Over the wire scapel

An over the wire scalpel for performing a dermatotomy that produces a skin nick features a triangular shaped blade with a pair of cutting edges that meet to define a tip. The blade is connected to a handle and a central lumen passes through both. The leading opening of the lumen is positioned at the blade tip so that it is symmetrically abutted by the cutting edges. A blocker that limits the depth of blade travel is positioned upon the handle adjacent to the blade. A stylus may be placed within the central lumen so that the scalpel may be used without a guidewire or with a guidewire that has a diameter significantly smaller than that of the central lumen.

BACKGROUND 
Recently, interventional radiologic techniques have been developed whereby 
procedures that previously required surgical intervention are instead 
performed percutaneously. With interventional radiology, tubular 
structures in the human body, such as the drainage system of the kidneys, 
the bile ducts and the vascular system, are accessed and navigated by a 
wire that is steerable by the doctor. The wire passes from outside of the 
patient's body, through his or her skin, that is, percutaneously, and then 
into the internal tubular structure of interest. Once the wire is 
positioned in the desired location, medical devices, such as catheters, 
may be passed over the wire and thereby guided into the tubular structure 
so that the desired medical procedure may be performed. 
To install the wire, a hollow needle is initially placed through the 
patient's skin and into the tubular structure of concern. The wire is then 
passed through the lumen of the needle and into position within tubular 
structure. The needle is then withdrawn. At this point in the procedure, 
it becomes necessary to pass over this guidewire catheters or other 
devices which allow investigation or treatment of the tubular structure. 
Such devices by necessity are larger than the guidewire over which they 
are passed and hence cannot pass through the skin via the small hole made 
by the initial needle puncture. For this reason, a dermatotomy is 
performed during which a small skin incision, also known as a "skin nick", 
is made adjacent to the point of entry of the guidewire into the skin. 
Skin nicks have traditionally been created using standard surgical 
scalpels. These scalpels are disposable and feature triangular blades that 
are attached to polymer plastic handles. The physician uses such a scalpel 
to made the small incision as close as possible to the wire and its point 
of puncture. 
The disadvantages of this procedure arise from the difficulties encountered 
in creating a skin nick of an appropriate size and depth which is centered 
on the entry point of the wire. Oftentimes, after the wire has been 
placed, there is a small amount of bleeding from the puncture site which 
obscures the precise point of entry of the guidewire. As a result, it is 
difficult for the physician to direct the standard scalpel blade to a 
position directly adjacent to the wire. Frequently, during such attempts, 
a small skin bridge remains between the guidewire and the skin nick. This 
skin bridge restricts the passage of larger devices over the wire and 
through the skin. If the physician attempts to force the device past the 
skin bridge, it will tear and bleeding will be increased. In such a 
situation the scalpel must be used again in an attempt to remove the skin 
bridge. This is time consuming and difficult. 
A further disadvantage of the procedure is that the current design of the 
scalpels does not limit the depth or length of the skin nick. This can be 
of great concern when the tubular structure in question is close to the 
skin surface. In this circumstance, an inadvertantly deep skin nick may 
sever the structure of concern with potentially disastrous consequences. 
Still another disadvantage of the procedure is that during the formation of 
the skin nick with the wire in place, it is possible to damage or sever 
the guidewire. The latter would require removing the wire and starting the 
procedure again. A severed wire could also become lost in the subcutaneous 
tissue and be very difficult to retrieve. If the wire were damaged, but 
not severed, it would be difficult to pass a device over the damaged 
portion. 
In response to the above difficulties, over the wire incision devices have 
been developed. U.S. Pat. No. 4,633,860 to Korth et al. discloses a device 
for forming a canal in the body of a patient through the skin and 
subcutaneous tissue to the kidney so that an endoscopic instrument may be 
inserted. The device features a pair of blades symmetrically mounted upon 
a tube through which a guidewire passes. While this device works for its 
intended purpose, the creation of a canal in the human body, its blade 
design is not well suited for use in creating skin nicks. More 
specifically, the blades of Korth et al. are arcuate shaped to allow 
complete insertion and withdrawal in different planes so as to create a 
canal. As such, it would be difficult to partially insert the blades of 
Korth et al. to create a shallow skin nick. Furthermore, it is desirable 
that the skin nick be deepest at the location of the wire and then 
gradually become shallower as the radial distance from the wire increases 
(ie: V-shaped). This allows a device such as a catheter, as it is guided 
along the wire, to smoothly pass into and through the skin. The arcuate 
shape of the blades of Korth et al. make the achievement of such an 
incision difficult. 
