Trocar having an improved cutting tip configuration

A surgical trocar has three integral single beveled blades having cutting edges which, when viewed head on, resemble a Y configuration. The distal end of each blade is formed with a leading cutting edge and a single trailing edge which define a single beveled face. The blades are arranged so that their leading edges converge to form a sharp point at the distal end of the trocar with the leading cutting edges extending proximally and radially from the point. The trocar is preferably extruded with three fins which are shifted relative to the longitudinal axis of the extrusion such that at most a first side of each fin lies along a ray from the longitudinal axis of the extrusion. Alternatively, both sides are shifted to one side of the longitudinal axis. The distal end of each fin is then ground to form a single bevel with at least a portion of the cutting edge of the beveled fin lying in a plane which includes the longitudinal axis of the extrusion and being angled proximally. The fins are preferably spaced at 120.degree. intervals from one another about the longitudinal axis of the extrusion. The extrusion is preferably stepped proximal of the cutting edges to form a descending step for stopping the distal movement of a spring biased safety shield. The fins may be ground using the same machine used to grind a pyramidal trocar tip and will result in cutting edges with half the angle of the cutting edges of the pyramidal tip.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to surgical trocars. More particularly, this 
invention relates to an improved trocar having an extremely sharp tip for 
making incisions. 
2. State of the Art 
Laparoscopic surgery is widely practiced throughout the world today and its 
acceptance is growing rapidly. In general, laparoscopic surgery involves 
creating an entry port into the body of a patient by forcing a trocar 
carrying a trocar tube through the abdominal wall, removing the trocar and 
leaving the trocar tube in place. Laparoscopic tools may be inserted 
through the trocar tube in order to perform minimally invasive surgery or 
diagnostic procedures. The trocar assembly generally includes a trocar 
having a sharp distal tip, and a proximal housing which carries a trocar 
tube which surrounds the trocar and includes a sealing or valve member 
associated with the trocar tube. In the assembled position ready for use, 
the sharp tip protrudes from the distal end of the trocar tube. The trocar 
is inserted into the body by pressing the trocar against the patient's 
skin, causing the trocar tip to make an incision in the skin so that the 
trocar tube can penetrate the body. After penetration, the trocar is 
removed from the trocar tube and valve housing, leaving the valve housing 
exterior of the body with the trocar tube extending into the peritoneal 
cavity. Surgical viewing endoscopes, cameras, lenses, or other viewing 
instrumentation are then inserted through the trocar tube while a cutter, 
dissector, or other surgical instrument is inserted through another trocar 
tube for the purpose of manipulating and/or cutting the internal organ or 
tissue. It is often desirable to have several trocar tubes in place at 
once in order to receive several surgical instruments. In this manner, 
organs or tissue may be grasped with one surgical instrument, and 
simultaneously may be cut with another surgical instrument; all under view 
of the surgeon via the viewing instrumentation in place. 
It is desirable for the trocar to make the smallest and least disfiguring 
incision possible. To this end, an extremely sharp trocar tip is preferred 
which requires the least amount of pushing pressure and makes a clean 
incision. A well known trocar tip design includes a solid cylindrical body 
with multiple bevels at the distal end forming a three faced pyramidal 
point. The pyramidal point is provided by feeding a solid aluminum or 
stainless steel rod through an automatic grinding machine which grinds a 
flat on the end of the rod at an angle of 17.degree. to the longitudinal 
axis of the rod. The grinding machine rotates the rod 120.degree. about 
its longitudinal axis and grinds a second 17.degree. flat, and then 
rotates the rod another 120.degree. about its longitudinal axis and grinds 
the third 17.degree. flat. This known design, however, requires a 
relatively large force to thrust the trocar into the abdomen. In addition, 
the incisions made by these designs often result in excessive tearing of 
the skin because the beveled surfaces of the pyramidal tip tend to push 
the skin apart before it is cut. This is because the actual cutting edges 
are formed by 68.degree. intersections of adjacent flats, whereas the 
optimal cutting edge for a durable knife is a 22.degree. intersection of 
flats. Nevertheless, the 68.degree. cutting edges of the three faced 
pyramidal tip are the sharpest possible edges for that configuration. If 
the grinding angle of 17.degree. is increased or decreased, the cutting 
edge angle of 68.degree. will increase according to the trigonometry of 
tetrahedrons. 
