 
As shown in FIG. 9, the pre-existing incision 32 is characterized by a 
"floor" F, a depth D, and a distal wall W. In accordance with the 
invention, in order to lengthen the incision 32 by a selected amount A, 
the surgeon utilizes a knife 10 having a sharp edge 14 at a tip portion 13 
of the blade 12, and a dull edge 20 set back from the plane of the sharp 
edge 14 by a selected distance S equal to the selected amount of 
lengthening. The knife is introduced into the incision 32 and moved from 
right to left in the drawing, so that sharp edge 14 cuts tissue in region 
A and extends the incision, substantially along the same path as the 
pre-existing incision, until dull portion 20 abuts the wall W of the 
pre-existing incision. 
This cutting operation lengthens the lower portion of pre-existing incision 
32 by a selected amount in region A, the selected amount being equal to 
the offset or set-back S of the blade. As shown in FIG. 10, the initial 
lengthening step of FIG. 9 leaves a "step" in the incision at upper region 
B. This step is removed, and the lengthening procedure of FIG. 9 is 
completed, using a scalpel as shown in FIG. 10. In particular, the knife 
is introduced into the incision and moved from right to left to cut tissue 
in region B, thereby completing the lengthening process. 
Those skilled in the art will appreciate that the invention can be embodied 
in other blade configurations. In each of these configurations, the 
surgical knife will have a blade portion including a sharp edge disposed 
in a first plane and a dull portion offset from the first plane by a 
selected amount substantially equal to the amount of desired lengthening. 
By providing a "step" in the blade as depicted, an incision can be 
lengthened by a controlled amount equal to the length of the step. When 
the blade is inserted into a previously-formed incision in tissue and 
moved in the direction of desired lengthening, the sharp edge cuts the 
tissue to lengthen the incision until the dull portion abuts against a 
wall of the incision to prevent further travel of the blade. The dull 
portion thus acts as a "stop" which prevents further travel of the blade 
beyond a desired point, enabling controlled lengthening of the incision. 
It will thus be seen that the invention efficiently attains the objects set 
forth above, among those made apparent from the preceding description. In 
particular, the invention provides a surgical knife that affords precisely 
controlled lengthening of a previously-formed surgical incision. 
It will be understood that changes may be made in the above construction 
and in the foregoing sequences of operation without departing from the 
scope of the invention. It is accordingly intended that all matter 
contained in the above description or shown in the accompanying drawings 
be interpreted as illustrative rather than in a limiting sense. It is also 
to be understood that the following claims are intended to cover all of 
the generic and specific features of the invention as described herein, 
and all statements of the scope of the invention which, as a matter of 
language, might be said to fall therebetween.