U.S. Pat. No. 4,955,890 to Yamamoto et al. discloses a surgical skin 
incision device that features a tube with a pair of blades mounted 
symmetrically thereon. This structure, which is shared with Korth et al., 
causes the Yamamoto et al. and Korth et al. devices to have a number of 
disadvantages. One such disadvantage is that the tube causes the device 
surface initially contacting the skin to be blunt rather than sharp. While 
this provides the benefit of dilated skin at the cutting site, thus 
resulting in a cleaner cut near the edges of the incision, it also causes 
the cutting function to be compromised near the wire. 
The manufacture of the Korth et al. and Yamamoto et al. devices require 
that cutting blades be individually attached to a tube. This is an 
intricate, and thus labor intensive and costly, procedure. Furthermore, 
the devices of Korth et al. and Yamamoto feature handles that are attached 
to their tubes. Such a configuration increases manufacturing costs even 
further. In addition, the handles disclosed by Korth et al. and Yamamato 
et al. are significantly larger than their blade portions. This decreases 
the ease at which the devices may be handled during intricate procedures. 
Accordingly, it is an object of the present invention to provide an over 
the wire scalpel that makes it easier to create shallow, V-shaped 
incisions. 
It is also an object of the present invention to provide an over the wire 
scalpel that dilates the skin at the cutting site without compromising 
cutting performance near the wire. 
It is a further object of the present invention to provide an over the wire 
scalpel that may be easily and inexpensively manufactured. 
It is a further object of the present invention to provide an over the wire 
scalpel that is easily manipulated for intricate cuts. 
It is a further object of the present invention to provide an over the wire 
scalpel that may be used to create skin nicks without a guidewire. 
It is a further object of the present invention to provide an over the wire 
scalpel whereby a single scalpel may be used with a variety of guidewire 
diameters. 
SUMMARY 
The present invention is directed to an over the wire scalpel for 
performing a dermatotomy whereby a skin nick is made. The over the wire 
scalpel features a blade having a pair of cutting edges that define a 
V-shape. A handle that a physician may easily hold between his or her 
fingers is connected to the blade. A blocker or stop is positioned upon 
the handle and adjacent to the blade so as to restrict travel of the blade 
into the patient's skin. The blade and handle have a central lumen passing 
therethrough that receives a guidewire. The central lumen has a leading 
opening through the tip of the blade. 
The blade, in cross section, is generally diamond shaped (see FIG. 2). The 
thickest portion of the blade is adjacent the central lumen. The blade 
tapers so as to ultimately define the pair of cutting edges. Such a blade 
shape allows the scalpel to dilate the skin so as to improve cutting 
without degrading cutting performance in the region of the central lumen. 
A stylus with a pointed end may be placed within the central lumen of the 
scalpel to allow its use without a guidewire. Alternatively, the stylus 
may itself include a lumen that allows the scalpel to be used with a 
guidewire that has a diameter that is significantly smaller than that of 
the central lumen. 
For a more complete understanding of the nature and scope of the invention, 
reference may now be had to the following detailed description of 
embodiments thereof taken in conjunction with the appended claims and 
accompanying drawings.

DESCRIPTION 
Referring to FIG. 1, an embodiment of the over the wire scalpel of the 
present invention is shown. This scalpel allows a dermatotomy to be 
performed during which a skin nick is created that extends from, and 
abuts, the entry site of a previously placed guidewire. 
As shown in FIG. 1, the scalpel features a blade, indicated generally at 
10, with a pair of cutting edges 12 and a pair of opposing triangular 
blade sides, one of which is indicated at 15. Cutting edges 12 meet to 
form the tip 16 of the blade 10. The blade 10 is preferably constructed of 
metal typically used for surgical scalpel blades, that is, surgical grade 
stainless steel. However, other suitable metals, or even biocompatible 
polymer plastics, could be used for its construction. 
Attached to the blade 10 is handle 20. Handle 20 is shaped so that it may 
be easily held between the fingers of the physician. By restricting the 
size of handle 20 near blade 10, the scalpel may be easily manipulated by 
the physician so that intricate incisions may be made with great accuracy. 
Handle 20 is preferably composed of plastic polymer and may be joined to 
blade 10 by an adhesive or corresponding notch formations within the two 
pieces. Alternatively, blade 10 and handle 20 may be formed as an integral 
piece of the same material. This could reduce manufacturing costs. 
Positioned between blade 10 and handle 20 is blocker 22. As may be seen in 
FIG. 1, blocker 22 has a width greater than that of the blade 10. As will 
be discussed below, this is necessary so that the depth of blade travel 
into the patient's skin is limited. Blocker 22 may be formed integral with 
blade 10, handle 20 or both. 