Other trocar tip designs exist providing certain advantages over the well 
known pyramidal tip. U.S. Pat. No. 4,601,710 to Moll discloses a trocar 
assembly including a trocar having a distally biased hollow frustroconical 
safety shield with three radial slots. The sharp point of the trocar 
includes three radially arranged blades each of which has a leading 
cutting edge and two trailing edges forming a double beveled blade edge 
which is angled proximally from the tip. When the frustroconical safety 
shield is pressed proximally against its biasing spring, the three slots 
in the safety shield permit exposure of the three blades. Moll's trocar 
design provides a sharp cutting tip and avoids the beveled surfaces of the 
pyramidal tip which tend to tear and scar the skin at the entry point of 
the trocar. However, the three blade tip taught by Moll is expensive to 
make because six surfaces must be ground, and the resulting trocar is 
still is not as sharp as desirable. 
SUMMARY OF THE INVENTION 
It is therefore an object of the invention to provide a trocar which 
requires only a little pressure to make an incision. 
It is also an object of the invention to provide a trocar having a tip 
which is very sharp and makes a clean incision with little or no tearing 
of skin. 
It is a further object of the invention to provide a trocar which is 
inexpensive and easy to manufacture. 
It is still another object of the invention to provide a trocar which can 
be manufactured using the same kind of grinding machine as is used to 
manufacture a trocar having a pyramidal tip. 
In accord with the objects of the invention a trocar is provided and 
generally includes a tip having three integral single beveled blades 
having cutting edges which, when viewed head on, resemble a slightly 
offset Y configuration. The distal ends of each of the blades are formed 
with a leading (cutting) edge and a single trailing edge which define a 
single beveled face. The blades are arranged so that their leading edges 
converge to form a sharp point at the distal end of the trocar with the 
leading cutting edges extending proximally and radially from the point. As 
only one face of each blade is ground to form a single bevel, the angle of 
the face can be made much smaller than in a double-bevelled blade, thereby 
providing a very sharp cutting edge. The trocar is also easier and less 
expensive to manufacture. 
According to one embodiment, the trocar is extruded with three fins which 
are shifted relative to the longitudinal axis of the extrusion such that a 
first side of each fin lies along a ray from the longitudinal axis of the 
extrusion. The distal end of each fin is then ground to form a single 
bevel with the cutting edge of the beveled fin lying in a plane which 
includes the longitudinal axis of the extrusion and being angled 
proximally. The fins are preferably spaced at 120.degree. intervals from 
one another about the longitudinal axis of the extrusion. The extrusion is 
preferably turned down proximal of the cutting edges to form a descending 
step for stopping the distal movement of a spring biased safety shield. 
The trocar tip can be ground using a conventional machine which grinds the 
first and second fin at an angle of 17.degree., rotates the trocar 
120.degree., grinds the second and third fins at an angle of 17.degree., 
rotates the trocar 120.degree., and grinds the third and first fins at an 
angle of 17.degree.. As will be better understood from the detailed 
description below, the first grinding step imparts a bevel and cutting 
edge to the first fin and only a leading edge to the second fin. The 
second grinding step imparts a bevel to the second fin and a leading edge 
to the third fin. The third grinding step imparts a bevel to the third 
fin. The resulting tip has three cutting edges, each of which has a 
cutting edge angle of 34.degree., half the angle of cutting edges of a 
pyramidal trocar tip. By using a more sophisticated grinding machine, and 
in accord with a second embodiment of the invention, the cutting edge 
angle can be reduced even further. 
According to third embodiment of the invention, the trocar is extruded with 
three fins which are shifted relative to the longitudinal axis of the 
extrusion such that both sides of each fin are shifted in the same 
direction away from the longitudinal axis of the extrusion. The distal end 
of each fin is then ground to form a single bevel with a distal portion of 
the cutting edge of the beveled fin lying in a plane which includes the 
longitudinal axis of the extrusion and a proximal portion of the cutting 
edge lying in a plane which is parallel to, but does not include the 
longitudinal axis of the extrusion. 
If the angle of the cutting edge relative to the longitudinal axis of the 
extrusion is the same as the angle of the bevel relative to the 
longitudinal axis of the extrusion, a distal portion of the trocar tip 
will have a pyramidal point with rays approximately equal to the thickness 
of the fins. Additional objects and advantages of the invention will 
become apparent to those skilled in the art upon reference to the detailed 
description taken in conjunction with the provided figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Turning now to FIGS. 1, 2, 3, and 4, the trocar 100 according to the 
invention includes a proximal handle 102, a central shaft 104, and a 
distal cutting tip 106. The distal cutting tip 106 includes three 
sharpened fins 106a-106c arranged in a slightly offset, substantially "Y" 
formation. The fins 106a-106c are spaced at approximately 120.degree. 
intervals about the longitudinal axis 108 of the cutting tip 106 which is 
preferably collinear with the longitudinal axis of the central shaft 104. 
Each fin 106a-106c generally includes first and second substantially 
parallel side faces 110a-110c and 112a-112c, a single bevel 116a-116c, and 
a leading cutting edge 114a-114c defined by the intersection of the first 
side 110a-110c and the bevel 116a-116c. 
As seen best in FIGS. 3 and 4, the fins are arranged so that their leading 
cutting edges 114a-114c extend radially outward from the longitudinal axis 
108 of the cutting tip 106 and angle proximally from the distal end 120 of 
the cutting tip 106. As mentioned above, the leading cutting edge 
114a-114c of each fin is defined by the intersection of the first side 
face 110a-110c with the single bevel 116a-116c. The leading cutting edge 
114a-114c. and the first side face 110a -110c of each fin preferably lie 
in a respective first plane which includes the longitudinal axis 108 of 
the cutting tip 106. The second parallel side face 112a-112c of each fin 
therefore lies in a respective second plane which is parallel to and 
spaced apart from the first plane by an amount equal to the thickness of 
the respective fin. 
According to one embodiment of the invention, the central shaft 104 and the 
trocar tip 106 are formed from a single integral extrusion such that the 
parallel sides 110a-110c and 112a-112c of the three fins are aligned with 
respect to the longitudinal axis 108 of the trocar 100 as described above. 
The distal ends of the fins 106a-106c are then ground to provide each fin 
with a single bevel 116a-116c as described above. Each fin is then 
preferably turned down to provide a step 122a-122c proximal of the cutting 
edge 114a-114c which continues proximally from the trocar tip 106 along 
the central shaft 104 to the handle 102. The steps 122a-122c are provided 
to accommodate a spring biased safety shield as described below. 
As seen best in FIGS. 1 and 2, each bevel 116a-116c is ground to form an 
acute angle .alpha. with respect to the first parallel side 110a -110c of 
the fin 106a-106c. Each bevel 116a-116c is also ground such that each 
cutting edge 114a-114c forms an acute angle .beta. with respect to the 
longitudinal axis 108 of the trocar 100. The angle .beta. is preferably 
approximately 17.degree.. It will be appreciated that the Figures are 
drawn with exaggerated angles to better illustrate the relative features 
of the invention. As mentioned above, each fin 106a-106c is preferably 
spaced 120.degree. apart from the other fins relative to the longitudinal 
axis 108 of the trocar 100. 
Turning now to FIGS. 2a and 2b, a trocar tip 206 is seen according to the 
invention where the trocar tip is ground using a conventional grinding 
machine such that the bevels 216a-216c are at the same angle as the 
cutting edges 214a-214c relative to the longitudinal axis 208; i.e., angle 
.alpha. equals angle .beta. which equals 17.degree.. In particular, the 
trocar tip 206 was ground using a conventional machine which ground the 
first and second fins 206a, 206b at an angle of 17.degree., rotated the 
trocar 120.degree., ground the second and third fins 206b, 206c at an 
angle of 17.degree., rotated the trocar 120.degree., and ground the third 
and first fins 206c, 206a at an angle of 17.degree.. The first grinding 
step imparted a bevel and cutting edge to the first fin and only a leading 
edge to the second fin. The second grinding step imparted a bevel to the 
second fin and a leading edge to the third fin. The third grinding step 
imparted a bevel to the third fin. The resulting tip has three cutting 
edges each of which has a cutting edge angle of 34.degree., half the angle 
of cutting edges of a pyramidal trocar tip of the prior art. Comparing 
FIGS. 2a and 2b, it will be appreciated that the cutting edge angle .phi. 