Extending through blade 10, handle 20 and blocker 22 is a central lumen, 
shown in phantom at 30 in FIG. 1. As may be seen in FIG. 1, central lumen 
30 has a leading opening 32 at blade tip 16. A central lumen trailing 
opening 34 is formed in handle 20. Central lumen 30 is sized so that it 
may receive a guidewire thus permitting the scalpel to slide along the 
guidewire to the patient's skin. Blade 10 is preferably symmetrical about 
the central lumen opening 32 so that symmetrical skin nicks may be 
produced. A scalpel may optionally include a number of blades 
symmetrically mounted about a common central lumen so that a spoke-wheel 
type incision may be created. This may be particularly desirable when 
larger devices must be passed over the guidewire and into the patient. 
FIG. 2 shows an end on view of the blade 10 looking into the leading 
opening 32 of the central lumen 30. As may be seen by FIG. 2, blade 
configuration is preferably diamond shaped in cross section with the 
thickest portion of the diamond surrounding leading opening 32 (and thus 
central lumen 30). The cross section of blade 10 tapers down from its 
diamond shape to ultimately define cutting edges 12. As a result, the 
portion of the blade surrounding the central lumen has a greater average 
thickness than other portions of the blade. This allows the blade to 
slightly dilate, or pull apart, the skin as it makes its incision. This 
facilitates creation of the skin nick and results in a sharper, better 
defined (ie: "cleaner") cut. Because the cutting edges symmetrically abut 
leading opening 32, and the blade thickness gradually decreases as the 
distance from it increases, the scalpel of the present invention provides 
skin dilation without compromising cutting in the vicinity of the 
guidewire entry site. 
Turning to FIGS. 3A and 3B, a method of using the over the wire scalpel of 
the present invention to perform a dermatotomy is illustrated. As shown in 
FIG. 3A, a guidewire 40 enters the patient's skin at site 42, having been 
previously inserted using an initial puncture needle as is well known in 
the art. Guidewire 40 is received in leading opening 32 so that it passes 
through the central lumen 30 (FIG. 3B) of the over the wire scalpel. 
Leading opening 32 and central lumen 30 are only very slightly larger than 
guidewire 40 so that, while the over the wire scalpel may slide along 
guidewire 40, minimal space is present between guidewire 40 and the 
leading opening 32. 
The physician slides the scalpel along guidewire 40, via handle 20, until 
the tip of blade 10 comes into contact with the patient's skin. As 
illustrated in FIG. 3B, blade 10 is then advanced into the patient's skin 
until blocker 22 impedes further travel. As such, blocker 22 limits the 
depth of the skin nick 44 thereby formed. As shown in phantom, skin nick 
44 is deepest at the location of the wire and then is gradually shallower 
as the distance from the wire increases. This allows a device such as a 
catheter, as it is guided along the wire, to smoothly pass into the skin. 
Once skin nick 44 is created, the dermatotomy is complete. The scalpel is 
then withdrawn from the skin and slid off of the free end of guidewire 40. 
As shown in FIGS. 4A and 4B, a stylus, indicated generally at 50, may be 
inserted into the central lumen 30 of the scalpel so that it may be used 
to create skin nicks without the use of a guidewire. Stylus 50 features a 
stem 52 that is preferably composed of the same metal as blade 10. One end 
of the stem 52 is sharpened so as to form pointed end 54 while the other 
end is connected to base 56. While the entire stylus 50 may be formed out 
of a single piece of material, base 56 is preferably made of plastic 
polymer and attached to stem 52 with adhesive or the like to make handling 
easier. 
As shown in FIG. 4B, stem 52 is placed through central lumen 30 by 
introducing pointed end 54 into trailing opening 34. The entire length of 
stem 52 is passed through central lumen 30 until its travel is halted by 
the engagement of base 56 with trailing opening 34. Base 56 and trailing 
opening 34 are sized so that they snap together so that stylus 50 doesn't 
fall out of the scalpel as it is being handled. Pointed end 54 is shaped 
so that it conforms with cutting edges 12 when stylus 50 is positioned 
within the scalpel. As a result, in this configuration, blade 10 features 
a continuous sharp surface. 
An alternative embodiment of the stylus is shown in FIG. 5 at 60. Stylus 60 
is identical to stylus 50 except that it features a lumen, indicated in 
phantom at 62, through its longitudinal axis. Stylus lumen 62 is sized so 
that it can accommodate a guidewire that has a diameter that is 
significantly smaller than that of central lumen 30 (FIG. 4A). As a 
result, when stylus 60 is placed within central lumen 30, the scalpel may 
be used with a smaller diameter guidewire. Furthermore, a physician with 
access to a number of styluses, with varying lumen diameters, can use a 
single scalpel with a variety of guidewire diameters. 
While preferred embodiments of the invention have been shown and described, 
it will be apparent to those skilled in the art that changes and 
modifications may be made therein without departing from the spirit of the 
invention, the scope of which is defined by the appended claims.