is the angle between the first side 210 of the fin and the bevel 216 as 
viewed in a plane which is perpendicular to the cutting edge 214. This 
angle is a trigonometric function of the angles .alpha. and .beta. and 
equals 34.degree. when .alpha. and .beta. are 17.degree.. If .alpha. is 
made smaller than .beta., as is the case in the embodiment of FIG. 2, an 
even sharper cutting edge may be provided. In the embodiment of FIGS. 2a 
and 2b, the distal end 220 of the trocar has a pyramidal point which is 
defined by the intersection of the bevels 216a, 216b, 216c of one fin with 
the side walls 210b, 210c, 210a of a respective adjacent fin. In other 
words, each bevel lies in the same plane as two adjacent cutting edges. 
Comparing FIG. 2, above, it will be appreciated that the embodiment of 
FIG. 2 does not have a pyramidal tip. 
Referring now to FIGS. 5-7, the trocar 100 (200) according to the invention 
is preferably provided with a safety shield 130 which is biased in the 
distal direction by a spring 132. The safety shield 130 is preferably a 
molded plastic piece having an substantially parabolical tip 134 and 
cylindrical base 136. The tip 134 is provided with three slots 134a-134c 
which are dimensioned and arranged relative to each other to receive the 
three fins 106a-106c of the trocar tip 106 described above. The 
cylindrical base 136 is provided with an annular stop 138 for receiving 
the spring 132. It will be appreciated that the annular stop 138 is 
dimensioned so that it abuts distal ends of the steps 122a-122c, i.e. the 
proximal ends of the fins 106a-106c when the safety shield 130 is in the 
first safety position as shown in FIG. 5. In this position, the tip 134 of 
the shield 130 extends slightly beyond the distal end 120 of the of the 
cutting tip 106 of the trocar 100 and the cutting edges 114a-114c are 
shielded by the outer surface of the tip 134 of the safety shield 130. 
When the safety shield is moved into the second, retracted, position, both 
the distal end 120 and the cutting edges 114a-114c of the cutting tip 106 
are exposed. The movement of the safety shield 130 is intended to be 
conventional. Although not shown in the Figures, the safety shield 130 may 
be provided with a locking mechanism which prevents it from moving to the 
retracted position after it has moved once from the safety position to the 
retracted position and back to the safety position. The main features of 
the safety shield 130 according to the invention are the cooperation of 
the annular stop 138 with the steps 122a-122c and the arrangement of the 
slots 134a-134c in the tip 134 which accommodate the fins 106a-106c. 
The cutting tip 106 according to the invention makes a quick and clean 
incision with little or no tearing of the skin and without requiring much 
effort on the part of the practitioner when inserting the trocar. In the 
preferred embodiment, the skin is incised in three directions with a 
substantially Y configuration (as the leading edges form a Y), thereby 
leaving three folded pieces of skin past which the trocar tube can enter 
the body. 
Turning now to FIGS. 8 through 11, a third embodiment of a trocar 300 
according to the invention is shown. The trocar 300 is similar to the 
trocars 100 and 200 described above in that it includes a proximal handle 
302, a central shaft 304, and a distal cutting tip 306. The distal cutting 
tip 306 includes three sharpened fins 306a-306c arranged in a slightly 
offset, substantially "Y" formation. The fins 306a-306c are spaced at 
approximately 120.degree. intervals about the longitudinal axis 308 of the 
cutting tip 306 which is preferably collinear with the longitudinal axis 
of the central shaft 304. Each fin 306a-306c generally includes first and 
second substantially parallel side faces 310a-310c and 312a-312c, a single 
bevel 316a-316c, and a leading cutting edge 314a-314c. Unlike the 
embodiments described above, both the first and second side faces 
310a-310c and 312a-312c are both offset from the longitudinal axis 308 of 
the trocar 300. Because of this arrangement, which is seen best in FIG. 9, 
a distal portion 313a-313c of each leading cutting edge 314a-314c is not 
defined by the intersection of the first side 310a-310c and the bevel 
316a-316c, but is defined by the intersection of adjacent bevels which 
intersect the longitudinal axis 308 of the trocar. In this embodiment, the 
distal portion 313a-313c of each cutting edge 314a-314c lies along a line 
which is substantially radial to the longitudinal axis 308 of the cutting 
tip and forms a distal pyramidal portion 320. The remainder of each 
cutting edge 314a-314c lies along a line which is substantially parallel 
to a line which is radial to the longitudinal axis 308 of the cutting tip. 
Thus, each cutting edge 314a-314c is provided with a slight step portion 
315a-315c where the bevel 316a-316c of one fin intersects the side face 
312a-312c of an adjacent fin. From the foregoing, those skilled in the art 
will appreciate that this embodiment of the invention offers the advantage 
that it is easier to grind the cutting tip to this configuration. 
Referring now to FIGS. 10 and 11, the trocar 300 according to the invention 
is preferably provided with a safety shield 330 which is biased in the 
distal direction by a spring 332. The safety shield 330 is preferably a 
molded plastic piece having an substantially parabolical tip 334 and 
cylindrical base 336. The safety shield 330 is provided with three slots 
334a-334c which are dimensioned and arranged relative to each other to 
receive the three fins 306a-306c of the trocar tip 306 described above. 
The cylindrical base 336 is provided with an annular flange 338 at its 
proximal end and the spring 332 biases the flange 338 in the distal 
direction inside the trocar handle 302. It will be appreciated that the 
annular flange 338 is dimensioned so that it abuts the interior of the 
handle 302 when the safety shield 330 is in the first safety position as 
shown in FIG. 10. In this position, the tip 334 of the shield 330 extends 
slightly beyond the distal end 320 of the of the cutting tip 306 of the 
trocar 300 and the cutting edges 314a-314c are shielded by the outer 
surface of the tip 334 of the safety shield 330. When the safety shield is 
moved into the second, retracted, position, shown in FIG. 11, both the 
distal end 320 and the cutting edges 314a-314c of the cutting tip 306 are 
exposed. 
The movement of the safety shield 330 is intended to be conventional. 
Although not shown in the Figures, the safety shield 330 may be provided 
with a locking mechanism which prevents it from moving to the retracted 
position after it has moved once from the safety position to the retracted 
position and back to the safety position. The main features of the safety 
shield 330 according to the invention are the arrangement of the slots 
334a-334c which accommodate the fins 306a-306c. 
There have been described and illustrated herein several embodiments of a 
surgical trocar having an improved cutting tip configuration. While 
particular embodiments of the invention have been described, it is not 
intended that the invention be limited thereto, as it is intended that the 
invention be as broad in scope as the art will allow and that the 
specification be read likewise. Thus, while the trocar has been disclosed 
as having three fins and thus three cutting edges, it will be appreciated 
that a different number of fins could also be used. In addition, while the 
fins have been disclosed as being arranged at intervals of 120.degree. 
relative to each other, it will be understood that other angles can be 
used. Also, while the grinding angle of 17.degree., and the cutting edge 
angle of 34.degree. have been stated as preferred angles in one embodiment 
of the invention, it will be appreciated that other angles could be used. 
Moreover, while particular configurations and mechanisms have been 
disclosed in reference to the retractable shield, it will be appreciated 
that other shield mechanisms and configurations could be used as well and 
that the trocar could be used without a shield. Further, while the 
preferred embodiment disclosed herein describes an integral trocar tip and 
shaft, it will be appreciated that the novel trocar tip disclosed herein 
can be used with any type of trocar shaft and the tip and shaft need not 
be an integral piece. Also, while the disclosed preferred embodiment of 
the invention is manufactured by finishing an extruded workpiece, it will 
be understood that the three fins of the novel trocar tip could be made 
from three separate pieces and mounted in the alignment described herein. 
It will therefore be appreciated by those skilled in the art that yet 
other modifications could be made to the provided invention without 
deviating from its spirit and scope as so claimed.